1392^2^Hoddinott,J^Scott,R^1996^1^The influence of light quality and carbon dioxide enrichment on the growth and physiology of seedlings of three conifer species .2. Physiological responses^188^74^3^391-402^^^^^Mar^^^^^5568
1072^130^1343^1482^243^417^456^493^513^664^d high or low R/FR ratios and growth was measured over a 16-week growth period. Far-red rich light enhanced the whole plant and height relative growth rates of Pinus banksiana. The three species showed species specific responses in plant organ relative growth rates and partitioning ratios. On the basis of their biomass partitioning the species would be ranked Pinus banksiana < Picea mariana < Picea glauca for shade tolerance. In commercial operations, seedlings grown for outplanting are selected, in part, on the basis of plant form as described by the stem height/diameter ratio. More desirable ratios were obtained at ambient CO2 concentrations for Pinus banksiana and Picea mariana in red rich light and for Picea glauca in far-red rich light.
 lA^5567^Pinus banksiana, Picea mariana, and Picea glauca were grown at 350, 700, or 1050 mu L . L(-1) CO2 and either high or low red/far-red quantum flux ratios. After a 16-week, long day growth period, seedlings were subjected sequentially to short daylengths, then short days with low temperatures. Various physiological parameters were determined at the end of each treatment phase to monitor how those treatments influenced the onset of seedling dormancy. After the long day treatments, high ratios increased the total chlorophyll content and reduced the original level of chlorophyll fluorescence and the shoot total nonstructural carbohydrate content in very shade-intolerant Pinus banksiana. In shade-tolerant Picea mariana, high CO2 levels caused the main effects on these parameters while neither light quality or CO2 had significant effects on them in shade-tolerant Picea glauca. Short days and low temperature induced a proportional increase in the partitioning of total nonstructural carbohydrate to the roots in all species and produced other species and treatment-specific responses.

1393^2^Norris,TS^Bailey,BJ^1996^1^Use of simulation analysis to improve the design of open-top chambers^107^78^3-4^259-275^^^^^Feb^^^^^5570
384^447^741^949^tially to short daylengths, then short days with low temperatures. Various physiological parameters were determined at the end of each treatment phase to monitor how those treatments influenced the onset of seedling dormancy. After the long day treatments, high ratios increased the total chlorophyll content and reduced the original level of chlorophyll fluorescence and the shoot total nonstructural carbohydrate content in very shade-intolerant Pinus banksiana. In shade-tolerant Picea mariana, high CO2 levels caused the main effects on these parameters while neither light quality or CO2 had significant effects on them in shade-tolerant Picea glauca. Short days and low temperature induced a proportional increase in the partitioning of total nonstructural carbohydrate to the roots iA^5569^A greenhouse climate simulation model, employing linked first- order integral and differential equations, was adapted to predict the microclimate within carbon-dioxide-enriched open- top chambers (OTCs) suitable for climate change research. The simulation model was validated using experimental measurements from a prototype OTC test rig constructed at Silsoe Research Institute; this model was then used to investigate the effect of employing a controlled combination of air recirculation and ventilation on carbon dioxide consumption for a chamber containing wheat plants. Control criteria for a controlled- ventilation OTC were investigated using the simulation and verified experimentally; results showed that a 2 degrees C temperature excess limit within the chamber could be achieved in practice for a chamber exhibiting minimal wind incursion through the open-top, provided that a mechanical ventilation rate of 6 air changes minute(-1) was provided during periods of peak solar flux. Furthermore, the simulation suggested that, by applying controlled ventilation and recirculation to OTCs, it is feasible to reduce the daily consumption of enrichment gas to achieve 560 mu mol mol(-1) concentration within a 3 m- diameter and 3 m-high chamber located at an exposed site to 15 kg in comparison to the estimated 100 kg required when continuous ventilation is employed.

1394^4^Ojala,A^Kankaala,P^Haapamaki,J^Tulonen,T^1995^1^Immediate responses of photosynthesis and dark respiration of late summer stands of Equisetum fluviatile L to increasing concentrations of atmospheric CO2^292^69^5-6^169-176^^^^^Dec^^^^^5572
1336^1878^2270^312^376^417^749^778^851^92^d using the simulation and verified experimentally; results showed that a 2 degrees C temperature excess limit within the chamber could be achieved in practice for a chamber exhibiting minimal wind incursion through the open-top, provided that a mechanical ventilation rate of 6 air changes minute(-1) was provided during periods of peak solar flux. Furthermore, the simulatA^5571^Short-term responses of net photosynthesis, apparent dark respiration and gross photosynthesis of Equisetum fluviatile to increasing concentrations of atmospheric CO2 were studied by using transplanted stands of natural origin. Three transplantations with biomasses of 274, 407, and 401 g dry weight m(-2) were established six weeks before the measurements in late August. Net photosynthesis and apparent dark respiration was measured from the change of CO2 concentration inside polycarbonate chambers with diameter of 0.455 m and volume of 0.207 m(3). Altogether 50 experiments for determination of CO2 influx rates and 24 for efflux rates were run without any pre-treatment to higher CO2 and each of them lasted 20-30 min. The response of net photosynthesis of E. fluviatile to CO2 enrichment was less clear than the response to temperature or irradiance. Nevertheless, the stands showed an increase of ca. 25 % in net photosynthesis when the CO2 concentration in air was increased from ambient to 500-600 ppm. When the CO2 concentration was > 600 ppm the increase was ca. 60 %. A multilinear regression model combining solar radiation, temperature and CO2 concentration could only explain 46.4 % of the variation in the observed rates of net photosynthesis. The apparent dark respiration was positively correlated with temperature but inversely related to CO2 concentration. When the CO2 concentration was doubled from ambient the stands of E. fluviatile reduced their apparent dark respiration by ca. 50 %. Under higher CO2 concentration E. fluviatile appeared more effective than in the ambient concentration, as the production lost through respiration decreased. When the concentration of atmospheric CO2 was < 500 ppm, 57.5 % of gross production was respired whereas above 500 ppm of CO2 the corresponding proportion was only 34.2 %. As the enrichment with CO2 resulted in decreased respiration rates and it was known from long-term growth and photosynthesis experiments that neither shoot growth in length in E. fluviatile is stimulated by higher CO2 concentrations nor do the stands show down-regulation of photosynthesis after several weeks of CO2 enrichment, it was concluded that the extra carbon fixed was allocated to storage through growth of below-ground biomass.

1395^1^Simon,JP^1996^1^Molecular forms and kinetic properties of pyruvate, P-i dikinase from two populations of barnyard grass (Echinochloa crus-galli) from sites of contrasting climates^92^23^2^191-199^^^^^^^^^^5574
130^1538^2077^2271^2272^2273^2274^349^367^503^r CO2 concentration E. fluviatile appeared more effective than in the ambient concentration, as the production lost through respiration decreased. When the concentration of atmospheric CO2 was < 500 ppm, 57.5 % of gross production was respired whereas above 500 ppm of CO2 the corresponding proportion was only 34.2 %. As the enrichment with CO2 resulted in decreased respiration rates and it was known from long-term growth and photosynthesis experiments that neither shoot growth in length in E. fluviatile is stimuA^5573^Plants from two populations of the C-4 barnyard grass (Echinochloa crus-galli (L.) Beauv.) from Quebec (QUE) and Mississippi (MISS) were acclimated under controlled conditions to 26/20 and 14/8 degrees C day/night. The apparent energy of activation (E(a)), K-m for pyruvate, V-max/K-m ratios, K-cat (substrate turnover number) and specific activity of pyruvate, P-i dikinase (PPDK, EC 2.7.9.1) were analysed from partially purified Sephadex G-25 extracts of PPDK from leaves and from highly purified PPDK. PPDK from both populations consisted of one isomorph with the same electrophoretic mobility in polyacrylamide gels and similar molecular weights for the native enzyme (385 kDa) and for the subunit of the tetramer (94.8 kDa). No significant differences were observed for any of the kinetic properties of partially purified or purified PPDK or for the specific activity per mg protein of purified PPDK extracted from plants of the two populations and acclimated to the two thermoperiods. Net photosynthetic rates (Ps) were positively correlated with PPDK activity levels (E) but E/Ps ratios were lower than 1.0, ranging from 0.43 to 0.67. Results indicate that differences in activity levels, thermal properties and in the kinetics of light activation and dark inactivation of PPDK extracted from cold-acclimated MISS and QUE plants, as reported in earlier studies, are due to causes other than kinetic properties or electrophoretic characteristics of PPDK.

1396^2^Beerling,DJ^Woodward,FI^1996^1^Palaeo-ecophysiological perspectives on plant responses to global change^57^11^1^20-23^^^^^Jan^^^^^5576
174^2096^251^593^ polyacrylamide gels and similar molecular weights for the native enzyme (385 kDa) and for the subunit of the tetramer (94.8 kDa). No significant differences were observed for any of the kinetic properties of partially purified or purified PPDK or for the specific activity per mg protein of purified PPDK extracted from plants of the two populations and acclimated to the two thermoperiods. Net photosynthetic ratesA^5575^Taxonomic classifications of plant species, based on morphological characteristics, provide a stable and robust approach for Inferring taxonomic and phylogenetic relationships between extant and extinct species. This implies that, although evolution is a continuous process for a species, there is no whole-scale change in those suites of morphological characteristics that define higher order (genus and greater) relationships. Recent research suggests that a higher order characteristic stomatal density - may reflect not only the atmospheric CO2 concentration during initial evolution, but may also strongly constrain the responses of higher order plant groups to future CO2-enrichment.

1397^2^Laitat,E^Boussard,H^1995^1^Comparative response on gas exchange of Picea spp exposed to increased atmospheric CO2 in open top chambers at two test sites^134^22^2-3^241-248^^^^^Mar-May^^^^^5578
243^312^ PPDK extracted from plants of the two populations and acclimated to the two thermoperiods. Net photosynthetic ratesA^5577^We took comparative measurements of gas exchange response curves of two species of spruce (Picea abies (L.) Karst and Picea sitchensis (Bong.) Carr.) exposed to high levels of atmospheric carbon dioxide (CO2) in two test stations: Vielsalm (Belgium) and Glendevon (United Kingdom). The photosynthetic response of these two species to variations in concentrations of intercellular CO2 and to variations in light intensity were measured in situ using an integrated transportable differential CO2 and water vapour exchange measuring system. The response curves were adjusted by the Mitscherlich function. The statistical analysis of our measurements and adjustments reveal similarities in the reaction of Picea abies and Picea sitchensis to a doubling of the present level of atmospheric CO2. Regarding the photosynthesis response curves to intercellular CO2 variation, we noted a decrease in the maximum photosynthesis rate and the carboxylation rate accompanied by an increased compensation point. Regarding the photosynthesis response curves to the light variation, we found that dark respiration and photochemical efficiency remained unchanged, and the maximum photosynthesis rate was slightly higher in an atmosphere enriched in CO2. These experimental contexts would seem to indicate that the current and forecast levels of CO2 are not ecological factors limiting primary productivity, and that the increase in atmospheric CO2 interacts with other environmental factors.

1398^2^Samarakoon,AB^Gifford,RM^1995^1^Soil water content under plants at high CO2 concentration and interactions with the direct CO2 effects: A species comparison^134^22^2-3^193-202^^^^^Mar-May^^^^^5580
243^256^264^312^385^409^434^442^674^92^on of Picea abies and Picea sitchensis to a doubling of the present level of atmospheric CO2. Regarding the photosynthesis response curves to intercellular CO2 variation, we noted a decrease in the maximum photosynthesis rate and the carboxylation rate accompanied by an increased compensation point. Regarding the photoA^5579^Wheat, maize and cotton, grown as spaced plants in large pots of soil, differed in the way high (2 X ambient) CO2 concentration affected the time-course of soil water use. For wheat, the tendency to conserve water owing to reduction in stomatal conductance in high CO2 was largely offset by the stimulation of leaf area development as the soil column dried. However, when the soil was maintained continuously wet, soil water conservation occurred because in the absence of water stress high CO2 did not maintain a greater leaf area. For maize, which has little or no photosynthetic response to CO2 concentrations above ambient but a strong stomatal response, water was conserved and the soil profile dried more slowly. Maize leaf area and dry matter growth increased in response to damper soil under high CO2, despite no growth response to CO2 in the absence of water stress. For cotton, which has a strong photosynthetic but weak stomatal response to CO2, the soil column dried faster under high CO2. Despite this drier soil, cotton still showed the greatest response to high CO2 of leaf area and dry matter growth of the three species compared. Under wet soil conditions, cotton exhibited a very large leaf area response to CO2 leading to much greater water use per plant. This contrasts with both wheat and maize which conserved water at high CO2 when wet. Despite these contrasting transpiration and growth responses, all three species exhibited a relatively similar increase in water use efficiency under high CO2 for both wet and dry conditions. It is concluded that the secondary effect of high CO2 on soil water content exerts a strong confounding influence on growth responses to CO2. In the longer term, the changed soil water status would influence hydrology, soil microbiology, nutrient relations and species composition. From indirect evidence it is proposed that the relative enhancement of growth owing to CO2 enrichment is greater under drought conditions than in wet soil because of the effect of water deficit on the intercellular CO2 concentration in the leaf, C-i. If water deficits cause C-i/C-a to decline then photosynthesis is operating in a more CO2-sensitive region of the CO2 response curve.

1399^1^Slafer,GA^1995^1^Wheat development as affected by radiation at two temperatures^161^175^4^249-263^^^^^Nov^^^^^5582
1010^1173^2275^2276^341^349^435^546^724^92^pite these contrasting transpiration and growth responses, all three species exhibited a relatively similar increase in water use efficiency under high CO2 for both wet and dry conditions. It is concluded that the secondary effect of high CO2 on soil water content exerts a strong confounding influence on growth responses to CO2. In the longer term, the changed soil water status would influence hydrology, soil microbiology, nutrient relations and species composition. From indirect evidence it is proposed that the relative enhancement of growth owing to CO2 enrichment is greater under drought conditions than in wet soil because of the effect of water deficit on the inteA^5581^A wheat cultivar (Condor) was grown in two experiments (thermal regimes 18/13 and 21/16 degrees C) under low (298 mu E m(-2) s(-1)) radiation regimes during either an early phase from seedling emergence to terminal spikelet initiation (S-1), a late phase from terminal spikelet initiation to anthesis (S-2), or for the full period from seedling emergence to anthesis (S- 12), or high (560 mu E m(-2) s(-1)) radiation throughout the growing period (S-0) to determine whether developmental events are affected by radiation. The main developmental events considered in this study were the timing of terminal spikelet initiation and anthesis, the final number of leaf and spikeler primordia initiated in the apex and the rare of leaf appearance. Number of grains per spike and culm height were also measured. The duration of each phenophase was not affected by radiation intensity. Temperature affected the rate of wheat development, but the acceleration of development due to temperature during the seedling emergence-terminal spikelet initiation phase only slightly reduced (from 24.8 to 23.2 days). Differences in time from terminal spikelet initiation to anthesis were greater than in the earlier phases, having been the duration reduced from 24.6 to 20.0 days due to high temperature. Associated with the lack of effect of radiation on phasic development and the negligible effect of temperature on the duration of the early phases of development, final leaf number was practically unchanged in this study by either the radiation level or the growing temperature. Thus, radiation did not affect the rate of leaf initiation. The number of spikelets was affected by neither the treatments nor the thermal environment. The rates of leaf appearance were accelerated by temperature. Radiation, on the other hand, did nor significantly alter the rates of leaf appearance in any of the treatments. As expected from many sources in the literature, the number of grains per spike was significantly affected by radiation during the phase from terminal spikelet initiation to anthesis. Due to the lack of significant effects of radiation on the developmental patterns of wheat, the changes in number of grains per spike were due to changes in the number of grains born in each spikelet. The results of the present study were compared with others available in the literature on the effects (or lack of them) of radiation and CO2 concentration on phasic development, plastochron and phyllochron in wheat to reach the general conclusion that the rate of developmental events in wheat, in contrast to other plants, is almost completely independent of the availability of assimilates, with a possible exception for the Equatorial latitudes.

1400^2^Vadstrup,M^Madsen,TV^1995^1^Growth limitation of submerged aquatic macrophytes by inorganic carbon^301^34^3^411-419^^^^^Dec^^^^^5584
1094^130^1453^188^243^362^519^778^ treatments. As expected from many sources in the literature, the number of grains per spike was significantly affected by radiation during the phase from termiA^5583^1. This study determined the effects of CO2 and HCO3- enrichment on in situ growth of two submerged macrophytes, Elodea canadensis and Callitriche cophocarpa, in two Danish lakes: Lake Hampen and Lake Vaeng. Lake Hampen is an oligotrophic low-alkaline lake (0.4 meg 1(-1)) and Lake Vaeng is mesotrophic with an alkalinity of 1.1 meg 1(-1). In Lake Hampen experiments were carried out throughout the growth season, whereas experiments in Lake Vaeng were restricted to late summer. The CO2 and HCO3- enrichment procedures used increased the concentration of free-CO2 by 500-1000 mu M and the concentration of HCO3- by about 80 CIM. 2. The concentration of free-CO2 in Lake Hampen was about five times atmospheric equilibrium concentration (55 mu M) in early summer declining to virtually zero at the end of summer. 3. Under ambient conditions Callitriche, which is restricted to CO2 use, was unable to grow and survive in both lakes. In contrast, Elodea, which has the potential to use HCO3- in photosynthesis, grew at rates varying from 0.046 to 0.080 day(-1) over the season. 4. Under CO2 enrichment the growth rate of Callitriche varied from 0.089 to 0.124 day-l and for Elodea from 0.076 to 0.117 day(-1) over the season. Enrichment with HCO3- affected Elodea only and only to a limited extent. This may be a result of insufficient increase in [HCO3-] upon enrichment or to a limited capacity of the plants to take up HCO3-. 5. The substantial stimulation of in situ growth of Elodea and Callitriche by enhanced concentrations of free-CO2 shows that inorganic carbon is an important determinant of growth of submerged macrophytes and that inorganic carbon limitation of in situ growth may be a common phenomenon in nature, even in lakes with an alkalinity as high a 1 meg 1(-1). Inorganic carbon, however, is only one of many parameters important for growth, and the growth rates of Elodea at both ambient and high free-CO2 were closely coupled to day length and photon irradiance, indicating that light had an ultimate control on growth.

1401^5^McKeehen,JD^Smart,DJ^Mackowiak,CL^Wheeler,RM^Nielsen,SS^9UNKNOWN YEAR^1^Effect of CO2 levels on nutrient content of lettuce and radish^297^^^85-92^^^^^^^^^^5586
204^2277^433^5^92^ over the season. Enrichment with HCO3- affected Elodea only and only to a limited extent. This may be a result of insufficient increase in [HCO3-] upon enrichment or to a limited capacity of the plants to take up HCO3-. 5. The substantial stimulation of in situ growth of Elodea and Callitriche by enhanced concentrations of free-CO2 shows that inorganic carbon is an important determinant of growth of submerged macrophytes and that inorganic carbon limitation of in situ growth may be a common phenomenon in nature, even in lakes with an alkalinity as high a 1 meg 1(-1). Inorganic carbon, however, is only one of many parameters important for growth, and the growth rates of Elodea at both ambient and high free-CO2 were closely coupled to day length and photon irradiance, indicating that light had an ultimate control on growthA^5585^Atmospheric carbon-dioxide enrichment is known to affect the yield of lettuce and radish grown in controlled environments, but little is known about CO2 enrichment effects on the chemical composition of lettuce and radish. These crops are useful model systems for a Controlled Ecological Life-Support System (CELSS), largely because of their relatively short production cycles. Lettuce (Lactuca sativa L.) cultivar 'Waldmann's Green' and radish (Raphanus sativus L.) cultivar 'Giant White Globe' were grown both in the field and in controlled environments, where hydroponic nutrient solution, light, and temperature were regulated, and where CO2 levels were controlled at 400, 1000, 5000, or 10,000 ppm. Plants were harvested at maturity, dried, and analyzed for proximate composition (protein, fat, ash, and carbohydrate), total nitrogen (N), nitrate N, free sugars, starch, total dietary fiber, and minerals. Total N, protein N, nonprotein N (NPN), and nitrate N generally increased for radish roots and lettuce leaves when grown under growth chamber conditions compared to field conditions. The nitrate-N level of lettuce leaves, as a percentage of total NPN, decreased with increasing levels of CO2 enrichment. The ash content of radish roots and of radish and lettuce leaves decreased with increasing levels of CO2 enrichment. The levels of certain minerals differed between field- and chamber-grown materials, including changes in the calcium (Ca) and phosphorus (P) contents of radish roots and lettuce leaves, resulting in reduced Ca/P ratio for chamber- grown materials. The free-sugar contents were similar between the field and chamber-grown lettuce leaves, but total dietary fiber content was much higher in the field-grown plant material. The starch content of growth-chamber lettuce increased with CO2 level.
sh, and carbohydrate), total nitrogen (N), nitrate N, free sugars, starch, total dietary fiber, and minerals. Total N, protein N, nonprotein N (NPN), and nitrate N generally increased for radish roots and lettuce le1402^3^Kwa,SH^Wee,YC^Kumar,PP^1995^1^Ammonium and nitrate uptake and nitrate reductase activity of photoautotrophic callus cultures of the fern Platycerium coronarium (Koenig) DESV^267^31^4^211-214^^^^^Oct-Dec^^^^^5588
1096^174^92^nd of radish and lettuce leaves decreased with increasing levels of CO2 enrichment. The levels of certain minerals differed between field- and chamber-grown materials, including changes in the calcium (Ca) and phosphorus (P) contents of radish roots and lettuce leaves, resulting in reduced Ca/P ratio for chamber- grown materials. The free-sugar contents were similar between the field and chamber-grown lettuce leaves, but total dietary fiber content was much higher in the field-grown plant material. The starch content of growth-chamber lettuce increased with CO2 level.
sh, and carbohydrate), total nitrogen (N), nitrate N, free sugars, starch, total dietary fiber, and minerals. Total N, protein N, nonprotein N (NPN), and nitrate N generally increased for radish roots and lettuce leA^5587^The uptake of nitrate and ammonium by callus of Platycerium coronarium from the culture medium was examined. Nitrate reductase activity of photoautotrophic callus cultures under CO2 enrichment was significantly lower compared to the cultures without CO2 enrichment, but higher than that of heterotrophic callus cultured on medium with 2% (wt/vol) sucrose. When sucrose concentration of the heterotrophic culture was lowered to 0.2%, nitrate reductase activity increased. The level of nitrate reductase activity increased by about 25% in the heterotrophic callus with an increase in 2,4-D from 2 mu M to 10 mu M, despite a decline in fresh weight gain. However, photoautotrophic cultures with 1% CO2 enrichment showed 20% decline in nitrate reductase activity and 45% decline in fresh weight gain with a similar increase in 2,4-D level. The rate of uptake of nitrate from the culture medium was unrelated to the level of nitrate reductase activity in the callus. For photoautotrophic callus under CO2 enrichment, the presence of 1% (vol/vol) CO2 generally resulted in the highest rate of nitrate uptake. The rate of uptake of ammonium was higher for callus cultured on 2 mu M 2,4-D compared to that on 10 mu M 2,4-D.

1403^2^Kramer,K^Mohren,GMJ^1996^1^Sensitivity of FORGRO to climatic change scenarios: A case study on Betula pubescens, Fagus sylvatica and Quercus robur in the Netherlands^50^34^2^231-237^^^^^Oct^^^^^5590
2278^243^314^465^92^ed to 0.2%, nitrate reductase activity increased. The level of nitrate reductase activity increased by about 25% in the heterotrophic callus with an increase in 2,4-D from 2 mu M to 10 mu M, despite a decline in fresh weight gain. However, photoautotrophic cultures with 1% CO2 enrichment showed 20% decline in nitrate reductase activity and 45% decline in fresh weight gain with a similar increase in 2,4-D level. The rate of uptake of nitrate from the culture medium was unrelated to the level of nitrate reductase activity in the callus. For photoautotrophic callus under CO2 enrichment, the A^5589^The impacts of the climate change predictions of four general circulation models (GFDL, GISS, OSU and UKMO) on net primary production (NPP) of Betula pubescens, Fagus sylvatica and Quercus robur in The Netherlands were analysed using the process-based model FORGRO. FORGRO is a model suitable to simulate growth of managed mono-species stands. For the GCMs mentioned, both transient and equilibrium 2 x CO2 scenarios of temperature and precipitation change were evaluated and compared with responses under current climate. It was found that the NPP increases in the transient scenarios, but remains the same or declines in the 2 x CO2 scenarios. This is because respiration increases more with rising temperature than photosynthesis. During the transient scenarios this effect gradually increases, while in the 2 x CO2 scenario this effect is operating over the entire simulation period. If water limitation is taken into account, then the NPP of the reference scenario is reduced. In both the transient and 2 x CO2 scenarios this water limitation is annulated, resulting in a stronger response of NPP compared to the situation without water limitation. This enhancement of the response is most pronounced in the transient scenario due to the gradual effect of temperature on respiration. Similar results were obtained with a version of FORGRO in which the photosynthesis module of HYBRID (PGEN) is incorporated, although the response in FORGRO- PGEN is usually higher than that of FORGRO. This is because the response of photosynthesis to CO2 rises with increasing temperature as defined in the PGEN-model, but not according to FORGRO.

1404^3^Makino,Y^Iwasaki,K^Hirata,T^1996^1^A theoretical model for oxygen consumption in fresh produce under an atmosphere with carbon dioxide^195^65^3^193-203^^^^^Nov^^^^^5592
1000^174^2279^2280^310^384^455^563^874^s effect is operating over the entire simulation period. If water limitation is taken into account, then the NPP of the reference scenario is reduced. In both the transient and 2 x CO2 A^5591^A practical model for fresh produce, which includes the effect of the depression of respiration caused by CO2, is proposed on the basis of the modified Langmuir adsorption theory. The O-2 consumption rates for several kinds of fresh produce under atmospheric conditions with enhanced CO2 were measured and the data was analysed using the proposed model. The rate parameters of the model for estimating respiration of fresh produce were determined, and the model was found to be adaptable for describing the O-2 consumption in terms of the depression by CO2. Mathematical analysis of a modified atmosphere packaging (MAP) system for shredded cabbage and broccoli was carried out using the proposed rate equation and the basic mass balance. The simulated results agreed well with the experimental data. The proposed O-2 consumption model is considered to be useful for the design of MAP systems under the atmospheric condition with CO2 gas. (C) 1996 Silsoe Research Institute
duced. In both the transient and 2 x CO2 1405^2^Topp,CFE^Doyle,CJ^1996^1^Simulating the impact of global warming on milk and forage production in Scotland .2. The effects on milk yields and grazing management of dairy herds^223^52^2-3^243-270^^^^^Oct-Nov^^^^^5594
1098^2159^227^2281^2282^2283^2284^2285^314^92^itions with enhanced CO2 were measured and the data was analysed using the proposed model. The rate parameters of the model for estimating respiration of fresh produce were determined, and the model was found to be adaptable for describing the O-2 consumption in terms of the depression by CO2. Mathematical analysis of a modified atmosphere packaging (MAP) system for shredded cabbage and broccoli was carried out using the proposed rate equation and the basic mass balance. The simulated results agreed well with the experimental data. The proposed O-2 consumption model is considered to be useful for the design of MAP systems under the atmospheric condition with CO2 gas. (C) 1996 Silsoe Research Institute
duced. In both the transient and 2 x CO2 A^5593^The potential impact of global warming and the enhanced atmospheric CO2 concentration on grassland management on dairy farms within the UK requires assessment. This has led to the development of a mathematical model of the grazing dairy cow. The model, that embraces grass and grass-white clover swards, has been used to assess the effects that the projected increases in temperature and rainfall under global warming and the increased levels of CO2 might have on milk production and on silage conservation for a typical dairy farm. The results suggest that the impact on milk production for grass-based systems will vary depending on the locality. On the other hand, for herds grazed on grass-white clover swards milk output might increase regardless of site, when the concentration of CO2 is enhanced. As regards silage production from grass-white clover swards, under global warming and at current levels of CO2 there is an apparent tendency to increase the percentage of total silage yield obtained from the first cut, although this does nor occur for grass swards. At the same time, there are also indications that global warming will increase the percentage of clover in the herbage cut for conservation. Copyright (C) 1996 Published by Elsevier Science Ltd

1406^3^Varoquaux,P^Mazollier,J^Albagnac,G^1996^1^The influence of raw material characteristics on the storage life of fresh-cut butterhead lettuce^259^9^2^127-139^^^^^Nov^^^^^5596
174^2286^2287^2288^57^874^ might have on milk production and on silage conservation for a typical dairy farm. The results suggest that the impact on milk production for grass-based systems will vary depending on the locality. On the other hand, for herds grazed on grass-white clover swards milk output might increase regardless of site, when the concentration of CO2 is enhanced. As regards silage production from grass-white clover swards, under global warming and at current levels of CO2 there is an apparent tendency to increase the percentage of total silage yield obtained from the firsA^5595^The physiological characteristics of 5 butterhead lettuce cultivars (Lactuca sativa L.) were investigated using etiolated leaves. Their storage life under modified and controlled atmospheres was assessed. When prepacked butterhead lettuce was maintained under a low oxygen atmosphere to prevent enzymatic browning, high CO2 content was the main factor increasing the rate of decay. Shelf life was negatively correlated with respiration rate and susceptibility to CO2. Potassium leakage was a good indicator of physiological disorders. High oxygen and low CO2 enhanced enzymatic browning, while low oxygen and, more significantly, high carbon dioxide enhanced CO2 injury (brown stain). Maintaining CO2 concentration within the packs below 5% resulted in an improved preservation of the lettuce leaves. Practical means for obtaining modified atmospheres which were in equilibrium yet were low in both O-2 and CO2 are discussed.
apparent tendency to increase the percentage of total silage yield obtained from the firs1407^3^Carlsson,AS^Wallin,G^Sandelius,AS^1996^1^Species- and age-dependent sensitivity to ozone in young plants of pea, wheat and spinach: Effects on acyl lipid and pigment content and metabolism^37^98^2^271-280^^^^^Oct^^^^^5598
2289^2290^2291^2292^348^420^ed under a low oxygen atmosphere to prevent enzymatic browning, high CO2 content was the main factor increasing the rate of decay. Shelf life was negatively correlated with respiration rate and susceptibility to CO2. Potassium leakage was a good indicator of physiological disorders. High oxygen and low CO2 enhanced enzymatic browning, while low oxygen and, more significantly, high carbon dioxide enhanced CO2 injury (brown stain). Maintaining CO2 concentration within the packs below 5% resulted in an improved preservation of the lettuce leaves. Practical means for obtaining modified atmospheres which were in equilibrium yet were low in both O-2 and CO2 are discussed.
apparent tendency to increase the percentage of total silage yield obtained from the firsA^5597^Acyl lipids and pigments were analyzed in young plants of garden pea, spring wheat and spinach exposed to <5 or 65 nl l(- 1) ozone 12 h per day for 6 days. In one set of experiments, the plants were exposed to (CO2)-C-14 for 2 h 3 days prior to ozone exposure. The plants responded differently to the moderately enhanced level of ozone used Spinach was not at all sensitive while in both pea and wheat, leaves of different ages differed in ozone sensitivity. In pea, ozone sensitivity increased with leaf age. In the second and third oldest leaves, the amounts of galactolipids per leaf area and the proportions of 18:3 of the total lipid extract and of phosphatidylglycerol decreased. In the second oldest leaf, ozone also caused a decreased proportion of 18:3 of monogalactosyldiacylglycerol. In the fourth oldest leaf, Lipid composition and galactolipid unsaturation was unaffected, but ozone caused decreased leaf expansion resulting in increased acyl lipid content per leaf area. In both the first and second leaves of wheat, ozone fumigation caused a marked decrease in the content of monogalactosyldiacylglycerol and in the first leaf, the contents of phosphatidylcholine and phosphatidylethanolamine increased. The proportion of 18:3 in phosphatidylcholine was larger in ozone-fumigated than in control plants, while the reverse applied for phosphatidylglycerol. In the oldest sampled leaves of pea and wheat, ozone caused an increase in the radioactivity associated with beta-carotene, indicating increased turnover. Thus, while spinach was unaffected, in both pea and wheat ozone caused a decrease in the proportion of chloroplast membrane lipids to non-chloroplast membrane lipids in older leaves while younger leaves were less sensitive.

1408^3^Talbott,LD^Srivastava,A^Zeiger,E^1996^1^Stomata from growth-chamber-grown Vicia faba have an enhanced sensitivity to CO2^9^19^10^1188-1194^^^^^Oct^^^^^5600
131^1754^1890^2149^2293^312^383^417^465^736^g in increased acyl lipid content per leaf area. In both the first and second leA^5599^Abaxial stomata from Vicia faba leaves grown in a growth chamber under constant light, temperature and humidity showed an elaborate pattern of aperture changes over the course of a light cycle. These aperture changes, were tightly correlated with changes in chamber COL concentration (r(2)=0.83). Changes in chamber [CO2] resulted, in turn, from substantial daily fluctuations in ambient [CO2], typical of the Los Angeles environment, with a constant offset caused by photosynthesis and respiration of the plants within the chamber, The dominant role of the stomatal response to CO2 in the control of aperture tvas confirmed by manipulation of chamber [CO2]. Fast (15 min) increases and decreases in [CO2] caused rapid decreases and increases in aperture, while constant [CO2] resulted in constant aperture. In contrast, aperture changes in comparable plants grown under greenhouse conditions were tightly correlated with changes in incident solar radiation (r(2)=0.80), and poorly correlated with changes in [CO2] (r(2)=0.09). Greenhouse-grown plants transferred to growth chamber conditions showed no apparent response to CO2. These data indicate that growth-chamber-grown V. faba leaves provide an experimental system optimally suited for the study of the stomatal response to CO2, and suggest that acclimation to environmental conditions alters the sensitivity of stomata to CO2.

1409^1^Harvey,LDD^1996^1^Development of a risk-hedging CO2-emission policy .2. Risks associated with measures to limit emissions, synthesis, and conclusions^50^34^1^41-71^^^^^Sep^^^^^5602
1055^1617^2294^2295^2296^2297^2298^2299^413^653^f aperture tvas confirmed by manipulation of chamber [CO2]. Fast (15 min) increases and decreases in [CO2] caused rapid decreases and increases in aperture, while constant [CO2] resulted in constant aperture. In contrast, aperture changes in comparable plants grown under greenhouse conditions were tightly correlated with changes in incident solar radiation (r(2)=0.80), and poorly correlated with changes in [CO2] (A^5601^This paper is Part II of a two-part series in which the risks associated with unrestrained greenhouse-gas emissions, and with measures to limit emissions, are reviewed. A sustained limitation of global CO2 emissions requires global population stabilization, a reduction in per capita emissions in the developed world, and a limitation of the increase in per capita emissions in the developing world. Reducing or limiting per capita emissions requires a major effort to improve the efficiency with which energy is transformed and used; urban development which minimizes the need for the private automobile and facilitates district heating, cooling, and cogeneration systems; and accelerated development of renewable energy. The following risks associated with these efforts to limit CO2 emissions are reviewed here: (i) resources might be diverted from other urgent needs; (ii) economic growth might be reduced; (iii) reduction measures might cost more than expected; (iv) early action might cost more than later action; (v) reduction measures might have undesired side effects; (vi) reduction measures might require heavy-handed government intervention; and (vii) reduction measures might not work. With gradual implementation of a diversified portfolio of measures, these risks can be greatly reduced. Net risk is further reduced by the fact that a number of non-climatic benefits would result from measures to limit CO2 emissions. Based on the review of risks associated with measures to limit emissions here, and the review of the risks associated with unrestrained emissions presented in Part I, it is concluded that a reasonable near- term (20-30 year) risk hedging strategy is one which seeks to stabilize global fossil CO2 emissions at the present (early 1990's) level. This in turn implies an emission reduction of 26% for industrialized countries as a whole and 40-50% for Canada and the USA if developing country emissions are to increase by no more than 60%, which in itself would require major assistance from the industrialized countries. The effectiveness of global CO2-emission stabilization in slowing down the buildup of atmospheric CO2 is enhanced by the fact that the airborne fraction (ratio of annual atmospheric CO2 increase to total annual anthropogenic emissions) decreases if emissions are stabilized, whereas it increases if emissions continue to grow exponentially. The framework and conclusions presented here are critically compared with so-called optimization frameworks.

1410^3^Kramer,K^Friend,A^Leinonen,I^1996^1^Modelling comparison to evaluate the importance of phenology and spring frost damage for the effects of climate change on growth of mixed temperate-zone deciduous forests^288^7^1^31-41^^^^^22 Aug^^^^^5604
243^674^705^t the present (early 1990's) level. This in turn implies an emission reduction of 26% for industrialized countries as a whole and 40-50% for Canada and the USA if developing country emissions are to increase by no more than 60%, which in itself would require major assistance from the industrializeA^5603^The importance of 3 phenological types of deciduous tree, and the effects of the occurrence of frost damage on growth of mixed-species forests, were evaluated using the models FORGRO and HYBRID, The climate change scenarios used were a doubling of the CO2 concentration (700 mu mol mol(-1)) and an increase in temperature ranging from 0 to 7 degrees C. Both FORGRO and HYBRID are mechanistic models treating eco-physiological processes in detail. FORGRO highlights potential growth in managed forests where all individuals of one species are of the same age and size, whereas HYBRID highlights growth in natural forests, including regeneration and mortality of individual trees that differ in age and size. Furthermore, the importance of inaccurate prediction of phenological events and frost hardiness for growth in mixed-species stands was evaluated by comparing dynamic models to regression models. The dynamic models predict the timing of phenological events annually and the progression of frost hardiness during dormancy, whereas the regression models represent empirical relationships between the change in the average date of phenological events with a rise in mean winter temperature and the level of frost hardiness at the moment of leaf unfolding. The results of the climate change scenarios indicate for both FORGRO and HYBRID that: (1) the differences in net primary production (NPP) of the 3 phenological types considered are enhanced when grown in a mixed-species stand compared to a monospecies stand; and (2) the effects of frost damage on growth are more prominent in mixed-species stands than in monospecies stands. Regarding the accuracy of the dynamic approach compared to the regression approach for predicting the timing of leaf unfolding and spring frost damage, the dynamic approach for leaf unfolding results in a similar response of NPP to the regression approach, both for the monospecies and the mixed-species situation. The dynamic approach, however, yields larger differences in the NPP between the phenological types because the model predicts a greater advancement of leaf unfolding than does the regression approach. Comparing the regression approach to the dynamic approach with regard to frost hardiness, the regression approach shows a greater frequency of frost damage; because, according to the dynamic approach the minimum level of frost hardiness is attained after the date of leaf unfolding, thus reducing this frequency.





















1411^1^Houghton,RA^1996^1^Converting terrestrial ecosystems from sources to sinks of carbon^221^25^4^267-272^^^^^Jun^^^^^5616
1134^1467^1547^174^1986^227^2317^362^673^892^ Regarding the accuracy of the dynamic approach compared to the regression approach for predicting the timing of leaf unfolding and spring frost damage, the dynamic approach for leaf unfolding results in a similar response of NPP to the regression approach, both for the monospecies and the mixed-species situation. The dynamic approach, however, yields larger differences in the NPP between the phenologiA^5615^It may be possible to sequester carbon in forests and forest products, but to date global trends in land management have resulted in a release of terrestrial carbon to the atmosphere. Over 100 PgC were released between 1850 and 1980, and during the 1980s global changes in land use (predominantly deforestation) caused a net release of 1.6 PgC yr(-1), about 25% of the total emissions of carbon dioxide from human activities and about 15% of the enhanced radiative forcing. Management practices that could change this release of terrestrial carbon to an accumulation include (i) a halt to deforestation; (ii) an expansion in the land area of forests; (iii) an increase in the stocks of carbon in existing forests; (iv) more efficient harvest and greater use of wood in long- lasting products; and (v) the substitution of wood fuels for fossil fuels. However, the rate of global warming needs management as well. Unless the warming is gradual enough to avoid widespread mortality of forests, the additional releases of carbon caused by the warming itself, through increased respiration, decay, and fires, may cancel the intended effects of forest management.

1412^2^Mbata,GN^Reichmuth,C^1996^1^The comparative effectiveness of different modified atmospheres for the disinfestation of Bambarra groundnuts, Vigna subterranea (L) Verde, infested by Callosobruchus subinnotatus (Pic) (Coleoptera:Bruchidae)^306^32^1^45-51^^^^^Jan^^^^^5618
 activities and about 15% of the enhanced radiative forcing. Management practices that could change this release of terrestrial carbon to an accumulation include (i) a halt to deforestation; (ii) an expansion in the land area of forests; (iii) an increase in the stocks of carbon in existing forests; (iv) more efficient harvest and greater use of wood in long- lasting products; and (v) the substitution of wood fuels for fossil fuels. However, the rate of global warming needs management as well. Unless the warming is gradual enough to avoid widespread mortality of forests, the additional releases oA^5617^Four atmospheres containing high levels of carbon dioxide (CO2) and different quantities of oxygen (0, 2.0, 3.7, 5.1%) were investigated for their toxicity to Callosobruchus subinnotatus (Pie), The quantity of oxygen contained in atmospheres influenced the disinfestation levels in bambarra groundnuts infested by C. subinnotatus. The different developmental stages had varying susceptibilities to the atmospheres, Atmospheres containing low concentrations of oxygen (2.0, 3.7%) enhanced the mortality of adults, The anoxic atmosphere of 100% CO2 was more toxic to eggs, larvae, and pupae than the other atmospheres, There was a progressive decrease in toxicity as the quantity of oxygen in the inert atmospheres increased. Copyright (C) 1996 Elsevier Science Ltd

1413^3^Ogasawara,N^Inden,H^Asahira,T^1996^1^Effects of lighting cycle on Caladium plantlets grown under ventilated and airtight culture vessels in relation to net daily CO2 uptakes^180^65^1^129-134^^^^^Jun^^^^^5620
781^ests, the additional releases oA^5619^Caladium plantlets were cultured in vitro under a long lighting cycle (16 hr light/8 hr dark) and a short lighting cycle (2 hr light/1 hr dark). When gas exchange between the inside and outside of the culture vessel was allowed, the short lighting cycle enhanced growth, but when the culture vessel was airtight, the lighting cycle had no effect on growth. The estimated net daily CO2 uptake under the short lighting cycle is greater than that under the long lighting cycle only when gas exchange occurs between the inside and outside of the vessel. These results demonstrate that the enhancement of growth by the short lighting cycle is due to an increase in the amount of available CO2 resulting from the reduced escape of CO2 from the vessel.

1414^6^Peiris,DR^Crawford,JW^Grashoff,C^Jefferies,RA^Porter,JR^Marshall,B^1996^1^A simulation study of crop growth and development under climate change^107^79^4^271-287^^^^^May^^^^^5622
1356^314^416^633^5^1^129-134^^^^^Jun^^^^^5620
781^ests, the additional releases oA^5621^Climate changes of the order predicted by Global Circulation Models have important implications for arable crop production. We have studied the impact in Scotland using simulation models for three crops of contrasting developmental type: faba or field bean, potato, spring and winter wheat. The models used were the FABEAN, SCRI water-constrained potato model and AFRCWHEAT2 models respectively. Consideration has been made of the natural year-to-year variation in weather which causes yield variability by using 100 years of input weather data produced by a weather generator. The models were run for four Scottish sites and five Scottish soils. Based on GCM predictions, we used eight scenarios of future climate which combine both temperature and rainfall changes. Current temperature (T-0) and rainfall (R(0)) were used as a baseline, and each of T-0 + 1 degrees C, T-0 + 2 degrees C, T-0 + 3 degrees C were used with rainfall unchanged at R(0), and increased by seasonally adjusted amounts ranging from 0 to 1.5 mm per wet day. Possible enhancements due to CO2 fertilisation were not included in the study. Increased temperatures increase crop development rate, which shortens the growing season for wheat and faba bean, but, given a fixed harvest date, lengthens the season for potatoes. Yields of potato increased by up to 33% over all our sites and scenarios, whereas wheat yields decreased by 5-15% and faba bean by 11-41%. Rainfall increases of the amount suggested here do not affect the yield of potatoes or spring wheat, but winter wheat yields are reduced, due to leaching, and faba bean yields increase through alleviation of water shortage. Faba beans also show a reduction in yield variability as a result of increased rainfall. Changes in variability in wheat and potato were less pronounced and tended to reflect the increase in variability which was assumed to accompany the increased rainfall. Predictions for the changes in the frequencies of high and low yields are also presented. The results give an indication of the level of changes in crop production which would be expected in these future climates.

1415^6^Seneweera,S^Blakeney,A^Milham,P^Basra,AS^Barlow,EWR^Conroy,J^1996^1^Influence of rising atmospheric CO2 and phosphorus nutrition on the grain yield and quality of rice (Oryza sativa cv. Jarrah)^281^73^2^239-243^^^^^Mar-Apr^^^^^5624
312^632^92^cenarios, whereas wheat yields decreased by 5-15% and faba bean by 11-41%. Rainfall increases of the amount suggested here do not affect the yield of potatoes or spring wheat, but winter wheat yields are reduced, due to leaching, and faba bean yields increase through alleviation of water shortage. Faba beans also show a reduction in yield variability as a result of increased rainfall. Changes in variability in wheat and potato were less pronounced and tended to reflect the increase in variability which was assumed to accompany the increased rainfall. Predictions for the changes in the frequencies of high and low yields are also presented. The results give an indication of A^5623^Raising the atmospheric CO2 concentration from 350 mu l of CO2 per liter to a level expected by the end of the next century (700 mu l/L) influenced both the grain yield and quality of the short-duration rice (Oryza sativa) cultivar, Jarrah. Yield was enhanced by up to 58%, primarily due to an increase in grain number, although grain size was also greater at high CO2. Varying the supply of phosphorus influenced the magnitude of the CO2 response with greatest responses occurring at medium rather than luxury or low phosphorus supplies. However, yield enhancement by high CO2 was observed even when phosphorus supply was severely growth limiting. Chemical (amylose and nutrient concentration) and physical (relative paste viscosity) measurements made on the ground grain indicated that cooked rice grain from plants grown under high levels of CO2 would be firmer. The nutritive value of grain was also changed at high CO2 due to a reduction in grain nitrogen and, therefore, protein concentration. However, total nitrogen content per grain was unaffected by high CO2. In contrast, phosphorus content per grain was greater at high CO2 and there was a strong correlation between magnesium and phosphorus concentrations. These results indicate that there is a need to plan for the inevitable rise in atmospheric CO2 concentrations by selecting genotypes that will maintain suitable quality characteristics under global change.

1416^2^Andrade,JL^Nobel,PS^1996^1^Habitat, CO2 uptake and growth for the CAM epiphytic cactus Epiphyllum phyllanthus in a Panamanian tropical forest^307^12^^291-306^^^^^Mar^^^^^5626
1669^2318^2319^2320^2321^385^739^779^everely growth limiting. Chemical (amylose and nutrient concentration) and physical (relative paste viscosity) measurements made on the ground grain indicated that cooked rice grain from plants grown under high levels of CO2 would be firmer. The nutritive value of grain was also changed at high CO2 due to a reduction in grain nitrogen and, therefore, protein concentration. However, total nA^5625^In the tropical forest of Barro Colorado Island, habitat characteristics, diel acidity changes, CO2 uptake and growth were investigated for the epiphytic cactus Epiphyllum phyllanthus (L.) Haw. It occurred most frequently in tree cavities with its roots in canopy soil and was especially abundant on two tree species: Platypodium elegans J. Vogel and Tabebuia guayacan (Seem.) Hemsl. Its maximum net CO2 uptake rates were low under natural conditions (1.4 mu mol m(-2) s(- 1)) but were comparable to those of other CAM and C-3 epiphytes under wet conditions in a screenhouse. Under both natural conditions and in the screenhouse, partial shade enhanced growth and CAM activity. When plants grew under a photosynthetic photon flux of c. 4 mol m(-2) d(-1), their nocturnal acidity increase and total net CO2 uptake were twice as much as for plants growing at lower (an average of 2.4 mol m(-2) d(-1)) and higher (7.7 mol m(-2) d(-1)) photosynthetic photon fluxes. Stem elongation was 27% greater at the intermediate photosynthetic photon flux. Seedlings of E. phyllanthus survived three months of drought and responded rapidly to rewetting, recovering fully within three days. Transpiration rates and nocturnal acidity increases also recovered to the values of well-watered plants a few days after rewetting, indicating that this species can take advantage of episodic rainfall during the dry season.

1417^2^Brandrud,TE^Roelofs,JGM^1995^1^Enhanced growth of the macrophyte Juncus bulbosus in S Norwegian limed lakes. A regional survey^94^85^2^913-918^^^^^Dec^^^^^5628
624^nditions in a screenhouse. Under both natural conditions and in the screenhouse, partial shade enhanced growth and CAM activity. When plants grew under a photosynthetic photon flux of c. 4 mol m(-2) d(-1), their nocturnal acidity increase and total net CO2 uptake were twice as much as for plants growing at lower (an average of 2.4 mol m(-2) d(-1)) and higher (7.7 mol m(-2) d(-1)) photosynthetic photon fluxes. Stem elongation was 27% greater at the intermediate phA^5627^The effects of liming on the aquatic macrophyte vegetation have been investigated in S and SW Norway. In the western part of the study area, Juncus bulbosus was considerably more frequent in the limed than in the unlimed lakes, whilst in the eastern part there were no such differences, and the J. bulbosus populations were generally not so vital. In some southwestern areas a luxuriant and massiv nuisance growth of Juncus bulbosus in the depth zone 0-4 m was recorded. The most vital plants produced up to 1 m long annual shoots, and developed extensive, dense and vital surface mats in shallow areas (depth zone 0-3 m) after 4-5 years. The original isoetid vegetation had disappeared in the areas of dense J. bulbosus populations, and this development seems to be more or less irreversible. The massive J. bulbosus expansion is seen mainly in directly limed lakes with a sometimes visible layer of calcium carbonate on the sediment surface, but enhanched growth has been observed also in lakes downstream liming. The massive expansion is believed to be due to an increase of CO2 and ammonium in the sediment pore water, combined with a mild climate with a very high precipitation. In many areas the liming has led to an increase in species diversity, and a (re-)establishment of some acid-intolerant species such as Myriophyllum alterniflorum and Potamogeton spp.

1418^1^DeMothes,MAG^1996^1^Effects of enhanced CO2 concentration on wheat photosynthesis and long- and short-term stomatal behaviour^79^32^2^193-202^^^^^^^^^^5630
264^385^399^al shoots, and developed extensive, dense and vital surface mats in shallow areas (depth zone 0-3 m) after 4-5 years. The original isoetid vegetation had disappeared in the areas of dense J. bulbosus populations, and this development seems to be more or less irreversible. The massive J. bulbosus expansion is seen mainly in directly limed lakes with a sometimes visible layer of calcium carbonate on the sediment surface, but enhanched growth has been observed also in lakes downstream liming. A^5629^Wheat (Triticum aestivum L.) plants were cultivated in a growth chamber at normal (35 Pa = c(35)) and increased (70 Pa = c(70)) CO2 partial pressure. Environmental conditions other than CO2 concentration were similar for the c(35) and the c(70) plants. For the c(35) and the c(70) plants stomatal density was similar. When both variants were measured at growth conditions, the net photosynthetic rate (P-N) Of c(70) plants was 44 % higher and stomatal conductance to water vapour pressure (g(s)) was 22 % lower than those of the c(35) plants, while the relation between internal partial pressure of CO2 (pci) and external partial pressure (pea) was similar for both variants. Plants were also submitted to a sequence of increments in CO2 concentration (from 10 Pa up to saturating CO2 concentration) at saturating photosynthetically active radiation (PAR). Following 1.5 h at saturating CO2 concentration and PAR, CO2 concentration was decreased stepwise. Both variants showed hysteresis in the response of P-N, transpiration rate (E), g(s) and water use efficiency (WUE) to pci. While CO2 concentration was incremented, P-N and g(s) were linearly related indicating that mesophyll activity and g(s) were correlated. At saturating CO2 concentration and PAR, end product feedback inhibition on photosynthesis disrupted this correlation for both variants. Plants were also submitted to a sequence of increments in PAR (from 40 mu mol m(-2), s(-1) up to saturating PAR) at saturating CO2 concentration. Following 1.5 h at saturating CO2 concentration and PAR, PAR was decreased stepwise. While both variants showed hysteresis in the response of P-N, E and g(s), the c(35) plants showed also hysteresis in the response of pci/pca and WUE to PAR. Stomatal conductance and activity of mesophyll remained co-ordinated during the whole experiment for the c(70) plants, while for the c(35) plants the correlation between g(s) and mesophyll activity present during step-up PAR response was disrupted at saturating CO2 concentration and PAR.
N, tran1419^2^Knapp,T^Mookerjee,R^1996^1^Population growth and global CO2 emissions - A secular perspective^308^24^1^31-37^^^^^Jan^^^^^5632
227^2322^312^607^727^ mesophyll activity and g(s) were correlated. At saturating CO2 concentration and PAR, end product feedback inhibition on photosynthesis disrupted this correlation for both variants. Plants were also submitted to a sequence of increments in PAR (from 40 mu mol m(-2), s(-1) up to saturating PAR) at saturating CO2 concentration. Following 1.5 h at saturating CO2 concentration and PAR, PAR was decreased stepwise. While both variants showed hysteresis in the response of P-N, E and g(s), the c(35) plants showed also hysteresis in the response of pci/pca and WUE to PAR. Stomatal conductance and activity of mesophyll remained co-ordinated during the whole experiment for the c(70) plants, while for the c(35) plants the correlation between g(s) and mesophyll activity present during step-up PAR response was disrupted at saturating CO2 concentration and PAR.
N, tranA^5631^Considerable scientific effort has been applied to the question of whether worldwide fossil fuel combustion and the resultant emission of CO2 (as well as emissions of other greenhouse gases) will cause a discernible enhancement of the greenhouse effect in the next century, A more precise understanding of the contribution of human activity to potential global warming (vis-ri-vis natural climatic variability) is of critical policy interest, Surprisingly little research has been devoted to establishing the underlying statistical relationship between human activities and CO2 emissions, In this paper, we explore the nature of the relationship between global population growth and CO2 emissions by employing the test of causality developed by Granger on annual data for 1880-1989, as well as more comprehensive error correction and cointegration models, The results suggest a lack of a long-term equilibrium relationship, but imply a short-term dynamic relationship from CO2 to population growth.
nd PAR.
N, tran1420^5^Miyachi,S^Burger,J^Kotzabasis,K^Thielmann,J^Senger,H^1996^1^Photosynthetic characteristics of three strains of cyanobacteria grown under low- or high-CO2 conditions^291^51^1-2^40-46^^^^^Jan-Feb^^^^^5634
1020^1085^188^2323^424^467^493^637^652^741^ffect in the next century, A more precise understanding of the contribution of human activity to potential global warming (vis-ri-vis natural climatic variability) is of critical policy interest, Surprisingly little research has been devoted to establishing the underlying statistical relationship between human activities and CO2 emissions, In this paper, we explore the nature of the relationship between global population growth and CO2 emissions by employing the test of causality developed by Granger on annual data for 1880-1989, as well as more comprehensive error correction and cointegration models, The results suggest a lack of a long-term equilibrium relationship, but imply a short-term dynamic relationship from CO2 to population growth.
nd PAR.
N, tranA^5633^Quantum requirements of photosynthetic oxygen evolution at 679 nm, fluorescence emission spectra at liquid nitrogen temperature (77 K) and fluorescence induction kinetics in the presence of DCMU, were measured in the cyanobacteria Anabaena variabilis M3, Anabaena variabilis ATCC 29413 and Anacystis nidulans R2, each grown under low- or high-CO2 conditions. Low- CO2 grown cells of the cyanobacteria showed a higher quantum requirement of photosynthetic oxygen evolution and a higher ratio of F-710-740 to F-680-700 fluorescence and a lower variable fluorescence in the presence of DCMU than high-CO2 grown cells. These findings indicate a change in excitation energy distribution in favour of photosystem I. The result might be an enhancement in ATP formation caused by cyclic electron now which in turn provokes dissolved inorganic carbon (DIG) accumulation in these low-CO2 grown cells.
-term equilibrium relationship, but imply a short-term dynamic relationship from CO2 to population growth.
nd PAR.
N, tran1421^3^Sonesson,M^Callaghan,TV^Carlsson,BA^1996^1^Effects of enhanced ultraviolet radiation and carbon dioxide concentration on the moss Hylocomium splendens^127^2^1^67-73^^^^^Feb^^^^^5636
174^188^2171^2324^2325^2326^2327^417^566^92^ria Anabaena variabilis M3, Anabaena variabilis ATCC 29413 and Anacystis nidulans R2, each grown under low- or high-CO2 conditions. Low- CO2 grown cells of the cyanobacteria showed a higher quantum requirement of photosynthetic oxygen evolution and a higher ratio of F-710-740 to F-680-700 fluorescence and a lower variable fluorescence in the presence of DCMU than high-CO2 grown cells. These findings indicate a change in excitation energy distribution in favour of photosystem I. The result might be an enhancement in ATP formation caused by cyclic electron now which in turn provokes dissolved inorganic carbon (DIG) accumulation in these low-CO2 grown cells.
-term equilibrium relationship, but imply a short-term dynamic relationship from CO2 to population growth.
nd PAR.
N, tranA^5635^In a laboratory experiment interaction effects of UV-B and CO2 on photosynthesis and growth of the moss Hylocomium splendens were studied. The plants were exposed to two CO2 levels (350 ppm and 600 ppm) and three UV-B levels (no UV-B, ambient UV-B and that corresponding to 20% ozone depletion) for 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants. There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO2 concentration, whereas there was no effect due to UV-B. There was a decreased growth due to both UV-B and CO2 and an interaction effect on growth (in length). The UV-B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV-B dose. This was a counter- intuitive result and the following tentative interpretation was made: differences in the measured UV-A/UV-B/PAR ratios between the treatments could explain the result provided there was a non-linear response to UV over the range of irradiance levels used.

1422^3^Kunz,RP^Schulze,RE^Scholes,RJ^1995^1^An approach to modelling spatial changes of plant carbon:nitrogen ratios in southern Africa in relation to anticipated global climate change^134^22^2-3^401-408^^^^^Mar-May^^^^^5638
or 5 months. The effects were recorded by measuring the photosynthetic response and growth of the plants. There was a statistically significant change in photosynthetic efficiency and maximum photosynthetic rates due to time and to enhanced CO2 concentration, whereas there was no effect due to UV-B. There was a decreased growth due to both UV-B and CO2 and an interaction effect on growth (in length). The UV-B dose corresponding to the ambient level had a larger reducing effect on growth than the highest UV-B dose. This was a counter- intuitive result and the following tentative interpretation was made: differences in the measured UV-A/UV-B/PAR ratios between the treatments could explain the result provided therA^5637^The carbon to nitrogen (C:N) ratio is the main factor determining the forage quality of a plant, with a low C:N ratio indicating relatively good plant digestibility and a high C:N ratio inferring relatively poor forage quality. Global atmospheric composition and climate change effects on plant carbon to nitrogen ratios are thus likely to be important when predicting possible second-order impacts of the enhanced greenhouse effect on rangeland forage quality and the resultant feeding habits of foraging animals and herbivorous insects. Equations relating the assimilation of total carbon and nitrogen rates to monthly air temperature, the ambient CO2 level and soil fertility were used together with detailed spatial climatic and soil databases to simulate regional patterns of C:N ratios over southern Africa. Carbon to nitrogen ratios were estimated for both the present climate and for a possible future climate scenario defined by a general 2 degrees C mean daily temperature increase over southern Africa (but with latitudinal, seasonal and diurnal adjustments made), an increase in atmospheric CO2 concentration from 360 to 560 ppmv, but with no changes in precipitation patterns. When C:N differences between future and present climates are examined, results indicate both relative increases and decreases over southern Africa in a regional context, ranging from - 8 to + 8%. Areas where the C:N ratios decreased indicate that for the future climate scenario which was assumed the relative increase in assimilated nitrogen would be greater than that for carbon. Similarly, areas where the C:N ratios increased indicate that the relative increase in assimilated carbon would be greater than that for nitrogen. In this study, regions sensitive to climate change effects on C:N ratios in southern Africa have therefore been identified and with that, those areas where the consumption of plant matter may be expected to increase or decrease as a result of anticipated global climate change.
erature increase over southern Africa (bu1423^2^Apel,P^Peisker,M^1995^1^Variability of photosynthetic gas exchange parameters, dark respiration, and stomatal numbers in species of Polygonum^37^95^3^365-372^^^^^Nov^^^^^5640
348^417^465^
A^5639^Within the genus Polygonum a large variation was found between species with regard to stomatal number, gas phase resistance, intracellular resistance and dark respiration. Interspecific variation in CO2 compensation concentration and intercellular CO2 concentration at constant external concentration were comparatively small. Correlations were found between stomatal number and gas phase resistance, stomatal number and Gamma, and Gamma and the product of dark respiration rate and intracellular resistance. The influence of dark respiration and stomatal number on photosynthetic gas exchange is discussed. It was concluded that dark respiration in light was enhanced by 22% as a mean value in 9 Polygonum species and by 62% in Polygonum lapathifolium.
 global climate change.
erature increase over southern Africa (bu1424^3^Sonesson,M^Callaghan,TV^Bjorn,LO^1995^1^Short-term effects of enhanced UV-B and CO2 on lichens at different latitudes^309^27^^547-557^^^^^^^^^^5642
1007^1077^2326^2328^312^417^493^566^694^92^39^Within the genus Polygonum a large variation was found between species with regard to stomatal number, gas phase resistance, intracellular resistance and dark respiration. Interspecific variation in CO2 compensation concentration and intercellular CO2 concentration at constant external concentration were comparatively small. Correlations were found between stomatal number and gas phase resistance, stomatal number and Gamma, and Gamma and the product of dark respiration rate and intracellular resistance. The influence of dark respiration and stomatal number on photosynthetic gas exchange is discussed. It was concluded that dark respiration in light was enhanced by 22% as a mean value in 9 Polygonum species and by 62% in Polygonum lapathifolium.
 global climate change.
erature increase over southern Africa (buA^5641^Interaction effects of UV-B and CO2 on three lichens species, Cladonia arbuscula, Cetraria islandica and Stereocaulon paschale, from two latitudinal sites, 68 degrees N and 56 degrees N, were studied in a laboratory experiment. The response of the plants was recorded by measuring their chlorophyll fluorescence. All species had a similar response to enhanced UV-B depending on the latitude from which the population came and the time of the season when they were sampled. Overall, there was a significant increase in photosystem II yield (as measured by a fluorescence technique) due to UV-B and no separate effect due to enhanced CO2, although there was a significant interaction between CO2 and UV-B. The increase due to UV-B was at the low CO2 level. There were also significant differences in response due to latitude. The results contradict our hypotheses that negative effects of UV-B would be larger in the North than in the South and that a negative response should be especially large during the early season. (C) 1995 The British Lichen Society

1425^2^Wangwacharakul,V^Bowonwiwat,R^1995^1^Economic evaluation of CO2 response options in the forestry sector: The case of Thailand^310^8^5^293-307^^^^^^^^^^5644

A^5643^Using the benefit-cost analysis approach, this paper attempts to evaluate the potential of the forestry sector in Thailand to reduce carbon emissions of the country. Protecting conserved forests can avoid a substantial amount of carbon emission from deforestation, although certain costs are attached. Reforestation also enhances carbon sequestration and, in most cases, incurs no cost to society. Under the present government's commitment to fully protect the conserved forests and reforest the deforested areas in the country, Thailand could reduce the growth of carbon emission by as much as 260 million tons over the next two decades. The costs to society, if any, would be small given other, non-quantifiable, benefits of the forests.
t a negative response should be especially large during the early seas1426^2^Beer,S^Koch,E^1996^1^Photosynthesis of marine macroalgae and seagrasses in globally changing CO2 environments^311^141^1-3^199-204^^^^^Oct^^^^^5646
2329^948^ Thailand^310^8^5^293-307^^^^^^^^^^5644

A^5643^Using the benefit-cost analysis approach, this paper attempts to evaluate the potential of the forestry sector in Thailand to reduce carbon emissions of the country. Protecting conserved forests can avoid a substantial amount of carbon emission from deforestation, although certain costs are attached. Reforestation also enhances carbon sequestration and, in most cases, incurs no cost to society. Under the present government's commitment to fully protect the conserved forests and reforest the deforested areas in the country, Thailand could reduce the growth of carbon emission by as much as 260 million tons over the next two decades. The costs to society, if any, would be small given other, non-quantifiable, benefits of the forests.
t a negative response should be especially large during the early seasA^5645^Photosynthetic rates of many marine macroalgae are saturated by the present day inorganic carbon (Ci) composition of seawater, while those of seagrasses (or marine angiosperms) are CO2- limited. In this study we attempted to simulate the Ci conditions of near-shore seawater during the time that seagrasses colonised the sea (in the Cretaceous), and compare the photosynthetic performance of representatives of the 2 plant groups under those versus present day conditions. The results show that the seagrasses have an affinity for Ci at least as high as the algae under the low pH and high CO2/HCO3- concentration ratios simulating near-shore areas of the Cretaceous seas, indicating that their photosynthetic capacity then matched that of macroalgae. However, in the high pH and high CO2/HCO3- ratios of today, their affinity for Ci is lower than that of the macroalgae, and it is suggested that this deficiency renders them a lower ability for Ci utilisation. This situation may possibly be reversed again as global CO2 levels of the atmosphere and, consequently, of near-shore marine habitats increase in the future.

1427^4^Buchmann,N^Brooks,JR^Rapp,KD^Ehleringer,JR^1996^1^Carbon isotope composition of C-4 grasses is influenced by light and water supply^9^19^4^392-402^^^^^Apr^^^^^5648
131^1859^243^344^348^439^494^603^643^698^nised the sea (in the Cretaceous), and compare the photosynthetic performance of representatives of the 2 plant groups under those versus present day conditions. The results show that the seagrasses have an affinity for Ci at least as high as the algae under the low pH and high CO2/HCO3- concentration ratios simulating near-shore areas of the Cretaceous seas, indicating that their photosynthetic capacity then matched that of macroalgae. However, in the high pH and high CO2/HCO3- ratios of today, their affinity for Ci is lower than that of the macroalgae, and it is suggested that this deficiency renders them a lower ability for Ci utilisation. This situation may possibly be reversed again as globaA^5647^The carbon isotope composition of C-4 grasses has the potential to be used as an indicator of changes in the isotopic composition and concentration of atmospheric CO2, especially for climate reconstruction. The usefulness of C-4 grasses far this purpose hinges on the assumption that their photosynthetic discrimination against C-13 remains constant in a wide range of environmental conditions. We tested this assumption by examining the effects of light and water stress on the carbon isotope composition of C-4 grasses using different biochemical subtypes (NADP-ME, NAD-ME, PCK) in glasshouse experiments. We grew 14 different C-4 grass species in four treatments: sun- watered, sun-drought, shade-watered and shade-drought. Carbon isotope discrimination (Delta) rarely remained constant. In general, Delta values were lowest in sun-watered grasses, greater for sun-drought plants and even higher for plants of the shade-watered treatment. The highest Delta values were generally found in the most stressed grasses, the shade-drought plants. Grasses of the NADP-ME subtype were the least influenced by a change in environmental variables, followed by PCK and NAD-ME subtypes. Water availability affected the carbon isotope discrimination less than light limitation in PCK and NAB-ME subtypes, but similarly in NADP-ME subtypes. In another experiment, we studied the effect of increasing light levels (150 to 1500 mu mol photons m(-2) s(-1)) on the Delta values of 18 well-watered C-4 grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 mu mol photons m(-2) s(-1). Below this light level, Delta values increased with decreasing irradiance for all biochemical subtypes. The change in Delta was less pronounced in NADP-ME and PCK than in NAD-ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C-4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composition of atmospheric CO2 in field/glasshouse studies or climate reconstruction.

1428^2^Gilmanov,TG^Oechel,WC^1995^1^New estimates of organic matter reserves and net primary productivity of the North American tundra ecosystems^134^22^4-5^723-741^^^^^Jul-Sep^^^^^5650
1105^227^31^547^681^737^738^739^791^ subtypes. In another experiment, we studied the effect of increasing light levels (150 to 1500 mu mol photons m(-2) s(-1)) on the Delta values of 18 well-watered C-4 grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 mu mol photons m(-2) s(-1). Below this light level, Delta values increased with decreasing irradiance for all biochemical subtypes. The change in Delta was less pronounced in NADP-ME and PCK than in NAD-ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C-4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composiA^5649^The reserves and fluxes of carbon in ecosystems of the circumpolar tundra biome should be among the most responsive to climatic change, including their transformation from a CO2 sink to a CO2 source with respect to the atmosphere. To estimate accurately the significance of Arctic tundra to global carbon stocks and balances, quantitative geographically referenced estimates of the masses and fluxes of carbon are needed. Although new empirically based estimates of reserves and productivity were recently obtained for the Eurasian part of the tundra biome using GIS technology, the figures currently used for carbon reserves and productivity of the North American tundra ecosystems are based on earlier expert estimates or large scale models based on data primarily for non-tundra areas. To obtain new more empirically based estimates of the reserves and fluxes of carbon in North American tundra ecosystems a set of records of North American tundra ecosystems was obtained from the Global Arctic/Alpine Climate/Soil/Plant Productivity Data Base (Global Change Research Group, San Diego State University). This data base contains phytomass, productivity, climatic and soil characteristics for nearly fifty tundra-type ecosystems studied during the past 30 years in Alaska and Northern Canada. This information was used to interpolate the necessary data for all the tundra cells (1 X 1 degree) of the simple GIS, based on the Global Vegetation Map and the FAO/UNESCO Soil Map of the World. By integrating the corresponding maps of phytomass and productivity the quantitative estimates of the reserves and. productivity fluxes of organic matter in tundra ecosystems of North America and Greenland (4.12 x 10(6) km(2) total area) were obtained: 2.26 Gt above-ground phytomass, 4.99 Gt total phytomass, 91.3 Gt soil organic matter of the active layer; 0.56 Gt/yr above- ground net primary production; 0.98 Gt/yrotal net primary production. As an alternative means of determining the productivity totals for North American tundra ecosystems, the phenomenological model of the form: NPP=f(T,H,G), relating net primary production of tundra ecosystems to climatic, soil and vegetation factors, was applied to the GIS layers of mean annual temperature (T), soil organic matter content (H), and above-ground phytomass density (G) to produce a map of modelled NPP estimates for North American tundra ecosystems. The subroutine of spatial integration of the local production estimates takes into account geographical changes in the landscape composition (proportions of the zonal, meadow, mire and aquatic ecosystem types) and results in totals of 0.58 Gt/yr for above-ground and 1.16 Gt/yr for total net primary production of tundra ecosystems of North America and Greenland.

1429^4^Huntley,B^Berry,PM^Cramer,W^McDonald,AP^1995^1^Modelling present and potential future ranges of some European higher plants using climate response surfaces^134^22^6^967-1001^^^^^Nov^^^^^5652
185^1933^2330^2331^248^667^668^670^673^oductivity totals for North American tundra ecosystems, tA^5651^It is hypothesized that the principal features of higher plant distributions at continental scales are determined by the macroclimate. Bioclimate data have been computed on a 50 km grid across Europe. Along with published maps of higher plant distributions based upon the same grid, these data have been used to derive climate response surfaces that model the relationship between a species' distribution and the present climate. Eight species representative of a variety of phytogeographic patterns have been investigated. The results support the hypothesis that the European distributions of all eight species are principally determined by macroclimate and illustrate the nature of the climatic constraints upon each species. Simulated future distributions in equilibrium with 2 x CO2 climate scenarios derived from two alternative GCMs show that all of the species are likely to experience major shifts in their potential range if such climatic changes take place. Some species may suffer substantial range and population reductions and others may face the threat of extinction. The rate of the forecast climate changes is such that few, if any, species may be able to maintain their ranges in equilibrium with the changing climate. In consequence, the transient impacts upon ecosystems will be varied but often may lead to a period of dominance by opportunist, early-successional species. Our simulations of potential ranges take no account of such factors as photoperiod or the direct effects of CO2, both of which may substantially alter the realized future equilibrium.

1430^2^Martin,PH^Guenther,AB^1995^1^Insights into the dynamics of forest succession and non-methane hydrocarbon trace gas emissions^134^22^2-3^493-499^^^^^Mar-May^^^^^5654
174^227^314^427^ distributions in equilibrium with 2 x CO2 climate scenarios derived from two alternative GCMs show that all of the species are likely to experience major shifts in their potential range if such climatic changes take place. Some species may suffer substantial range and poA^5653^Natural biogenic non-methane hydrocarbon (NMHC) emissions significantly influence the concentrations of free hydroxyl and peroxy radicals, carbon monoxide and tropospheric ozone. Present concerns with air pollution and the global carbon balance call for a better understanding of the respective roles of climate dynamics and vegetation succession in determining NMHC emissions. This constitutes the focus of the present paper. The approach consists in coupling the Energy, Water and Momentum Exchange and Ecological Dynamics model, a climatically sensitive, physically based gap phase forest dynamics model, and NMHC trace gas emission algorithms to assess possible changes in NMHC emissions from forests under stationary and changing climatic conditions. In summary, it is possible to follow the temporal evolution of foliar emissions over centuries using a vegetation dynamics model coupled with an NMHC emissions module. Significant changes in isoprene and terpene emissions can take place as vegetation succession occurs under stationary climatic conditions and as climatic perturbations of the type and magnitude foreseen for global change alter the local microclimate. As illustrated by two examples, emissions may decrease or increase depending on the local climate and vegetation. The respective actions of changes in species absolute and relative abundance and changes in temperature interact very non-linearly making changes in emissions difficult to predict. None the less, coupled models of the kind described here may provide useful insights into the direction of such changes.

1431^4^Melillo,JM^Houghton,RA^Kicklighter,DW^McGuire,AD^1996^1^Tropical deforestation and the global carbon budget^312^21^^293-310^^^^^^^^^^5656
1134^1466^2332^2333^2334^2335^2336^2337^393^931^ary, it is possible to follow the temporal evolution of foliar emissions over centuries using a vegetation dynamics model coupled with an NMHC emissions module. Significant changes in isoprene and terpene emissions can take place as vegetation successioA^5655^The CO2 concentration of the atmosphere has increased by almost 30% since 1800. This increase is due largely to two factors: the combustion of fossil fuel and deforestation to create croplands and pastures. Deforestation results in a net flux of carbon to the atmosphere because forests contain 20-50 times more carbon per unit area than agricultural lands. In recent decades, the tropics have been the primary region of deforestation. The annual rate of CO2 released due to tropical deforestation during the early 1990s has been estimated at between 1.2 and 2.3 gigatons C. The range represents uncertainties about both the rates of deforestation and the amounts of carbon stored in different types of tropical forests at the time of cutting. An evaluation of the role of tropical regions in the global carbon budget must include both the carbon flux to the atmosphere due to deforestation and carbon accumulation, if any, in intact forests. In the early 1990s, the release of CO2 from tropical deforestation appears to have been mostly offset by CO2 uptake occurring elsewhere in the tropics, according to an analysis of recent trends in the atmospheric concentrations of O-2 and N-2. Interannual variations in climate and/or CO2 fertilization may have been responsible for the CO2 uptake in intact forests. These mechanisms are consistent with site-specific measurements of net carbon fluxes between tropical forests and the atmosphere, and with regional and global simulations using process-based biogeochemistry models.

1432^2^Pacala,SW^Deutschman,DH^1995^1^Details that matter: The spatial distribution of individual trees maintains forest ecosystem function^15^74^3^357-365^^^^^Dec^^^^^5658
174^314^374^rent types of tropical forests at the time of cutting. An evaluation of the role of tropical regions in the global carbon budget must include both the carbon flux to the atmosphere due to deforestation and carbon accumulation, if any, in intact forests. In the early 1990s, the release of CO2 from tropical deforestation appearA^5657^This paper shows that the processes controlling tree-scale spatial heterogeneity in forests have large effects on system- level properties such as standing crop, and on community-level properties such as successional species turnover. A ''mean field'' version of the forest simulation model SORTIE is developed in which horizontal spatial heterogeneity is eliminated while vertical structure is retained. The mean-field model maintains only approximately one half the standing crop and looses successional diversity approximately twice as fast as the full spatial model. Data from natural stands support the spatial model. A partial differential equation limit of the mean-field simulator is also derived. The results are set in the context of ongoing efforts to develop models intended to predict the biosphere's response to global change. The importance of processes governing fine-scale spatial heterogeneity implies that biospheric models will agree with nature only ii they are phenomenological (e.g. fitted to data) at large scale, or if spatial scaling rules are discovered that allow one to derive system-level properties from individual- level processes.

1433^5^Paustian,K^Elliott,ET^Collins,HP^Cole,CV^Paul,EA^1995^1^Use of a network of long-term experiments for analysis of soil carbon dynamics and global change: The North American model^289^35^7^929-939^^^^^^^^^^5660
534^57^while vertical structure is retained. The mean-field model maintains only approximately one half the standing crop and looses successional diversity approximately twice as fast as the full spatial model. Data from natural stands support the spatial model. A partial differential equation limit of the mean-field simulator is also derived. The results are set in the context of ongoing efforts to develop models intended to predict the biosphere's response to global change. The importance of processes governing fine-scale spatial heterogeneity implies that biospheric models will agree with nature only ii they are phenomenological (e.g. fitted to A^5659^Soils contain a large proportion of the carbon (C) in the terrestrial biosphere, yet the role of soils as a sink or a source of net atmospheric C flux is uncertain. In agricultural systems, soil C is highly influenced by management practices and there is considerable interest in adapting management systems to promote soil C sequestration, thereby helping to mitigate atmospheric CO2 increases. Long-term field experimental sites represent a unique source of information on soil C dynamics, and networks of such sites provide a key ingredient for making large-scale assessments of soil C change across ranges in climate and soil conditions and management regimes. Currently, there are collaborative efforts to develop such site networks in Australia, Europe, and North America. A network of long-term experiments in North America was established to provide baseline information on the effects of management (i.e. tillage, crop rotations, fertilisation, organic amendments) on soil organic matter. Historical data on soils, primary productivity, climate, and management were synthesised by scientists from the individual field sites, representing a total of 35 long-term field experiments. An additional cross-site soil sampling campaign was carried out to provide uniform comparisons of soil C and nitrogen (N), both within and across sites. Long-term field experiments are a principle component necessary for regional assessments of soil C dynamics. We describe a general methodology for combining long-term data with process-oriented simulation models and regional-level, spatially resolved databases. Such analyses are needed to assess past and present changes in soil C at regional to global scales and to make projections of the potential impacts of changes in climate, CO2, and landuse patterns on soil C in agroecosystems.

1434^2^Potvin,C^Tousignant,D^1996^1^Evolutionary consequences of simulated global change: Genetic adaptation or adaptive phenotypic plasticity^2^108^4^683-693^^^^^Dec^^^^^5662anic matter. Historical data on137^1381^174^1954^2338^2339^2340^386^417^797^agement were synthesised by scientists from the individual field sites, representing a total of 35 long-term field experiments. An additional cross-site soil sampling campaign was carried out to provide uniform comparisons of soil C and nitrogen (N), both within and across sites. Long-term field experiments are a principle component necessary for regional assessments of soil C dynamics. We describe a general methodology for combining long-term data with process-oriented simulation models and regional-level, spatially resolved databases. Such analyses are needed to assess past and present changes in soil C at regional to global scales and to make projections of the potential impacts of changes in climate, CO2, and landuse patterns on soil C in agroecosystems.

1434^2^Potvin,C^Tousignant,D^1996^1^Evolutionary consequences of simulated global change: Genetic adaptation or adaptive phenotypic plasticity^2^108^4^683-693^^^^^Dec^^^^^5662anic matter. Historical data onA^5661^During the next century, natural and agricultural systems might need to adjust to a rapid increase in atmospheric CO2 concentration and global temperature. Evolution of genotypes adapted to this global change could play a central role in plants' response. The main purpose of this study was to determine the relative importance of phenotypic and genotypic responses of plants to global change. To do so, we selected two populations of the short-lived Brassica juncea, one under ambient conditions and another one under conditions simulating global change. After seven generations of selection, differences between the two populations were examined using a reciprocal transplant garden. We monitored 14 different traits and found evidence for genetic adaptation only once, for vegetative biomass early in the growth cycle. Of the 14 traits, 11 responded plastically to the environment, but only one of these plastic changes had a possible adaptive value. Overall, the long-term evolutionary consequences of global change will depend on the response of fitness-related traits. None of the five reproductive traits measured showed any evolutionary responses. The main conclusion of our study is that Brassica juncea was apparently unable to respond evolutionarily to simulated global change either by genetic adaptation or by adaptive phenotypic plasticity. The Limit to selection was apparently due to inbreeding depression induced by the harsh conditions of the ''predicted'' environment.

1435^2^Schneider,SH^Root,TL^1996^1^Ecological implications of climate change will include surprises^313^5^9^1109-1119^^^^^Sep^^^^^5664
1167^174^en the two populations were examined using a reciprocal transplant garden. We monitored 14 different traits and found evidence for genetic adaptation only once, for vegetative biomass early in the growth cycle. Of the 14 traits, 11 responded plastically to the environment, but only one of these plastic changes had a possible adaptive value. Overall, the long-term evolutionary consequences of global chaA^5663^In addition to assessing the impacts of CO2 doubling on environment and society, more consideration is needed to estimate extreme events or 'surprises'. This is particularly important at the intersection of disciplines like climate and ecology because the potential for large discontinuities is high given all the possible climate/biota interactions. The vast disparities in scales encountered by those working in traditional ecology (typically 20 m) and climatology (typically 200 km) make diagnoses of such interactions difficult, but these can be addressed by an emerging research paradigm we call strategic cyclical scaling (SCS). The need to anticipate outlier events and assign them subjective probabilities suggests emphasis on interdisciplinary research associations. The desire to reduce societal vulnerability to such events suggests the need to build adaptive management and diverse economic activities into social organizations. The effectiveness of adaptation responses to anticipated climatic changes is complicated when consideration of transient changes, regional disturbances, large unforseeable natural fluctuations and surprises are considered. Slowing down the rate of disturbances and decreasing vulnerability are advocated as the most prudent responses to the prospect of human-induced climatic changes.

1436^4^Steffen,WL^Cramer,W^Plochl,M^Bugmann,H^1996^1^Global vegetation models: Incorporating transient changes to structure and composition^42^7^3^321-328^^^^^Jun^^^^^5666
1234^1547^174^407^611^614^656^664^672^812^ns difficult, but these can be addressed by an emerging research paradigm we call strategic cyclical scaling (SCS). The need to anticipate outlier events and assign them subjective probabilities suggests emphasis on interdisciplinary research associations. The desire to reduce societal vulnerability to such events suggests the need to build adaptive management and diverse economic activities into social organizations. The effectiveness of adaptation responses to anticipated climatic changes iA^5665^We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.

1437^3^Sukumar,R^Suresh,HS^Ramesh,R^1995^1^Climate change and its impact on tropical montane ecosystems in southern India^134^22^2-3^533-536^^^^^Mar-May^^^^^5668
1594^1933^2341^2342^593^s that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of foA^5667^The montane regions (>2000 m MSL) of the Western Ghats in southern India feature stunted evergreen forests (C3 plant type) interspersed with extensive grasslands (C3 or C4 plant types). We have studied the vegetational history of this ecosystem in relation to climate change during the late Quaternary through stable-carbon isotope analysis of peat deposits as indicators of C3 or C4 plant types. Grasslands (of C4 type) were predominant during the last glacial maximum (20- 18 kyr sp) and again during 6-3.5 kyr sp, while forest and possibly C3 grassland expanded during the deglaciation, attaining their peak distribution at 10 kyr sp. The shift in C3 and C4 plant types seems related to changes in moisture and atmospheric CO2, with lower moisture and CO2 levels favouring the latter plant types. The oscillating climate and vegetation has influenced the structure and composition of the montane ecosystem. Plant diversity of the near-pristine montane forests is relatively lower than other comparable sites in the neotropics. The implications of global change on the tropical montane ecosystem, in particular the composition of the angiosperm and vertebrate communities, are discussed. In particular, an expansion of montane forest and replacement of C4 with C3 grassland can be expected. Human impact on the natural vegetation, such as conversion of grasslands to monoculture plantations of wattle and eucalypts may, however, interfere with natural succession caused by global climate change. Endemic mammals such as the Nilgiri tahr would face increased risk of extinction.

1438^2^Williams,DW^Liebhold,AM^1995^1^Herbivorous insects and global change: Potential changes in the spatial distribution of forest defoliator outbreaks^134^22^4-5^665-671^^^^^Jul-Sep^^^^^5670
209^2343^els favouring the latter plant types. The oscillating climate and vegetation has influenced the structure and composition of the montane ecosystem. Plant diversity of the near-pristine montane forests is relatively lower than other comparable sites in thA^5669^The geographical ranges and the spatial extent of outbreaks of herbivorous species are likely to shift with climatic change. We investigated potential changes in spatial distribution of outbreaks of the western spruce budworm, Choristoneura occidentalis Freeman, in Oregon, U.S.A. and the gypsy moth, Lymantria dispnr (L.), in Pennsylvania, U.S.A. using maps of historical defoliation, climate and forest composition in a geographic information system. Maps of defoliation frequency were assembled using historical aerial reconnaissance data. Maps of monthly means of daily temperature maxima and minima and of monthly precipitation averaged over 30 years were developed using an interpolation technique. All maps were at a spatial resolution of 2 x 2 km. Relationships between defoliation status and the environmental variables were modelled using a linear discriminant function. Five climatic change scenarios were investigated: an increase of 2 degrees C, a 2 degrees increase with an increase of 0.5 mm per day in precipitation, a 2 degrees C increase with an equivalent decrease in precipitation, and equilibrium projections of temperature and precipitation by two general circulation models (GCMs) at doubled CO2. With an increase in temperature alone, the projected defoliated area decreased relative to ambient conditions for the budworm and increased slightly for the gypsy moth. With an increase in temperature and precipitation the defoliated area increased for both species. Conversely, the defoliated area decreased for both when temperature increased and precipitation decreased. Results for the GCM scenarios contrasted sharply. For the Geophysical Fluids Dynamics Laboratory model, defoliation by budworm was projected to cover Oregon completely, whereas no defoliation was projected by gypsy moth in Pennsylvania. For the Goddard Institute for Space Studies model, defoliation disappeared completely for the budworm and slightly exceeded that under ambient conditions for the gypsy moth. The results are discussed :in terms of potential changes in forest species composition.

1439^5^Batts,GR^Morison,JIL^Ellis,RH^Hadley,P^Wheeler,TR^1997^1^Effects of CO2 and temperature on growth and yield of crops of winter wheat over four seasons^314^7^1-3^43-52^^^^^Sep^^^^^5672
1356^2344^264^312^314^372^374^58^590^elative to ambient conditions for the budworm and increased slightly for the gypsy moth. With an increase in temperature and precipitation the defoliated area increased for both species. Conversely, the defoliated area decreased for both when temperature increased and precipitation decreased. Results for the GCM scenarios contrasted sharply. For the Geophysical Fluids Dynamics Laboratory model, defoliation by budworm was projected to cover Oregon completely, whereas no defoliation was projected by gypsy moth in Pennsylvania. For the Goddard Institute for Space Studies model, defoliation disappeared completely for the budworm and slightly exceeded that under ambient conditions for the gypsy moth. The results are discussed :in termA^5671^Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown in the field in four consecutive seasons from 1991/1992 to 1994/1995 at Reading, UK, within polyethylene-covered tunnels along which a temperature gradient was superimposed on the ambient temperature variation at normal atmospheric (ca. 370) or an increased [CO2] (ca. 700 mu mol CO2 mol(-1) air), producing many environments from one sowing date in each season at one location. Mean seasonal temperatures varied by up to 4 degrees C along the temperature gradient. Increased [CO2] had no effect on crop duration, or on the rate of reproductive development, which had the same temperature sensitivity across all years, A 2 degrees C warming, on the 4-year ambient mean temperature (10 degrees C), reduced crop duration by 42 days (from 254), and reduced the reproductive phase by 16 days (from 130). Crop biomass generally declined with increase in mean temperature, and was greater at increased [CO2], with the effect of increased [CO2] varying with temperature and between years (6-34% range in relative stimulation by increased [CO2]). Grain yield was substantially reduced by warmer temperatures, and increased by doubling [CO2], but the effect varied greatly between pears and with temperature (7-168% range). There were both positive and negative interactions of temperature and increased [CO2] on biomass and grain yield. In all 4 years, the increase in grain yield from doubling [CO2] was negated by an increase in mean seasonal temperature of only 1.0-2.0 degrees C, Year-to-year variation in the responses of biomass and grain yield to [CO2] and temperature resulted from differences in environmental conditions, influencing biomass partitioning and altering the role of different yield components. (C) 1997 Elsevier Science B.V.

1440^2^Beerling,DJ^Kelly,CK^1997^1^Stomatal density responses of temperate woodland plants over the past seven decades of CO2 increase: A comparison of Salisbury (1927) with contemporary data^5^84^11^1572-1583^^^^^Nov^^^^^5674 w1517^1807^2345^344^372^376^384^400^627^92^nge in relative stimulation by increased [CO2]). Grain yield was substantially reduced by warmer temperatures, and increased by doubling [CO2], but the effect varied greatly between pears and with temperature (7-168% range). There were both positive and negative interactions of temperature and increased [CO2] on biomass and grain yield. In all 4 years, the increase in grain yield from doubling [CO2] was negated by an increase in mean seasonal temperature of only 1.0-2.0 degrees C, Year-to-year variation in the responses of biomass and grain yield to [CO2] and temperature resulted from differences in environmental conditions, influencing biomass partitioning and altering the role of different yield components. (C) 1997 Elsevier Science B.V.

1440^2^Beerling,DJ^Kelly,CK^1997^1^Stomatal density responses of temperate woodland plants over the past seven decades of CO2 increase: A comparison of Salisbury (1927) with contemporary data^5^84^11^1572-1583^^^^^Nov^^^^^5674 wA^5673^We investigated the possible effect of recent (1927-1995) increases in the concentration of atmospheric CO2 on the stomatal densities of leaves of a wide range of tree, shrub, and herb species (N = 60) by making new measurements for comparison with corresponding data reported by E. J. Salisbury in 1917-a time when ice core studies indicate CO2 concentrations similar to 55 mu L/L lower than present. A detailed intraspecific study of the herb Mercurialis perenius showed plants of M. perennis in a Cambridgeshire woodland in 1994 had significantly lower stomatal densities, irrespective of leaf insertion point, compared with their 1927 counterparts. Comparisons made across species using evolutionary comparative methods (independent contrasts revealed a significant (P < 0.01) decrease in stomatal density over the past 70 yr. The results of both the inter-and intraspecific comparisons are consistent with the hypothesis that historical CO2 increases have influenced leaf morphology in a manner consistent with recent experiments and the palaeoecological record. Further analyses suggested that the strength of the stomatal density response was independent of life form but dependent on ''exposure'' and the initial leaf stomatal density. Consequently firmer predictions for future changes in stomatal density across all species, expected as a possible result of authropogenically related CO2 increases, may now be possible.

1441^5^Booker,FL^Reid,CD^BrunschonHarti,S^Fiscus,EL^Miller,JE^1997^1^Photosynthesis and photorespiration in soybean [Glycine max (L.) Merr.] chronically exposed to elevated carbon dioxide and ozone^78^48^315^1843-1852^^^^^Oct^^^^^5676
1262^1431^1676^1691^2346^2347^344^384^435^550^ evolutionary comparative methods (independent contrasts revealed a significant (P < 0.01) decrease in stomatal density over the past 70 yr. The results of both the inter-and intraspecific comparisons are consistent with the hypothesis that historical CO2 increases have influenced leaf morphology in a manner consistent with A^5675^The effects of elevated carbon dioxide (CO2) and ozone (O-3) on soybean [Glycine max (L.) Merr.] photosynthesis and photorespiration-related parameters were determined periodically during the growing season by measurements of gas exchange, photorespiratory enzyme activities and amino acid levels, Plants were treated in open-top field chambers from emergence to harvest maturity with seasonal mean concentrations of either 364 or 726 mu mol mol(-1) CO2 in combination with either 19 or 13 nmol mol(-1) O-3 (12 h daily averages). On average at growth CO2 concentrations, net photosynthesis (A) increased 56% and photorespiration decreased 36% in terminal mainstem leaves with CO2-enrichment. Net photosynthesis and photorespiration were suppressed 30% and 41%, respectively, by elevated O-3 during late reproductive growth in the ambient CO2 treatment, but not in the elevated CO2 treatment. The ratio of photorespiration to A at growth CO2 was decreased 61% by elevated CO2. There was no statistically significant effect of elevated O-3 in the ratio of photorespiration to A. Activities of glycolate oxidase, hydroxypyruvate reductase and catalase were decreased 10-25% by elevated CO2, and by 46-66% by elevated O-3 at late reproductive growth. The treatments had no significant effect on total amino acid or glycine levels, although serine concentration was lower in the elevated CO2 and O-3 treatments at several sampling dates. The inhibitory effects of elevated O-3 on photorespiration-related parameters were generally commensurate with the O-3-induced decline in A. The results suggest that elevated CO2 could promote productivity both through increased photoassimilation and suppressed photorespiration.

1442^4^Bouma,TJ^Nielsen,KL^Eissenstat,DM^Lynch,JP^1997^1^Estimating respiration of roots in soil: Interactions with soil CO2, soil temperature and soil water content^206^195^2^221-232^^^^^Aug^^^^^5678
264^312^361^372^374^376^389^417^857^92^owth CO2 was decreased 61% by elevated CO2. There was no statistically significant eA^5677^Little information is available on the variability of the dynamics of the actual and observed root respiration rate in relation to abiotic factors. In this study, we describe I) interactions between soil CO2 concentration, temperature, soil water content and root respiration, and II) the effect of short-term fluctuations of these three environmental factors on the relation between actual and observed root respiration rates. We designed an automated, open gas-exchange system that allows continuous measurements on 12 chambers with intact roots in soil. By using three distinct chamber designs with each a different path for the air flow, we were able to measure root respiration over a 50-fold range of soil CO2 concentrations (400 to 25000 ppm) and to separate the effect of irrigation on observed vs. actual root respiration rate. All respiration measurements were made on one-year-old citrus seedlings in sterilized sandy soil with minimal organic material. Root respiration was strongly affected by diurnal fluctuations in temperature (Q(10) = 2), which agrees well with the literature. In contrast to earlier findings for Douglas-fir (Qi et al., 1994), root respiration rates of citrus were not affected by soil CO2 concentrations (400 to 25000 ppm CO2; pH around 6). Soil CO2 was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO2 concentration to that of incoming air. Irrigation caused a temporary reduction in CO2 diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.
rial. Root respiration was strongly affected by diurnal f1443^2^Cotrufo,MF^Gorissen,A^1997^1^Elevated CO2 enhances below-ground C allocation in three perennial grass species at different levels of N availability^84^137^3^421-431^^^^^Nov^^^^^5680
2032^2348^312^344^349^374^56^57^803^92^to 25000 ppm CO2; pH around 6). Soil CO2 was strongly affected by soil water content but not by respiration measurements, unless the air flow for root respiration measurements was directed through the soil. The latter method of measuring root respiration reduced soil CO2 concentration to that of incoming air. Irrigation caused a temporary reduction in CO2 diffusion, decreasing the observed respiration rates obtained by techniques that depended on diffusion. This apparent drop in respiration rate did not occur if the air flow was directed through the soil. Our dynamic data are used to indicate the optimal method of measuring root respiration in soil, in relation to the objectives and limitations of the experimental conditions.
rial. Root respiration was strongly affected by diurnal fA^5679^Three perennial grass species, Lolium perenne L., Agrostis capillaris L. and Festuca ovina L., were homogeneously labelled in phytotrons with (CO2)-C-14 at two CO2 concentrations (350 and 700 mu l l(-1)). Plants were grown under two nitrogen regimes: one with a minor addition of 8 kg N ha(-1), the other with an addition of 278 kg N ha2(-1). Carbon allocation over the different compartments of the plant/soil systems was measured: shoots, roots, rhizosphere soil (soil solution, microbial biomass and soil residue), and bulk soil. Elevated CO2 increased total net C-14 recovery in all species by 14%, and significantly enhanced the below-ground C-14 allocation by 26%, this enhancement was 24%, 39% and 21%, for root, rhizosphere soil and bulk soil, respectively. Within the rhizosphere soil, the C-14 amounts in the soil solution (+ 69 %) and soil residue (+ 49 %) increased significantly. Total microbial biomass-C in the rhizosphere soil was also increased (15%) by the elevated CO2 treatment, but only in proportion to the increased root mass. No interactions were observed between the elevated CO2 and N treatments. The N treatment increased total net C-14 recovery by more than 300% and C-14 was preferentially allocated to the shoots, leading to a significant increase in shoot-to-root ratio. However, N fertilization also increased(+ 111 %)the absolute amount of C- 14 in soil. The three species behaved differently, but no interactions were observed between CO2 treatment and plant species. These results show that elevated CO2 induces an increased C input into soil for all three grass species at both N levels. However, the highest absolute amounts were found in the soils of the fastest growing species and at the highest N level.

1444^3^Ehleringer,JR^Cerling,TE^Helliker,BR^1997^1^C-4 photosynthesis, atmospheric CO2 and climate^2^112^3^285-299^^^^^Nov^^^^^5682
1097^2349^2350^2351^2352^503^526^534^625^713^crobial biomass-C in the rhizosphere soil was also increased (15%) by the elevated CO2 treatment, but only in propoA^5681^The objectives of this synthesis are (1) to review the factors that influence the ecological, geographical, and palaeoecological distributions of plants possessing C-4 photosynthesis and (2) to propose a hypothesis/model to explain both the distribution of C-4 plants with respect to temperature and CO2 and why C-4 photosynthesis is relatively uncommon in dicotyledonous plants (hereafter dicots), especially in comparison with its widespread distribution in monocotyledonous species (hereafter monocots). Our goal is to stimulate discussion of the factors controlling distributions of C-4 plants today, historically, and under future elevated CO2 environments. Understanding the distributions of C-3/C-4 plants impacts not only primary productivity, but also the distribution, evolution, and migration of both invertebrates and vertebrates that graze on these plants. Sixteen separate studies all indicate that the current distributions of C-4 monocots are tightly correlated with temperature: elevated temperatures during the growing season favor C-4 monocots. In contrast, the seven studies on C-4 dicot distributions suggest that a different environmental parameter, such as aridity (combination of temperature and evaporative potential), more closely describes their distributions. Differences in the temperature dependence of the quantum yield for CO2 uptake (light-use efficiency) of C-3 and C-4 species relate well to observed plant distributions and light-use efficiency is the only mechanism that has been proposed to explain distributional differences in C-3/C-4 monocots. Modeling of C-3 and C-4 light- use efficiencies under different combinations of atmospheric CO2 and temperature predicts that C-4-dominated ecosystems should not have expanded until atmospheric CO2 concentrations reached the lower levels that are thought to have existed beginning near the end of the Miocene. At that time, palaeocarbonate and fossil data indicate a simultaneous, global expansion of C-4-dominated grasslands. The C-4 monocots generally have a higher quantum yield than C-4 dicots and it is proposed that leaf venation patterns play a role in increasing the light-use efficiency of most C-4 monocots. The reduced quantum yield of most C-4 dicots is consistent with their rarity, and it is suggested that C-4 dicots may not have been selected until CO2 concentrations reached their lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency advantage of C-4 monocots, C-4 dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed ecosystems. All C-4 plants have a significant advantage over C- 3 plants under low atmospheric CO2 conditions and are predicted to have expanded significantly on a global scale during full- glacial periods, especially in tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C-4 ecosystems were more extensive during the last glacial maximum and then decreased in abundance following deglaciation as atmospheric CO2 levels increased.

1445^7^Fitter,AH^Graves,JD^Wolfenden,J^Self,GK^Brown,TK^Bogie,D^Mansfield,TA^1997^1^Root production and turnover and carbon budgets of two contrasting grasslands under ambient and elevated atmospheric carbon dioxide concentrations^84^137^2^247-255^^^^^Oct^^^^^5684
349^454^738^92^ir lowest levels during glacial maxima in the Quaternary. Given the intrinsic light-use efficiency advantage of C-4 monocots, C-4 dicots may have been limited in their distributions to the warmest ecosystems, saline ecosystems, and/or to highly disturbed ecosystems. All C-4 plants have a significant advantage over C- 3 plants under low atmospheric CO2 conditions and are predicted to have expanded significantly on a global scale during full- glacial periods, especially in tropical regions. Bog and lake sediment cores as well as pedogenic carbonates support the hypothesis that C-4 ecosystems were more extensive during the last glacial maximum and then decreased in abundance fA^5683^Monoliths of two contrasting vegetation types, a species-rich grassland on a brown earth soil over limestone and a species- poor community on a peaty gley, were transferred to solardomes and grown under ambient (350 mu l l(-1)) and elevated (600 mu l l(-1)) CO2 for 2 yr. Shoot biomass was unaltered but root biomass increased by 40-50% under elevated CO2. Root production was increased by elevated CO2 in the peat soil, measured both as instantaneous and cumulative rates, but only the latter measure was increased in the limestone soil. Root growth was stimulated more at 6 cm depth than at 10 cm in the limestone soil. Turnover was faster under elevated CO2 in the peat soil, but there was only a small effect on turnover in the limestone soil. Elevated CO, reduced nitrogen concentration in roots and might have increased mycorrhizal colonization. Respiration rate was correlated with N concentration, and was therefore lower in roots grown at elevated CO2. Estimates of the C budget of the two communities, based upon root production and on net C uptake, suggest that C sequestration in the peat soil increases by c. 0.2 kg C m(-2) yr(-1) (= 2 t ha yr(-1)) under elevated CO2.

1446^4^Fredeen,AL^Randerson,JT^Holbrook,NM^Field,CB^1997^1^Elevated atmospheric CO2 increases water availability in a water-limited grassland ecosystem^315^33^5^1033-1039^^^^^Oct^^^^^5686
1166^1167^2353^374^410^529^547^674^711^740^evated CO2 in the peat soil, measured both as instantaneous and cumulative rates, but only the latter measure was increased in the limestone soil. Root growth was stimulated more at 6 cm depth than at 10 cm in the limestone soil. Turnover was faster under elevated CO2 in the peat soil, but there was only a small effect on turnover in the limestone soil. Elevated CO, reduced nitrogen concentration in roots and might have increased mycorrhizal colonization. Respiration rate was correlated with N concentration, and was therefore lower in roots grown at elevated CO2. Estimates of the C budget of the two communities, baseA^5685^Californian annual grassland on sandstone (moderately fertile) and serpentine (very infertile) soils at the Jasper Ridge Biological Preserve, Stanford, California, were exposed to ambient or elevated (ambient + 36 Pa CO2) atmospheric CO2 in open-top chambers since December 1991. We measured ecosystem evapotranspiration with open gas-exchange systems, and soil moisture with time-domain reflectometry (TDR) over 0-15 cm (serpentine) and 0-30 cm (sandstone) depths, at times of peak above ground physiological activity. Evapotranspiration decreased by 12 to 63 percent under elevated CO2 in three consecutive years in the sandstone ecosystem (p = 0.053, p = 0.162, p = 0.082 in 1992, 1993, and 1994, respectively). In correspondence with decreased evapotranspiration, late-season soil moisture reserves in the sandstone were extended temporally by 10 +/- 3 days in 1993 and by 28 +/- 11 days in 1994. The effect of elevated CO2 on soil moisture was greater in the drier spring of 1994 (419 mm annual rainfall) than in 1993 (905 mm annual rainfall). In the serpentine ecosystem, evapotranspiration and soil moisture reserves were not clearly affected by elevated CO2. Soil water may be conserved in drought-affected ecosystems exposed to elevated CO2, but the amount of conservation appears to depend on the relative importance of transpiration and soil evaporation in controlling water flux.

1447^3^Godbold,DL^Berntson,GM^Bazzaz,FA^1997^1^Growth and mycorrhizal colonization of three North American tree species under elevated atmospheric CO2^84^137^3^433-440^^^^^Nov^^^^^5688
1096^1850^2354^2355^312^361^374^376^483^791^secutive years in the sandstone ecosystem (p = 0.053, p = 0.162, p = 0.082 in 1992, 1993, and 1994, respectively). In correspondence with decreased evapotranspiration, late-season soil moisture reserves in the sandstone were extended temporally by 10 +/- 3 days in 1993 and by 28 +/- 11 days in 1994. The effect of elevated CO2 on soil moisture was greater in the drier spring of 1994 (419 mm annual rainfall) than iA^5687^We investigated the effect of elevated CO2 on the growth and mycorrhizal colonization of three tree species native to north- eastern American forests (Betula papyrifera Marsh., Pinus strobus L. and Tsuga canadensis L. Carr). Saplings of the tree species were collected from Harvard Forest, Massachusetts, and grown in forest soil under ambient (c. 375 ppm) and elevated (700 ppm) atmospheric CO2 concentrations for 27-35 wk. In all three species there was a trend to increasing whole-plant, total-root and fine-root biomass in elevated CO2, and a significant increase in the degree of ectomycorrhizal colonization in B. papyrifera and P. strobus, but not in T. canadensis. However, in T. canadensis the degree of colonization with arbuscular mycorrhizas increased significantly. In both the ambient and elevated environments, on the roots of B. papyrifera and P. strobus 12 distinct ectomycorrhizal morphotypes were identified. Distinct changes in the ectomycorrhizal morphotype assemblage of B. papyrifera were observed under CO2 enrichment. This change resulted in an increase in the frequency of ectomycorrhizas with a higher incidence of emanating hyphae and rhizomorphs, and resulted in a higher density of fungal hyphae in a root exclusion chamber.

1448^5^Hirose,T^Ackerly,DD^Traw,MB^Ramseier,D^Bazzaz,FA^1997^1^CO2 elevation, canopy photosynthesis, and optimal leaf area index^11^78^8^2339-2350^^^^^Dec^^^^^5690
130^2356^245^310^374^384^430^672^92^957^species there was a trend to increasing whole-plant, total-root and fine-root biomass in elevated CO2, and a significant increase in the degree of ectomycorrhizal colonization in B. papyrifera and P. strobus, but not in T. canadensis. However, in T. canadensis the degree of colonization with arbuscular mycorrhizas increased significantly. In both the ambient and elevated environments, on the roots of B. papyrifera and P. strobus 12 distinct ectomycorrhizal morphotypes were identified. Distinct changes in the ectomycorrhizal morphotype assemblage of B. papyrifera were obseA^5689^We studied the effects of CO2 elevation on leaf and canopy photosynthesis and optimal leaf area index (LAI) for stands of the annual species Abutilon theophrasti and Ambrosia artemisiifolia. Leaf photosynthesis was modeled as a function of photosynthetic photon flux density (PPFD) and nitrogen content per unit leaf area (N-L). There was a curvilinear relationship between the light-saturated rates of leaf photosynthesis (P-max) and N-L. CO2 elevation significantly increased P-max as a function of N, in both species. Dark respiration (R-d) was linearly correlated with N-L. CO2 elevation slightly but significantly increased R-d in Abutilon, while it had no significant effect on R-d in Ambrosia. The initial slope of a light-response curve was determined from quantum yield (phi(abs)) multiplied by leaf absorptance and then calibrated against N-L. Daily canopy photosynthesis, calculated by integration of leaf photosynthesis with the actual distribution of leaf area, leaf N, and PPFD within a canopy, showed fairly good agreement with the canopy photosynthesis estimated from growth analysis. CO2 elevation increased canopy photosynthesis by 30-50%. Based on the leaf photosynthesis model for Abutilon, we calculated daily canopy photosynthesis for a given LAI and N availability, in which N was assumed to be distributed optimally within a leaf canopy to maximize daily canopy photosynthesis. An optimal LAI to maximize daily canopy photosynthesis was obtained for each level of N availability and this optimum increased with increasing N availability. Contrary to the often predicted increase in LAI with CO2 elevation, the optimum LAI did not increase at high CO2 when N availability was limited. Two factors were suggested to be involved in counteracting the increase in LAI in a high-CO2 world. One is the higher phi(abs) of plants grown in elevated CO2, which makes leaves in the canopy more N limited, favors higher N-L and thus lowers optimal LAI. The other is the higher R-d in elevated CO2, which leads to higher light compensation points, and lowers optimal LAI.

1449^3^Karowe,DN^Seimens,DH^Mitchell-Olds,T^1997^1^Species-specific response of glucosinolate content to elevated atmospheric CO2^112^23^11^2569-2582^^^^^Nov^^^^^5692
1080^1086^2357^2358^2359^2360^338^628^847^92^N availability, in which N was assumed to be distributed optimally within a leaf canopy to maximize daily canopy photosynthesis. An optimal LAI to maximize daily canopy photosynthesis was obtained for each level of N availability and this optimum increased with increasing N availability. Contrary to the often predicted increase in LAI with CO2 elevation, the optimum LAI did not increase at high CO2 when N availability was limited. Two factors were suggested to be involved in counteracting the increase in LAI in a high-CO2 world. One is the higher phi(abs) of plants grown in elevated CO2, which makes leaves in the canopy more N limited, favors higher N-L and thus lowers optimal LAI. The other is the higher R-d in elevated CO2, which leads to higher light coA^5691^The carbon/nutrient balance hypothesis has recently been interpreted to predict that plants grown under elevated CO2 environments will allocate excess carbon to defense, resulting in an increase in carbon-based secondary compounds. A related prediction is that, because plant growth will be increasingly nitrogen-limited under elevated CO2 environments, plants will allocate less nitrogen to defense, resulting in decreased levels of nitrogen-containing secondary compounds. We present the first evidence of decreased investment in nitrogen- containing secondary compounds for a plant grown under elevated CO2. We also present evidence that plant response is species specific and is not correlated with changes in leaf nitrogen content or leaf carbon-nitrogen ratio. When three crucifers were grown at 724 +/- 8 ppm CO2, total foliar glucosinolate content decreased significantly for mustard, but not for radish or turnip. Glucosinolate content of the second and fourth young est mustard leaves decreased by 45% and 31%, respectively. In contrast, no significant change in total glucosinolate content was observed in turnip or radish leaves, despite significant decreases in leaf nitrogen content. Total glucosinolate content differed significantly among leaves of different age; however, the trend differed among species. For both mustard and turnip, glucosinolate content was significantly higher in older leaves, while the opposite was true for radish. No significant CO2 x leaf age interaction was observed, suggesting that intraplant patterns of allocation to defense will not change for these species. Changes in nitrogen allocation strategy are likely to be species-specific as plants experience increasing atmospheric CO2 levels. The ecological consequences of CO2-induced changes in plant defensive investment remain to be investigated.

1450^3^Keith,H^Raison,RJ^Jacobsen,KL^1997^1^Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability^206^196^1^81-99^^^^^Sep^^^^^5694eased by 45% and 1031^137^1660^1829^2361^2362^310^672^733^738^ change in total glucosinolate content was observed in turnip or radish leaves, despite significant decreases in leaf nitrogen content. Total glucosinolate content differed significantly among leaves of different age; however, the trend differed among species. For both mustard and turnip, glucosinolate content was significantly higher in older leaves, while the opposite was true for radish. No significant CO2 x leaf age interaction was observed, suggesting that intraplant patterns of allocation to defense will not change for these species. Changes in nitrogen allocation strategy are likely to be species-specific as plants experience increasing atmospheric CO2 levels. The ecological consequences of CO2-induced changes in plant defensive investment remain to be investigated.

1450^3^Keith,H^Raison,RJ^Jacobsen,KL^1997^1^Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability^206^196^1^81-99^^^^^Sep^^^^^5694eased by 45% and A^5693^Pools and annual fluxes of carbon (C) were estimated for a mature Eucalyptus pauciflora (snowgum) forest with and without phosphorus (P) fertilizer addition to determine the effect of soil P availability on allocation of C in the stand. Aboveground biomass was estimated from allometric equations relating stem and branch diameters of individual trees to their biomass. Biomass production was calculated from annual increments in tree diameters and measurements of litterfall. Maintenance and construction respiration were calculated for each component using equations given by Ryan (1991a). Total belowground C flux was estimated from measurements of annual soil CO2 efflux less the C content of annual litterfall (assuming forest floor and soil C were at approximate steady state for the year that soil CO2 efflux was measured). The total C content of the standing biomass of the unfertilized stand was 138 t ha(-1), with approximately 80% aboveground and 20% belowground. Forest floor C was 8.5 t ha(-1). Soil C content (0-1 m) was 369 t ha(-1) representing 70% of the total C pool in the ecosystem. Total gross annual C flux aboveground (biomass increment plus litterfall plus respiration) was 11.9 t ha(-1) and gross flux belowground (coarse root increment plus fine root production plus root respiration) was 5.1 t ha(-1). Total annual soil efflux was 7.1 t ha(-1), of which 2.5 t ha(- 1) (35%) was contributed by litter decomposition. The short- term effect of changing the availability of P compared with C on allocation to aboveground versus belowground processes was estimated by comparing fertilized and unfertilized stands during the year after treatment. In the P-fertilized stand annual wood biomass increment increased by 30%, there was no evidence of change in canopy biomass, and belowground C allocation decreased by 19% relative to the unfertilized stand. Total annual C flux was 16.97 and 16.75 t ha(-1) yr(-1) and the ratio of below-to aboveground C allocation was 0.43 and 0.35 in the unfertilized and P-fertilized stands, respectively. Therefore, the major response of the forest stand to increased soil P availability appeared to be a shift in C allocation; with little change in total productivity. These results emphasise that both growth rate and allocation need to be estimated to predict changes in fluxes and storage of C in forests that may occur in response to disturbance or climate change.

1451^3^Kellomaki,S^Vaisanen,H^Kolstrom,T^1997^1^Model computations on the effects of elevating temperature and atmospheric CO2 on the regeneration of Scots pine at the timber line in Finland^50^37^4^683-708^^^^^Dec^^^^^5696
2363^238^243^269^416^51^57^664^705^ment. In the P-fertilized stand annual wood biomass increment increased by 30%, there was no evidence of change in canopy biomass, and belowground C allocation decreased by 19% relative to the unfertilized stand. Total annual C flux was 16.97 and 16.75 t ha(-1) yr(-1) and the ratio of below-to aboveground C allocation was 0.43 and 0.35 in the unfertilized and P-fertilized stA^5695^Based on model computations, the regeneration of Scots pine (Pinus sylvestris L.) was studied at the northern timber line in Finland (70 degrees N) in relation to elevating temperature and atmospheric CO2. If a transient increase of 4 degrees C was assumed during the next 100 years, the length of growing season increased from the current 110-120 days to 150-160 days. This was associated with ca. 5 degrees C increase in the soil temperature over June-August with larger variability in temperature and deeper freezing of the soil due to the reduced depth and duration of the snow cover, At the same time, the moisture content of the surface soil decreased ca. 10% and was more variable, due to less infiltration of water into the soil as a consequence of the enhanced evapotranspiration and deeper freezing of the soil. The temperature elevation alone, or combined with elevating CO2, increased flowering and the subsequent seed crop of Scots pine with a decrease in the frequency of zero crops. In both cases, temperature elevation substantially increased the success of regeneration in terms of the number of seedlings produced after each seed crop. The increasing number of mature seeds was mainly responsible for the enhanced regeneration, but increasing soil temperature also increased the success of regeneration. The soil moisture was seldom limited for seed germination. In terms of the density of seedling stands, and the height and diameter growth of the seedlings, the establishment of a seedling stand was substantially improved under the combined elevation of temperature and CO2 in such a way that the temperature increased the number of mature seeds and enhanced germination of seeds and CO2 increased seedling growth. Even under the changing climatic conditions, however, the growth of the seedling stands was slow, which indicated that the northward advance of the timber line would probably be very slow, even though regeneration was no longer a limiting factor.
ease in the frequency of zero crops. In both cases, tem1452^3^King,JS^Thomas,RB^Strain,BR^1997^1^Morphology and tissue quality of seedling root systems of Pinus taeda and Pinus ponderosa as affected by varying CO2, temperature, and nitrogen^206^195^1^107-119^^^^^Aug^^^^^5698
2364^372^374^376^377^416^417^437^483^92^also increased the success of regeneration. The soil moisture was seldom limited for seed germination. In terms of the density of seedling stands, and the height and diameter growth of the seedlings, the establishment of a seedling stand was substantially improved under the combined elevation of temperature and CO2 in such a way that the temperature increased the number of mature seeds and enhanced germination of seeds and CO2 increased seedling growth. Even under the changing climatic conditions, however, the growth of the seedling stands was slow, which indicated that the northward advance of the timber line would probably be very slow, even though regeneration was no longer a limiting factor.
ease in the frequency of zero crops. In both cases, temA^5697^Rising atmospheric carbon dioxide, nitrogen deposition and warmer temperatures may alter the quantity and quality of plant-derived organic matter available to soil biota, potentially altering rates of belowground herbivory and decomposition. Our objective was to simulate future growth conditions for an early successional (loblolly) and late successional (ponderosa) species of pine to determine if the physical and chemical properties of the root systems would change. Seedlings were grown for 160 days in greenhouses at the Duke University Phytotron at 35 or 70 Pa CO2 partial pressure, ambient or ambient +5 degrees C temperature, and 1 or 5 mMNH(4)O(3). Roots from harvested seedlings were analyzed for changes in surface area, specific root length, mass, total nonstructural carbohydrates (TNC), and concentrations of macro- nutrients. Surface area increased in both species under elevated CO2, due primarily to increases in root length, and this response was greatest (+138%) in loblolly pine at high temperature. Specific root length decreased in loblolly pine at elevated CO2 but increases in mass more than compensated for this, resulting in net increases in total length. TNC was unaffected and nutrient concentrations decreased only slightly at elevated CO2, possibly from anatomical changes to the root tissues. We conclude that future growth conditions will enhance soil exploration by some species of pine, but root carbohydrate levels and nutrient concentrations will not be greatly affected, leaving rates of root herbivory and decomposition unaltered.

1453^6^Klironomos,JN^Rillig,MC^Allen,MF^Zak,DR^Pregitzer,KS^Kubiske,ME^1997^1^Increased levels of airborne fungal spores in response to Populus tremuloides grown under elevated atmospheric CO2^188^75^10^1670-1673^^^^^Oct^^^^^5700
2365^312^57^tes (TNC), and concentrations of macro- nutrients. Surface area increased in both species under elevated CO2, due primarily to increases in root length, and this response was greatest (+138%) in loblolly pine at high temperatA^5699^Soil fungi are important components of terrestrial ecosystems. They function as decomposers, pathogens, parasites, and mutualistic symbionts. Their main mode of dispersal is to liberate spores into the atmosphere. In this study we tested the hypothesis that a higher atmospheric CO2 concentration will induce greater sporulation in common soil fungi, leading to higher concentrations of fungal propagules in the atmosphere. In our field experiment, the concentration of airborne fungal propagules, mostly spores, increased fourfold under twice- ambient CO2 concentrations. Analysis of decomposing leaf litter (likely the main source of airborne fungal propagules) indicated that the fungi produced fivefold more spores under elevated CO2. Our results provide evidence that elevations in atmospheric CO2 concentration can directly affect microbial function, which may have important implications for litter decay, fungal dispersal, and human respiratory health.
was greatest (+138%) in loblolly pine at high temperat1454^2^Laisk,A^Edwards,GE^1997^1^CO2 and temperature-dependent induction in C-4 photosynthesis: an approach to the hierarchy of rate-limiting processes^92^24^4^505-516^^^^^^^^^^5702
1549^1803^2058^2271^2366^348^367^384^448^635^ study we tested the hypothesis that a higher atmospheric CO2 concentration will induce greater sporulation in common soil fungi, leading to higher concentrations of fungal propagules in the atmosphere. In our field experiment, the concentration of airborne fungal propagules, mostly spores, increased fourfold under twice- ambient CO2 concentrations. Analysis of decomposing leaf litter (likely the main source of airborne fungal propagules) indicated that the fungi produced fivefold more spores under elevated CO2. Our results provide evidence that elevations in atmospheric CO2 concentration can directly affect microbial function, which may have important implications for litter decay, fungal dispersal, and human respiratory health.
was greatest (+138%) in loblolly pine at high temperatA^5701^Rate-limiting processes for C-4 photosynthesis were examined in Sorghum bicolor, an NADP-ME type species, and Amaranthus cruentus, an NAD-ME type C-4 species, by studying the kinetics of transient changes in photosynthetic rates following rapid changes in CO2 or temperature. Primary responses (faster than 15 s) to increasing CO2 or temperature are considered direct effects on the turnover rate of the C-4 cycle, whereas medium transient changes (2-3 min) are considered due to build-up of C-4 cycle intermediates, and the slowest transient changes (20- 30 min) are thought to be related to end product synthesis. Reciprocal plot of carboxylation rates versus cell wall (dissolved) CO2 concentration (C-w) gives an apparent K-m (CO2) of 8 mu M and a V-m of 200 mu mol m(-2) s(-1) for PEP carboxylase, which is about 4 times higher than the maximum rate of photosynthesis. Under strictly limiting CO2, the rate of PEP carboxylation in C-4 photosynthesis is independent of temperature (20-35 degrees C), suggesting a physical rather than a biochemical limitation. It is suggested that the rates of C-3 and C-4 cycles are coordinated through the pool sizes of the C-4 cycle, which are in equilibrium with the pool of 3- phosphoglyceric acid. At low CO2, the C-4 pools decrease and are slowly regenerated at elevated CO2, restricting the CO2 response of C-4 photosynthesis.

1455^4^Lashof,DA^DeAngelo,BJ^Saleska,SR^Harte,J^1997^1^Terrestrial ecosystem feedbacks to global climate change^312^22^^75-118^^^^^^^^^^5704
1192^1262^1637^1917^2349^2367^2368^372^377^681^ent changes (20- 30 min) are thought to be related to end product synthesis. Reciprocal plot of carboxylation rates versus cell wall (dissolved) CO2 concentration (C-w) gives an apparent K-m (CO2) of 8 mu M and a V-m of 200 mu mol m(-2) s(-1) for PEP carboxylase, which is about 4 times higher than the maximum rate of photosynthesis. Under strictly limiting CO2, the rate of PEP carboxylation in C-4 photosynthesis is independent of temperature (20-35 degrees C), suggesting aA^5703^Anthropogenic greenhouse gases are expected to induce changes in global climate that can alter ecosystems in ways that, in turn, may further affect climate. Such climate-ecosystem interactions can generate either positive or negative feedbacks to the climate system, thereby either enhancing or diminishing the magnitude of global climate change. Important terrestrial feedback mechanisms include CO2 fertilization (negative feedbacks), carbon storage in vegetation and soils (positive and negative feedbacks), vegetation albedo (positive feedbacks), and peatland methane emissions (positive and negative feedbacks). While the processes involved are complex, not readily quantifiable, and demonstrate both positive and negative feedback potential, we conclude that the combined effect of the feedback mechanisms reviewed here will likely amplify climate change relative to current projections that have not yet adequately incorporated these mechanisms.
 is independent of temperature (20-35 degrees C), suggesting a1456^3^McKee,IF^Eiblmeier,M^Polle,A^1997^1^Enhanced ozone-tolerance in wheat grown at an elevated CO2 concentration: ozone exclusion and detoxification^84^137^2^275-284^^^^^Oct^^^^^5706
1633^1676^1950^2369^2370^243^312^344^374^550^negative feedbacks to the climate system, thereby either enhancing or diminishing the magnitude of global climate change. Important terrestrial feedback mechanisms include CO2 fertilization (negative feedbacks), carbon storage in vegetation and soils (positive and negative feedbacks), vegetation albedo (positive feedbacks), and peatland methane emissions (positive and negative feedbacks). While the processes involved are complex, not readily quantifiable, and demonstrate both positive and negative feedback potential, we conclude that the combined effect of the feedback mechanisms reviewed here will likely amplify climate change relative to current projections that have not yet adequately incorporated these mechanisms.
 is independent of temperature (20-35 degrees C), suggesting aA^5705^Elevated [CO2] has been shown to protect photosynthesis and growth of wheat against moderately elevated [O-3]. To investigate the role of ozone exclusion and detoxification in this protection, spring wheat (Triticum aestivum L. cv. Wembley) was grown from seed, in controlled-environment chambers, under reciprocal combinations of [CO2] at 350 or 700 mu mol mol(-1) and [O-3] peaking at < 5 or 60 nmol mol(-1), respectively. Cumulative ozone dose to the mesophyll and antioxidant status were determined throughout flag leaf development. Catalase activity correlated with rates of photorespiration and declined in response to elevated [CO2] and/or [O-3]. Superoxide dismutase activity was not significantly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO2]. In wheat, at moderately elevated [O-3], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO2] against O-3 damage.
emperature (20-35 degrees C), suggesting a1457^6^Miller,A^Tsai,CH^Hemphill,D^Endres,M^Rodermel,S^Spalding,M^1997^1^Elevated CO2 effects during leaf ontogeny - A new perspective on acclimation^8^115^3^1195-1200^^^^^Nov^^^^^5708
1347^1871^2371^344^384^685^92^iticum aestivum L. cv. Wembley) was grown from seed, in controlled-environment chambers, under reciprocal combinations of [CO2] at 350 or 700 mu mol mol(-1) and [O-3] peaking at < 5 or 60 nmol mol(-1), respectively. Cumulative ozone dose to the mesophyll and antioxidant status were determined throughout flag leaf development. Catalase activity correlated with rates of photorespiration and declined in response to elevated [CO2] and/or [O-3]. Superoxide dismutase activity was not significantly affected by either condition. Neither ascorbate nor glutathione content was enhanced by elevated [CO2]. In wheat, at moderately elevated [O-3], our results show that stomatal exclusion plays a major role in the protective effect of elevated [CO2] against O-3 damage.
emperature (20-35 degrees C), suggesting aA^5707^For many plants growth in elevated CO2 leads to reduced rates of photosynthesis. To examine the role that leaf ontogeny plays in the acclimation response, we monitored photosynthesis and some related parameters at short intervals throughout the ontogenetic development of tobacco (Nicotiana tabacum L.) leaves under ambient (350 mu L L-1)- and high (950 mu L L-1)- CO2 conditions. The pattern of photosynthetic rate over time was similar between the two treatments and consistent with the expected pattern for a typical dicot leaf. However, the photosynthesis pattern in high-CO2-grown tobacco was shifted temporally to an earlier maximum and subsequent senescent decline. Ribulose-1,5-biphosphate carboxylase/oxygenase activity appeared to be the main factor regulating photosynthetic rates in both treatments. Therefore, we propose a new model for interpreting the acclimation response. Lowered photosynthetic rates observed during acclimation appear to be the result of a shift in the timing of the normal photosynthetic stages of leaf ontogeny to an earlier onset of the natural decline in photosynthetic rates associated with senescence.

1458^6^Mulholland,BJ^Craigon,J^Black,CR^Colls,JJ^Atherton,J^Landon,G^1997^1^Impact of elevated atmospheric CO2 and O-3 on gas exchange and chlorophyll content in spring wheat (Triticum aestivum L.)^78^48^315^1853-1863^^^^^Oct^^^^^5710
1262^1553^2185^2372^2373^312^399^444^446^685^ynthetic rate over time was similar between the two treatments and consistent with the expected pattern for a typical dicot leaf. However, the photosynthesis pattern in high-CO2-grown tobacco was shifted temporally to an earlier maximum and subsequent senescent decline. Ribulose-1,5-biphosphate carboxylase/oxygenase activity appeared to be the main factor regulating photosynthetic rates in both treatments. Therefore, we propose a new model for interpreting the acclimation response. Lowered photosynthetic rates observed during acclimation appear to be the result of a shift in the timing of the normal photosyA^5709^Stands of spring wheat grown in open-top chambers (OTCs) were used to assess the individual and interactive effects of season-long exposure to elevated atmospheric carbon dioxide (CO2) and ozone (O-3) on the photosynthetic and gas exchange properties of leaves of differing age and position within the canopy. The observed effects were related to estimated ozone fluxes to individual leaves. Foliar chlorophyll content was unaffected by elevated CO2, but photosynthesis under saturating irradiances was increased by up to 100% at 680 mu mol mol(-1) CO2 relative to the ambient CO2 control; instantaneous water use efficiency was improved by a combination of increased photosynthesis and reduced transpiration. Exposure to a seasonal mean O-3 concentration (7 h d(-1)) of 84 nmol mol(-1) under ambient CO2 accelerated leaf senescence following full expansion, at which time chlorophyll content was unaffected. Stomatal regulation of pollutant uptake was limited since estimated O-3 fluxes to individual leaves were not reduced by elevated atmospheric CO2. A common feature of O-3-treated leaves under ambient CO2 was an initial stimulation of photosynthesis and stomatal conductance for up to 4 d and 10 d, respectively, after full leaf expansion, but thereafter both variables declined rapidly. The O-3-induced decline in chlorophyll content was less rapid under elevated CO2 and photosynthesis was increased relative to the ambient CO2 treatment. A/C-i analyses suggested that an increase in the amount of in vivo active RuBisCO may be involved in mitigating O-3-induced damage to leaves. The results obtained suggest that elevated atmospheric CO2 has an important role in restricting the damaging effects of O-3 on photosynthetic activity during the vegetative growth of spring wheat, and that additional direct effects on reproductive development were responsible for the substantial reductions in grain yield obtained at final harvest, against which elevated CO2 provided little or no protection.
3 fluxes to individual leaves were no1459^6^Nakamura,T^Osaki,M^Koike,T^Hanba,YT^Wada,E^Tadano,T^1997^1^Effect of CO2 enrichment on carbon and nitrogen interaction in wheat and soybean^316^43^4^789-798^^^^^Dec^^^^^5712
1171^1290^343^355^360^384^417^426^733^92^ansion, but thereafter both variables declined rapidly. The O-3-induced decline in chlorophyll content was less rapid under elevated CO2 and photosynthesis was increased relative to the ambient CO2 treatment. A/C-i analyses suggested that an increase in the amount of in vivo active RuBisCO may be involved in mitigating O-3-induced damage to leaves. The results obtained suggest that elevated atmospheric CO2 has an important role in restricting the damaging effects of O-3 on photosynthetic activity during the vegetative growth of spring wheat, and that additional direct effects on reproductive development were responsible for the substantial reductions in grain yield obtained at final harvest, against which elevated CO2 provided little or no protection.
3 fluxes to individual leaves were noA^5711^Effect of CO2 enrichment on the carbon-nitrogen balance in whole plant and the acclimation of photosynthesis was studied in wheat (spring wheat) and soybean (A62-1 [nodulated] and A62- 2 [non-nodulated]) with a combination of two nitrogen application rates (0 g N land area m(-2) and 30 g N land area m(-2)) and two temperature treatments (30/20 degrees C (day/night) and 26/16 degrees C), Results were as follows. 1. Carbon (dry matter)-nitrogen balance of whole plant throughout growth was remarkably different between wheat and soybean, as follows: 1) in wheat, the relationship between the amount of dry matter (DMt) and amount of nitrogen absorbed (Nt) in whole plant was expressed by an exponential regression, in which the regression coefficient was affected by only the nitrogen application rate, and not by CO2 and temperature treatments, and 2) in soybean the DMt-Nt relationship was basically expressed by a linear regression, in which the regression coefficient was only slightly affected by the nitrogen treatment (at ON, DMt-Nt balance finally converged to a linear regression), Thus, carbon-nitrogen interaction in wheat was strongly affected by the underground environment (nitrogen nutrition), but not by the above ground environment (CO2 enrichment and temperature), while that in soybean was less affected by both under and above ground environments, 2. The photosynthetic response curve to CO2 concentration in wheat and soybean was less affected by the CO2 enrichment treatment, while that in wheat and soybean (A62-2) was affected by the nitrogen treatment, indicating that nitrogen nutrition is a more important factor for the regulation of photosynthesis regardless of the CO2 enrichment, 3. Carbon isotope discrimination (d) in soybean was similar to that in wheat under ambient CO2, while lower than that in wheat under CO2 enrichment, suggesting that the carbon metabolism is considerably different between wheat and soybean under the CO2 enrichment conditions.
icient was only slightly affected by the nitrogen1460^2^Olszyk,DM^Wise,C^1997^1^Interactive effects of elevated CO2 and O-3 on rice and flacca tomato^169^66^1^1-10^^^^^17 Nov^^^^^5714
1102^2374^2375^361^374^430^446^73^738^92^rogen nutrition), but not by the above ground environment (CO2 enrichment and temperature), while that in soybean was less affected by both under and above ground environments, 2. The photosynthetic response curve to CO2 concentration in wheat and soybean was less affected by the CO2 enrichment treatment, while that in wheat and soybean (A62-2) was affected by the nitrogen treatment, indicating that nitrogen nutrition is a more important factor for the regulation of photosynthesis regardless of the CO2 enrichment, 3. Carbon isotope discrimination (d) in soybean was similar to that in wheat under ambient CO2, while lower than that in wheat under CO2 enrichment, suggesting that the carbon metabolism is considerably different between wheat and soybean under the CO2 enrichment conditions.
icient was only slightly affected by the nitrogenA^5713^Atmospheric concentrations of both carbon dioxide (CO2) and ozone (O-3) are increasing, with potentially dramatic effects on plants. This study was conducted to determine interactive effects of CO2 and O-3 on rice (Oryza sativa L. cv. IR 74) and a 'wilty' mutant of tomato (Lycopersicon esculentum Mill. flacca). Plants were grown from seed in a glasshouse and exposed for 28 days to ambient or elevated CO2 (approximate to 400 or 700 mu l l(-1) CO2) and/or ambient or elevated O-3 (peak/valley pattern of exposure with cumulative totals of approximate to 1 or 44 mu l l(-1) h). Elevated CO2 alleviated O-3-associated decreases in allocation of biomass to roots, as indicated by a decreased root:shoot ratio (p < 0.05), and also reduced injury from O-3 as indicated by leaf greenness readings for one experiment(p < 0.05). By itself, elevated CO2 resulted in increases in total plant and individual organ(root, leaf, stem) dry weights and root:shoot ratio and elevated O-3 resulted in increases in main culm leaf number and a decrease in stem dry weight (p < 0.05). Elevated CO2 had no significant effect on the tendency for O-3-induced biomass reductions of flacca tomato. For flacca, elevated CO2 alone increased shoot and root biomass (p < 0.05), and elevated O-3 alone tended to decrease biomass for both parameters, but only at p = 0.09 and O.11, respectively. This study was preliminary, as the environmental conditions in these experiments may have altered O-3 and CO2 responses of the plants. However, these results provided additional evidence that elevated CO2 inhibits adverse effects of O-3 on plants, and that the interactive response may be mediated by stomata. (C) 1997 Elsevier Science B.V.

1461^3^Reinert,RA^Eason,G^Barton,J^1997^1^Growth and fruiting of tomato as influenced by elevated carbon dioxide and ozone^84^137^3^411-420^^^^^Nov^^^^^5716
130^1728^344^349^374^434^529^673^685^881^and individual organ(root, leaf, stem) dry weights and root:shoot ratio and elevated O-3 resulted in increases in main culm leaf numA^5715^'Tiny Tim' tomato plants were exposed to five CO2 treatments (375 (ambient), 450, 525, 600 or 675 mu mol mol(-1)) in combination with O-3 (O or 80 nmol mol(-1)). Biomass was evaluated following 3, 5, 7 and 13 wk exposure. Biomass following 13 wk exposure also included weekly harvests of mature tomato fruit beginning week 8. Carbon dioxide enrichment significantly enhanced total vegetative plant d. wt at each harvest, as well as cumulative yield of mature fruit, whereas O-3 significantly suppressed total Vegetative plant d. wt at each harvest and reduced total cumulative fruit yield. The magnitude of these changes varied with the development of tomato from early growth to mature fruit yield. Carbon dioxide enrichment reduced the detrimental effects of O-3 on total vegetative plant d. wt of tomato following 3, 5, 7 and 13 wk exposure. Final mature fruit yield was 24% higher under enriched CO2 treatments than in ambient CO2. Ozone suppressed final yield by 31% following exposure to 80 nmol mol(-1) O-3 when compared with exposure to charcoal-filtered (CF) air. The impacts of both CO2 and O-3 on yield were, however, dependent upon the presence or absence of the other gas. In the absence of O-3, yields were very similar for the ambient and elevated CO2 treatments, but in the presence of O-3, yields under ambient CO2 were greatly suppressed whereas yields under elevated CO2 were similar to those in the absence of O-3. Thus, enriched CO2 ameliorated most of the suppressive effect of O-3 on yield of mature fruit.

1462^6^Sato,H^Sakurai,N^Sendo,S^Saneoka,H^Nobuyasu,H^Fujita,K^1997^1^Factors affecting leaf area development in husk leaf of flint corn^164^37^6^1826-1831^^^^^Nov-Dec^^^^^5718
1636^2376^2377^2378^348^372^436^92^hment reduced the detrimental effects of O-3 on total vegetative plant d. wt of tomato following 3, 5, 7 and 13 wk exposure. Final mature fruit yield was 24% higher under enriched CO2 treatments than in ambient CO2. Ozone suppressed final yield by 31% following exposure to 80 nmol mol(-1) O-3 whA^5717^Some corn (Zea mays L.) genotypes produce husk leaves (laminae extending from the husk) that on a per unit area basis, contribute more photosynthate to grain production than culm leaves. Furthermore, a high correlation between husk leaf area and dry weight has been observed, but little is known about the changes in cell components during development of husk leaves. A field experiment was conducted to quantify methanol (MeOH)- soluble fraction (cytosol) and incorporation of C-13-labeled photosynthate in cell walls from 9 d before silking (DBS) to silking. The ear leaf of flint corn (F-1 of N-19 by X-15) was subjected to (CO2)-C-13, eight DBS. Leaf area, dry weight, and photosynthetic activity of the husk leaves, and sugar content of various cell components were measured continuously during the 9-d period. The husk leaf attained one-half of its maximum apparent photosynthetic rate (P-0,) when it had 8% of its maximum leaf area at 4 DES. At 9 DBS, neutral sugars in the MeOH-soluble fraction accounted for most of nonstarch carbohydrates within the husk leaf (68%), while hemicellulose and cellulose fractions accounted for <10%. At silking, however, sugars in the hemicellulose and cellulose fractions increased by 23 and 56%, respectively. Results of (CO2)-C-13 labeling suggest that during rapid husk leaf development, MeOH- soluble fraction decreases, while the hemicellulose fraction fluctuates, and cellulose fraction increases.

1463^4^Smart,DR^Ritchie,K^Stark,JM^Bugbee,B^1997^1^Evidence that elevated CO2 levels can indirectly increase rhizosphere denitrifier activity^317^63^11^4621-4624^^^^^Nov^^^^^5720
1163^2379^2380^409^417^529^881^13, eight DBS. Leaf area, dry weight, and photosynthetic activity of the husk leaves, and sugar content of various cell components were measured continuously during the 9-d period. The husk leaf attained one-half of its maximum apparent photosynthetic rate (P-0,) when it had 8% of its maximum leaf area at 4 DES. At 9 DBS, neutral sugars in the MeOH-soluble fraction accounted forA^5719^We examined the influence of elevated CO2 concentration on denitrifier enzyme activity in wheat rhizoplanes by using controlled environments and solution culture techniques. Potential denitrification activity was from 3 to 24 times higher on roots that were grown under an elevated CO2 concentration of 1,000 mu mol of CO2 mol(-1) than on roots grown under ambient levels of CO2. Nitrogen loss, as determined by a nitrogen mass balance, increased with elevated CO2 levels in the shoot environment and with a high NO3- concentration in the rooting zone. These results indicated that aerial CO2 concentration can play a role in rhizosphere denitrifier activity.

1464^8^Street-Perrott,FA^Huang,YS^Perrott,RA^Eglinton,G^Barker,P^BenKhelifa,L^Harkness,DD^Olago,DO^1997^1^Impact of lower atmospheric carbon dioxide on tropical mountain ecosystems^32^278^5342^1422-1426^^^^^21 Nov^^^^^5722
1619^174^2381^2382^2383^2384^2385^417^534^625^af area at 4 DES. At 9 DBS, neutral sugars in the MeOH-soluble fraction accounted forA^5721^Carbon-isotope values of bulk organic matter from high-altitude lakes on Mount Kenya and Mount Elgon, East Africa, were 10 to 14 per mil higher during glacial times than they are today. Compound-specific isotope analyses of leaf waxes and algal biomarkers show that organisms possessing CO2-concentrating mechanisms, including C-4 grasses and freshwater algae, were primarily responsible for this large increase. Carbon limitation due to lower ambient CO2 partial pressures had a significant impact on the distribution of forest on the tropical mountains, in addition to climate. Hence, tree line elevation should not be used to infer palaeotemperatures.

1465^2^Taylor,K^Potvin,C^1997^1^Understanding the long-term effect of CO2 enrichment on a pasture: the importance of disturbance^188^75^10^1621-1627^^^^^Oct^^^^^5724
1072^188^2070^245^372^374^417^540^765^92^^^^^21 Nov^^^^^5722
1619^174^2381^2382^2383^2384^2385^417^534^625^af area at 4 DES. At 9 DBS, neutral sugars in the MeOH-soluble fraction accounted forA^5723^This study is part of a research program examining the effects of elevated atmospheric carbon dioxide on a pasture. It was designed to examine (i) the interaction between disturbance and the atmospheric CO2 concentration at the community level, and (ii) the response of a major weed Chenopodium album to CO2 enrichment in a natural field situation. Although both the total number of species and Simpson's index increased upon disturbance, these traits did not respond to CO2 fertilization. Counter to our expectation, we found no significant interaction between disturbance and CO2. The composition of the community that established in the open, disturbed spaces was a function of seed availability and as such independent of the atmospheric CO2 concentration. Using height of the background vegetation to assess the impact of elevated CO2, we found some evidence for density dependence in the undisturbed quadrats but not in the disturbed ones. For C. album, the disturbance regimes outweigh the CO2 increase in importance. Neighboring plants have a strong influence on C. album growth, this even though the C. album photosynthetic mechanisms are potentially responsive to elevated CO2. The present study highlights the complex feed- back interactions occurring when a community is exposed to elevated CO2 concentration.

1466^2^Vivin,P^Guehl,JM^1997^1^Changes in carbon uptake and allocation patterns in Quercus robur seedlings in response to elevated CO2 and water stress: an evaluation with C-13 labelling^186^54^7^597-610^^^^^Oct-Nov^^^^^5726
2032^229^344^376^384^483^595^682^771^975^rbance and CO2. The composition of the community that established in the open, disturbed spaces was a function of seed availability and as such independent of the atmospheric CO2 concentration. Using height of the background vegetation to assess the impact of elevated CO2, we found some evidence for density dependence in the undisturbed quadrats but not in the disturbed ones. For C. album, the disturbance regimes outweigh the CO2 increase in impA^5725^A semi-closed (CO2)-C-13 labelling system (1.5% C-13) was used to assess both carbon uptake and allocation within pedunculate oak seedlings (Quercus robur L) grown under ambient (350 vpm) and elevated (700 vpm) atmospheric CO2 concentration ([CO2]) and in either well-watered or droughted conditions. Pulse-chase C-13 labelling data highlighted the direct positive effect of elevated CO2 on photosynthetic carbon acquisition. Consequently, in well-watered conditions, CO2-enriched plants produced 1.52 times more biomass (dry mass at harvest) and 1.33 times more dry root matter (coarse plus fine roots) over the 22-week growing period than plants grown under ambient [CO2]. The root/shoot biomass ratio was decreased both by drought and [CO2], despite lower N concentrations in CO2-enriched plants. However, both long-term and short-term C allocation to fine roots were not altered by CO2, and relative specific allocation (RSA), a parameter expressing sink strength, was hip her in all plant organs under 700 vpm compared to 350 vpm. Results showed that C availability for growth and metabolic processes was greater in fine roots of oaks grown under an elevated CO2 atmosphere irrespective of soil water availability.

1467^4^Walker,RF^Geisinger,DR^Johnson,DW^Ball,JT^1997^1^Elevated atmospheric CO2 and soil N fertility effects on growth, mycorrhizal colonization, and xylem water potential of juvenile ponderosa pine in a field soil^206^195^1^25-36^^^^^Aug^^^^^5728
1334^2093^224^2386^341^374^386^419^610^680^duced 1.52 times more biomass (dry mass at harvest) and 1.33 times more dry root matter (coarse plus fine roots) over the 22-week growing period than plants grown under ambient [CO2]. The root/shoot biomass ratio was decreased both by drought and [CO2], despite lower N concentrations in CO2-enriched plants. However, both long-term and short-term C allocation to fine roots were not altered by CO2, and relative specific allocation (RSA), a parameter expressing sink strength, was hip her in all plant organs under 700 vpm cA^5727^Interactive effects of atmospheric CO2 enrichment and soil N fertility on above- and below-ground development and water relations of juvenile ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were examined. Open-top field chambers permitted creation of atmospheres with 700 mu L L-1, 525 mu L L-1, or ambient CO2 concentrations. Seedlings were reared from seed in field soil with a total N concentration of approximately 900 mu g g(-1) or in soil amended with sufficient (NH4)(2)SO4 to increase total N by 100 mu g g(-1) or 200 mu g g(-1). The 525 mu L L-1 CO2 treatment within the intermediate N treatment was excluded from the study. Following each of three consecutive growing seasons, whole seedlings of each combination of CO2 and N treatment were harvested to permit assessment of shoot and root growth and ectomycorrhizal colonization. In the second and third growing seasons, drought cycles were imposed by withholding irrigation during which predawn and midday xylem water potential and soil water potential were measured. The first harvest revealed that shoot weight and coarse and fine root weights were increased by growth in elevated CO2. Shoot and root volume and weights were increased by CO2 enrichment at the second harvest, but growth stimulation by the 525 mu L L-1 CO2 concentration exceeded that in 700 mu L L-1 CO2 during the first two growing seasons. At the third harvest, above-and below-ground growth increases were largely confined to the 700 mu L L-1 CO2 treatment, an effect accentuated by high soil N but evident in all N treatments. Ectomycorrhizal formation was reduced by elevated CO2 after one growing season, but thereafter was not significantly affected by CO2 and was unaffected by soil N throughout the study. Results of the xylem water potential measurements were variable, as water potentials in seedlings grown in elevated CO2 were intermittently higher on some measurement days but lower on others than that of seedlings grown in the ambient atmosphere. These results suggest that elevated CO2 exerts stimulatory effects on shoot and root growth of juvenile ponderosa pine under held conditions which are somewhat dependent on N availability, but that temporal variation may periodically result in a greater response to a moderate rise in atmospheric CO2 than to a doubling of the current ambient concentration.

1468^2^Arnone,JA^Hirschel,G^1997^1^Does fertilizer application alter the effects of elevated CO2 on Carex leaf litter quality and in situ decomposition in an alpine grassland?^318^18^3^201-206^^^^^^^^^^5730
374^57^672^ treatments. Ectomycorrhizal formation was reduced by elevated CO2 after one growing season, but thereafter was not significantly affected by CO2 and was unaffected by soil N throughout the study. Results of the xylem water potential measurements were variable, as water potentials in seedlings grown in elevated CO2 were intermittently higher on some measurement days but lower on others than that of seedlings grown in the ambient atmosphere. These results suggest that elevated CO2 exerA^5729^The purpose of our investigation was to determine: (1) whether fertilization with NPK would result in an improvement in leaf litter quality of the dominant species (Carer curvula) in a high alpine grassland in Switzerland; and especially (2) if fertilization improves the quality of leaf litter produced under elevated atmospheric CO2 and compensates for the suppressive effects of high CO2 on the in situ decomposition rates of C. curvula litter, observed at this site in an earlier study. Fertilizer application (40 k(g) N ha(-1) yr(-1)) resulted in 34% higher leaf litter [N] but did not change C:N or lignin N ratios, when viewed across both CO2 treatments. Improvement in the mean N quality of litter produced under elevated CO2 resulting from fertilization appeared to lead to a significantly faster mean decomposition rate (+ 60%), but fertilization had no significant effect on decomposition of litter produced under ambient CO2. We conclude that the potential stimulatory effect of an increase in atmospheric N deposition on litter quality and decomposition rates may partially compensate for the inhibitory effects of rising atmospheric CO2 in these high alpine grassland ecosystems.

1469^3^Brearley,J^Venis,MA^Blatt,MR^1997^1^The effect of elevated CO2 concentrations on K+ and anion channels of Vicia faba L. guard cells^6^203^2^145-154^^^^^Oct^^^^^5732
1008^1224^2128^2387^2388^2389^2390^2391^383^543^ the in situ decomposition rates of C. curvula litter, observed at this site in an earlier study. Fertilizer application (40 k(g) N ha(-1) yr(-1)) resulted in 34% higher leaf litter [N] but did not change C:N or lignin N ratios, when viewed across both CO2 treatments. Improvement in the mean N quality of litter produced under elevated CO2 resulting from fertilization appeared to lead to a significantly faster mean decomposition rate (+ 60%), but fertilization had no significant effect on decomposition of litter produced under ambient CO2. We conclude that the potential stimulatory effect of an increase in atmospheriA^5731^The effects of elevated CO2 concentrations on stomatal movement, anion-and K+-channel activities were examined in guard cells from epidermal strips of Vicia faba. Membrane voltage was measured using intracellular, double-barrelled microelectrodes and ion-channel currents were recorded under voltage clamp during exposure to media equilibrated with ambient (350 mu l . l(-1)), 1000 mu l . l(-1) and 10 000 mu l . l(-1) CO2 in 20% O-2 and 80% N-2. The addition of 1000 mu l . l(-1) CO2 to the bathing solution caused stomata to close with a halftime of approx. 40 min, and with 10 000 mu l . l(-1) CO2 closure occurred with a similar time course. Under voltage clamp, exposure to 1000 mu l . l(-1) and 10 000 mu l . l(-1) CO2 resulted in a rapid increase (mean, 1.5 +/- 0.2-fold, n = 8; range 1.3- to 2.5-fold) in the magnitude of current carried by outward-rectifying K+ channels (I-K,I-out). The effect of CO2 on I-K,I-out was essentially complete within 30 s and was independent of clamp voltage, but was associated with 25-40% (mean, 30 +/- 4%) decrease in the halftime for current activation. Exposure to CO2 also resulted in a four-fold increase in background current near the free-running membrane voltage, recorded as the instantaneous current at the start of depolarising and hyperpolarising voltage steps, and a decrease in the magnitude of current carried by inward-rectifying K+ channels (I-K,I-in). The effect of CO2 on I-K,I-in was generally slower than on I-K,I-out; it was allied with a transient acceleration of its activation kinetics during the first 60-120 s of treatment; and it was associated with a negative shift in the voltage-sensitivity of gating over a period of 3-5 min. Measurements carried out to isolate the background currents attributable to anion channels (I-Cl), using tetraethylammonium chloride and CsCl, showed that CO2 also stimulated I-CL and dramatically altered its relaxation kinetics. Within the timeframe of CO2 action at the membrane, no significant effect was observed on cytosolic pH, measured using the fluorescent dye 2',7'-bis-(2-carboxyethyl)-5,6- carboxyflourescein (BCECF) and ratio fluorescence microphotometry. These results are broadly consistent with the pattern of guard-cell response to abscisic acid, and indicate that guard cells control both anion and K+ channels to achieve net solute loss in CO2. By contrast with the effects of abscisic acid, however, the data indicate that CO2 action is not mediated through changes in cytosolic pH and thereby implicate new and, as yet, unidentified pathway(s) for channel regulation in the guard cells.

1470^5^Ceulemans,R^Taylor,G^Bosac,C^Wilkins,D^Besford,RT^1997^1^Photosynthetic acclimation to elevated CO2 in poplar grown in glasshouse cabinets or in open top chambers depends on duration of exposure^78^48^314^1681-1689^^^^^Sep^^^^^5734
130^2000^2056^2392^2393^312^344^356^384^618^lated I-CL and dramatically altered its relaxation kinetics. Within the timeframe of CO2 action at the membrane, no significant effect was observed on cytosolic pH, measurA^5733^The effects of elevated CO2 were studied on the photosynthetic gas exchange behaviour and leaf physiology of two contrasting poplar (Populus) hybrids grown and treated in open top chambers (OTCs in Antwerp, Belgium) and in closed glasshouse cabinets (GHCs in Sussex, UK). The CO2 concentrations used in the OTCs were ambient and ambient +350 mu mol mol(-1), while in the GHCs they were c, 360 mu mol mol(-1) versus 719 mu mol mol(-1). Measurements of photosynthetic gas exchange were made for euramerican and interamerican poplar hybrids in combination with measurements of dark respiration rate and Rubisco activity. Significant differences in the leaf anatomy and structure (leaf mass per area and chlorophyll content) were observed between the leaves grown in the OTCs and those grown in the GHCs. Elevated CO2 stimulated net photosynthesis in the poplar hybrids after 1 month in the GHCs and after 4 months in the OTCs, and there was no evidence of downward acclimation (or downregulation) of photosynthesis when the plants in the two treatments were measured in their growth CO2 concentration. There was also no evidence of downregulation of Rubisco activity and there were even examples of increases in Rubisco activity. Rubisco exerted a strong control over the light- saturated rate of photosynthesis, which was demonstrated by the close agreement between observed net photosynthetic rates and those that were predicted from Rubisco activities and Michaelis-Menten kinetics. After 17 months in elevated CO2 in the OTCs there was a significant loss of Rubisco activity for one of the hybrid clones, i.e. Beaupre, but not for clone Robusta, The effect of the CO2 measurement concentration (i.e. the short-term treatment effect) on net photosynthesis was always larger than the effect of the growth concentration in both the OTCs or GHCs (i.e. the long-term growth CO2 effect), with one exception, For the interamerican hybrid Beaupre dark respiration rates in the OTCs were not significantly affected by the elevated CO2 concentrations. The results suggest that for rapidly growing tree species, such as poplars, there is little evidence for downward acclimation of photosynthesis when plants are exposed to elevated CO2 for up to 4 months; longer term exposure reveals loss of Rubisco activity.

1471^1^Diemer,M^1997^1^Effects of elevated CO2 on gas exchange characteristics of alpine grassland^318^18^3^177-182^^^^^^^^^^5736
699^re predicted from Rubisco activities and Michaelis-Menten kinetics. After 17 months in elevated CO2 in the OTCs there was a significant loss of Rubisco activity for one of the hybrid clones, i.e. Beaupre, but not for clone Robusta, The effect of the CO2 measurement concentration (i.e. the short-term treatment effect) on net photosynthesis was always larger than the effect of the growth concentration in both the OTCs or GHCs (i.e. the long-term growth CO2 effect), with one exception, For the interamerican hybrid Beaupre dark respiration rates in the OTCs were not significantly affected by the elevated CO2 concentratioA^5735^The ecosystem-level gas exchange characteristics of an alpine grassland treated with a combination of elevated CO2 and moderate additions of NPK fertilizer during the third season of experimental treatments are described. Mid-season maximum daytime net ecosystem CO2 flux (NEC)increased significantly under elevated CO2 (+45%), whereas nighttime NEC was unaffected by the CO2 treatment. Since daytime NEC under elevated CO2 underwent a seasonal decline, only moderate carbon surpluses accumulated under elevated CO2. The observed seasonal decline in daytime NEC may be due to reduced sink strength once maximum aboveground biomass is attained, and appears to be a reg ulatory mechanism of ecosystem carbon accumulation. Moderate additions of NPK fertilizer stimulated both day- (+39%) and nighttime NEC (+29%) due to increased plant biomass, independent of CO2 treatment. Yet there is no indication that enhanced mineral nutrient status will increase ecosystem responsiveness to elevated CO2.
vated CO2 concentratio1472^3^Fischer,M^Matthies,D^Schmid,B^1997^1^Responses of rare calcareous grassland plants to elevated CO2: a field experiment with Gentianella germanica and Gentiana cruciata^12^85^5^681-691^^^^^Oct^^^^^5738
1142^130^1317^2394^2395^2396^344^457^506^92^me net ecosystem CO2 flux (NEC)increased significantly under elevated CO2 (+45%), whereas nighttime NEC was unaffected by the CO2 treatment. Since daytime NEC under elevated CO2 underwent a seasonal decline, only moderate carbon surpluses accumulated under elevated CO2. The observed seasonal decline in daytime NEC may be due to reduced sink strength once maximum aboveground biomass is attained, and appears to be a reg ulatory mechanism of ecosystem carbon accumulation. Moderate additions of NPK fertilizer stimulated both day- (+39%) and nighttime NEC (+29%) due to increased plant biomass, independent of CO2 treatment. Yet there is no indication that enhanced mineral nutrient status will increase ecosystem responsiveness to elevated CO2.
vated CO2 concentratioA^5737^1 Endangered plant species may be particularly vulnerable to global change. We investigated differences in the behaviour of the rare calcareous grassland species Gentiana cruciata and Gentianella germanica under ambient (360 mu l l(-1)) and elevated CO2 (600 mu l l(-1)) in a field experiment. 2 Rosettes of G. germanica and C. cruciata were planted into grassland plots with 29 other plant species. Each of the 30 rosettes of G. germanica in a plot represented a different maternal seed family, whereas G. cruciata was grown from a mixture of seeds from one field site. After overwintering, eight of the 12 plots were equipped with open-top chambers, four of which were run at ambient and four at elevated CO2 concentrations; the remaining four plots were left without chambers. 3 CO2 concentration did not significantly affect growth and survival of G. cruciata. Rosette diameter increased by 70% over 1 year. 4 Overall only 13.6% of transplanted G. germanica survived for 1 year. Elevated CO2 reduced survival by 57% (this reduction was only marginally significant due to large variation between plots) and seed set by 46%. Both these effects appeared to be mediated by competition from other species since survival and seed set were negatively correlated with total plot biomass at the time of fastest growth in June 1994 and at the time of fruit set in October, respectively. Compared with plots under ambient CO2, population growth rate (based on survival and reproduction) was reduced by 56% under elevated CO2. 5 There were no significant effects of elevated CO2 on leaf characters in either species. 6 The sugar concentration of the nectar of G. germanica was increased by 36% under elevated CO2 but its composition remained unchanged. 7 Significant interactions between the effects of seed family and CO2 concentration on demographic parameters in G. germanica indicated large genetic variation in the response to elevated CO2, which represents evolutionary potential. Although predictions based on mean responses are therefore unreliable, the majority of genotypes reacted negatively to elevated CO2, suggesting that competitive exclusion and extinction of G. germanica would occur at many sites before populations could adapt to increased concentrations of CO2.

1473^5^Hamerlynck,EP^McAllister,CA^Knapp,AK^Ham,JM^Owensby,CE^1997^1^Photosynthetic gas exchange and water relation responses of three tallgrass prairie species to elevated carbon dioxide and moderate drought^104^158^5^608-616^^^^^Sep^^^^^5740
1317^2397^2398^2399^269^344^474^57^740^956^ficant effects of elevated CO2 on leaf characters in either species. 6 The sugar concentration of the nectar of G. germanica was increased by 36% under elevated CO2 but its composition remained unchanged. 7 Significant interactions between the effects of seed family and CO2 concentration on demographic parameters in G. germanica indicated large genetic variation in the response to elevated CO2, which represents evolutionary potential. Although predictions based on mean responses are therefore uA^5739^Undisturbed tallgrass prairie was exposed to ambient and elevated (twice-ambient) levels of atmospheric CO, and experimental dry periods. Seasonal and diurnal midday leaf water potential (Psi(leaf)), net photosynthesis (A(net)), and stomatal conductance (g(s)) responses of three tallgrass prairie growth forms-a C-4 grass, Andropogon gerardii; a broad- leaved woody C, shrub, Symphiocarpos orbiculatus; and a C-3 perennial forb, Salvia pitcheri-were assessed. Psi(leaf) in A. gerardii and S, orbiculatus was higher under elevated CO2, regardless of soil moisture, while Psi(leaf) in S. pitcheri responded only to drought. Elevated CO2 always stimulated A(net) in the C-3 species, while A. gerardii A(net) increased only under dry conditions. However, A(net) under elevated CO2 in the C-3 species declined with drought but not in the C,grass, Under wet conditions, g(s) reduced in elevated CO2 for all species. During dry periods, g, at elevated CO, was sometimes higher than in ambient CO2. Our results support claims that elevated CO2 will stimulate tallgrass prairie productivity during dry periods and possibly reduce temporal and spatial variability in productivity in these grasslands.

1474^4^Hattenschwiler,S^Miglietta,F^Raschi,A^Korner,C^1997^1^Thirty years of in situ tree growth under elevated CO2: a model for future forest responses?^127^3^5^463-471^^^^^Oct^^^^^5742
227^2400^2401^312^344^417^58^672^673^culatus; and a C-3 perennial forb, Salvia pitcheri-were assessed. Psi(leaf) in A. gerardii and S, orbiculatus was higher under elevated CO2, regardless of soil moisture, while Psi(leaf) in S. pitcheri responded only to drought. Elevated CO2 always stimulated A(net) in the C-3 species, while A. gerardii A(net) increased only under dry conditions. However, A(net) under elevated CO2 in the C-3 species declined with drought but not in the C,grass, Under wet conditions, g(s) reduced in elevated CO2 for all species. During dry periods, g, at elevated CO, was sometimes higher than in ambient CO2. Our results support claiA^5741^Rising concentrations of atmospheric carbon dioxide have been predicted to stimulate the growth of forest trees. However, long-term effects on trees growing to maturity and to canopy closure while exposed to elevated CO2 have never been examined. We compared tree ring chronologies of Mediterranean Quercus ilex which have been continuously exposed to elevated CO2 (around 650 mu mol mol(-1)) since they were seedlings, near two separate natural CO2 springs with those from trees at nearby ambient-CO2 'control' sites. Trees grown under high CO2 for 30 years (1964-93) showed a 12% greater final radial stem width than those growing at the ambient-CO2 control sites. However, this stimulation was largely due to responses when trees were young. By the time trees were 25-30 y old the annual difference in tree ring width between low and high CO2 grown trees had disappeared. At any given tree age, elevated CO2 had a relatively greater positive effect on tree ring width in years with a dry spring compared to years with more rainfall between April and May. This indicates a beneficial effect of elevated CO2 on tree water relations under drought stress. Our data suggest that the early regeneration phase of forest stands can be accelerated in CO2-enriched atmospheres and that maximum biomass per land area may be reached sooner than under lower CO2 concentrations. In our study, high CO2 grown Q. ilex trees reached the same stem basal area at the age of 26 y as control trees at 29 y,i.e. three years earlier (faster turnover of carbon?). Reliable predictions of the future development of forests need to account for the variable responses of trees over their entire lifetime. Such responses to elevated CO2 can presently only be assessed at such unique field sites.

1475^2^Kellomaki,S^Wang,KY^1997^1^Effects of elevated O-3 and CO2 on chlorophyll fluorescence and gas exchange in Scots pine during the third growing season^35^97^1-2^17-27^^^^^^^^^^5744
1064^2402^2403^312^343^444^602^635^692^728^with a dry spring compared to years A^5743^Naturally regenerated, 30-year-old Scots pines (Pinus Sylvestris L.) were grown in open-top chambers and exposed in situ to doubled ambient O-3, doubled ambient CO2 and a combination of elevated O-3 and CO2 from 15 April to 15 September for three growing seasons (1994-1996). To examine the effects of O-3 and/or CO2 on photosynthesis, chlorophyll a fluorescence and gas exchange were measured simultaneously. Doubled ambient O-3 significantly decreased the rates of photosynthesis at all levels of photon flux density. This was related mainly to a significant decrease in the photochemical efficiency of photosystem II (PS II) and the rate of whole electron transport, rather than to a decrease in stomatal conductance. When measurements were made at doubled ambient concentration of CO2 (700 mu mol mol(-1)), doubled ambient CO2 treatment did not lend to a significant change in the intrinsic capacity of photosynthesis, as manifested by no changes in PS II, the rate of electron transport, the maximal rate of photosynthesis and the apparent quantum yield of CO2 assimilation. However, elevated CO2 increased the sensitivity of stomatal conductance to light and decreased maximal stomatal conductance. When O-3 and CO2 were combined, the O-3-induced decrease in photosynthesis rate was reduced significantly by a high concentration of CO2. This may be partly related to the decrease in stomatal conductance induced by the high concentration of CO2. The complete mechanism behind this interaction is, however, still unclear. (C) 1997 Elsevier Science Ltd.

1476^7^Kinsman,EA^Lewis,C^Davies,MS^Young,JE^Francis,D^Vilhar,B^Ougham,HJ^1997^1^Elevated CO2 stimulates cells to divide in grass meristems: a differential effect in two natural populations of Dactylis glomerata^9^20^10^1309-1316^^^^^Oct^^^^^5746
130^1531^2404^2405^2406^2407^2408^417^661^92^2 treatment did not lend to a significant change in the intrinsic capacity of photosynthesis, as manifested by no changes in PS II, the rate of electron transport, the maximal rate of phoA^5745^In this study, we tested the hypothesis that elevated [CO2] shortens the cell cycle in meristems of Dactylis glomerata, more in a Portuguese population (38 degrees 53'N) than in a Swedish population (63 degrees 09'N). In the shoot meristem, the cell cycle shortened to about the same extent (approximate to 26%) in both populations exposed to the elevated [CO2] treatment, In the root meristem, the cell cycle shortened by 17% in the Portuguese and by 8% in the Swedish population, However, the proportion of rapidly cycling cells increased in the Portuguese much more than in the Swedish population in both meristems, In the root meristem, there was a 1.86-fold increase in the Portuguese compared with a 1.31-fold increase in the Swedish, In the shoot meristem, the increases were 1.5-3-fold for the Portuguese and 1.2-fold for the Swedish, The data are consistent in showing that a major response to the elevated [CO2] treatment was an increase in the proportion of cells that were cycling and that this was more marked for the Portuguese population, A more general response to the elevated [CO2] treatment was a shortening of the cell cycle regardless of population.

1477^3^Kitao,M^Lei,TT^Koike,T^1997^1^Comparison of photosynthetic responses to manganese toxicity of deciduous bread-leaved trees in northern Japan^35^97^1-2^113-118^^^^^^^^^^5748
113^130^188^1989^2125^2409^422^528^665^92^ In the root meristem, the cell cycle shortened by 17% in the Portuguese and by 8% in the Swedish population, However, the proportion of rapidly cycling cells increased in the Portuguese much more than in the Swedish population in both meristems, In the root meristem, there was a 1.86-fold increase in the Portuguese compared with a 1.31-fold increase in the Swedish, In the shoot meristem, the increases were 1.5-3-fold for the Portuguese and 1.2-fold for the Swedish, The data are consistent in showing that a major response to the elevated [CO2] treatment was an increase in the proportion of cells that were cycling and that this was more A^5747^The effects of manganese (Mn) toxicity on photosynthesis of four tree species in northern Japan representing different successional traits were examined. The four species are: Betula ermanii (Be) and Alnus hirsuta (Ah) representing two early successional species, Ulmus davidiana var. japonica (Ud) as the mid-successional species, and Acer mono (Am) as the late successional species. Seedlings were grown hydroponically in a solution containing nutrients and Mn of four concentrations (1, 10, 50, 100 mg litre(-1)) for 50 days. Gas exchange measurements indicate that in all species, Mn accumulation in leaves resulted in the decline of light-saturated net photosynthetic rate at ambient CO2 pressure (35 Pa, Pn(amb)) and at saturating (5%) CO2 pressure (Pn(sat)), and of carboxylation efficiency but has little effect on the maximum efficiency of photochemistry. Sensitivity to elevated levels of Mn differed among species where the decline of Pn(amb) was much more modest in the two early successional species of Be and Ah than the mid-and late successional species of Ud and Am. The same trends were observed in both Pn(sat) and carboxylation efficiency. Based on these results, we suggest that early successional species (Betula ermanii and Alnus hirsuta) have greater tolerance for excess Mn in leaves than mid-and late successional species. (C) 1997 Elsevier Science Ltd.

1478^1^Korner,C^1997^1^From alpine grassland to tropical forests: Biological consequences of elevated atmospheric CO2 (a synthesis of Swiss research) - Introduction^318^18^3^163-164^
374^
1479^5^Korner,C^Diemer,M^Schappi,B^Niklaus,P^Arnone,J^1997^1^The responses of alpine grassland to four seasons of CO2 enrichment: a synthesis^318^18^3^165-175^^^^^^^^^^5751
1781^312^417^733^ (5%) CO2 pressure (Pn(sat)), and of carboxylation efficiency but has little effect on the maximum efficiency of photochemistry. Sensitivity to elevated levels of Mn differed among species where the decline of Pn(amb) was much more modest in the two early successional species of A^5750^Alpine grassland at 2 470 m altitude in the Swiss Central Alps was exposed to elevated CO2 by using open top chambers (16 ambient, 16 elevated CO2). Some plots received mineral fertilizer at a rate of N-deposition commonly measured in low altitude parts of Europe. Here we present a summary of results and data from the final harvest. Above-ground biomass measured after the completion of growth in the fourth season of treatment was not affected by CO2 enrichment as was found by previous biometric estimates, but mean below-ground biomass was slightly stimulated (+ 12%, n.s.). In con trast, net CO2 uptake per unit land area was strongly stimulated by CO2 enrichment al the beginning of the experiment, and during the early part of each season. However, the CO2 stimulation decreased during the later part of each growing season. By year four, also mid- season differences in CO2 uptake per unit land area had disappeared. Neither microbial biomass, soil respiration in the laboratory, nor in situ land-area-based CO2 evolution during the 10 week growing season increased under elevated CO2. The total biomass N-pool and free soil nitrate and ammonium (capture by ion exchange resin bags) remained unaffected, whereas leaf nitrogen concentration was reduced and nonstructural carbohydrate concentration increased under elevated CO2 in forbs. These differences in tissue composition largely disappeared during senescence and litter formation. Despite low CO2 responsiveness at ecosystem level, species responses differed in terms of nitrogen, carbohydrates, tillering and flowering, suggesting the possibility for long- term changes in community structure. Addition of NPK equivalent to 40 kg N ha(-1) a(-1) had massive effects on all plant traits studied, but did not enable stimulated growth under CO2 enrichment. However, when fertilizer and CO2 enrichment were provided jointly, soil microbes were stimulated indicating a co-limitation by carbon and nutrients (most likely nitrogen). Since responses to elevated CO2 were absent in both warm and cold growing seasons, we conclude that this late successional plant community is carbon saturated at current atmospheric CO2 concentrations for reasons not directly related to nutrient supply and climate. Perhaps, contrary to our expectation, evolutionary adjustments of this ''old'' ecosystem to the life conditions at high altitudes caused carbon to become a surplus resource today.

1480^6^Laporte,MM^Galagan,JA^Shapiro,JA^Boersig,MR^Shewmaker,CK^Sharkey,TD^1997^1^Sucrose-phosphate synthase activity and yield analysis of tomato plants transformed with maize sucrose-phosphate synthase^6^203^2^253-259^^^^^Oct^^^^^5753
1247^130^1584^174^2410^243^312^348^845^ kg N ha(-1) a(-1) had massive effects on all plant traits studied, but did not enable stimulated growth under CO2 enrichment. However, when fertilizer and CO2 enrichment were provided jointly, soil microbes were stimulated indicating a co-limitation by carbon and nutrients (most likely nitrogen). Since responses to elevated CO2 were absent in boA^5752^Sucrose synthesis is a major element of the interactions between photosynthesis and plant growth and development. Tomato (Lycopersicon esculentum Mill. cv. UC82B) plants transformed with maize sucrose-phosphate synthase (SPS; EC 2.3.1.14) expressed from either a ribulose-1,5-bisphosphate carboxylase- oxygenase (Rubisco) small subunit promoter (SSU) or the cauliflower mosaic virus 35S promoter (35S) were used to study effects of increased sucrose synthesis rates on plant growth. The plants were grown in growth chambers, field plots, and open-top chambers. The 35S plants had a 2 to 3-fold increase in young-leaf SPS activity, a 10 to 20-fold increase in young-root SPS activity and no increase in young-fruit SPS activity. The leaf SPS activity in;one of the 35S lines fell to control levels by two months of age. The SSU plants had a 4 to 5-fold increase in leaf SPS activity and no significant increase in root or young-fruit SPS activity. One 35S line, which maintained high leaf SPS activity throughout development, yielded 70-80% more than controls at both normal and elevated CO2 in open-top chambers in the field and 20-30% more than controls in two additional field trials. The other 35S line and the two SSU lines either yielded less or did not differ from controls under several growth conditions. Since only one of four transformed lines showed an increase in yield, we can not yet conclude that increased leaf SPS activity leads to increased yield. However, increased leaf SPS activity appears to result in increased fruit sugar content since all three lines with increased leaf SPS usually also had increased fruit sugars.

1481^2^Lauber,W^Korner,C^1997^1^In situ stomatal responses to long-term CO2 enrichment in calcareous grassland plants^318^18^3^221-229^^^^^^^^^^5755
1208^312^348^360^384^465^641^73^733^956^s of age. The SSU plants had a 4 to 5-fold increase in leaf SPS activity and no significant increase in root or young-fruit SPS activity. One 35S line, which maintained high leaf SPS activity throughout deveA^5754^A calcareous grassland community growing under full season CO? enrichment at low altitude in the Swiss Jura mountains was investigated for diurnal and seasonal variations of leaf diffusive conductance. A new CO2 enrichment method (Screen aided CO2 control, SACC) permitted irt situ leaf porometry under natural climatic conditions without disturbance of plants. At 600 ppm CO2, leaf conductance in the dominant species, Bromus erectus (a species so far not showing a growth response to elevated CO2) was reduced to half the values measured in controls. Tn contrast, leaf conductance in Carex flacca, a species of low cover (the only species so far exhibiting a dramatic growth stimulation by CO2 fertilization) remained almost unaffected by elevated CO2. Sanguisorba minor; Plantago media, and Cirsium acaule showed intermediate responses. Trifolium montanum, studied only on a single day, showed a reduction like Bromus. Differences between treatments were largest under humid conditions and disappeared during dry periods. In none of the species studied did stomatal density or stomatal index differ between treatments. A parallel investigation of whole ecosystem evapotranspiration indicated only small (< 10%) and non significant CO2 responses, suggesting that both aerodynamic effects at the canopy level and a great interspecific variation of leaf level responses overshadow the clear CO2 response of Bromus stomata. The different stomatal responses to CO2 enrichment are likely to alter species specific water consumption, and may thus affect community structure in the long run.

1482^4^Leadley,PW^Niklaus,P^Stocker,R^Korner,C^1997^1^Screen-aided CO2 control (SACC): a middle ground between FACE and open-top chambers^318^18^3^207-219^^^^^^^^^^5757
264^376^881^ed CO2. Sanguisorba minor; Plantago media, and Cirsium acaule showed intermediate responses. Trifolium montanum, studied only on a single day, showed a reduction like Bromus. Differences between treatments were largest under humid conditions and disappeared during dry A^5756^We have developed a novel CO2 exposure system for natural vegetation that is a middle ground between Free Air CO2 Enrichment (FACE) and traditional open-top chambers (OTC). Screen-Aided CO2 Control (SACC) technology uses much less CO2 per experiment and per replicate than FACE and is superior to OTCs in terms of its effects on microclimate. A SACC unit consists of a thin metal frame, a clear plastic ''screen'', and a pipe at the base of the screen through which CO2 enriched jets of air are directed into the unit. There is a gap between the ground and the bottom of the pipe and the screen is relatively short in comparison to the maximum height of the vegetation. Our SACC units are hexagonal and enclose a ground area of 1.27 m(2). SACC works in the following way: 1) the screen breaks the wind and creates turbulent mixing within the unit, 2) the mixing of the outside air with the CO2 enriched jets of air,generates relatively uniform CO2 concentrations within the screened-in vegetation, and 3) a fully automated system monitors CO2 concentrations and adjusts CO2 injection rates for each unit every ca. IO minutes to maintain preset CO2 concentrations. Twenty-four hour means of CO2 concentrations in the middle of a unit are typically maintained within 1 mu l l(- 1) of their set points. Spatial variation and short-term fluctuations in CO2 concentration are similar to those in OTCs and FACE. CO2 consumption at our site is 5 kg CO2 day(-1) replicate(-1) for a total of ca. 30 tons per year for 20 elevated CO2 SACC units. Compared to OTCs, SACC units have reduced temperature peaks at full sunlight, minimal effects on solar radiation, reduced rainfall interception by chamber walls, and freer access of small animals to experimental plots. We believe that SACC is the best method for exposing short stature vegetation to elevated CO2 when financial constraints do not allow for a properly replicated FACE experiment.
 air,generates relatively uniform CO2 concentrations within the screened-in vegetation, and 3) a fully aut1483^5^Lee,EH^Pausch,RC^Rowland,RA^Mulchi,CL^Rudorff,BFT^1997^1^Responses of field-grown soybean (cv. Essex) to elevated SO2 under two atmospheric CO2 concentrations^173^37^2-3^85-93^^^^^Jun^^^^^5759
1461^2411^243^312^376^417^446^461^466^962^ithin 1 mu l l(- 1) of their set points. Spatial variation and short-term fluctuations in CO2 concentration are similar to those in OTCs and FACE. CO2 consumption at our site is 5 kg CO2 day(-1) replicate(-1) for a total of ca. 30 tons per year for 20 elevated CO2 SACC units. Compared to OTCs, SACC units have reduced temperature peaks at full sunlight, minimal effects on solar radiation, reduced rainfall interception by chamber walls, and freer access of small animals to experimental plots. We believe that SACC is the best method for exposing short stature vegetation to elevated CO2 when financial constraints do not allow for a properly replicated FACE experiment.
 air,generates relatively uniform CO2 concentrations within the screened-in vegetation, and 3) a fully autA^5758^The objective of this research was to determine the effects of elevated concentrations of carbon dioxide (CO2) and sulfur dioxide (SO2) on field-grown soybean. Soybeans (Glycine max L. Merr. cv. 'Essex') were grown a full-season in open-top field chambers exposed to either ambient (350 mu l L-1) or elevated CO2 (500 mu l L-1) levels under two levels of SO2 (0.00 and 0.12 mu l L-1). Enriched CO2, with or without SO2 treatments, significantly increased net photosynthesis rates, leaf area index (LAI; in R4 growth stage) and leaf dry weight, but did not significantly affect stomatal resistance, transpiration rates, leaf area, plant height, total biomass or grain yield. Elevated SO2 treatments significantly decreased photosynthesis and LAI during pod fill stages, but did not significantly affect stomatal resistance, transpiration, total biomass, plant height or grain yield. Sulfur dioxide inhibited growth and development (i.e., LAI) during canopy coverage before any effects on photosynthesis were detected. The interactive effects of CO2 and SO2 treatments on the gas exchange parameters were significant during pod fill, where high SO2 reduced photosynthesis at ambient CO2 but not under elevated CO2. Leaf area index values were likewise reduced by SO2 exposure under ambient CO2 during late flowering and pod fill stages. Thus, enriched CO2 under high SO2 exposure partially compensated for the negative impact of SO2 stress on PS and LAI during the pod fill stages. (C) 1997 Elsevier Science B.V.

1484^4^Miglietta,F^Lanini,M^Bindi,M^Magliulo,V^1997^1^Free air CO2 enrichment of potato (Solanum tuberosum, L.): design and performance of the CO2-fumigation system^127^3^5^417-427^^^^^Oct^^^^^5761
2250^2412^312^409^442^73^906^ased photosynthesis and LAI during pod fill stages, but did not significantly affect stomatal resistance, transpiration, total biomass, plant height or grain yield. Sulfur dioxide inhibited growth and development (i.e., LAI) during canopy coverage before any effects on photosynthesis were detected.A^5760^Free Air CO2 Enrichment (FACE) systems are used to fumigate unconfined field plots with CO2. As these installations can treat a sufficiently large area without interfering with natural climatic conditions, they are considered important tools for global change research worldwide. However, there is general consensus that elevated capital costs of existing FACE systems as well as high running costs may prevent their application at the required level of scale. A new and small FACE system that was designed to reduce both capital costs and CO2 use, is described in this paper. Due to its intermediate size (8 m diameter) between the smaller Mini-FACE systems that were developed in Italy and the larger systems designed by the Brookhaven National Laboratory in the USA, it was named Mid- FACE. The Mid-FACE was at first developed as a prototype and then used to enrich field grown potato crops in a CO2 concentration gradient experimental design. Technical details of a Mid-FACE prototype and of the operational set-up are presented in this paper together with performance data in terms of temporal and spatial control of CO2 concentrations within the experimental area.

1485^4^Nitschelm,JJ^Luscher,A^Hartwig,UA^VanKessel,C^1997^1^Using stable isotopes to determine soil carbon input differences under ambient and elevated atmospheric CO2 conditions^127^3^5^411-416^^^^^Oct^^^^^5763
1298^1345^1768^2087^2413^417^429^506^534^57^vent their application at the required level of scale. A new and small FACE system that was designed to reduce both capital costs and CO2 use, is described in this paper. Due to its intermediate size (8 m diameter) between the smaller Mini-FACE systems that were developed in Italy and the larger systems designed by the Brookhaven National Laboratory in the USA, it was named Mid- FACE. The Mid-FACE was at first developed as a prototype and then used to enrich field grown potato crops in a CO2 concentration gradient experimental design. Technical details of a Mid-FACE prototype and of the operational set-A^5762^Quantitative estimates of soil C input under ambient (35 Pa) and elevated (60 Pa) CO2-partial pressure (pCO(2)) were determined in a Free-Air Carbon dioxide Enrichment (FACE) experiment. To facilitate C-13-tracing, Trifolium repens L. was grown in a soil with an initial delta(13)C distinct by at least 5 parts per thousand from the delta(13)C of T. repens grown under ambient or elevated pCO(2). A shift in delta(13)C Of the soil organic C was detected after one growing season. Calculated new soil C inputs in soil under ambient and elevated pCO(2) were 2 and 3 t ha(-1), respectively. Our findings suggest that under elevated CO2 conditions, soil C sequestration may be altered by changes in plant biomass production and quality.

1486^4^Polle,A^Eiblmeier,M^Sheppard,L^Murray,M^1997^1^Responses of antioxidative enzymes to elevated CO2 in leaves of beech (Fagus sylvatica L.) seedlings grown under a range of nutrient regimes^9^20^10^1317-1321^^^^^Oct^^^^^5765
1633^164^2173^225^2414^2415^344^417^885^989^al set-A^5764^To study whether responses of antioxidative enzymes to enhanced atmospheric CO2 concentrations are affected by plant nutrition, the activities of superoxide dismutase, catalase and peroxidase were investigated in leaves of 3-year-old beech trees grown with low (0.1 x optimum), intermediate (0.5 x optimum) and high (2 x optimum) nutrient supply rates in open-top chambers at either ambient (approximate to 355 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) CO2 concentrations, These treatments resulted in foliar C/N ratios of about 20 in the presence of high and > 30 in the presence of low nutrient supply rates, Pigment and malondialdehyde contents were determined to assess plant stress levels, Low nutrient supply rates caused pigment loss, whereas elevated CO2 had no effect on pigmentation, Guaiacol peroxidase activities did not respond to either CO2 or nutrient treatment, Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO2. Superoxidase dismutase activity was affected by both nutrient supply and CO2 concentration, In leaves from trees grown with the high-nutrient treatment, superoxide dismutase activity was low irrespective of CO2 concentration, In chlorotic leaves, superoxide dismutase activity was increased, suggesting an enhanced need for detoxification of reactive oxygen species, Leaves from plants grown under elevated CO2 with medium nutrient supply rates showed decreased malondialdehyde contents and superoxide dismutase activities, This suggests that the intrinsic oxidative stress of leaves was decreased under these conditions, These results imply that intrinsic oxidative stress is modulated;by the balance between N and C assimilation.

1487^1^Polley,HW^1997^1^Implications of rising atmospheric carbon dioxide concentration for rangelands^319^50^6^562-577^^^^^Nov^^^^^5767
1298^137^1917^230^2416^343^399^497^745^956^ment, Catalase activity decreased with decreasing nutrient supply rate and also in response to elevated CO2. Superoxidase dismutase activA^5766^Extensive rangelands and other vegetation types that we know today formed while atmospheric carbon dioxide (CO2) concentration was low (50 to 75% of today's concentration). Fossil fuel burning and deforestation and other land me changes during the last 200 years have increased CO2 concentration by about 30%, to the present 360 parts per million (ppm). Atmospheric CO2 will continue to rise during the next century, possibly to concentrations that are unprecedented for the last several million years. Much of the potential importance of CO2 concentration to vegetation derives from its influence on plant carbon balance and water relations. Plants grow by assimilating CO2 that diffuses into leaves through stomatal pores. Inevitably associated with CO2 uptake is transpirational loss of water vapor through stomata. Transpiration rates usually decline as CO2 increases, while, in many plants, photosynthesis and growth increase. These ''primary'' responses to CO2 can lead to a multitude of changes at the plant and ecosystem levels, ranging from alteration of the chemical composition of plant tissues to changes in ecosystem function and the species composition of plant communities. The direct physiological responses of plants to CO2 and expression of these responses at higher scales differ among species and growing conditions. Growth response to CO2 is usually highest in rapidly-growing plants that quickly export the carbohydrates formed in leaves and use them for storage or new growth and allocate a high proportion of fixed carbon to produce leaves. Growth is also more responsive to CO2 in plants with the C-3 (most woody plants and 'cool-season' grasses) than C-4 photosynthetic pathway (most 'warm-season' grasses), These and other differences among species could lead to changes in the composition of rangeland vegetation, but generalizations are difficult. On many rangelands, species abundances are determined more by morphological and phenological attributes that influence plant access to essential resources like nitrogen and light and reaction to fire, grazing, and other disturbances than by physiological traits that are sensitive to CO2 concentration. Species composition probably will be most responsive to CO2 on moderately water-limited and disturbed rangelands where multiple positive effects of CO2 on plant water relations can be expressed and competition for light is minimized. Greatest initial changes in species composition likely will occur on C-3/C-4 grasslands and at the transition between grasslands and woodlands. Plant production should also increase on water-limited rangelands, but CO2 may have little influence on production when nutrient elements like nitrogen are severely Limiting.

1488^4^Reid,CD^Tissue,DT^Fiscus,EL^Strain,BR^1997^1^Comparison of spectrophotometric and radioisotopic methods for the assay of Rubisco in ozone-treated plants^37^101^2^398-404^^^^^Oct^^^^^5769
112^2417^2418^355^356^372^444^451^550^557^ical and phenological attributes that influence plant access to essential resources like niA^5768^Radioisotopic and spectrophotometric assays for ribulose-1,5- bisphosphate carboxy lase/oxygenase (Rubisco) initial and final activities and Rubisco content were compared in plants chronically exposed to ozone (O-3) in a greenhouse and the field. In a greenhouse experiment, Glycine max was treated in exposure chambers with either charcoal-filtered air (CF air) or 100 nl O-3 l(-1) for 6 h daily during vegetative growth. Samples were collected after 7 days of exposure. In a field experiment, G. max was treated in open-top chambers with either CF air or nonfiltered air with O-3 added at 1.5 times ambient O-3 for 12 h daily. Average daily O-3 concentrations were 21 and 92 nl l(-1) in the CF and O-3 treatments, respectively samples were collected during vegetative and reproductive growth, Both assays generally yielded comparable Rubisco initial and final activities for greenhouse-grown plants regardless of the O-3 treatment. However for field-grown plants, Rubisco initial and final activities averaged 15 and 23% lower when assayed by the spectrophotometric rather than the radioisotopic method. For Rubisco content estimated by the spectrophotometric method, lower r(2) values for the regression of Rubisco activity vs concentration of carboxyarabinitol-1,5- bisphosphate were observed in O3- than in CF-treated plants. Both assays yielded comparable Rubisco contents in the greenhouse and in the field although the variation was larger with the spectrophotometric method in field-grown plants. Growth conditions, field vs greenhouse, were more critical to the spectrophotometric assay performance than the O-3 treatments for measurement of Rubisco activity and content.

1489^3^Roth,S^McDonald,EP^Lindroth,RL^1997^1^Atmospheric CO2 and soil water availability: consequences for tree-insect interactions^155^27^8^1281-1290^^^^^Aug^^^^^5771
1282^243^312^361^372^374^384^386^489^92^ies for greenhouse-grown plants regardless of the O-3 treatment. However for field-grown plants, Rubisco initial and final activities averaged 15 aA^5770^The consequences of elevated CO2 for interactions between trees and associated insects will be influenced by the availability of other plant resources. We investigated the effects of CO2 and water availability on phytochemistry of quaking aspen (Populus tremuloides Michx.) and sugar maple (Acer saccharum Marsh.) and the associated performance of the forest tent caterpillar (Malacosoma disstria Hbn.). Seedlings were grown under ambient or elevated CO2 concentrations and under well- watered or drought conditions. We measured rates of gas exchange and subjected foliage to phytochemical assays. Bioassays were conducted to quantify larval performance on foliage from the various treatments. In general, elevated CO2 increased photosynthetic rates and had no effect on stomatal conductance, while drought reduced both parameters. Foliar nitrogen levels declined and secondary metabolite concentrations increased under enriched CO2, but starch and sugar levels were unaffected. All phytochemicals measured, with the exception of simple sugars, declined or did not change in response to drought. CO2- and drought-mediated changes in phytochemistry reduced forest tent caterpillar growth and food processing efficiencies, but the patterns were host-species specific. This work demonstrates that CO2 effects on forest trees will be mediated by the availability of water and that the direction and magnitude of responses will depend on the tree species involved, which will, in turn, affect patterns of host use by herbivorous insects.

1490^3^Sage,RF^Schappi,B^Korner,C^1997^1^Effect of atmospheric CO2 enrichment on Rubisco content in herbaceous species from high and low altitude^318^18^3^183-192^^^^^^^^^^5773
2417^2419^245^348^372^417^685^845^92^ed photosynthetic rates and had no effect on stomatal conductance, while drought reduced both parameters. Foliar nitrogen levels declined and secondary metabolite concentrations increased under enriched CO2, but starch and sugar levels were unaffected. All phytochemicals measured, with theA^5772^Atmospheric CO2 enrichment reduces Rubisco content in many species grown in controlled environments; however, relatively few studies have examined CO2 effects on Rubisco content of plants grown in their natural habitat. We examined the response of Rubisco content to atmospheric CO2 enrichment (600-680 mu mol mol-l in place of ppm) in 5 herbaceous species growing in a low altitude grassland (550 m) near Basel, Switzerland, and 3 herbaceous species from Swiss alpine grassland at 2 470 m. At low elevation, the dominant grass Bromus erectus and the subdominant dicot Sanquisorba miller exhibited 20% to 25% reduction of Rubisco content following high CO2 exposure; no CO2 effect was observed in the subdominants Carex flacca, Lotus corniculatus and Trifolium repens. At the Alpine site, the subdominant grass Pea alpina maintained 27% less Rubisco content when grown at high CO2 while the co-dominant forb Leontodon helveticus had 19% less Rubisco in high CO2: Rubisco content was unaffected in the tundra dominant Carer curvula. Because the degree of Rubisco modulation was similar between high and low elevation sites, it does not appear that differences in local partial pressure of CO2 (altitude) or differences in stress in general induce different patterns of modulation of photosynthetic capacity in response to high CO2. In addition, the degree of Rubisco reduction (<30%) was less than might be indicated by the low biomass response to CO2 enrichment previously observed al these sites. Thus, plants in Swiss lowland and alpine grassland appear to main tain greater Rubisco concentration and photosynthetic capacity than whale plants can effectively exploit in terms of harvestable biomass.

1491^4^Schaffer,B^Whiley,AW^Searle,C^Nissen,RJ^1997^1^Leaf gas exchange, dry matter partitioning, and mineral element concentrations in mango as influenced by elevated atmospheric carbon dioxide and root restriction^154^122^6^849-855^^^^^Nov^^^^^5775
349^374^409^417^57^685^92^CO2: Rubisco content was unaffected in the tundra dominantA^5774^The effects of atmospheric CO2 enrichment and root restriction on net CO2 assimilation (A), dry mass partitioning, and leaf mineral element concentrations in 'Kensington' and 'Tommy Atkins' mango (Mangifera indica L.) were investigated. Trees were grown in controlled-environment glasshouse rooms at ambient CO2 concentrations of 350 or 700 mu mol.mol(-1). At each CO2 concentration, trees were grown in 8-L containers, which restricted root growth, or grown aeroponically in 200-L root mist chambers, which did not restrict root growth. Trees grown in 350 mu mol.mol(-1) CO2 were more efficient at assimilating CO2 than trees grown in 700 mu mol.mol(-1) CO2. However, total plant and organ dry mass was generally higher for plants grown at 700 mu mol.mol(-1) CO2 due to increased A as a result of a greater internal partial pressure of CO2 (Ci) in leaves of plants in the CO2 enriched environment. Root restriction reduced A resulting in decreased organ and plant dry mass. In root-restricted plants, reduced A and dry matter accumulation offset the increases in these variables resulting from atmospheric CO2 enrichment. Atmospheric CO2 enrichment and root restriction did not affect dry mass partitioning. Leaf mineral element concentrations were generally lower for trees grown at the higher ambient CO2 concentration, presumably due to a dilution effect from an increased growth rate.

1492^3^Scholes,MC^Powlson,D^Tian,GL^1997^1^Input control of organic matter dynamics^320^79^1-4^25-47^^^^^Sep^^^^^5777
19^2069^2143^2336^2413^2420^2421^398^456^977^owth. Trees grown in 350 mu mol.mol(-1) CO2 were more efficient at assimilating CO2 than trees grown in 700 mu mol.mol(-1) CO2. However, total plant and organ dry mass was generally higher for plants grown at 700 mu mol.mol(-1) CO2 due to increased A as a result of a greater internal partial pressure of CO2 (Ci) in leaves of plants in the CO2 enriched environment. Root restriction reduced A resulting in decreased organ and plant dry mass. In root-restricted plants, reduced A and A^5776^The amount and quality of inputs into soil organic matter will be altered by both climate and landuse change. The increase in growth of plants caused by increasing CO2 concentration implies not only potential increases in yields but also increases in plant residues. Simulation models using doubled CO2 levels predict global net primary productivity (NPP) to increase by 16.3%, over half of which will occur in the tropics. For tropical ecosystems increases in NPP will be dominated by the effects of elevated CO2, with water and nitrogen availability and temperature playing a less significant role. Phosphorus limitation may determine whether the potential for increased plant growth will be realized. The distribution of C3 and C4 species in the tropics could be affected by landuse change and estimates of yield increases will be dependent on their proportions. The allocation of photosynthate to the root will increase under elevated CO2, resulting in increased fine root dry weight and root length. Root sink strength and the turnover of roots and associated symbionts are critical knowledge gaps. Carbon:nitrogen ratios in tissues will increase resulting in decreased decomposition rates. The concentration of secondary compounds will be affected more by nitrogen limitations than a direct CO2 effect. Changes in lignin, tannin and polyphenol levels are more important in the decomposability of tropical liners than changes in the C:N ratios. Decomposition models will have to be altered to take into account changes in plant composition. The role of models in predicting the effects of management practice on long-term fertility is addressed. (C) 1997 Elsevier Science B.V.

1493^1^Sicher,RC^1997^1^Irradiance and spectral quality affect chlorosis of barley primary leaves during growth in elevated carbon dioxide^104^158^5^602-607^^^^^Sep^^^^^5779
1519^1672^204^2422^2423^376^417^739^741^965^n of photosynthate to the root will increase under elevated CO2, resulting in increased fine root dry weight and root length. Root sink sA^5778^The development of chlorosis was studied in primary leaves of barley plants (Hordeum vulgare L. cv. Brant) grown at ambient and twice-ambient CO, partial pressures. Leaf yellowing was observed 17 d after sowing when plants were grown in controlled environment chambers equipped with high-intensify discharge lamps at an irradiance of 800 mu mol quanta m(-2) s(-1). The extent of leaf yellowing, measured as changes of total chlorophyll, increased when the CO, partial pressure was raised from 37 to 70 Pa. Chlorosis was increased further by increasing the irradiance from 800 to 1100 mu mol quanta m(-2) s(-1). Rates of photosynthetic O-2 evolution by primary leaves,measured 17 d after sowing, were 20% lower for elevated compared with ambient CO2-grown plants. This result agreed with the level of chlorosis. However soluble protein, Rubisco protein (ribulose, 1,5-bisphosphate carboxylase/oxygenase), and initial and total Rubisco activity 17 d after sowing were unaffected by CO2 enrichment and the extent of chlorosis. Leaf starch, sucrose, and glucose were increased by elevated CO2 treatment at almost every sampling. However,only glucose was correlated with leaf damage. Leaf yellowing also was observed on primary leaves of plants grown under microwave-powered sulfur lamps at 800 but not at 550 mu mol quanta m(-2) s(-1). The extent of leaf yellowing on plants grown under microwave- powered sulfur lamps was unaffected by CO2 enrichment. It was concluded that leaf yellowing was influenced by irradiance, photoquality, and CO2 enrichment. Photobleaching of antenna chlorophyll, rather than premature senescence, was the most Likely cause of visible leaf injury in barley.

1494^3^Thron,C^Hahn,K^Lutz,C^1997^1^In situ effects of elevated CO2 on chlorophyll fluorescence and chloroplast pigments of alpine plants^318^18^3^193-200^^^^^^^^^^5781
1092^2407^2424^2425^243^264^312^348^73^phosphate carboxylase/oxygenase), and initial and total Rubisco activity 17 d after sowing were unaffected by CO2 enrichment and the extent of chlA^5780^Alpine vegetation responds to elevated CO2 with downward adjustment of photosynthesis. The experiments should show if doubling of ambient CO2 reduces the maximum quantum yield and the chlorophylls thus altering the pigment composition of the thylakoid membranes in typical species of an alpine grassland (Caricetum curvulae). The studies were part of a CO2 enrichment experiment with open-top chambers in the Swiss Central Alps in 2 470 m altitude over a period of four years. The leaves of Carer curvula and Trifolium alpinum were analysed ill situ under ambient (355 mu l/l) or elevated (680 mu l/l) CO2 and at two different nutrient levels. In each vegetation period both species showed a tendency to lower ratios of variable to maximum fluorescence (F-v/F-m) in plants with elevated CO2 treatment compared to the ambient variants. These reductions in F-v/F-m were statistically different only for Carer curvula in 1993 and 1995. CO2 enrichment caused reductions of leaf pigment concentrations of 10-30% especially far Trifolium alpinum whereas Carer curvula was less affected. The lower pigment contents per leaf were probably due to reductions of thylakoid membranes. In most cases, the influences of elevated CO2 or of nutrient treatments on pigment composition and primary photochemistry were very small. This indicates that the downward regulation begins at early stages in the photosynthetic process. Some changes of the photosynthetic apparatus are species-specific and possibly reflect different strategies of protective acclimation processes of alpine vegetation.

1495^5^Tingey,DT^Phillips,DL^Johnson,MG^Storm,MJ^Ball,JT^1997^1^Effects of elevated CO2 and N fertilization on fine root dynamics and fungal growth in seedling Pinus ponderosa^173^37^2-3^73-83^^^^^Jun^^^^^5783
130^23^2426^376^377^419^483^538^57^672^pared to the ambient variants. These reductions in F-v/F-m were statistically different only for Carer curvula in 1993 and 1995. CO2 enrichment caused reductions of leaf pigment concentrations of 10-30% especiallA^5782^The effects of elevated CO2 and N fertilization on fine root growth of Pinus ponderosa Dougl. ex P. Laws. C. Laws., grown in native soil in open-top held-exposure chambers at Placerville, CA, were monitored for a 2-year period using minirhizotrons. The experimental design was a replicated 3 x 3 factorial with a treatment missing; plants were exposed to ambient (approximate to 365 mu mol mol(-1)) air or ambient air plus either 175 or 350 mu mol mol(-1) CO2 and three levels of N addition (0, 100 and 200 kg ha(-1) year(-1)). By the second year, elevated CO2 increased fine root occurrence and root length while N fertilization had no effect. The CO2 x N interactions were not significant. Neither elevated CO2 nor N fertilization altered fine root diameter. Fine root mortality was increased by increasing soil N but was reduced in elevated CO2. Highest fine root mortality occurred during summer and was lowest during winter. Elevated CO2 increased mycorrhizal and fungal occurrence earlier than N fertilization. (C) 1997 Elsevier Science B.V.

1496^2^Watling,JR^Press,MC^1997^1^How is the relationship between the C-4 cereal Sorghum bicolor and the C-3 root hemi-parasites Striga hermonthica and Striga asiatica affected by elevated CO2?^9^20^10^1292-1300^^^^^Oct^^^^^5785
1305^1810^243^264^312^374^376^384^91^92^factorial with a treatment missing; plants were exposed to ambient (approximate to 365 mu mol mol(-1)) air or ambient air plus either 175 or 350 mu mol mol(-1) CO2 and three levels of N addition (0, 100 and 200 kg ha(-1) year(-1)). By the second year, elevated CO2 increased fine root occurrence and root length while N fertilization had no effect. The CO2 x N interactions were not significant. Neither elevated CO2 nor N fertilization altered fine root diameter. Fine root mortality was increased by increasing soil N but was reduced in elevated CO2. Highest fine root mortality occurred during summer and was lowest during winter. Elevated CO2 increased mycorrhizal and fungal occurrence earlier than N fertilization.A^5784^The C-4 cereal Sorghum bicolor was grown under either ambient (350 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) [CO2] in either the presence or absence of the C-3 obligate root hemi- parasites Striga hermonthica or S. asiatica. Both uninfected and infected sorghum plants were taller and had greater biomass, photosynthetic rates, water-use efficiencies and leaf areas under elevated compared with ambient [CO2]. There was no evidence of any downregulation of photosynthesis in sorghum grown at elevated [CO2]. Biomass of infected sorghum was lower under both ambient and elevated [CO2], and although infected plants were larger under elevated [CO2] the relative impact of infection on host biomass was either the same (S. asiatica) or only slightly less (S. hermonthica) than under ambient [CO2]. In contrast, biomass of S. hermonthica and S. asiatica per host was lower under elevated than ambient [CO2], although rates of photosynthesis were higher at elevated [CO2] and parasite stomatal conductance was not responsive to [CO2]. Parasites emerged above-ground and flowered earlier under ambient compared with elevated [CO2]. It appears that the mechanism(s) by which the parasites affect host growth is (are) relatively insensitive to increased atmospheric [CO2] although the parasites themselves were adversely affected by growth at elevated [CO2].

1497^7^Wu,WH^Lu,JY^Jones,AR^Mortley,DG^Loretan,PA^Bonsi,CK^Hill,WA^1997^1^Proximate composition, amino acid profile, fatty acid composition, and mineral content of peanut seeds hydroponically grown at elevated CO2 levels^321^45^10^3863-3866^^^^^Oct^^^^^5787
454^hough infected plants were larger under elevated [CO2] the relative impact of infection on host biomass was either the same (S. asiatica) or only slightly less (S. hermonthica) than under ambient [CO2]. In contrast, biomass of S. hermonthica and S. asiatica per host was lower under elevated than ambient [CO2], although rates of photosynthesis were higher at elevated [CO2] and parasite stomatal conductance was not A^5786^Peanut plants (Arachis hypogaea L. cv. Georgia Red) were grown hydroponically using a recirculating nutrient film technique. The effect of CO2 enrichment on nutritive composition of hydroponic peanut seeds was examined at two elevated CO2 levels (700 and 1400 ppm) that simulate potential conditions in National Aeronautics and Space Administration (NASA) Controlled Ecological Life-Support Systems (CELSS) and compared to ambient CO2 condition in hydroponics (the control). Plants were harvested at 97 days after planting, and the seeds were air- dried and analyzed for composition. Percentages of crude protein, crude fat, ash, and carbohydrate of hydroponic peanut seeds were around 30%, 30%, 3%, and 30%, respectively. The major amino acids were aspartic acid, glutamic acid, and arginine. The limiting amino acid of peanut, methionine, was 1.2%. Linoleic acid was the major fatty acid, followed by oleic and palmitic acids. The major mineral elements were K, P, Mg, and Ca. The results showed that certain peanut varieties can be grown hydroponically. The composition of the hydroponically grown peanuts is generally similar to reported peanut composition The nutrient composition was not affected at the elevated CO2 concentrations investigated.

1498^4^Zimmerman,RC^Kohrs,DG^Steller,DL^Alberte,RS^1997^1^Impacts of CO2 enrichment on productivity and light requirements of eelgrass^8^115^2^599-607^^^^^Oct^^^^^5789
1538^2427^2428^243^312^360^363^372^618^92^ion in hydroponics (the control). Plants were harvested at 97 days after planting, and the seeds were air- dried and analyzed for composition. Percentages of crude protein, crude fat, ash, and carbohydrate of hydroponic peanut seeds were around 30%, 30%, 3%, and 30%, respectively. The major amino acids were aspartic acid, glutamic acid, and arginine. The limiting amino acid of peanut, methionine, was 1.2%. Linoleic acid was the major fatty acid, followed by oleic and palmitic acids. The major mineral elements were K, P, Mg, and Ca. The results showed that certain peanuA^5788^Seagrasses, although well adapted for submerged existence, are CO2-limited and photosynthetically inefficient in seawater. This leads to high light requirements for growth and survival and makes seagrasses vulnerable to light limitation. We explored the long-term impact of increased CO2 availability on light requirements, productivity, and C allocation in eelgrass (Zostera marina L.). Enrichment of seawater CO2 increased photosynthesis 3-fold, but had no longterm impact on respiration. By tripling the rate of light-saturated photosynthesis, CO2 enrichment reduced the daily period of irradiance-saturated photosynthesis (H-sat) that is required for the maintenance of positive whole-plant C balance from 7 to 2.7 h, allowing plants maintained under 4 h of H-sat to perform like plants growing in unenriched seawater with 12 h of H-sat. Eelgrass grown under 4 h of H-sat without added CO2 consumed internal C reserves as photosynthesis rates and chlorophyll levels dropped. Growth ceased after 30 d. Leaf photosynthesis, respiration, chlorophyll, and sucrose-phosphate synthase activity of CO2-enriched plants showed no acclimation to prolonged enrichment. Thus, the CO2-stimulated improvement in photosynthesis reduced light requirements in the long term, suggesting that globally increasing CO2 may enhance seagrass survival in eutrophic coastal waters, where populations have been devastated by algal proliferation and reduced water-column light transparency.

1499^1^Arnone,JA^1997^1^Temporal responses of community fine root populations to long- term elevated atmospheric CO2 and soil nutrient patches in model tropical ecosystems^318^18^3^367-376^^^^^^^^^^5791
2091^2429^2430^312^376^393^470^738^92^941^nt C balance from 7 to 2.7 h, allowing plants maintained under 4 h of H-sat to perform like plants growing in unenriched seawater with 12 h of H-sat. Eelgrass grown under 4 h of H-sat without added CO2 consumed internal C reserves as photosynthesis rates and chlorophyll levels dropped. Growth ceased after 30 d. Leaf photosA^5790^Biomass and length density of fine roots, as well as overall allocation of dry matter to root growth, of C-3 plants has been shown to increase under elevated CO2. However, it is uncertain whether the stimulatory effect of elevated CO2 on fine root population size in plant communities will persist, or whether fine root populations at high CO2 simply reach their maximum sooner (or possibly later) than those produced under ambient CO2. It is also unclear whether increased nutrient demand at the stand-level under elevated CO2 will lead to more intense nutrient foraging via enhanced fine root proliferation into relatively nutrient-rich soil microsites. I addressed these questions in a 530 day experiment with model tropical plant communities established in four equivalent ecosystem (17 m(3)) in which plants shared a common low fertility soil. Fine root (less than or equal to 2 mm empty set) populations (biomass and length density) in ecosystems maintained at elevated CO2 (610 mu l l(-1)) increased more rapidly than those in ecosystems maintained at ambient CO2 (340 mu l l(-1)) during the first half of the experiment and also remained greater over the entire experiment. The data also indicate that: (1) fine root populations at both CO2 levels eventually stabilize, (2) stabilization occurs sooner under elevated CO2 (occupation of the soil volume), and (3) steady-state populations under elevated CO2 may be slightly larger than those maintained under ambient CO2. Fine root proliferation into artifically nutrient- enriched microsites was dramatic in all ecosystems (22% to 75% greater than into non-enriched soil). However, proliferation into enriched microsites was not enhanced by elevated CO2. Thus, elevated CO2 may not enhance exploitation of nutrient- rich microsites even in low fertility soils, suggesting that increased plant nutrient capture under elevated CO2 also may be unlikely.
 empty set) populations (biomass and length density) in ecosystems maintained at elevated CO2 (610 mu l l(-1)) increased more rapi1500^3^Ball,MC^Cochrane,MJ^Rawson,HM^1997^1^Growth and water use of the mangroves Rhizophora apiculata and R-stylosa in response to salinity and humidity under ambient and elevated concentrations of atmospheric CO2^9^20^9^1158-1166^^^^^Sep^^^^^5793
1262^2431^2432^2433^312^376^384^442^677^685^under elevated CO2 (occupation of the soil volume), and (3) steady-state populations under elevated CO2 may be slightly larger than those maintained under ambient CO2. Fine root proliferation into artifically nutrient- enriched microsites was dramatic in all ecosystems (22% to 75% greater than into non-enriched soil). However, proliferation into enriched microsites was not enhanced by elevated CO2. Thus, elevated CO2 may not enhance exploitation of nutrient- rich microsites even in low fertility soils, suggesting that increased plant nutrient capture under elevated CO2 also may be unlikely.
 empty set) populations (biomass and length density) in ecosystems maintained at elevated CO2 (610 mu l l(-1)) increased more rapiA^5792^Two mangrove species, Rhizophora apiculata and R. stylosa, mere grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m(-3) NaCl), humidity (43 and 86% relative humidity at 30 degrees C) and atmospheric CO2 concentration (340 and 700 cm(3) m(-3)). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt-tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended an both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity x aridity gradients.

1501^3^Blum,H^Hendrey,G^Nosberger,J^1997^1^Effects of elevated CO2, N fertilization, and cutting regime on the production and quality of Lolium perenne L. shoot necromass^318^18^3^291-295^^^^^^^^^^5795
d growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt-tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratA^5794^In the Swiss grassland FACE experiment, we measured the effect of elevated CO2 on the shoot necromass production and quality of Lolium perenne in 1995. Dead stubble of reproductive tillers and dead leaf sheaths were the main components of necromass. Elevated CO2 did not significantly change the amount and the nitrogen concentration of necromass. Significantly more necromass was produced and the N concentration was lower in the low N supply treatments. Total necromass amounted to 250-500 g m(-2). Necromass N content was in the order of 5-6 g m(-2) This underscores the importance of the carbon and nitrogen fluxes included in necromass and their importance for soil biology and fertility.

1502^2^Egli,P^Korner,C^1997^1^Growth responses to elevated CO2 and soil quality in beech- spruce model ecosystems^318^18^3^343-349^^^^^^^^^^5797
1234^417^705^778^ apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratA^5796^Growth responses of beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) to elevated atmospheric CO2 (366 and 550 mu l CO2 l(-1)) and increased wet deposition of nitrogen (2.5 and 25 kg N ha(-1) a(-1)) in combination with two soil types were studied in open-top chambers. Eight young beech and spruce trees, together with five understory species, were established in each of 32 model ecosystems. We present initial growth responses of trees during the first year of treatment which may set the trends for longer term responses to elevated CO2. Above-ground biomass production at the system level (biometric data) during the first year and root biomass (coring data) did not show significant responses to elevated CO2, irrespectively of other cc-treatments. Increased nitrogen deposition (treatment commencing by mid-season) also had no effect on above-ground biomass, whereas end of season root biomass was significantly increased in the high-nitrogen treated low fertility acidic soil (74 g m(-2) in the high-N versus 49 g m(-2)? in the low N-treatment), but not-in the more fertile calcareous soil. Stem diameter increment of beech was significantly increased (+9%) under elevated CO, in the calcareous soil, but not in the acidic soil. The opposite was found for spruce stems, which responded positively to elevated CO2 in the acidic soil (+ 11%; P < 0.05) but nor in the calcareous soil. These results suggest that soil type co- determines the CO2 response of young forest trees and that these interactions are species specific. These initial differences are likely to affect long-term responses of community structure and ecosystem functioning. Soil type appears to be a key factor in predictions of forest responses to continued atmospheric CO2 enrichment.

1503^2^Erhardt,A^Rusterholz,HP^1997^1^Effects of elevated CO2 on flowering phenology and nectar production^318^18^3^249-253^^^^^^^^^^5799
of season root biomass was significantly increased in the high-nitrogen treated low fertility acidic soil (74 g m(-2) in thA^5798^Effects of elevated CO2 on flowering phenology and nectar production were studied in five important nectar plants of calcareous grasslands, i.e. Lotus corniculatus, Trifolium pratense, Betonica officinalis, Scabiosa columbaria ia and Centaurea jacea. Glasshouse experiments showed that flowering probability was significantly enhanced in C. jacea. B. officinalis flowered earlier and L. corniculatus produced more flowers under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar produced per flower was not affected in the investigated legumes (T. pratense, L. corniculatus), but was significantly reduced in the other forbs. Elevated CO2 did not significantly affect nectarsugar concentration and sugar composition. However, S. columbaria and C: jacea produced significantly less total sugar per flower under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species whereas the total of amino acids produced per flower was significantly reduced in all nan-legumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as most butterflies which have no alternative food resources except nectar. Changes in nectar production due to elevated CO2 could also generally have detrimental effects on the interactions of flowers and their pollinators.

1504^6^Frehner,M^Luscher,A^Hebeisen,T^Zanetti,S^Schubiger,F^Scalet,M^1997^1^Effects of elevated partial pressure of carbon dioxide and season of the year on forage quality and cyanide concentration of Trifolium repens L. from a FACE experiment^318^18^3^297-304^^^^^^^^^^5801
1239^1282^130^243^2434^373^374^417^57^742^umbaria and C: jacea produced significantly less total sugar per flower under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species whereas the total of amino acids produced per flower was A^5800^Differently managed (cutting frequency and N fertilization) Trifolium repens monocultures were grown at 60 Pa and 35 Pa of pCO(2) (partial pressure of CO2) in a Free Air Carbon dioxide Enrichment (FACE) array. The concentrations of cyanide, digestible organic matter, crude protein and net energy for lactation were measured at different harvests throughout the growing season. The average cyanide concentrations differed significantly in the years and the seasons within the year; however, the concentrations were not affected by CO2. Digestible organic matter, crude protein and net energy for lactation differed significantly with the seasons of the year and cutting frequencies. While digestible organic matter and net energy for lactation were not affected by elevated pCO(2), the concentration of crude protein decreased from 288 g kg(-1) at ambient to 251 g kg(-1) at elevated pCO(2). Since the crude protein concentration in herbage from Trifolium monocultures was very high even at elevated CO2, it is suggested that this decrease in crude protein concentration does not negatively affect forage quality. We conclude that, in Trifolium herbage, the seasons of the year and management practices are more decisive for forage quality than changes in pCO(2). We shall discuss how forage quality and cyanide intake by ruminants may, however, be affected by CO2-induced shifts in the proportion of species in mixed plant communities.

1505^1^GunthardtGoerg,MS^1997^1^Leaf and shoot formation of young spruce and beech exposed to elevated CO2^318^18^3^335-341^^^^^^^^^^5803
1262^360^58^705^92^ein and net energy for lactation differed significantly with the seasons of the year and cutting frequencies. While digestible organic matter and net energy for lactation were not affected by elevated pCO(2), the concentration of crude protein decreased from 288 g kg(-1) at ambient to 251 g kg(-1) at elevated pCO(2). Since the crude protein concentration in herbage from Trifolium monocultures was very high even at elevated CO2, it is suggeA^5802^Sixteen open-top chambers (divided into two halves each containing either calcareous or acidic soil) were supplied in four combinations with either 366 or 550 mu l CO2 L-1, and either 2.5 or 25 kg N ha-(1) y(-1) (ammonium nitrate by irrigation). The development of young spruce (Picea abies) and beech (Fagus sylvatica) trees planted in the chambers together with understory plants will be studied over four years. The presented data are preliminary results from the first year of this experiment and refer to 64 spruce and 64 beech trees from two different Swiss spruce and beech provenances; two trees each per soil type, sampled in July and September in each chamber. Specific current-year spruce nee die length (length/dry mass) was reduced by elevated CO2 due to an increase in dry mass. Beech specific leaf area was only temporarily reduced in July. Elevated CO2 induced an earlier autumnal leaf discoloration. Total current-year shoot length per spruce and total number of leaves per beech tree were not influenced by the first year treatment with elevated CO2. N deposition had no effect on these parameters, but soil type influenced spruce needle colour Spruce, in contrast to beech, may therefore profit from elevated CO2 (when other resources are unlimited) by increasing shoot and needle dry mass.

1506^2^Hattenschwiler,S^Korner,C^1997^1^Annual CO2 budget of spruce model ecosystems in the third year of exposure to elevated CO2^318^18^3^319-325^^^^^^^^^^5805
2419^312^374^661^irst year of this experiment and refer to 64 spruce and 64 beech trees from two different Swiss spruce and beech provenances; two trees each per soil type, sampled in July and September in each chamber. Specific current-year spruce nee die length (length/dry mass) was reduced by elevated CO2 due to an increase in dry mass. Beech specific leaf area was only temporarily reduced in July. Elevated CO2 induced an earlier autumnal leaf discoloration. Total current-year shoot length per spruce and total number of leaves per beech tree were not influA^5804^Clones of 4-year-old spruce trees (Picea abies) were grown in competition in model ecosystems with nutrient-poor natural forest soil and natural understory vegetation and were exposed to three CO, concentrations (280, 420 and 560 mu mol mol(-1)) for three years. Diurnal net ecosystem CO2 uptake (NECd), nocturnal net ecosystem CO2 loss (NECn) and soil CO2 efflux were measured repeatedly in the third year of CO2 exposure and were used to estimate an annual ecosystem CO2 budget. The CO2 induced stimulation of NECd varied over the year with no measurable stimulation in spring and fall but a high mid-season CO2 stimulation. Respiratory losses of whole ecosystems and soil CO2 efflux alone were both progressively increased with increasing CO2, thus counteracting the CO2 stimulation of photosynthesis per unit ground area. Consequently, the annual net ecosystem CO2 uptake was only moderately and non-linearly stimulated by CO2 (+8% = 84 g C m(-2) a(-1) at 420 and +9% = 90 g C m(-2) a(-1) at 560 compared to 280 mu mol CO2 mol(-1)). We conclude that the rising atmospheric CO2 concentration may lead to an increase in annual net ecosystem carbon gain of rather nutrient-poor spruce communities. Our results further suggest that CO2 fertilization effects may be greatest under current CO2 concentration and that relative increases of net ecosystem CO2 uptake will become relatively smaller as atmospheric CO2 will continue to rise.

1507^2^Hattenschwiler,S^Korner,C^1997^1^Growth of autotrophic and root-hemiparasitic understory plants under elevated CO2 and increased N deposition^318^18^3^327-333^^^^^^^^^^5807
427^672^-season CO2 stimulation. Respiratory losses of whole ecosystems and soil CO2 efflux alone were both progressively increased with increasing CO2, thus counteracting the CO2 stimulation of photosynthesis per unit ground area. Consequently, the annual net ecosystem CO2 uptake was only moderately and non-linearly stimulated by CO2 (+8% = 84 g C m(-2) a(-1) at 420 and +9% = 90 g C m(-2) a(-1) at 560 compared to 280 A^5806^Effects of atmospheric CO2 enrichment (280, 420 and 560 mu mol CO2 mol(-1)) and increased N deposition (0, 30 and 90 kg ha(-1) a(-1)) on Oxalis acetosella, Homogyne alpina, and Melampyrum sylvaticum, growing in model ecosystems beneath spruce stands, were studied. Aboveground biomass in the less-shade-tolerant Homogyne and in the annual hemiparasite Melampyrum was strongly increased with increasing CO2, but not in the more shade- adapted Oxalis. In contrast, increased N deposition stimulated growth in Oxalis, but had no effect on Homogyne and Melampyrum. Due to spruce canopy closure Homogyne,le became light limited and its survivorship was strongly correlated with spruce canopy LAI in the second year of the experiment. Our results suggest, that elevated CO2 facilitates the expansion of Hamogyne into less favourable micro-habitats (deeper shade) and that increasing N deposition enables more vigorously growing species like Oxalis to increase in abundance. Growth of the hemiparasite Melampyrum was stimulated indirectly by increased heterotrophic carbon supply (carbon isotope data) from the host (Picea abies), and thus, this species may also increase in abundance with increasing CO2. However, possible indirect effects (canopy feedbacks) make predictions of long-term understory development difficult.

1508^4^Hattenschwiler,S^Miglietta,F^Raschi,A^Korner,C^1997^1^Morphological adjustments of mature Quercus ilex trees to elevated CO2^318^18^3^361-365^^^^^^^^^^5809
361^376^92^ed N deposition stimulated growth in Oxalis, but had no effect on Homogyne and Melampyrum. Due to spruce canopy closure Homogyne,le became light limited and its survivorship was strongly correlated with spruce canopy LAI in the second year of the experiment. Our results suggest, that elevated CO2 facilitates the expansion of Hamogyne into less favourable micro-habitats (deeper shade) and that increasing N deposition enables more vigorously growing species like Oxalis to increase in abundance. Growth of the hemiparasite Melampyrum was stimulA^5808^It is still not known whether mature forest trees. respond to increasing atmospheric CO2 concentrations in similar ways as seedlings do. Mature Mediterranean oaks (Quercus ilex) growing in a CO2 enriched atmosphere around natural CO2 vents since the seedling stage showed a moderate, age dependent increase in stem biomass production, but had significantly lower biomass of 6-year-old branches, decreased branching, and lower leaf area per unit branch biomass, compared to control trees at a nearby unenriched site. Our data indicate that trees in natural forest stands morphologically adjust to increasing CO2 and reduce CO2 induced initial growth stimulations. Allometric adjustments such as reduction in leaf area may be regarded as a ''down- regulation'' of canopy photosynthesis and may be an effective mechanism for saving water.
tats (deeper shade) and that increasing N deposition enables more vigorously growing species like Oxalis to increase in abundance. Growth of the hemiparasite Melampyrum was stimul1509^3^Hebeisen,T^Luscher,A^Nosberger,J^1997^1^Effects of elevated atmospheric CO2 and nitrogen fertilisation on yield of Trifolium repens and Lolium perenne^318^18^3^277-284^^^^^^^^^^5811
1030^1098^376^427^506^92^sphere around natural CO2 vents since the seedling stage showed a moderate, age dependent increase in stem biomass production, but had significantly lower biomass of 6-year-old branches, decreased branching, and lower leaf area per unit branch biomass, compared to control trees at a nearby unenriched site. Our data indicate that trees in natural forest stands morphologically adjust to increasing CO2 and reduce CO2 induced initial growth stimulations. Allometric adjustments such as reduction in leaf area may be regarded as a ''down- regulation'' of canopy photosynthesis and may be an effective mechanism for saving water.
tats (deeper shade) and that increasing N deposition enables more vigorously growing species like Oxalis to increase in abundance. Growth of the hemiparasite Melampyrum was stimulA^5810^Trifolium repens L. and Lolium perenne L. were grown in monocultures and bi-species mixture in a Free Air Carbon Dioxide Enrichment (FACE) experiment at elevated (60 Pa) and ambient (35 Pa) CO2 partial pressure (pCO(2)) for two years. The effects of nitrogen fertilisation (10 and 42 g N m(-2) a(- 1) in 1993; 14 and 56 g N m(-2) a(-1) in 1994) on the growth response to pCO, were investigated in frequently defoliated (7 cuts in 1993; 8 cuts in 1994) swards. The yield of Trifolium in monocultures increased by 22% when grown at elevated pCO(2). In contrast, the yield of Lolium monocultures was not affected (2%) by elevated pCO(2), whereas Lolium increased its root mass considerably. The consequence of these interspecific differences in the CO2 response was an increase in the proportion of Trifolium in the mixed swards from 39% at ambient to 50% at elevated pCO(2). However, the proportion of the species was more strongly affected by N fertilisation than by elevated pCO(2). Based on these 2' results, we conclude that the species proportion in managed grassland may change as the CO2 concentration increases. However, an adapted management may, at least partially, counteract such CO2 induced changes in the proportion of the species.

1510^6^Heifetz,PB^Lers,A^Turpin,DH^Gillham,NW^Boynton,JE^Osmond,CB^1997^1^dr and spr/sr mutations of Chlamydomonas reinhardtii affecting D1 protein function and synthesis define two independent steps leading to chronic photoinhibition and confer differential fitness^9^20^9^1145-1157^^^^^Sep^^^^^5813
1240^1552^243^2435^2436^2437^2438^2439^492^493^f Lolium monocultures was not affected (2%) by elevated pCO(2), whereas Lolium increased its root mass considerably. The consequence of these interspecific differences in the CO2 response was an increase in the proportion of Trifolium in the mixed swards from 39% at ambient to 50% at elevated pCO(2). However, the proportion of the species was more strongly affected by N fertilisation than by elevated pCO(2). Based on these 2' results, we conA^5812^The effects of introduced chloroplast gene mutations affecting D1 synthesis, turnover and function on photosynthesis, growth and competitive ability were examined in autotrophic cultures of Chlamydomonas reinhardtii (Chlorophyta) adapted to low or high irradiance. Few discernible effects were evident when the mutants were grown in low light (LL, 70 mu mol m(-2) s(-1)). The herbicide-resistant psbA mutation Ser(264) --> Ala (dr) slowed electron transfer and accelerated D1 degradation in cells grown under high light (HL, 600 mu mol m(-2) s(-1)). The maximum rate of light- and CO2-saturated photosynthesis, cell growth rate and competitive ability in the dr mutant were reduced compared to wild type under HL. However, the wild-type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. In spr/sr cells grown under HL, D1 synthesis was reduced by 40-60% compared to wild type and D1 degradation was accelerated, leading to a 4-fold reduction in D1 pool size. The reduced D1 levels were accompanied by an elevation of F-o and a decline in F-v/F-m, quantum yield and maximum rate of CO2-saturated photosynthesis. Chemostat experiments showed that the growth rate and competitive ability of spr/sr were reduced against both wild type and dr.

1511^2^Landolt,W^Pfenninger,I^1997^1^The effect of elevated CO2 and soil type on non-structural carbohydrates in beech leaves and Norway spruce needles growing in model ecosystems^318^18^3^351-359^^^^^^^^^^5815
312^344^417^439^57^692^912^92^ed to wild type under HL. However, the wild-type rate of D1 synthesis in dr was adequate to compensate for accelerated D1 degradation. 16S rRNA mutations conferring resistance to streptomycin and spectinomycin (spr/sr) that altered chloroplast ribosome structure and assembly were used to inhibit chloroplast protein synthesis. A^5814^Young beech and Norway spruce trees from two Swiss provenances were both planted in an acidic and calcareous soil in 16 open- top chambers. Half of the plants were exposed to elevated CO2 (ambient, ambient + 200 mu l l(-1), 24 hrs/day, 365 days/year) and enhanced nitrogen deposition (2.5, 25 kg ha(-1) yr(-1)) throughout a single growing season. Leaf and needle samples from all 64 trees were collected (2 provenances x 2 soil types x 4 treatments x 4 replications) at the end of July and September. These were analysed for starch, soluble carbohydrates and total non-structural carbohydrates (TNC). Increased starch and TNC levels were found in plants under elevated CO2 and those growing on the acidic soil. These effects were not consistent in both species or on both sampling dates. Soluble carbohydrates were only effected significantly by sail type. So far no interactions have been found between CO2, N or soil type on any date and in any fraction. It is concluded that soil type should be considered when discussing the effects of elevated CO2 on starch, soluble carbohydrate or TNC contents in beech and spruce trees.

1512^3^Ledergerber,S^Thommen,GH^Baur,B^1997^1^Grazing damage to plants and gastropod and grasshopper densities in a CO2-enrichment experiment on calcareous grassland^318^18^3^255-261^^^^^^^^^^5817
174^418^764^ghout a single growing season. Leaf and needle samples from all 64 trees were collected (2 provenances x 2 soil types x 4 treatments x 4 replications) at the end of July and September. These were analysed for starch, soluble carbohydrates and total non-structural carbohydrates (TNC). Increased starch and TNC levels were found in plants under elevated CO2 and those growing on the acidic soil. These effects were not consistent in both species or on both sampling dates. Soluble carbohydrates were only effected significantly by sail type. So far no interactions have been found between CO2, N or soil type on any date and in any fraction. It is concluded that soil type should be considered when diA^5816^Plant-herbivore interactions may change as atmospheric CO2 concentrations continue to rise. We examined the effects of elevated atmospheric CO2 and CO2-exposure chambers on the grazing damage to plants, and on the abundances of potential herbivores (terrestrial gastropods and grasshoppers) in a calcareous grassland in the Jura mountains of Switzerland (village of Nenzlingen). Individuals of most plant species examined showed slight grazing damage. However, plots with CO2 enrichment and plots with ambient atmosphere did not differ in the extent of grazing damage. Similarly, plots with CO2 enrichment and plots with ambient atmosphere did not differ in either gastropod or grasshopper density. Experimental plots with and without chambers did not differ in the number of gastropods. However, the densities of gastropods and grasshoppers and extent of grazing damage to plants were generally lower in the experimental area than in the grassland outside the experimental field.
 type should be considered when di1513^2^Luscher,A^Nosberger,J^1997^1^Interspecific and intraspecific variability in the response of grasses and legumes to free air CO2 enrichment^318^18^3^269-275^^^^^^^^^^5819
1292^224^312^372^417^57^975^ts, and on the abundances of potential herbivores (terrestrial gastropods and grasshoppers) in a calcareous grassland in the Jura mountains of Switzerland (village of Nenzlingen). Individuals of most plant species examined showed slight grazing damage. However, plots with CO2 enrichment and plots with ambient atmosphere did not differ in the extent of grazing damage. Similarly, plots with CO2 enrichment and plots with ambient atmosphere did not differ in either gastropod or grasshopper density. Experimental plots with and without chambers did not differ in the number of gastropods. However, the densities of gastropods and grasshoppers and extent of grazing damage to plants were generally lower in the experimental area than in the grassland outside the experimental field.
 type should be considered when diA^5818^Nine to fourteen genotypes of seven grass and two legume species from permanent grassland were grown at two levels of atmospheric CO2 concentration in gaps of established Lolium perenne swards in a Free Air Carbon dioxide Enrichment (FACE) experiment. Cumulative biomass of individual plants was determined for two growing seasons. In the first year, elevated CO2 increased biomass production in all species. The CO2- induced increase in the biomass of Trifolium repens and I: pratense (159%) was much greater than the increase in the grass species (27%). In the second year the response to elevated CO2 was weaker in gasses (2%, ns) and legumes (73%). However, interspecific differences in the response to CO2 remained significant. Interspecific differences in the response to elevated CO2 occurred between the two functional groups of grasses and legumes, while within these groups no significant interspecific differences were found. In contrast to the interspecific variability in the response to CO2, no significant intraspecific variability in the response to CO2 was detected. Our results suggest that significant interspecific differences in the response to CO2, occur. Intraspecific differences in the response to elevated CO2 were, however, not detected. Thus, it seems unlikely that evolutionary adaptation of the species' response to elevated CO2 will level out the inter specific differences in the response to CO2.

1514^4^Meier,M^Saurer,M^Haldemann,C^Fuhrer,J^1997^1^Effect of elevated CO2 on the carbon balance of a grass-clover mixture^318^18^3^313-317^^^^^^^^^^5821
 second year the response to elevated CO2 was weaker in gasses (2%, ns) and legumes (73%). However, interspecific differences in the response to CO2 remained significant. Interspecific differences in the response to elevated CO2 occurred between the two functional groups of grasses and legumes, while within these groups no significant interspecific differences were found. In contrast to the interspecific variability in the response to CO2, no signifiA^5820^Experiments were carried out to investigate the effect of elevated CO2 (780 mu mol mol(-1)) on the C-balance and carbon release from the roots of a mixture of Dactylis glomerata and Trifolium pratense. The plants were grown for 67 days in a growth chamber with controlled watering and fertilisation, with an intermediate harvest after 41 days. Elevated CO2 increased total net uptake of carbon (C) by about 30% by the end of regrowth. Total net C-uptake and the amount of C recovered in the second harvest were balanced at both CO2 concentrations, and the root: shoot ratio was not affected by elevated CO2. C- 13-allocation to roots, and C-13 released into the root environment were measured following pulse-labelling with (CO2)- C-13 at the end of regrowth. Relative to the amount of C-13 taken up by the shoot, C-13 allocation to roots was 1.6%, and C-13 released from roots was only 0.4%. No significant difference in these proportions was observed at elevated CO2, but in absolute terms, plants grown at elevated CO2 released more C-13 from the roots.

1515^2^Murthy,R^Dougherty,PM^1997^1^Effect of carbon dioxide, fertilization and irrigation on loblolly pine branch morphology^252^11^8^485-493^^^^^Oct^^^^^5823
1144^1747^229^345^3467^372^400^456^512^546^a growth chamber with controlled watering and fertilisation, with an intermediate harvest after 41 days. Elevated CO2 increased total net uptake of carbon (C) by about 30% by the end of regrowth. Total net C-uptake and the amount of C recovered in the second harvest were balanced at both CO2 concentrations, and the root: shoot ratio was not affected by elevated CO2. C- 13-allocation to roots, and C-13 released into the root environment were measured following pulse-labelling with (CO2)- C-13 at the end of regrowth. Relative to the amount of C-13 taken up by the shoot, C-13 allocation to roots was 1.6%, and C-13 released from roots was only 0.4%. No significant difference in these proportions was observed at elevated CO2, but in absolute terms, plants grown at elevateA^5822^Foliage and wood parameters of branches of 12-year-old loblolly pine (Pinus taeda L.) trees were characterized after 21 months of exposure to fertilizer, irrigation and elevated CO2 treatments. Branches of loblolly pine trees were enclosed in plastic chambers and exposed to ambient, ambient +175 and ambient +350 umol mol(-1) CO2 concentrations. Measurements of foliage and wood at the fascicle, flush and branch levels were made at the end of the 21 month study period. The +350 CO2 treatment did not significantly increase fascicle radius or length but did increase the number of fascicles on the first flush. Fertilization significantly increased fascicle radius and length, while irrigation significantly increased number of fascicles and flush length of first flush. The +350 CO2 treatment also significantly increased flush length of the first flush. Significant interaction of fertilization and irrigation with CO2 was observed for fascicle length. Significant interactions of fertilization and irrigation were also observed for flush length, number of fascicles and fascicle length. Observed increases in fascicle radius, fascicle length, number of fascicles and flush length may have been responsible for the significantly higher flush leaf area observed for the all three treatments. Also, a combination of fertilization and irrigation increased leaf area by 82% compared to that in the control when averaged across CO2 treatments. At the branch level +350 CO2 treatment significantly increased shoot length but not the number of flushes on the branch. In general with the exception of bark density and total number of needle scales, neither fertilization nor irrigation had any significant effect on other branch level parameters. Results from this study indicate that with 'global change' an increase in CO2 alone may increase leaf area via an increase in flush length and number of fascicles. Combining increases in CO2 with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO2 could greatly increase productivity of loblolly pine trees.

1516^4^Nussbaumer,U^Ascher,J^Kraft,A^Insam,H^1997^1^Litter decomposition of a tropical understory species (Ctenanthe lubbersiana) grown under ambient and elevated CO2^318^18^3^377-381^^^^^^^^^^5825
344^407^427^738^778^874^
A^5824^A CO2 evolution and a disserved organic carbon (DOC)-die-away test were used to determine the inherent decomposability of plant litter of Ctenanthe lubbersiana grown under ambient (340 ppm) and elevated CO2 (610 ppm). The CO2 evolution of leaf lifter in a 10 day decomposition assay was retarded by 7% (P = 0.046). Tn the DOG-die-away test, the decomposition of a leaf litter hot water extract was retarded by 8% (P = 0.039). The decomposition of the solid litter fraction was retarded by 16% (P = 0.101). The decomposition rate of petioles was not affected by elevated CO,. Despite the differences were small, the results suggest possible effects on ecosystem C cycling.
ncrease1517^5^Pritchard,S^Peterson,C^Runion,GB^Prior,S^Rogers,H^1997^1^Atmospheric CO2 concentration, N availability, and water status affect patterns of ergastic substance deposition in longleaf pine (Pinus palustris Mill.) foliage^252^11^8^494-503^^^^^Oct^^^^^5827
1086^2173^2441^2442^348^362^374^417^57^690^^^5825
344^407^427^738^778^874^
A^5824^A CO2 evolution and a disserved organic carbon (DOC)-die-away test were used to determine the inherent decomposability of plant litter of Ctenanthe lubbersiana grown under ambient (340 ppm) and elevated CO2 (610 ppm). The CO2 evolution of leaf lifter in a 10 day decomposition assay was retarded by 7% (P = 0.046). Tn the DOG-die-away test, the decomposition of a leaf litter hot water extract was retarded by 8% (P = 0.039). The decomposition of the solid litter fraction was retarded by 16% (P = 0.101). The decomposition rate of petioles was not affected by elevated CO,. Despite the differences were small, the results suggest possible effects on ecosystem C cycling.
ncreaseA^5826^Leaf chemistry alterations due to increasing atmospheric CO2 will reflect plant physiological changes and impact ecosystem function. Longleaf pine was grown for 20 months at two levels of atmospheric CO2 (720 and 365 mu mol mol(-1)), two levels of soil N (4 g m(-2) year(-1) and 40 g m(-2) year(-1)), and two soil moisture levels (-0.5 and -1.5 MPa) in open top chambers. After 20 months of exposure, needles were collected and ergastic substances including starch grains and polyphenols were assessed using light microscopy, and calcium oxalate crystals were assessed using light microscopy, scanning electron microscopy, and transmission electron microscopy. Polyphenol content was also determined using the Folin-Denis assay and condensed tannins were estimated by precipitation with protein. Evaluation of phenolic content histochemically was compared to results obtained using the Folin-Denis assay. Total leaf polyphenol and condensed tannin content were increased by main effects of elevated CO2, low soil N and well- watered conditions. Elevated CO2 and low soil N decreased crystal deposition within needle phloem. Elevated CO2 had no effect on the percentage of cells within the mesophyll, endodermis, or transfusion tissue which contained visible starch inclusions. With respect to starch accumulation in response to N stress, mesophyll > endodermis > transfusion tissue. The opposite was true in the case of starch accumulation in response to main effects of water stress: mesophyll < endodermis < transfusion tissue. These results indicate that N and water conditions significantly affect deposition of leaf ergastic substances in longleaf pine, and that normal variability in leaf tissue quality resulting from gradients in soil resources will be magnified under conditions of elevated CO2.

1518^4^Reitz,SR^Karowe,DN^Diawara,MM^Trumble,JT^1997^1^Effects of elevated atmospheric carbon dioxide on the growth and linear furanocoumarin content of celery^321^45^9^3642-3646^^^^^Sep^^^^^5829effects of elevated CO2, low soil N a1080^1086^1142^1323^2184^2443^2444^2445^374^376^ soil N decreased crystal deposition within needle phloem. Elevated CO2 had no effect on the percentage of cells within the mesophyll, endodermis, or transfusion tissue which contained visible starch inclusions. With respect to starch accumulation in response to N stress, mesophyll > endodermis > transfusion tissue. The opposite was true in the case of starch accumulation in response to main effects of water stress: mesophyll < endodermis < transfusion tissue. These results indicate that N and water conditions significantly affect deposition of leaf ergastic substances in longleaf pine, and that normal variability in leaf tissue quality resulting from gradients in soil resources will be magnified under conditions of elevated CO2.

1518^4^Reitz,SR^Karowe,DN^Diawara,MM^Trumble,JT^1997^1^Effects of elevated atmospheric carbon dioxide on the growth and linear furanocoumarin content of celery^321^45^9^3642-3646^^^^^Sep^^^^^5829effects of elevated CO2, low soil N aA^5828^The effects of elevated atmospheric carbon dioxide on the growth and development of celery (Apium graveolens) were examined to determine if anticipated global increases in CO2 will affect the nutritional quality and secondary chemistry of celery. The size (fresh and dry mass), nitrogen and carbon composition, and concentrations of linear furanocoumarins of celery grown under ambient (363 mu L L-1) and elevated (718 mu L L-1) carbon dioxide were analyzed. Growth under elevated CO2 resulted in larger petioles, reduced nitrogen content, and higher C:N ratios in both leaves and petioles. However, CO2 treatment did not affect plant water content or carbon content. Moreover, in contrast to the carbon-nutrient balance hypothesis, the increased C:N ratios of plants grown under elevated CO2 were not associated with increased concentrations of potentially harmful linear furanocoumarins. Levels of linear furanocoumarins in the petioles of plants from each treatment did not exceed concentrations reported to cause acute or chronic contact dermatitis.

1519^2^Reuveni,J^Bugbee,B^1997^1^Very high CO2 reduces photosynthesis, dark respiration and yield in wheat^52^80^4^539-546^^^^^Oct^^^^^5831
1206^188^2076^2446^312^348^376^422^879^92^ secondary chemistry of celery. The size (fresh and dry mass), nitrogen and carbon composition, and concentrations of linear furanocoumarins of celery grown under ambient (363 mu L L-1) and elevated (718 mu L L-1) carbon dioxide were analyzed. Growth under elevated CO2 resulted in larger petioles, reduced nitrogen content, and higher C:N ratios in both leaves and petioles. However, CO2 treatment did not affect plant water content or carbon content. Moreover, in contrast to the carbon-nutrient balance hypothesis, the increased C:N ratios of plants grown under elevated CO2 were not associated with increased concentrations of potentially harmful linear furanocoumarins. Levels of linear furanocoumarins in the petioles of plants from each treatment did not exceed concentrations reported to causeA^5830^Although terrestrial CO2 concentrations, [CO2], are not expected to reach 1000 mu mol mol(-1) for many decades, CO2 levels in closed systems such as growth chambers and glasshouses, can easily exceed this concentration. CO2 levels in life support systems in space can exceed 10 000 mu mol mol(- 1) (1 %). Here we studied the effect of six CO2 concentrations, from ambient up to 10000 mu mol mol(-1), on seed yield, growth and gas exchange of two wheat cultivars (USU-Apogee and Veery- 10). Elevating [CO2] from 350 to 1000 mu mol mol(-1) increased seed yield (by 33 %), vegetative biomass (by 25 %) and number of heads m(-2) (by 34 %) of wheal plants. Elevation of [CO2] from 1000 to 10000 mu mol mol(-1) decreased seed yield (by 37 %), harvest index (by 14%), mass per seed (by 9 %) and number of seeds per head (by 29 %). This very high [CO2] had a negligible, non-significant effect on vegetative biomass, number of heads m(-2) and seed mass per head. A sharp decrease in seed yield, harvest index and seeds per head occurred by elevating [CO2] from 1000 to 2600 mu mol mol(-1). Further elevation of [CO2] from 2600 to 10000 mu mol mol(-1) caused a further but smaller decrease. The effect of CO2 on both wheal cultivars was similar for all growth parameters. Similarly there were no differences in the response to high [CO2] between wheal grown hydroponically in growth chambers under fluorescent lights and those grown in soilless media in a glasshouse under sunlight and high pressure sodium lamps. There was no correlation between high [CO2] and ethylene production by flag leaves or by wheal heads. Therefore, the reduction in seed set in wheal plants is not mediated by ethylene. The photosynthetic rate of whole wheat plants was 8 % lower and dark respiration of the wheat heads 25 % lower when exposed to 2600 mu mol mol(- 1) CO2 compared to ambient [CO2]. It is concluded that the reduction in the seed set can be mainly explained by the reduction in the dark respiration in wheat heads, when most of the respiration is functional and is needed for seed development. (C) 1997 Annals of Botany Company.

1520^5^Riedo,M^Gyalistras,D^Grub,A^Rosset,M^Fuhrer,J^1997^1^Modelling grassland responses to climate change and elevated CO2^318^18^3^305-311^^^^^^^^^^5833
407^427^659^. Similarly there were no differences in the response to high [CO2] between wheal grown hydroponically in growth chambers under fluorescent lights and those grown in soilless media in a glasshouse under sunlight and high pressure sodium lamps. There was no correlation between high [CO2] and ethylene production by flag leaves or by wheal heads. Therefore, the reduction in seed set in wheal plants is not mediated by ethylene. The photosynthetic rate of whole wheat plants was 8 % lower and dark respiration of the wheat heads 25 % lower when exposed to 2600 mu mol mol(- 1) CO2 compared to ambient [CO2]. It is concluded that the reduction in the seed set can be mainly explained by the reduction in the dark respiration in wheat heads, when most of the respiration is functioA^5832^A mechanistic model for productive grassland was used to simulate the annual production of above-and belowground plant biomass in relation to fluxes of C, N, and water, and to test the sensitivity of yield, shoot/root ratio, evapotranspiration, and water use efficiency (WUE) to climate change scenarios (CC) and to elevated CO2 (2 x CO2) with or without consideration oi photosynthetic acclimation of the plants. Validation with data from two Swiss sites revealed satisfactory agreement between simulation and measurement for yield, energy fluxes, and N- dynamics. Local weather scenarios were derived from the results of two General Circulation Models (GCM) for 2 x CO2 by a statistical down-scaling procedure. Biomass production changed by a maximum of 8% in response to CC without 2 x CO2 effects, by 1-17% in response to 2 x CO2 alone, and by 6-20% in response to the combination of CC and 2 x CO2. With plant acclimation, biomass Production increased only up to 8% with elevated CO2, as compared to a maximum increase of 20% in the absence of plant acclimation. Reduced yield with CC was obtained for sites with low soil water holding capacity. Decreased evapotranspiration and increased WUE with 2 x CO2 were partially offset by CC. The simulations indicated that productivity of managed grassland is sensitive to different assumptions about changes in climate, CO2 concentration, and photosynthetic acclimation, and that the effects of elevated CO2 are modified by CC and depend on local soil conditions.

1521^3^Rotzel,C^Leadley,PW^Korner,C^1997^1^Non-destructive assessment of the effects of elevated CO2 on plant community structure in a calcareous grassland^318^18^3^231-239^^^^^^^^^^5835
344^376^92^own-scaling procedure. Biomass production changed by a maximum of 8% in response to CC without 2 x CO2 effects, by 1-17% in response to 2 x CO2 alone, and by 6-20% in response to the combination of CC and 2 x CO2. With plant acclimation, biomass Production increased only up to 8% with elevated CO2, as compared to a maximum iA^5834^Calcareous grassland was exposed to ambient or elevated CO2 using a Screen-Aided CO2 Control (SACC) system starting in March 1994. The effects of elevated CO2 on plant community structure were studied using the paint intercept method. Measurements were made in March 1994 prior to the start of CO2 exposure and again in June 1994 at peak plant biomass. There were no significant differences in the initial structure of the communities based on their assigned CO2 treatments in March. After 9 weeks of exposure of the community to elevated CO2, the total number of intercepts per plot was not significantly different between CO2 treatments; however, Carex flacca and Cirsium acaule had marginally significant (P = 0.055 and P = 0.06) increases in the % sward of the community at elevated CO2 (number of intercepts for a single species divided by the total number of intercepts for all species). Measurements of leaf extension in Carex flacca showed that at least part of the increase in % sward at elevated CO2 could be explained by greater leaf length per plant (P = 0.02). These measurements and other experiments with calcareous grassland species and communities suggest that rising atmospheric CO2 concentrations will probably alter the structure of calcareous grassland communities.

1522^5^Steinger,T^Lavigne,C^Birrer,A^Groppe,K^Schmid,B^1997^1^Genetic variation in response to elevated CO2 in three grassland perennials - a field experiment with two competition regimes^318^18^3^263-268^^^^^^^^^^5837
417^792^eeks of exposure of the community to elevated CO2, the total number of intercepts per plot was not significantly different between CO2 treatments; however, Carex flacca and Cirsium acaule had marginally significant (P = 0.055 and P = 0.06) increases in the % sward of the community at elevated CO2 (number of intercepts for a single species divided by the total number of intercepts for all species). Measurements of leaf extension in Carex flacca showed that at least part of the increase in % sward at elevated CO2 could A^5836^Intraspecific Variation in the response to increased concentrations of atmospheric CO2 was investigated in three plant species (Bromus erectus, Prunella vulgaris, P. grandiflora) in a calcareous grass land. Genotypes of each species were grown both in multispecies communities and under reduced competition pressure in tubes buried in the soil. Plant growth was reduced in the artificial communities but no significant effect of CO2 was observed on any of the measured traits. Significant genotype by-CO2 interactions were found in two species when plants were grown under reduced competition in the tubes. No genotype-by-CO2 interactions were found for the same genotypes grown in the multispecies communities indicating that genetic variation was swamped by large environmental variation. Furthermore, no correlations were observed between CO2 responses of identical genotypes grown individually in tubes and in multispecies communities. This result cautions about the ability to predict CO2-induced evolutionary changes from data of individually-grown plants.

1523^3^Stocklin,J^Leadley,PW^Korner,C^1997^1^Community and species level responses to elevate CO2 in designed calcareous grassland communities^318^18^3^241-248^^^^^^^^^^5839
2447^2448^92^ies were grown both in multispecies communities and under reduced competition pressure in tubes buried in the soil. Plant growth was reduced in the artificial communities but no significant effect of CO2 was observed on any of the measured traits. Significant genotype by-CO2 interactions were found in two species when plants were grown under reduced competition in the tubes. No genotype-by-CO2 interactions were found for the same genotypes grown in the multispecies communities indicating that genetic variation was swamped by large environmental variation. Furthermore, no correlations were observed between CO2 responses of identical genotypes grown individually in tubes and in multispecies communities. This result cautions about the ability to predict CO2-induced evolutionary cA^5838^We present a synthesis of two independent glasshouse experiments in which we investigated the short term response of model communities of calcareous grassland species to CO2- enrichment. Communities consisted of six species in the first study and of 14 species in-the second study. Communities were grown in containers filled with ca. 20 liters of natural soil. Total aboveground biomass production was increased by 14% (n.s., p=0.21) in the first study and by 8.5% (p=0.03) in the second study. This community level response was due to a significant stimulation of growth in 2 and 5 species, respectively. In each of the experiments, one species responded negatively to CO2-enrichment. The remaining species, including all legumes, remained unaffected by CO2-enrichment. Positive or negative responding species did not belong to specific functional groups, hence responses could not have been predicted from a priori knowledge of individual plant traits. Bromus erectus, which is the dominant species in calcareous grasslands of the Jura mountains, did not exhibit a CO2- response at the species level, but genotype-specific responses in this species varied significantly and included positive as well as negative responses. No such genotypic differentiation of CO2-response was observed in Fes tuca ovina. In the long term, we expect directional selection of positively responding genotypes and shifts in species composition to alter both population and community structure of calcareous grass lands - a conclusion that may also hold for other diverse plant communities.

1524^5^Taulavuori,E^Taulavuori,K^Laine,K^Pakonen,T^Saari,E^1997^1^Winter hardening and glutathione status in the bilberry (Vaccinium myrtillus) in response to trace gases (CO2, O-3) and nitrogen fertilization^37^101^1^192-198^^^^^Sep^^^^^5841
1482^1633^2449^2450^2451^2452^312^344^446^482^nctional groups, hence responses could not have been predicted from a priori knowledge of individual plant traits. Bromus erectus, which is the dominant species in calcareous A^5840^Bilberry plants (Vaccinium myrtillus L.) at a field site in northern Finland (65 degrees N) were subjected to nitrogen fertilization [6.5 mmol m(-2) NH4NO3 x Ca(OH)(2)] at the beginning of 3 growing seasons in late May and to trace gas fumigation (CO2 and O-3) for 5 months (May-September) in 1993- 1995 in order to investigate frost resistance and glutathione concentrations during the winter hardening period, and to assess the correlation between these variables. Harvesting was performed twice in the autumn of both 1994 and 1995, and the two-year data for each harvest were pooled. The frost resistance of the bilberry stems increased by about 10 degrees C during the hardening period between the two harvests. Nitrogen fertilization increased the frost resistance towards late autumn. The fumigation treatments had no marked effect on it. The combination of elevated CO2 and nitrogen fertilization induced a decrease in frost resistance. Increases in total glutathione concentrations and the proportion of reduced glutathione (GSH) in the stems were evident during hardening. Nitrogen fertilization positively affected the total glutathione concentration and the proportion of GSH at the beginning of the hardening period but the effect disappeared during the hardening process. Trace gas fumigation as such had no marked effect on glutathione concentration. Increases in glutathione concentrations during hardening did not correlate with frost resistance, possibly due to different timing of the appearence of the response to fertilization treatment, i.e., glutathione responded in the beginning of hardening while frost resistance at the end. The lack of correlation with frost resistance, and especially the different responses to nitrogen fertilization, may reflect the indirect role of glutathione in the development of winter hardening, as a transport and storage form of reduced nitrogen and sulphur. In conclusion, winter hardening and glutathione status in the bilberry seems to be sensitive to nitrogen fertilization, and not affected by elevated CO2 and O-3.

1525^3^Tissue,DT^Thomas,RB^Strain,BR^1997^1^Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field^9^20^9^1123-1134^^^^^Sep^^^^^5843
1262^1985^2012^2060^2453^2454^398^483^546^857^gas fumigation as such had no marked effect on glutathione concentration. Increases in glutathione concentrations during hardening did not correlate with frost resistance, possibly due to different timing of the appearence of the response to fertilization treatment, i.e., glutathione responded in the beginning of hardening while frost resistance at the end. The lack of correlation with frost resistance, and especially the different responses to nitrogen fertilization, may reflect the indirect role of glutathione in the development of winter hardening, as a transport and storage form of reduced nitrogen and sulphur. In conclusion, winter hardening and glutathione status in the bilberry seems to be sensitive to nitrogen fertilization, and nA^5842^Forest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long- term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size-dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60-130% increase) than in the winter (14-44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non-structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy-level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.

1526^2^Will,RE^Teskey,RO^1997^1^Effect of elevated carbon dioxide concentration and root restriction on net photosynthesis, water relations and foliar carbohydrate status of loblolly pine seedlings^13^17^10^655-661^^^^^Oct^^^^^5845
2455^344^360^374^384^385^386^442^705^92^al variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non-structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy-level adjustments in carbon assimilatiA^5844^To determine the effects of CO2-enriched air and root restriction on photosynthetic capacity, we measured net photosynthetic rates of 1-year-old loblolly pine seedlings grown in 0.6-, 3.8- or 18.9-liter pots in ambient (360 mu mol mol(-1)) or 2x ambient CO2 (720 mu mol mol(-1)) concentration for 23 weeks. We also measured needle carbohydrate concentration and water relations to determine whether feedback inhibition or water stress was responsible for any decreases in net photosynthesis. Across all treatments, carbon dioxide enrichment increased net photosynthesis by approximately 60 to 70%. Net photosynthetic rates of seedlings in the smallest pots decreased over time with the reduction occurring first in the ambient CO2 treatment and then in the 2x ambient CO2 treatment. Needle starch concentrations of seedlings grown in the smallest pots were two to three times greater in the 2x ambient CO2 treatment than in the ambient CO2 treatment, but decreased net photosynthesis was not associated with increased starch or sugar concentrations. The reduction in net photosynthesis of seedlings in small pots was correlated with decreased needle water potentials, indicating that seedlings in the small pots had restricted root systems and were unable to supply sufficient water to the shoots. We conclude that the decrease in net photosynthesis of seedlings in small pots was not the result of CO2 enrichment or an accumulation of carbohydrates causing feedback inhibition, but was caused by water stress.

1527^3^Yeates,GW^Tate,KR^Newton,PCD^1997^1^Response of the fauna of a grassland soil to doubling of atmospheric carbon dioxide concentration^263^25^3^307-315^^^^^Sep^^^^^5847
1334^2258^230^2456^372^376^797^occurring first in the ambient CO2 treatment and then in the 2x ambient CO2 treatment. Needle starch concentrations of seedlings grown in the smallest pots were two to three times greater in the 2x ambient CO2 treatment than in the ambient CO2 treatment, but decreased net photosynthesis was not associated with increaseA^5846^The effects of elevated CO2 on rhizosphere processes, including the response of soil faunal populations and community structure, have so far received little attention. We report on significant responses in the soil fauna of ryegrass/white clover swards to both increasing CO2 from 350 to 750 mu l . l(- 1) and, to a period of 60 days when some of the turves were subject to drought, in a controlled climate growth room experiment. The nematodes which increased were predominantly Enoplia, including dorylaimids, alaimids and trichodorids. This accords with both the doubling of Alaimus under elevated CO2 conditions reported in a similar experiment and with the common association of Enoplia with less disturbed habitats. The most marked decrease was in the bacterial-feeding Rhabditis (Secernentea). The increase in omnivorous and predacious nematodes may have been responsible for the decrease in populations of bacterial-feeding nematodes. However, in contrast to their standing crops, the turnover rate of bacterial-feeding nematodes and soil microbial biomass probably increased as a result of increased grazing by these omnivorous and predacious nematodes. Increases in earthworm and enchytraeid populations were related to increased below-ground productivity reported for the same trial.

1528^3^Yoo,KS^Andersen,CR^Pike,LM^1997^1^Internal CO2 concentrations in onion bulbs at different storage temperatures and in response to sealing of the neck and base^259^12^2^157-163^^^^^Oct^^^^^5849
antly Enoplia, including dorylaimids, alaimids and trichodorids. This accords with both the doubling of Alaimus under elevated CO2 conditions reported in a similar experiment and with the common association of Enoplia with less disturbed habitats. The most marked decrease was in the bacterial-feeding Rhabditis (Secernentea). The increase in omnivorous and predacious nematodes may have been responsible for the decrease in populations of bacterial-feeding nematodes. However, in contrast to their standing crops, the turnover rate of bacterA^5848^Internal CO2 concentrations were measured in onion (Allium cepa L. cv. TG 1015Y) bulbs stored at 1, 7, 13, 20, 27, or 34 degrees C for 12 weeks and their relationships with shoot growth and respiration rates were investigated. Maximum shoot growth was observed at 13 and 20 degrees C. Respiration rates were greatest at 13 and 20 degrees C for 8 weeks, then linearly increased with storage temperatures after 12 weeks. Internal CO2 concentrations ranging from 2 to 5% increased with increasing storage temperatures, while internal gas volume decreased. Bicarbonate concentrations in outer scales ranged from 130 to 190 mu M and increased with increasing storage temperatures. The centre scale tissues contained 11-17% CO2, which paralleled respiration rates. Searing the neck area of onion bulbs stored at 1 or 27 degrees C significantly increased internal CO2 concentrations, but had no effect on inhibiting shoot growth. Internal CO2 concentrations appeared to be regulated by gas exchange rates through the neck area and/or elevated HCO3- concentrations in outer scales. Elevated internal CO2 concentrations or high levels in centre scale tissues did not appear to be a primary reason for inhibited shoot growth at high storage temperatures. There seems to be thermo-dormancy controlling shoot growth and respiration in onion bulbs. (C) 1997 Elsevier Science B.V.

1529^2^Zanetti,S^Hartwig,UA^1997^1^Symbiotic N-2 fixation increases under elevated atmospheric pCO(2) in the field^318^18^3^285-290^^^^^^^^^^5851
1531^174^2259^2457^766^92^ile internal gas volume decreased. Bicarbonate concentrations in outer scales ranged from 130 to 190 mu M and increased with increasing storage temperatures. The centre scale tissues contained 11-17% CO2, which paralleled respiration rates. Searing the neck area of onion bulbs stored at 1 or 27 degrees C significantly increased internal CO2 concentrations, but had no effect on inhibiting shoot growth. Internal CO2 concentrations appeared to be regulated by gas exchange rates through the neck aA^5850^Plant growth is stimulated by elevated atmospheric pCO(2), and hence demand for nutrients increases. In this context, nitrogen is a very prominent element; it can either be supplied from the limited available soil N or through biological (e.g. symbiotic) nitrogen fixation. In this study, the effect of elevated pCO(2) (60 Pa) on symbiotic N-2 fixation (N-15-isotope dilution method) was investigated using Free-Air-CO2-Enrichment (FACE) technology over a period of two growing seasons. Trifolium repens L, was cultivated either alone or in mixed swards together with Lolium perenne L. (non-fixing reference crop). In T. repens, percentage of plant N derived from symbiotic N-2 fixation (%Nsym) increased from 59 to 66% under elevated pCO(2). The major part of the additionally assimilated N was derived from symbiotic N-2 fixation. In the mixed swards, increased N yield was entirely due to increased symbiotic N-2 fixation. It is suggested that increased N-2 fixation is an important factor in the satisfaction of increased N demand in both clover and the associated grass under elevated pCO(2).

1530^3^Baxter,R^Ashenden,TW^Farrar,JF^1997^1^Effect of elevated CO2 and nutrient status on growth, dry matter partitioning and nutrient content of Poa alpina var vivipara L^78^48^312^1477-1486^^^^^Jul^^^^^5853
1123^1302^2125^224^243^374^377^423^448^57^ symbiotic N-2 fixation (N-15-isotope dilution method) was investigated using Free-Air-CO2-Enrichment (FACE) technology over a period of two growing seasons. Trifolium repens L, was cultivated either alone or in mixed swards together with Lolium perenne L. (non-fixing reference crop). In T. repens, percentage of plant N derived from symbiotic N-2 fixation (%Nsym) increased from 59 to 66% under elevated pCO(2). The major part of the additionally assimilated N was derived from symbiotic N-2 fixation. In the mixed swards, increased N yield was entirely due to increased symbiotic N-2 fixation. It is suggested that increased N-2 fixation is an important factor in the satisfaction of A^5852^Poa alpina var, vivipara L, was grown in an atmosphere containing either 340 or 680 mu mol CO2 mol(-1) within controlled environment chambers, The available nutrient regime was varied by altering the supply of nitrogen and phosphorus within a complete nutrient solution, At a high, but not low, N and P supply regime, elevated CO2 markedly increased growth, Differences between nutrient supply, but not atmospheric CO2 concentration, altered the allometric relations between root and shoot, Net photosynthesis of mature leaf blades and leaf N and P concentration were reduced in plants grown at the elevated CO, concentration, The question was asked: is it possible to ascribe all of these effects to elevated CO2 or are some due to nutrient deficiency caused by dilution with excess carbon? Several criteria, including the nutrient content of sink tissue, root:shoot allometry and the use of divalent cations to estimate integrated water flows are suggested in order to make this distinction, It is concluded that only at a low supply of N and P, and elevated CO2 concentration, was low leaf N concentration due to induced nutrient deficiency, The data are consistent with a model where the capacity of sinks to use photosynthetically assimilated carbon sets both the rate of import into those sinks (and thus rate of export from source leaves) and the rate of photosynthesis of source leaves themselves.

1531^1^Booker,FL^1997^1^Effects of elevated CO2 and nitrogen on proanthocyanidins in cotton^8^114^3^489^^^^^Jul

1532^1^Campbell,WJ^1997^1^Intraspecific variation of rubisco and rubisco activase protein levels in tomato leaves grown at elevated CO2 concentration^8^114^3^1056^^^^^Jul

1533^2^Chen,CT^Setter,TL^1997^1^Potato response to elevated CO2 and temperature^8^114^3^490^^^^^Jul

1534^4^Chernikova,T^Robinson,JM^Lee,EH^Mulchi,CL^1997^1^Evaluation of ozone tolerance mechanisms in soybean cultivars exposed to ambient and elevated CO2^8^114^3^201^^^^^Jul
are suggested in order to make this distinction, It is concluded that o1535^3^Dalen,LS^Johnsen,O^Ogner,G^1997^1^Frost hardiness development in young Picea abies seedlings under simulated autumn conditions in a phytotron - effects of elevated CO2, nitrogen and provenance^8^114^3^576^^^^^Jul

1536^3^Fonseca,F^Bowsher,CG^Stulen,I^1997^1^Impact of elevated atmospheric CO2 on nitrate reductase transcription and activity in leaves and roots of Plantago major^37^100^4^940-948^^^^^Aug^^^^^5860
2249^243^244^2458^312^346^537^639^845^92^ocyanidins in cotton^8^114^3^489^^^^^Jul

1532^1^Campbell,WJ^1997^1^Intraspecific variation of rubisco and rubisco activase protein levels in tomato leaves grown at elevated CO2 concentration^8^114^3^1056^^^^^Jul

1533^2^Chen,CT^Setter,TL^1997^1^Potato response to elevated CO2 and temperature^8^114^3^490^^^^^Jul

1534^4^Chernikova,T^Robinson,JM^Lee,EH^Mulchi,CL^1997^1^Evaluation of ozone tolerance mechanisms in soybean cultivars exposed to ambient and elevated CO2^8^114^3^201^^^^^Jul
are suggested in order to make this distinction, It is concluded that oA^5859^Vegetative plants of an inbred line, A4, of Plantage major ssp. pleiosperma (L.) Pilger were grown at 350 mu l 1(-1) or at elevated (700 mu l l(-1)) CO2 in non-limiting nutrient solution with nitrate. Both the relative growth rate (RGR) and the root to total plant weight ratio (RWR) were increased by elevated CO2. However, the stimulation of both RGR and RWR was transient and did not last longer than 8 days. To investigate the physiological mechanisms involved in this stimulation, related changes in C/N metabolism were examined. In the roots soluble sugar concentration increased during the transient period of RGR stimulation (up to 23%), as did the root respiration rate. Changes in nitrogen metabolism were also restricted to this period and consisted of an increase in (1) in vivo and in vitro root nitrate reductase (EC 1.6.6.1) activity, (2) in vitro leaf nitrate reductase activity, (3) leaf and root nitrate reductase mRNA and (4) reduced nitrogen concentration in the roots. The elevated CO2-related signal for the increase in nitrate reductase transcript levels in the roots is discussed in terms of the increased availability of soluble sugars. The results suggest that the short-term enhancement of root carbon and nitrogen metabolism may be responsible for the transient effect of elevated CO, on whole plant RGR.

1537^4^George,V^Cantin,D^Gerant,D^Dizengremel,P^1997^1^Long-term effects of elevated CO2 concentration on respiratory enzymes and dark respiration in pedunculate oak leaves^8^114^3^657^^^^^Jul

1538^2^Grotenhuis,TP^Bugbee,B^1997^1^Super-optimal CO2 reduces seed yield but not vegetative growth in wheat^164^37^4^1215-1222^^^^^Jul-Aug^^^^^5863
188^2446^2459^310^312^348^376^384^685^867^en metabolism were also restricted to this period and consisted of an increase in (1) in vivo and in vitro root nitrate reductase (EC 1.6.6.1) activity, (2) in vitro leaf nitrate reductase activity, (3) leaf and root nitrate reductase mRNA and (4) reduced nitrogen concentration in the roots. The elevated CO2-related sA^5862^Although terrestrial atmospheric CO2 levels will not reach 1000 mu mol mol(-1) (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10 000 mu mol mol(-1)(1%). Numerous studies have examined CO2 effects up to 1000 mu mol mol(-1), but biochemical measurements indicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near-optimal (approximate to 1200 mu mol mol(-1)) and super-optimal CO2 levels (2400 mu mol mol(-1)) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub-optimal to near- optimal (350-1200 mu mol mol(-1)) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 mu mol mol(-1) reduced seed yield by 22% (P < 0.001) in cv. Veery-10 and by 15% (P < 0.001) in cv. USU-Apogee. Super-optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels from half to full sunlight. Subsequent trials revealed that super- optimal CO2 during the interval between 2 wk before and after anthesis mimicked the effect of constant super-optimal CO2. Furthermore, near-optimal CO2 during the same interval mimicked the effect of constant near-optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results suggest that super optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.

1539^3^Heath,J^Kerstiens,G^Tyree,MT^1997^1^Stem hydraulic conductance of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) grown in elevated CO2^78^48^312^1487-1489^^^^^Jul^^^^^5865
312^361^417^508^514^22% (P < 0.001) iA^5864^Over two seasons in c. 600 ppm CO2, oak had lower stomatal conductance in CO2-enriched compared to ambient air, Beech showed no response to CO2 concentration on sunny days, Mirroring this pattern, exposure to elevated CO2 reduced whole- shoot hydraulic conductance per unit leaf area in oak, but not in beech.

1540^6^Jitla,DS^Rogers,GS^Seneweera,SP^Basra,AS^Oldfield,RJ^Conroy,JP^1997^1^Accelerated early growth of rice at elevated CO2 - Is it related to developmental changes in the shoot apex?^8^115^1^15-22^^^^^Sep^^^^^5867
1347^2123^2124^344^348^360^385^417^434^leaves and heads was not affected by CO2. These results suggest that super optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.

1539^3^Heath,J^Kerstiens,G^Tyree,MT^1997^1^Stem hydraulic conductance of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) grown in elevated CO2^78^48^312^1487-1489^^^^^Jul^^^^^5865
312^361^417^508^514^22% (P < 0.001) iA^5866^The influence of elevated CO2 on the development of the shoot apex and on subsequent vegetative growth and grain yield was investigated using rice (Oryza sativa L. cv Jarrah) grown in flooded soil at either 350 or 700 mu L CO2 L-1. At 8 d after planting (DAP), elevated CO2 increased the height and diameter of the apical dome and lengths of leaf primordia and tiller buds but had no effect on their numbers. By 16 DAP, there were five tiller buds in the apex at 700 mu L CO2 L-1 compared with only three tiller buds at 350 mu L CO2 L-1. These changes in development of the shoot apex at high CO2 were forerunners to faster development of the vegetative shoot at elevated CO2 between 11 and 26 DAP as evidenced by increases in the relative growth rates of the shoot and tillers. Accelerated development at high CO2 was responsible for the 42% increase in tiller number at the maximum tillering stage and the 57% enhancement of grain yield at the final harvest. The link between high CO2 effects on development during the first 15 DAP and final tiller number and grain yield was demonstrated by delaying exposure of plants to high CO2 for 15 d. The delay totally inhibited the tillering response to high CO2, and the increase in grain yield of 20% arose from a greater number of grains per panicle. Consequently, it can be concluded that accelerated development in the shoot apex early in development is crucial for obtaining maximum increases in grain yield at elevated atmospheric CO2 concentrations.

1541^2^Kellomaki,S^Wang,KY^1997^1^Effects of elevated O-3 and CO2 concentrations on photosynthesis and stomatal conductance in Scots pine^9^20^8^995-1006^^^^^Aug^^^^^5869
1064^1633^1951^312^343^384^389^444^692^728^AP as evidenced by increases in the relative growth rates of the shoot and tillers. Accelerated development at high CO2 was responsible for the 42% increase in tiller number at the maximum tillering stage and the 57% enhancement of grain yield at the final harvest. The link between high CO2 effects on development duringA^5868^Naturally regenerated Scots pines (Pinus sylvestris L.), aged 28-30 years old, were grown in open-top chambers and subjected in situ to three ozone (O-3) regimes, two concentrations of CO2, and a combination of O-3 and CO2 treatments from 15 April to 15 September for two growing seasons (1994 and 1995), The gas exchanges of current-year and 1-year-old shoots were measured, along with the nitrogen content of needles, In order to investigate the factors underlying modifications in photosynthesis, five parameters linked to photosynthetic performance and three to stomatal conductance were determined, Elevated O-3 concentrations led to a significant decline in the CO2 compensation point (I*), maximum RuP2-saturated rate of carboxylation (V-emax), maximum rate of electron transport (J(max)) maximum stomatal conductance (g(smax)) and sensitivity of stomatal conductance to changes in leaf-to-air vapour pressure difference (partial derivative g(s)/partial derivative D-v) in both shoot-age classes, However, the effect of elevated O-3 concentrations on the respiration rate in light (R-d) was dependent on shoot age, Elevated CO2 (700 mu mol mol(-1)) significantly decreased J(max) and g(smax) but increased R-d in 1-year-old shoots and the partial derivative(s)/partial derivative D-v in both shoot-age classes, The interactive effects of O-3 and CO2 on some key parameters (e.g. V-emax and J(max)) were significant. This may be closely related to regulation of the maximum stomatal conductance and stomatal sensitivity induced by elevated CO2. As a consequence, the injury induced by O-3 was reduced through decreased ozone uptake in 1-year-old shoots, but not in the current-year shoots, Compared to ambient O-3 concentration, reduced O-3 concentrations (charcoal-filtered air) did not lead to significant changes in any of the measured parameters, Compared to the control treatment, calculations showed that elevated O-3 concentrations decreased the apparent quantum yield by 35% and by 18%, and the maximum rate of photosynthesis by 21% and by 29% in the current-year and 1-year-old shoots, respectively, Changes in the nitrogen content of needles resulting from the various treatments were associated with modifications in photosynthetic components.

1542^1^Kerstiens,G^1997^1^Why is increasing shade-tolerance of trees correlated with increasing stimulation of growth by elevated CO2?^8^114^3^371^^^^^Jul

1543^3^Kurschner,WM^Stulen,I^Kuiper,PJC^1997^1^PREDICTIONS for plant and vegetation responses to global change (elevated CO2) within a palaeo-ecophysiological perspective^8^114^3^21002^^^^^Jul

1544^4^Kurschner,WM^Wagner,F^Visscher,EH^Visscher,H^1997^1^Predicting the response of leaf stomatal frequency to a future CO2-enriched atmosphere: constraints from historical observations^322^86^2^512-517^^^^^Aug^^^^^5873
1262^1635^227^2460^2461^312^372^376^458^634^ Compared to the control treatment, calculations showed that elevated O-3 concentrations decreased the apparent quantum yield by 35% and by 18%, and the maximum rate of photosynthesisA^5872^The majority of the water flux from the earth's land surface to the atmosphere passes through the tiny pores (stomata) in the leaves of land plants. The maximum conductance to diffusion of the leaves, determined by the number and geometry of stomata, has a profound effect on the terrestrial water and energy balance. Among tree species, there is ever increasing evidence that anthropogenic increase in atmospheric CO2 concentrations results in a decrease in stomatal frequency. The rate of historical CO2 responsiveness of individual tree species can be used to calibrate empirical models of non-linear (sigmoid) stomatal frequency response to CO2 increase. Modelled response curves for European tree birches (Betula pendula, Betula pubescens) and Durmast oak (Quercus petraea) predict different response limits to CO2 increase (similar to 350 and similar to 400 ppmv, respectively), indicating that non-linear stomatal frequency responses may vary from one tree species to another. Information on a wider selection of species is needed, but the models suggest that the maximum effect of anthropogenic CO2 increase on stomatal frequency has already been reached. Further research is required to establish the effect of rapidly declining response rates on future stomatal conductance of the ecologically contrasting trees of boreal, temperate, subtropical and tropical forests.

1545^2^Leonardos,ED^Grodzinski,B^1997^1^Photosynthesis, export and carbon partitioning in source leaves of C-3, C-3-C-4 intermediate and C-4 Panicum species at ambient and elevated CO2 levels^8^114^3^221^^^^^Jul

1546^3^Madsen,TV^Prins,HBA^Bowe,G^1997^1^Will elevated CO2 affect aquatic plants?^8^114^3^21001^^^^^Jul

1547^5^Makino,A^Harada,M^Sato,T^Nakano,H^Mae,T^1997^1^Growth and N allocation in rice plants under CO2 enrichment^8^115^1^199-203^^^^^Sep^^^^^5877
130^2161^243^372^400^434^448^674^698^724^ ppmv, respectively), indicating that non-linear stomatal frequency responses may vary from one tree species to another. Information on a wider selectionA^5876^The effects of CO2 enrichment on growth and N allocation of rice (Oryza sativa L.) were examined. The plants were grown hydroponically in growth chambers with a 14-h photoperiod (1000 mu mol quanta m(-2) s(-1)) and a day/night temperature of 25/20 degrees C. From the 28th to 70th d after germination, the plants were exposed to two CO2 partial pressures, namely 36 and 100 Pa. The CO2 enrichment increased the final biomass, but this was caused by a stimulation of the growth rate during the first week of the exposure to elevated CO2 partial pressures. The disappearance of the initial stimulation of the growth rate was associated with a decreased leaf area ratio. Furthermore, CO2 enrichment decreased the investment of N in the leaf blades, whereas the N allocation into the leaf sheaths and roots increased. Thus, the decrease in leaf N content by CO2 enrichment was not due to dilution of N caused by a relative increase in the plant biomass but was due to the change in N allocation at the whole-plant level. We conclude that the growth responses of rice to CO2 enrichment are mainly controlled by leaf area expansion and N allocation into leaf blades at the whole-plant level.

1548^8^Makino,A^Nakano,H^Mae,T^Shimada,T^Matsuoka,M^Shimamoto,K^Tokutomi,MM^Yamamoto,N^1997^1^Rubisco and N allocation in rice under elevated CO2. Optimization of Rubisco content by antisense rbc S^8^114^3^1091^^^^^Jul

1549^3^Moore,BD^Palmquist,DE^Seemann,JR^1997^1^Influence of plant growth at high CO2 concentrations on leaf content of ribulose-1,5-bisphosphate carboxylase/oxygenase and intracellular distribution of soluble carbohydrates in tobacco, snapdragon, and parsley^8^115^1^241-248^^^^^Sep^^^^^5880
1116^1790^1950^2108^243^2462^2463^2464^372^384^N in the leaf blades, whereas the N allocation into the leaf sheaths and roots increased. Thus, the decrease in leaf N content by CO2 enrichment was not due to dilution of N caused by a relative increase in the plant biomass but was due to the change in N allocation at the whole-plant level.A^5879^We have examined the possible role of leaf cytosolic hexoses and the expression of mannitol metabolism as mechanisms that may affect the repression of photosynthetic capacity when plants are grown at 1000 versus 380 mu L L-1 CO2. In plants grown at high CO2, leaf ribulose-1,5-bisphosphate carboxylase/oxygenase content declined by greater than or equal to 20% in tobacco (Nicotiana sylvestris) but was not affected in the mannitol-producing species snapdragon (Antirrhinum majus) and parsley (Petroselinum hortense). In the three species mesophyll glucose and fructose at midday occurred almost entirely in the vacuole (>99%), irrespective of growth CO2 levels. The estimated cytosolic concentrations of glucose and fructose were less than or equal to 100 mu M. In the three species grown at high CO2, total leaf carbohydrates increased 60 to 100%, but mannitol metabolism did not function as an overflow mechanism for the increased accumulation of carbohydrate. In both snapdragon and parsley grown at ambient or high CO2, mannitol occurred in the chloroplast and cytosol at estimated midday concentrations of 0.1 M or more each. The compartmentation of leaf hexoses and the metabolism of alternate carbohydrates are further considered in relation to photosynthetic acclimation to high levels of CO2.

1550^3^Nakano,H^Makino,A^Mae,T^1997^1^The effect of elevated partial pressures of CO2 on the relationship between photosynthetic capacity and N content in rice leaves^8^115^1^191-198^^^^^Sep^^^^^5882
1702^2465^343^356^377^384^449^550^635^665^ three species mesophyll glucose and fructose at midday occurred almost entirely in the vacuole (>99%), irrespective of growth CO2 levels. The estimated cytosolic concentrations of glucose and fructose were less than or equal to 100 mu M. In the three species grown at high CO2, total leaf carbohydrates increased 60 to 100%, but mannitol metabolism did not function as an overflow mechanism for the increased accumulation of carbohydrate. In both snapdragon and parsley grown at ambient or hA^5881^The effects of growth CO2 levels on the photosynthetic rates; the amounts of ribulose-1,5-bisphosphate carboxylase (Rubisco), chlorophyll (Chl), and cytochrome f;sucrose phosphate synthase activity; and total N content were examined in young, fully expanded leaves of rice (Oryza sativa L.). The plants were grown hydroponically under two CO2 partial pressures of 36 and 100 Pa at three N concentrations. The light-saturated photosynthesis at 36 Pa CO2 was lower in the plants grown in 100 Pa CO2 than those grown in 36 Pa CO2. Similarly, the amounts of Rubisco, Chl, and total N were decreased in the leaves of the plants grown in 100 Pa CO2. However, regression analysis showed no differences between the two CO2 treatments in the relationship between photosynthesis and total N or in the relationship between Rubisco and Chl and total N. Although a relative decrease in Rubisco to cytochrome for sucrose phosphate synthase was found in the plants grown in 100 Pa CO2, this was the result of a decrease in total N content by CO2 enrichment. The activation state of Rubisco was also unaffected by growth CO2 levels. Thus, decreases in the photosynthetic capacity of the plants grown in 100 Pa CO2 could be simply accounted for by a decrease in the absolute amount of leaf N.

1551^5^Nijs,I^Ferris,R^Blum,H^Hendrey,G^Impens,I^1997^1^Stomatal regulation in a changing climate: a field study using Free Air Temperature Increase (FATI) and Free Air CO2 enrichment (FACE)^9^20^8^1041-1050^^^^^Aug^^^^^5884
1345^243^312^372^385^442^507^674^91^92^ Pa CO2. Similarly, the amounts of Rubisco, Chl, and total N were decreased in the leaves of the plants grown in 100 Pa CO2. However, regression analysis showed no differences between the two CO2 treatments in the relationship between photosynthesis and total N or in the relationship between Rubisco and Chl and total N. Although a relative decrease in Rubisco to cytochrome for sucrose phosphate synthase was found in the plants grown in 100 Pa CO2, this was the result of a decrease in total N A^5883^This study investigates effects of climate warming (+2.5 degrees C above ambient) and elevated CO2 concentration (600 mu mol mol(-1)) on the stomatal functioning and the water relations of Lolium perenne, using Free Air Temperature Increase (FATI) and Free Air CO2 Enrichment (FACE), Compared to growth at ambient temperature, whole-season temperature increase reduced leaf stomatal conductance, but only at the top of the canopy (-14.6 and -8.8% at ambient and elevated CO2, respectively), However, because higher canopy temperature raised the leaf-to-air vapour pressure difference, leaf transpiration rate increased (+28% at ambient and +48% at elevated CO2) and instantaneous leaf water use efficiency, derived from short-term measurements of assimilation and transpiration rate, declined (-11% at ambient and -13% at elevated CO2). Nevertheless, at the stand level, growth at +2.5 degrees C reduced transpiration due to fewer tillers per plant and a smaller leaf area per tiller, This sparser vegetation was also more closely coupled to the atmosphere and maintained a drier internal microclimate. To assess whether the stomatal behaviour observed in this experiment could be explained by prevailing concepts of stomatal functioning, three models were applied (Cowan 1977; Ball, Woodrow & Berry 1987; Leuning 1995), The latter model accounted for the highest proportion of variability in the data (58%) and was insensitive to CO2 and temperature regime, which suggests that the principles of stomatal regulation are not affected by changes in CO2 or climate.

1552^3^Picon,C^Ferhi,A^Guehl,JM^1997^1^Concentration and delta C-13 of leaf carbohydrates in relation to gas exchange in Quercus robur under elevated CO2 and drought^78^48^313^1547-1556^^^^^Aug^^^^^5886
1434^2466^344^348^386^399^539^642^665^742^ined (-11% at ambient and -13% at elevated CO2). Nevertheless, at the stand level, growth at +2.5 degrees C reduced transpiration due to fewer tillers per plant and a smaller leaf area per tiller, This sparser vegetation was alsA^5885^The variations of leaf carbohydrate concentration, carbon isotope discrimination (Delta) of leaf soluble carbohydrate, gas-exchange and growth during a soil drying cycle under 350 and 700 mu mol mol(-1) CO2 concentrations ([CO2]) in Quercus robur seedlings were analysed. In well-watered conditions, a doubling of [CO2] caused an increase of CO2 assimilation rate (A) (+47%) and a decrease of stomatal conductance for water vapour (g) (-25%), and doubled the intrinsic water-use efficiency (A/g). The values of Delta were not affected by elevated [CO2] which was consistent with the 2-fold increase of A/g. Elevated [CO2] also significantly increased sucrose and starch leaf concentrations as well as aerial growth and plant dry weight. The stimulating effect of CO2 enrichment on A and A/g was maintained in moderate drought conditions, but disappeared in the most severe drought conditions, Drought induced an increase of hexose concentrations in both [CO2], but this effect was more pronounced under elevated [CO2], which may contribute to increase osmoregulation, From the onset of drought, starch was depleted in both [CO2]. Carbon isotope discrimination decreased in response to drought, which corresponded to an increase in A/g according to the two-step model of isotopic discrimination, In contrast, the A/g values derived from instantaneous leaf gas-exchange measurements decreased along the drying cycle, The discrepancy observed between the two independent estimates of water-use efficiency is discussed in terms of time-scale integration. The results obtained with the isotopic approach using soluble carbohydrate suggest a predominant stomatal limitation of CO2 assimilation in response to drought.

1553^5^Prior,SA^Pritchard,SG^Runion,GB^Rogers,HH^Mitchell,RJ^1997^1^Influence of atmospheric CO2 enrichment, soil N, and water stress on needle surface wax formation in Pinus palustris (Pinaceae)^5^84^8^1070-1077^^^^^Aug^^^^^5888
1262^1788^1901^243^348^361^385^398^57^92^ut this effect was more pronounced under elevated [CO2A^5887^Interactive effects of increasing atmospheric CO2 with resource limitations on production of surface wax in plants have not been studied. Pinus palustris seedlings were grown for 1 yr at two levels of soil N (40 or 400 kg N.ha(-1).yr(-1)) and water stress (-0.5 or -1.5 MPa xylem pressure potential) in open-top field chambers under two levels of CO2 (365 or 720 mu mol/mol). Needle surface wax content was determined at 8 mo (fall) and 12 mo (spring) and epicuticular wax morphology was examined using scanning electron microscopy (SEM) at 12 mo. Wax content expressed on both a leaf area and dry mass basis was increased due to main effects of low N and water stress. No main effects of CO2 were observed; however, a CO2 x N interaction at 12 mo indicated that under low soil N the elevated CO2 treatment had less wax (surface area or dry mass basis) compared to its ambient counterpart. Morphologically, low N needle surfaces appeared rougher compared to those of high N needles due to more extensive wax ridges. Although the main effect of water treatment on wax density was not reflected by changes in wax morphology, the CO2 x N interaction was paralleled by alterations in wax appearance. Decreases in density and less prominent epicuticular wax ridges resulting from growth under elevated CO2 and limiting N suggest that dynamics of plant/atmosphere and plant/pathogen interactions may be altered.

1554^6^Reichenauer,T^BolharNordenkampf,HR^Ehrlich,U^Soja,G^Postl,WF^Halbwachs,F^1997^1^The influence of ambient and elevated ozone concentrations on photosynthesis in Populus nigra^9^20^8^1061-1069^^^^^Aug^^^^^5890
1517^1553^256^348^386^417^444^446^493^73^s of low N and water stress. No main effects of CO2 were observed; however, a CO2 x N interaction at 12 mo indicated that under low soil N the elevated CO2 treatment had less wax (surface area or dry mass basis) compared to its ambient counterpart. Morphologically, low N needle surfaces appeared rougher compared to those of high N needles due to more extensive wax ridges. A^5889^Light-saturated net leaf photosynthesis (A(sat)), CO2 response curves (A/C-i), current photochemical capacity (F-v/F-m) and pigment contents were measured in leaves of Populus nigra (Clone T107) which had been exposed to ozone stress in open-top chambers for the entire growth period. Surprisingly, not only elevated (ao(+), i.e. ambient air + 50 mm(3) m(-3) ozone) but also ambient (aa) ozone concentrations led to a reduction in A(sat) in comparison with leaves exposed to air containing almost no ozone (cf(-), i.e. charcoal filtered ambient air). The very small change in leaf conductance (g(l)) indicated that the decrease in A(sat) was not due to stomatal limitation. This finding was supported by the fact that, a decrease in carboxylation efficiency (CE) correlated with a loss in A(sat). In comparison to cf-leaves, aa leaves showed no change in current photochemical capacity (F-v/F-m) throughout the whole experiment. However, a marked decline in F-v/F-m in ao(+) leaves was observed at a time when A(sat) and CE were already decreased by about 45% and 60% respectively. As the chlorophyll b content of leaves is known to correlate with the amount of LHC and PSII centres, it was used to normalize fluorescence parameters in relation to PSII centres present. The normalized values for F-m and F-O increased with the dosage of ozone in ao(+) leaves but not in aa leaves, indicating a change of the pigment content of PSII in the former, but not in the latter. These data led to the conclusion that ozone interacts primarily with components of the Calvin cycle, which results in a decrease in A(sat) with subsequent feedback on the current photochemical capacity of PSII centres.

1555^4^Rillig,MC^Scow,KM^Klironomos,JN^Allen,MF^1997^1^Microbial carbon-substrate utilization in the rhizosphere of Gutierrezia sarothrae grown in elevated atmospheric carbon dioxide^130^29^9-10^1387-1394^^^^^Sep-Oct^^^^^5892
1044^1096^174^1781^2467^374^56^711^778^ver, a marked decline in F-v/F-m in ao(+) leaves was observed at a time when A(sat)A^5891^Differences in rhizosphere microbial community function in response to Gutierrezia sarothrae plants grown in elevated CO2 (750 mu l l(-1)) and fertilized with nitrogen were studied using the Biolog microplate analysis of sole C substrate utilization. Compared to ambient CO2 under elevated CO2, polymers were more slowly oxidized by the microbial community, amides showed no change in usage, and all other substrate groups were more rapidly utilized, although there was no significant change in the number of viable bacteria. No microbial community responses to N fertilization were detected. The results indicate that potential functional changes in the soil microbial community in response to elevated CO2 have to be taken into account in future experiments. Differential use of rhizo-deposits in elevated CO2 may have important consequences for biogeochemistry and plant growth. (C) 1997 Elsevier Science Ltd.
67^374^56^711^778^ver, a marked decline in F-v/F-m in ao(+) leaves was observed at a time when A(sat)1556^2^Syvertsen,J^Graham,JH^1997^1^Carbon budgets of two Citrus sp. in response to elevated CO2 VA mycorrhizae and phosphorus status^8^114^3^111^^^^^Jul

1557^5^Tingey,DT^Phillips,DL^Johnson,DG^Johnson,DW^Weber,JA^1997^1^Elevated CO2 increases fine root growth and fine root turnover in Pinus ponderosa^8^114^3^1358^^^^^Jul

1558^4^Vu,JCV^Allen,LH^Bowes,G^Boote,KJ^1997^1^Kinetic properties of rubisco in rice and soybean grown under elevated CO2, supraoptimal temperature, and drought^8^114^3^1092^^^^^Jul

1559^2^Watling,JR^Press,MC^1997^1^How does elevated CO2 affect the relationship between the C-3 root hemiparasite Striga hermonthica and the C-4 host Sorghum bicolor?^8^114^3^46^^^^^Jul

1560^2^Will,RE^Ceulemans,R^1997^1^Effects of elevated CO2 concentration on photosynthesis, respiration and carbohydrate status of coppice Populus hybrids^37^100^4^933-939^^^^^Aug^^^^^5898
1014^147^2468^2469^341^344^358^384^520^92^^56^711^778^ver, a marked decline in F-v/F-m in ao(+) leaves was observed at a time when A(sat)A^5897^To determine how increased atmospheric CO2 will affect the physiology of coppiced plants, sprouts originating from two hybrid poplar clones (Populus trichocarpa x P. deltoides - Beaupre and P. deltoides x P. nigra - Robusta) were grown in open-top chambers containing ambient or elevated (ambient + 360 mu mol mol(-1)) CO2 concentration. The effects of elevated CO2 concentration on leaf photosynthesis, stomatal conductance, dark respiration, carbohydrate concentration and nitrogen concentration were measured. Furthermore, dark respiration of leaves was partitioned into growth and maintenance components by regressing specific respiration rate vs specific growth rate. Sprouts of both clones exposed to CO2 enrichment showed no indication of photosynthetic down-regulation. During reciprocal gas exchange measurements, CO2 enrichment significantly increased photosynthesis of all sprouts by approximately 60% (P < 0.01) on both an early and late season sampling date, decreased stomatal conductance of all sprouts by 10% (P < 0.04) on the early sampling date and nonsignificantly decreased dark respiration by an average of 11%. Growth under elevated CO2 had no consistent effect on foliar sugar concentration but significantly increased foliar starch by 80%. Respiration rate was highly correlated with both specific growth rate and percent nitrogen. Long-term CO2 enrichment did not significantly affect the maintenance respiration coefficient or the growth respiration coefficient. Carbon dioxide enrichment affected the physiology of the sprouts the same way it affected these plants before they were coppiced.

1561^8^Willekens,H^Chamnongpol,S^Davey,M^Schraudner,M^Langebartels,C^VanMontagu,M^Inze,D^VanCamp,W^1997^1^Catalase is a sink for H2O2 and is indispensable for stress defence in C-3 plants^323^16^16^4806-4816^^^^^15 Aug^^^^^5900
1676^1677^1950^2128^2369^2470^2471^2472^2473^2474^ of all sprouts by approximately 60% (P < 0.01) on both an early and late season sampling date, decreased stomatal conductance of all sproutA^5899^Hydrogen peroxide (H2O2) has been implicated in many stress conditions, Control of H2O2 levels is complex and dissection of mechanisms generating and relieving H2O2 stress is difficult, particularly in intact plants, We have used transgenic tobacco with similar to 10% wild-type catalase activity to study the role of catalase and effects of H2O2 stress in plants, Catalase-deficient plants showed no visible disorders at low Light, but in elevated light rapidly developed white necrotic lesions on the leaves, Lesion formation required photorespiratory activity since damage was prevented under elevated CO2, Accumulation of H2O2 was not detected during leaf necrosis, Alternative H2O2-scavenging mechanisms may have compensated for reduced catalase activity, as shown by increased ascorbate peroxidase and glutathione peroxidase levels, Leaf necrosis correlated with accumulation of oxidized glutathione and a 4-fold decrease in ascorbate, indicating that catalase is critical for maintaining the redox balance during oxidative stress, Such control may not be limited to peroxisomal H2O2 production, Catalase functions as a cellular sink for H2O2, as evidenced by complementation of catalase deficiency by exogenous catalase, and comparison of catalase- deficient and control leaf discs in removing external H2O2. Stress analysis revealed increased susceptibility-of catalase- deficient plants to paraquat, salt and ozone, but not to chilling.

1562^3^Wolfe,DW^Melkonian,JJ^Boese,SR^1997^1^Elevated CO2 ameliorates chilling-induced water stress, photosynthetic depression, and leaf damage^8^114^3^483^^^^^Jul

1563^3^Yearsley,CW^Banks,NH^Ganesh,S^1997^1^Effect of carbon dioxide on the internal lower oxygen limits of apple fruit^259^12^1^1-13^^^^^Aug^^^^^5903
1000^130^174^2475^310^418^wn by increased ascorbate peroxidase and glutathione peroxidase levels, Leaf necrosis correlated with accumulation of oxidized glutathione and a 4-fold decrease in ascorbate, indicating that catalase is critical for maintaining the redox balance durA^5902^The effect of elevated CO2 between 0 and 8 kPa on steady-state lower O-2 limits based on internal atmospheres (LOLi) was estimated for postclimacteric 'Cox's Orange Pippin' and 'Braeburn' apples at 0 and 20 degrees C. Two types of LOLi were estimated: the anaerobic compensation point (ACP(i)), and the internal fermentation threshold based either on the respiratory quotient (FTRQi) or ethanol (EtOH) accumulation (FTEtOHi). ACP(i), for both cultivars and temperatures, remained constant at 0.5 kPa O-2 for 'Cox's Orange Pippin' and 0.8-1.0 O-2 for 'Braeburn' apples for levels of CO2 external to the fruit between 0 and 8 kPa. However, for FTRQi and FTEtOHi no consistent trend with level of CO2 was evident at 20 degrees C for either cultivar. In contrast, at 0 degrees C FTRQi and FTEtOHi were 0.2-0.8 kPa O-2 higher at 8 kPa CO2 than at 0 kPa CO2 (with the exception of FTRQi for 'Cox's Orange Pippin'). A small decrease in O-2 uptake (estimated from the difference in external and internal O-2 atmospheres) was observed between 2 and 8 kPa CO2 at 20 degrees C. Elevated CO2 slightly lowered the respiratory quotient (RQ(i), estimated from the ratio of differences between external and internal atmosphere partial pressures of CO2 and O-2) of 'Cox's Orange Pippin' in 8 kPa CO2 and 'Braeburn' in 2 to 8 kPa CO2 at 20 degrees C, and more markedly in 8 kPa CO2 at 0 degrees C. The RQ(i) of 'Cox's Orange Pippin' and 'Braeburn' apples was slightly and markedly higher respectively at 0 degrees C compared to 20 degrees C, The lower RQ(i) of 'Braeburn' at 20 degrees C compared to 'Cox's Orange Pippin' apples indicated 'Braeburn had a higher permeance to CO2 relative to O-2 compared to 'Cox's Orange Pippin'. This study indicates the tolerance of 'Cox's Orange Pippin' and 'Braeburn' apples to low O-2 levels may be affected by levels of CO2. (C) 1997 Elsevier Science B.V.
th the exception of FTRQi for 'Cox's Orange Pippin'). A small decrease in O-2 uptake (estimated from the difference in external and internal O-2 atmospheres) was1564^10^Zanetti,S^Hartwig,UA^vanKessel,C^Luscher,A^Hebeisen,T^Frehner,M^Fischer,BU^Hendrey,GR^Blum,H^Nosberger,J^1997^1^Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes?^2^112^1^17-25^^^^^^^^^^5905
130^2476^344^372^376^427^506^56^672^92^burn' in 2 to 8 kPa CO2 at 20 degrees C, and more markedly in 8 kPa CO2 at 0 degrees C. The RQ(i) of 'Cox's Orange Pippin' and 'Braeburn' apples was slightly and markedly higher respectively at 0 degrees C compared to 20 degrees C, The lower RQ(i) of 'Braeburn' at 20 degrees C compared to 'Cox's Orange Pippin' apples indicated 'Braeburn had a higher permeance to CO2 relative to O-2 compared to 'Cox's Orange Pippin'. This study indicates the tolerance of 'Cox's Orange Pippin' and 'Braeburn' apples to low O-2 levels may be affected by levels of CO2. (C) 1997 Elsevier Science B.V.
th the exception of FTRQi for 'Cox's Orange Pippin'). A small decrease in O-2 uptake (estimated from the difference in external and internal O-2 atmospheres) wasA^5904^The extent of the response of plant growth to atmospheric CO2 enrichment depends on the availability of resources other than CO2. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO2 response of plants. The effect of elevated CO2 (60 Pa) partial pressure (pCO(2)) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO(2), the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N- limited biomass production) under elevated pCO(2), the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO(2) than under ambient pCO(2) in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO(2) was evoked indirectly by a reduction of plant- available N. For L. perenne grown in association with T. repens and exposed to elevated pCO(2) there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained by an increased apparent transfer of N from the associated N-2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under elevated pCO(2). All the additional N yielded was due to symbiotically fixed N. Through the presence of an N-2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation under elevated pCO(2).
N- limited biomass production) under elevated pCO(2), the index of1565^1^Ball,AS^1997^1^Microbial decomposition at elevated CO2 levels: effect of litter quality^127^3^4^379-386^^^^^Aug^^^^^5907
1823^2015^2477^344^374^407^430^658^672^693^nocultures. Thus, we suggest that reduced N yield under elevated pCO(2) was evoked indirectly by a reduction of plant- available N. For L. perenne grown in association with T. repens and exposed to elevated pCO(2) there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained by an increased apparent transfer of N from the associated N-2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under elevated pCO(2). All the additional N yielded was due to symbiotically fixed N. Through the presence of an N-2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation under elevated pCO(2).
N- limited biomass production) under elevated pCO(2), the index ofA^5906^The decomposition of senesced plant litter represents an important intermediate step in the cycling of nutrients between above-and below-ground systems. The rate of decomposition of plant litter is sensitive to fluctuations in a number of parameters, including environmental conditions, and particularly to changes in the quality of the litter. Increased C:N ratios of litter are thought to be one possible consequence of growth of plants under elevated [CO2]. This response is likely to reduce the rate of decomposition of the litter. Evidence from the growth of plants in both pot and field studies suggests that growth of C3 plants in elevated atmospheric [CO2] (600-700 mu mol mol(-1)) may lead to a significant increase in either/both the C:N and the lignin: N ratios of litter. Short-term decomposition of lifter from plants showing this response in elevated [CO2] has confirmed that decomposition occurs at a significantly lower rate. The limited studies of both the response of C4 plants to elevated [CO2] and the subsequent degradability of the senescent litter suggest that no differences in litter quality or degradability occur. In terms of litter quality the response of plants therefore appears to be dependent upon photosynthetic type; the C:N and lignin:N ratios of litter from C3 plants exposed to elevated [CO2] are increased, leading to lower degradation rates, while the nutrient ratios and degradation rates of lifter from C4 plants grown in elevated [CO2] remain unchanged. To date, very few ecosystem studies of decomposition have been carried out. Further work is required at the ecosystem level to determine whether the effects observed in laboratory, pot and field studies are also observed in long-term, complex ecosystem studies. Clearly if these results are repeated at the ecosystem level then significant changes in the cycling of C and N in important terrestrial ecosystems may occur as a results of elevated [CO2].
tly lower rate. The limited studies of both the response of C4 plants to elevated [CO2] an1566^2^Berntson,GM^Bazzaz,FA^1997^1^Elevated CO2 and the magnitude and seasonal dynamics of root production and loss in Betula papyrifera^206^190^2^211-216^^^^^Mar^^^^^5909
1829^2478^2479^374^377^538^57^672^ upon photosynthetic type; the C:N and lignin:N ratios of litter from C3 plants exposed to elevated [CO2] are increased, leading to lower degradation rates, while the nutrient ratios and degradation rates of lifter from C4 plants grown in elevated [CO2] remain unchanged. To date, very few ecosystem studies of decomposition have been carried out. Further work is required at the ecosystem level to determine whether the effects observed in laboratory, pot and field studies are also observed in long-term, complex ecosystem studies. Clearly if these results are repeated at the ecosystem level then significant changes in the cycling of C and N in important terrestrial ecosystems may occur as a results of elevated [CO2].
tly lower rate. The limited studies of both the response of C4 plants to elevated [CO2] anA^5908^The impact of elevated atmospheric CO2 on belowground plant growth is poorly understood relative to its effects on aboveground growth. We carried out a study of the seasonal dynamics of gross root production and death to determine how elevated CO2 affected the dynamics of net and gross root production through a full growing season. We quantified gross root production and root loss from sequential, in situ images of fine roots of Betula papyrifera in ambient (375 ppm.) and elevated (700 ppm) CO2 atmospheres from 2 weeks following germination through leaf senescence. We found that elevated CO2 led to increases in the magnitude of cumulative gross production (Sigma P) and cumulative gross loss (Sigma L) of roots. However, the effect of elevated CO2 on these processes was seasonally dependent. Elevated CO2 led to greater levels of enhancement in Sigma P early in the growing season, prior to maximum standing root length (NP). In contrast, elevated CO2 led to greater levels of enhancement in Sigma L in the last half of the growing season, after maximum NP had been reached. This difference in the timing of when elevated CO2 affects Sigma P and Sigma L led to a transitory, early enhancement in NP. By the end of the growing season, there was no significant effect of elevated CO2 on NP, and Sigma P was 87% greater than NP for ambient CO2 and 117% greater in elevated CO2. We conclude that static assessments of belowground productivity may greatly underestimate gross fine root productivity and turnover and this bias can be exaggerated with elevated CO2.

1567^4^Bertani,A^Brambilla,I^Mapelli,S^Reggiani,R^1997^1^Elongation growth in the absence of oxygen: The rice coleoptile^236^44^4^543-547^^^^^Jul-Aug^^^^^5911
1191^2480^2481^2482^2483^2484^361^519^629^739^CO2 on these processes was seasonally dependent. Elevated CO2 led to greater levels of enhancement in Sigma P early in the growing season, prior to maximum standing root length (NP). In contrast, elevated CO2 led to greater levels of enhancement in Sigma L in the A^5910^Rice, one of the few plant species adapted to growth in wetland conditions, is able to germinate in waterlogged soils promoting only the growth of a white coleoptile in order to reach the surface of the water, contact the atmosphere, and transfer oxygen to the seed, allowing subsequent growth of the radicle and leaf. In the anoxic cells of rice coleoptiles, an efficient alcoholic fermentation allows an elevated energy charge to be maintained. Significant RNA and protein syntheses including phosphorylation and glycosylation occur too. The cytoplasmic pH is maintained at a level far from acidosis. The anoxic growth of rice coleoptiles, essentially an elongation growth, is sustained by a high turgor pressure, with free amino acids and potassium as main components. Among the metabolic processes involved in the regulation of the elongation of rice coleoptiles, a crucial role is played by amino acid metabolism and the accumulation of putrescine, which is able to stimulate plasmalemma ATPase activity. Anaerobic elongation is also stimulated in the presence of 20% CO2 in the growth medium, inhibited by light and abscisic acid, unaffected by ethylene, and slightly promoted by auxin. The role of both metabolites and hormones along with environmental factors in maintaining cellular homeostasis and coleoptile elongation are reconsidered and discussed in Light of new data.

1568^3^Bukhov,NG^Boucher,N^Carpentier,R^1997^1^Aftereffect of short-term heat shock on photosynthetic reactions in barley leaves^236^44^4^526-532^^^^^Jul-Aug^^^^^5913
1085^1092^1116^1190^130^2233^2485^2486^493^637^a level far from acidosis. The anoxic growth of rice coleoptiles, essentially an elongation growth, is sustained by a high turgor pressure, with free amino acids and potassium as main components. Among the metabolic processes involved in the regulation of the elongation of rice coleoptiles, a crucial role is played by amino acid metabolism and the accumulation of putrescine, which is able to stimulate plasmalemma ATPase activity. AnaeroA^5912^Effects of preheating 8- to 10-day-old barley (Hordeum vulgare L.) leaves at 40-46 degrees C on oxygen evolution, chlorophyll fluorescence, and photoacoustic signals were examined. Preheating of leaves at 40 degrees C led to a threefold decrease in the initial slope of the light-response curve of photosynthesis and a marked enhancement of the nonphotochemical quenching of chlorophyll fluorescence, which indicates a drastic increase in the nonradiative dissipation of absorbed light quanta. The maximum photosynthetic activity attained at saturating light and elevated CO2 concentration was suppressed by this heat treatment by no more than 30%. The photochemical activity of PS LT reaction centers in dark-adapted leaves also decreased to the same extent after the heat treatment. In preheated leaves, strong light pulses increased the photobaric component of the photoacoustic signal (measured at 35 Hz) instead of suppressing the signal. The magnitude of the rise- phase of the photoacoustic signal increased with the preheating temperature. An enhancement of the photoacoustic signal induced by strong light pulses was also observed in leaves in which the normal photosynthetic process was disturbed by feeding them methylviologen. It is concluded that the short-term heating of leaves impairs photochemical conversion of light quanta in reaction centers of PS II due to an increase in the magnitude of the proton gradient across the thylakoid membrane. This indicates that dark reactions of photosynthesis in preheated leaves cannot efficiently use the ATP and reduced NADP formed in the course of photosynthetic electron transport.

1569^2^Casella,E^Soussana,JF^1997^1^Long-term effects of CO2 enrichment and temperature increase on the carbon balance of a temperate grass sward^78^48^311^1309-1321^^^^^Jun^^^^^5915
1234^1262^1290^2487^360^372^444^507^57^92^baric component of the photoacoustic signal (measured at 35 Hz) instead of suppressing the signal. The magnitude of the rise- phase of the photoacoustic signal increased wA^5914^Perennial ryegrass swards were grown in large containers on a soil, at two N fertilizer supplies and were exposed during two years in highly ventilated plastic tunnels to elevated (700 mu l l(-1) [CO2]) or ambient atmospheric CO2 concentration at outdoor temperature and to a 3 degrees C increase in air temperature in elevated CO2. The irrigation was adjusted to obtain a soil water deficit during summer. The daily net C assimilation was increased in elevated CO2 by 29 and 36% at the low and high N supplies, respectively, Canopies grown in elevated CO2 for 14 to 27 months photosynthetized significantly less rapidly, in both elevated and normal CO2 concentrations, than their counterparts developed in ambient CO2, but the magnitude of this effect was small (-8% to -13%). Elevated CO2 resulted in a large increase in the fructan concentration in the pseudostems and laminae (+46% and +189%, respectively). In elevated CO2, the hexose and sucrose pool increased by 28% in the laminae, whereas it did not vary significantly in the pseudo-stems, A 3 degrees C temperature increase in elevated CO2 did not affect significantly the average WSC concentrations in the pseudostems and laminae, The elevated CO2 effects on the net C assimilation and on the nocturnal shoot respiration were greater in summer than in spring. On average, a 35% increase in the below-ground respiration was measured in elevated CO2. At the high N supply, a 3 degrees C increase in air temperature led to a decline in the below-ground respiration due to a low soil moisture, The below-ground carbon storage was increased by 32% and 96% in elevated CO2 at the low and high N supplies, respectively, with no significant increased temperature effect. The role for the below-ground carbon storage of CO2-induced changes in the root fraction of the grass and of temperature- induced changes in the moisture content of the soil are discussed.
189%, respectively). In elevated CO2, the hexose and sucrose pool increased by 28% in the laminae, whereas it did not vary si1570^2^Coughenour,MB^Chen,DX^1997^1^Assessment of grassland ecosystem responses to atmospheric change using linked plant-soil process models^56^7^3^802-827^^^^^Aug^^^^^5917
1298^137^2488^2489^256^312^497^508^687^742^imilation and on the nocturnal shoot respiration were greater in summer than in spring. On average, a 35% increase in the below-ground respiration was measured in elevated CO2. At the high N supply, a 3 degrees C increase in air temperature led to a decline in the below-ground respiration due to a low soil moisture, The below-ground carbon storage was increased by 32% and 96% in elevated CO2 at the low and high N supplies, respectively, with no significant increased temperature effect. The role for the below-ground carbon storage of CO2-induced changes in the root fraction of the grass and of temperature- induced changes in the moisture content of the soil are discussed.
189%, respectively). In elevated CO2, the hexose and sucrose pool increased by 28% in the laminae, whereas it did not vary siA^5916^Models of photosynthesis, plant growth, and biophysical processes were linked with models that simulate water, nutrient, and carbon flows through plant-soil ecosystems. The linked ecosystem model was applied to examine ecosystem-level responses to CO2, temperature, precipitation, and global- warming scenarios in grasslands of Colorado and Kansas, USA, and Kenya. The model predicted that increased temperatures would decrease primary production at current CO2 levels, but decreases were reversed by doubling atmospheric CO2 concentration. Greater increases in daily minimum temperatures than daily maximum temperatures mitigated reductions in photosynthesis and water-use efficiency (WUE) later in the day, more than offseting increases in nighttime respiration rates under warmer temperatures. A temperature increase of 5 degrees C reduced organic carbon in grassland soils by 20-30%, through effects on plant growth and decomposition, but the doubled CO2 negated soil carbon losses by increasing plant growth. Under higher precipitation and doubled CO2, soil carbon stocks increased, or decreased little, in response to warmer temperatures. Doubling CO2 increased net primary production (NPP) by 31-45% in a simulated Colorado C-4 grassland, by 20- 70% in a Colorado C-3 grassland, by 23-31% in a Kansas C-4 grassland, and by 23-35% in a Kenya C-4 grassland at ambient precipitation levels. Growth was shifted belowground, thus weakening aboveground responses. Higher temperatures strengthened the positive NPP responses to CO2. Larger positive responses to elevated CO2 were modeled under drier conditions, and smaller responses were modeled under wetter conditions. NPP increases under elevated CO2 were mostly caused by increased plant WUE at all sites, which was brought about by partial stomatal closure. Decreased N concentrations in plant litter under elevated CO2 slowed N mineralization, but greater plant production and thus greater litter inputs into the soil under elevated CO2 offset the negative effects of lower litter quality. Decreases in plant N concentration under elevated CO2 also reduced plant N requirements. At current atmospheric CO2 (350 mu mol/mol), a general circulation model (GCM) climate- change scenario decreased NPP and soil organic matter (SOM) in Colorado but not in Kansas or Kenya. A second GCM climate- change scenario either affected NPP and SOM little, or increased NPP and SOM at current CO2. NPP and SOM responses in the simulated grasslands were very sensitive to precipitation, which GCMs predict with relatively low confidence. Doubled CO2 partially or completely offset decreases in NPP and SOM under climate-change scenarios.

1571^2^Crowley,TJ^Baum,SK^1997^1^Effect of vegetation on an ice-age climate model simulation^278^102^D14^16463-16480^^^^^27 Jul^^^^^5919
1595^2349^2368^2490^2491^2492^2493^2494^656^905^n plant litter under elevated CO2 slowed N mineralization, but greater plant production and thus greater litter inputs into the soil under elevated CO2 offset the negative effects of lower litter qA^5918^A growing number of studies suggest that vegetation changes can significantly influence regional climate variations. Herein we utilize a climate model (GENESIS) with a land surface vegetation package to evaluate the potential role of the very large vegetation changes that occurred during the last glacial maximum (LGM), In particular, we focus on the potential response to a significant reduction in the area of tropical rainforest. Simulations employed a global vegetation reconstruction for the LGM and Climate/Long-Range Investigation, Mapping and Prediction (CLIMAP) sea surface temperature (SST) estimates. Results indicate that expansion of dryland vegetation causes a 15-30% additional LGM cooling for Australia (0.4 degrees C) and Africa (0.9 degrees C), respectively, Turnover from conifer to tundra also causes cooling of 2 degrees-4 degrees C or mon in western Europe and Siberia. However, for the largest rainforest area (Amazon Basin), inclusion of realistic vegetation increased modeled temperatures 2 degrees-4 degrees C and decreased precipitation by 10-35%. These latter results are similar to those obtained with sensitivity experiments of the effects of future Amazon deforestation, Initial assessment of the potential effect of decreased stomatal resistance due to lower ice age CO2 levels indicates little significant response to this effect. Comparison of model-predicted low-elevation LGM temperature Changes with estimates from proxy data indicate that inclusion of realistic vegetation estimates for the LGM results in slightly more than 50% agreement between models and data for low-elevation sites in low-mid latitudes. Data at variance with model predictions would appear to be explainable by considering additional changes in vegetation, ice age dust, or a 1 degrees- 2 degrees C cooling below CLIMAP values. This conclusion is at Variance with a 3 degrees-4 degrees C tropical cooling suggested by some studies for explaining estimated land temperature changes during the LGM. In some western European sites model temperatures are colder than proxy data by 2 degrees-8 degrees C. This model-data discrepancy may be explained by less sea ice in the subpolar North Atlantic than stipulated by CLIMAP, a conclusion consistent with new marine data from that region.

1572^4^Falge,E^Ryel,RJ^Alsheimer,M^Tenhunen,JD^1997^1^Effects of stand structure and physiology on forest gas exchange: a simulation study for Norway spruce^252^11^7^436-448^^^^^Aug^^^^^5921
2036^243^2495^314^372^385^465^484^729^783^tation estimates for the LGM results in slightly more than 50% agreement between models and data for low-elevation sites in low-mid latitudes. Data at variance with model predictions would appear to be explainable by considering additional changes in vegetation, ice age dust, or a 1 degrees- 2 degrees C cooling below CLIMAP values. This conclusion is at Variance with a 3 degrees-4 degrees C tropical cooling suggested by some studies for explaining estimated land temperature changes during the LGM. In some western European sites A^5920^The process-based simulation model STAND-FLUX describes canopy water vapor and carbon dioxide exchange based on rates calculated for individual trees and as affected by local gradients in photon flux density (PFD), atmospheric humidity, atmospheric carbon dioxide concentration, and air temperature. Direct, diffuse, and reflected PFD incident on foliage elements within compartments of individual trees (defined by vertical layers and a series of concentric cylinders centered on the trunk) is calculated for a 3-dimensional matrix of points. Foliage element gas exchange rates are based on estimates of carboxylation, RuBP regeneration, and respiratory capacities as well as the correlated behavior found between stomatal conductance and assimilation rate. Because of the difficulties associated with effective sampling and description of spatial variation in structure and leaf level gas exchange parameters for trees comprising the forest canopy, the significance for canopy water and carbon dioxide exchange of varied representations of tree foliage distribution and of physiology is examined. The additional interactive effects encountered due to changes in tree density and, thus, spatial aggregation or disaggregation of foliage is also studied. The analysis is conducted within the context of observed structural and physiological variation encountered in Norway spruce (Picea abies) stands in the Fichtelgebirge region of central Germany. Potentials for simplifying the three-dimensional canopy gas exchange model without sizable influence on canopy flux rates were small. A relatively large number of sample points within the tree crowns is necessary to obtain consistent calculations of flux rates because of the nonlinear relationship between PFD and net photosynthesis. Transpiration and net photosynthesis for stands with a low leaf area index (LAI) may be obtained from single tree estimates for each tree class weighted by class frequency, while 30 or more trees per class in differing relation to neighboring trees may be necessary to calculate reliable estimates of net photosynthesis in canopies with high LAI. The complexity in structure assumed for modeled trees was important, especially when overall canopy foliage area was either high or low due to spatial heterogeneity in clumping, e.g., potential canopy overlaps or side-lighting. Effects were greater for calculated net photosynthesis than for transpiration, reflecting higher sensitivity of net photosynthesis to differences in light distribution within individual trees. Accuracy in estimates of physiological parameters is equally important, and these characteristics have profound effects on estimated canopy gas exchange rates. While one-dimensional representations of canopy structure or approximations of tree physiological characteristics from other canopies or species may often be necessary in assessing vegetation/atmosphere exchanges, especially in the study of water balance of landscapes or regions, STANDFLUX provides a tool that can aid in evaluating the limitations of these simpler approaches.

1573^5^FerrarioMery,S^Thibaud,MC^Betsche,T^Valadier,MH^Foyer,CH^1997^1^Modulation of carbon and nitrogen metabolism, and of nitrate reductase, in untransformed and transformed Nicotiana plumbaginifolia during CO2 enrichment of plants grown in pots and in hydroponic culture^6^202^4^510-521^^^^^Aug^^^^^5923
1768^1846^188^243^2496^2497^344^360^618^813^r transpiration, reflecting higher sensitivity of net photosynthesis to differences in light distribution within individual trees. Accuracy in estimates of physiological parameters is equally important, and these characteristics have profound effects on estimated canopy gas exchange rates. While one-dimensional representations of canopy structure or approximations of tree physiological characteristics from other canopies or species may often be necessary in assessing vegetation/atmosphere exchanges, especially in the study of water balance of landscapes or regions, STANDFLUX provides a tool that can aid in evaluating the limitations A^5922^Transformed plants of Nicotiana plumbaginifolia Viv. constitutively expressing nitrate reductase (35S-NR) or beta- glucuronidase (35S-GUS) and untransformed controls were grown for two weeks in a CO2-enriched atmosphere. Whereas CO2 enrichment (1000 mu l. 1(-1)) resulted in an increase in the carbon (C) to nitrogen (N) ratio of both the tobacco lines grown in pots with vermiculite, the C/N ratio was only slightly modified when plants were grown in hydroponic culture in high CO2 compared to those grown in air. Constitutive nitrate reductase (NR) expression per se did not change the C/N ratio of the shoots or roots. Biomass accumulation was similar in both types of plant when hydroponic or pot-grown material, grown in air or high CO2, were compared. Shoot dry matter accumulation was primarily related to the presence of stored carbohydrate (starch and sucrose) in the leaves. In the pot- grown tobacco, growth at elevated CO2 levels caused a concomitant decrease in the N content of the leaves involving losses in NO3- and amino contrast, the N content and composition were similar in all plants grown in hydroponic culture. The 35S-NR plants grown in air had higher foliar maximum extractable NR activities and increased glutamine levels (on a chlorophyll or protein basis) than the untransformed controls. These increases were maintained following CO2 enrichment when the plants were grown in hydroponic culture, suggesting that an increased flux through nitrogen assimilation was possible in the 35S-NR plants. Under CO2 enrichment the NR activation state in the leaves was similar in all plants. When the 35S-NR plants were grown in pots, however, foliar NR activity and glutamine content fell in the 35S-NR transformants to levels similar to those of the untransformed controls. The differences in NR activity between untransformed and 35S-NR leaves were much less pronounced in the hydroponic than in the pst-grown material but the difference in total extractable NR activity was more marked following CO2 enrichment. Foliar NR message levels were decreased by CO2 enrichment in all growth conditions but this was much more pronounced in pot-grown material than in that grown hydroponically. Since beta-glucuronidase (GUS) activity and message levels in 35S-GUS plants grown under the same conditions of CO2 enrichment (to test the effects of CO2 enrichment on the activity of the 35S promoter) were found to be constant, we conclude that NR message turnover was specifically accelerated in the 35S-NR plants as well as in the untransformed controls as a result of CO2 enrichment. The molecular and metabolic signals involved in increased NR message and protein turnover are not known but possible effecters include NO3-, glutamine and asparagine. We conclude that plants grown in hydroponic culture have greater access to N than those grown in pots. Regardless of the culture method, CO2 enrichment has a direct effect on NR mRNA stability.
ial but the difference in total extractable NR activity was more marked following CO2 enrichment. Foliar1574^3^Gouk,SS^Yong,JWH^Hew,CS^1997^1^Effects of super-elevated CO2 on the growth and carboxylating enzymes in an epiphytic CAM orchid plantlet^4^151^2^129-136^^^^^Aug^^^^^5925
1124^130^1502^1669^243^312^376^779^781^788^evels in 35S-GUS plants grown under the same conditions of CO2 enrichment (to test the effects of CO2 enrichment on the activity of the 35S promoter) were found to be constant, we conclude that NR message turnover was specifically accelerated in the 35S-NR plants as well as in the untransformed controls as a result of CO2 enrichment. The molecular and metabolic signals involved in increased NR message and protein turnover are not known but possible effecters include NO3-, glutamine and asparagine. We conclude that plants grown in hydroponic culture have greater access to N than those grown in pots. Regardless of the culture method, CO2 enrichment has a direct effect on NR mRNA stability.
ial but the difference in total extractable NR activity was more marked following CO2 enrichment. FoliarA^5924^Responses of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPCase) to super-elevated CO2 were determined along with dry mass production, chlorophyll, soluble protein and nocturnal malate increases (NMI) for an epiphytic Crassulacean acid metabolism (CAM) orchid plantlet, Mokara Yellow. After S-month culture period, the total dry mass under super-elevated CO2 was 170% higher than the plantlets grown in 0.03% CO2; young leaf dry mass was 4-fold higher while the root dry mass increased 278% and 344% under 1% and 5% CO2 respectively. Higher root:shoot ratio was observed under super-elevated CO2; 0.22 in 0.03% CO2, 0.32 in 1% CO2 and 0.38 in 5% CO2. The averaged increase in total young leaf area was 244% and 373% under 1% and 5% CO2 respectively Leaf chlorophyll expressed per unit fresh weight was reduced under 5% CO2 but it increased 19% and 67% in old and young leaves of 3-month plantlets under 1% CO2. The root chlorophyll content increased 108% and 154% under 1%;, and 5% CO2 respectively. Soluble protein in young leaves increased 32% under 1% CO2 and 75% under 5% CO2, while the increase in root protein varied from 36% to 100%. The activities of Rubisco and PEPCase el:pressed per unit protein were reduced under super- elevated CO2, particularly in 5% CO2, the decreases ranged from 12% to 90% in Rubisco and 27% to 90% in PEPCase. Nevertheless, the leaf Rubisco:PEPCase ratio increased 110% to 362% under super-elevated CO2. Increased NMI, ranged from 23% to 182% under super-elevated CO2, contributed to the increased dry matter accumulation in Mokara plantlets. Throughout the S-month culture period, the CO2-enriched plantlets showed enhanced growth particularly under 1% CO2 in terms of biomass production, chlorophyll, soluble protein and NMI despite a concomitant decrease in the activities of the carboxylating enzymes.
O2 but it increased 19% and 67% in old and young leaves of 3-month plantlets under 1% CO2. The root chlorophyll content increased 108% and 154% 1575^5^Hogan,KP^Fleck,I^Bungard,R^Cheeseman,JM^Whitehead,D^1997^1^Effect of elevated CO2 on the utilization of light energy in Nothofagus fusca and Pinus radiata^78^48^311^1289-1297^^^^^Jun^^^^^5927
1092^130^243^2498^374^417^441^493^635^786^ were reduced under super- elevated CO2, particularly in 5% CO2, the decreases ranged from 12% to 90% in Rubisco and 27% to 90% in PEPCase. Nevertheless, the leaf Rubisco:PEPCase ratio increased 110% to 362% under super-elevated CO2. Increased NMI, ranged from 23% to 182% under super-elevated CO2, contributed to the increased dry matter accumulation in Mokara plantlets. Throughout the S-month culture period, the CO2-enriched plantlets showed enhanced growth particularly under 1% CO2 in terms of biomass production, chlorophyll, soluble protein and NMI despite a concomitant decrease in the activities of the carboxylating enzymes.
O2 but it increased 19% and 67% in old and young leaves of 3-month plantlets under 1% CO2. The root chlorophyll content increased 108% and 154% A^5926^Red beech (Nothofagus fusca (Hook. F.) Oerst.; Fagaceae) and radiata pine (Pinus radiata D. non; Pinaceae) were grown for 16 months in large open-top chambers at ambient (37 Pa) and elevated (66 Pa) atmospheric partial pressure of CO2, and in control plots (no chamber). Summer-time measurements showed that photosynthetic capacity was similar at elevated CO2 (light and CO2-saturated value of 17.2 mu mol m(-2) s(-1) for beech, 13.5 mu mol m(-2) s(-1) for pine), plants grown at ambient CO2 (beech 21.0 mu mol m(-2) s(-1), pine 14.9 mu mol m(-2) s(-1)) or control plants grown without chambers (beech 23.2 mu mol m(- 2) s(-1), pine 12.9 mu mol m(-2) s(-1)). However, the higher CO2 partial pressure had a direct effect on photosynthetic rate, such that under their respective growth conditions, photosynthesis for the elevated CO2 treatment (measured at 70 Pa CO2 partial pressure: beech 14.1 mu mol m(-2) s(-1) pine 10.3) was greater than in ambient (measured at 35 Pa CO2: beech 9.7 mu mol m(-2) s(-1), pine 7.0 mu mol m(-2) s(-1)) or control plants (beech 10.3 mu mol m(-2) s(-1), pine 7.2 mu mol m(-2) s(-1)). Measurements of chlorophyll fluorescence revealed no evidence of photodamage in any treatment for either species. the quantity of the photoprotective xanthophyll cycle pigments and their degree of de-epoxidation at midday did not differ among treatments for either species. The photochemical efficiency of photosystem II (yield) was lower in control plants than in chamber-grown plants, and was higher in chamber plants at ambient than at elevated CO2. These results suggest that at lower (ambient) CO2 partial pressure, beech plants may have dissipated excess energy by a mechanism that does not involve the xanthophyll cycle pigments.

1576^6^Hungate,BA^Holland,EA^Jackson,RB^Chapin,FS^Mooney,HA^Field,CB^1997^1^The fate of carbon in grasslands under carbon dioxide enrichment^36^388^6642^576-579^^^^^7 Aug^^^^^5929
243^374^416^456^57^715^803^812^894^92^nt (measured at 35 Pa CO2: beech 9.7 mu mol m(-2) s(-1), pine 7.0 mA^5928^The concentration of carbon dioxide (CO2) in the Earth's atmosphere is rising rapidly(1), with the potential to alter many ecosystem processes. Elevated CO2 often stimulates photosynthesis(2), creating the possibility that the terrestrial biosphere will sequester carbon in response to rising atmospheric CO2 concentration, partly offsetting emissions from fossil-fuel combustion, cement manufacture, and deforestation(3,4). However, the responses of intact ecosystems to elevated CO2 concentration, particularly the below-ground responses, are not well understood. Here we present an annual budget focusing on below-ground carbon cycling for two grassland ecosystems exposed to elevated CO2 concentrations. Three years of experimental CO2 doubling increased ecosystem carbon uptake, but greatly increased carbon partitioning to rapidly cycling carbon pools below ground, This provides an explanation for the imbalance observed in numerous CO2 experiments, where the carbon increment from increased photosynthesis is greater than the increments in ecosystem carbon stocks. The shift in ecosystem carbon partitioning suggests that elevated CO2 concentration causes a greater increase in carbon cycling than in carbon storage in grasslands.

1577^9^McGuire,AD^Melillo,JM^Kicklighter,DW^Pan,YD^Xiao,XM^Helfrich,J^Moore,B^Vorosmarty,CJ^Schloss,AL^1997^1^Equilibrium responses of global net primary production and carbon storage to doubled atmospheric carbon dioxide: Sensitivity to changes in vegetation nitrogen concentration^137^11^2^173-189^^^^^Jun^^^^^5931
230^243^416^431^494^664^714^741^765^975^resent an annual budget focusing on below-ground carbon cycling for two grassland ecosystems exposed to elevated CO2 concentrations. Three years of experimental CO2 doubling increased ecosystem carbon uptake, but greatly increased carbon partitioning to rapidly cycling carbon pools below ground, This provides an explanation for the imbalance observed in numerous CO2 experiments, where the carbon increment from increased photosynthesis isA^5930^We ran the terrestrial ecosystem model (TEM) for the globe at 0.5 degrees resolution for atmospheric CO2 concentrations of 340 and 680 parts per million by volume (ppmv) to evaluate global and regional responses of net primary production (NPP) and carbon storage to elevated CO2 for their sensitivity to changes in vegetation nitrogen concentration. At 340 ppmv, TEM estimated global NPP of 49.0 10(15) g (Pg) C yr(-1) and global total carbon storage of 1701.8 Pg C; the estimate of total carbon storage does not include the carbon content of inert soil organic matter. For the reference simulation in which doubled atmospheric CO2 was accompanied with no change in vegetation nitrogen concentration, global NPP increased 4.1 Pg C yr(-1) (8.3%), and global total carbon storage increased 114.2 Pg C. To examine sensitivity in the global responses of NPP and carbon storage to decreases in the nitrogen concentration of vegetation, we compared doubled CO2 responses of the reference TEM to simulations in which the vegetation nitrogen concentration was reduced without influencing decomposition dynamics (''lower N'' simulations) and to simulations in which reductions in vegetation nitrogen concentration influence decomposition dynamics (''lower N+D'' simulations). We conducted three lower N simulations and three lower N+D simulations in which we reduced the nitrogen concentration of vegetation by 7.5, 15.0, and 22.5%. In the lower N simulations, the response of global NPP to doubled atmospheric CO2 increased approximately 2 Pg C yr(-1) for each incremental 7.5% reduction in vegetation nitrogen concentration, and vegetation carbon increased approximately an additional 40 Pg C, and soil carbon increased an additional 30 Pg C, for a total carbon storage increase of approximately 70 Pg C. In the lower N+D simulations, the responses of NPP and vegetation carbon storage were relatively insensitive to differences in the reduction of nitrogen concentration, but soil carbon storage showed a large change. The insensitivity of NPP in the N+D simulations occurred because potential enhancements in NPP associated with reduced vegetation nitrogen concentration were approximately offset by lower nitrogen availability associated with the decomposition dynamics of reduced litter nitrogen concentration. For each 7.5% reduction in vegetation nitrogen concentration, soil carbon increased approximately an additional 60 Pg C, while vegetation carbon storage increased by only approximately 5 Pg C. As the reduction in vegetation nitrogen concentration gets greater in the lower N+D simulations, more of the additional carbon storage tends to become concentrated in the north temperate- boreal region in comparison to the tropics. Other studies with TEM show that elevated CO2 more than offsets the effects of climate change to cause increased carbon storage. The results of this study indicate that carbon storage would be enhanced by the influence of changes in plant nitrogen concentration on carbon assimilation and decomposition rates. Thus changes in vegetation nitrogen concentration may have important implications for the ability of the terrestrial biosphere to mitigate increases in the atmospheric concentration of CO2 and climate changes associated with the increases.

1578^6^Melack,JM^Dozier,J^Goldman,CR^Greenland,D^Milner,AM^Naiman,RJ^1997^1^Effects of climate change on inland waters of the Pacific Coastal Mountains and Western Great Basin of North America^324^11^8^971-992^^^^^30 Jun^^^^^5933
182^2499^2500^2501^2502^2503^2504^2505^2506^2507^concentration gets greater in the lower N+D simulations, more of the additional carbon storage tends to become concentrated in the north temperate- boreal region in comparison to the tropics. Other studies with TEM show that elevated CO2 more than offsets the effects of climate change to cause increased carbon storage. The results of this study indicate that carbon storage would be enhanced by the influence of changes in plant nitrogen concentration on carbon assimilation and decomposition rates. Thus changes in vegA^5932^The region designated as the Pacific Coastal Mountains and Western Great Basin extends from southern Alaska (64 degrees N) to southern California (34 degrees N) and ranges in altitude from sea level to 6200 m. Orographic effects combine with moisture-laden frontal systems originating in the Pacific Ocean to produce areas of very high precipitation on western slopes and dry basins of internal drainage on eastern hanks of the mountains. In the southern half of the region most of the runoff occurs during winter or spring, while in the northern part most occurs in summer, especially in glaciated basins, Analyses of long-term climatic and hydrological records, combined with palaeoclimatic reconstructions and simulations of future climates, are used as the basis for likely scenarios of climatic variations. The predicted hydrological response in northern California to a climate with doubled CO2 and higher temperatures is a decrease in the amount of precipitation falling as snow, and substantially increased runoff during winter and less in late spring and summer. One consequence of the predicted earlier runoff is higher salinity in summer and autumn in San Francisco Bay. In saline lakes, the incidence of meromixis and the associated reduction in nutrient supply and algal abundance is expected to vary significantly as runoff fluctuates. In subalpine lakes, global warming will probably will lead to increased productivity. Lacustrine productivity can also be altered by changes in wind regimes, drought- enhanced forest fires and maximal or minimal snowpacks associated with atmospheric anomalies such as Fl Nino-Southern Oscillation (ENSO) events. Reduced stream temperature from increased contributions of glacial meltwater and decreased channel stability from changed runoff patterns and altered sediment loads has the potential to reduce the diversity of zoobenthic communities in predominately glacier-fed rivers. Climatic warming is likely to result in reduced growth and survival of sockeye salmon in freshwater, which would, in turn, increase marine mortality. Further research activities should include expanded studies at high elevations and of glacier mass balances and glacial runoff, applications of remote sensing to monitor changes, further refinement of regional climatic models to improve forecasts of future conditions and continued analyses of long-term physical, chemical and biological data to help understand responses to future climates. (C) 1997 by John Wiley & Sons, Ltd.

1579^4^Osborne,CP^Drake,BG^LaRoche,J^Long,SP^1997^1^Does long-term elevation of CO2 concentration increase photosynthesis in forest floor vegetation? Indian strawberry in a Maryland forest (vol 114, pg 337, 1997)^8^114^4^1571^^^^^Aug^^^^^5935
twater and decreased channel stability from changed runoff patterns and altered sediment loads has the potential to reduce the diversity of zoobenthic communities in predominately glacier-fed rivers. Climatic warming is likely to result in reduced growth and survival of sockeye salmon in freshwater, which A^5934^As the partial pressure of CO2 (pCO(2)) in the atmosphere rises, photorespiratory loss of carbon in C-3 photosynthesis will diminish and the net efficiency of light-limited photosynthetic carbon uptake should rise. We tested this expectation for Indian strawberry (Duchesnea indica) growing on a Maryland forest floor. Open-top chambers were used to elevate the pCO(2) of a forest floor habitat to 67 Pa and were paired with control chambers providing an ambient pCO(2) of 38 Pa. After 3.5 years, D. indica leaves grown and measured in the elevated pCO(2) showed a significantly greater maximum quantum efficiency of net photosynthesis (by 22%) and a lower light compensation point (by 42%) than leaves grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O-2, was the same for controls and plants grown at elevated pCO(2). This showed that the maximum efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited photosynthesis at elevated pCO(2) was simply a function of the decrease in photorespiration. Acclimation did decrease the ribulose-1,5-bisphospbate carboxylase/oxygenase and light-harvesting chlorophyll protein content of the leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO(2) showed greater light- saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO(2). In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO(2), relative to controls, in both summer and fall. The increase in efficiency of light- limited photosynthesis with elevated pCO(2) allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric pCO(2).

1580^6^Paterson,E^Hall,JM^Rattray,EAS^Griffiths,BS^Ritz,K^Killham,K^1997^1^Effect of elevated CO2 on rhizosphere carbon flow and soil microbial processes^127^3^4^363-377^^^^^Aug^^^^^5937
1049^1345^137^1803^2508^344^506^507^715^931^ content of the leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO(2) showed greater light- saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO(2). In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO(2), relative to controls, in both summer and fall. The increase in efficiency of light- limited photosynthesis with elevated pCO(2) allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric pA^5936^Direct effects of increased above-ground CO2 concentration on soil microbial processes are unlikely, due to the high pCO(2) of the soil atmosphere in most terrestrial ecosystems. However, below-ground microbial processes are likely to be affected through altered plant inputs at elevated CO2. A major component of plant input is derived from litter fall and root turnover. Inputs also derive from rhizodeposition (loss of C-compounds from active root systems) which may account for up to 40% of photoassimilate. This input fuels the activity of complex microbial communities around roots. These communities are centrally important not only to plant-microbe interactions and consequent effects on plant growth, but also, through their high relative activity and abundance, to microbially mediated processes in soil generally. This review focuses on approaches to measure C-flow from roofs, in particular, as affected by increased atmospheric CO2 concentration. The available evidence for impacts on microbial communities inhabiting this niche, which constitutes an interface for possible perturbations on terrestrial ecosystems through the influence of environmental change, will also be discussed. While methodologies for measuring effects of increased CO2 concentration on plant growth, physiology and C-partitioning are abundant and widely reported, there is relatively little information on plant- mediated effects on soil microbial communities and processes. Importantly, many studies have also neglected to recognize that any secondary effects on microbial communities may have profound effects on plant parameters measured in relation to environmental change. We critically review approaches which have been used to measure rhizodeposition under conditions of increased atmospheric CO2 concentration, and then consider evidence for changes in microbial communities and processes, and the methodologies which have been recently developed, and are appropriate to study such changes.
vailable evidence for impacts on microbial communit1581^9^Prior,SA^Torbert,HA^Runion,GB^Rogers,HH^Wood,CW^Kimball,BA^LaMorte,RL^Pinter,PJ^Wall,GW^1997^1^Free-air carbon dioxide enrichment of wheat: Soil carbon and nitrogen dynamics^204^26^4^1161-1166^^^^^Jul-Aug^^^^^5939
374^547^56^733^CO2 concentration on plant growth, physiology and C-partitioning are abundant and widely reported, there is relatively little information on plant- mediated effects on soil microbial communities and processes. Importantly, many studies have also neglected to recognize that any secondary effects on microbial communities may have profound effects on plant parameters measured in relation to environmental change. We critically review approaches which have been used to measure rhizodeposition under conditions of increased atmospheric CO2 concentration, and then consider evidence for changes in microbial communities and processes, and the methodologies which have been recently developed, and are appropriate to study such changes.
vailable evidence for impacts on microbial communitA^5938^The predicted positive impact of elevated atmospheric carbon dioxide (CO2) concentration on crop biomass production suggests that more C will reach the soil. An aspect of soil C sequestration that requires further study is the effect of elevated CO2 on C and N dynamics; this relationship is the keg to understanding potential longterm C storage in soil. Soil samples (0-5, 5-10, and 10-20 cm increments) were collected after 2 yr of wheat (Triticum aestivum L.) production under two CO2 levels [370 (ambient) and 550 mu L L-1 (free-air CO2 enrichment) (FACE)] and two water treatments [100% of ET replaced (wet) and 50% of ET replaced (dry)] on a Trix clay loam [fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvents] at Maricopa, AZ. Organic C, total N, potential C and N mineralization, and C turnover were determined during a 60-d incubation study. Organic C content increased at all three soil depths under FACE and the total N content increased at the 5 to 10 and 10 to 20 cm depths. In general, increased N mineralization under dry conditions corresponded well with patterns of higher C mineralization and turnover. Nitrogen mineralization was unaffected by CO2 treatment, indicating that factors other than N may limit C mineralization and turnover. Soil respiration and C turnover patterns were not affected by CO2 treatment level at the 0 to 5 cm depth; however, these measures were Lower under FACE at the lower depths. Soil respiration and C turnover at the 10 to 20 cm depth were increased by water stress under ambient CO2; these measures under both water levels for FACE were similar to the ambient CO2/wet treatment, suggesting that more C storage in wheat cropping systems is likely under elevated CO2 regardless of mater treatment.

1582^2^Sicher,RC^Bunce,JA^1997^1^Relationship of photosynthetic acclimation to changes of Rubisco activity in field-grown winter wheat and barley during growth in elevated carbon dioxide^91^52^1^27-38^^^^^Apr^^^^^5941
1347^344^376^417^434^448^ to 20 cm depths. In general, inA^5940^The responses of photosynthesis, Rubisco activity, Rubisco protein, leaf carbohydrates and total soluble protein to three carbon dioxide treatments were studied in winter wheat [Triticum aestivum (L.)] and barley [Hordeum vulgare (L.)]. Barley and wheat plants were grown in small field plots during 1995 and 1996 in clear, acrylic chambers (1.2-2.4 m(2)) and were provided with continuous carbon dioxide fertilization at concentrations of 350, 525 and 700 mu mol mol(-1). Photosynthetic rates of barley penultimate leaves and wheat flag leaves measured at growth carbon dioxide concentrations decreased with leaf age in all three CO2 treatments during 1995 and 1996. Photosynthetic acclimation to elevated CO2 was observed on seven of eight measurement dates for barley and ten of eleven measurement dates for wheat over both years. Initial Rubisco activity, total soluble protein and Rubisco protein in barley penultimate leaves and wheat flag leaves also decreased with leaf age. Total Rubisco activity was not used because of enzyme degradation. There was a significant CO2 treatment effect on initial Rubisco activity, total soluble protein and Rubisco protein for wheat in 1995 and 1996 and for barley in 1995. Responses of barley penultimate leaf Rubisco activity and leaf protein concentrations to elevated carbon dioxide were nonsignificant in 1996. A significant CO2 treatment effect also was detected when means of Rubisco activity, soluble protein and Rubisco protein for wheat flag leaves were combined over harvests and years. These three flag leaf parameters were not significantly different in the 350 and 525 mu mol mol(-1) CO2 treatments but were decreased during growth in 700 mu mol mol(- 1) CO2 relative to the other two CO2 treatments. Ratios of photosynthesis at 700 and 350 mu mol mol(-1) were compared to ratios of Rubisco activity at 700 and 350 mu mol mol(-1) using wheat flag leaf data from 1995 and 1996. Regression analysis of these data were linear [y = 0.586 + 1.103x(r(2) = 0.432)] and were significant at P less than or equal to 0.05. This result indicated that photosynthetic acclimation was positively correlated with changes of initial Rubisco activity in wheat flag leaves in response to CO2 enrichment. Effects of elevated CO2 on wheat leaf proteins during 1995 and 1996 and on barley during 1995 were consistent with an acceleration of senescence.

1583^2^Thornley,JHM^Cannell,MGR^1997^1^Temperate grassland responses to climate change: An analysis using the Hurley pasture model^52^80^2^205-221^^^^^Aug^^^^^5943
1588^1649^344^372^407^454^507^738^855^92^s were not significantly different in the 350 and 525 mu mol mol(-1) CO2 treatments but were decreased during growth in 700 mu mol mol(- 1) CO2 relative to the other two CO2 treatments. Ratios of photosynthesis at 700 and 350 mu mol mol(-1) were compared to ratios of Rubisco activity at 700 and 350 mu mol mol(-1) using wheat flag leaf data from 1995 and 1996. Regression analysis of these data were linear [y = 0.586 + 1.103x(r(2) = 0.432)] and were significant at A^5942^The Hurley Pasture Model is process-based and couples the carbon, nitrogen and water cycles in the soil-grass-animal system. It was used to examine the responses of grasslands in southern, lowland and northern, upland climates in Britain. Short-term response to step-wise increases in CO2 concentration (350 to 700 mu mol mol(-1)) and temperature (5 degrees C) were contrasted with long-term equilibrium (the term 'equilibrium' is equivalent to 'steady state' throughout this paper) responses and with responses to gradually increasing [CO2] and temperature. Equilibrium responses to a range of climate variables were also examined. Three conclusions were drawn regarding the interpretation of experiments: (1) initial ecosystem responses to stepwise changes can be different in both magnitude and sign to equilibrium responses, and this can continue for many years; (2) grazing can drastically alter the magnitude and sign of the response of grasslands to climate change, be highly site-specific. It was concluded that experiments should try to lessen uncertainty about processes within models rather than try to predict ecosystem responses directly. Three conclusions were also drawn about the operation of grasslands as carbon sinks: (1) increasing [CO2] alone will produce a carbon sink, as long as it continues to accelerate photosynthesis and increase net primary productivity; (2) by contrast, increasing temperatures alone are likely to produce a carbon source, because soil respiration is accelerated more than net primary productivity, even when assuming the same temperature function for most soil and plant biochemical processes; and (3) the net effect of projected increases in [CO2] and temperature is likely to be a carbon sink of 5-15 g C m(-2) yr(-1) in humid, temperate grasslands for several decades, which is consistent with the magnitude of the hypothesized current global terrestrial carbon sink. (C) 1997 Annals of Botany Company.
esponse of grasslands to climate change, be highly site-specific. It was concluded t1584^3^Wilsey,BJ^Coleman,JS^McNaughton,SJ^1997^1^Effects of elevated CO2 and defoliation on grasses: A comparative ecosystem approach^56^7^3^844-853^^^^^Aug^^^^^5945
1333^2509^2510^2511^2512^2513^378^417^429^92^n sinks: (1) increasing [CO2] alone will produce a carbon sink, as long as it continues to accelerate photosynthesis and increase net primary productivity; (2) by contrast, increasing temperatures alone are likely to produce a carbon source, because soil respiration is accelerated more than net primary productivity, even when assuming the same temperature function for most soil and plant biochemical processes; and (3) the net effect of projected increases in [CO2] and temperature is likely to be a carbon sink of 5-15 g C m(-2) yr(-1) in humid, temperate grasslands for several decades, which is consistent with the magnitude of the hypothesized current global terrestrial carbon sink. (C) 1997 Annals of Botany Company.
esponse of grasslands to climate change, be highly site-specific. It was concluded tA^5944^Three plant species from each of three grassland ecosystems were grown under elevated (700 mL/m(3)) and ambient (350 mL/m(3)) CO2 and were defoliated or left undefoliated to test whether species response to elevated CO2 and grazing is related to evolutionary grazing history or to mode of photosynthesis. The three ecosystems represented a tropical grassland dominated by C-4 species (the Serengeti of Africa), a temperate grassland dominated by a mixture of C-3 and C-4 species (Flooding Pampa of South America), and a northern temperate grassland dominated by C-3 species (Yellowstone National Park of North America). Plants were grown in growth chambers under common conditions to compare relative responses to grazing and elevated CO2. Elevated CO2 caused an increase in total biomass and total productivity (biomass + clippings) only in Yellowstone species, and increases in growth occurred primarily in crowns and roots (storage organs). There were no significant CO2 effects on biomass or productivity in Serengeti or Flooding Pampa species, and no CO2 effects on aboveground biomass or productivity (aboveground biomass + clippings) in species from any of the three ecosystems. Since aboveground plant parts are the portions that are available to grazing mammals, this suggests that increased atmospheric CO2 may not affect food quantity in these three grasslands. There was no interaction between CO2 and defoliation for any species; thus, it appears that herbivores will not affect how grasses respond to elevated CO2 (at least under average nutrient conditions). Elevated CO2 caused a reduction in leaf percentage of N in species from Yellowstone and Flooding Pampa (especially the C-3 species, Briza subaristata), but not in Serengeti species. Because the quantity of food was unaffected by the CO2 treatments and forage N was reduced, grazing mammals in Yellowstone (elk, Cervus elaphus, and bison, Bison bison) and the Flooding Pampa (cattle) may be negatively affected. Responses to defoliation were fairly consistent among ecosystems in aboveground productivity, which did not differ between defoliated and undefoliated plants, and in leaf water potentials and percentage of N, both of which increased in response to defoliation. However, differences among ecosystems were found for crown and root biomass in response to defoliation: Serengeti species, on average, had higher crown and similar root biomasses after defoliation, whereas defoliated species from the other two ecosystems had reduced crown and root biomass. We suggest that the lower intensity and increased temporal variance in grazing pressure in Yellowstone vs. the Serengeti, selected for plants that shift allocation away from roots and crowns in order to compensate for aboveground herbivory.

1585^4^Wullschleger,SD^Norby,RJ^Love,JC^Runck,C^1997^1^Energetic costs of tissue construction in yellow-poplar and white oak trees exposed to long-term CO2 enrichment^52^80^3^289-297^^^^^Sep^^^^^5947
1260^2514^2515^341^348^374^419^520^733^966^foliation were fairly consistent among A^5946^Two methods were used to estimate construction costs for leaves, stems, branches and woody roots of yellow-poplar (Liriodendron tulipifera L.) trees grown at ambient (35 Pa) and elevated (65 Pa) CO2 for 2.7 years and trees of white oak (Quercus alba L.) grown at these same CO2 partial pressures for 4 years. Sample combustion in a bomb calorimeter combined with measurements of ash and nitrogen content provided the primary method of estimating tissue construction costs (W-G; g glucose g(-1) dry mass). These values were compared with a second, simpler method in which cost estimates were derived from tissue ash, carbon and nitrogen content (V-G). Estimates of W-G were lower for leaves, branches and roots of yellow-poplar and for leaves of white oak grown at elevated compared with ambient CO2 partial pressures. These CO2-induced differences in W-G ranged from 3.7% in yellow-poplar roots to 2.1% in white oak leaves. Only in the case of yellow-poplar leaves, however were differences in V-G observed between CO2 treatments. Leaf V-G was 1.46 g glucose g(-1) dry mass in ambient-grown trees compared with 1.41 g glucose g(-1) dry mass for CO2-enriched trees. Although paired-estimates of W-G and V-G clustered about a 1:1 line for leaves and branches, estimates of V-G were consistently lower than W-G for stems and roots. Construction costs per unit leaf area were 95 g glucose m(-2) for yellow- poplar trees grown at ambient CO2 and 106 g glucose m(-2) for trees grown at elevated CO2 partial pressures. No differences in area-based construction costs were observed for white oak. Whole-plant energy content was 1220 g glucose per tree in ambient-grown white oak compared with 2840 g glucose per tree for those grown at elevated CO2 partial pressures. These differences were driven largely by CO2-induced changes in total biomass. We conclude that while construction costs were lower at elevated CO2 partial pressures, the magnitude of this response argues against an increased efficiency of carbon use in the growth processes of trees exposed to CO2 enrichment. (C) 1997 Annals of Botany Company.

1586^2^Zaller,JG^Arnone,JA^1997^1^Activity of surface-casting earthworms in a calcareous grassland under elevated atmospheric CO2^2^111^2^249-254^^^^^Jul^^^^^5949
1239^1298^1317^2070^224^2516^312^374^407^57^ lower than W-G for stems and roots. Construction costs per unit leaf area were 95 g glucose m(-2) for yellow- poplar trees grown at ambient CO2 and 106 g glucose m(-2) for trees grown at elevated CO2 partial pressures. No differences in area-based construction costs were observed for white oak. Whole-plant energy content was 1220 g glucose per tree in ambient-grown white oak compared with 2840 g glucose per tree for those grown at elevated CO2 partial pressures. These differences were driven largely by CO2-induced changes in total biomass. We conclude that while construction costs were lower at elevated CO2 partial pressures, the magnitude of this response argues against an increased efficiency of carbon use in the growth processes of tA^5948^Earthworms make up the dominant fraction of the biomass of soil animals in most temperate grasslands and have important effects on the structure and function of these ecosystems. We hypothesized that the effects of elevated atmospheric CO2 on soil moisture and plant biomass production would increase earthworm activity, expressed as surface cast production. Using a screen-aided CO2, control facility (open top and open bottom rings), eight 1.2-m(2) grassland plots in Switzerland have been maintained since March 1994 at ambient CO2 concentrations (350 mu l CO2 l(-1)) and eight at elevated CO2 (610 mu l CO2 l(-1)). Cumulative earthworm surface cast production measured 40 times over 1 year (April 1995-April 1996) in plots treated with elevated CO2 (2206 g dry mass m(-2) year(-1)) was 35% greater (P<0.05) than that measured in plant communities maintained at ambient CO2 (1633 g dry mass m(-2) year(-1)). At these rates of surface cast production, worms would require about 100 years to egest the equivalent of the amount of soil now found in the Ah horizon (top 15 cm) under current ambient CO2 concentrations, and 75 years under elevated CO2. Elevated atmospheric CO2 had no influence on the seasonality of earthworm activity. Cumulative surface cast production measured over the 7-week period immediately following the 6-week summer dry period in 1995 (no surface casting) was positively correlated (P<0.05) with the mean soil water content calculated over this dry and subsequent wetter period, when viewed across all treatments. However, no correlations were observed with soil temperature or with annual aboveground plant biomass productivity. No CO2- related differences were observed in total nitrogen (N-tot) and organic carbon (C-org) concentration of surface casts, although concentrations of both elements varied seasonally. The CO2- induced increase in earthworm surface casting activity corresponded to a 30% increase of the amount of N-tot (8.9 mg N m(-2) vs. 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-2)) egested by the worms in one year. m Thus, our results demonstrate an important indirect stimulatory effect of elevated atmospheric CO2 on earthworm activity which may have profound effects on ecosystem function and plant community structure in the long term.

1587^2^Zeng,W^Heilman,JL^1997^1^Sensitivity of evapotranspiration of cotton and sorghum in west Texas to changes in climate and CO2^325^57^3-4^245-254^^^^^^^^^^5951
2092^264^312^344^376^407^409^410^51^881^uent wetter period, when viewed across all treatments. However, no correlations were observed with soil temperature or with annual aboveground plant biomass productivity. No CO2- related differences were observed in total nitrogen (N-tot) and organic carbon (C-org) concentration of surface casts, although concentrations of both elements varied seasonally. The CO2- induced increase in earthworm surface casting activity corresponded to a 30% increase of the amount of N-tot (8.9 mg N m(-2) vs. 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-2A^5950^In regions such as west Texas where water is scarce, changes in the water balance may have a significant impact on agricultural production and management of water resources. We used the mechanistic soil-plant-atmosphere simulation model ENWATBAL to evaluate changes in soil water evaporation (E) and transpiration (T) in cotton and grain sorghum that may occur due to climate change and elevated CO2 in west Texas. Climatic and plant factors were varied individually, and in combination, to determine their impact on E and T. Of the climatic factors, E was most sensitive to changes in vapor pressure, and T to changes in irradiance. Simulations suggest that if warming is accompanied by higher humidity, the impact of climate change may be minimal. However, if the climate becomes warmer and less humid, ET may increase substantially. Simulations also suggest that enhanced growth due to elevated CO2 may have a greater impact on ET than climatic change.
 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-21588^1^Arnone,JA^1997^1^Indices of plant N availability in an alpine grassland under elevated atmospheric CO2^206^190^1^61-66^^^^^Mar^^^^^5953
1781^2026^2517^282^312^374^529^587^778^99^ed the mechanistic soil-plant-atmosphere simulation model ENWATBAL to evaluate changes in soil water evaporation (E) and transpiration (T) in cotton and grain sorghum that may occur due to climate change and elevated CO2 in west Texas. Climatic and plant factors were varied individually, and in combination, to determine their impact on E and T. Of the climatic factors, E was most sensitive to changes in vapor pressure, and T to changes in irradiance. Simulations suggest that if warming is accompanied by higher humidity, the impact of climate change may be minimal. However, if the climate becomes warmer and less humid, ET may increase substantially. Simulations also suggest that enhanced growth due to elevated CO2 may have a greater impact on ET than climatic change.
 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-2A^5952^The objective of this study was to estimate whether elevated atmospheric [CO2] alters plant N availability in a native high- elevation grassland in the Swiss Alps using two integrative, relatively non-disruptive methods. Estimates based on seasonal net plant N uptake, and those based on the amounts of NH4+-N plus NO3--N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 mu L L-1) and elevated (680 mu L L-1) [CO2] in either the second (1993) or third (1994) growing season under treatment with elevated [CO2]. The results of this study suggest that the effects of rising atmospheric [CO2] on plant N availability may be negligible in this grassland. The results also contrast the relatively large effects of elevated atmospheric [CO2] (increases and decreases) reported for highly disturbed artificial systems.
est that enhanced growth due to elevated CO2 may have a greater impact on ET than climatic change.
 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-21589^4^BassiriRad,H^Griffin,KL^Reynolds,JF^Strain,BR^1997^1^Changes in root NH4+ and NO3- absorption rates of loblolly and ponderosa pine in response to CO2 enrichment^206^190^1^1-9^^^^^Mar^^^^^5955
1304^1443^2518^2519^312^437^544^678^733^92^ on seasonal net plant N uptake, and those based on the amounts of NH4+-N plus NO3--N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 mu L L-1) and elevated (680 mu L L-1) [CO2] in either the second (1993) or third (1994) growing season under treatment with elevated [CO2]. The results of this study suggest that the effects of rising atmospheric [CO2] on plant N availability may be negligible in this grassland. The results also contrast the relatively large effects of elevated atmospheric [CO2] (increases and decreases) reported for highly disturbed artificial systems.
est that enhanced growth due to elevated CO2 may have a greater impact on ET than climatic change.
 6.9 mg N m(-2)) and C-org (126 mg C m(-2) vs. 94 mg C m(-2A^5954^Root growth and physiological uptake capacity for NH4+ and NO3- were examined for seedlings of loblolly and ponderosa pine grown for 160 days under two CO2 levels, ambient (35 Pa) and ambient plus 35 Pa (70 Pa). Fraction of biomass allocated to active fine roots as well as total N (NH4+ + NO3-) absorption per unit root dry mass were unaffected by CO2. On a whole-plant basis, elevated CO2 led to a significant increase in N acquisition in loblolly but not in ponderosa pine. However, even in loblolly pine where CO2 significantly increased plant N acquisition, the relative increase, in biomass far exceeded the gain in N, i.e. a 60% increase in total dry weight was accompanied by only a 30% increase in N gain in response to high CO2. We suggest that the commonly reported decline in tissue N concentration of these and other species at high CO2 is largely caused by inability of the root systems to sufficiently compensate for increased N demand. Elevated CO2 significantly altered root uptake capacity of the different N forms, i.e., high CO2 significantly increased NO3- absorption rates, but decreased NH4+ absorption rates in both species though the decrease in loblolly was insignificant. However, elevated CO2 increased root respiration rate in loblolly pine while significantly decreasing it in ponderosa pine. This indicates that CO2-induced changes in plant preference for inorganic N forms is not simply regulated by root energy status. If changes in plant preference for inorganic N forms represent typical responses to elevated CO2, the results could have important implications for N dynamics in managed and natural plant communities.

1590^4^Bassirirad,H^Reynolds,JF^Virginia,RA^Brunelle,MH^1997^1^Growth and root NO3- and PO43- uptake capacity of three desert species in response to atmospheric CO2 enrichment^92^24^3^353-358^^^^^^^^^^5957
1334^229^312^361^372^417^436^540^57^640^ty of the root systems to sufficiently compensate for increased N demand. Elevated CO2 significantly altered root uptake capacity of the dA^5956^In a phytotron experiment, we examined growth and rates of NO3- and PO43- uptake in seedlings of two desert C-3 shrubs (Larrea tridentata and Prosopis glandulosa) and a desert C-4 perennial grass (Bouteloua eriopoda) grown under CO2 partial pressures of 35 or 70 Pa. Plants were grown in soil but uptake studies were conducted on roots of intact seedlings placed in nutrient solutions containing both NO3- and PO43-. Elevated CO2 increased total biomass by 69 and 55% in Larrea and Prosopis seedlings and by 25% in Bouteloua. NO3- and PO43- uptake rates were more than doubled in Bouteloua at high compared to ambient CO2. In contrast, CO2 enrichment inhibited root NO3- uptake capacity in Larrea by about 55% without a significant effect on PO43- absorption rate; rates of NO3- and PO43- and uptake in Prosopis were insensitive to CO2 treatment. Elevated CO2 enhanced the proportion of biomass allocated to the fine roots in Bouteloua but markedly reduced this fraction in Larrea and Prosopis. Foliar N concentration of both shrubs decreased in response to elevated CO2, but was unaffected in Bouteloua. We suggest that compensatory changes in root size and activity are critical in determining interspecies variation in plant nutrient relations under high CO2.

1591^7^Beckmann,K^Dzuibany,C^Biehler,K^Fock,H^Hell,R^Migge,A^Becker,TW^1997^1^Photosynthesis and fluorescence quenching, and the mRNA levels of plastidic glutamine synthetase or of mitochondrial serine hydroxymethyltransferase (SHMT) in the leaves of the wild-type and of the SHMT-deficient stm mutant of Arabidopsis thaliana in relation to the rate of photorespiration^6^202^3^379-386^^^^^Jul^^^^^5959
1584^188^2125^312^344^360^372^529^761^845^in Larrea by about 55% without a significant effect on PO43- absorption rate; rates of NO3- and PO43- and uptake in Prosopis were insensitive to CO2 treatment. Elevated CO2 enhanced the proportion of biomass allocated to the fine roots in Bouteloua but markedly reduced this fraction in Larrea and Prosopis. Foliar N concentratioA^5958^The regulation by photorespiration of the transcript level corresponding to plastidic glutamine synthetase (GS-2) was investigated in the leaves of Arabidopsis thaliana (L.) Heynh.. Photorespiration was suppressed by growing the plants in an atmosphere containing 300 Pa CO2. Suppression of photorespiration was demonstrated by the ability of the conditionally lethal serine hydroxymethyltransferase (SHMT)- deficient stm mutant of A. thaliana to grow normally under these conditions. In contrast to previous studies with bean or pea that were performed at very high CO2 partial pressure (2-4 kPa; Edwards and Coruzzi, 1989, Plant Cell 1: 241-248; Cock et al., 1991, Plant Mol Biol 17: 761-771), suppression of photorespiration during growth of A. thaliana in an atmosphere with 300 Pa CO2 had no effect on the leaf GS-2 transcript level. In the short term, neither suppression of photorespiration induced by the transfer of air-grown A. thaliana plants into a CO2-enriched atmosphere, nor an increase in the rate of photorespiration achieved by the transfer of high-CO2-grown A. thaliana plants into air resulted in a change in the GS-2 mRNA level. The absence of photorespiratory ammonium release in leaves of the stm mutant had no effect on the GS-2 transcript level. Overall, our data argue against a control by photorespiration of the A. thaliana leaf GS-2 mRNA pool. In contrast, regulation of the leaf SHMT mRNA level may involve a negative feedback effect of at least one metabolite derived from the glycine/serine conversion during photorespiration, as indicated by the overexpression of SHMT transcripts in the leaves of the stm mutant.

1592^2^Berntson,GM^Bazzaz,FA^1997^1^Nitrogen cycling in microcosms of yellow birch exposed to elevated CO2: Simultaneous positive and negative below-ground feedbacks^127^3^3^247-258^^^^^Jun^^^^^5961
1638^178^1823^1829^2520^2521^2522^2523^377^693^ssion of photorespiration induced by the transfer of air-grown A. thaliana plants into a CO2-enriched atmosphere, nor an increase in the rate ofA^5960^This study investigated simultaneous plant and soil feedbacks on growth enhancement with elevated [CO2] within microcosms of yellow birch (Betula alleghaniensis Britt.) in the second year of growth. Understanding the integrated responses of model ecosystems may provide key insight into the potential net nutrient feedbacks on [CO2] growth enhancements in temperate forests. We measured the net biomass production, C:N ratios, root architecture, and mycorrhizal responses of yellow birch, in situ rates gross nitrogen mineralization and the partitioning of available NH4+ between yellow birch and soil microbes. Elevated atmospheric [CO2] resulted in significant alterations in the cycling of N within the microcosms. Plant C/N ratios were significantly increased, gross mineralization and NH4+ consumption rates were decreased, and relative microbial uptake of NH4+ was increased, representing a suite of N cycling negative feedbacks on N availability. However, increased C/N ratios may also be a mechanism which allows plants to maintain higher growth with a constant or reduced N supply. Total plant N content was increased with elevated [CO2], suggesting that yellow birch had successfully increased their ability to acquire nutrients during the first year of growth. However, plant uptake rates of NH4+ had decreased in the second year. This discrepancy implies that, in this study, nitrogen uptake skewed a trend through ontogeny of decreasing enhancement under elevated [CO2]. The reduced N mineralization and relatively increased N immobilization are a potential feedback which may drive this ontogenetic trend. This study has demonstrated the importance of using an integrated approach to exploring potential nutrient-cycling feedbacks in elevated [CO2].

1593^4^Burton,AJ^Zogg,GP^Pregitzer,KS^Zak,DR^1997^1^Effect of measurement CO2 concentration on sugar maple root respiration^13^17^7^421-427^^^^^Jul^^^^^5963
1103^130^1538^2362^2524^2525^364^376^520^749^ability. However, increased C/N ratios may also be a mechanism which alA^5962^Accurate estimates of root respiration are crucial to predicting belowground C cycling in forest ecosystems. Inhibition of respiration has been reported as a short-term response of plant tissue to elevated measurement [CO2]. We sought to determine if measurement [CO2] affected root respiration in samples from mature sugar maple (Acer saccharum Marsh.) forests and to assess possible errors associated with root respiration measurements made at [CO2]s lower than that typical of the soil atmosphere. Root respiration was measured as both CO2 production and O-2 consumption on excised fine roots (less than or equal to 1.0 mm) at [CO2]s ranging from 350 to > 20,000 mu l l(-1). Root respiration was significantly affected by the [CO2] at which measurements were made for both CO2 production and O-2 consumption. Root respiration was most sensitive to [CO2] near and below normal soil concentrations (< 1500 mu l l(-1)). Respiration rates changed little at [CO2]s above 3000 mu l l(-1) and were essentially constant above 6000 mu l l(-1) CO2. These findings call into question estimates of root respiration made at or near atmospheric [CO2], suggesting that they overestimate actual rates in the soil. Our results indicate that sugar maple root respiration at atmospheric [CO2] (350 mu l l(-1)) is about 139% of that at soil [CO2]. Although the causal mechanism remains unknown, the increase in root respiration at low measurement [CO2] is significant and should be accounted for when estimating or modeling root respiration. Until the direct effect of [CO2] on root respiration is fully understood, we recommend making measurements at a [CO2] representative of, or higher than, soil [CO2]. In all cases, the [CO2] at which measurements are made and the [CO2] typical of the soil atmosphere should be reported.

1594^3^Campbell,BD^Smith,DMS^McKeon,GM^1997^1^Elevated CO2 and water supply interactions in grasslands: A pastures and rangelands management perspective^127^3^3^177-187^^^^^Jun^^^^^5965
1298^2526^413^were essentially constant aA^5964^Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO2 concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO2 and water interactions, and (ii) knowledge of how precisely the effects of CO2 must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non-linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosystems remain to be precisely determined through ecosystem-level experiments. A simplified simulation of the impact of different levels of productivity change in a water- limited Australian rangeland system was conducted by varying effects of CO2 on radiation and water use efficiency. The results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.
microcosm experiment illustrates that non-linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosy1595^4^Cantin,D^Tremblay,MF^Lechowicz,MJ^Potvin,C^1997^1^Effects of CO2 enrichment, elevated temperature, and nitrogen availability on the growth and gas exchange of different families of jack pine seedlings^155^27^4^510-520^^^^^Apr^^^^^5967
1343^137^1727^2527^2528^2529^344^374^62^711^e results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.
microcosm experiment illustrates that non-linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosyA^5966^Many economically important tree species respond positively to an elevated CO2 environment. However, the variability and stability in growth responses among genotypes grown in a global change environment are generally not documented. The present study investigated the differences, at the seedling stage, among 15 maternal families of jack pine (Pinus banksiana Lamb.) in response to an elevated CO2-temperature environment (CO2T) (700 mu L CO2.L-1 with temperatures 4 degrees C higher than in the ambient CO2T environment), with different nitrogen concentrations. While the elevated CO2T did not significantly alter the overall height growth of seedlings, it significantly increased their total biomass, with needle and root biomass being most responsive. Growth in the elevated CO2T resulted in a 24% reduction in the leaf weight ratio as more biomass was allocated to roots. Significant genotypic differences were observed for height, biomass, and water-use efficiency. Generally, most families kept their rank relative to other families, from the ambient to the elevated CO2T. Also, rank correlations between height of families grown in elevated CO2T and height of families at 10 years of age in the field were significant. This result, combined with the stability we observed in family response from the ambient to the elevated CO2T, suggested that jack pine families currently chosen for their fast-growing capacity will probably remain as such in a global change environment, at least during the seedling establishment stage.

1596^3^Carter,EB^Theodorou,MK^Morris,P^1997^1^Responses of Lotus corniculatus to environmental change .1. Effects of elevated CO2, temperature and drought on growth and plant development^84^136^2^245-253^^^^^Jun^^^^^5969
1292^243^310^312^376^434^506^546^751^867^vated CO2T resulted in a 24% reduction in the leaf weight ratio as more biomass was allocated to roots. Significant genotypic differences were observed for height, biomass, and water-use efficiency. Generally, most families kept their rank reA^5968^Five clonal plants of three genotypes of Lotus corniculatus were grown in each of eight controlled environments under combinations of two temperature regimes (18/10 degrees C and 25/15 degrees C), two CO2 concentrations (ambient and 700 ppmv) and two water applications (ad libitum or 60% droughted). Plants were harvested at full flower and measurements made of plant growth and development. Of the three environmental variables studied, higher growth temperatures resulted in the largest number of significant changes to the measured variables. Reproductive capacity, growth rate, shoot biomass, water use efficiency and chlorophyll content were all enhanced by raising the growth temperature from 18 to 25 degrees C. Doubling the CO2 concentration enhanced the growth rate, shoot biomass and water use efficiency and ameliorated some of the effects of drought, including reproductive capacity, and biomass production, but reduced flowering lime, specific leaf area, and chlorophyll content of both droughted and undroughted plants. Drought alone reduced reproductive capacity, growth rate and above ground biomass but significantly increased root biomass in all environments. The agronomic effects resulting from a combined increase in growth temperature, doubled CO2 concentration and mild drought in this experiment were a shorter vegetative period and an increase in biomass, but a fall in reproductive capacity.

1597^4^Field,CB^Lund,CP^Chiariello,NR^Mortimer,BE^1997^1^CO2 effects on the water budget of grassland microcosm communities^127^3^3^197-206^^^^^Jun^^^^^5971
1251^2188^256^372^374^376^442^674^740^757^ water use efficiency and chlorophyll content were all enhanced by raising the growth temperature from 18 to 25 degrees C. Doubling the CO2 concentration enhanced the growth rate, shoot biomass and water use efficiency and ameliorated some of the effects of drought, including reproductive capacity, and biomass production, but reduced flowering lime, specific leaf area, and chlorophyll content of both droughted and uA^5970^Experimental grassland ecosystems, in microcosms 0.2 m in diameter and with a 0.95 m soil column, varied in their responses to elevated partial pressure of CO2 (pCO(2)) and altered moisture inputs. Ecosystems on moderately fertile sandstone soil and with a typical mix of moderately fast- growing sandstone species, responded to elevated pCO(2) with decreases in mid-season evapotranspiration of nearly 50%. This pattern reversed at the end of the growing season, and sandstone ecosystems under elevated pCO(2) continued active transpiration farther into the summer drought. The sandstone ecosystems appeared to convert mid-season water conservation into increased late-season growth. Effects of increased pCO(2) on ecosystem evapotranspiration were much smaller in ecosystems with very infertile serpentine soil and a diverse mixture of slow-growing serpentine species.
g reproductive capacity, and biomass production, but reduced flowering lime, specific leaf area, and chlorophyll content of both droughted and u1598^10^Fischer,BU^Frehner,M^Hebeisen,T^Zanetti,S^Stadelmann,F^Luscher,A^Hartwig,UA^Hendrey,GR^Blum,H^Nosberger,J^1997^1^Source-sink relations in Lolium perenne L. as reflected by carbohydrate concentrations in leaves and pseudo-stems during regrowth in a free air carbon dioxide enrichment (FACE) experiment^9^20^7^945-952^^^^^Jul^^^^^5973
1098^130^1684^1958^1960^310^372^385^417^92^otranspiration of nearly 50%. This pattern reversed at the end of the growing season, and sandstone ecosystems under elevated pCO(2) continued active transpiration farther into the summer drought. The sandstone ecosystems appeared to convert mid-season water conservation into increased late-season growth. Effects of increased pCO(2) on ecosystem evapotranspiration were much smaller in ecosystems with very infertile serpentine soil and a diverse mixture of slow-growing serpentine species.
g reproductive capacity, and biomass production, but reduced flowering lime, specific leaf area, and chlorophyll content of both droughted and uA^5972^The effect of an elevated partial pressure of CO2 (P-CO2) on carbohydrate concentrations in source leaves and pseudostems (stubble) of Lolium perenne L., (perennial ryegrass) during regrowth was studied in a regularly defoliated grass sward in the field, The free air carbon dioxide enrichment (FACE) technology enabled natural environmental conditions to be provided, Two levels of nitrogen (N) supply were used to modulate potential plant growth. Carbohydrate concentrations in source leaves were increased at elevated P-CO2, particularly at low N supply, Elevated leaf carbohydrate concentrations were related to an increased structural carbon (C) to N ratio and thus reflected an increased C availability together with a N- dependent sink limitation, Immediately after defoliation, apparent assimilate export rates (differences in the carbohydrate concentrations of young source leaves measured in the evening and on the following morning) showed a greater increase at elevated p(CO2) than at ambient p(CO2); however, replenishment of carbohydrate reserves was not accelerated Distinct, treatment-dependent carbohydrate concentrations in pseudo-stems suggested an increasing degree of C-sink limitation from the treatment at ambient p(CO2) with high N supply to that at elevated P-CO2 With low N supply. During two growing seasons, no evidence of a substantial change in the response of the carbohydrate source in L. perenne to elevated p(CO2) was found, Our results support the view that the response of L. perenne to elevated p(CO2) is restricted by a C- sink limitation, which is particularly severe at low N supply.

1599^4^Griffin,KL^Bashkin,MA^Thomas,RB^Strain,BR^1997^1^Interactive effects of soil nitrogen and atmospheric carbon dioxide on root/rhizosphere carbon dioxide efflux from loblolly and ponderosa pine seedlings^206^190^1^11-18^^^^^Mar^^^^^5975
1334^1781^2530^372^374^376^524^547^672^92^es measured in the evening and on the following morning) showed a greater increase at elevated p(CO2) than at ambient p(CO2); howA^5974^We measured CO2 efflux from intact root/rhizosphere systems of 155 day old loblolly (Pinus taeda L.) and ponderosa (Pinus ponderosa Dougl, ex Laws.) pine seedlings in order to study the effects of elevated atmospheric CO2 on the below-ground carbon balance of coniferous tree seedlings. Seedlings were grown in sterilized sand culture, watered daily with either 1, 3.5 or 7 mM NH4+, and maintained in an atmosphere of either 35 or 70 Pa CO2. Carbon dioxide efflux (mu mol CO2 plant(-1) s(-1)) from the root/rhizosphere system of both species significantly increased when seedlings were grown in elevated CO2, primarily due to large increases in root mass. Specific CO2 efflux (mu mol CO2 g root(-1) s(-1)) responded to CO2 only under conditions of adequate soil nitrogen availability (3.5 mM). Under these conditions, CO2 efflux rates from loblolly pine increased 70% from 0.0089 to 0.0151 mu mol g(-1) s(-1) with elevated CO2 while ponderosa pine responded with a 59% decrease, from 0.0187 to 0.0077 mu mol g(-1) s(-1). Although below ground CO2 efflux from seedlings grown in either sub- optimal (I mM) or supra-optimal (7 mM) nitrogen availability did not respond to CO2, there was a significant nitrogen treatment effect. Seedlings grown in supra-optimal soil nitrogen had significantly increased specific CO2 efflux rates, and significantly lower total biomass compared to either of the other two nitrogen treatments. These results indicate that carbon losses from the root/rhizosphere systems are responsive to environmental resource availability, that the magnitude and direction of these responses are species dependent, and may lead to significantly different effects on whole plant carbon balance of these two forest tree species.

1600^4^Hendrey,GR^Long,SP^McKee,IF^Baker,NR^1997^1^Can photosynthesis respond to short-term fluctuations in atmospheric carbon dioxide?^91^51^3^179-184^^^^^Mar^^^^^5977
1069^1814^348^635^) with elevated CO2 while ponderosa pine responded with a 59% decrease, from 0.0187 to 0.0077 mu mol g(-1) s(A^5976^Rapid and irregular variations of atmospheric CO2 concentrations (c(a)) occur in nature but are often very much more pronounced and frequent when artificially enriching CO2 concentrations in simulating the future atmosphere. Therefore, there is the danger that plant responses at elevated CO2 in fumigation experiments might reflect the increased Frequency and amplitude of fluctuation in concentration as well as the increase in average concentration. Tests were conducted to determine whether the photosynthetic process could sense such fluctuations in c(a). Instantaneous chlorophyll fluorescence (F-t) was monitored for wheat leaves (Triticum aestivum cv. Hereward) exposed to c(a) oscillating symmetrically by 225 mu mol mol(-1) about a c(a) set point concentration of 575 or 650 mu mol mol(-1). No F-t response was detected to half-cycle step changes in c(a) lasting less than two seconds, but at half- cycles of two seconds or longer, the response of F-t was pronounced. In order to determine the in vivo linear electron transport rate (J) the O-2 concentration was maintained at 21 mmol mol(-1) to eliminate photorespiration. J which is directly proportional to the rate of CO2 uptake under these conditions, was not significantly changed at half-cycles of 30 s or less but was decreased by half-cycles of 60 s or longer. It was inferred that if duration of an oscillation is less than 1 minute and is symmetrical with respect to mean CO2 concentration, then there is no effect on current carbon uptake, but oscillations of 1 minute or more decrease photosynthetic CO2 uptake in wheat.

1601^3^Johnson,DW^Ball,JT^Walker,RF^1997^1^Effects of CO2 and nitrogen fertilization on vegetation and soil nutrient content in juvenile ponderosa pine^206^190^1^29-40^^^^^Mar^^^^^5979
1206^1747^1781^224^312^376^438^512^669^733^No F-t response was detected to half-cycle step changes in c(a) lasting less than two seconds, but at half- cycles of two seconds or longer, the response of F-t was pronounced. In order to determine the in vivo lineA^5978^This paper summarizes the data on nutrient uptake and soil responses in opentop chambers planted with ponderosa pine (Pinus ponderosa Laws.) treated with both N and CO2. Based upon the literature, we hypothesized that 1) elevated CO2 would cause increased growth and yield of biomass per unit uptake of N even if N is limiting, and 2) elevated CO2 would cause increased biomass yield per unit uptake of other nutrients only by growth dilution and only if they are non-limiting. Hypothesis 1 was supported only in part: there were greater yields of biomass per unit N uptake in the first two years of growth but not in the third year. Hypothesis 2 was supported in many cases: elevated CO2 caused growth dilution (decreased concentrations but not decreased uptake) of P, S, and Mg. Effects of elevated CO2 on K, Ca, and B concentrations were smaller and mostly non-significant. There was no evidence that N responded in a unique manner to elevated CO2, despite its unique role in rubisco. Simple growth dilution seemed to explain nutrient responses in almost all cases. There were significant declines in soil exchangeable K+, Ca2+, Mg2+ and extractable P over time which were attributed to disturbance effects associated with plowing. The only statistically significant treatment effects on soils were negative effects of elevated CO2 on mineralizeable N and extractable P, and positive effects of both N fertilization and CO2 on exchangeable Al3+. Soil exchangeable K+, Ca2+, and Mg2+ pools remained much higher than vegetation pools, but extractable P pools were lower than vegetation pools in the third year of growth. There were also large losses of both native soil N and fertilizer N over time. These soil N losses could account for the observed losses in exchangeable K+, Ca2+, Mg2+ if N was nitrified and leached as NO3-.

1602^3^Kellomaki,S^Karjalainen,T^Vaisanen,H^1997^1^More timber from boreal forests under changing climate?^45^94^1-3^195-208^^^^^30 Jun^^^^^5981
130^243^269^344^372^384^427^51^605^991^e growth dilution seemeA^5980^The effects of increases in temperature, precipitation and atmospheric CO2 concentration on timber yields from stands of Scots pine (Pinus sylvestris L.) in southern Finland (61 degrees N) are addressed. The assessment is based on simulations using a process-based model in which temperature, precipitation, and atmospheric CO2 are among the main drivers linking the dynamics of the tree stands directly and indirectly with the changing climate. These factors control photosynthesis, respiration, transpiration and the uptake of nitrogen and water, with consequent effects on the growth and development of tree stands. The timing of thinnings and the length of the rotation were related to the dynamics of the tree stand in compliance with the thinning rules applied in practical forestry. The simulations indicated that an increase in precipitation of 9 mm per decade alone did not affect timber yields. However, a temperature increase of 0.4 degrees C per decade, and the combination of temperature and precipitation increases would increase timber yields by 10% during one rotation. An elevation in the concentration of atmospheric CO2 by 33 mu mol mol(-1) per decade alone would increase removals of timber by 20%, and a combination of increases in temperature, precipitation and CO2 concentration would increase removals by 30%. A rise in precipitation did not have any effect on the length of the rotation, but the other combinations shortened the rotation; by 9 years in the case of elevating temperature, by 17 years in the case of elevating atmospheric CO2 concentration, and by 23 years in the case of the combined elevation of temperature, precipitation, and CO2 concentration due to more rapid tree growth and development. These changes can be expected to affect the supply of timber and also the profitability of forestry. (C) 1997 Elsevier Science B.V.

1603^1^Krupa,SV^1997^1^Global climate change: Processes and products - An overview^326^46^1-2^73-88^^^^^Jun^^^^^5983
1076^1077^1079^174^2054^2324^2531^2532^374^673^pitatiA^5982^Our knowledge of global climate change has many uncertainties. Whether global air temperature will increase, by how much, and when, are subject to debate, but there is little doubt that tropospheric concentrations of several trace gases are increasing. While possible increases in the average air temperature is a product of these changes, the increases in the trace gases alone will have an effect on agriculture. Increases in the ambient concentrations of carbon dioxide are expected to have a positive net effect on crop production. In contrast, any increases in the penetration of surface-level ultraviolet-B (280-320 nm) radiation, and known increases in surface ozone concentrations, are considered to have adverse effects on certain crops. Our present knowledge of the joint effects on crops of elevated levels of carbon dioxide, ultraviolet-B radiation and ozone, and possible alterations in air temperature and precipitation patterns, is virtually zero. Therefore, any predictions of the effects of global climate change on agriculture are subject to significant uncertainties. In contrast, coupling of climate change (only temperature and precipitation) models to crop production has led to a number of future scenarios. In spite of their present limitations, results from these efforts can be useful in planning for future agriculture.

1604^5^Lindroth,RL^Roth,S^Kruger,EL^Volin,JC^Koss,PA^1997^1^CO2-mediated changes in aspen chemistry: Effects on gypsy moth performance and susceptibility to virus^127^3^3^279-289^^^^^Jun^^^^^5985
1401^1652^1997^2533^2534^2535^2536^417^690^733^ penetration of surface-level ultraviolet-B (280-320 nm) radiation, and known increases in surface ozone concentrations, are considered to have adverse effects on certain crops. Our present knowledge of the joint effects on crops of elevated levels of carbon dioxide, ultraviolet-B radiation and ozone, and possible alterations in air temperature and precipitation patterns, is virtually zero. Therefore, any predictions of the effects of global cA^5984^We investigated the effects of long-term CO2 enrichment on foliar chemistry of quaking aspen (Populus tremuloides) and the consequences of chemical changes for performance of the gypsy moth (Lymantria dispar) and susceptibility of the gypsy moth to a nucleopolyhedrosis virus (NPV). Foliage was collected from outdoor open-top chambers and fed to insects in a quarantine rearing facility. Under enriched CO2, levels of leaf nitrogen declined marginally, levels of starch and phenolic glycosides did not change, and levels of condensed tannins increased. Long-term bioassays revealed reduced growth (especially females), prolonged development and increased consumption in larvae fed high-CO2 foliage but no significant differences in final pupal weights or female fecundity. Short-term bioassays showed weaker, and sex-specific, effects of CO2 treatment on larval performance. Correlation analyses revealed strong, negative associations between insect performance and phenolic glycoside concentrations, independent of CO2 treatment. Larval susceptibility to NPV did not differ between CO2 treatments, suggesting that effects of this natural enemy on gypsy moths are buffered from CO2-induced changes in foliar chemistry. Our results emphasize that the impact of enriched CO2 on plant- insect interactions will be determined Rot only by how concentrations of plant compounds are altered, but also by the relevance of particular compounds for insect fitness. This work also underscores the need for studies of genetic variation in plant responses to enriched CO2 and long-term population-level responses of insects to CO2-induced changes in host quality.

1605^2^Manderscheid,R^Weigel,HJ^1997^1^Photosynthetic and growth responses of old and modern spring wheat cultivars to atmospheric CO2 enrichment^169^64^1^65-73^^^^^15 Jun^^^^^5987
130^2537^2538^312^348^372^411^417^434^724^n larval performance. Correlation analyses revealed strong, negative associations between insect performance and phenolic glycoside concentrations, independent ofA^5986^Cultivars of spring wheat (Triticum aestivum L.) introduced between 1890 and I988 were cultivated in pots under optimal growth conditions and exposed during the whole growing season to normal (379 p.p.m.) and elevated CO2 concentrations (689 p.p.m.) in open-top chambers. CO2 effects were measured at anthesis on flag leaf composition (chlorophyll and protein) and photosynthetic parameters, and at maturity on plant growth and yield. CO2 enrichment did not affect light saturated rate of photosynthesis measured at 400 p.p.m. CO2 or protein, total chlorophyll and dry weight content per unit leaf area. However, single flag leaf area and fresh weight per leaf area were increased by CO2. This increase was possibly responsible for a significant decrease in the chlorophyll a/b ratio. Under normal atmospheric CO2 concentration, the total above-ground biomass, stem weight and height, and ear number were negatively correlated with the year of cultivar release. Despite no evidence of CO2 acclimation, i.e, changes in flag leaf composition, CO2 enrichment resulted in a greater growth stimulation of the older than the modern cultivars. This was due to a greater CO2 effect on those growth components that were altered during plant breeding of wheat in the past, i.e. stem weight and height, and ear number. The average CO2-related increase in biomass and grain yield amounted to ca 46% and 28% for the three old (1890-1943) and three modem cultivars (1965- 1988), respectively. Differences in yield response to CO2 enrichment between old and modern cultivars could be mainly explained by changes in ear number. (C) 1997 Elsevier Science B.V.

1606^2^Moorhead,DL^Linkins,AE^1997^1^Elevated CO2 alters belowground exoenzyme activities in tussock tundra^206^189^2^321-329^^^^^Feb^^^^^5989
2117^2118^2539^2540^2541^2542^2543^30^312^344^O2 concentration, the total above-ground biomass, stem weight and height, and ear number were negatively correlated with the year of cultivar release. Despite no evidence of CO2 acclimation, i.e, changes iA^5988^A three-year exposure to a CO2 concentration of 680 mu mol mol(-1) altered the enzymic characteristics of root surfaces, associated ectomycorrhizae, and in soils surrounding roots in a tussock tundra ecosystem of north Alaska, USA. At elevated CO2, phosphatase activity was higher on Eriophorum vaginatum root surfaces, ectomycorrhizal rhizomorphs and mantles associated with Betula nana roots, and in Oe and Oi soil horizons associated with plant roots. Also, endocellulase and exocellulase activities at elevated CO2 were higher in ectomycorrhizal rhizomorphs and lower in Oe and Oi soil horizons associated with roots. These results suggest that arctic plants respond to raised CO2 by increasing activities associated with nutrient acquisition, e.g. higher phosphatase activities on surfaces of roots and ectomycorrhizae, and greater cellulase activity in ectomycorrhizae. Changes in enzyme activities of surrounding soils are consistent with an increase in carbon exudation from plant roots, which would be expected to inhibit cellulase activities and stimulate phosphatase activities of soil microflora. These data were used to modify existing simulation models describing tussock phosphatase activities and litter decay. Model projections suggest that observed increases in phosphatase activities at 680 mu mol mol(-1) CO2, could augment total annual phosphorus release within tussocks by more than 40%, at present levels of root and ectomycorrhizae biomass. This includes a nearly three- fold increase in potential phosphatase activity of E. vaginatum roots, per unit of surface area. Observed reductions in cellulase activities could diminish cellulose turnover by 45% in soils within rooting zones, which could substantially increase mineral nitrogen availability in soils due to lowered microbial immobilization.

1607^6^Norby,RJ^Edwards,NT^Riggs,JS^Abner,CH^Wullschleger,SD^Gunderson,CA^1997^1^Temperature-controlled open-top chambers for global change research^127^3^3^259-267^^^^^Jun^^^^^5991
1262^1317^264^361^372^798^ expecA^5990^To enable experiments on the interactive effects of elevated atmospheric CO2 and increased air temperature on physiological processes in trees to be carried out, we altered the standard design of open-top chambers by replacing blowers with evaporative coolers and in-line heaters, with a feedback control system to maintain ambient or elevated air temperatures within the chambers. Ambient and elevated (+ 4 degrees C) temperature regimes were attained consistently and reliably throughout the growing season, with high reproducibility between chambers. From May through December the average of nearly 300,000 temperature measurements was 18.5 degrees C in ambient air, 18.9 +/- 0.6 degrees C in six ambient chambers, and 22.4 +/- 0.9 degrees C in six elevated temperature chambers. The difference in soil temperature between ambient and elevated chambers was 1.2 degrees C. Absolute humidity (vapour pressure) in the chambers was higher than that of ambient air, but it was generally similar between temperature treatments. Vapour pressure deficit therefore was higher in elevated temperature chambers than in ambient chambers, and this difference is considered an inseparable part of the temperature treatment. The addition of a temperature control system to open-top chambers removes what has been an important flaw in this important tool for global change research.

1608^2^Nosberger,J^Campbell,B^1997^1^Interactions between elevated CO2 and water supply in grasslands - an introduction^127^3^3^175^^^^^Jun

1609^5^Owensby,CE^Ham,JM^Knapp,AK^Bremer,D^Auen,LM^1997^1^Water vapour fluxes and their impact under elevated CO2 in a C4-tallgrass prairie^127^3^3^189-195^^^^^Jun^^^^^5994
1146^312^344^374^495^634^672^740^745^956^ent chambers, and 22.4 +/- 0.9 degrees C in six elevated temperature chambers. The difference in soil temperature between ambient and elevated chambers was 1.2 degrees C. Absolute humidity (vapour pressure) in the chambers was higher than that of ambient air, but it was generally similar between temperature treA^5993^We measured leaf-level stomatal conductance, xylem pressure potential, and stomate number and size as well as whole plant sag now and canopy-level water vapour fluxes in a C4-tallgrass prairie in Kansas exposed to ambient and elevated CO2. Stomatal conductance was reduced by as much as 50% under elevated CO2 compared to ambient. In addition, there was a reduction in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO2 compared to ambient. The result was an improved water status for plants exposed to elevated CO2 which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO2. Sap flow rates were 20 to 30% lower for plants exposed to elevated CO2 than for those exposed to ambient CO2. At the canopy level, evapotranspiration was reduced by 22% under elevated CO2. The reduced water use by the plant canopy under elevated CO2 extended the photosynthetically-active period when water became limiting in the ecosystem. The result was an increased above- and belowground biomass production in years when water stress was frequent.

1610^3^Reekie,JYC^Hicklenton,PR^Reekie,EG^1997^1^The interactive effects of carbon dioxide enrichment and daylength on growth and development in Petunia hybrida^52^80^1^57-64^^^^^Jul^^^^^5996
130^131^230^243^245^2544^372^374^568^740^tion in stomate number of the C4 grass, Andropogon gerardii Vitman, and the C3 dicot herb, Salvia pitcheri Torr., under elevated CO2 compared to ambient. The result was an improved water status for plants exposed to elevated CO2 which was reflected by a less negative xylem pressure potential compared to plants exposed to ambient CO2. Sap flow rates were 20 to 30% lower for plants exposed to elevated CO2 than for those exposed to ambient CO2. At the canopy level, evapotranspiration was reduced by 22% under elevated CO2. The reduced water use by the plant canopy under elevated CO2 extended the photosynthetically-active period when water became limitA^5995^Plants were grown at either 350 or 1000 mu l l(-1) CO2 and in one of three photoperiod treatments: continuous short days (SD), continuous long days (LD), or short switched to long days at day 41 (SD-LD). All plants received 9 h of light at 450 mu mol m(-2) s(-1) and LD plants received an additional 4 h of light at 8 mu mol m(-2) s(-1). Growth of SD plants responded more positively to elevated CO2 than did LD plants, due largely to differences in the effect of CO2 on unit leaf rate. High CO2 increased height and decreased branching under SD conditions, but had no effect under LD conditions. Elevated CO2 also increased the number of buds and open flowers, the effect for flower number being greater in short than in long days. The specific leaf area of plants grown at 1000 mu l l(-1) CO2 was reduced regardless of daylength. High CO2 also decreased leaf and increased reproductive allocation, the magnitude of these effects being greater under SD conditions. Bud formation and flower opening was advanced under high CO2 conditions in SD plants but bud formation was delayed and there was no effect on flower opening under LD conditions. The effects of CO2 on plants switched from SD to LD conditions were largely intermediate between the two continuous treatments, but for some parameters, more closely resembled one or the other. The results illustrate that daylength is an important factor controlling response of plants to elevated CO2. (C) 1997 Annals of Botany Company.

1611^5^Rygiewicz,PT^Johnson,MG^Ganio,LM^Tingey,DT^Storm,MJ^1997^1^Lifetime and temporal occurrence of ectomycorrhizae on ponderosa pine (Pinus ponderosa Laws) seedlings grown under varied atmospheric CO2 and nitrogen levels^206^189^2^275-287^^^^^Feb^^^^^5998
1829^23^2426^2545^2546^2547^372^419^427^669^s grown at 1000 mu l l(-1) CO2 was reduced regardless of daylength. High CO2 also decreased leaf and increased reproductive allocation, the magnitude of these effects being greater under SD conditions. Bud formation and flower opening was advanced undeA^5997^Climate change (elevated atmospheric CO2, and altered air temperatures, precipitation amounts and seasonal patterns) may affect ecosystem processes by altering carbon allocation in plants, and carbon flux from plants to soil. Mycorrhizal fungi, as carbon sinks, are among the first soil biota to receive carbon from plants, and thereby influence carbon release from plants to soil. One step in this carbon release is via fine root and mycorrhizal turnover. It is necessary to know the lifetime and temporal occurrence of roots and mycorrhizae to determine the capacity of the soil ecosystem to sequester carbon assimilated aboveground. In this study, ponderosa pine (Pinus ponderosa Laws) seedlings were grown under three levels of atmospheric CO2 (ambient, 525 and 700 mu mol CO2 mol(-1)) and three levels of annual nitrogen additions (0,100 and 200 kg N ha(-1)) in open-top chambers. At a two-month frequency during 18 months, we observed ectomycorrhizal root tips observed using minirhizotron tubes and camera. The numbers of new mycorrhizal root tips, the numbers of tips that disappeared between two consecutive recording events, and the standing crop of tips at each event were determined. There were more mycorrhizal tips of all three types seen during the summer compared with other times of the year. When only the standing crop of mycorrhizal tips was considered, effects of the CO2 and N addition treatments on carbon allocation to mycorrhizal tips was weakly evident. However, when the three types of tips were considered collectively, tips numbers flux of carbon through mycorrhizae was greatest in the: (1) high CO2 treatment compared with the other CO2 treatments, and (2) intermediate N addition treatment compared with the other N addition treatments. A survival analysis on the entire 18 month cohort of tips was done to calculate the median lifetime of the mycorrhizal root tips. Average median lifetime of the mycorrhizal tips was 139 days and was not affected by nitrogen and CO2 treatments.
tron tubes and camera. Th1612^2^Sadowsky,MJ^Schortemeyer,M^1997^1^Soil microbial responses to increased concentrations of atmospheric CO2^127^3^3^217-224^^^^^Jun^^^^^6000
1262^1298^1334^2426^376^398^474^507^680^962^more mycorrhizal tips of all three types seen during the summer compared with other times of the year. When only the standing crop of mycorrhizal tips was considered, effects of the CO2 and N addition treatments on carbon allocation to mycorrhizal tips was weakly evident. However, when the three types of tips were considered collectively, tips numbers flux of carbon through mycorrhizae was greatest in the: (1) high CO2 treatment compared with the other CO2 treatments, and (2) intermediate N addition treatment compared with the other N addition treatments. A survival analysis on the entire 18 month cohort of tips was done to calculate the median lifetime of the mycorrhizal root tips. Average median lifetime of the mycorrhizal tips was 139 days and was not affected by nitrogen and CO2 treatments.
tron tubes and camera. ThA^5999^Terrestrial ecosystems respond to an increased concentration of atmospheric CO2. While elevated atmospheric CO2 has been shown to alter plant growth and productivity, it also affects ecosystem structure and function by changing below-ground processes. Knowledge of how soil microbiota respond to elevated atmospheric CO2 is of paramount importance for understanding global carbon and nutrient cycling and for predicting changes at the ecosystem-level. An increase in the atmospheric CO2 concentration not only alters the weight, length, and architecture of plant roots, but also affects the biotic and abiotic environment of the root system. Since the concentration of CO2 in soil is already 10-50 times higher than that in the atmosphere, it is unlikely that increasing atmospheric CO2 will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO2 will affect the microbe-soil- plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil water deficit. Consequently, the increased amounts and altered composition of rhizosphere-released materials will have the potential to alter both population and community structure, and activity of soil- and rhizosphere-associated microorganisms. This occurrence could in turn affect plant health and productivity and plant community structure. This review covers current knowledge about the response of soil microbes to elevated concentrations of atmospheric CO2.

1613^5^Schapendonk,AHCM^Dijkstra,P^Groenwold,J^Pot,CS^vandeGeijn,SC^1997^1^Carbon balance and water use efficiency of frequently cut Lolium perenne L swards at elevated carbon dioxide^127^3^3^207-216^^^^^Jun^^^^^6002
1030^1098^130^243^310^344^428^465^661^812^ in the atmosphere, it is unlikely that increasing atmospheric CO2 will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO2 will affect the microbe-soil- plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil A^6001^The impact of doubled atmospheric [CO2] on the carbon balance of regularly cut Lolium perenne L. swards was studied for two years under semi-field conditions in the Wageningen Rhizolab. CO2 and H2O vapour exchange rates of the swards were measured continuously for two years in transparent enclosures. The light utilization efficiencies of the swards ranged between 1.5 g CO2 MJ(-1) global radiation (high light, ambient [CO2]) and 2.8 g CO2 MJ(-1) (low light, doubled [CO2]). The above-ground net primary productivity (NPP) in the enclosures was greater by 29% in 1994 and 43% in 1995 in the doubled [CO2] treatments, but only 20% and 25% more carbon was recovered in the periodical cuts. Thus, NPP increased significantly more than did the harvested aboveground biomass. The positive [CO2] effect on net carbon assimilation is therefore associated with a preferential allocation of extra carbon to the roots and soil. In addition to higher canopy photosynthesis and leaf elongation rates, a small part of the positive [CO2] effects on NPP could be attributed to a decrease of the specific respiration of the shoots. On a canopy basis however, respiration was equal or slightly higher at doubled [CO2] due to the higher amount of standing biomass. Comparison of NPP and carbon recovered in different harvests showed that allocation to roots and soil was highest in spring, it was low in early summer and increased again in late summer and autumn. The total gross amount of carbon partitioned to the roots and soil during the two year period was 57% more at doubled [CO2]. The total amount of carbon that was sequestered in the soil after subtraction of the respiratory losses was 458 g m(-2) and 779 g m(-2) in the ambient and doubled [CO2] treatments, respectively. The average water use efficiency (WUE) of the swards was increased by a factor 1.5 at doubled [CO2]. Both WUE and its positive interaction with [CO2] varied between years and were positively correlated with global irradiance. At doubled [CO2], the higher WUE was fully compensated for by a higher leaf area index. Therefore, total transpiration on a canopy basis was equal for the ambient and the doubled [CO2] concentrations in both years.

1614^4^Stirling,CM^Davey,PA^Williams,TG^Long,SP^1997^1^Acclimation of photosynthesis to elevated CO2 and temperature in five British native species of contrasting functional type^127^3^3^237-246^^^^^Jun^^^^^6004
312^344^374^376^384^417^639^698^73^92^d autumn. The total gross amount of carbon partitioned to the roots and soil during the two year period was 57% more at doubled [CO2]. The total amount of carbon that was sequestered in the soil after subtraction of the respiratory losses was 458 g m(-2) and 779 g m(-2) in the ambient and doubled [CO2] treatments, respectively. The average water use efficiency (WUE) of the swards was increased by a factor 1.5 at doubled [CO2]. Both WUE and its positive interaction with [CO2] varied between years and were positively correlated with global irradiance. At doubled [CO2], the higher WUE was fully coA^6003^Acclimation of photosynthesis to growth at elevated CO2 concentration varies markedly between species. Species functionally classified as stress-tolerators (S) and ruderals (R), are thought to be incapable, or the least capable, of responding positively in terms of growth to elevated [CO2]. Is this pattern of response also apparent in leaf photosynthesis of wild S- and R-strategists? Acclimatory loss of a photosynthetic and growth response to elevated [CO2] is assumed to reflect limitation on capacity to utilize additional photosynthate. The doubling of pre-industrial global [CO2] is expected to coincide with a 3 degrees C increase in mean temperature which could stimulate growth; will photosynthetic capacity at elevated [CO2] be greater when the concurrent temperature increase is simulated? Five species from natural grassland of NW Europe and of contrasting ecological strategy were grown in hemispherical greenhouses, environmentally controlled to track the external microclimate. Within a replicated design, plants were grown at (i) current ambient [CO2] and temperature, (ii) elevated [CO2] (ambient + 340 mu mol mol(-1)) and ambient temperature, (iii) ambient [CO2] and elevated temperature (ambient + 3 degrees C), or (iv) elevated [CO2] and elevated temperature. After 75-104 days, the CO2 response of light-saturated rates of photosynthesis (A(sat)) was analysed in controlled-environment cuvettes in a field laboratory. There was no acclimatory loss of photosynthetic capacity with growth in elevated [CO2] or elevated temperature over this period in Poa alpina (S), Bellis perennis (R) or Plantago lanceolata (mixed C-S-R strategist), and a significant (P < 0.05) increase in capacity in Helianthemum nummularium (S) and Poa annua (R). Photosynthetic rates of leaves grown and measured in elevated [CO2] were therefore significantly higher than rates for leaves grown and measured in ambient [CO2], for all species. With the exception of Poa alpina, stomatal conductance and stomatal limitation on A(sat) showed no acclimatory response to growth in elevated [CO2]. Carboxylation efficiency, determined from the initial slope of the response of A(sat) to intercellular CO2 concentration was significantly increased by elevated [CO2] and elevated temperature in H. nummularium, implying a possible increase in in vivo RubisCO activity. Increased carboxylation efficiency of this species was also reflected by an increase in the CO2- and light- saturated rates of photosynthesis, indicating an increased capacity for regeneration of the primary CO2 acceptor in photosynthesis. The results show that R-strategists and slow- growing S-strategists, are inherently capable of large increases in leaf photosynthetic capacity with growth in elevated [CO2] in contrast to expectations from growth studies. With the exception of P. annua, where there was a significant negative interaction between CO2 and temperature, concurrent increase in growth temperature had little effect on this pattern of response.
stomatal limitation on A(sat) showed no ac1615^2^Tate,KR^Ross,DJ^1997^1^Elevated CO2 and moisture effects on soil carbon storage and cycling in temperate grasslands^127^3^3^225-235^^^^^Jun^^^^^6006
1262^1298^137^2116^2548^344^362^376^535^57^elevated [CO2] and elevated temperature in H. nummularium, implying a possible increase in in vivo RubisCO activity. Increased carboxylation efficiency of this species was also reflected by an increase in the CO2- and light- saturated rates of photosynthesis, indicating an increased capacity for regeneration of the primary CO2 acceptor in photosynthesis. The results show that R-strategists and slow- growing S-strategists, are inherently capable of large increases in leaf photosynthetic capacity with growth in elevated [CO2] in contrast to expectations from growth studies. With the exception of P. annua, where there was a significant negative interaction between CO2 and temperature, concurrent increase in growth temperature had little effect on this pattern of response.
stomatal limitation on A(sat) showed no acA^6005^In grassland ecosystems, most of the carbon (C) occurs below- ground. Understanding changes in soil fluxes induced by elevated atmospheric CO2 is critical for balancing the global C budget and for managing grassland ecosystems sustainably. In this review, we use the results of short-term (1-2 years) studies of below-ground processes in grassland communities under elevated CO2 to assess future prospects for longer-term increases in soil C storage. Results are broadly consistent with those from other plant communities and include: increases in below-ground net primary productivity and an increase in soil C cycling rate, changes in soil faunal community, and generally no increase in soil C storage. Based on other experimental data, future C storage could be favoured in soils of moderate nutrient status, moderate-to-high clay content, and low (or moderately high) soil moisture status. Some support for these suggestions is provided by preliminary results from direct measurements of soil C concentrations near a New Zealand natural CO2-venting spring, and by simulations of future changes in grassland soils under the combined effects of CO2 fertilization and regional climate change. Early detection of any increase in soil C storage appears unlikely in complex grassland communities because of (a) the difficulty of separating an elevated CO2 effect from the effects of soil factors including moisture status, (b) the high spatial variability of soil C and (c) the effects of global warming. Several research imperatives are identified for reducing the uncertainties in the effects of elevated atmospheric CO2 on soil C.

1616^5^Vose,JM^Elliott,KJ^Johnson,DW^Tingey,DT^Johnson,MG^1997^1^Soil respiration response to three years of elevated CO2 and N fertilization in ponderosa pine (Pinus ponderosa Dong Ex Laws)^206^190^1^19-28^^^^^Mar^^^^^6008
130^1686^1689^2367^2549^580^711^782^946^l moisture status. Some support for these suggestions is provided by preliminary results from direct measurements of soil C concentrations neA^6007^We measured growing season soil CO2 evolution under elevated atmospheric [CO2] and soil nitrogen (N) additions. Our objectives were to determine treatment effects, quantify seasonal variation, and compare two measurement techniques. Elevated [CO2] treatments were applied in open-top chambers containing ponderosa pine (Pinus ponderosa L.) seedlings. N applications were made annually in early spring. The experimental design was a replicated factorial combination of CO2 (ambient, +175, and +350 mu L L-1 CO2) and N (0, 10, and 20 g m(-2) N as ammonium sulphate). Soils were irrigated to maintain soil moisture at > 25 percent. Soil CO2 evolution was measured over diurnal periods (20-22 hours) in October 1992, and April, June, and October 1993 and 1994 using a flow- through, infrared gas analyzer measurement system and corresponding pCO(2) measurements were made with gas wells. Significantly higher soil CO2 evolution was observed in the elevated CO2 treatments; N effects were not significant. Averaged across all measurement periods, fluxes, were 4.8, 8.0, and 6.5 for ambient + 175 CO2, and +350 CO2 respectively). Treatment variation was linearly related to fungal occurrence as observed in minirhizotron tubes. Seasonal variation in soil CO2 evolution was non-linearly related to soil temperature; i.e., fluxes increased up to approximately soil temperature (10cm soil depth) and decreased dramatically at temperatures > 18 degrees C. These patterns indicate exceeding optimal temperatures for biological activity. The dynamic, flow-through measurement system was weakly correlated (r = 0.57; p < 0.0001; n = 56) with the pCO(2) measurement method.

1617^2^Wang,KY^Kellomaki,S^1997^1^Effects of elevated CO2 and soil-nitrogen supply on chlorophyll fluorescence and gas exchange in Scots pine, based on a branch- in-bag experiment^84^136^2^277-286^^^^^Jun^^^^^6010
1206^130^1344^243^312^361^374^376^417^92^tly higher soil CO2 evolution was observed in the elevated CO2 treatments; N effects were not significant. Averaged acrossA^6009^Applying the branch-in-bag method, naturally seeded Scots pine (Pinus sylvestris L.) trees, 25-30 yr old, were subjected to two CO2 concentrations (350 and 700 mu mol mol(-1)) and two soil-nitrogen-supply regimes for three growing seasons (1994- 96). Gas exchange and chlorophyll a fluorescence in detached shoots were measured simultaneously in a diffuse radiation field. Elevated CO2 did not lead to a significant 'downward regulation' in the light-saturated rate of net photosynthesis (P-n.max), the maximum apparent quantum yield (alpha(A.max)) or the maximum photochemical efficiency (F-v/F-m) of photosystem II (PS II). However, the elevated CO2 significantly decreased the light-saturated stomatal conductance and increased the sensitivity of stomatal conductance to change in low photon- flux densities. The high soil-nitrogen supply significantly increased photosynthetic capacity, as manifested by increases in P-n.max, alpha(A.max), F-v/F-m, and the effective photochemical efficiency (Delta F/F'(m)) at low photon-flux densities, did not, on the other hand, enhance the magnitude of photosynthetic response to elevated CO2 concentration. In addition, the treatment-induced modifications in fluorescence parameters are discussed in detail.

1618^1^Ferguson,SA^1997^1^A climate-change scenario for the Columbia River basin^327^^499^CP1-CP&^^^^^Apr^^^^^6012
130^314^413^5^937^on field. Elevated CO2 did not lead to a significant 'downward regulation' in the light-saturated rate of net photosynthesis (P-n.max), the maximum apparent quantum yield (alpha(A.max)) or the maximum photochemical efficiency (F-v/F-m) of photosystem II (PS II). However, the elevated CO2 significantly decreased the light-saturated stomatal conductance and increased the sensitivity of stomatal conductance to change in low photon- flux densities. The high soil-nitrogen supply significantly increased photosynthetic capacity, as manifested by increases in P-n.max, alpha(A.max), F-v/F-m, and the effective photochemical efficiency (Delta F/F'(m)) at lA^6011^This work describes the method used to generate a climate- change scenario for the Columbia River basin. The scenario considers climate patterns that may change if the atmospheric concentration of carbon dioxide (CO2), or its greenhouse gas equivalent, were to double over pre-Industrial Revolution values. Given the current rate of increase in atmospheric CO2 concentration, doubling could occur within the next 50 to 100 years. The Columbia River basin is in a transition climate zone between predominating maritime to the west, arctic to the north, and continental to the east. Consequently, it is difficult to characterize through means and averages. Therefore, many of the current stochastic methods for developing climate-change scenarios cannot directly apply to the basin. To circumvent this problem, a composite approach was taken to generate a climate scenario that considers knowledge of current regional climate controls, available output from general circulation and regional climate models, and observed changes in climate. The resulting climate-change scenario suggests that precipitation could increase substantially during winter (+20 to +50 percent) and moderately during spring and autumn (+5 to +35 percent). A slight decrease (0 to -5 percent) in summer precipitation is possible, except for the southeastern portions of the basin that may experience an increase in convective precipitation (+5 percent). Low- elevation (<1 kilometer) temperatures throughout the year may increase 1 to 3 degrees C, with greatest increases during winter. This amount of temperature change is possible because of an expected loss of low-elevation snow cover. At high elevations, increased cloud cover could cause average temperatures to decrease during winter but be synchronized with possible warming at low elevations during summer. The diurnal range of temperature could decrease, especially in summer and autumn.
 current regional climate controls, available output from general circulation and regional climate models, and observe1619^2^Arnone,JA^Kestenholz,C^1997^1^Root competition and elevated CO2: Effects on seedling growth in Linum usitatissimum populations and Linum Silene cretica mixtures^43^11^2^209-214^^^^^Apr^^^^^6014
245^312^344^374^376^417^672^740^778^957^rcent) in summer precipitation is possible, except for the southeastern portions of the basin that may experience an increase in convective precipitation (+5 percent). Low- elevation (<1 kilometer) temperatures throughout the year may increase 1 to 3 degrees C, with greatest increases during winter. This amount of temperature change is possible because of an expected loss of low-elevation snow cover. At high elevations, increased cloud cover could cause average temperatures to decrease during winter but be synchronized with possible warming at low elevations during summer. The diurnal range of temperature could decrease, especially in summer and autumn.
 current regional climate controls, available output from general circulation and regional climate models, and observeA^6013^1. Root competition can be an important determinant of the performance of neighbours within plant populations and communities. Because plants often maintain larger root systems and allocate more of their carbon to root systems under elevated atmospheric CO2 than they do at lower CO2 concentrations, root-root interactions could play an increasingly important role in determining competitive outcomes among individuals and plant species as global CO2 concentration continues to rise. 2. We established 12 pure stands of Linum usitatissimum (flax) and 12 mixed stands of Linum and its naturally co-occurring weed species Silene cretica in opaque plastic trays each filled with the same amount of nutrient-rich soil mix. In half of the trays from each of these stand types, vertical waterproof partitions separated the root systems of individual plants from each other to prevent root competition, while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under low atmospheric CO2 concentration (320 mu ll(-1)) and the other half under elevated CO2 (600 mu ll(-1)), in daylight growth: chambers for 30 days from seedling emergence until harvest in mid-June. All trays received equal amounts of water so that soils in the low CO2 treatment were maintained at field capacity. 3. Our results indicate that under high soil fertilities: (1) intra-specific root-root interactions alone play a relatively insignificant role in determining plant biomass production within pure Linum populations and (2) the impact of an aggressive species (Silene) on co-occurring less aggressive species (Linum) becomes more severe under elevated CO2 as a result of amplified interspecific root competition.

1620^2^Berntson,GM^Bazzaz,FA^1996^1^Belowground positive and negative feedbacks on CO2 growth enhancement^206^187^2^119-131^^^^^^^^^^6016
1829^2032^2116^2550^372^376^377^547^56^689^while in the other half no partitions were present. Half of the trays from all treatments were allowed to grow under lowA^6015^In this paper we present a conceptual model of integrated plant-soil interactions which illustrates the importance of identifying the primary belowground feedbacks, both positive and negative, which can simultaneously affect plant growth responses to elevated CO2. The primary negative feedbacks share the common feature of reducing the amount of nutrients available to plants. These negative feedbacks include increased litter C/N ratios, and therefore reduced mineralization rates, increased immobilization of available nutrients by a larger soil microbial pool, and increased storage of nutrients in plant biomass and detritus due to increases in net primary productivity (NPP). Most of the primary positive feedbacks share the common feature of being plant mediated feedbacks, the only exception being Zak et al.'s hypothesis that increased microbial biomass will be accompanied by increased mineralization rates. Plant nutrient uptake may be increased through alterations in root architecture, physiology, or mycorrhizal symbioses. Further, the increased C/N ratios of plant tissue mean that a given level of NPP can be achieved with a smaller supply of nitrogen. Identification of the net plant-soil feedbacks to enhanced productivity with elevated CO2 are a critical first step for any ecosystem. It is necessary, however, that we first identify how universally applicable the results are from one study or one ecosystem before ecosystem models incorporate this information. The effect of elevated CO2 on plant growth (including NPP, tissue quality, root architecture, mycorrhizal symbioses) can vary greatly for different species and environmental conditions. Therefore it is reasonable to expect that different ecosystems will show different patterns of interacting positive and negative feedbacks within the plant-soil system. This inter-ecosystem variability in the potential for long-term growth responses to rising CO2 levels implies that we need to parameterize mechanistic models of the impact of elevated CO2 on ecosystem productivity using a detailed understanding of each ecosystem of interest.

1621^3^Drake,BG^GonzalezMeler,MA^Long,SP^1997^1^More efficient plants: A consequence of rising atmospheric CO2?^208^48^^609-639^^^^^^^^^^6018
1344^2489^341^343^372^399^448^550^692^966^rst step for any ecosystem. It is necessary, however, that we first identify how universally applicable the results are from one study or one ecosystem before ecosystem models incorporate this information. The effect of elevated CO2 on plant growth (including NPP, tissue quality, root architecture, mycorrhizal symbioses) can vary greatly for different species and environmental conditions. Therefore it is reasonable to expect that different ecosystems will show different patterns of interacting positive and negative feedbacks within the plant-soil system. This inter-ecosystem variability in the potential for long-term growth responses to rising CO2 levels implies that we need to parameterize mechanistic models of the impact of elevated CO2 on ecosystem pA^6017^The primary effect of the response of plants to rising atmospheric CO2 (C-a) is to increase resource use efficiency. Elevated C-a reduces stomatal conductance and transpiration and improves water use efficiency, and at the same time it stimulates higher rates of photosynthesis and increases light- use efficiency. Acclimation of photosynthesis during long-term exposure to elevated C-a reduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil-water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated C-a. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric C-a and climate change.
esponses to rising CO2 levels implies that we need to parameterize mechanistic models of the impact of elevated CO2 on ecosystem p1622^5^Drake,BG^Muehe,MS^Peresta,G^GonzalezMeler,MA^Matamala,R^1996^1^Acclimation of photosynthesis, respiration and ecosystem carbon flux of a wetland on Chesapeake Bay, Maryland to elevated atmospheric CO2 concentration^206^187^2^111-118^^^^^^^^^^6020
2455^264^376^378^384^547^728^73^968^99^ases light- use efficiency. Acclimation of photosynthesis during long-term exposure to elevated C-a reduces key enzymes of the photosynthetic carbon reduction cycle, and this increases nutrient use efficiency. Improved soil-water balance, increased carbon uptake in the shade, greater carbon to nitrogen ratio, and reduced nutrient quality for insect and animal grazers are all possibilities that have been observed in field studies of the effects of elevated C-a. These effects have major consequences for agriculture and native ecosystems in a world of rising atmospheric C-a and climate change.
esponses to rising CO2 levels implies that we need to parameterize mechanistic models of the impact of elevated CO2 on ecosystem pA^6019^Acclimation of photosynthesis and respiration in shoots and ecosystem carbon dioxide fluxes to rising atmospheric carbon dioxide concentration (C-a) was studied in a brackish wetland. Open top chambers were used to create test atmospheres of normal ambient and elevated C-a(=normal ambient+34 Pa CO2) over mono-specific stands of the C-3 sedge Scirpus olneyi, the dominant C-3 species in the wetland ecosystem, throughout each growing season since April of 1987. Acclimation of photosynthesis and respiration were evaluated by measurements of gas exchange in excised shoots. The impact of elevated C-a on the accumulation of carbon in the ecosystem was determined by ecosystem gas exchange measurements made using the open top chamber as a cuvette. Elevated C-a increased carbohydrate and reduced Rubisco and soluble protein concentrations as well as photosynthetic capacity(A) and dark respiration (R-d; dry weight basis) in excised shoots and canopies (leaf area area basis) of Scirpus olneyi, Nevertheless, the rate of photosynthesis was stimulated 53% in shoots and 30% in canopies growing in elevated C-a compared to normal ambient concentration. Elevated C-a inhibited R-d measured in excised shoots (-19 to -40%) and in seasonally integrated ecosystem respiration (R-e; -36 to -57%). Growth of shoots in elevated C- a was stimulated 14-21%, but this effect was not statistically significant at peak standing biomass in midseason. Although the effect of elevated C-a on growth of shoots was relatively small, the combined effect of increased number of shoots and stimulation of photosynthesis produced a 30% stimulation in seasonally integrated gross primary production (GPP). The stimulation of photosynthesis and inhibition of respiration by elevated C-a increased net ecosystem production (NEP=GPP-R-e) 59% in 1993 and 50% in 1994. While this study consistently showed that elevated C-a produced a significant increase in NEP, we have not identified a correspondingly large pool of carbon below ground.
neyi, Nevertheless, the ra1623^5^Fangmeier,A^Gruters,U^Hogy,P^Vermehren,B^Jager,HJ^1997^1^Effects of elevated CO2 nitrogen supply and tropospheric ozone on spring wheat .2. Nutrients (N, P, K, S, Ca, Mg, Fe, Mn, Zn)^35^96^1^43-59^^^^^^^^^^6022
204^229^243^312^344^360^386^673^692^975^; -36 to -57%). Growth of shoots in elevated C- a was stimulated 14-21%, but this effect was not statistically significant at peak standing biomass in midseason. Although the effect of elevated C-a on growth of shoots was relatively small, the combined effect of increased number of shoots and stimulation of photosynthesis produced a 30% stimulation in seasonally integrated gross primary production (GPP). The stimulation of photosynthesis and inhibition of respiration by elevated C-a increased net ecosystem production (NEP=GPP-R-e) 59% in 1993 and 50% in 1994. While this study consistently showed that elevated C-a produced a significant increase in NEP, we have not identified a correspondingly large pool of carbon below ground.
neyi, Nevertheless, the raA^6021^CO2 enrichment is expected to alter leaf demand for nitrogen and phosphorus in plant species with C-3 carbon dioxide fixation pathway, thus possibly causing nutrient imbalances in the tissues and disturbance of distribution and redistribution patterns within the plants. To test the influence of CO2 enrichment and elevated tropospheric ozone in combination with different nitrogen supply, spring wheat (Tritium aestivum L. cv. Minaret) was exposed to three levels of CO2 (361, 523, and 639 mu l liter(-1), 24 h mean from sowing to final harvest), two levels of ozone (28.4 and 51.3 nl litre(-1)) and two levels of nitrogen supply (150 and 270 kg ha(-1)) in a full-factorial design in open-top field chambers. Additional fertilization experiments (120, 210, and 330 kg N ha(-1)) were carried out at low and high CO2 levels. Macronutrients (N, P, K, S, Ca, Mg) and three micronutrients (Mn, Fe, Zn) were analysed in samples obtained at three different developmental stages: beginning of shoot elongation, anthesis, and ripening. At each harvest, plant samples were separated into different organs (green and senescent leaves, stem sections, ears, grains). According to analyses of tissue concentrations at the beginning of shoot elongation, the plants were sufficiently equipped with nutrients. Elevated ozone levels neither affected tissue concentrations nor shoot uptake of the nutrients. CO2 and nitrogen treatments affected nutrient uptake, distribution and redistribution in a complex manner. CO2 enrichment increased nitrogen-use efficiency and caused a lower demand for nitrogen in green tissues which was reflected in a decrease of critical nitrogen concentrations, lower leaf nitrogen concentrations and lower nitrogen pools in the leaves. Since grain nitrogen uptake during grain filling depended completely on redistribution from vegetative pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO2 enrichment in a similar manner to nitrogen. Phosphorus concentrations in green tissues, on the other hand, were not, or only slightly, affected by elevated CO2. In stems, 'dilution' of all nutrients except manganese was observed, caused by the huge accumulation of water soluble carbohydrates, mainly fructans, in these tissues under CO2 enrichment. Whole shoot uptake was either remarkably increased (K, Mn, P, Mg), nearly unaffected (N, S, Fe, Zn) or decreased (Ca) under CO2 enrichment. Thus, nutrient cycling in plant-soil systems is expected to be altered under CO2 enrichment. (C) 1997 Elsevier Science Ltd.

1624^2^Gorny,JR^Kader,AA^1997^1^Low oxygen and elevated carbon dioxide atmospheres inhibit ethylene biosynthesis in preclimacteric and climacteric apple fruit^154^122^4^542-546^^^^^Jul^^^^^6024
1068^1678^1864^2077^2551^618^829^845^ve pools in green tissues, grain nitrogen concentrations fell considerably with severe implications for grain quality. Ca, S, Mg and Zn in green tissues were influenced by CO2 enrichment in aA^6023^Autocatalytic C2H4 biosynthesis in preclimacteric apple fruit (Malus domestica Borkh, 'Golden Delicious') was prevented by storage in atmospheres of 20% CO2-enriched air (17% O-2+ 63% N- 2) or 0.25% O-2 (balance N-2). In preclimacteric fruit, both treatments inhibited C2H4 biosynthesis by suppressing expression of ACC synthase (ACC-S) at the mRNA level. ACC oxidase (ACC-O) mRNA abundance and in vitro enzyme activity also were impaired by these treatments. However, the conversion of ACC to C2H4 never became the rate limiting step in C2H4 biosynthesis, C2H4 biosynthesis also was effectively inhibited in climacteric apple fruit kept in air + 20% CO2 or 0.25% O-2. Climacteric apples also exhibited suppressed expression of ACC- S at the mRNA level, while ACC-O transcript abundance, enzyme activity, and protein abundance mere reduced only slightly. ACC-S is the key regulatory enzyme of C2H4 biosynthesis and is the major site at which elevated CO2 and reduced O-2 atmospheres inhibit C2H4 biosynthesis, irrespective of fruit physiological maturity. Chemical names used: 1- aminocyclopropane-1-carboxcylic acid (ACC).

1625^3^Hao,XM^Hale,BA^Ormrod,DP^1997^1^The effects of ultraviolet-B radiation and carbon dioxide on growth and photosynthesis of tomato^188^75^2^213-219^^^^^Feb^^^^^6026
1155^1163^174^2327^417^434^447^73^747^874^ ACC synthase (ACC-S) at the mRNA level. ACC oxidase (ACC-O) mRNA abundance and in vitro enzyme activity also were impaired by these treatments. However, the conversion of ACC to C2H4 never became the rate limiting step in C2H4 biosynthesis, C2H4 biosynthesis also was effectively inhibited in climacteric apple fruit kept in air + 20% CO2 or 0.25% O-2. Climacteric apples also exhibited suppressed expression of ACC- S at the mRNA level, while ACC-O transcript abundance, enzyme activity, and protein abundance mere reduced only slightly. ACC-S is the key regulatory enzyme of C2H4 biosynthesis and is the major site at which elevated CO2 and reduced O-2 atmospheres inhibit C2H4 biosynthesis, irrespA^6025^Tomato (Lycopersicon esculentum Mill.) plants were exposed, in controlled environments with 2.7 Wi(m(2).day) background ultraviolet-B (UV-B) radiation from fluorescent and incandescent lamps, to ambient (380 mu L.L-1) or elevated (600 mu L.L-1) CO2 combined with a total of 7.2 or 13.1 kJ/(m(2).day) UV-B radiation to determine effects on growth and photosynthesis. Ten consecutive days of exposure to the higher level of UV-B significantly reduced total and stem dry weight, leaf area, and plant height compared with the lower level. Only leaf area and plant height were significantly reduced after 19 consecutive days of exposure. To investigate whether plants recover from UV-B damage, the UV-B exposures were halted for 3 days after 19 days of UV-B exposure and then restarted for a further 2 days. The largest reduction in plant growth was found after 3 days with no UV-B followed by 2 days of the higher level of UV-B. Plants did not recover from UV-B damage during the 3 days with background UV-B. Significant CO(2)xUV-B interactions were detected on stem dry weight after 10 consecutive days of the higher level of UV-B and on total dry weight, leaf dry weight, stem dry weight, and plant height after 3 days with no UV-B followed by 2 days of the higher level of UV-B. The higher dose of enhanced UV-B resulted in more severe damage at 600 mu L.L-1 CO than at ambient CO2. The higher level of UV-B did not affect the leaf net photosynthesis rate on a leaf area basis, although this UV-B level may have inhibited tomato growth through reducing the photosynthetic area. UV-absorbing compounds in leaves in the highest UV-B radiation level for 19 days were greater than for leaves with the lower dose. These UV-absorbing compounds in the higher UV-B dose diminished more than in the lower dose plants during the 3 days without UV-B. The UV-absorbing compounds maintained by plants exposed to the highest level of UV-B radiation may have protected plants from UV-B damage, particularly between 10 and 19 consecutive days of exposure.
1626^4^Hungate,BA^Jackson,RB^Field,CB^Chapin,FS^1996^1^Detecting changes in soil carbon in CO2 enrichment experiments^206^187^2^135-145^^^^^^^^^^6028
1030^1298^130^1317^372^374^417^429^57^740^ 3 days with no UV-B followed by 2 days of the higher level of UV-B. The higher dose of enhanced UV-B resulted in more severe damage at 600 mu L.L-1 CO than at ambient CO2. The higher level of UV-B did not affect the leaf net photosynthesis rate on a leaf area basis, although this UV-B level may have inhibited tomato growth through reducing the photosynthetic area. UV-absorbing compounds in leaves in the highest UV-B radiation level for 19 days were greater than for leaves with the lower dose. These UV-absorbing compounds in the higher UV-B dose diminished more than in the lower dose plants during the 3 days without UV-B. The UV-absorbing compounds maintained by plants exposed to the highest level of UV-B radiation may have protected plants from UV-B damage, particularly between 10 and 19 consecutive days of exposure.
A^6027^After four growing seasons, elevated CO did not significantly alter surface soil C pools in two intact annual grasslands. However, soil C pools in these systems are large compared to the likely changes caused by elevated CO2. We calculated statistical power to detect changes in soil C, using an approach applicable to all elevated CO2 experiments. The distinctive isotopic signature of the fossil-fuel-derived CO2 added to the elevated CO2 treatment provides a C tracer to determine the rate of incorporation of newly-fixed C into soil. This rate constrains the size of the possible effect of elevated CO2 on soil C, Even after four years of treatment, statistical power to detect plausible changes in soil C under elevated CO2 is quite low. Analysis of other elevated CO2 experiments in the literature indicates that either CO2 does not affect soil C content, or that reported CO2 effects on soil C are too large to be a simple consequence of increased plant carbon inputs, suggesting that other mechanisms are involved, or that the differences are due to chance. Determining the effects of elevated CO2 on total soil C and long-term C storage requires more powerful experimental techniques or experiments of longer duration.

1627^1^Jablonski,LM^1997^1^Responses of vegetative and reproductive traits to elevated CO2 and nitrogen in Raphanus varieties^188^75^4^533-545^^^^^Apr^^^^^6030
243^2552^2553^341^348^433^439^58^665^92^ved CO2 added to the elevated CO2 treatment provides a C tracer to determine the rate of incorporation of newly-fixed C into soil. This rate constrains the size of the possible effect of elevated CO2 on soil C, Even after four years of treatment, statistical power to detect plausible changes in soil C under elevated CO2 is quite low. Analysis of other elevated CO2 experiments in the literature indicates that either CO2 does not affect soil C content, or that reported CO2 effects on soil C are too large to be a simple consequence of increased plant carbon inputs, suggesting that other mechanisms are invA^6029^The relationships between the responses to elevated CO2 of the vegetative and reproductive phase were investigated in radish, used as a test system. The hypothesis that an increase in nonfoliar vegetative storage capacity promotes reproductive output was tested. Three cultivars of Raphanus sarivus and the wild, Raphanus raphanistrum, differing in root to shoot ratios, were grown under two levels of CO2 and two levels of nitrogen fertilization. Varieties possessed different strategies of carbon storage and showed distinct responses to CO2 at each vegetative harvest time. Vegetative sinks of hypocotyls, petioles, and young blades were enhanced by CO2. Nitrogen promoted vegetative shoot growth, but did not enhance the reproductive response to CO2. By the end of the reproductive phase, varieties did not differ in total biomass. Reproductive response to CO2 may have been limited by the lack of an effect on the timing of flowering. Correlations in CO2 enhancement ratios were examined in 12 traits of each phase. Only vegetative total leaf area correlated with reproductive mass. Foliar starch correlated with decreased abortion. Enhancements in vegetative biomass did not correlate with any reproductive response. Detailed studies of the reproductive phase are needed to understand the whole-plant response to elevated CO2.

1628^2^Kinney,KK^Lindroth,RL^1997^1^Responses of three deciduous tree species to atmospheric CO2 and soil NO3- availability^155^27^1^1-10^^^^^Jan^^^^^6032
29^312^361^372^417^57^664^672^n storage and showed distinct responses to CO2 at each vegetative harvest time. Vegetative sinks of hypocotyls, petioles, and young blades were enhanced by CO2. Nitrogen promoted vegetative shoot growth, but did not enhance the reproductive response to CO2. By the end of the reproductive phase, varieties did not differ in total biomass. Reproductive response to CO2 may have been limited by the lack of an effect on the timing of flowering. Correlations in CO2 enhancement ratios were examined in 12 traits of each phA^6031^This research evaluated the direct and interactive effects of atmospheric CO2 and soil NO3- availability on growth and biomass partitioning of quaking aspen (Populus tremuloides Michx.), red oak (Quercus rubra L.), and sugar maple (Acer saccharum Marsh.). In the split split plot experimental design, NO3- availability (low and high) and tree species were nested in two levels of atmospheric CO2 (ambient, 355 mu L/L; elevated, 650 mu L/L). Seedlings were grown for 57 days in environmental control rooms. Increased CO2 and NO3- availability positively and (mostly) independently influenced total growth and relative growth rates. Moderate to weak interactions between CO2 and NO3- for several growth parameters (e.g., leaf production, shoot length, root collar diameter) in some species indicated an enhanced response to CO2 enrichment under conditions of high NO3- availability. Interactive effects were most pronounced in aspen. Seedling growth and allocation responses to CO2 and NO3- were frequently species specific and associated with successional status. For example, proportional increases in growth in response to elevated CO2 were greatest for sugar maple and least for quaking aspen, whereas the converse was hue with respect to response to high NO3- availability. This research indicates that the impact of enriched CO2 atmospheres on forest communities will be influenced by both nutrient availability and unique species characteristics.

1629^9^Li,AG^Trent,A^Wall,GW^Kimball,BA^Hou,YS^Pinter,PJ^Garcia,RL^Hunsaker,DV^Lamorte,RL^1997^1^Free-air CO2 enrichment effects on rate and duration of apical development of spring wheat^164^37^3^789-796^^^^^May-Jun^^^^^6034
1173^130^2276^2554^2555^2556^264^434^724^92^parameters (e.g., leaf production, shoot length, root collar diameter) in some species indicated an enhanced response to CO2 enrichment under conditions of high NO3- availability. Interactive effects were most pronounced in aspen. Seedling growth and allocation responses to CO2 and NO3- were frequently species speA^6033^Rates and durations of individual phases of wheat (Triticum aestivum L.) apical development are among the most important factors that determine yield components. Because atmospheric CO2 has been increasing steadily, it is important to evaluate the effects of elevated CO2 on wheat development. This study was conducted to determine rates and durations of leaf, spikelet, and floret primordium initiation in a Free-Air Carbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two CO2 concentrations were 550 (elevated) and 370 (ambient) mu mol mol(-1) CO2. Individual plant samples were collected every 3 to 4 d. We dissected the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, T11, and T12) and counted primordia. Apex primordium data were fitted to a four-piece linear-spline segmented regression model with the SAS proc NLIN. No influence of elevated CO2 (550 mu mol mol(- 1)) on leaf primordium initiation of MS was detected. Nevertheless, CO2 enrichment significantly increased rates of spikelet primordium initiation of MS, T1, T2, T10, and T11, and diminished the durations of spikelet development phase of MS, T1, T2, T3, T10, and T11. Within the floret phase, CO2 enrichment significantly increased rates of floret primordium initiation of MS, T0, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

1630^10^Makino,A^Shimada,T^Takumi,S^Kaneko,K^Matsuoka,M^Shimamoto,K^Nakano,H^MiyaoTokutomi,M^Mae,T^Yamamoto,N^1997^1^Does decrease in ribulose-1,5-bisphosphate carboxylase by antisense RbcS lead to a higher N-use efficiency of photosynthesis under conditions of saturating CO2 and light in rice plants?^8^114^2^483-491^^^^^Jun^^^^^6036O2 (1702^1950^2465^2557^372^384^550^552^665^686^ation of MS was detected. Nevertheless, CO2 enrichment significantly increased rates of spikelet primordium initiation of MS, T1, T2, T10, and T11, and diminished the durations of spikelet development phase of MS, T1, T2, T3, T10, and T11. Within the floret phase, CO2 enrichment significantly increased rates of floret primordium initiation of MS, T0, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

1630^10^Makino,A^Shimada,T^Takumi,S^Kaneko,K^Matsuoka,M^Shimamoto,K^Nakano,H^MiyaoTokutomi,M^Mae,T^Yamamoto,N^1997^1^Does decrease in ribulose-1,5-bisphosphate carboxylase by antisense RbcS lead to a higher N-use efficiency of photosynthesis under conditions of saturating CO2 and light in rice plants?^8^114^2^483-491^^^^^Jun^^^^^6036O2 (A^6035^Rice (Oryza sativa L.) plants with decreased ribulose-1,5- bisphosphate carboxylase (Rubisco) were obtained by transformation with the rice rbcS antisense gene under the control of the rice rbcS promoter. The primary transformants were screened for the Rubisco to leaf N ratio, and the transformant with 65% wild-type Rubisco was selected as a plant set with optimal Rubisco content at saturating. CO2 partial pressures for photosynthesis under conditions of high irradiance and 25 degrees C. This optimal Rubisco content was estimated from the amounts and kinetic constants of Rubisco and the gas-exchange data. The R-1 selfed progeny of the selected transformant were grown hydroponically with different N concentrations. Rubisco content in the R-1 population was distributed into two groups: 56 plants had about 65% wild-type Rubisco, whereas 23 plants were very similar to the wild type. Although the plants with decreased Rubisco showed 20% lower rates of light-saturated photosynthesis in normal air (36 Pa CO2), they had 5 to 15% higher rates of photosynthesis in elevated partial pressures of CO2 (100-115 Pa CO2) than the wild-type plants for a given leaf N content. We conclude that the rice plants with 65% wild-type Rubisco show a higher N-use efficiency of photosynthesis under conditions of saturating CO2 and high irradiance.

1631^1^Mortensen,LM^1997^1^Effects of carbon dioxide concentrations on three grass species grown in mixture in two soil types at different ozone concentrations or temperatures^200^47^1^14-19^^^^^Mar^^^^^6038
1262^1345^1828^188^2258^372^409^506^57^nstants of Rubisco and the gas-exchange data. The R-1 selfed progeny of the selected transformant were grown hydroponically with different N concentrations. Rubisco content in the R-1 population was distributed into two groups: 56 plants had about 65% wild-type Rubisco, whereas 23 plants were very similar to the wild type. Although the plants with decreased Rubisco showed 20% lower rates of light-saturated photosynthesis in normal air (36 Pa CO2A^6037^A seed mixture of Phleum pratense L., Lolium perenne L. and Festuca pratensis Huds. was grown in spaghnum peat or sandy soil in six growth chambers placed in a greenhouse compartment. Two different experiments were performed. Increasing the CO2 concentration from 375 to 740 mu mol mol(-1) increased the total dry weight of the grass mixture by about 30%, while an increase in the O-3 concentration from < 10 to 50 nmol mol(-1) decreased the dry weight by 18% as a mean in both experiments. The relative dry weights of the three species were not significantly affected by elevated CO2 concentrations at low O- 3, while Lolium increased its relative dry weight at high O-3 concentrations at low CO2 on the expenditure of Phleum dry weight. CO2 enrichment counteracted some of this O-3 effect. No significant interaction between CO2 concentration and temperature (14 and 19 degrees C mean temperature) was found with respect to the dry weights of the three species. The soil type had generally no influence on the effect of CO2 and O-3. However, plant growth was significantly slower in sandy soil than in peat.

1632^4^Osborne,CP^Drake,BG^LaRoche,J^Long,SP^1997^1^Does long-term elevation of CO2 concentration increase photosynthesis in forest floor vegetation? Indiana strawberry in a Maryland forest^8^114^1^337-344^^^^^May^^^^^6040
1121^1347^2096^312^344^360^57^713^845^92^%, while an increase in the O-3 concentration from < 10 to 50 nmol mol(-1) decreased the dry weight by 18% as a mean in both experiments. The relative dry weights of the three species were not significantly affected by elevated CO2 concentrations at low O- 3, while Lolium increased its relative dry weight at high O-3 concentrations at low CO2 on the expenditure of Phleum dry weight. CO2 enrichment counteracted some of this O-3 effect. No significant interaction between CO2 concentration and temperature (14 and 19 degrees C mean temperature) was found with respect to the dry weights of the three species. The soil type had generally no influence on the effeA^6039^As the partial pressure of CO2 (pCO(2)) in the atmosphere rises, photorespiratory loss of carbon in C-3 photosynthesis will diminish and the net efficiency of light-limited photosynthetic carbon uptake should rise. We tested this expectation for Indiana strawberry (Duchesnea indica) growing on a Maryland forest floor. Open-top chambers were used to elevate the pCO(2) of a forest floor habitat to 67 Pa and were paired with control chambers providing an ambient pCO(2) of 38 Pa. After 3.5 years, D. indica leaves grown and measured in the elevated pCO(2) showed a significantly greater maximum quantum efficiency of net photosynthesis (by 22%) and a lower light compensation point (by 42%) than leaves grown and measured in the control chambers. The quantum efficiency to minimize photorespiration, measured in 1% O-2, was the same for controls and plants grown at elevated pCO(2). This showed that the maximum efficiency of light-energy transduction into assimilated carbon was not altered by acclimation and that the increase in light-limited photosynthesis at elevated pCO(2) was simply a function of the decrease in photorespiration. Acclimation did decrease the ribulose-1,5-bisphosphate carboxylase/oxygenase and light-harvesting chlorophyll protein content of the Leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO(2) showed greater light- saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO(2). In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO(2), relative to controls, in both summer and fall. The increase in efficiency of light- limited photosynthesis with elevated pCO(2) allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric pCO(2).

1633^5^Osborne,JL^Awmack,CS^Clark,SJ^Williams,IH^Mills,VC^1997^1^Nectar and flower production in Vicia faba L (field bean) at ambient and elevated carbon dioxide^328^28^1^43-55^^^^^Jan-Feb^^^^^6042
130^174^2558^2559^2560^417^rotein content of the Leaf by more than 30%. These changes were associated with a decreased capacity for light-saturated, but not light-limited, photosynthesis. Even so, leaves of D. indica grown and measured at elevated pCO(2) showed greater light- saturated photosynthetic rates than leaves grown and measured at the current atmospheric pCO(2). In situ measurements under natural forest floor lighting showed large increases in leaf photosynthesis at elevated pCO(2), relative to controls, in both summer and fall. The increase in efficiency of light- limited photosynthesis with elevated pCO(2) allowed positive net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric A^6041^Atmospheric CO2 has been predicted to double by the year 2100. Elevated CO2 causes an increase in photosynthetic rate and extra assimilate is allocated to plant growth, seed and fruit production. Increased investment in flowers may have implications for pollination in entomophilous plants. Floral nectar standing crop, flower production and longevity were examined in Vicia faba, field bean, at ambient and elevated CO2. Nectar standing crop did not differ significantly between treatments but plants grown at elevated CO2 produced approximately 25% more flowers per plant and these lived 17% longer than those grown at ambient CO2. A plant grown at elevated CO2 may thus produce more nectar in total and, together with its increased floral display, may be more attractive to pollinators, but pollen flow will not necessarily be improved.
e net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric 1634^2^Penuelas,J^Llusia,J^1997^1^Effects of carbon dioxide, water supply, and seasonality on terpene content and emission by Rosmarinus officinalis^112^23^4^979-993^^^^^Apr^^^^^6044
1674^174^2561^2562^374^417^423^vestment in flowers may have implications for pollination in entomophilous plants. Floral nectar standing crop, flower production and longevity were examined in Vicia faba, field bean, at ambient and elevated CO2. Nectar standing crop did not differ significantly between treatments but plants grown at elevated CO2 produced approximately 25% more flowers per plant and these lived 17% longer than those grown at ambient CO2. A plant grown at elevated CO2 may thus produce more nectar in total and, together with its increased floral display, may be more attractive to pollinators, but pollen flow will not necessarily be improved.
e net photosynthetic carbon uptake on days and at locations on the forest floor that light fluxes were insufficient for positive net photosynthesis in the current atmospheric A^6043^Rosmarinus officinalis L. plants were grown under carbon dioxide concentrations of 350 and 700 mu mol/mol (atmospheric CO2 and elevated CO2) and under two levels of irrigation (high water and low water) from October 1, 1994 to May 31, 1996. Elevated CO2 led to increasingly larger monthly growth rates than the atmospheric CO2 treatments. The increase was 9.5% in spring 1995, 23% in summer 1995, and 53% in spring 1996 in the high-water treatments, whereas in low-water treatments the growth response to elevated CO2 was constrained until the second year spring, when there was a 47%, increase. The terpene concentration was slightly larger in the elevated CO2 treatments than in atmospheric CO2 treatments and reached a maximum 37% difference in spring 1996. There was no significant effect of water treatment, likely as a result of a mild low water treatment for a Mediterranean plant. Terpene concentration increased throughout the period of study, indicating possible age effects. The most abundant terpenes were alpha-pinene, cineole, camphor, borneol, and verbenone, which represented about 75% of the total. No significant differences were found in the terpene composition of the plants in the different treatments or seasons. The emission of volatile terpenes was much larger in spring (about 75 mu g/dry wt/hr) than in autumn (about 10 mu g/dry wt/hr), partly because of higher temperature and partly because of seasonal effect, but no significant difference was found because of CO2 or water treatment. The main terpene emitted was alpha-pinene, which represented about 50% of the total. There was no clear correlation between content and emission, either quantitatively or qualitatively. More volatile terpenes were proportionally more important in the total emission than in total content and in autumn than in spring.

1635^4^Polley,HW^Mayeux,HS^Johnson,HB^Tischler,CR^1997^1^Viewpoint: Atmospheric CO2, soil water, and shrub/grass ratios on rangelands^319^50^3^278-284^^^^^May^^^^^6046ffects. The most abundant terpenes wer1298^1317^1445^1783^2563^398^509^687^941^956^ verbenone, which represented about 75% of the total. No significant differences were found in the terpene composition of the plants in the different treatments or seasons. The emission of volatile terpenes was much larger in spring (about 75 mu g/dry wt/hr) than in autumn (about 10 mu g/dry wt/hr), partly because of higher temperature and partly because of seasonal effect, but no significant difference was found because of CO2 or water treatment. The main terpene emitted was alpha-pinene, which represented about 50% of the total. There was no clear correlation between content and emission, either quantitatively or qualitatively. More volatile terpenes were proportionally more important in the total emission than in total content and in autumn than in spring.

1635^4^Polley,HW^Mayeux,HS^Johnson,HB^Tischler,CR^1997^1^Viewpoint: Atmospheric CO2, soil water, and shrub/grass ratios on rangelands^319^50^3^278-284^^^^^May^^^^^6046ffects. The most abundant terpenes werA^6045^The abundance of woody plants on grasslands and savannas often is controlled by the availability of water and its location in soil. Water availability to plants is limited by precipitation, but the distribution of soil water and period over which it is available in these ecosystems are influenced by the transpiration rates of grasses, We discuss implications of recent and projected increases in atmospheric CO2 concentration for transpiration, soil water availability, and the balance of grasses and shrubs, An increase in CO2 concentration often reduces potential transpiration/leaf area by reducing stomatal conductance. On grasslands where effects of stomatal closure on transpiration are not negated by an increase in leaf temperature and leaf area, rising CO2 concentration should slow the depletion of soil water by grasses and potentially favor shrubs and other species that might otherwise succumb to water stress. Predicted effects of CO2 are supported by results from CO2-enrichment studies in the field and are compatible with recent models of interactions between resource levels and vegetation pattern and structure.

1636^5^Prior,SA^Runion,GB^Mitchell,RJ^Rogers,HH^Amthor,JS^1997^1^Effects of atmospheric CO2 on longleaf pine: Productivity and allocation as influenced by nitrogen and water^13^17^6^397-405^^^^^Jun^^^^^6048
1144^1262^224^312^345^372^376^386^437^92^ of recent and projected increases in atmospheric CO2 concentration for transpiration, soil water availability, and the balance of grasses and shrubs, An increase in CO2 concentration often reduces potential transpiration/leaf area by reducing stomatal conductance. On grasslands where effects of stomatal closure on transpiration are not negated by an increase in leaf temperature and leaf area, rising CO2 concentration should slow the depletion of soil water by grasses and potentially favor shrubs and other species that might otherwise succumb to water stress. Predicted effects of CO2 are supported by results from CO2-enrichment studies in the fieldA^6047^Longleaf pine (Pinus palustris Mill.) seedlings were exposed to two concentrations of atmospheric CO2 (365 or 720 mu mol mol(- 1)) in combination with two N treatments (40 or 400 kg N ha(-1) year(-1)) and two irrigation treatments (target values of -0.5 or -1.5 MPa xylem pressure potential) in open-top chambers from March 1993 through November 1994. Irrigation treatments were imposed after seedling establishment (i.e., 19 weeks after planting). Seedlings were harvested at 4, 8, 12, and 20 months. Elevated CO2 increased biomass production only in the high-N treatment, and the relative growth enhancement was greater for the root system than for the shoot system. In water-stressed trees, elevated CO2 increased root biomass only at the final harvest. Root:shoot ratios were usually increased by both the elevated CO2 and low-N treatments. In the elevated CO2 treatment, water-stressed trees had a higher root:shoot ratio than well-watered trees as a result of a drought-induced increase in the proportion of plant biomass in roots. Well- watered seedlings consistently grew larger than water-stressed seedlings only in the high-N treatment. We conclude that available soil N was the controlling resource for the growth response to elevated CO2 in this study. Although some growth enhancement was observed in water-stressed trees in the elevated CO2 treatment, this response was contingent on available soil N.

1637^2^Schappi,B^Korner,C^1997^1^In situ effects of elevated CO2 on the carbon and nitrogen status of alpine plants^43^11^3^290-299^^^^^Jun^^^^^6050
189^1912^2564^343^344^362^378^426^739^92^ative growth enhancement was greater for the root system than for the shoot system. In water-stressed trees, elevated CO2 increased root biomass only at the final harvest. Root:shoot ratios were usually increased by both the elevated CO2 and low-N treatments. In the elevated CO2 treatment, water-stressed trees had a higher root:shoot ratio than well-watered trees as a result of a drought-induced increase in the proportion of plA^6049^1. The effect of elevated CO2 on tissue composition in an alpine grassland (Swiss Central Alps, 2500m) under both natural and increased nutrient supply (NPK) is summarized. 2. During 3 years of CO2 enrichment the concentration of total non- structural carbohydrates (TNC) in leaves increased by 32% in Leontodon helveticus (largely sugar) and by 56% in Trifolium alpinum (largely starch) but did not change significantly in the dominant sedge Carex curvula and in Poa alpina, currently a rare species at this site. 3. Enhanced mineral nutrient supply (unlike elevated CO2) greatly stimulated growth but did not reduce the CO2-induced TNC accumulation, 4. Under elevated CO2 nitrogen concentrations (per g TNC-free dry matter) of green leaves decreased in Leontodon (-21%) and in Trifolium (-24%) but not or only slightly in Carer and in Pea. NPK addition compensated this CO2 effect an nitrogen concentration in Trifolium bur not in the other species. 5. In below-ground tissue neither TNC nor nitrogen concentration responded to CO2 fertilization. 6. The nitrogen pool per unit land area at peak season biomass remained unaffected by the CO2 treatment. 7. Overall our results suggest that the late successional dominant sedge Carex curvula remains unaffected by elevated CO2, independently of mineral nutrient supply, whereas the co- dominant and sub-dominant forbs Leontodon helveticus and Trifolium alpinum show both an increase of TNC as well as N depletion under elevated CO2. 8. None of these changes in active plant tissue translate into compositional changes in naturally senesced litter suggesting caution with predictions of CO2 effects on decomposition based on data from green plant material.

1638^1^Stange,G^1997^1^Effects of changes in atmospheric carbon dioxide on the location of hosts by the moth, Cactoblastis cactorum^2^110^4^539-545^^^^^May^^^^^6052
1666^2433^2565^2566^2567^2568^372^489^490^728^concentration in Trifolium bur not in the other species. 5. In below-ground tissue neither TNC nor nitrogen concentrationA^6051^Sensory organs that detect CO2 are common in herbivorous moths and butterflies, but their function has been unclear until now. As the CO2 gradients in the vicinity of a host plant depend on its physiological condition, CO2 could provide a sensory cue for the suitability of the plant as a larval food source. This study investigated whether changing the atmospheric CO2 concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO2 concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask the much smaller CO2 signals generated by the plants, this suggests that those signals constitute an important component of the host identification process. On host plants exposed to a constant background of doubled CO2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as a consequence of a general principle of sensory physiology (Weber-Fechner's law), and partially due to other factors specific to CO2-receptor neurons.

1639^3^Stocker,R^Leadley,PW^Korner,C^1997^1^Carbon and water fluxes in a calcareous grassland under elevated CO2^43^11^2^222-230^^^^^Apr^^^^^6054
189^2347^243^344^362^384^547^698^742^92^. This study investigated whether changing the atmospheric CO2 concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO2 concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask the much smaller CO2 signals generated by the plants, this suggests that those signals constitute an important component of the host identification process. On host plants exposed to a constant background of doubled CO2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as a consequence of a generaA^6053^1. As part of a long-term study of the effects of elevated CO2 on biodiversity and ecosystem function in a calcareous grassland, we measured ecosystem carbon dioxide and water- vapour fluxes over 24-h periods during the 1994 and 1995 growing seasons. Data were used to derive CO2 and H2O gas- exchange response functions to quantum flux density (QFD). 2. The relative increase in net ecosystem CO2 flux (NEC) owing to CO2 enrichment increased as QFD rose. Daytime NEC at high QFD under elevated CO2 increased by 25% to 60%, with the greatest increases in the spring and after mowing in June when above- ground biomass was lowest. There was much less stimulation of NEC in early June and again in October when the canopy was fully developed. Night-time NEC was not significantly altered under elevated CO2. 3. Short-term reversal of CO2 concentrations between treatments after two seasons of CO2 exposure provided evidence for a 50% downward adjustment of NEC expressed per unit above-ground plant dry weight. However, when expressed on a land area basis, this difference disappeared because of a c. 20% increase in above-ground biomass under elevated CO2. 4. Ecosystem evapotranspiration (ET) was not significantly altered by elevated CO2 when averaged over all measurement dates and positions. However, ET was reduced 3-18% at high QFD in plots at the top of the slope at our study site. In summary, CO2 enrichment resulted in a large stimulation of ecosystem CO2 capture, especially during periods of a large demand of carbon in relationship to its supply, and resulted in a relatively small and variable effect on ecosystem water consumption.

1640^2^Tinker,B^Mooney,H^1996^1^Plant-soil carbon belowground: The effects of elevated CO2 selected papers from an International GCTE Workshop, 20-23 September 1995, Mansfield College, University of Oxford, UK - Introduction^206^187^2^107^

1641^2^Treonis,AM^Lussenhop,JF^1997^1^Rapid response of soil protozoa to elevated CO2^263^25^1^60-62^^^^^Jun^^^^^6057
1334^1781^312^344^376^797^oweverA^6056^Short-term changes in bacterial and protozoan populations from the soil of plants grown under elevated atmospheric CO2 were quantified. We grew Brassica nigra at either ambient or twice- ambient CO2 levels within open-top chambers in the field for 4 weeks. Plant biomass, above- and belowground, was unaffected by elevated CO2. Direct count bacterial density was unchanged under elevated CO2. Flagellate density tended to increase, whereas amoebal density significantly declined under elevated CO2. This change in protozoan community structure suggests trophic transfer of the elevated CO2 fertilization effect through the soil food chain.

1642^3^vanGinkel,JH^Gorissen,A^vanVeen,JA^1997^1^Carbon and nitrogen allocation in Lolium perenne in response to elevated atmospheric CO2 with emphasis on soil carbon dynamics^206^188^2^299-308^^^^^Jan^^^^^6059
130^1334^1781^362^376^409^535^538^547^92^F^1997^1^Rapid response of soil protozoa to elevated CO2^263^25^1^60-62^^^^^Jun^^^^^6057
1334^1781^312^344^376^797^oweverA^6058^The effect of elevated CO2 on the carbon and nitrogen distribution within perennial ryegrass (L. perenne L.) and its influence on belowground processes were investigated. Plants were homogeneously C-14-labelled in two ESPAS growth chambers in a continuous C-14-CO2 atmosphere of 350 and 700 mu L L-1 CO2 and at two soil nitrogen regimes, in order to follow the carbon flow through all plant and soil compartments. After 79 days, elevated CO2 increased the total carbon uptake by 41 and 21% at low (LN) and high nitrogen (HN) fertilisation, respectively. Shoot growth remained unaffected, whereas CO2 enrichment stimulated root growth by 46% and the root/soil respiration by 111%, irrespective of the nitrogen concentration. The total C- 14-soil content increased by 101 and 28% at LN and HN, respectively. The decomposition of the native soil organic matter was not affected either by CO2 or by the nitrogen treatment. Elevated CO2 did not change the total nitrogen uptake of the plant either at LN or at HN. Both at LN and HN elevated CO2 significantly increased the total amount of nitrogen taken up by the roots and decreased the absolute and relative amounts translocated to the shoots. The amount of soil nitrogen immobilised by micro-organisms and the size of the soil microbial biomass were not affected by elevated CO2, whereas both were significantly increased at the higher soil N content. Most striking was the 88% increase in net carbon input into the soil expressed as: C-14-roots plus total C-14-soil content minus the C-12-carbon released by decomposition of native soil organic matter. The net carbon input into the soil at ambient CO2 corresponded with 841 and 1662 kg ha(-1) at LN and HN, respectively. Elevated CO2 increased these amounts with an extra carbon input of 950 and 1056 kg ha(-1). Combined with a reduced decomposition rate of plant material grown at elevated CO2 this will probably lead to carbon storage in grassland soils resulting in a negative feed back an the increasing CO2 concentration of the atmosphere.

1643^2^Wang,KY^Kellomaki,S^1997^1^Stomatal conductance and transpiration in shoots of Scots pine after 4-year exposure to elevated CO2 and temperature^188^75^4^552-561^^^^^Apr^^^^^6061
188^2569^312^344^384^399^509^718^861^923^and the size of the soil microbial biomass were not affected by elevated CO2, whereas both were significantly increased at the higher soil N content. Most striking was the 88% increase in net carbon input into the soil expressed as: C-14-roots plus total C-14-soil content minus the C-12-carbon released by decomposition of native soil organic matter. The net carbon input into the soil at ambient CO2 corresponded with 841 and 1662 kg ha(-1) at LN and HN, respectively. Elevated CO2 increased these amounts with an extra carbon input of 950 and 1056 kg ha(-1). Combined with a reduced decomposition rate of plant material grown at elevated CO2 this will probably lead to carbon storage in grassland soils resulting in a negative feed back an the increasing CO2 concentration of the atmospA^6060^Single Scots pines (Pinus sylvestris L.) trees were subjected to elevated temperature (year-round elevation), elevated CO2 (elevation from April 15 to September 15), and a combination of elevated temperature and CO2 for 4 years in open-topped chambers. Measurements and modelling were performed to determine if long-term growth at elevated CO2 concentration and temperature altered water use efficiency (W-e) and the responses of stomatal conductance (g(s)) to photon flux density (Q(p)), the leaf-to-air vapour pressure difference (D-v), leaf temperature (T-l), and intercellular concentration of CO2 (C- i). Long-term elevation of CO2 led to a significant decline in the absolute value of g(s) at almost all levels of Q(p), D-v, C-i and T-l. Elevated temperature treatment increased the absolute value of g(s) only at higher D-v and T-l. The effect of the combination of elevated CO2 and temperature did not appear as a mean of the effects of the two single factors, while there was an interaction between the two factors. The modifications in the sensitivity of stomata, resulting from different treatments, did not have the same pattern as the change in g(s), but depended on levels of Q(p), D-v, and T-l. Compared with the control treatment, elevated concentration of CO2 or a combination of elevated CO2 and temperature led, on average, to 50 and 30% increases in W-E, respectively, which can be attributed mainly to an increase in the rate of net assimilation. In contrast, elevated temperature alone did not significantly change W-E, although transpiration rate was increased.

1644^4^Welsh,DT^Bourgues,S^deWit,R^Auby,I^1997^1^Effect of plant photosynthesis, carbon sources and ammonium availability on nitrogen fixation rates in the rhizosphere of Zostera noltii^329^12^3^285-290^^^^^29 May^^^^^6063
2384^2433^2570^2571^2572^2573^92^931^er D-v and T-l. The effect of the combination of elevated CO2 and temperature did not appear as a mean of the effects of the two single factors, while there was an interaction between the two A^6062^Rates of nitrogen fixation (measured as acetylene reduction) in the rhizosphere of the seagrass Zostera noltii were highly dependent upon plant photosynthetic activity being significantly stimulated at elevated CO2 concentrations and by light, both in the short-term and over diurnal cycles. Stimulation by light became insignificant when 5 mM sucrose was added to the sediment porewater, indicating that in the absence of added carbon sources, light stimulation was due to direct inputs of plant photosynthate to the rhizosphere. Addition of a range of carbon sources to the rhizosphere sediment stimulated rates of acetylene reduction, with this stimulation being significant for sucrose and lactate. Surprisingly, whilst low additions of ammonium to the sediment porewater (10 to 50 mu M) inhibited 50% of acetylene reduction activity, approximately 30% of this activity persisted in the presence of 1 mM ammonium chloride; this indicating that in at least a proportion of the N-fixing community, nitrogenase activity was not regulated in the short term by the availability of alternative nitrogen sources.

1645^3^Agar,IT^Streif,J^Bangerth,F^1997^1^Effect of high CO2 and controlled atmosphere (CA) on the ascorbic and dehydroascorbic acid content of some berry fruits^259^11^1^47-55^^^^^May^^^^^6065
2369^417^563^ulation by light became insignificant when 5 mM sucrose was added to the sediment porewater, indicating that in the absence of added carbon sources, light stimulation was due to direct inputs of plant photosynthate to the rhizosphere. Addition of a range of carbon sources to the rhizosphere sediment stimulated rates of acetylene reduction, with this stimulation being significant for sucrose and lactate. Surprisingly, whilst low additions of ammonium to the sediment porewater (10 to 50 mu M) inhibited 50% of acetylene reduction activity, approximately 30% of this activity persisted in the presence of 1 mM ammonium chloride; this indicating that in at least a proportion of the N-fixing community, nitrogenase actiA^6064^High CO2 concentrations as well as controlled atmosphere storage are widely used to extend the storage and shelf-life of many fruits. To investigate the effect of these storage procedures on several berry fruits, strawberries, raspberries, currants and blackberries were stored at three different elevated CO2 concentrations, with or without a parallel reduction in O-2. Vitamin C content (ascorbic acid plus dehydroascorbic acid) was reduced by high CO2 concentrations (10-30% CO2), particularly in strawberries. This reduction in vitamin C was moderate in black currants and blackberries and almost absent in raspberries and red currants when compared with strawberries. Reducing the O-2 concentration in the storage atmosphere in the presence of high CO2 had little effect on the vitamin C content. Ascorbic acid was more diminished al high CO2 than dehydroascorbic acid. This suggests a stimulating effect of high CO2 concentrations on the oxidation of ascorbic acid and/or an inhibition of mono- or dehydroascorbic acid reduction to ascorbic acid. (C) 1997 Elsevier Science B.V.

1646^4^Atkinson,CJ^Taylor,JM^Wilkins,D^Besford,RT^1997^1^Effects of elevated CO2 on chloroplast components, gas exchange and growth of oak and cherry^13^17^5^319-325^^^^^May^^^^^6067
1871^2000^2574^2575^312^344^374^58^685^705^fferent elevated CO2 concentrations, with or without a parallel reduction in O-2. Vitamin C content (ascorbic acid plus dehydroascorbic acid) was reduced by high CO2 concentrations (10-30% CO2), particularly in strawberries. This reduction in vitamin C was moderate in black currants and blackberries and almost absent in raspberries and red currants when compared with strawberries. Reducing the O-2 concentration in the storage atmosphere in the presence of high CO2 had little effect on the vitamin C content. Ascorbic acid was more diminished al high CO2 than dehydroascorbic acid. This suggests a stimulating effect of high CO2 concentrations on the oxidation of ascorbic acid and/or an inhibition of mono- or dehydroascorA^6066^Specific chloroplast proteins, gas exchange and dry matter production in oak (Quercus robur L.) seedlings and clonal cherry (Prunus avium L. x pseudocerasus Lind.) plants were measured during 19 months of growth in climate-controlled greenhouses at ambient (350 vpm) or elevated (700 vpm) CO2. In both species, the elevated CO2 treatment increased the PPFD saturated-rate of photosynthesis and dry matter production. After two months at elevated CO2, Prunus plants showed significant increases in leaf (55%) and stem (61%) dry mass but not in root dry mass. However, this initial stimulation was not sustained: treatment differences in net assimilation rate (A) and plant dry mass were less after 10 months of growth than after 2 months of growth, suggesting acclimation of A to elevated CO2 in Prunus. In contrast, after 10 months of growth at elevated CO2, leaf dry mass of Quercus increased (130%) along with shoot (356%) and root (219%) dry mass, and A was also twice that of plants grown and measured at ambient CO2. The amounts of Rubisco and the thylakoid-bound protein cytochrome f were higher in Quercus plants grown for 19 months in elevated CO2 than in control plants, whereas in Prunus there was less Rubisco in plants grown for 19 months in elevated CO2 than in control plants. Exposure to elevated CO2 for 10 months resulted in increased mean leaf area in both species and increased abaxial stomatal density in Quercus. There was no change in leaf epidermal cell size in either species in response to the elevated CO2 treatment. The lack of acclimation of photosynthesis in oak grown at elevated CO2 is discussed in relation to the production and allocation of dry matter. We propose that differences in carbohydrate utilization underlie the differing long-term CO2 responses of the two species.

1647^1^Bugmann,H^1997^1^Sensitivity of forests in the European Alps to future climatic change^288^8^1^35-44^^^^^27 Mar^^^^^6069
174^314^991^root (219%) dry mass, and A was also twice that of plants grown and measured at ambientA^6068^Model-based assessments of the impacts of climatic change on forests are confronted with 2 fundamental problems: first, there is a considerable uncertainty in the predictions of future climate; second, the forest models contain simplified parameterizations of ecological processes. In this paper, the sensitivity of forest models to different steady-state climate scenarios, to different process formulations and to different assumptions on the transient behaviour of climate is studied. The effects of 3 scenarios of climatic change and the behaviour of 5 forest gap models of the FORECE/FORCLIM family are compared at sites along an elevational gradient in the European Alps. A wide variety of species compositions may be obtained al a given site depending on the scenario of future climate. At some sites all future forests differ radically from today's forest, suggesting that these current forests are highly sensitive to climatic change. At some sites, the results of the 5 forest models differ strongly with respect to species composition and carbon storage when subjected to the same climate scenario, showing that the models need to be improved in order to arrive at reliable and robust parameterizations of abiotic and biotic influences in forest models. When comparing the effects of step, Linear, and sigmoid changes of the mean climatic parameters over 100 yr, it becomes evident that the type of change modelled is not crucial because the climatic change proceeds fast compared to the successional dynamics. It is concluded that simulations of the possible effects of climatic change on forests should be considered as sensitivity tests, not as predictions. Given the current uncertainties in atmospheric sciences (climate predictions) and in ecology (modelling of long-term forest dynamics), the most promising research strategy is to compare the effects of several climate scenarios and the projections of several forest models to arrive at slate-of-the-art ecological impact assessments.
est models differ strongly with r1648^3^Canadell,JG^Pitelka,LF^Ingram,JSI^1996^1^The effects of elevated [CO2] on plant-soil carbon below- ground: A summary and synthesis^206^187^2^391-400^^^^^^^^^^6071
1030^1099^243^362^374^384^534^538^57^672^ biotic influences in forest models. When comparing the effects of step, Linear, and sigmoid changes of the mean climatic parameters over 100 yr, it becomes evident that the type of change modelled is not crucial because the climatic change proceeds fast compared to the successional dynamics. It is concluded that simulations of the possible effects of climatic change on forests should be considered as sensitivity tests, not as predictions. Given the current uncertainties in atmospheric sciences (climate predictions) and in ecology (modelling of long-term forest dynamics), the most promising research strategy is to compare the effects of several climate scenarios and the projections of several forest models to arrive at slate-of-the-art ecological impact assessments.
est models differ strongly with rA^6070^We undertake a synthesis of the most relevant results from the presentations at the meeting ''Plant-Soil Carbon Below-Ground: The Effects of Elevated CO2'' (Oxford-UK, September 1995), many of which are published in this Special Issue. Below-ground responses to elevated [CO2] are important because the capacity of soils for long-term carbon sequestration. We draw the following conclusions: (i) several ecosystems exposed to elevated [CO2] showed sustained increased CO2 uptake at the plot level for many years. A few systems, however, showed complete down-regulation of net CO2 uptake after several years of elevated [CO2] exposure; (ii) under elevated [CO2], a greater proportion of fixed carbon is generally allocated below-ground, potentially increasing the capacity of below- ground sinks; and (iii) some of the increased capacity of these sinks may lead to increased long-term soil carbon sequestration, although strong evidence is still lacking. We highlight the need for more soil studies to be undertaken within ongoing ecosystem-level experiments, and suggest that while some key experiments already established should be maintained to allow long term effects and feedbacks to lake place, more research effort should be directed to mechanisms of soil organic matter stabilization.

1649^1^Cardon,ZG^1996^1^Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter^206^187^2^277-288^^^^^^^^^^6073
1096^1298^1334^374^376^377^56^57^672^92^increased CO2 uptake at the plot level for many years. A few systems, however, showed complete down-regulation of net CO2 uptake after several years of elevated [CO2] exposure; (ii) under elevated [CO2], a greater proportion of fixed carbon is generally allocated below-ground, potentially increasing the capacity of below- ground sinks; and (iii) some of the increased capacity of these sinks may lead to increased long-term soil carbon sequestration, although strong evidence is still lacking. We highlight the need for more soil studies to be undertaken wA^6072^Atmospheric CO2 concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO2, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM). From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO2 on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO2 on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m(-2) NPK) nutrients; measurements of soil atmosphere delta(13)C combined with soil respiration rates show that during vegetative growth in February, elevated CO2 decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils. This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO2 concentrations.

1650^4^Clark,H^Newton,PCD^Bell,CC^Glasgow,EM^1997^1^Dry matter yield, leaf growth and population dynamics in Lolium perenne Trifolium repens-dominated pasture turves exposed to two levels of elevated CO2^39^34^2^304-316^^^^^Apr^^^^^6075
130^1317^1958^230^243^312^374^376^506^751^itA^6074^1. Dry matter yield, leaf growth and population dynamics of turves taken from an old Lolium perenne/Trifolium repens- dominated pasture were studied in controlled environment rooms at CO2 concentrations of 350 mu mol mol(-1), 525 mu mol mol(-1) and 700 mu mol mol(-1). Starting with September data the turves were subjected sequentially to the mean monthly temperature and photoperiod taken from long-term climatic data for the area of New Zealand where the pasture was located. Each temperature and photoperiod regime was applied for 21 days to provide 12 different simulated 'months' of environmental conditions. The experiment ran for 14 simulated months, with September and October conditions being repeated at the end of the first simulated 'year'. Mean photon flux density throughout was 500 mu E m(-2) s(-1). 2. The total quantity of herbage harvested was increased by 7% and 14% at 525 mu mol mol(-1) and 700 mu mol mol(-1) CO2, respectively. The increase in the amount of T. repens harvested by the end of the experiment was 63% at 525 mu mol mol(-1) CO2 and 48% at 700 mu mol mol(-1) CO2. In contrast, neither the yield of C3 grasses nor the yield of the only C4 grass present, Paspalum dilatatum, was significantly affected by CO2 concentration. The implications of this increase in the proportion of T. repens in temperate pastures at elevated CO2 is discussed briefly. 3. With the exception of a small increase in the specific leaf area of T. repens, detailed measurements of leaf growth on marked tillers (L. perenne and P. dilatatum) and growing points (T. repens) showed no consistent effects of exposure to elevated CO2 concentrations. 4. Differences in yield between CO2 concentrations were mainly attributable to changes in the number and balance of population units. By the middle of the 'winter' conditions T. repens growing point densities at 700 mu mol mol(-1) CO2 were more than double those found at 350 mu mol mol(-1) but total grass tiller densities were unchanged. Growing point densities were also more than doubled at 525 mu mol mol(-1) CO2 compared with 350 mu mol mol(-1) but grass tiller densities were reduced significantly below those recorded in the other two treatments. The relationship between the stability of herbage production and population densities is discussed and the potential interaction between population density, elevated CO2 and grazing considered. 5. Although exposure to elevated levels of CO2 did result in large changes in population numbers, this did not happen immediately and so the yield response of this particular community to CO2 varied with time. The average yield increases recorded here at elevated CO2 may therefore tend to underestimate those likely to be shown by communities that, at the population level, have become fully adapted to growth in a CO2-enriched atmosphere.

1651^1^Daniel,E^1997^1^The temperature dependence of photoinhibition in leaves of Phaseolus vulgaris (L) - Influence of CO2 and O-2 concentrations^330^124^1^1-8^^^^^18 Apr^^^^^6077oint densities were also more than do1240^188^2576^2577^493^514^546^555^639^989^h 350 mu mol mol(-1) but grass tiller densities were reduced significantly below those recorded in the other two treatments. The relationship between the stability of herbage production and population densities is discussed and the potential interaction between population density, elevated CO2 and grazing considered. 5. Although exposure to elevated levels of CO2 did result in large changes in population numbers, this did not happen immediately and so the yield response of this particular community to CO2 varied with time. The average yield increases recorded here at elevated CO2 may therefore tend to underestimate those likely to be shown by communities that, at the population level, have become fully adapted to growth in a CO2-enriched atmosphere.

1651^1^Daniel,E^1997^1^The temperature dependence of photoinhibition in leaves of Phaseolus vulgaris (L) - Influence of CO2 and O-2 concentrations^330^124^1^1-8^^^^^18 Apr^^^^^6077oint densities were also more than doA^6076^The interactive effect of temperature and CO2 concentration on the susceptibility to photoinhibition was assessed using chlorophyll a fluorescence to estimate the reduction of the quantum yield of PSII photochemistry (F-w/F-m) after high-light exposure. Leaves exposed to high photon flux density always exhibit a decrease in F-w/F-m, resulting from both a decrease in the rate constant for photochemistry and an increase in the rate constant for non photochemical dissipation of excess excitation energy. At a-given CO2 concentration, there was almost no difference in the degree of photoinhibition between leaves exposed to high light in 10 or 210 mmol O-2/mol. But photoinhibition was more pronounced at 10 mmol O-2/mol and 0 mu mol CO2/mol than at 210 mmol O-2/mol and 50 pmol CO2/mol, i.e. when both photorespiration and CO2 refixation are suppressed. Despite this photoprotective role of photorespiration, photoinhibition was enhanced by decreasing CO2 concentration in bean leaves, especially at elevated (30-35 degrees C)temperatures. (C) 1997 Elsevier Science Ireland Ltd.

1652^1^Darrah,PR^1996^1^Rhizodeposition under ambient and elevated CO2 levels^206^187^2^265-275^^^^^^^^^^6079
1049^1803^2372^2578^2579^2580^2581^2582^2583^2584^
A^6078^As global CO2 levels rise, can soils store more carbon and so buffer atmospheric CO2 levels? Answering this question requires a knowledge of the rates of C inputs to soil and of CO2 outputs via decomposition. Below-ground inputs from roots are a major component of the C flow into soils but are still poorly understood. In this article, new techniques for measuring rhizodeposition are reviewed and discussed and the need for cross-comparisons between methods is identified. One component of rhizodeposition, root exudation, is examined in more detail and evidence is presented which suggests that current estimates of exudate flow into soils are incorrect. A mechanistic mathematical model is used to explore how exudate hows might change under elevated CO2.
especially at elevated (30-1653^3^Dhillion,SS^Roy,J^Abrams,M^1996^1^Assessing the impact of elevated CO2 on soil microbial activity in a Mediterranean model ecosystem^206^187^2^333-342^^^^^^^^^^6081
1016^1096^1334^2426^310^374^376^377^738^778^2583^2584^
A^6078^As global CO2 levels rise, can soils store more carbon and so buffer atmospheric CO2 levels? Answering this question requires a knowledge of the rates of C inputs to soil and of CO2 outputs via decomposition. Below-ground inputs from roots are a major component of the C flow into soils but are still poorly understood. In this article, new techniques for measuring rhizodeposition are reviewed and discussed and the need for cross-comparisons between methods is identified. One component of rhizodeposition, root exudation, is examined in more detail and evidence is presented which suggests that current estimates of exudate flow into soils are incorrect. A mechanistic mathematical model is used to explore how exudate hows might change under elevated CO2.
especially at elevated (30-A^6080^The fate, as well as the consequence for plant nutrition, of the additional carbon entering soil under elevated CO2 is largely determined by the activity of soil microorganisms. However, most elevated CO2 studies have documented changes (generally increases) in microbial biomass and total infection by symbiotic organisms, which is only a first step in the understanding of the modification of soil processes. Using a Mediterranean model ecosystem, we complemented these variables by analyzing changes in enzymatic activities, hyphal lengths, and bacterial substrate assimilation, to tentatively identify the specific components affected under elevated CO2 and those which suggest changes in soil organic matter pools. We also investigated changes in the functional structures of arbuscular mycorrhizas. Most of the microbial variables assessed showed significant and substantial increase under elevated CO? of the same order or less than those observed for root mass and length. The increase in dehydrogenase activity indicates that the larger biomass of microbes was accompanied by an increase in their activity. The increase in hyphal length (predominantly of saprophytic fungi), and xylanase, cellulase and phosphatase activities, suggests an overall stimulation of organic matter decomposition. The higher number of substrates utilized by microorganisms from the soil under elevated CO2 was significant for the amine/amide group. Total arbuscular and vesicular mycorrhizal infection of roots was higher under elevated CO2, but the proportion of functional structures was not modified. These insights into the CO2-induced changes in soil biological activity point towards potential areas of investigation complementary to a direct analysis of the soil organic matter pools.

1654^1^Diaz,S^1996^1^Effects of elevated [CO2] at the community level mediated by root symbionts^206^187^2^309-320^^^^^^^^^^6083
1702^2585^2586^2587^2588^377^419^474^680^91^ess than those observed for root mass and length. The increase in dehydrogenase activA^6082^This review examines the effects of elevated [CO2] on plant symbioses with mycorrhizal fungi and root nodule bacteria, with emphasis on community and ecosystem processes. The effects of elevated [CO2] on the relationships between single plant species and root symbionts are considered first. There is some evidence that plant infection by and/or biomass of root symbionts are stimulated by elevated [CO2], but growth enhancement of the host seemingly depends on its degree of dependence on symbiosis and on soil nutrient availability. Second, the effects of elevated [CO2] on the relationships between plant multispecies assemblages and soil, and likely impacts on above-ground and belowground diversity, are analysed. Experimental and modelling work have suggested the existence of complex feedbacks in the responses of plants and the rhizosphere to CO2 enrichment. By modifying C inputs from plants to soil, elevated [CO2] may affect the biomass, the infectivity, and the species/isolate composition of root symbionts. This has the potential to alter community structure and ecosystem functioning. Finally, the incorporation of type and degree of symbiotic dependence into the definition of plant functional types, and into experimental work within the context of global change research, are discussed. More experimental work on the effects of elevated [CO2] at the community/ecosystem level, explicitly considering the role of root symbioses, is urgently needed.

1655^8^Fitter,AH^Self,GK^Wolfenden,J^vanVuuren,MMI^Brown,TK^Williamson,L^Graves,JD^Robinson,D^1996^1^Root production and mortality under elevated atmospheric carbon dioxide^206^187^2^299-306^^^^^^^^^^6085
349^374^538^541^664^711^92^ and belowground diversity, are analysed. Experimental and modelling work have suggested the existence of complex feedbacks in the responses of plants and the rhizosphere to CO2 enrichment. By modifying C inputs from plants to soil, elevated [CO2] may affect the biomass, the infectivity, and the species/isolate composition of root symbioA^6084^An essential component of an understanding of carbon flux is the quantification of movement through the root carbon pool. Although estimates have been made using radiocarbon, the use of minirhizotrons provides a direct measurement of rates of root birth and death. We have measured root demographic parameters under a semi-natural grassland and for wheat. The grassland was studied along a natural altitudinal gradient in northern England, and similar turf from the site was grown in elevated CO2 in solardomes. Root biomass was enhanced under elevated CO2. Root birth and death rates were both increased to a similar extent in elevated CO2, so that the throughput of carbon was greater than in ambient CO2, but root half-lives were shorter under elevated CO2 only under a Juncus/Nardus sward on a peaty gley soil, and not under a Festuca turf on a brown earth soil. In a separate experiment, wheat also responded to elevated CO2 by increased root production, and there was a marked shift towards surface rooting: root development at a depth of 80-85 cm was both reduced and delayed. In conjunction with published results for trees, these data suggest that the impact of elevated CO2 will be system- dependent, affecting the spatio-temporal pattern of root growth in some ecosystems and the rate of turnover in others. Turrnover is also sensitive to temperature, soil fertility and other environmental variables, all of which are likely to change in tandem with atmospheric CO2 concentrations. Differences in turnover and time and location of rhizodeposition may have a large effect on rates of carbon cycling.

1656^8^Fordham,M^Barnes,JD^Bettarini,I^Polle,A^Slee,N^Raines,C^Miglietta,F^Raschi,A^1997^1^The impact of elevated CO2 on growth and photosynthesis in Agrostis canina L ssp monteluccii adapted to contrasting atmospheric CO2 concentrations^2^110^2^169-178^^^^^Apr^^^^^6087
1347^360^374^376^409^417^528^672^867^881^o responded to elevated CO2 by increased root production, and there was a marked shift towards surface rooting: roA^6086^The aim of this study was to characterise growth and photosynthetic capacity in plants adapted to long-term contrasting atmospheric CO2 concentrations (C-a). Seeds of Agrostis canina L. ssp. monteluccii were collected from a natural CO2 transect in central-western Italy and plants grown in controlled environment chambers at both ambient and elevated CO2 (350 and 700 mu mol mol(-1)) in nutrient-rich soil. Seasonal mean C-a at the source of the plant material ranged from 610 to 451 mu mol CO2 mol(-1), derived from C-4 leaf stable carbon isotope discrimination (delta(13)C). Under chamber conditions, CO2 enrichment stimulated the growth of all populations. However, plants originating from elevated C-a exhibited higher initial relative growth rates (RGRs) irrespective of chamber CO2 concentrations and a positive relationship was found between RGR and C-a at the seed source. Seed weight was positively correlated with C-a, but differences in seed weight were found to explain no more than 34% of the variation in RGRs at elevated CO2. Longer-term experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 mu mol CO2 mol(-1)) indicated that differences in growth between populations were maintained when plants were grown at both 350 and 700 mu mol CO2 mol(-1). Analysis of leaf material revealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO2, with plants originating from high C-a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO2 saturated rates of photosynthesis and carboxylation efficiency between populations or with CO2 treatment. Moreover, SDS-PAGE/LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rubisco content between populations or CO2 treatments. These findings suggest that long-term adaptation to growth at elevated CO2 may be associated with a potential for increased growth, but this does not appear to be linked with differences in the intrinsic capacity for photosynthesis.

1657^2^Gao,Q^Zhang,XS^1997^1^A simulation study of responses of the northeast China transect to elevated CO2 and climate change^56^7^2^470-483^^^^^May^^^^^6089
1181^243^2589^314^58^664^673^vealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO2, with plants originating from high C-a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO2 saturated rates of photosynthesis and carboxylation efficiency between populations or with CO2 treatment. Moreover, SDS-PAGE/LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rubisco content between populations or CO2 treatments. These findings suggest that long-term adaptation to growth at elevated CO2 may be associated withA^6088^The spatiotemporal variations of vegetation biomass of the ecological transect in northeast China were simulated. Slate variables of the model included green biomass and nongreen biomass of 12 vegetation categories and water contents of three soil layers. The simulated monthly green biomass was converted into NDVI, or Normalized Differential Vegetation Index of AVHRR (Advanced Very High Resolution Radiometry). A comparison between the modeled and the observed NDVI was made at 10' spatial resolution, Atmospheric CO2 concentration and montiiiy precipitation were used as two driving variables for global change simulation. Effects of precipitation increments on percentage sunshine, relative humidity, radiation, evapotranspiration, and eventually soil water and plant growth, were considered, Two levers of CO2 concentration (present, doubled) and seven levels of precipitation increments (0, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.30) were prescribed for a total of 14 simulation runs. A steady-state solution was obtained for each simulation run. The results of simulation showed that with the present climate conditions, doubling atmospheric CO2 concentration led approximately to a 20.3% increase in green biomass, 11.0% increase in nongreen biomass, 19,0% increase in green NPP, 12.8% increase in nongreen NPP, and 24.9% increase in overall average NPP at steady state, These increases go, respectively, to 32.9, 13.9, 30.0, 20.1, and 23.4% when a 30% precipitation increase was superimposed on the doubled CO2 concentration.

1658^3^Gifford,RM^Lutze,JL^Barrett,D^1996^1^Global atmospheric change effects on terrestrial carbon sequestration: Exploration with a global C- and N-cycle model (CQUESTN)^206^187^2^369-387^^^^^^^^^^6091
1375^2590^372^407^428^454^547^57^741^789^l water and plant growth, were considered, Two levers of CO2 concentration (present, doubled) and seven levels of precipitation increments (0, 0.05, 0.1, 0.15, 0.2, 0.25, and 0.30) were prescribed for a total of 14 simulation runs. A steady-state solution was oA^6090^A model of the interacting global carbon and nitrogen cycles (CQUESTN) is developed to explore the possible history of C- sequestration into the terrestrial biosphere in response to the global increases (past and possible future) in atmospheric CO2 concentration, temperature and N-deposition. The model is based on published estimates of pre-industrial C and N pools and fluxes into vegetation, litter and soil compartments. It was found necessary to assign low estimates of N pools and fluxes to be compatible with the more firmly established C-cycle data. Net primary production was made responsive to phytomass N level, and to CO2 and temperature deviation from preindustrial values with sensitivities covering the ranges in the literature. Biological N-fixation could be made either unresponsive to soil C:N ratio, or could act to tend to restore the preindustrial C:N of humus with different N-fixation intensities. As for all such simulation models, uncertainties in both data and functional relationships render it more useful for qualitative evaluation than for quantitative prediction. With the N-fixation response turned off, the historic CO2 increase led to standard-model sequestration into terrestrial ecosystems in 1995AD of 1.8 Ct C yr(-1). With N-fixation restoring humus C:N strongly, C sequestration was 3 Ct yr(-1) in 1995. In both cases C:N of phytomass and litter increased with time and these increases were plausible when compared with experimental data on CO2 effects. The temperature increase also caused net C sequestration in the model biosphere because decrease in soil organic matter was more than offset by the increase in phytomass deriving from the extra N mineralised. For temperature increase to reduce system C pool size, the biosphere ''leakiness'' to N would have to increase substantially with temperature. Assuming a constant N-loss coefficient, the historic temperature increase alone caused standard-model net C sequestration to be about 0.6 Gt C in 1995. Given the disparity of plant and microbial C:N, the modelled impact of anthropogenic N-deposition on C- sequestration depends substantially on whether the deposited N is initially taken up by plants or by soil microorganisms. Assuming the latter, standard-model net sequestration in 1995 was 0.2 Ct C in 1995 from the N-deposition effect alone. Combining the effects of the historic courses of CO2, temperature and N-deposition, the standard-model gave C- sequestration of 3.5 Ct in 1995. This involved an assumed weak response of biological N-fixation to the increased carbon status of the ecosystem. For N-fixation to track ecosystem C- fixation in the long term however, more phosphorus must enter the biological cycle. New experimental evidence shows that plants in elevated CO2 have the capacity to mobilize more phosphorus from so-called ''unavailable'' sources using mechanisms involving exudation of organic acids and phosphatases.
ase alone caused standard-model net C sequestration to be about 0.6 Gt C in 1995. Given the disparity of plant and microbia1659^3^Gil,MI^Holcroft,DM^Kader,AA^1997^1^Changes in strawberry anthocyanins and other polyphenols in response to carbon dioxide treatments^321^45^5^1662-1667^^^^^May^^^^^6093
2591^2592^2593^2594^455^874^ standard-model net sequestration in 1995 was 0.2 Ct C in 1995 from the N-deposition effect alone. Combining the effects of the historic courses of CO2, temperature and N-deposition, the standard-model gave C- sequestration of 3.5 Ct in 1995. This involved an assumed weak response of biological N-fixation to the increased carbon status of the ecosystem. For N-fixation to track ecosystem C- fixation in the long term however, more phosphorus must enter the biological cycle. New experimental evidence shows that plants in elevated CO2 have the capacity to mobilize more phosphorus from so-called ''unavailable'' sources using mechanisms involving exudation of organic acids and phosphatases.
ase alone caused standard-model net C sequestration to be about 0.6 Gt C in 1995. Given the disparity of plant and microbiaA^6092^Carbon dioxide-enriched atmospheres are used to reduce the incidence and severity of decay and to extend the postharvest life of strawberries. The influence of CO2 on the postharvest quality parameters of strawberries, particularly the stability of anthocyanins and other phenolic compounds, was investigated. Freshly harvested strawberries were placed in jars ventilated continuously with air or air enriched with 10%, 20%, or 40% CO2 at 5 degrees C for 10 days. Samples were taken initially, and after 5 and 10 days of storage, and color (L* a* b* color space), pH, TA, TSS, and firmness were measured. Anthocyanins and other phenolics were analyzed by HPLC. Elevated CO2 degraded internal color while air-treated fruit remained red. Internal and external tissues differed in composition and concentration of phenolic compounds. CO2 had a minimal effect on the anthocyanin content of external tissues but induced a remarkable decrease in anthocyanin content of internal tissues. Factors, such as pH and copigmentation, that could explain this degradation are discussed.

1660^2^Godbold,DL^Berntson,GM^1997^1^Elevated atmospheric CO2 concentration changes ectomycorrhizal morphotype assemblages in Betula papyrifera^13^17^5^347-350^^^^^May^^^^^6095
1096^1850^2595^312^361^374^425^849^92^other phenolic compounds, was investigated. Freshly harvested strawberries were placed in jars ventilated continuously with air or air enriched with 10%, 20%, or 40% CO2 at 5 degrees C for 10 days. Samples were taken initially, and after 5 and 10 days of storage, and color (L* a* b* color space), pH, TA, TSS, and firmness were measured. Anthocyanins and other phenolics were analyzed by HPLC. Elevated CO2 degraded internal color while air-treated fruit remained red. Internal and external tissues differed in composition and concentration of phenolic compounds. CO2 had a minimal effect on the anthocyanin content of external tissues but induced a remarkable decrease in anthocyanin content of internal tissues. Factors, such as pH and copigmentatA^6094^Ectomycorrhizae are extremely diverse, with different species of fungi having very different physiologies and morphologies that, in turn, confer a range of different benefits to the host plant. To test the hypothesis that elevated CO2 leads to changes in the assemblage of ectomycorrhizae associated with trees, we examined the number and frequency of ectomycorrhizal morphotypes colonizing roots of Betula papyrifera Marsh. saplings grown at an ambient or elevated (700 ppm) atmospheric CO2 concentration for 24 weeks. Elevated CO2 resulted in significant changes in the composition of the ectomycorrhizal assemblage toward morphotypes with a higher incidence of emanating hyphae and rhizomorphs. We conclude that B. papyrifera saplings will be able to support a more costly mycorrhization in future elevated-CO2 atmospheres.
s. CO2 had a minimal effect on the anthocyanin content of external tissues but induced a remarkable decrease in anthocyanin content of internal tissues. Factors, such as pH and copigmentat1661^3^Goodfellow,J^Eamus,D^Duff,G^1997^1^Diurnal and seasonal changes in the impact of CO2 enrichment on assimilation, stomatal conductance and growth in a long-term study of Mangifera indica in the wet-dry tropics of Australia^13^17^5^291-299^^^^^May^^^^^6097
1690^2453^264^312^385^417^444^509^705^733^d with trees, we examined the number and frequency of ectomycorrhizal morphotypes colonizing roots of Betula papyrifera Marsh. saplings grown at an ambient or elevated (700 ppm) atmospheric CO2 concentration for 24 weeks. Elevated CO2 resulted in significant changes in the composition of the ectomycorrhizal assemblage toward morphotypes with a higher incidence of emanating hyphae and rhizomorphs. We conclude that B. papyrifera saplings will be able to support a more costly mycorrhization in future elevated-CO2 atmospheres.
s. CO2 had a minimal effect on the anthocyanin content of external tissues but induced a remarkable decrease in anthocyanin content of internal tissues. Factors, such as pH and copigmentatA^6096^We studied assimilation, stomatal conductance and growth of Mangifera indica L. saplings during long-term exposure to a CO2-enriched atmosphere in the seasonally wet-dry tropics of northern Australia. Grafted saplings of M. indica were planted in the ground in four air-conditioned, sunlit, plastic-covered chambers and exposed to CO2 at the ambient or an elevated (700 mu mol mol(-1)) concentration for 28 months. Light-saturating assimilation (A(max)), stomatal conductance (g(s)), apparent quantum yield (phi), biomass and leaf area were measured periodically. After 28 months, the CO2 treatments were changed in all four chambers from ambient to the elevated concentration or vice versa, and A(max) and g(s) were remeasured during a two-week exposure to the new regime. Throughout the 28-month period of exposure, A(max) and apparent quantum yield of leaves in the elevated CO2 treatment were enhanced, whereas stomatal conductance and stomatal density of leaves were reduced. The relative impacts of atmospheric CO2 enrichment on assimilation and stomatal conductance were significantly larger in the dry season than in the wet season. Total tree biomass was substantially increased in response to atmospheric CO2 enrichment throughout the experimental period, but total canopy area did not differ between CO2 treatments at either the first or the last harvest. During the two-week period following the change in CO2 concentration, A(max) of plants grown in ambient air but measured in CO2-enriched air was significantly larger than that of trees grown and measured in CO2-enriched air. There was no difference in A(max) between trees grown and measured in ambient air compared to trees grown in CO2-enriched air but measured in ambient air. No evidence of down-regulation of assimilation in response to atmospheric CO2 enrichment was observed when rates of assimilation were compared at a common intercellular CO2 concentration. Reduced stomatal conductance in response to atmospheric CO2 enrichment was attributed to a decline in both stomatal aperture and stomatal density.

1662^1^Gorissen,A^1996^1^Elevated CO2 evokes quantitative and qualitative changes in carbon dynamics in a plant/soil system: Mechanisms and implications^206^187^2^289-298^^^^^^^^^^6099
1044^1829^2032^344^531^534^535^538^56^57^ did not differ between CO2 treatments at either the first or the last harvest. During the two-week period following the change in CO2 concentration, A(max) of plants grown in ambient air but measured in CO2-enriched air was significantly larger than that of trees grown and measured in CO2-enriched air. There was no difference in A(max) between trees grown and measured in ambient air compared to trees grown in CO2-enriched air but measured in ambient air. No evidence of down-regulation of assimilation in response to atmospheric CO2 enrichment was observed when rates of assimilation were compared at a common intercellular CO2 concentration. Reduced stomatal conductance in response to atmospheric CO2 enrichment was attributed to a decline in boA^6098^It is hypothesized that carbon storage in soil will increase under an elevated atmospheric CO2 concentration due to a combination of an increased net CO2 uptake, a shift in carbon allocation pattern in the plant/soil system and a decreased decomposition rate of plant residues. An overview of several studies, performed in our laboratory, on the effects of elevated CO2 on net carbon uptake, allocation to the soil and decomposition of roots is given to test this hypothesis. The studies included wheat, ryegrass and Douglas-fir and comprised both short-term and long-term studies. Total dry weight of the plants increased up to 62%, but depended on nutrient availability. These results were supported by the data on net (CO2)-C-14 uptake. A shift in C-14-carbon distribution from shoots to roots was found in perennial species, although this depended on nutrient availability. The decomposition experiments showed that roots cultivated at 700 mu L L-1 CO2 were decomposed more slowly than those cultivated at 350 mu L L-1 CO2. Even after two growing seasons differences up to 13% were observed, although this was found to be dependent on the nitrogen level at which the roots were grown. Both an increased carbon allocation to the soil due to an increased carbon uptake, whether or not combined with a shift in distribution pattern, and a decreased decomposition of root residues will enhance the possibilities of carbon sequestration in soil, thus supporting our hypothesis. However, nutrient availability and the response of the soil microbial biomass (size and activity) play a major role in the processes involved and require attention to clarify plant/soil responses in the long term with regard to sustained stimulation of carbon input into soils and the decomposability of roots and rhizodeposition. Soil texture will also have a strong effect on decomposition rates as a result of differences in the protecting capacity for organic matter. More detailed information on these changes is needed for a proper use of models simulating soil carbon dynamics in the long term.

1663^3^Gregory,PJ^Palta,JA^Batts,GR^1996^1^Root systems and root:mass ratio - Carbon allocation under current and projected atmospheric conditions in arable crops^206^187^2^221-228^^^^^^^^^^6101
1262^1434^1701^2596^2597^2598^349^508^521^724^h a shift in distribution pattern, and a decreased decomposition of root residues will enhance the possibilities of carbon sequestration in soil, thus supporting our hypothesis. However, nutrient availability and the response of the soil microbial biomass (size and activity) play a major role in the processes involved and require attention to clarify plant/soil responses in the long term with regard to sustained stimulation of carbon input into soils and the decomposability of roots and rhizodeposition. Soil texture will also have a strong effect on decomposition rates as a result of differences in the protecting capacity for organic matter. More detailed information on these changes is needed for a proper use of models simulatingA^6100^Roots of annual crop plants are a major sink for carbon particularly during early, vegetative growth when up to one- half of all assimilated carbon may be translocated belowground. Flowering marks a particularly important change in resource allocation, especially in determinate species, with considerably less allocation to roots and, depending on environmental conditions, there may be insufficient for maintenance. Studies with C-14 indicate the rapid transfer belowground of assimilates with typically 50% translocated in young cereal plants of which 50% is respired; exudation/rhizodeposition is generally <5% of the fixed carbon. Root:total plant mass decreases through the season and is affected by soil and atmospheric conditions. Limited water availability increased the allocation of C-13 to roots of wheat grown in columns so that at booting 0.38 of shoot C (ignoring shoot respiration) was belowground compared to 0.31 in well- watered plants. Elevated CO2 (700 mu mol CO2 mol(-1) air) increased the proportion of root:total mass by 55% compared with normal concentration, while increasing the air temperature by a mean of 3 degrees C decreased the proportion from 0.093 in the cool treatment to 0.055 in the warm treatment.

1664^5^Ineson,P^Cotrufo,MF^Bol,R^Harkness,DD^Blum,H^1996^1^Quantification of soil carbon inputs under elevated CO2:C-3 plants in a C-4 soil^206^187^2^345-350^^^^^^^^^^6103
1096^362^374^376^467^504^nce. Studies with C-14 indicate the rapid transfer belowground of assimilates with typically 50% translocated in young cereal plants of which 50% is respired; exudation/rhizodeposition is generally <5% of the fixed carbon. Root:total plant mass decreases through the season and is affected by soil and atmospheric conditions. Limited water availability increased the allocation of C-13 to roots of wheat grown in columns so that at booting 0.38 of shoot C (ignoring shoot respiration) was belowground compared to 0.31 in well- watered plants. Elevated CO2 (700 mu mol CO2 mol(-1) air) increased the propA^6102^The objective of this investigation was to quantify the differences in soil carbon stores after exposure of birch seedlings (Betula pendula Roth.) over one growing season to ambient and elevated carbon dioxide concentrations. One-year- old seedlings of birch were transplanted to pots containing 'C- 4 soil' derived from beneath a maize crop, and placed in ambient (350 mu L L-1) and elevated (600 mu L L-1) plots in a free-air carbon dioxide enrichment (FACE) experiment. After 186 days the plants and soils were destructively sampled, and analysed for differences in root and stem biomass, total plant tissue and soil C contents and delta(13)C values. The trees showed a significant increase (+50%) in root biomass, but stem and leaf biomasses were not significantly affected by treatment. C isotope analyses of leaves and fine roots showed that the isotopic signal from the ambient and elevated CO2 supply was sufficiently distinct from that of the 'C-4 soil' to enable quantification of net root C input to the soil under both ambient and elevated CO2. After 186 days, the pots under ambient conditions contained 3.5 g of C as intact root material, and had gained an additional 0.6 g C added to the soil through root exudation/turnover; comparable figures for the pots under elevated CO2 were 5.9 g C and 1.5 g C, respectively. These data confirm the importance of soils as an enhanced sink for C under elevated atmospheric CO2 concentrations. We propose the use of 'C-4 soils' in elevated CO2 experiments as an important technique for the quantification of root net C inputs under both ambient and elevated CO2 treatments.

1665^2^Kalina,J^Ceulemans,R^1997^1^Clonal differences in the response of dark and light reactions of photosynthesis to elevated atmospheric CO2 in poplar^79^33^1^51-61^^^^^^^^^^6105
1121^1240^2125^2599^312^360^417^448^493^92^ots showed that the isotopic signal from the ambient and elevated CO2 supply was sufficiently distinct from that of the 'C-4 soil' to enable quantification of net root C input to the sA^6104^Two hybrid poplar (Populus) clones (i.e., fast growing clone Beaupre and slow growing clone Robusta) were grown for two years from cuttings at close spacings in open top chambers (OTCs) under ambient (AC) and elevated [EC = AC + 350 mu mol(CO2) mol(-1)] CO2 treatments, For clone Beaupre no down- regulation of photosynthesis was observed. Two years of growing under EC resulted in an increase in quantum yield of photosystem 2 (PS2), steady state irradiance saturated rate of net photosynthesis (P-Nmax), chlorophyll (Chl) content, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC) activity for this clone. We suppose that under nonlimiting conditions of nitrogen and phosphorus content the response to EC was by building up light-harvesting complexes of PS2 and increasing photochemical efficiency of PS2, Due to a high rate of the primary reactions of photosynthesis and a high RuBPCO activity the end product of the response to EC was an increase in P-Nmax and a larger saccharides content, The Robusta clone showed a depression in the primary reactions of photosynthesis under EC, We found a decrease in quantum yield of PS2, Chl and phosphorus contents, and in RuBPCO activity. However, an increase in P-Nmax, saccharides content and Chi a/b ratio was observed. We speculate (1) that the phosphorus deficiency in combination with an increase in CO2 concentrations may lead to a potential damage of the assimilation apparatus of the primary reactions of photosynthesis and to a decrease in photochemical efficiency of PS2; (2) that the primary target of ''down- regulation'' takes place at PS2 for irradiances above 150 mu mol m(-2) s(-1).

1666^3^Keutgen,N^Chen,K^Lenz,F^1997^1^Responses of strawberry leaf photosynthesis, chlorophyll fluorescence and macronutrient contents to elevated CO2^4^150^4^395-400^^^^^Mar^^^^^6107
1871^2575^2600^348^384^92^primary reactions of photosynthesis and a high RuBPCO activity the end product of the response to EC was an increase in P-Nmax and a larger saccharides content, The RobustaA^6106^Gas exchange, chlorophyll fluorescence parameters, and macronutrient contents were investigated in young (< 3 weeks), medium (4 - 6 weeks) and old (7 - 9 weeks) strawberry leaves growing at 300, 450, 600, 750, and 300 ppm CO2. An increase of the CO2 level to 600 ppm promoted leaf net photosynthesis, but a further rise led to a decrease of net CO2 assimilation. The reduction of net photosynthetic rate was less distinct in young leaves exposed to CO2 levels above 600 ppm for less than 3 weeks, indicating that the reduction might depend on the period of exposition or leaf age. Transpiration and stomatal conductance were significantly affected by leaf age, but not by CO2 concentrations. Medium leaves were characterised by a higher transpiration rate and stomatal conductance than young and old ones. In leaves growing at high CO2 levels Chl a and b contents as well as the a/b ratio decreased. The contents of N, P, K, Ca and Mg were lower in leaves growing at high CO2 concentrations than in those at low ones. An elevated CO2 level above 750 ppm led to a general macronutrient deficiency and was accompanied by a distinct decrease of optimal quantum yield, due to a rise of basal fluorescence, and an increase of non- photochemical energy dissipation in old leaves.

1667^3^Lambers,H^Stulen,I^vanderWerf,A^1996^1^Carbon use in root respiration as affected by elevated atmospheric CO-2^206^187^2^251-263^^^^^^^^^^6109
130^2601^2602^2603^349^389^57^712^92^999^d to CO2 levels above 600 ppm for less than 3 weeks, indicating that the reduction might depend on the period of exposition or leaf age. Transpiration and stomatal conductance were significantly affected by leaf age, but not by CO2 concentrations. Medium leaves were characterised by a higher transpiration rate and stomatal conductance than young and old ones. In leaves growing at high CO2 levels Chl a and b contents as well as the a/b ratio decreased. The contents of N, P, K, Ca and Mg were lower in leaves growing at high CO2 concentrations than in those at low onesA^6108^The use of fossil fuel is predicted to cause an increase of the atmospheric CO2 concentration, which will affect the global pattern of temperature and precipitation. It is therefore essential to incorporate effects of temperature and water supply on the carbon requirement for root respiration of plants to predict effects of elevated [CO2] on the carbon budget of natural and managed systems. There is insufficient information to support the contentention that an increase in the concentration of CO2 in the atmosphere will enhance the CO2 concentration in the soil to an extent that is likely to affect root respiration. Moreover, there is no convincing evidence for a direct effect of elevated atmospheric [CO2] on the rate of root respiration per unit root mass or the fraction of carbon required for root respiration. However, there are likely to be indirect effects of elevated [CO2] on the carbon requirement of plants in natural systems. Firstly, it is very likely that the carbon requirement of root respiration relative to that fixed in photosynthesis will increase when elevated [CO2] induces a decrease in nutrient status of the plants. Although earlier papers have emphasized that elevated [CO2] favours investment of biomass in roots relative to that in leaves, these are in fact indirect effects. The increase in root weight ratio is due to the more rapid depletion of nutrients in the root environment as a consequence of enhanced growth. This will decrease the specific rate of root respiration, but increase the carbon requirement as a fraction of the carbon fixed in photosynthesis. It is likely that these effects will be minor in systems where the nutrient supply is very high, e.g, in many managed arable systems, and increase with decreasing soil fertility, i.e. in many natural systems. Secondly, a decrease in rainfall in some parts of the world may cause a shortage in water supply which favours the carbon partitioning to roots. Water stress is likely to reduce rates of root respiration per unit root mass, but enhance the fraction of total assimilates required for root respiration, due to greater allocation of biomass to roots. Increased temperatures are unlikely to affect the specific rate of root respiration in all species. Broadly generalized, the effect of temperature on biomass allocation is that the relative investment of biomass in roots is lowest at a certain optimum temperature and increases at both higher and lower temperatures. The root respiration of some species acclimates to growth temperature, so that the effect of global temperature rise is entirely accounted for by the effect of temperature on biomass allocation. The specific rate of root respiration of other species will increase with global warming. In response to global warming the carbon requirement of roots is likely to decrease in temperate regions, when temperatures are suboptimal for the roots' capacity to acquire water. Here global warming will induce a smaller biomass allocation to the roots. Conversely, the carbon requirements are more likely to increase in mediterranean environments, where temperatures are often supraoptimal and a rise in temperature will induce greater allocation of biomass to the roots.

1668^7^Leavitt,SW^Paul,EA^Galadima,A^Nakayama,FS^Danzer,SR^Johnson,H^Kimball,BA^1996^1^Carbon isotopes and carbon turnover in cotton and wheat FACE experiments^206^187^2^147-155^^^^^^^^^^6111
178^2604^362^429^nd increases at both higher and lower temperatures. The root respiration of some species acclimates to growth temperature, so that the effect of global temperature rise is entirely accounted for by the effect of temperature on biomass allocation. The specific rate of root respiration of other species will increase with global warming. In response to global warming the carbon requirement of roots is likely to decrease in temperate regions, when temperatures are suboptimal for the roots' capacity to acquire water. Here global warming will induce a smaller biomass allocation to the roots. Conversely, the carbon requirements are more A^6110^The Maricopa cotton and wheat FACE (free-air CO2 enrichment) experiments offer propitious opportunity to quantify carbon turnover. The commercial CO2 (delta(13)C approximate to-37 parts per thousand) used to elevate CO2 concentration in field plots provided a strongly C-12-depleted tracer. Soil CO2 and delta(13)C of soil organic carbon (SOC) in CO2-enriched and Control plots were measured between the final cotton FACE project (October 1991) and the end of the second wheat experiment (June 1994). The initial C-13-depletion in SOC of cotton FACE plots (measured by the difference in delta(13)C between FACE and Control plots) persisted at the same level (1.9 parts per thousand) 1.5 years after the experiment ended. A similar depletion was observed in soil CO2 evolved in the same plots, indicating ongoing decomposition of the new SOC. The SOC delta(13)C of wheat plots before and after two growing seasons showed increasing C-13-depletion in FACE relative to Control. Isotopic mass balance was consistent with 5-6% new carbon input from the two wheat crops. This is lower than the 12-13% calculated for FACE cotton and perhaps a consequence of the larger root system of cotton or the 3-year duration of the cotton experiments versus 2 years for the wheat.

1669^5^Lindner,M^Bugmann,H^Lasch,P^Flechsig,M^Cramer,W^1997^1^Regional impacts of climatic change on forests in the state of Brandenburg, Germany^107^84^1-2^123-135^^^^^Mar^^^^^6113
2605^314^372^429^51^672^778^ end of the second wheat experiment (June 1994). The initial C-13-depletion in SOC of cotton FACE plots (measured by the difference in delta(13)C between FACE and Control plots) persisted at the same level (1.9 parts per thousand) 1.5 years after the experiment ended. A similar depletion was observed in soil CO2 evolved in the same plots, indicating ongoing decomposition of the new SOC. The SOC delta(13)C of wheat plots before and after two growing seasons showed increasing C-13-depletion in FACE relative to Control. Isotopic mass balance was consistent withA^6112^The changes of climate projected for the next century will most likely alter both the environment and the growth of forests, In a regional case study, the two forest gap models FORSKA and FORCLIM were applied to simulate vegetation composition using spatially differentiated site data on a 10 x 10-km grid across the state of Brandenburg, Northeast Germany, Three climate scenarios were used to investigate the possible consequences of a changing climate on the environmental constraints of forest,growth in the state. To test the: plausibility of the forest composition simulated by the two models, their results were compared with a map of potential natural vegetation as well as with each other. The simulation results show that both models respond realistically to the spatial variability of the environment and thus are suitable for regional applications. However, there are a number of quantitative differences between the simulation results of the models. FORSKA's strength is in simulating the ecological effects of the spatial variability of soil water holding capacity and nitrogen availability, whereas FORCLIM realistically portrays the climate-induced distribution limits of trees, e.g. beech (Fagus sylvatica L.). The study suggests that climatic change could have considerable consequences for future competitive relationships between species. According to the two models, the main driving force of vegetation change would be the increased occurrence of drought, which already today determines some distribution limits of tree species in Brandenburg, Under the strongest change of climate investigated in the present study, none of the species currently present on the landscape could grow any more in certain areas of Brandenburg. Conclusions are drawn concerning the importance of regional model applications for testing model performance under a wide variety of environmental conditions as well as for forest planning, Regional analyses of the impacts of climate change on forests may help to develop forest management strategies to cope with the risk of changing environmental conditions.

1670^4^Lippert,M^Steiner,K^Pfirrmann,T^Payer,HD^1997^1^Assessing the impact of elevated O-3 and CO2 on gas exchange characteristics of differently K supplied clonal Norway spruce trees during exposure and the following season^252^11^5^306-315^^^^^Apr^^^^^6115
1633^1951^312^344^447^482^546^685^798^92^the main driving force of vegetation change would be the increased occurrence of drought, which already today determines some distribution limits of tree species in Brandenburg, Under the strongest change of climate investigated in the present study, none of the species currently present on the landscape could grow any more in certain areas of Brandenburg. Conclusions are drawn concerning the importance of regional model applications for testing model performance under a wide variety of environmental conditions as well as for forest planning, Regional analyses of the impacts of climate change on forests may help to develop forest management stA^6114^Well-supplied and K-deficient 4-year-old clonal Norway spruce trees were exposed to combinations of two levels of ozone (20 and 80 nl 1(-1) O-3) and carbon dioxide (350 and 750 mu 1 1(-1) CO2) to study the effects of possible future climate factors on gas exchange characteristics. The fumigation was performed in environmental chambers for a complete growing season. After the exposure, plants were cultivated outdoors to investigate possible recovery and delayed effects. During the exposure 1- year-old needles responded to the 80 nl 1(-1) O-3 treatment by a sharp but transient decrease of both apparent carboxylation efficiency (CE) and maximum photosynthetic capacity (A(2500)). Elevated CO2 also reduced CE and A(2500). The effect became stronger in the course of the exposure and was accompanied by decreases of N and P as well as chlorophyll contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower sink capacities for carbon metabolites. The joint application of elevated O-3 and CO2 resulted in the lowest values of gas exchange parameters and chlorophyll contents. At the beginning of the growing season after the exposure and under outdoor conditions, all these treatment effects disappeared in the needles which had developed during the fumigation. In the course of the development of the new flush, however, the well- supplied 1-year-old needles which had been treated with 80 nl 1(-1) O-3 and 350 mu 1 1(-1) CO2 in the year before, exhibited a sharp decline of CE and A(2500). Simultaneously, chlorotic mottle and bands developed. These delayed symptoms are discussed in the context of the previously published ''memory'' effect for O-3 (Sandermann et al. 1989). Additionally, evidence is presented that shoot development is altered in plants which had been exposed to elevated O-3.
hyll contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower sink capacities for carbon metabolites.1671^3^Marek,MV^Sprtova,M^Kalina,J^1997^1^The photosynthetic irradiance-response of Norway spruce exposed to a long-term elevation of CO2 concentration^79^33^2^259-268^^^^^^^^^^6117
2063^312^344^348^360^376^441^493^639^92^hese treatment effects disappeared in the needles which had developed during the fumigation. In the course of the development of the new flush, however, the well- supplied 1-year-old needles which had been treated with 80 nl 1(-1) O-3 and 350 mu 1 1(-1) CO2 in the year before, exhibited a sharp decline of CE and A(2500). Simultaneously, chlorotic mottle and bands developed. These delayed symptoms are discussed in the context of the previously published ''memory'' effect for O-3 (Sandermann et al. 1989). Additionally, evidence is presented that shoot development is altered in plants which had been exposed to elevated O-3.
hyll contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower sink capacities for carbon metabolites.A^6116^During an open-top chamber experiment performed in a mountain stand of young (12-year-old) Norway spruce (Picea abies [L.] Karst.), the trees were exposed to one of two CO2 concentrations (ambient CO2, AC, or AC + 350 mu mol mol(-1) = elevated CO2, EC) continuously over three growing seasons. To evaluate the EC influence, measurements of the relations between the rate of net CO2 uptake (P-N) and incidental photosynthetically active photon flux density (PPFD), as well as the content of photosynthetic pigments and chlorophyll (Chl) a fluorescence were taken in the third growing season. The short-term response to EC was evident mainly on ribulose-1,5- bisphosphate carboxylase/oxygenase kinetics without any significant change to the utilization of radiant energy. The long-term effect of EC was responsible for a decrease in P-N, Content of Chl a + b, F-v/F-m ratio, quantum yield of fluorescence, and photochemical quenching. Changes of stoichiometry between the electron transport, Calvin cycle and the end-product synthesis were confirmed for responses to the longterm import of EC and led to a definition of the photosynthetic acclimation to EC an Norway spruce.

1672^7^McKane,RB^Rastetter,EB^Shaver,GR^Nadelhoffer,KJ^Giblin,AE^Laundre,JA^Chapin,FS^1997^1^Climatic effects on tundra carbon storage inferred from experimental data and a model^11^78^4^1170-1187^^^^^Jun^^^^^6119
146^174^230^2606^30^534^681^691^715^737^tal photosynthetically active photon flux density (PPFD), as well as the content of photosynthetic pigments and chlorophyll (Chl) a fluorescence were taken in the third growing season. The short-term response to EC was evident mainly on ribulose-1,5- bisphosphate carboxylase/oxygenase kinetics without any significant change to the utilization of radiant energy. The long-term effect of EC was responsible for a decrease in P-N, Content of Chl a + b, F-v/F-m ratio, quantum yield of fluorescence, and photochemical quenching. Changes of stoichiometry between the electron transport, Calvin cycle and the end-pA^6118^We used a process-based model of ecosystem carbon (C) and nitrogen (N) dynamics, MEL-GEM (Marine Biological Laboratory General Ecosystem Model), to integrate and analyze the results of several experiments that examined the response of arctic tussock tundra to manipulations of CO2, temperature, light, and soil nutrients. The experiments manipulated these variables over 3- to 9-yr periods and were intended to simulate anticipated changes in the arctic environment. Our objective was to use the model to extend the analysis of the experimental data so that unmeasured changes in ecosystem C storage and the underlying mechanisms controlling those changes could be estimated and compared. Using an inverse calibration method, we derived a single parameter set for the model that closely simulated the measured responses of tussock tundra to all of the experimental treatments. This parameterization allowed us to infer confidence limits for ecosystem components and processes that were not directly measured in the experiments. Thus, we used the model to estimate changes in ecosystem C storage by inferring key soil processes within the constraints imposed by measured components of the ecosystem C budget. Because tussock tundra is strongly N limited, we hypothesized that changes in ecosystem C storage in response to the experimental treatments would be constrained by several key aspects of C-N interactions: (1) changes in the amount of N in the ecosystem, (2) changes in the C:N ratios of vegetation and soil, and (3) redistribution of N between soil (with a low C:N ratio) and vegetation (with a high C:N ratio). The model results reveal widely differing patterns of change in C-N interactions and constraints on change in ecosystem C storage among treatments. For example, after 9 yr the elevated CO2 (2 x ambient) treatment and the N fertilized (10 g N.m(-2) yr(-1)) treatment increased ecosystem C stocks by 1.4 and 2.9%, respectively. Whereas the increase in the CO2 treatment was due solely to an increase in the C:N ratios of vegetation and soil, the increase in the fertilized treatment was due to increased ecosystem N content and a shift of N from soil to vegetation. In contrast, the greenhouse (3.5 degrees C above ambient) and shade (one-half ambient light) treatments decreased ecosystem C stocks by 1.9 and 2.7%, respectively. The primary reason for the net C losses in these treatments was an increase in respiration relative to photosynthesis, with a consequent decrease in the ecosystem C:N ratio, However, when we simulated the elevated temperatures in the greenhouse treatment without the confounding effects of decreased light intensity (an artifact of the greenhouse structures), there was a long-term increase in ecosystem C stocks because of increased photosynthetic response to the temperature-induced shift of N from soil to vegetation. If our simulated changes in ecosystem C storage are extrapolated for the approximate to 43 Pg C contained in arctic tundras globally, the maximum net gain or loss (approximate to 0.3% per yr) from tundra would be equivalent to 0.13 Pg C/yr. Although fluxes of this magnitude would have a relatively minor impact on current changes in atmospheric CO2, the long-term impact on tundra C stores could be significant. The synthesis and insights provided by the model should make it possible to extrapolate into the future with a better understanding of the processes governing long- term changes in tundra C storage.

1673^3^Penuelas,J^Estiarte,M^Llusia,J^1997^1^Carbon-based secondary compounds at elevated CO2^79^33^2^313-316^^^^^^^^^^6121
1080^1086^2562^2607^362^376^417^546^56^92^ effects of decreased light intensity (an artifact of the greenhouse structures), there was a long-term increase in ecosystem C stocks because of increased photosynthetic response to the temperature-induced shift of N from soil to vegetation. If our simulated changes in ecosystem C storage are extrapolated for the approximate to 43 Pg C contained in arctic tundras globally, the maximum net gain or loss (approximate to 0.3% per yr) A^6120^From literature sources we compiled the data on carbon-based- secondary compounds CBSC (phenolics and terpenoids) and biomass of 17 plant species grown at different CO2 concentrations under low and high nutrient availabilities. With a low nutrient availability a possible inverse correlation was found between the biomass and CBSC changes. On the contrary, under a high nutrient availability, both the CBSC and biomass increased with elevated CO2. The wide variation in the CBSC production among species and compounds (larger responses in phenolics than in terpenoids) indicates that the allocation to CBSC may not completely be governed by changes in CO2 and nutrient availabilities per se. Yet the comparison shows that elevated CO2 generally loads the carbon into CBSC [their leaf concentration increased an overall average of 14 % at 700 mu mol(CO2) mol(-1)] which may improve our understanding of the carbon storage and cycling in ecosystems under the ''global change'' of climate.
approximate to 0.3% per yr) 1674^4^Rogers,HH^Prior,SA^Runion,GB^Mitchell,RJ^1996^1^Root to shoot ratio of crops as influenced by CO2^206^187^2^229-248^^^^^^^^^^6123
1392^230^2608^2609^341^346^372^436^546^685^ntrations under low and high nutrient availabilities. With a low nutrient availability a possible inverse correlation was found between the biomass and CBSC changes. On the contrary, under a high nutrient availability, both the CBSC and biomass increased with elevated CO2. The wide variation in the CBSC production among species and compounds (larger responses in phenolics than in terpenoids) indicates that the allocation to CBSC may not completely be governed by changes in CO2 and nutrient availabilities per se. Yet the comparison shows that elevated CO2 generally loads the carbon into CBSC [their leaf concentration increased an overall average of 14 % at 700 mu mol(CO2) mol(-1)] which may improve our understanding of the carbon storage and cycling in ecosystems under the ''global change'' of climate.
approximate to 0.3% per yr) A^6122^Crops of tomorrow are likely to grow under higher levels of atmospheric CO2. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will affect roots and shoots of crop plants proportionally. Since elevated CO2 can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability, Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO2 and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will add substantially to the global change response data base.

1675^3^Saralabai,VC^Vivekanandan,M^Babu,RS^1997^1^Plant responses to high CO2 concentration in the atmosphere^79^33^1^7-37^^^^^^^^^^6125
1066^1977^343^388^389^398^399^448^507^575^there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability, Herein we review root to shoot allocation as affected by increased concentrations oA^6124^The impact of continuous rise in ambient CO2 concentration (AC) in the atmosphere on different facets of growth of crop plants is assessed. The effects of CO2 enrichment (EC) on plant growth, C-3 and C-4 photosynthesis, source-sink ratio, partitioning and translocation of metabolites, photosynthetic enzymes, respiratory rate, leaf area index, stomatal conductance (g(s)), transpiration rate, biomass production and water use efficiency are reviewed. The CO2 fertilization effects are studied in both short-term (open top chambers) and long-term experiments. Long-term experiments suggest that ribulose-1,5-bisphosphate carboxylase is inactivated at high CO2 concentrations. Also g(s) is lowered. One of the conspicuous effects of EC is the closure of stomata in C-3 plants. Photosystem (PS) 2 electron transport is more affected than PS1. Starch is the immediate product accumulated in the leaf of C-3 plants. The ''CO2 fertilization effect'' does not confer any great advantage even in C-3 plants.
ncentrations o1676^4^Schortemeyer,M^Hartwig,UA^Hendrey,GR^Sadowsky,MJ^1996^1^Microbial community changes in the rhizospheres of white clover and perennial ryegrass exposed to free air carbon dioxide enrichment (FACE)^130^28^12^1717-1724^^^^^Dec^^^^^6127
2610^2611^2612^372^374^456^540^56^803^92^tabolites, photosynthetic enzymes, respiratory rate, leaf area index, stomatal conductance (g(s)), transpiration rate, biomass production and water use efficiency are reviewed. The CO2 fertilization effects are studied in both short-term (open top chambers) and long-term experiments. Long-term experiments suggest that ribulose-1,5-bisphosphate carboxylase is inactivated at high CO2 concentrations. Also g(s) is lowered. One of the conspicuous effects of EC is the closure of stomata in C-3 plants. Photosystem (PS) 2 electron transport is more affected than PS1. Starch is the immediate product accumulated in the leaf of C-3 plants. The ''CO2 fertilization effect'' does not confer any great advantage even in C-3 plants.
ncentrations oA^6126^Increases in the global atmospheric concentration of CO2 will not only directly affect the growth of plants, but might also alter the living conditions for soil biota. This could lead to shifts in the size and composition of the soil microbial communities. In this study we investigated the response of heterotrophic bacteria, NH4+-oxidising bacteria, and Rhizobium leguminosarum by. trifolii populations to elevated atmospheric CO2 concentrations in a model field-scale grassland ecosystem. The Free Air CO2 Enrichment (FACE) facility in Eschikon, Switzerland, releases CO2-enriched air into three large circular areas, each of 18 m dia, to a final CO2 concentration of 600 mu mol mol(-1), while three control areas of the same size receive ambient CO2 concentrations (similar to 350 mu mol mol(-1)). For this study, white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were grown as replicated monocultures within the FACE rings. Soil samples were taken from 0-10 cm depth in May and November 1994 (the second year of CO2-enrichment), and rhizosphere soil was obtained from clover and ryegrass roots for enumeration of bacteria. While the total numbers of culturable heterotrophic bacteria (determined by plate counts) in the rhizospheres of both plant species were little affected by CO2-enrichment, the populations of R. leguminosarum by. trifolii (enumerated by MPN) were increased two-fold in the rhizospheres of white clover exposed to elevated atmospheric CO2. There was no effect of the CO2 concentration on the populations of R. leguminosarum by. trifolii in the rhizospheres of perennial ryegrass, indicating that the increase of Rhizobium numbers is a host- related response to elevated atmospheric CO2. The numbers of autotrophic NH4+-oxidizing bacteria in the rhizospheres (enumerated by MPN) were unaffected by the atmospheric CO2 concentration. There was also no effect of the CO2 concentration on the amount of microbial biomass C in the bulk, non-rhizosphere soils in white clover or perennial ryegrass plots. These data indicate that under a legume crop, at least in terms of inoculum quality in the rhizosphere soil, symbiotic nitrogen-fixing organisms might be favoured by elevated atmospheric CO2 concentrations. (C) 1997 Elsevier Science Ltd.

1677^2^Soussana,JF^Hartwig,UA^1996^1^The effects of elevated CO2 on symbiotic N-2 fixation: A link between the carbon and nitrogen cycles in grassland ecosystems^206^187^2^321-332^^^^^^^^^^6129
2003^2613^2614^2615^2616^2617^344^457^506^859^ect of the CO2 concentration on the populations of R. leguminosarum by. trifolii in the rhizospheres of perennial ryegrass, indicating that the increase of Rhizobium numbers is a host- related response to elevated atmospheric CO2. The numbers of autotrophic NH4+-oxidizing bacteria in the rhizospheres (enumerated by MPN) were unaffected by the atmospheric CO2 concentration. There was also no effect of the CO2 concentration on the amount of microbial biomass C in the bulk, non-rhizosphere soils in white clover or perennial ryA^6128^The response of plants to elevated CO2 is dependent on the availability of nutrients, especially nitrogen. It is generally accepted that an increase in the atmospheric CO2 concentration increases the C:N ratio of plant residues and exudates. This promotes temporary N-immobilization which might, in turn, reduce the availability of soil nitrogen. In addition, both a CO2 stimulated increase in plant growth (thus requiring more nitrogen) and an increased N demand for the decomposition of soil residues with a large C:N will result under elevated CO2 in a larger N-sink of the whole grassland ecosystem. One way to maintain the balance between the C and N cycles in elevated CO2 would be to increase N-import to the grassland ecosystem through symbiotic N-2 fixation. Whether this might happen in the context of temperate ecosystems is discussed, by assessing the following hypothesis: i) symbiotic N-2 fixation in legumes will be enhanced under elevated CO2, ii) this enhancement of N- 2 fixation will result in a larger N-input to the grassland ecosystem, and iii) a larger N input will allow the sequestration of additional carbon, either above or below- ground, into the ecosystem. Data from long-term experiments with model grassland ecosystems, consisting of monocultures or mixtures of perennial ryegrass and white clover, grown under elevated CO2 under free-air or field-like conditions, supports the first two hypothesis, since: i) both the percentage and the amount of fixed N increases in white clover grown under elevated CO2 ii) the contribution of fixed N to the nitrogen nutrition of the mixed grass also increases in elevated CO2. Concerning the third hypothesis? an increased nitrogen input to the grassland ecosystem from N-2 fixation usually promotes shoot growth (above-ground C storage) in elevated CO2. However, the consequences of this larger N input under elevated CO2 on the belowground carbon fluxes are not fully understood. On one hand, the positive effect of elevated CO2 on the quantity of plant residues might be overwhelming and lead to an increased long-term below-ground C storage; on the other hand, the enhancement of the decomposition process by the N-rich legume material might favour carbon turn-over and, hence, limit the storage of below-ground carbon.

1678^2^Williams,M^Harwood,JL^1997^1^Effects of carbon dioxide concentration and temperature on lipid synthesis by young wheat leaves^129^45^2^243-250^^^^^May^^^^^6131
1936^244^2618^2619^2620^372^417^685^724^741^ N increases in white clover grown under elevated CO2 ii) the contribution of fixed N to the nitrogen nutrition of the mixed grass also increases in elevated CO2. Concerning the third hypothesis? an increased nitrogen input to the grassland ecosystem from N-2 fixation usually promotes shoot growth (above-ground C storage) in elevated CO2. However, the consequences of this larger N input under elevated CO2 on the belowground carbon fluxes are not fully understood. On one hand, the positive effect of elevated CO2 on the quantity of plant residues mighA^6130^The effects of incubation temperature and CO2 concentration on lipid synthesis in leaves from 7-day-old wheat plants were studied. Plants were cultivated at 350 mu mol mol(-1) (approximately ambient CO2) and 20 degrees so that, irrespective of the subsequent incubation conditions, the samples were all derived from plants at the same phenological stage of development. Leaf tissue was incubated with [1-C- 14]acetate at 350 mu mol mol(-1) or 700 mu mol mol(-1) CO2 concentration and at 20 degrees or 24 degrees. Doubling the CO2 concentration had little or no effect on lipid metabolism. In contrast, a 4 degrees rise in incubation temperature not only increased the rate of radiolabelling but also altered lipid synthesis qualitatively. Most noticeable of these changes was a marked increase in phosphatidylcholine labelling evidently at the expense of that of diacylglycerol. The increase in carbon flux to this extrachloroplastic lipid appeared to be restricted to the distal portions of the leaf tissue, thus indicating that the stage of tissue development was critical. Surprisingly, an increase of polyunsaturated fatty acid labelling was found at the higher incubation temperature. This increase was accompanied by a decrease in labelling of oleate in the main radiolabelled membrane lipids. In phosphatidylcholine the decrease in oleate labelling was compensated by a rise in that of linoleate while in monogalactosyldiacylglycerol, both linoleate and a-linolenate were better labelled at 24 degrees. A molecular basis for these alterations in lipid synthesis and acyl desaturation is suggested. (C) 1997 Elsevier Science Ltd.

1679^6^Winter,K^Richter,A^Engelbrecht,B^Posada,J^Virgo,A^Popp,M^1997^1^Effect of elevated CO2 on growth and crassulacean-acid- metabolism activity of Kalanchoe pinnata under tropical conditions^6^201^4^389-396^^^^^Apr^^^^^6133
1669^188^2621^2622^312^374^529^547^698^749^crease in carbon flux to this extrachloroplastic lipid appeared to be restricted to the distal portions of the leaf tissue, thus inA^6132^Kalanchoe pinnata (Lam.) Pers. (Crassulaceae), a succulent- leaved crassulacean-acid-metabolism plant, was grown in open- top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42-51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six- to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day- night fluctuations.

1680^2^Ziska,LH^Bunce,JA^1997^1^The role of temperature in determining the stimulation of CO2 assimilation at elevated carbon dioxide concentration in soybean seedlings^37^100^1^126-132^^^^^May^^^^^6135
344^348^360^376^417^509^687^92^ However, under elevated CO2, dry matter accumulation increased by 42-51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six- to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both tA^6134^Soybean (Glycine max cv. Clark) was gown at both ambient (ca 350 mu mol mol(-1)) and elevated (ca 700 mu mol mol(-1)) CO2 concentration at 5 growth temperatures (constant day/night temperatures of 20, 25, 30, 35 and 40 degrees C) for 17-22 days after sowing to determine the interaction between temperature and CO2 concentration on photosynthesis (measured as A, the rate of CO2 assimilation per unit leaf area) at both the single leaf and whole plant level. Single leaves of soybean demonstrated increasingly greater stimulation of A at elevated CO2 as temperature increased from 25 to 35 degrees C (i.e. optimal growth rates). At 40 degrees C, primary leaves failed to develop and plants eventually died. in contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO2 concentration. For whole plants, increased CO2 stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO2 for single leaves and whole plants may be related to increased self-shading experienced by whole plants at elevated CO2 as temperature increased. Results from the present study suggest that self-shading could limit the response of CO2 assimilation rate and the growth response of soybean plants if temperature and CO2 increase concurrently, and illustrate that light may be an important consideration in predicting the relative stimulation of photosynthesis by elevated CO2 at the whole plant level.

1681^4^Baker,JT^Allen,LH^Boote,KJ^Pickering,NB^1997^1^Rice responses to drought under carbon dioxide enrichment .2. Photosynthesis and evapotranspiration^127^3^2^129-138^^^^^Apr^^^^^6137
130^1337^230^344^360^372^449^528^575^674^n contrast, for both whole plant A and total biomass production, increasing temperature resulted in less stimulation by elevated CO2 concentration. For whole plants, increased CO2 stimulated leaf area more as growth temperature increased. Differences between the response of A to elevated CO2 for single leavA^6136^Future climate change is projected to include a strong likelihood of continued increases in atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Due mainly to uncertainties in the timing and amounts of monsoonal rainfall, drought is common in rainfed rice production systems. The objectives of this study were to quantify the effects and possible interactions of [CO2] and drought stress on rice (Oryza sativa, L.) photosynthesis, evapotranspiration and water-use efficiency. Rice (cv. IR-72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 mu mol CO2 mol(-1) air. In both [CO2], water management treatments included continuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long-term [CO2] growth treatments of 350 and 700 mu mol mol(-1) was tested by comparing canopy photosynthesis rates across short-term [CO2] ranging from 160 to 1000 mu mol mol(-1). These tests showed essentially no acclimation response with photosynthetic rate being a function of current short-term [CO2] rather than long- term [CO2] growth treatment. In both long-term [CO2] treatments, photosynthetic rate saturated with respect to [CO2] near 510 mu mol mol(-1). Carbon dioxide enrichment significantly increased both canopy net photosynthetic rate (21-27%) and water-use efficiency while reducing evapotranspiration by about 10%. This water saving under [CO2] enrichment allowed photosynthesis to continue for about one to two days longer during drought in the enriched compared with the ambient [CO2] control treatments.
nuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long-term [CO2] growth treatments of 350 and 700 mu mol mol(-1) wa1682^18^Bjorn,LO^Callaghan,TV^Johnsen,I^Lee,JA^Manetas,Y^Paul,ND^Sonesson,M^Wellburn,AR^Coops,D^HeideJorgensen,HS^Gehrke,C^GwynnJones,D^Johanson,U^Kyparissis,A^Levizou,E^Nikolopoulos,D^Petropoulou,Y^Stephanou,M^1997^1^The effects of UV-B radiation on European heathland species^331^128^1-2^252-264^^^^^Jan-Feb^^^^^6139
1008^1079^1434^243^2531^2623^2624^348^514^92^ to [CO2] near 510 mu mol mol(-1). Carbon dioxide enrichment significantly increased both canopy net photosynthetic rate (21-27%) and water-use efficiency while reducing evapotranspiration by about 10%. This water saving under [CO2] enrichment allowed photosynthesis to continue for about one to two days longer during drought in the enriched compared with the ambient [CO2] control treatments.
nuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long-term [CO2] growth treatments of 350 and 700 mu mol mol(-1) waA^6138^The effects of enhanced UV-B radiation on three examples of European shrub-dominated vegetation were studied in situ. The experiments were in High Arctic Greenland, northern Sweden and Greece, and at all sites investigated the interaction of enhanced UV-B radiation (simulating a 15% reduction in the ozone layer) with artificially increased precipitation, The Swedish experiment also involved a study of the interaction between enhanced UV-B radiation and elevated CO2 (600 ppm). These field studies were supported by an outdoor controlled environment study in the United Kingdom involving modulated enhancement of UV-B radiation in combination with elevated CO2 (700 ppm). Effects of the treatments on plant growth, morphology, phenology and physiology were measured. The effects observed were species specific, and included both positive and negative responses to the treatments. In general the negative responses to UV-B treatments of up to three growing seasons were small, but included reductions in shoot growth and premature leaf senescence. Positive responses included a marked increase in flowering in some species and a stimulation of some photosynthetic processes. UV-B treatment enhanced the drought tolerance of Pinus pinea and Pinus halepensis by increasing leaf cuticle thickness. In general, there were few interactions between the elevated CO2 and enhanced UV-B treatments. There was evidence to suggest that although the negative responses to the treatments were small, damage may be increasing with time in some long-lived woody perennials. There was also evidence in the third year of treatments for effects of UV-B on insect herbivory in Vaccinium species. The experiments point to the necessity for long-term field investigations to predict the likely ecological consequences of increasing UV-B radiation.

1683^3^Boese,SR^Wolfe,DW^Melkonian,JJ^1997^1^Elevated CO2 mitigates chilling-induced water stress and photosynthetic reduction during chilling^9^20^5^625-632^^^^^May^^^^^6141 included reductions in shoot grow1069^1092^188^1912^2489^2625^2626^2627^383^550^nses included a marked increase in flowering in some species and a stimulation of some photosynthetic processes. UV-B treatment enhanced the drought tolerance of Pinus pinea and Pinus halepensis by increasing leaf cuticle thickness. In general, there were few interactions between the elevated CO2 and enhanced UV-B treatments. There was evidence to suggest that although the negative responses to the treatments were small, damage may be increasing with time in some long-lived woody perennials. There was also evidence in the third year of treatments for effects of UV-B on insect herbivory in Vaccinium species. The experiments point to the necessity for long-term field investigations to predict the likely ecological consequences of increasing UV-B radiation.

1683^3^Boese,SR^Wolfe,DW^Melkonian,JJ^1997^1^Elevated CO2 mitigates chilling-induced water stress and photosynthetic reduction during chilling^9^20^5^625-632^^^^^May^^^^^6141 included reductions in shoot growA^6140^Bean, cucumber and corn plants were grown in controlled- environment chambers at 25/18 degrees C day/night temperature and either ambient (350 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) CO2 concentration, and at 20-30 d after emergence they were exposed to a 24 h chilling treatment (6.5 +/- 1.5 degrees C) at their growth CO2 concentration. Whole-plant transpiration rates (per unit leaf area basis) during the first 3 h of chilling were about 26, 28 and 13% lower at elevated than at ambient CO2 for bean, cucumber and corn, respectively. The decline in leaf water potential (Psi(L)) and visible wilting of bean and cucumber during chilling were significantly less at elevated than at ambient CO2. Corn Psi(L) was not significantly affected by chilling, and corn did not exhibit any other symptoms of chilling-induced water stress. Leaf osmotic potentials (measured before chilling only) of bean and cucumber were more negative at elevated than at ambient CO2, and the corresponding calculated leaf turgor potentials were significantly higher at elevated than at ambient CO2. Leaf relative water content (RWC) during chilling at ambient CO2 fell to 62 and 48% for bean and cucumber, respectively, RWC during chilling at elevated CO2 was never below 79% for bean or 63% for cucumber. Corn RWC was not measured, After 24 h of chilling at ambient CO2, net photosynthetic rate (PN) reductions were 83, 89 and 24% for bean, cucumber and corn, respectively. P-N reductions during chilling were less at elevated CO2: 53, 40 and 4% for bean, cucumber and corn, respectively. At ambient CO2, none of the species fully recovered to pre-chilling P-N, but at elevated CO2 both bean and corn recovered fully. The average percentage leaf area with visible leaf damage due to chilling was 20.6 and 9.6% at ambient and elevated CO2, respectively, for bean, and 32.4 and 23.6% at ambient and elevated CO2, respectively, for cucumber. Corn showed no significant permanent leaf damage from chilling at either CO2 concentration. These results indicate that cucumber was most sensitive to chilling as imposed in this study, followed by bean and corn. The results support the hypothesis that, at least in young plants under controlled- environment conditions, elevated CO2 improves plant water relations during chilling and can mitigate photosynthetic depression and chilling damage. The implications for long-term growth and reproductive success in managed and natural ecosystems will require testing of this hypothesis under field conditions.

1684^3^Chen,SG^Impens,I^Ceulemans,R^1997^1^Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers^127^3^2^97-106^^^^^Apr^^^^^6143
2067^2599^312^417^467^664^92^damage due to chilling was 20.6 and 9.6% at ambient and elevated CO2, respectively, for bean, and 32.4 and 23.6% at ambient and elevated CO2, respectively, for cucumber. Corn showed no significant permanent leaf damage from chilling at either CO2 concentration. These results indicateA^6142^An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO2] on architectural as well as on physiological characteristics of two poplar clones (Populus trichocarpa x P. deltoides clone Beaupre and P. deltoides x P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO2] (ambient + 350 mu mol mol(-1)) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO2] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO2] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO2] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above- ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO2] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO2] enrichment had little effect on daily canopy light interception and photosynthesis.

1685^4^Ghannoum,O^vonCaemmerer,S^Barlow,EWR^Conroy,JP^1997^1^The effect of CO2 enrichment and irradiance on the growth, morphology and gas exchange of a C-3 (Panicum laxum) and a C-4 (Panicum antidotale) grass^92^24^2^227-237^^^^^^^^^^6145
130^312^35^360^374^417^639^641^698^733^eason. The first year experiments and modelling results showed that the [CO2] enrichment had effects on light intercepting canopy structA^6144^The effect of CO2 enrichment and irradiance on the growth and gas exchange of two tropical grasses, Panicum laxum (C-3) and Panicum antidotale (C-4) were investigated. The two species were grown at either 350 (low) or 700 (high) mu L L-1 CO2 concentration, under 40% (low) or 100% (high) of direct sunlight and supplied with ample water and nutrition. Elevated CO2 enhanced plant dry weight at both irradiances in the C-3 species (1.41-fold and 1.71-fold increase at low and high light, respectively) but only at high light in the C-4 species (1.28 fold increase). CO2 enrichment had no effect on the dry weight of P. antidotale, when stem development was suppressed by growth under artificial lighting. When measured at the CO2 concentration at which they were grown, assimilation rates were similar in the low and high CO2 grown plants, for both species. However, when measurements made at low CO2 were compared, CO2 assimilation rates of the high light, high CO2 grown C-3 and C- 4 species were lower than those of their low CO2 grown counterparts. High CO2 strongly reduced the stomatal conductance of both species, while it affected the Rubisco content (30% decrease) of the high light C-3 species only. This work shows clearly that C-4 species can respond to CO2 enrichment under favourable growth conditions, and that acclimation to elevated CO2 in pasture grasses does not necessarily involve accumulation of non-structural carbohydrates or reduction of total N or soluble proteins in source leaves.

1686^3^GwynnJones,D^Lee,JA^Callaghan,TV^1997^1^Effects of enhanced UV-B radiation and elevated carbon dioxide concentrations on a sub-Arctic forest heath ecosystem^331^128^1-2^242-249^^^^^Jan-Feb^^^^^6147
174^1922^2628^2629^374^417^92^he CO2 concentration at which they were grown, assimilation rates were similar in the low and high CO2 grown plants, for both species. However, when measurements made at low CO2 were compared, CO2 assimilation rates of the high light, high CO2 grown C-3 and C- 4 species were lower than those oA^6146^An experiment is described which studies the effects of enhanced UV-B radiation (simulating a 15% reduction in the Ozone layer) and elevated atmospheric concentrations of CO2 (600 ppm) on the dwarf shrub layer of a sub-arctic forest heath ecosystem at Abisko, North Sweden. The experimental treatments were first applied in 1993, and have covered most of the snow- free season (late May to early September) 1993-1995. Effects of the treatments on the four dwarf shrub species have been recorded largely using non-destructive measures (Vaccinium uliginosum, Vaccinium myrtillus - deciduous species and Vaccinium vitis-idaea and Empetrum hermaphroditum - evergreen species). Effects of the treatments on stem growth and leaf thickness have so far been small, although CO2 treatments initially stimulated stem extension in Vaccinium myrtillus 1993 and depressed growth in V. vitis idaea in 1994 and E. hermaphroditum during 1995. UV-B treatments stimulated fruit production in V. myrtillus in both 1994 and 1995, but there was no effect on reproductive phenology. There were also marked effects of UV-B treatments on insect herbivory in the deciduous dwarf shrubs; with leaf area loss being greater than the control in the UV-B treatment in V. myrtillus and less in V. uliginosum. The results point to the possibility of important effects of the treatments on physiological and chemical processes within the plants. The ecological results of such effects may not be immediately apparent, but may be far reaching, pointing to the need for long-term in situ experimentation in predicting the effects of these global change variables.

1687^9^Hebeisen,T^Luscher,A^Zanetti,S^Fischer,BU^Hartwig,UA^Frehner,M^Hendrey,GR^Blum,H^Nosberger,J^1997^1^Growth response of Trifolium repens L and Lolium perenne L as monocultures and bi-species mixture to free air CO2 enrichment and management^127^3^2^149-160^^^^^Apr^^^^^6149
1098^1298^229^2630^344^372^430^506^750^977^ treatments stimulated fruit production in V. myrtillus in both 1994 and 1995, but thA^6148^Trifolium repens L. and Lolium perenne L. were grown in monocultures and bi-species mixture in a Free Air Carbon Dioxide Enrichment (FACE) experiment at elevated (60 Pa) and ambient (35 Pa) CO2 partial pressure (pCO(2)) for three years. The effects of defoliation frequencies (4 and 7 cuts in 1993; 4 and 8 cuts in 1994/95) and nitrogen fertilization (10 and 42 g m(-2) y(-1) N in 1993; 14 and 56 g m(-2) y(-1) in 1994/95) on the growth response to pCO(2) were investigated. There were significant interspecific differences in the CO2 responses during the first two years, while in the third growing season, these interspecific differences disappeared. Yield of T. repens in monocultures increased in the first two years by 20% when grown at elevated pCO(2). This CO2 response was independent of defoliation frequency and nitrogen fertilization. In the third year, the CO2 response of T. repens declined to 11%. In contrast, yield of L. perenne monocultures increased by only 7% on average over three years at elevated pCO(2). The yield response of L. perenne to CO2 changed according to defoliation frequency and nitrogen fertilization, mainly in the second and third year. The ratio of root/yield of L. perenne increased under elevated pCO(2), low N fertilizer rate, and frequent defoliation, but it remained unchanged in T. repens. We suggest that the more abundant root growth of L. perenne was related to increased N limitation under elevated pCO(2). The consequence of these interspecific differences in the CO2 response was a higher proportion of T. repens in the mixed swards at elevated pCO(2). This was evident in all combinations of defoliation and nitrogen treatments. However, the proportion of the species was more strongly affected by N fertilization and defoliation frequency than by elevated pCO(2). Based on these results, we conclude that the species proportion in managed grassland may change as the CO2 concentration increases. However, an adapted management could, at least partially, counteract such CO2 induced changes in the proportion of the species. Since the availability of mineral N in the soil may be important for the species' responses to elevated pCO(2), more long-term studies, particularly of processes in the soil, are required to predict the entire ecosystem response.

1688^3^Hirschel,G^Korner,C^Arnone,JA^1997^1^Will rising atmospheric CO2 affect leaf litter quality and in situ decomposition rates in native plant communities?^2^110^3^387-392^^^^^Apr^^^^^6151
1030^312^372^374^429^57^58^669^672^738^response was a higher proportion of T. repens in the mixed swards at elevated pCO(2). This was evident in all combinations of defoliation and nitrogen treatments. However, the proportion of the species was more strongly affected by N fertilization and defoliation frequency than by elevated pCO(2). Based on these results, we conclude that the species proportion in managed grassland may change as the CO2 concentration increases. However, an adapted management could, at least partially, counteract such CO2 induced chanA^6150^Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the quality of naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant species produced in alpine, temperate and tropical communities maintained at elevated CO2 (600-680 mu l(- 1)) was not significantly different from that produced in similar communities maintained at current ambient CO2 concentrations (340-355 mu l l(-1)). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.
pecies mixtur1689^3^Huang,BR^Johnson,JW^NeSmith,DS^1997^1^Responses to root-zone CO2 enrichment and hypoxia of wheat genotypes differing in waterlogging tolerance^164^37^2^464-468^^^^^Mar-Apr^^^^^6153
1871^2631^2632^310^543^563^91^he Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.
pecies mixturA^6152^Knowledge of wheat (Triticum aestivum L.) responses to CO2 and O-2 in the root environment could improve understanding of the mechanisms of waterlogging tolerance and thus help develop waterlogging-tolerant wheat plants. This experiment was designed to investigate the responses to elevated CO2 and hypoxia of two wheat genotypes, Bayles and Savannah, which differ in waterlogging tolerance. Plants were grown in a growth chamber in nutrient solutions. Nutrient solutions were bubbled with ambient air (control), N-2 containing 5 kPa O-2 and ambient CO2 (hypoxia), N-2 containing 10 kPa CO2 and ambient O- 2 (high CO2, ambient O-2), and N-2 containing 10 kPa CO2 and 5 kPa O-2 (high CO2, low O-2). Hypoxia alone had adverse effects on net photosynthesis (P-n), stomatal conductance (g(s)), water relations, leaf chlorophyll (chi) content, and shoot and root growth. The effects were greater for waterlogging-sensitive Bayles. When compared with the aerated control, the combination of elevated CO2 and hypoxia caused significant reductions in P- n, g(s), leaf water potential, and leaf chi content for Bayles, and in shoot and root growth for both Bayles and Savannah. Photosynthetic rate and leaf chi content of Savannah were increased when roots of hypoxic plants were exposed to elevated CO2, but this was not true for Bayles. Root-zone CO2 enrichment at ambient O-2 had no significant effects on shoot growth, but reduced root growth In both genotypes. The results showed that CO2 enrichment under root hypoxia can alleviate some negative effects of hypoxia on P-n, leaf chl content, and shoot growth, the effect being larger for waterlogging-tolerant Savannah.

1690^4^Hungate,BA^Lund,CP^Pearson,HL^Chapin,FS^1997^1^Elevated CO2 and nutrient addition alter soil N cycling and N trace gas fluxes with early season wet-up in a California annual grassland^26^37^2^89-109^^^^^May^^^^^6155
2087^2308^2633^535^56^57^669^893^ogging-sensitive Bayles. When compared with the aerated control, the combination of elevated CO2 and hypoxia causedA^6154^We examined the effects of growth carbon dioxide (CO2) concentration and soil nutrient availability on nitrogen (N) transformations and N trace gas fluxes in California grassland microcosms during early-season wet-up, a time when rates of N transformation and N trace gas flux are high. After plant senescence and summer drought, we simulated the first fall rains and examined N cycling. Growth at elevated CO2 increased root production and root carbon:nitrogen ratio, Under nutrient enrichment, elevated CO2 increased microbial N immobilization during wet-up, leading to a 43% reduction in gross nitrification and a 55% reduction in NO emission from soil. Elevated CO2 increased microbial N immobilization at ambient nutrients, but did not alter nitrification or NO emission. Elevated CO2 did not alter soil emission of N2O at either nutrient level. Addition of NPK fertilizer (1:1:1) stimulated N mineralization and nitrification, leading to increased N2O and NO emission from soil, The results of our study support a mechanistic model in which elevated CO2 alters soil N cycling and NO emission: increased root production and increased C:N ratio in elevated CO2 stimulate N immobilization, thereby decreasing nitrification and associated NO emission when nutrients are abundant. This model is consistent with OUT basic understanding of how C availability influences soil N cycling and thus may apply to many terrestrial ecosystems.

1691^2^Idso,SB^Kimball,BA^1997^1^Effects of long-term atmospheric CO2 enrichment on the growth and fruit production of sour orange trees^127^3^2^89-96^^^^^Apr^^^^^6157
1706^189^2453^264^312^372^374^685^73^968^duction in NO emission from soil. Elevated CO2 increased microbial N immobilization at ambient nutrients, but did not alter nitrification or NO emission. Elevated CO2 did not alter soil emission of N2O at either nutrient level. Addition of NPK fertilizer (1:1:1) stimulated N mineralization and nitrification, leading to increased N2O and NO emission from soil, The results of our study supporA^6156^In July of 1987, we planted eight 30-cm-tall sour orange tree seedlings in a field of Avondale loam at Phoenix, Arizona and enclosed them in pairs in clear-plastic-wall open-top chambers. Since 18 November of that year, we have continuously pumped ambient air of approximate to 400 ppmv [CO2] through two of these enclosures, while through the other two we have continuously pumped air of approximate to 700 ppmv [CO2]. By the end of the second year of the study, the trunk plus branch volume of the [CO2]-enriched trees was approximate to 2.75 times greater than that of the ambient-treatment trees. Three years later, this factor had dropped to approximate to 2.0; but the decline in the [CO2]-enriched/ambient-treatment ratio of trunk plus branch volume was nearly perfectly offset by the relative fruit production advantage enjoyed by the [CO2]- enriched trees over that period. In Years 6, 7 and 8, however, there was a moderate drop in total productivity enhancement. This decline may be a delayed acclimation response, or it could be due to enhanced self-shading in the [CO2]-enriched trees or to the fact that, starting early in Year 6, many branches of the [CO2]-enriched trees grew all the way to the walls of their enclosures, so that many blossoms and young fruit were destroyed by intermittent physical trauma produced by the action of wind against the taut plastic in that year and in all succeeding years. Hence, we will have to maintain our experiment for several more years for this lateral growth obstruction to occur to the same degree in the ambient-air chambers as it has in the [CO2]-enriched chambers, in order to determine the long-term equilibrium effects of atmospheric [CO2] enrichment in a spatially confined environment.

1692^4^Karunaratne,C^Moore,GA^Jones,R^Ryan,R^1997^1^Phosphine and its effect on some common insects in cut flowers^259^10^3^255-262^^^^^Mar^^^^^6159
2634^312^418^ 6, 7 and 8, however, there was a moderate drop in total productivity enhancement. This decline may be a delayed acclimation A^6158^The most effective fumigant for insect disinfestation of cut flowers is currently methyl bromide, which will soon be unavailable in several countries. The toxicity of an alternative fumigant, phosphine (2% PH3 and 98% N-2), was tested at 24 degrees C on adult greenhouse thrips (Heliothrips haemorrhoidalis), adult aphids (Myzus persicae) and lightbrown apple moth larvae (LBAM; Epiphyas postvittana). These are commonly found as insect pests on many cut flower crops. Thrips were exposed to phosphine concentrations ranging from 20-600 mu l/l for 1 or 2 h. All thrips were killed within 18 h of exposure after a treatment of 300 mu l/l phosphine for 2 h. Adult aphids and fifth instar LBAM larvae were more resistant to phosphine, and trials were therefore conducted using higher phosphine concentrations (> 500 mu l/l) combined with atmospheric (0.035%) or elevated (33%) CO2. The most effective treatment for aphids was 1000 mu l/l phosphine +33% CO2 for 4 h, which killed all insects within 36 h of exposure. Under atmospheric CO2 levels, 92% of aphids were killed within 36 h after exposure to 1000 mu l/l phosphine for 6 h, with 100% kill attained after exposure to 5000-8000 mu l/l phosphine for 6 h. Elevated CO2 levels did not improve the efficacy of phosphine on LBAM larvae. The optimal treatment was 2000-2500 mu l/l phosphine for 4 or 6 h, which killed 96 or 100% of the larvae, respectively. Under atmospheric CO2 levels, 4000 mu l/l phosphine killed 74% of LBAM larvae after 4 h. and 94% after 6 h exposure. (C) 1997 Elsevier Science B.V.

1693^2^Kellomaki,S^Vaisanen,H^1997^1^Modelling the dynamics of the forest ecosystem for climate change studies in the boreal conditions^81^97^1-2^121-140^^^^^15 Apr^^^^^6161
131^238^243^2635^310^372^384^51^57^605^e therefore conducted using higher phosphine concentrations (> 500 mu l/l) combined with atmospheric (0.035%) or elevated (33%) CO2. The most effective treatment for aphids was 1000 mu l/l phosphine +33% CO2 for 4 h, which killed all insects within 36 h of exposure. UndA^6160^This paper summarizes a forest ecosystem model developed for assessing the effects of climate change on the functioning and structure of boreal coniferous forests under the assumption that temperature and precipitation are the basic dimensions of the niche occupied by any one tree species. Special attention is paid to specifying weather patterns to a level representing the time constant of different physiological and ecological processes relevant to the regeneration, growth and death of trees. The long-term dynamics of the forest ecosystem have been coupled with climatic factors at the level of mechanisms, e.g., photosynthesis and respiration, in terms of the energy flow through the ecosystem. Furthermore, hydrological and nutrient cycles couple the dynamics of the forest ecosystem with climate change through soil processes representing the thermal and hydraulic properties of the soil and the decomposition of litter and humus with the mineralization of nutrients. Simulations for southern Finland (62 degrees N) and northern Finland (66 degrees N) indicated that a transient increase in temperature by 4 degrees C over a period of 100 years could substantially increase soil temperature and reduce soil moisture in forest ecosystems dominated by Scots pine. At the same time, the temperature increase could enhance photosynthetic production and consequent stemwood growth in southern Finland by about 8% and in northern Finland by about 19%. Given the current temperature but elevating CO2 concentration, the increase in photosynthesis in southern Finland could be about 23% and in northern Finland about 21%, but the concurrent elevation in temperature and CO2 concentration increased photosynthesis by about 32% in southern Finland and by about 40% in northern Finland. Transpiration decreased by as much as 10-20% under the changing climate with the consequence that water-use efficiency increased by as much as 25-45%, the higher values representing southern Finland. (C) 1997 Elsevier Science B.V.
outhern Finland (62 d1694^2^Kellomaki,S^Wang,KY^1997^1^Photosynthetic responses of Scots pine to elevated CO2 and nitrogen supply: Results of a branch-in-bag experiment^13^17^4^231-240^^^^^Apr^^^^^6163
312^344^356^384^389^635^665^713^722^92^cosystems dominated by Scots pine. At the same time, the temperature increase could enhance photosynthetic production and consequent stemwood growth in southern Finland by about 8% and in northern Finland by about 19%. Given the current temperature but elevating CO2 concentration, the increase in photosynthesis in southern Finland could be about 23% and in northern Finland about 21%, but the concurrent elevation in temperature and CO2 concentration increased photosynthesis by about 32% in southern Finland and by about 40% in northern Finland. Transpiration decreased by as much as 10-20% under the changing climate with the consequence that water-use efficiency increased by as much as 25-45%, the higher values representing southern Finland. (C) 1997 Elsevier Science B.V.
outhern Finland (62 dA^6162^Naturally seeded Scots pine (Pinus sylvestris L.) trees, age 25-30 years, were subjected to two soil-nitrogen-supply regimes and to elevated atmospheric CO2 concentrations by the branch- in-bag method from April 15 to September 15 for two or three years. Gas exchange in detached shoots was measured in a diffuse radiation field. Seven parameters associated with photosynthetic performance and two describing stomatal conductance were determined to assess the effects of treatments on photosynthetic components. An elevated concentration of CO2 did not lead to a significant downward regulation in maximum carboxylation rate (V-cmax) or maximum electron transport rate (J(max)), but it significantly decreased light-saturated stomatal conductance (g(sat)) and increased minimum stomatal conductance (g(min)). Light-saturated rates of CO2 assimilation were higher (24-31 %) in shoots grown and measured at elevated CO2 concentration than in shoots grown and measured ured at ambient CO2 concentration, regardless of treatment time or nitrogen-supply regime. High soil-nitrogen supply significantly increased photosynthetic capacity, corresponding to significant increases in V-cmax and J(max). However, the combined elevated CO2 + high nitrogen-supply treatment did not enhance the photosynthetic response above that observed in the elevated CO2 treatment alone.

1695^2^Kubiske,ME^Pregitzer,KS^1997^1^Ecophysiological responses to simulated canopy gaps of two tree species of contrasting shade tolerance in elevated CO2^43^11^1^24-32^^^^^Feb^^^^^6165
1291^2489^2636^312^342^344^345^665^91^975^ant downward regulation in maximum carboxylation rate (V-cmax) or maximum electron transport rate (J(max)), but it significantly decreased light-saturated stomatal conductance (g(sat)) and increased minimum stomatal conductance (g(min)). Light-saturated rates of CO2 assimilation were higher (24-31 %) in shoots grown and measured at elevated CO2 concentration than in shoots grown and measured ured at ambient CO2 concentration, regardless of tA^6164^1. One-year-old seedlings of shade tolerant Acer rubrum and intolerant Betula papyrifera were grown in ambient and twice ambient (elevated) CO2, and in full sun and 80% shade for 90 days. The shaded seedlings received 30-min sun patches twice during the course of the day, Gas exchange and tissue-wafer relations were measured at midday in the sun plants and following 20 min of exposure to full sun in the shade plants to determine the effect of elevated CO2 on constraints to sun- patch utilization in these species. 2. Elevated CO2 had the largest stimulation of photosynthesis in B. papyrifera sun plants and A. rubrum shade plants, 3. Higher photosynthesis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology, Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade. 4. Betula papyrifera exhibited CO2 responses that would facilitate tolerance to leaf water deficits in large sun patches, including osmotic adjustment and higher transpiration and stomatal conductance at a given leaf-water potential, whereas A. rubrum exhibited large increases in photosynthetic nitrogen-use efficiency. 5. Results suggest that species of contrasting successional ranks respond differently to elevated CO2, in ways that are consistent with the habitats in which they typically occur.

1696^6^Kubiske,ME^Pregitzer,KS^Mikan,CJ^Zak,DR^Maziasz,JL^Teeri,JA^1997^1^Populus tremuloides photosynthesis and crown architecture in response to elevated CO2 and soil N availability^2^110^3^328-336^^^^^Apr^^^^^6167
1701^2068^2637^2638^2639^344^384^417^57^672^sis per unit leaf area in sun plants than in shade plants of B. papyrifera was largely owing to differences in leaf morphology, Acer rubrum exhibited sun/shade differences in photosynthesis per unit leaf mass consistent with biochemical acclimation to shade. 4. Betula papyrifera exhibited CO2 responses that would facilitate tolerance to leaf water deficitsA^6166^We tested the hypothesis that elevated CO2 would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO2. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO2 and in low and high soil N availability (89 +/- 7 and 333 +/- 16 ng N g(-1) day(-1) net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO2 resulted in significantly higher maximum leaf photosynthesis (A(max)) at both soil N levels. A(max) was higher at high N than at low N soil in elevated, but not ambient CO2. Photosynthetic N use efficiency was higher at elevated than ambient CO2 in both soil types. Elevated CO2 resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO2 and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport capacity (V-cmax/J(max)) than at ambient CO2 and/or low N availability. From the top to the bottom of the tree crowns, V-cmax/J(max) increased in ambient CO2, but it decreased in elevated CO2 indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO2. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A(leaf) for each segment. This analysis indicated that increased A(leaf) at elevated CO2 did not result in a proportional increase in local stem segment mass, suggest ing that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation to roots in young trees may increase in elevated CO2.

1697^6^Lovelock,CE^Kyllo,D^Popp,M^Isopp,H^Virgo,A^Winter,K^1997^1^Symbiotic vesicular-arbuscular mycorrhizae influence maximum rates of photosynthesis in tropical tree seedlings grown under elevated CO2^92^24^2^185-194^^^^^^^^^^6169
224^229^2640^374^376^377^407^417^820^849^lative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO2. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A(leaf) for each segment. This analysis indicated that increased A(leaf) at elevated CO2 did not result in a proportional increase in local stem segment mass, suggest ing that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suA^6168^To investigate the importance of phosphorus and carbohydrate concentrations in influencing photosynthetic capacity of tropical forest tree seedlings under elevated CO2, we grew seedlings of Beilschmiedia pendula (Sw.) Hemsl. (Lauraceae) under elevated CO2 concentrations either with or without vesicular-arbuscular (VA) mycorrhizae. VA-mycorrhizae increased phosphorus concentrations in all plant organs (leaves, stems and roots). Maximum rates of photosynthesis (A(max)) measured under saturating levels of CO2 and light were correlated with leaf phosphorus concentrations. VA-mycorrhizae also increased leaf carbohydrate concentrations, particularly under elevated CO2, but levels were low and within the range observed in naturally occurring forest species. Root carbohydrate concentrations were reduced in VA-mycorrhizal plants relative to non-mycorrhizal plants. These results indicate an important role for VA-mycorrhizae in controlling photosynthetic rates and sink strength in tropical trees, and thus in determining their response to future increases in atmospheric CO2 concentrations.

1698^2^Magan,N^Baxter,ES^1996^1^Effect of increased CO2 concentration and temperature on the phyllosphere mycoflora of winter wheat flag leaves during ripening^332^129^2^189-195^^^^^Oct^^^^^6171
1850^434^447^461^730^92^ vesicular-arbuscular (VA) mycorrhizae. VA-mycorrhizae increased phosphorus concentrations in all plant organs (leaves, stems and roots). Maximum rates of photosynthesis (A(max)) measured under saturating levels of CO2 and light were correlated with leaf phosphorus concentrations. VA-mycorrhizae also increased leaf carbohydrate concentrations, particularly under elevated CO2, but levels were low and within the range observed in naturally occurring forest species. Root carbohydrate concentrations were reduced in VA-mycorrhizal plants relative to non-mycorrhizal plants. These results indicate an important role for VA-mycorrhizae in controlling photosynthetic rates and sink strength in tropical trees, and thus in detA^6170^The impact of elevated carbon dioxide (CO2, 600/700 mu mol mol(-1)) and temperature (+ 4 degrees C) on phyllosphere fungi colonising flag leaves of mini crops of winter wheat cv. Mercia between anthesis and harvest was determined in a computer- controlled environment facility in 1993 and 1994. In both years the total fungal populations (cm(2) leaf) were found to have increased due to exposure to either elevated CO2 and elevated CO2 + temperature treatments. This was mainly due to significant increases in populations of Cladosporium spp. (C. cladosporioides and C. herbarum) on the flag leaves during ripening. Other phyllosphere component species such as white and pink yeasts were not markedly affected by treatments. The range of fungal species found in such controlled environment chambers was narrower than that commonly found on nag leaves of field grown crops. Common and important colonisers of leaves and ripening ears such as Aureobasidium pullulans, Epicoccum nigrum and Fusarium spp. were seldom isolated.

1699^2^Mark,U^Tevini,M^1997^1^Effects of solar ultraviolet-B radiation, temperature and CO2 on growth and physiology of sunflower and maize seedlings^331^128^1-2^224-234^^^^^Jan-Feb^^^^^6173
1240^1538^376^377^384^389^409^444^566^626^computer- controlled environment facility in 1993 and 1994. In both years the total fungal populations (cm(2) leaf) were found to have increased due to exposure to either elevated CO2 and elevated CO2 + temperature treatments. This was mainly due to significant increases in populations of Cladosporium spp. (C. cladosporioides and C. herbarum) on the flag leaves during ripening. Other phyllosphere component species such as white and pink yeasts were not markedly affected by treatments. The range of fungal species found in such controlled environment chambers was narrower than that commonly found on nag leaves of field grown crops. Common and important colonisers of leaves and ripening ears such as Aureobasidium pullulans, Epicoccum nigrum and Fusarium spp. were seldom isoA^6172^The effects of solar UV-B radiation, in combination with elevated temperature (4 degrees C) and CO2 (680 mu L L-1) concentration, on sunflower and maize seedlings were studied from May to August in 1991 at the research station Quinta de Sao Pedro in Portugal (38.7 degrees N). The ambient solar radiation of Portugal was reduced to levels of Central European latitudes by using the ozone filter technique. This radiation served as control, while the ambient solar radiation of Portugal was to simulate intense UV-B treatment (+30%). All plants were grown up to 18 days in 4 climate controlled growth chambers simulating a daily course of temperature with T-max=28 degrees C or 32 degrees C, resp., and ambient CO2 concentrations (340 mu L L-1); in one chamber the CO2 concentration was twice as high (680 mu L L-1). Under intense UV-B and at 28 degrees C (T-max) all growth parameters (height, leaf area, fresh and dry weight, stem elongation rate, relative growth rate) of sunflower and maize seedlings were reduced down to 35% as compared to controls. An increase in growing temperature by 4 degrees C, alone or in combination with doubled CO2, compensated or even overcompensated the UV-B effect so that the treated plants were comparable to controls. Chlorophyll content, on a leaf area basis, increased under intense UV-B radiation. This increase was compensated by lower leaf areas, resulting in comparable chlorophyll contents. Similar to growth, also the net photosynthetic rates of sunflower and maize seedlings were reduced down to 29% by intense UV-B calculated on a chlorophyll basis. This reduction was compensated by an increased temperature. Doubling of CO2 concentration had effects only on sunflower seedlings in which the photosynthetic rates were higher than in the controls. Dark respiration rates of the seedlings were not influenced by any experimental condition. Transpiration and water use efficiency (wue) were not influenced by intense UV-B. Higher temperatures led to higher transpiration rates and lower water use efficiencies, resp.. Doubling of CO2 reduced the transpiration rate drastically while for wue maximum values were recorded.

1700^4^Matsui,T^Namuco,OS^Ziska,LH^Horie,T^1997^1^Effects of high temperature and CO2 concentration on spikelet sterility in indica rice^207^51^3^213-219^^^^^Apr^^^^^6175
341^374^434^92^ation. This increase was compensated by lower leaf areas, resulting in comparable chlorophyll contents. Similar to growth, also the net photosynthetic rates of sunflower and maize seedlings were reduced down to 29% by intense UV-B calculated on a chlorophyll basis. This reduction was compensated by an increased temperature. Doubling of CO2 concentration had effects only on sunflower seedlings in which the photosynthetic rates were higher than in the controls. Dark respiration rates of the seedlings were not influenced by any experimental condition. Transpiration and water use efficiency (wue) were not influenced by intense UV-B. Higher temperatures led to higher transpiration rates and lower water uA^6174^The effects of increasing temperature and CO2 concentration on floral sterility were examined for rice (cv. IR 72) using open- top chambers located at the International Rice Research Institute in Los Banes, Philippines. The field-based open-top chamber system was used to simulate four different environments: ambient temperature and CO2 concentration (control); ambient temperature, ambient +300 mu l l(-1) CO2; ambient +4 degrees C temperature, ambient CO2 concentration; ambient +4 degrees C temperature, ambient + 300 mu 1 l(-1) CO2. High temperature during flowering resulted in increased pollen sterility with the degree of sterility exacerbated if rice was exposed to both high temperature and increased CO2 concentration. The critical air temperature for spikelet sterility (as determined from the number of germinated pollen grains on the stigma) was reduced by ca 1 degrees C at elevated concentrations of carbon dioxide. We speculate that this downward shift in critical temperature may be due to the observed increase in air temperature within the canopy at high CO2 concentrations. This increase in air temperature, in turn, may be related to stomatal closure and reduced transpirational cooling in an elevated CO2 environment. Data from this experiment indicate that increasing CO2 concentration could limit rice yield if average air temperature increased simultaneously.

1701^2^Megonigal,JP^Schlesinger,WH^1997^1^Enhanced CH4 emissions from a wetland soil exposed to elevated CO2^26^37^1^77-88^^^^^Apr^^^^^6177
1192^1239^130^1484^1949^2455^2641^312^344^360^ure during flowering resulted in increased pollen sterility with the degree of sterility exacerbated if rice was exposed to both high temperature and increased CO2 concentration. The critical air temperature for spikelet sterility (as determined from the number of germinated pollen grains on the stigma) was reduced by ca 1 degrees C at elevated concentrations of carbon dioxide. We speculate that this downward shift in critical temperature may be due to the obseA^6176^Methane emissions from wetland soils are generally a positive function of plant size and primary productivity, and may be expected to increase due to enhanced rates of plant growth in a future atmosphere of elevated CO2. We performed two experiments with Orontium aquaticum, a common emergent aquatic macrophyte in temperate and sub-tropical wetlands, to determine if enhanced rates of photosynthesis in elevated CO2 atmospheres would increase CH4 emissions from wetland soils. O. aquaticum was grown from seed in soil cores under ambient and elevated (ca. 2-times ambient) concentrations of CO2 in an initial glasshouse study lasting 3 months and then a growth chamber study lasting 6 months. Photosynthetic rates were 54 to 71% higher under elevated CO2 than ambient CO2, but plant biomass was not significantly different at the end of the experiment. In each case, CH4 emissions were higher under elevated than ambient CO2 levels after 2 to 4 months of treatment, suggesting a close coupling between photosynthesis and methanogenesis in our plant-soil system. Methane emissions in the growth chamber study increased by 136%. We observed a significant decrease in transpiration rates under elevated CO2 in the growth chamber study, and speculate that elevated CO2 may also stimulate CH4 emissions by increasing the extent and duration of flooding in some wetland ecosystems. Elevated CO2 may dramatically increase CH4 emissions from wetlands, a source that currently accounts for 40% of global emissions.

1702^3^Murakami,A^Kim,SJ^Fujita,Y^1997^1^Changes in photosystem stoichiometry in response to environmental conditions for cell growth observed with the cyanophyte Synechocystis PCC 6714^231^38^4^392-397^^^^^Apr^^^^^6179
1548^2642^2643^2644^2645^2646^2647^2648^2649^652^ than ambient CO2, but plant biomass was not significantly different at the end of the experiment. In each case, CH4 emissions were higher under elevated than ambient CO2 levels after 2 to 4 months of treatment, suggesting a close coupling between photosynthesiA^6178^Changes in photosystem stoichiometry in response to shift of environments for cell growth other than light regime were studied with the cyanophyte Synechocystis PCC 6714 in relation to the change induced by light-quality shift. Following two environment-shifts were examined: the shift of molecular form of inorganic carbon source for photosynthesis from CO2 to HCO3- (CO2 stress) and the increase in salinity of the medium with NaCl (0.5 M) (Na+ stress). Both CO2 and Na+ stresses induced the increase in PSI abundance resulting in a higher PSI/PSII stoichiometry. CO2 stress was found to elevate simultaneously Cyt c oxidase activity (V-max). The feature was the same as that caused by light-quality shift from preferential excitation of PSI to PSII (light stress) though the enhancement by either stress was smaller than that by light stress. Under our experimental conditions, PSI/PSII stoichiometry appeared to increase at a fairly constant rate to the basal level even when the basal level had been differently determined by the light- quality. Enhancing rates for PSI/PSII stoichiometry and for Cyt c oxidase activity were also similar to each other. Since the two stresses affect the thylakoid electron transport similarly to the shift of light-quality, we interpreted our results as follows: three environmental stresses, CO2, Na+, and light stresses, cause changes in electron turnover capacity of PSI and Cyt c oxidase under a similar, probably a common, mechanism for monitoring redox state of thylakoid electron transport system.

1703^3^Murthy,R^Zarnoch,SJ^Dougherty,PM^1997^1^Seasonal trends of light-saturated net photosynthesis and stomatal conductance of loblolly pine trees grown in contrasting environments of nutrition, water and carbon dioxide^9^20^5^558-568^^^^^May^^^^^6181
1144^1706^2453^344^345^372^374^376^385^794^than that by light stress. Under our experimental conditions, PSI/PSII stoichiometry appeared to increase at a fairly constant rate to the basal level even when the basal level had been differentlyA^6180^Repeated measures analysis was used to evaluate the effect of long-term CO2 enhancement on seasonal trends of light-saturated rates of net photosynthesis (A(sat)) and stomatal conductance to water vapour (g(sat)) of 9-year-old loblolly pine (Pious taeda L.) trees grown in a 2 x 2 factorial experimental design of nutrition and water. A significant interaction effect of CO2 and nutrition on mean A(sat) was observed for juvenile foliage. Also, juvenile foliage exposed to + 350 mu mol mol(-1) CO2 had a higher rate of increase of A(sat) between late summer and early autumn. This would lead to a greater potential for recharging carbohydrate reserves for winter. Mature foliage was affected by CO2, water and nutrient treatments in two ways. First, A(sat) was significantly increased as a result of elevated CO2 in January, a period when stomatal conductance was only 47% of the maximum observed rate. Secondly, the rate of increase of A(sat) from winter to early spring was accelerated asa result of both nutrient + water and + 350 mu mol mol(-1) CO2 treatments. This accelerated response resulted in a greater potential for photosynthate production during the period when growth initiation occurred. Nutrient, water or carbon dioxide treatments did not significantly alter trends in g(sat) for mature or juvenile foliage. A significant nutrition x CO2 interaction was observed for the mature foliage, suggesting that g(sat) increased with increasing CO2 and nutrition. These results may have important consequences for the determination of the water use efficiency of loblolly pine. In spite of low g(sat) in the winter to early spring period, there was a substantial gain in A(sat) attributable to elevated CO2 concentrations.

1704^4^Penuelas,J^Idso,SB^Ribas,A^Kimball,BA^1997^1^Effects of long-term atmospheric CO2 enrichment on the mineral concentration of Citrus aurantium leaves^84^135^3^439-444^^^^^Mar^^^^^6183
130^1628^312^372^423^545^715^764^857^92^at) from winter to early spring was accelerated asa result of both nutrient A^6182^Leaf mineral concentration of Citrus aurantium (sour orange tree) was measured at bi-monthly intervals from 30 to 85 months of exposure in a long-term study on the effects of a 300 mu mol mol(-1) enrichment of atmospheric CO2, under conditions of high nutrient and water supply. There were clear seasonal trends in the concentrations of most of the elements studied. There were initial decreases in the leaf concentrations of N and the xylem-mobile, phloem-immobile elements Mn, Ca and Mg, as well as a significant and sustained increase in the leaf concentration of B, and no changes in the concentrations of K, Fe, Na, P, S, Zn and Cu. Interestingly, the initial reductions in the leaf concentrations of Mn, N, Ca and Mg gradually disappeared with time.

1705^10^Poorter,H^VanBerkel,Y^Baxter,R^DenHertog,J^Dijkstra,P^Gifford,RM^Griffin,KL^Roumet,C^Roy,J^Wong,SC^1997^1^The effect of elevated CO2 on the chemical composition and construction costs of leaves of 27 C-3 species^9^20^4^472-482^^^^^Apr^^^^^6185trient 1035^1260^2514^341^344^417^57^698^789^975^ aurantium (sour orange tree) was measured at bi-monthly intervals from 30 to 85 months of exposure in a long-term study on the effects of a 300 mu mol mol(-1) enrichment of atmospheric CO2, under conditions of high nutrient and water supply. There were clear seasonal trends in the concentrations of most of the elements studied. There were initial decreases in the leaf concentrations of N and the xylem-mobile, phloem-immobile elements Mn, Ca and Mg, as well as a significant and sustained increase in the leaf concentration of B, and no changes in the concentrations of K, Fe, Na, P, S, Zn and Cu. Interestingly, the initial reductions in the leaf concentrations of Mn, N, Ca and Mg gradually disappeared with time.

1705^10^Poorter,H^VanBerkel,Y^Baxter,R^DenHertog,J^Dijkstra,P^Gifford,RM^Griffin,KL^Roumet,C^Roy,J^Wong,SC^1997^1^The effect of elevated CO2 on the chemical composition and construction costs of leaves of 27 C-3 species^9^20^4^472-482^^^^^Apr^^^^^6185trient A^6184^We determined the proximate chemical composition as well as the construction costs of leaves of 27 species, grown at ambient and at a twice-ambient partial pressure of atmospheric CO2, These species comprised wild and agricultural herbaceous plants as well as tree seedlings, Both average responses across species and the range in response were considered, Expressed on a total dry weight basis, the main change in chemical composition due to CO2 was the accumulation of total non- structural carbohydrates (TNC), To a lesser extent, decreases were found for organic N compounds and minerals, Hardly any change was observed for total structural carbohydrates (cellulose plus hemicellulose), lignin and lipids, When expressed on a TNC-free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics, In terms of glucose required for biosynthesis, the increase in costs for one chemical compound - TNC - was balanced by a decrease in the costs for organic N compounds, Therefore, the construction costs, the total amount of glucose required to produce 1 g of leaf, were rather similar for the two CO2 treatments; on average a small decrease of 3% was found, This decrease was attributable to a decrease of up to 30% in the growth respiration coefficient, the total CO2 respired [mainly for NAD(P)H and ATP] in the process of constructing 1 g of biomass, The main reasons for this reduction were the decrease in organic N compounds and the increase in TNC.

1706^2^Potvin,C^Vasseur,L^1997^1^Long-term CO2 enrichment of a pasture community: Species richness, dominance, and succession^11^78^3^666-677^^^^^Apr^^^^^6187
1030^1239^146^2650^32^372^374^437^540^72^NC-free basis, decreases in organic N compounds and minerals were still present. On this basis, there was also an increase in the concentration of soluble phenolics, In terms of glucose required for biosynthesis, the increase in costs for one chemical compound - TNC - was balanced by A^6186^The present study addresses responses of a pasture community to CO2 enrichment in situ. It focused on two levels of organization. We examined changes in both community properties and species-specific responses during long-term exposure to high CO2 concentration. The underlying hypothesis is that CO2 enrichment could change community composition. At the community level, we observed higher species richness and lesser dominance under enriched than ambient CO2. Two species were apparently central in explaining our results, Agropyron repens and Plantago major. The cover of this first species increased only under ambient CO2. Conversely, the cover of the latter species decreased under ambient CO2 but remained stable under enriched CO2. Species were pooled into dicots and monocots to examine space acquisition. Changes in monocot cover through time were more tightly coupled with that of dicots under ambient than high CO2. Enrichment with CO2 appeared to have a positive effect on the early-successional species, preventing the complete dominance by late-successional species. In fact, under elevated CO2 early- and late-successional species were coexisting. Therefore, our results suggest the possibility that succession patterns might be altered by CO2 enrichment apparently because enriched CO2 stimulates the growth of dicots.

1707^4^Pritchard,SG^Peterson,CM^Prior,SA^Rogers,HH^1997^1^Elevated atmospheric CO2 differentially affects needle chloroplast ultrastructure and phloem anatomy in Pinus palustris: Interactions with soil resource availability^9^20^4^461-471^^^^^Apr^^^^^6189
1262^224^243^2651^341^348^360^361^820^92^er ambient CO2. Conversely, the cover of the latter species decreased under ambient CO2 but remained stable under enriched CO2. Species were pooled into dicots and monocots to examine space acquisition. Changes in monocot cover through time were more tightly coupled with that of dicots under ambient than high CO2. Enrichment with CO2 appeared to have a positive effect on the early-successional speciesA^6188^The response of forest species to increasing atmospheric CO2, particularly under resource limitations, will require study in order to predict probable changes which may occur at the plant, community and ecosystem levels, Longleaf pine (Pinus palustris Mill.) seedlings were grown for 20 months at two levels of CO2 (365 and 720 mu mol mol(-1)) in two levels of soil nitrogen (4 and 40 g m(-2)), and with two levels of soil moisture (-0.5 and -1.5 MPa xylem pressure potential), Leaf tissue was collected in the spring (12 months exposure) and autumn (20 months exposure) and examined using transmission electron microscopy (TEM) and light microscopy, During early spring, elevated CO2 magnified effects of N and water treatment on starch accumulation and in some cases contributed to altered organization of mesophyll chloroplasts. Disruption of chloroplast integrity was pronounced under elevated CO2, low N and water stress, In autumn, needles contained little starch; however, chloroplasts grown under high CO2 exhibited stress symptoms including increased plastoglobuli and shorter grana, A trend for reduced needle phloem cross-sectional area resulting from fewer sieve cells was also observed under elevated CO2, These results suggest that, in nature, longleaf pine seedlings may not benefit from a doubling of CO2, especially when soil resources are limiting.

1708^6^Rozema,J^Lenssen,GM^vandeStaaij,JWM^Tosserams,M^Visser,AJ^Broekman,RA^1997^1^Effects of UV-B radiation on terrestrial plants and ecosystems: Interaction with CO2 enrichment^331^128^1-2^182-191^^^^^Jan-Feb^^^^^6191
1163^1206^243^341^92^g transmission electron microscopy (TEM) and light microscopy, During early spring, elevated CO2 magnified effects of N and water treatment on starch accumulation and in some cases contributed to altered organization of mesophyll chloroplasts. Disruption of chloroplast integrity was pronounced under elevated CO2, low N and water stress, In autumn, needles contained little starch; however, chloroplasts grown under high CO2 exA^6190^UV-B radiation is just one of the environmental factors, that affect plant growth. It is now widely accepted that realistic assessment of plant responses to enhanced UV-B should be performed at sufficiently high Photosynthetically Active Radiation (PAR), preferably under field conditions. This will often imply, that responses of plants to enhanced UV-B in the field will be assessed under simultaneous water shortage, nutrient deficiency and variation of temperature. Since atmospheric CO2 enrichment, global warming and increasing UV-B radiation represent components of global climatic change, interactions of UV-B with CO2 enrichment and temperature are particularly relevant. Only few relevant UV-B x CO2 interaction studies have been published. Most of these studies refer to greenhouse experiments. We report a significant CO2 x UV-B interaction for the total plant dry weight and root dry weight of the C-3-grass Elymus athericus. At elevated CO2 (720 mu mol mol(-1)), plant growth was much less reduced by enhanced UV-B than at ambient atmospheric CO2 although there were significant (positive) CO2 effects and (negative) UV-B effects on plant growth. Most other CO2 x UV-B studies do not report significant interactions on total plant biomass. This lack of CO2 x UV-B interactions may result from the fact that primary metabolic targets for CO2 and UVB are different. UV-B and CO2 may differentially affect plant morphogenetic parameters: biomass allocation, branching, flowering, leaf thickness, emergence and senescence. Such more subtle interactions between CO2 and UV-B need careful and long term experimentation to be detected. In the case of no significant CO2 x UV-B interactions, combined CO2 and UV-B effects will be additive. Plants differ in their response to CO2 and UV-B, they respond in general positively to elevated CO2 and negatively to enhanced UV-B. Moreover, plant species differ in their responsiveness to CO2 and UV-B. Therefore, even in case of additive CO2 and UV-B effects, plant competitive relationships may change markedly under current climatic change with simultaneous enhanced atmospheric CO2 and solar UV-B radiation.

1709^1^Sullivan,JH^1997^1^Effects of increasing UV-B radiation and atmospheric CO2 on photosynthesis and growth: Implications for terrestrial ecosystems^331^128^1-2^194-206^^^^^Jan-Feb^^^^^6193
1282^1435^2652^2653^342^345^398^725^953^968^ UV-B and CO2 may differentially affect plant morphogenetic parameters: biomass allocation, branching, flowering, leaf thickness, emergence and senescence. Such more subtle interactions between CO2 and UV-B need careful and long term experimentation to be detected. In the case of no significant CO2 x UV-B interactions, combined CO2 and UV-B effects will be additive. Plants differ in their response to CO2 and UV-B, they respond in general positively to elevated CO2 and negatively to enhanced UV-B. Moreover, plant species differ in their responsiveness to CO2 and UV-B. Therefore, even in case of additive CO2 and UV-B effects, plant competitive relationshipA^6192^Increases in UV-B radiation reaching the earth as a result of stratospheric ozone depletion will most likely accompany increases in atmospheric CO2 concentrations. Many studies have examined the effects of each factor independently, but few have evaluated the combined effects of both UV-B radiation and elevated CO2. In general the results of such studies have shown independent effects on growth or seed yield. Although interspecific variation is large, high levels of UV-B radiation tends to reduce plant growth in sensitive species, while CO2 enrichment tends to promote growth in most C-3 species. However, most previous studies have not looked at temporal effects or at the relationship between photosynthetic acclimation to CO2 and possible photosynthetic limitations imposed by UV-B radiation. Elevated CO2 may provide some protection against UV-B for some species. In contrast, UV-B radiation may limit the ability to exploit elevated CO2 in other species. Interactions between the effects of CO2 enrichment and UV-B radiation exposure have also been shown for biomass allocation. Effects on both biomass allocation and photosynthetic acclimation may be important to ecosystem structure in terms of seedling establishment, competition and reproductive output. Few studies have evaluated ecosystem processes such as decomposition or nutrient cycling. Interactive effects may be subtle and species specific but should not be ignored in the assessment of the potential impacts of increases in CO2 and W-B radiation on plants.

1710^4^vandeStaaij,JWM^Bolink,E^Rozema,J^Ernst,WHO^1997^1^The impact of elevated UV-B (280-320 nm) radiation levels on the reproduction biology of a highland and a lowland population of Silene vulgaris^331^128^1-2^172-179^^^^^Jan-Feb^^^^^6195
1055^1432^1657^1922^243^417^441^633^694^92^ion. Elevated CO2 may provide some protection against UV-B for some species. In contrast, UV-B radiation may limit the ability to exploit elevated CO2 in other species. Interactions between the effects of CO2 enrichmentA^6194^A highland (altitude 1600 m) and a lowland (altitude -2 m) population of the perennial herb Silene vulgaris were tested on the effects of elevated levels of UV-B radiation on their reproductivity. Highland populations receive higher natural UV- B doses than lowland populations. Therefore adaptation to high W-B levels of the highland population is to be expected. The lowland population showed a decrease in the number of seed producing flowers and the number of seeds produced per plant under elevated UV-B levels. The highland population increased the number of seeds per plant under elevated UV-B levels. In both populations individual seed mass as well as seed germination percentages were unaffected by the UV-B flux received by the parental plant. Possible effects of UV-B induced alterations in reproductivity on the geographical distribution of the different populations are discussed.
ation may limit the ability to exploit elevated CO2 in other species. Interactions between the effects of CO2 enrichment1711^6^VanVuuren,MMI^Robinson,D^Fitter,AH^Chasalow,SD^Williamson,L^Raven,JA^1997^1^Effects of elevated atmospheric CO2 and soil water availability on root biomass, root length, and N, P and K uptake by wheat^84^135^3^455-465^^^^^Mar^^^^^6197
1262^243^264^312^376^57^724^92^opulations. Therefore adaptation to high W-B levels of the highland population is to be expected. The lowland population showed a decrease in the number of seed producing flowers and the number of seeds produced per plant under elevated UV-B levels. The highland population increased the number of seeds per plant under elevated UV-B levels. In both populations individual seed mass as well as seed germination percentages were unaffected by the UV-B flux received by the parental plant. Possible effects of UV-B induced alterations in reproductivity on the geographical distribution of the different populations are discussed.
ation may limit the ability to exploit elevated CO2 in other species. Interactions between the effects of CO2 enrichmentA^6196^We investigated interactions between the effects of elevated atmospheric carbon dioxide concentrations ([CO2]) and soil water availability on root biomass, root length and nutrient uptake by spring wheat (Triticum aestivum cv. Tonic). We grew plants at 350 and 700 mu mol mol(-1) CO2 and with frequent and infrequent watering ('wet' and 'dry' treatments, respectively). Water use per plant was 1.25 times greater at 350 than at 700 mu mol CO2 mol(-1), and 1.4 times greater in the 'wet' than in the 'dry' treatment. Root biomass increased with [CO2] and with watering frequency. Elevated [CO2] changed the vertical distribution of the roots, with a greater stimulation of root growth in the top layers of the soil. These data were confirmed by the video data of root lengths in the 'dry' treatment, which showed a delayed root development at depth under elevated [CO2]. The apparent amount of N mineralized appeared to be equal for all treatments. Nutrient uptake was affected by [CO2] and by watering frequency, and there were interactions between these treatments. These interactions were different for N, K and P, which appeared to be related to differences in nutrient availability and mobility in the soil. Moreover, these interactions changed with time as the root system became larger with [CO2] and with watering frequency, and as fluctuations in soil moisture contents increased. Elevated [CO2] affected nutrient uptake in contrasting ways. Potassium uptake appeared to be reduced by the smaller mass how of water reaching the root surface. However, this might be countered with time by the greater root biomass at elevated [CO2], by the greater soil moisture contents at elevated [CO2], enabling faster diffusion, or both. Phosphorus uptake appeared to be increased by the greater root biomass at elevated [CO2]. We conclude that plant nutrient uptake at elevated [CO2] is affected by interactions with water availability, though differences between nutrients preclude generalizations of the response.
by watering frequency, and1712^7^Visser,AJ^Tosserams,M^Groen,MW^Kalis,G^Kwant,R^Magendans,GWH^Rozema,J^1997^1^The combined effects of CO2 concentration and enhanced UV-B radiation on faba bean .3. Leaf optical properties, pigments, stomatal index and epidermal cell density^331^128^1-2^208-222^^^^^Jan-Feb^^^^^6199
1077^1922^2623^2654^2655^2656^372^377^626^92^ in soil moisture contents increased. Elevated [CO2] affected nutrient uptake in contrasting ways. Potassium uptake appeared to be reduced by the smaller mass how of water reaching the root surface. However, this might be countered with time by the greater root biomass at elevated [CO2], by the greater soil moisture contents at elevated [CO2], enabling faster diffusion, or both. Phosphorus uptake appeared to be increased by the greater root biomass at elevated [CO2]. We conclude that plant nutrient uptake at elevated [CO2] is affected by interactions with water availability, though differences between nutrients preclude generalizations of the response.
by watering frequency, andA^6198^Seedlings of Vicia faba L. (cv. Minica) were grown in a factorial experiment in a greenhouse. The purpose of the study was to determine whether CO2 enrichment and supplemental UV-B radiation affect leaf optical properties and whether the combined effects differ from single factor effects. Seedlings were grown at either 380 mu mol mol(-1) 750 mu mol mol(-1) CO2 and at four levels of W-B radiation. After 20 and 40 days of treatment, absorptance, transmittance and reflectance of photosynthetically active radiation (PAR) were measured on the youngest fully developed leaf. On the same leaf, the specific leaf area on a fresh weight basis (SLA(fw)), chlorophyll content, UV-B absorbance, transmittance of UV light and stomatal index were measured. W-B radiation significantly increased PAR absorptance and decreased PAR transmittance. The increased PAR absorptance can be explained by an increased chlorophyll content in response to W-B radiation. Leaf transmittance of UV radiation decreased with increasing UV-B levels mainly caused by increased absorbance of UV absorbing compounds. UV-B radiation decreased both the stomatal density and epidermal cell density of the abaxial leaf surface, leaving the stomatal index unchanged. Effects of CO2 enrichment were less pronounced than those of W-B radiation. The most important CO2 effect was an increase in stomatal density and epidermal cell density of the adaxial leaf surface. The stomatal index was not affected. No interaction between CO2 and UV-B radiation was found. The results are discussed in relation to the internal light environment of the leaf.

1713^3^Vogel,CS^Curtis,PS^Thomas,RB^1997^1^Growth and nitrogen accretion of dinitrogen-fixing Alnus glutinosa (L) Gaertn under elevated carbon dioxide^331^130^1^63-70^^^^^May^^^^^6201
137^2026^229^2489^2657^2658^2659^424^456^708^PAR transmittance. The increased PAR absorptance can be explained by an increased chlorophyll content in response to W-B radiation. Leaf transmittance of UV radiation decreased with increasing UV-B lA^6200^Short-term studies of tree growth at elevated CO2 suggest that forest productivity may increase as atmospheric CO2 concentrations rise, although low soil N availability may limit the magnitude of this response. There have been few studies of growth and N-2 fixation by symbiotic N-2-fixing woody species under elevated CO2 and the N inputs these plants could provide to forest ecosystems in the future. We investigated the effect of twice ambient CO2 on growth, tissue N accretion, and N-2 fixation of nodulated Alnus glutinosa (L.) Gaertn. grown under low soil N conditions for 160 d. Root, nodule, stem, and leaf dry weight (DW) and N accretion increased significantly in response to elevated CO2. Whole-plant biomass and N accretion increased 54% and 40%, respectively. Delta-N-15 analysis of leaf tissue indicated that plants from both treatments derived similar proportions of their total N from symbiotic fixation suggesting that elevated CO2 grown plants fixed approximately 40% more N than did ambient CO2 grown plants. Leaves from both CO2 treatments showed similar relative declines in leaf N content prior to autumnal leaf abscission, but total N in leaf litter increased 24% in elevated compared to ambient CO2 grown plants, These results suggest that with rising atmospheric CO2 N-2-fixing woody species will accumulate greater amounts of biomass N through N-2 fixation and may enhance soil N levels by increased litter N inputs.

1714^3^Whitehead,SJ^Caporn,SJM^Press,MC^1997^1^Effects of elevated CO2, nitrogen and phosphorus on the growth and photosynthesis of two upland perennials: Calluna vulgaris and Pteridium aquilinum^84^135^2^201-211^^^^^Feb^^^^^6203
130^2298^2660^2661^2662^2663^2664^29^376^673^2. Whole-plant biomass and N accretion increased 54% and 40%, respectively. Delta-N-15 analysis of leaf tissue indicated that plants from both treatments derived similar proportions of their total N from symbiotic fixation suggesting that elevated CO2 grown plants fixed approximately 40% more N than did ambient CO2 grA^6202^Bracken (Pteridium aquilinum (L.) Kuhn) and heather (Calluna vulgaris (L.) Hull) are important upland species which often grow in close proximity in the UK. The effects of factorial treatments of elevated atmospheric CO2 (539 mu mol mol(-1) as opposed to ambient atmospheric CO2 concentrations of 355 mu mol mol(-1)), added N (50 kg N hs(-1) as NH4NO3) and added P (20 kg P ha(-1) as NaH2PO4) on the performance of these two species were studied under controlled environmental conditions using container-grown plants. Plants grown and measured at high CO2 had higher rates of net photosynthesis than those grown and measured in ambient CO2. This increase was greater in heather than in bracken and resulted in a large stimulation of growth in the former. In bracken there was no significant change in plant size or phenology. The increase in biomass of heather in high CO2 was greatest in the absence of added nutrients and lowest when both N and P were supplied. The growth and photosynthesis of both plants responded positively to the supply of P alone or P with N (in both CO2 atmospheres), but there was little response to N alone. The implications of these findings for bracken and heather growing in the held under conditions of an elevated CO2 atmosphere and greater nutrient availability are discussed.

1715^1^Beerling,DJ^1997^1^Interpreting environmental and biological signals from the stable carbon isotope composition of fossilized organic and inorganic carbon^333^154^^303-309^^^^^Mar^^^^^6205
137^1595^1917^2665^344^362^372^399^494^745^n and measured at high CO2 had higher rates of net photosynthesis than those grown and measured in ambient CO2. This increase was greater in heather than in bracken and resulted in a large stimulation of growth in the former. In bracken there was no significant change in plant size or phenology. The increase in biomass of heather in high CO2 was greatest in the absence of added nutrients and lowest when both N and P were supplied. The growth and photosynthesis of both plants respondA^6204^Stable carbon isotope studies on marine and terrestrial organic and inorganic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric CO2. Comparison between the CO2 estimates reconstructed from carbon isotope studies for the past 150 Ma show good agreement with the predictions of a long-term carbon- cycle model based on mass-balance studies. Further, the CO2 estimates from these sources over the entire Phanerozoic show agreement with the fossil record of leaf stomatal density change-a feature inversely related to the concentration of atmospheric CO2. Isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the C-4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species. The long-term perspective offered by these studies provides critical information for assessing the responses of biological systems to future global environmental change.

1716^5^Bindi,M^Fibbi,L^Gozzini,B^Orlandini,S^Miglietta,F^1996^1^Modelling the impact of future climate scenarios on yield and yield variability of grapevine^288^7^3^213-224^^^^^31 Dec^^^^^6207
1007^130^174^e studies for the past 150 Ma show good agreement with the predictions of a long-term carbon- cycle model based on mass-balance studies. Further, the CO2 estimates from these sources over the entire Phanerozoic show agreement with the fossil record of leaf stomatal density change-a feature inversely related to the concentration of atmospheric CO2. Isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the C-4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species. The long-term perspective offered by these studies provides critical information for assessing the resA^6206^A mechanistic growth model was used to evaluate the mean yield and yield variability of grapevine Vitis vinifera L. under current and future climates. The model used was previously validated using field experiment data. The effect of elevated CO2 on grapevine growth was also considered. Adaptation of 2 varieties (Sangiovese and Cabernet Sauvignon) to scenarios of increased CO2 and climate change, and potential changes in agricultural risk (i.e. inter-seasonal variability), were examined. Before testing the effect of climate scenarios, we analysed the sensitivity of modelled grapevine yield to arbitrary changes in the 3 driving variables (temperature, solar radiation and CO2). The results showed the model to be more sensitive to changes in CO2 concentration and temperature than to changes in radiation. Analyses made using transient GCM (general circulation model) scenarios (UKTR and GFDL) showed different changes in mean fruit dry matter for the different scenarios, whereas mean total dry matter, and fruit and total dry matter variability, were predicted to increase under almost all the scenarios. Predictions based on equilibrium scenarios (UKLO and UKHI) gave similar results. For Sangiovese, variety adaptation analysis suggested a better adaptation in terms of mean production, but a worse adaptation in terms of yield variability.

1717^2^Chen,JL^Reynolds,JF^1997^1^GePSi: A generic plant simulator based on object-oriented principles^81^94^1^53-66^^^^^1 Jan^^^^^6209
1668^2666^885^92^xamined. Before testing the effect of climate scenarios, we analysed the sensitivity of modelled grapevine yield to arbitrary changes in the 3 driving variables (temperature, solar radiation and CO2). The results showed the model to be more sensitive to changes in CO2 concentration and temperature than to changes in radiation. Analyses made using transient GCM (general circulation model) scenarios (UKTR and GFDL) showed different changes in mean fruit dry matter for the different scenarios, whereas mean total dry matter, and fA^6208^The Generic Plant Simulator (GePSi) is a physiologically-based model that combines modules for canopy, root environment, water relations, and potential growth to generate whole-plant carbon, nitrogen, and water balances. The version presented here is coded in the object-oriented programming (OOP) language, C++, to enhance the implementation of modularity. In the aboveground aerial environment, the Weather module defines the weather conditions above a canopy, and MicroWeather defines the vertical profiles of micro-meteorological variables in a canopy. The belowground soil environment contains the SoilProperty modules, which define vertical profiles of physical and chemical variables in a soil column. The 'part-of' hierarchy in GePSi follows the structure of a real plant: the Plant module calls canopy and root system modules; the Canopy module, in turn, calls leaf, stem and fruit modules, and the RootSystem module calls coarse and fine root modules, etc. Our long-term goal is for GePSi to serve as a template for building a plant growth simulator by simply selecting appropriate modules for the question being asked. We are building a suite of plant modules (and their interfaces) based on general principles that are fundamentally similar for different kinds of plants. This includes photosynthesis, growth, nutrient and carbon allocation, water uptake, etc. These modules can be parameterized for specific species, related groups of species, life-forms, or broader groups depending on how variable the processes are across the groupings and the amount of unexplained variability that is acceptable for the question being investigated. Our modular-based approach has numerous advantages, including improving the understanding of the model, reducing duplication of effort, and facilitating the adaptation of the model for different sites and ecosystems. (C) 1997 Elsevier Science B.V.

1718^2^Cushman,JC^Bohnert,HJ^1997^1^Molecular genetics of Crassulacean acid metabolism^8^113^3^667-676^^^^^Mar^^^^^6211Si to serve as a tem1085^2622^2667^2668^2669^2670^2671^367^383^645^imply selecting appropriate modules for the question being asked. We are building a suite of plant modules (and their interfaces) based on general principles that are fundamentally similar for different kinds of plants. This includes photosynthesis, growth, nutrient and carbon allocation, water uptake, etc. These modules can be parameterized for specific species, related groups of species, life-forms, or broader groups depending on how variable the processes are across the groupings and the amount of unexplained variability that is acceptable for the question being investigated. Our modular-based approach has numerous advantages, including improving the understanding of the model, reducing duplication of effort, and facilitating the adaptation of the model for different sites and ecosystems. (C) 1997 Elsevier Science B.V.

1718^2^Cushman,JC^Bohnert,HJ^1997^1^Molecular genetics of Crassulacean acid metabolism^8^113^3^667-676^^^^^Mar^^^^^6211Si to serve as a temA^6210^Most higher plants assimilate atmospheric CO2 through the C-3 pathway of photosynthesis using ributose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). However, when CO2 availability is reduced by environmental stress conditions, the incomplete discrimination of CO2 over O-2 by Rubisco leads to increased photorespiration, a process that reduces the efficiency of C-3 photosynthesis. To overcome the wasteful process of photorespiration, approximately 10% of higher plant species have evolved two alternate strategies for photosynthetic CO2 assimilation, C-3 photosynthesis and Crassulacean acid metabolism. Both of these biochemical pathways employ a ''CO2 pump'' to elevate intracellular CO2 concentrations in the vicinity of Rubisco, suppressing photorespiration and therefore improving the competitiveness of these plants under conditions of high light intensity, high temperature, or low water availability. This CO2 pump consists of a primary carboxylating enzyme, phosphoenolpyruvate carboxylase. In C-4 plants, this CO2-concentrating mechanism is achieved by the coordination of two carboxylating reactions that are spatially separated into mesophyll and bundle-sheath cell types (for review, see R.T. Furbank, W.C. Taylor [1995] Plant Cell 7:797-802; M.S.B. Ku, Y. Kano-Murakami, M. Matsuoka [1996] Plant Physiol 111:949-957). In contrast, Crassulacean acid metabolism plants perform both carboxylation reactions within one cell type, but the two reactions are separated in time. Both pathways involve cell- specific changes in the expression of many genes that are not present in C-3 plants.

1719^4^Fiscus,EL^Reid,CD^Miller,JE^Heagle,AS^1997^1^Elevated CO2 reduces O-3 flux and O-3-induced yield losses in soybeans: Possible implications for elevated CO2 studies^78^48^307^307-313^^^^^Feb^^^^^6213
1102^1260^1530^2170^243^376^377^447^465^92^r conditions of high light intensity, high temperature, or low water availability. This CO2 pump consists of a primary carboxylating enzyme, phosphoenolpyruvate carboxylase. In C-4 plaA^6212^Soybeans were grown for three seasons in open-top field chambers to determine (1) whether elevated CO2 (360 Versus 700 mu mol mol(-1)) alleviates some of the yield loss due to pollutant O-3, (2) whether the partial stomatal closure resulting froth chronic O-3 exposure (charcoal-filtered air versus 1.5 x ambient concentrations) is a cause or result of decreased photosynthesis, and (3) possible implications of CO2/O-3 interactions to climate change studies using elevated CO2. Leaf conductance was reduced by elevated CO2, regardless of O-3 level, or by exposure to O-3 alone. AS a result of these effects on conductance, high CO2 reduced estimated midday O-3 flux into the leaf by an average of 50% in charcoal-filtered air and 35% in the high O-3 treatment. However, while exposure to O-3 reduced seed yields by 41% at ambient CO2 levels, the yield reduction was completely ameliorated by elevated CO2. The threshold midday O-3 flux for yield loss appears to be 20-30 nmol m(-2) s(-1) in this study. Although elevated CO2 increased total biomass production, it did not increase seed yields. A/C- i curves show a large reduction in the stomatal limitation to photosynthesis due to elevated CO2, but no effect of O-3. These data demonstrate that (1) reduced conductance due to O-3 is the result, and not the cause, of reduced photosynthesis, (2) 700 mu mol mol(-1) CO2 can completely ameliorate yield losses due to O-3 within the limits of these experiments, and (3) some reports of increased yields under elevated CO2 treatments may, at least in part, reflect the amelioration of unrecognized suppression of yield by O-3 or other stresses.

1720^4^Franck,VM^Hungate,BA^Chapin,FS^Field,CB^1997^1^Decomposition of litter produced under elevated CO2: Dependence on plant species and nutrient supply^26^36^3^223-237^^^^^Mar^^^^^6215
1044^2672^344^362^374^376^392^57^874^92^ld reduction was completely ameliorated by elevated CO2. The threshold midday O-3 flux for yield loss appears to be 20-30 nmol m(-2) s(-1) in this study. Although eleA^6214^We investigated the effect of CO2 concentration and soil nutrient availability during growth on the subsequent decomposition and nitrogen (N) release from litter of four annual grasses that differ in resource requirements and native habitat. Vulpia microstachys is a native grass found on California serpentine soils, whereas Avena fatua, Bromus hordaceus, and Lolium multiflorum are introduced grasses restricted to more fertile sandstone soils (Hobbs & Mooney 1991). Growth in elevated CO2 altered litter C:N ratio, decomposition, and N release, but the direction and magnitude of the changes differed among plant species and nutrient treatments, Elevated CO2 had relatively modest effects on C:N ratio of litter, increasing this ratio in Lolium roots (and shoots at high nutrients), but decreasing C:N ratio in Avena shoots. Growth of plants under elevated CO2 decreased the decomposition rate of Vulpia litter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated CO2 on N loss from litter also differed among species, with Vulpia litter from high-CO2 plants releasing N more slowly than ambient-CO2 litter, whereas growth under elevated CO2 caused increased N loss from Avena litter. CO2 effects on N release in Lolium and Bromus depended on the nutrient regime in which plants were grown. There was no overall relationship between litter C:N ratio and decomposition rate or N release across species and treatments. Based on our study and the literature, we conclude chat the effects of elevated CO2 on decomposition and N release from litter are highly species-specific. These results do not support the hypothesis that CO2 effects on litter quality consistently lead to decreased nutrient availability in nutrient-limited ecosystems exposed to elevated CO2.
ecreasing C:N ratio in Avena shoots. Growth of plants under elevated CO2 decreased the decomposition rate of Vulpia litter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated 1721^4^Groninger,JW^Seiler,JR^Zedaker,SM^Berrang,PC^1996^1^Effects of CO2 concentration and water availability on growth and gas exchange in greenhouse-grown miniature stands of Loblolly Pine and Red Maple^43^10^6^708-716^^^^^Dec^^^^^6217
1144^2673^2674^344^345^374^376^386^398^752^nutrient regime in which plants were grown. There was no overall relationship between litter C:N ratio and decomposition rate or N release across species and treatments. Based on our study and the literature, we conclude chat the effects of elevated CO2 on decomposition and N release from litter are highly species-specific. These results do not support the hypothesis that CO2 effects on litter quality consistently lead to decreased nutrient availability in nutrient-limited ecosystems exposed to elevated CO2.
ecreasing C:N ratio in Avena shoots. Growth of plants under elevated CO2 decreased the decomposition rate of Vulpia litter, but increased decomposition of Avena litter from the high-nutrient treatment. The impact of elevated A^6216^1. The study assesses the effects of atmospheric CO2 concentration and water availability on stand development and photosynthetic characteristics of Loblolly Pine (Pinus taeda) and Red Maple (Acer rubrum). Miniature stands of these species were grown from seed in monoculture and in a 50:50 replacement mixture for two accelerated growing seasons. 2. Both species had greater biomass under the higher levels of CO2 and water availability. Biomass of Loblolly Pine seedlings in mixed stands exceeded that in monocultures, while the opposite was true for Red Maple. No significant treatment interactions were detected for total biomass. Significant main effects for water and stand type were detected for stem height of Loblolly Pine. CO2, water and stand type interactions were observed for height of Red Maple. 3. Net photosynthetic rates were measured on miniature stand canopies and constituent seedlings from these stands. Both species exhibited higher photosynthetic rates under elevated CO2. However, expression of photosynthesis on a leaf mass or soil area basis affected conclusions regarding the role of water availability on stand-level response to elevated CO2.

1722^2^Harrison,PA^Butterfield,RE^1996^1^Effects of climate change on Europe-wide winter wheat and sunflower productivity^288^7^3^225-241^^^^^31 Dec^^^^^6219
10^130^2675^2676^2677^2678^416^614^741^92^Both species had greater biomass under the higher levels of CO2 and water availability. Biomass of Loblolly Pine seedlings in mixed stands exceeded that in monocultures, while the opposite was true for Red Maple. No significant treatment interactions were detected for total biomass. Significant main effects for water and stand type were detected for stem height of Loblolly Pine. CO2, water and stand type interactions were observed for height of Red Maple. 3. Net photosynthetic rates were measured on miniature stand canopies and constituent seedlings from these stands. Both species exhibited higher photosynthetic rates under elevated CO2. However, expressionA^6218^Spatially explicit crop models were developed from mechanistic principles to investigate the regional impacts of climate change. The approach highlights the spatial variability of crop responses to altered environmental conditions. The mechanistic nature of the models allows some confidence to be placed in the results that are produced under climate change scenarios. Two crop models have been constructed and applied across a large European region: EuroWheat (winter wheat) and EuroSunfl (sunflower). Model results were compared with observed phenology and yield across a variety of scales and found to capture the current spatial variability in wheat and sunflower productivity. Climate change scenarios from both equilibrium and transient general circulation model experiments were applied to each crop model. Wheat yields are predicted to increase throughout Europe for all climate change scenarios. Conversely, water-limited sunflower yields decrease in most regions and scenarios. More positive effects are predicted for winter wheat than sunflower due to a lower sensitivity to increased temperature and a higher sensitivity to elevated concentrations of CO2. The lowest yield increases for wheat and the largest yield decreases for sunflower are found in western Europe, whilst the most positive responses for both crops occur in central and eastern Europe. Predictions for southern Europe are highly sensitive both within the region and between the scenarios. The old generation of equilibrium climate change scenarios gives the worst predictions (lowest yield increases or highest yield decreases). More beneficial responses are observed for the new generation of transient scenarios for both wheat and sunflower. Area averaged results for Europe, based on the United Kingdom Meterorological Office transient experiment (UKTR), indicate a rate of increase in winter wheat yields of 0.2 t ha(-1) decade(-1) up to the 2020s and 0.36 t ha(-1) decade(-1) beyond. Smaller changes are predicted for sunflower: a rate of decrease of 0.05 t ha(-1) decade(-1) up to the 2020s followed by an increase of 0.05 t ha(-1) decade(-1).

1723^2^Lange,DL^Kader,AA^1997^1^Effects of elevated carbon dioxide on key mitochondrial respiratory enzymes in 'Hass' avocado fruit and fruit disks^154^122^2^238-244^^^^^Mar^^^^^6221
244^418^517^560^655^874^r both crops occur in central and eastern Europe. Predictions for southern Europe are highly sensitive both within the region and between the scenarios. The old generation of equilibrium climate change scenarios gives the worst predictions (lowest yield increases or highest yield decreases). More beneficial responses are observed for the new generation of transient scenarios for both wheat and sunflower. Area averaged results for Europe, based on the United Kingdom Meterorological Office transient experiment (UKTR), indicate a rate of increase in winter wheat yields of 0.2 t ha(-1) decade(-1) up to the 2020s and 0.36 t ha(-1) decade(-1) beyond. Smaller changes are predicted for sunflower: a rate of decrease of 0A^6220^Preclimacteric avocado [Persea americana (Mill.) cv, Hass] fruit or fruit disks as well as fruit harvested in either June (midseason) or August (late season) and partially ripened were kept in air (21% O-2 + 78% N-2), 20% CO2 + 17% O-2 (63% N-2), or 40% CO2 + 13% O-2 (47% N-2) at either 10 or 20 degrees C. Ethylene production by preclimacteric fruit completely inhibited during CO2 exposure, whereas there was only partial inhibition of ethylene production when partially ripened fruit were exposed, Compared to the fruit stored in air, O-2 uptake of fruit stored in 20% CO2 was decreased by 20%, whereas the fruit stored in 40% CO2 showed 25% more O-2 uptake than air- stored fruit, Fruit subjected to a storage regime of 40% CO2 at 10 degrees C followed by 2 d in air had the best visual quality, In general, climacteric fruit treated with 20% CO2 at 10 degrees C showed increased pyruvate dehydrogenase (PDH) activity and decreased cytochrome oxidase (CytOx) activity, Fruit stored in 40% CO2 had reduced CytOx activity compared to air-stored fruit, and PDH activity was variable depending on the harvest season of the fruit, Our results show that the effect of elevated CO2 on a given enzyme depends on concentration of CO2, duration of exposure, physiological state of the fruit, and type of tissue exposed.

1724^2^Lange,DL^Kader,AA^1997^1^Changes in alternative pathway and mitochondrial respiration in avocado in response to elevated carbon dioxide levels^154^122^2^245-252^^^^^Mar^^^^^6223
1678^2125^244^2679^2680^2681^2682^560^ fruit stored in air, O-2 uptake of fruit stored in 20% CO2 was decreased by 20%, whereas the fruit stored in 40% CO2 showed 25% more O-2 uptake than air- stored fruit, Fruit subjected to a storage regime of 40% CO2 at 10 degrees C followed by 2 d in air had the best visual quality, In general, climacteric fruit treated with 20% CO2 at 10 degrees C showed increased pyruvate dehydrogenase (PDH) activity and decreased cytochrome oxidase (CytOx) activity, Fruit stored in 40% CO2 had reduced CytOx A^6222^Partially ripened avocado [Persea americana (Mill.) cv, Hass] fruit harvested in either June or Aug, 1994 were kept at 10 degrees C in air (21% O-2), 20% CO2 (17% O-2, balance N-2), or 40% CO2 (13% O-2, balance N-2) for 7 to 12 days and then were transferred to air at 10 degrees C for 2 to 3 days, Mitochondrial respiration was stimulated in response to elevated CO, treatments at 10 degrees C. A shift to alternative pathway (Alt) respiration occurred on day 4 in experiments using avocados from both harvest dates, with a return to initial levels in only the 20% CO2-treated fruit (June- harvested fruit after return to air), Elevated CO2 at 20 degrees C decreased the in vitro O-2 consumption of isolated mitochondria compared to mitochondria kept in air, The Alt pathway contributed less to the total O-2 uptake of CO2-treated mitochondria compared to mitochondria kept in air, The respiratory control ratios of the CO2-treated fruit and mitochondria were higher and lower, respectively, than the air controls. Induction of 33 to 37 kD proteins (corresponding to the size of the alternative oxidase proteins) occurred in avocados after 4 days in 40% CO2. These results indicate that elevated CO2 has various effects depending on concentration, duration and temperature of exposure, and mitochondrial function of avocado fruit, such as increased and altered respiratory oxidation and up-regulation of alternative oxidase proteins.

1725^2^Lange,DL^Kader,AA^1997^1^Elevated carbon dioxide exposure alters intracellular pH and energy charge in avocado fruit tissue^154^122^2^253-257^^^^^Mar^^^^^6225
174^2683^310^948^ted fruit after return to air), Elevated CO2 at 20 degrees C decreased the in vitro O-2 consumption of isolated mitochondria compared to mitochondria kept in air, The Alt pathway contributed less to the total O-2 uptake of CO2-treated mitochondria compared to mitochondria kept in air, The respiratory control ratios of the CO2-treated fruit and mitochondria were higher and lower, respectively, than the air controls. A^6224^Changes in cytosolic and vacuolar pH, ATP, ADP, and the ATP : ADP ratio were measured in whole fruit or mesocarp disks of avocado [Persea americana (Mill.) cv, Hass] during brief exposures to elevated CO2. Intact climacteric fruit exposed to air (21% O-2), 20% CO2(17% O-2, balance N-2), or 40% CO2 (13% O-2, balance N-2) had cytosolic pH values of 7.0, 6.6, and 6.4, respectively, while mesocarp disks had cytosolic pH values of 6.9, 6.7, and 6.4, respectively. The beta-ATP levels of intact climacteric fruit exposed to 20% CO2 or 40% CO2 for 2 h were reduced by 25% or 43%, respectively, relative to air-exposed fruit. HPLC analysis of nucleotide phosphates from preclimacteric avocados revealed that ATP levels and the ATP : ADP ratio increased in 40% compared to the air-stored fruit. However, 1 day after transfer to air, the effects of elevated CO2 had dissipated. These modifications in cellular state could alter the activity of respiratory enzymes in fruit exposed to elevated CO2 atmospheres.
 controls. 1726^3^Lovelock,CE^Kyllo,D^Winter,K^1996^1^Growth responses to vesicular-arbuscular mycorrhizae and elevated CO2 in seedlings of a tropical tree, Beilschmiedia pendula (vol 10, pg 662, 1996)^43^10^6^784^^^^^Dec

1727^3^Luo,Y^Field,CB^Mooney,HA^1997^1^Adapting GePSi (generic plant simulator) for modeling studies in the Jasper Ridge CO2 project^81^94^1^81-88^^^^^1 Jan^^^^^6228
2684^361^372^376^427^483^57^641^92^cytosolic pH values of 6.9, 6.7, and 6.4, respectively. The beta-ATP levels of intact climacteric fruit exposed to 20% CO2 or 40% CO2 for 2 h were reduced by 25% or 43%, respectively, relative to air-exposed fruit. HPLC analysis of nucleotide phosphates from preclimacteric avocados revealed that ATP levels and the ATP : ADP ratio increased in 40% compared to the air-stored fruit. However, 1 day after transfer to air, the effects of elevated CO2 had dissipated. These modifications in cellular state could alter the activity of respiratory enzymes in fruit exposed to elevated CO2 atmospheres.
 controls. A^6227^In order to conduct modeling studies on the effects of elevated atmospheric carbon dioxide concentration ([CO2]) on plant and ecosystem processes at the Jasper Ridge grassland in northern California, the generic plant simulator (GePSi) (Chen: J.-L. and Reynolds, J.F., 1997. Ecol. Model., 94: 53-66), is modified to simulate grass dynamics. This modification was attempted by the authors of this paper, who had no prior experience with the model. Prior to this project, GePSi, which is implemented in the object-oriented programming (OOP) language, C++, had only been used to model trees and woody shrubs. This exercise addressed several of the concepts presented in this volume concerning the purported benefits of genericness, modularity, and OOP in plant modeling. The objective of this paper is to briefly summarize the extent to which these benefits were realized and some of the problems encountered. Our evaluation is presented in terms of: (1) design considerations, including the importance of how the modules in GePSi were defined; and (2) the implementation phase, which critiques the use of OOP for facilitating the transfer of the model. This study suggests that generic, modular models such as GePSi will facilitate the interactions of model developers and users and reduce duplication of effort in model development. (C) 1997 Elsevier Science B.V.

1728^2^Malmstrom,CM^Field,CB^1997^1^Virus-induced differences in the response of oat plants to elevated carbon dioxide^9^20^2^178-188^^^^^Feb^^^^^6230
1026^244^2685^2686^2687^344^409^739^741^92^P) language, C++, had only been used to model trees and woody shrubs. This exercise addressed several of the concepts presented in this volume concerning the purported benefits of genericness, modularity, and OOP in plant modeling. The objective of this paper is to briefly summarize the extent to which these benefits were realized and some of the problems encountered. Our evaluation is presented in terms of: (1) design considerations, including the importance of how the modulA^6229^Disease is an integral element of agricultural and natural systems, but the roles pathogens play in determining ecosystem response to elevated CO2 have rarely been examined. To investigate whether disease can alter the response of plants to CO2, we examined the effects of doubled CO2 (approximate to 700 mu mol mol(-1)) on Avena sativa infected with barley yellow dwarf virus (BYDV), a common pathogen of cereals and grasses. Oats infected with BYDV showed a significantly greater biomass response to CO2 enrichment than did healthy plants. Root mass of diseased plants increased by 37-60% with CO2 enrichment, but was largely unaffected in healthy plants. CO2 enrichment increased midday leaf-level photosynthesis and instantaneous water use efficiency by 34 and 93% in healthy plants and by 48 and 174% in infected plants. Foliar carbohydrates increased with both CO2 enrichment and BYDV infection, but the two factors affected individual peals dissimilarly. CO2 enrichment may alter the epidemiology of BYDV by increasing the persistence of infected plants.

1729^1^Pukhalskaya,NV^1997^1^Generative development of barley at an elevated atmospheric concentration of CO2 and varying temperature conditions^236^44^2^152-157^^^^^Mar-Apr^^^^^6232
314^376^434^435^633^92^e examined the effects of doubled CO2 (approximate to 700 mu mol mol(-1)) on Avena sativa infected with barley yellow dwarf virus (BYDV), a common pathogen of cereals and grasses. Oats infected with BYDV showed a significantly greater biomass response to CO2 enrichment than did healthy plants. Root mass of diseased plants increased by 37-60% with CO2 enrichment, but was largely unaffected in healthy plants. CO2 enrichment increased midday leaf-level photosynthesis and instantaneous water use efficiency by 34 and 93% in healthy plants and by 48 and 174% in infected plants. Foliar carbohydrates increased with both CO2 enrichment and BYDV infection, but the two factors affected individual peals dissimilarly. CO2 enrichment may alter the epidemiology of BYDV by iA^6231^Ear development in barley (Hordeum vulgare L.) was studied at normal (350 mu l/l) and elevated (700 mu l/l) atmospheric CO2 concentrations and two temperature regimes. Plant productivity was found to increase by 63 and 47% at temperatures of 20/14 and 23/17 degrees C (day/night), respectively. Analysis of production showed that elevated CO2 may induce an increase in the number of spikelets in the inflorescence primordium and in the size of the primordium beginning from the early stages of development. At 20/14 degrees C, a high level of CO2 significantly elevated the yield of the main ear, increasing the number of caryopses by 18-28% and the grain weight in the main ear by 42-49%. At 23/17 degrees C, a double concentration of CO2 increased plant production due to increased tiller formation (by 75-106%). It was found that the CO2 concentration did not affect pollen fertility in barley at low temperature, but at elevated temperature, the number of sterile pollen grains increased. Thus, the experiments showed that an elevated CO2 concentration affected the development of the barley ear during its whole ontogeny, including the early stages.

1730^3^Pukhalskaya,NV^Romin,N^Akanov,EN^1997^1^Growth and CO2 exchange in wheat seedlings grown at an elevated concentration of CO2^236^44^2^147-151^^^^^Mar-Apr^^^^^6234
376^434^ction showed that elevated CO2 may induce an increase in the number of spikelets in the inflorescence primordium and in the size of the primordium beginning from the early stages of development. At 20/14 degrees C, a high level of CO2 significantly elevated the yield of the main ear, increasing the number of caryopses by 18-28% and the grain weight in the main ear by 42-49%. At 23/17 degrees C, a double concentration of CO2 increased plant production due to increased tiller formation (by 75-106%). It was found that the CO2 concentration did not affect pollen fertility in barley at low temperature, but at elevated temperature, the number of sterile pollen grains increased. Thus, the experiments sA^6233^The effect of an elevated concentration of CO2 (700 mu l/l) on the growth and gas exchange of wheat (Triticum aestivum L.) seedlings was studied on the 4th day (germination), the 8th day (etiolated seedlings), and the 13th day (2-leaf stage) after sowing. The elevated concentration of CO2 activated respiration of seeds germinating in the air but did not significantly affect their growth, gas exchange, and the time of shoot formation when the seeds were in soil. The increase in CO2 concentration lowered the rate of respiration in etiolated seedlings by 25-40% and in the 13-day-old seedlings-by 30-35%. In the 13-day-old seedlings, the elevated concentration of CO2 in the air increased the rate of photosynthesis and, as a result, augmented twofold the net (per day) assimilation of CO2 and activated growth processes. Thus, it was found that the CO2 concentration in the air significantly affected the growth and gas exchange of the seedlings before the formation of assimilating machinery.
the experiments s1731^3^Reich,PB^Oleksyn,J^Tjoelker,MG^1996^1^Needle respiration and nitrogen concentration in Scots Pine populations from a broad latitudinal range: A common garden test with field-grown trees^43^10^6^768-776^^^^^Dec^^^^^6236
130^137^243^2688^389^417^520^670^762^798^levated concentration of CO2 activated respiration of seeds germinating in the air but did not significantly affect their growth, gas exchange, and the time of shoot formation when the seeds were in soil. The increase in CO2 concentration lowered the rate of respiration in etiolated seedlings by 25-40% and in the 13-day-old seedlings-by 30-35%. In the 13-day-old seedlings, the elevated concentration of CO2 in the air increased the rate of photosynthesis and, as a result, augmented twofold the net (per day) assimilation of CO2 and activated growth processes. Thus, it was found that the CO2 concentration in the air significantly affected the growth and gas exchange of the seedlings before the formation of assimilating machinery.
the experiments sA^6235^1. Models of tree function and forest ecosystem carbon budgets often assume that potential global changes in temperature and/or other factors may alter tissue nitrogen (N) and dark respiration rates (R(d)). However, little is known of patterns of co-variation in tissue N and R(d) among intraspecific populations originating along climatic gradients, and of whether an N-based model of R(d) can link these two variables. To address these issues, we studied N and R(d) in fully expanded needles of 10-year-old trees of 14 Scots Pine (Pinus sylvestris) populations of wide-ranging origin (43 degrees to 60 degrees N), grown under common garden conditions. 2. For 11 lowland populations (elevation <200 m) from the contiguous part of the species range (48 degrees to 60 degrees N) grown at a field site in Kornik, western Poland (52 degrees N), there were greater needle %N in populations from increasing latitude of origin or decreasing mean annual temperature (r greater than or equal to 0.93, P<0.01). Similar %N and latitude of origin correlations were observed in another year at this site and in retrospective analyses of published data for different sets of Scots Pine populations grown in common gardens at 48 degrees, 52 degrees C and 62 degrees N latitudes. Needle R(d) rates of the 11 lowland populations growing at Kornik and measured at a common temperature (20 degrees C) were greater, by as much as 50%, for more northerly than southerly populations. Mean R(d) rates were positively correlated to latitude of origin and to mean annual temperature (P<0.05, r=0.7 to 0.8). R(d) and needle %N were positively correlated (P<0.01, r=0.75), with one relationship fitting all data. Across the entire range from 1.15 to 1.55 needle %N, R(d) increased from 4.5 to 6.9 nmol g(- 1) s(-1). 3. Mean needle %N and R(d) values for two montane southern populations (43 degrees and 44 degrees N, elevation greater than or equal to 885 m) growing in the same common garden at Kornik were consistent with the relationships between mean annual temperature, needle %N and R(d) observed for the more northerly populations but did not fit the latitudinal patterns. This suggests that temperature and/or associated climate variables are likely the driving force for observed genetic variation in Scots Pine needle %N and R(d) across latitudinal and altitudinal gradients. 4. Results of these common garden studies support the idea of a general relationship between needle dark respiration and N concentration, and indicate that there is intraspecific genetic variation in physiology that is selected by climate that persists in a common environment, resulting in higher needle %N and respiration in plants originating from colder habitats. Such patterns need to be better understood and quantified, and merit consideration in modelling of current and potential global change effects on plant function and global carbon cycles.
evation greater than or equal to 885 m) growing in the same common garden at Kornik were consistent with the relationships between mean annual tem1732^6^Ringelberg,DB^Stair,JO^Almeida,J^Norby,RJ^ONeill,EG^White,DC^1997^1^Consequences of rising atmospheric carbon dioxide levels for the belowground microbiota associated with white oak^204^26^2^495-503^^^^^Mar-Apr^^^^^6238
1262^1334^2426^2689^2690^372^376^419^738^92^d) across latitudinal and altitudinal gradients. 4. Results of these common garden studies support the idea of a general relationship between needle dark respiration and N concentration, and indicate that there is intraspecific genetic variation in physiology that is selected by climate that persists in a common environment, resulting in higher needle %N and respiration in plants originating from colder habitats. Such patterns need to be better understood and quantified, and merit consideration in modelling of current and potential global change effects on plant function and global carbon cycles.
evation greater than or equal to 885 m) growing in the same common garden at Kornik were consistent with the relationships between mean annual temA^6237^The consequences for belowground microbiota under conditions of rising atmospheric CO2 are largely unknown. In this research we examined the microbiota associated with white oak (Quercus alba L.). It was our hypothesis that an increase in CO2 level would induce a change in the rhizosphere-associated microbial abundance and community composition. To provide an in situ estimation of microbial abundance and community composition, ester-linked polar lipid fatty acid (PLFA) technology was utilized. This technology, based on the quantitative measurement of membrane lipid fatty acids, has been utilized in the accurate identification and description of bacterial isolates and communities. Initial experiments demonstrated that a clear distinction in lipid patterns and microbial biomass existed between sterile roots and those of roots containing an associated viable microbiota. Statistical approaches were then used to determine what differences existed between individual PLFA and PLFA patterns obtained from white oak fine roots and bulk soils. An analysis of variance (ANOVA) showed significant differences to exist in the relative percentages of individual prokaryotic PLFA collected under ambient vs. elevated CO2 and between those associated with fine roots and bulk soils. Multivariate statistics showed distinct differences in the patterns of prokaryotic PLFA detected in the rhizosphere vs. the surrounding bulk soil, but did not identify differences related to elevated CO2 exposures. An artificial neural network recognized PLFA patterns unique to three different CO2 exposures: similar to 35, similar to 50, and similar to 65 Pa. Results of the three statistical tests were viewed as supportive of the hypothesis describing significant differences in individual PLFA and patterns of PLFA as a result of elevated CO2 exposure.

1733^3^Roden,JS^Wiggins,DJ^Ball,MC^1997^1^Photosynthesis and growth of two rain forest species in simulated gaps under elevated CO2^11^78^2^385-393^^^^^Mar^^^^^6240 PLFA patterns obtained from whit1092^188^1914^2467^2691^360^361^374^635^705^of variance (ANOVA) showed significant differences to exist in the relative percentages of individual prokaryotic PLFA collected under ambient vs. elevated CO2 and between those associated with fine roots and bulk soils. Multivariate statistics showed distinct differences in the patterns of prokaryotic PLFA detected in the rhizosphere vs. the surrounding bulk soil, but did not identify differences related to elevated CO2 exposures. An artificial neural network recognized PLFA patterns unique to three different CO2 exposures: similar to 35, similar to 50, and similar to 65 Pa. Results of the three statistical tests were viewed as supportive of the hypothesis describing significant differences in individual PLFA and patterns of PLFA as a result of elevated CO2 exposure.

1733^3^Roden,JS^Wiggins,DJ^Ball,MC^1997^1^Photosynthesis and growth of two rain forest species in simulated gaps under elevated CO2^11^78^2^385-393^^^^^Mar^^^^^6240 PLFA patterns obtained from whitA^6239^Two species common to the temperate rain forests of New South Wales, Australia (Doryphora sassafras and Acmena smithii) were grown for 2 wk in either ambient (350 mu L/L) or elevated (700 mu L/L) CO2 concentrations and low light (30 mu mol photons . m(-2). s(-1)) after which the seedlings were exposed for over 9 wk to a midday 2-h highlight period (1250 mu mol photons . m(- 2). s(-1), maximum) to simulate a tree fall gap. For both species, plants grown in elevated CO2 had greater biomass than plants grown in ambient CO2. However, relative increases in biomass were greater in Acmena, which is an early-successional species, than Doryphora, which is a late-successional species. Doryphora sassafras also had greater reductions in photosynthetic efficiency, as measured by chlorophyll fluorescence techniques (F-v/F-m) upon exposure to the high- light treatment than Acmena. Recovery in quantum efficiencies over time was observed for Doryphora, implying physiological acclimation to the new light environment. Plants grown in elevated CO2 had lower values of F-v/F-m than plants grown in ambient CO2, but these differences between CO2 treatments were only significant for the late-successional Doryphora. Although exposure to the simulated tree fall gap dramatically increased the conversion of pigments of the xanthophyll cycle, as well as increased the total pool size of xanthophyll cycle pigments relative to total chlorophyll concentration, there were no differences in either parameter between CO2 treatments. Leaves of Doryphora and those seedlings grown in elevated CO2 had greater starch concentrations than Acmena and those seedlings grown in ambient CO2, respectively. The reduction in quantum efficiencies for plants grown in elevated CO2 and exposed to a simulated tree fall gap is discussed in the context of the importance of gap phase regeneration for species in rain forest ecosystems and the potential effects of global change on those processes.
, implying physiological acclimation to the new light environment. P1734^2^Tateno,M^Chapin,FS^1997^1^The logic of carbon and nitrogen interactions in terrestrial ecosystems^16^149^4^723-744^^^^^Apr^^^^^6242
146^243^2692^372^374^417^431^541^711^791^l Doryphora. Although exposure to the simulated tree fall gap dramatically increased the conversion of pigments of the xanthophyll cycle, as well as increased the total pool size of xanthophyll cycle pigments relative to total chlorophyll concentration, there were no differences in either parameter between CO2 treatments. Leaves of Doryphora and those seedlings grown in elevated CO2 had greater starch concentrations than Acmena and those seedlings grown in ambient CO2, respectively. The reduction in quantum efficiencies for plants grown in elevated CO2 and exposed to a simulated tree fall gap is discussed in the context of the importance of gap phase regeneration for species in rain forest ecosystems and the potential effects of global change on those processes.
, implying physiological acclimation to the new light environment. PA^6241^Simple ecosystem models of carbon (C) and nitrogen (N) interactions between plants and soil show that differences in N-use efficiency cause convergence of plant growth in ecosystems with a closed N cycle because rapid growth associated with high N-use efficiency results in litter with a high C:N ratio and a low N mineralization rate, whereas slow growth associated with low N-use efficiency leads to a low C:N ratio and a high N mineralization rate. This plant-induced negative feedback on production contrasts with the positive feedback that had previously been hypothesized. Our model explains the causes and results of several important ecological patterns. First, all ecosystems with a fixed N pool will show a small increase in C storage (especially in soils) in response to elevated CO2 despite constraints by litter-quality feedbacks to N mineralization rate. Second, the decreased N-use efficiency and plateauing of primary production in forest ecosystems with a high N supply reflect saturation of photosynthetic rate with high plant N pools. Finally, the addition of inorganic N to ecosystems induces a quick increase in productivity and N supply. However, these increases disappear if N additions are not sustained. These findings suggest that those global changes that alter N input to or output from ecosystems are likely to have larger long-term impact on biomass, productivity, and C storage of ecosystems with a tightly closed N cycle than would changes in plant N-use efficiency.

1735^1^Teskey,RO^1997^1^Combined effects of elevated CO2 and air temperature on carbon assimilation of Pinus taeda trees^9^20^3^373-380^^^^^Mar^^^^^6244
243^264^361^374^376^384^385^633^92^st, all ecosystems with a fixed N pool will show a small increase in C storage (especially in soils) in response to elevated CO2 despite constraints by litter-quality feedbacks to N mineralization rate. Second, the decreased N-use efficiency and plateauing of primary production in forest ecosystems with a high N supply reflect saturation of photosyA^6243^Branches of 22-year-old loblolly pine (Pinus taeda, L.) trees growing in a plantation were exposed to ambient CO2, ambient + 165 mu mol mol(-1) CO2 or ambient + 330 mu mol mol(-1) CO2 concentrations in combination with ambient or ambient + 2 degrees C air temperatures for 3 years. Field measurements in the third year indicated that net carbon assimilation was enhanced in the elevated CO2 treatments in all seasons. On the basis of A/C-i curves, there was no indication of photosynthetic down-regulation. Branch growth and leaf area also increased significantly in the elevated CO2 treatments. The imposed 2 degrees C increase in air temperature only had slight effects on net assimilation and growth. Compared with the ambient CO2 treatment, rates of net assimilation were approximate to 1.6 times greater in the ambient + 165 mu mol mol(-1) CO2 treatment and 2.2 times greater in the ambient + 330 mu mol mol(-1) CO2 treatment. These ratios did not change appreciably in measurements made in all four seasons even though mean ambient air temperatures during the measurement periods ranged from 12.6 to 28.2 degrees C. This indicated that the effect of elevated CO2 concentrations on net assimilation under field conditions was primarily additive. The results also indicated that the effect of elevated CO2 (+ 165 or + 330 mu mol mol(-1)) was much greater than the effect of a 2 degrees C increase in air temperature on net assimilation and growth in this species.

1736^5^Visser,AJ^Tosserams,M^Groen,MW^Magendans,GWH^Rozema,J^1997^1^The combined effects of CO2 concentration and solar UV-B radiation on faba bean grown in open-top chambers^9^20^2^189-199^^^^^Feb^^^^^6246
1206^131^1431^243^2623^312^344^360^372^962^rowth. Compared with the ambient CO2 treatment, rates of net assimilation were approximate to 1.6 times greater in the ambient + 165 mu mol mol(-1) CO2 treatment and 2.2 times greater in the ambient + 330 mu mol mol(-1) CO2 treatment. These ratios did not change appreciably in measurements made in all four seasons eveA^6245^The response of faba bean seedlings to the combined effects of increased atmospheric CO2 concentrations ([CO2]) and solar UV-B irradiance was studied using open-top chambers transparent to W-B radiation. The purpose of the study was to determine whether effects of increased [CO2] on growth and physiology are modified by the present solar UV-B fluence rate in the Netherlands. Seedlings were exposed to 350 or 700 mu mol mol(- 1) CO2. At both [CO2], solar UV-B irradiance was either present or reduced using polyester foil opaque to UV-B radiation. To obtain information on the time dependence of increased [CO2] and UV-B radiation effects, three harvests were performed during the experiment, CO2 enrichment resulted in increased biomass production at all harvests. At the final harvest, UV-B radiation did not affect biomass production but a significant decrease was observed after 14 d of treatment. A reduction of the UV-B fluence increased shoot length at both [CO2] throughout the experiment, UV-B radiation slightly altered biomass allocation. Plants grown at reduced levels of UV-B radiation invested less biomass in flowers and more in stem material compared to plants grown at ambient UV-B levels. CO2 enrichment resulted in a stimulation of net photosynthesis after 26 and 38 d of treatment. UV-B reduction did not alter this response. After 26 d of treatment, photosynthetic acclimation to CO2 enrichment was observed, which was probably the result of accumulation of carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV-B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV-B radiation was limited to UV- A transmittance of leaves. Under prevalent experimental conditions, UV-B radiation did not affect the measured physiological parameters. Most open-top chambers used for climate change research are constructed of materials which do not transmit UV-B radiation. Our results indicate that part of the 'chamber effects' on plant height often described in the literature might be explained by the absence of solar UV-B radiation in these chambers.

1737^2^Ward,JK^Strain,BR^1997^1^Effects of low and elevated CO2 partial pressure on growth and reproduction of Arabidopsis thaliana from different elevations^9^20^2^254-260^^^^^Feb^^^^^6248
1380^1980^243^2564^312^344^374^376^417^740^carbohydrates in the leaves. After 38 d, photosynthetic acclimation was no longer present. The UV absorbance of methanolic leaf extracts was increased by CO2 enrichment only. Both CO2 enrichment and solar UV-B reduced the transmittance of radiation through intact attached leaves. Interaction between [CO2] and UV-B radiation was limited to UV- A transmittance of leaves. Under prevalent experimental conditions, UV-B radiation did not affect the measured physiological parameters. Most open-top chambers used for climate change research are constructed of mA^6247^Atmospheric CO2 partial pressure may have been as low as 18 Pa during the Pleistocene and is expected to increase from 35 to 70 Pa before the end of the next century. Low CO2 reduces the growth and reproduction of C-3 plants, whereas elevated CO2 often increases growth and reproduction. Plants at high elevation are exposed to reduced CO2 partial pressure and may be better adapted to the low CO2 of the Pleistocene, me examined genotypes of Arabidopsis thaliana from different elevations for variation in growth and reproduction at the CO2 levels of the Pleistocene, the present and the future. Genotypes exhibited limited genetic variation in the response of the production of biomass to changes in CO2, but showed significant variation in reproductive characters. We found evidence that plants from high elevations may be better adapted to low CO2 when considering seed number, which is an important component of fitness. Genotypes showed greater variation in the response of seed number between 35 and 20 Pa CO2 compared to 35 and 70 Pa CO2. We conclude that present-day C-3 annuals may have greater potential for evolution in response to the low CO2 of the Pleistocene relative to the elevated CO2 predicted for the future.

1738^2^Wayne,PM^Bazzaz,FA^1997^1^Light acquisition and growth by competing individuals in CO2- enriched atmospheres: Consequences for size structure in regenerating birch stands^12^85^1^29-42^^^^^Feb^^^^^6250
1388^2693^2694^2695^2696^312^372^376^692^792^ from different elevations for variation in growth and reproduction at the CO2 levels of the Pleistocene, the present and the future. Genotypes exhibited limited genetic variation in the response of the production of biomass to changes in CO2, but showed significant variation in reproductive characters. We found evidence that plants from high elevations may be better adapted to low CO2 when considering seed number, which is an important component of fitness. Genotypes showed greater variation in the response of seed number between 35 and 20 Pa CO2A^6249^1 To investigate how CO2-enriched atmospheres may influence plant competition and stand size structure in regenerating forests, experimental populations comprised of three maternal families of yellow birch (Betula alleghaniensis Britt.) were grown in both ambient (350 mu L L(-1)) and elevated (700 mu L L(-1)) CO2 concentrations in a controlled environment facility. Individual seedling growth, light acquisition, and stand size structure were monitored throughout the first year of growth. 2 Elevated CO2 increased average seedling biomass in stands by 14%, a value much lower than the average enhancement reported elsewhere for individually grown yellow birch seedlings. Maternal families within stands differed significantly in their growth responsiveness to elevated CO2, ranging from +51% to - 16%. As a result, CO2 altered the genetic identity of dominants in regenerating stands. 3 Seedling size inequalities were generally lower in CO2-enriched environments, a result that contrasts with other studies that have reported increased size inequality with increased productivity in resource-rich environments. Distribution modifying functions relating initial seedling size and subsequent growth suggest that there was a relatively smaller advantage to being larger in elevated vs. ambient CO2 environments. Together, these results suggest that competition in CO2-enriched environments was less size- asymmetric. 4 Differences in stand size structure between CO2 treatments were related to competition for light. Empirical measures of seedling light acquisition per unit biomass suggest competition for light was less size-asymmetric in CO2-enriched environments. Decreased size-asymmetric competition for light was attributable both to differences in the CO2-use efficiency of high-light canopy dominants vs. low-light canopy subordinates, and to CO2-induced differences in plant allometry. 5 This study highlights the importance of stand- level competition studies in global change research, and more generally, the value of studies that combine phenomenological descriptions of stand development with physiological mechanisms of competition.

1739^2^Wilson,KB^Bunce,JA^1997^1^Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean^9^20^2^230-238^^^^^Feb^^^^^6252
1338^1386^2065^243^314^372^374^431^639^923^riched environments was less size- asymmetric. 4 Differences in stand size structure between CO2 treatments were related to competition for light. Empirical measures of seedling light acquisition per unit biomass suggest competition for light was less size-asymmetric in CO2-enriched environments. Decreased size-asymmetric competition for light was attributable both to differences in the CO2-use efficiency of high-light canopy dominants vs. low-light canopy subordinates, and to CO2-induced differences in plant allometry. 5 This study highlights the importance of stand- level competition studies in global change research, and more generally, the value of studiesA^6251^Soybeans were grown at three CO2 concentrations in outdoor growth chambers and at two concentrations in controlled- environment growth chambers to investigate the interactive effects of CO2, temperature and leaf-to-air vapour pressure difference (LAVPD) on stomatal conductance, The decline in stomatal conductance with CO2 was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO2 at 30 degrees C but not at 35 degrees C, There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations, Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO2. Measurements in the environmental growth chamber mere also performed at the opposing CO2, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO2 than by measurement CO2. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO2, LAVPD and temperature.

1740^3^Zhu,J^Bartholomew,DP^Goldstein,G^1997^1^Effect of elevated carbon dioxide on the growth and physiological responses of pineapple, a species with Crassulacean acid metabolism^154^122^2^233-237^^^^^Mar^^^^^6254
1121^1669^243^2622^2697^2698^384^417^739^763^ensitive to LAVPD at low CO2 at 30 degrees C but not at 35 degrees C, There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations, Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO2. Measurements in the environmental growth chamber mere also performed at the opposing CO2, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO2 than by measurement CO2. Two models that descrA^6253^Despite the potential impact of rising global CO2 levels, only a limited number of studies have been conducted on the effects of ambient and elevated CO2 on plants having Crassulacean acid metabolism (CAM), To our knowledge, there are no studies for pineapple [Ananas comosus (L.) Merr.], the most commercially important CAM plant, Pineapple plants were grown at CO2 levels of approximate to 330 (ambient) and approximate to 730 (elevated) mu mol . mol(-1) in open-top chambers for 4 months, The mean air temperature in the chambers was approximate to 39 degrees C day/24 degrees C night, Average plant dry mass at harvest was 180 g per plant at elevated CO2 and 146 g per plant at ambient CO2. More biomass was partitioned to stem and root but less to leaf for plants grown at elevated CO2; leaf thickness was 11% greater at elevated than at ambient CO2. The diurnal difference in leaf titratable acidity (H+) at elevated CO2 reached 347 mmol . m(-2), which was up to 42% greater than levels in plants grown in ambient CO2. Carbon isotopic discrimination (Delta) of plants was 3.75% at ambient CO2 and 3.17% at elevated CO2, indicating that CO2 uptake via the CAM pathway was enhanced more by elevated CO2 than uptake via the C-3 pathway, The nonphotochemical quenching coefficient (q(N)) of leaves was approximate to 45% lower in the early morning for plants grown at elevated than at ambient CO2, while afternoon values were comparable, The q(N) data suggested that the fixation of external CO2 was enhanced by elevated CO2 in the morning but not in the afternoon when leaf temperature was greater than or equal to 40 degrees C. We found no effect of CO2 levels on leaf N or chlorophyll content, Pineapple dry matter gain was enhanced by elevated CO2, mainly due to increased CO2 dark fixation in environments with day temperatures high enough to suppress C-3 photosynthesis.
he diurnal difference in leaf titratable acidity (H+) at elevated CO2 reached 347 mmol . m(-2), which was up to 42% greater than levels in plants grown in ambi1741^4^Ziska,LH^Namuco,O^Moya,T^Quilang,J^1997^1^Growth and yield response of field-grown tropical rice to increasing carbon dioxide and air temperature^48^89^1^45-53^^^^^Jan-Feb^^^^^6256
1528^243^344^360^372^376^738^hway, The nonphotochemical quenching coefficient (q(N)) of leaves was approximate to 45% lower in the early morning for plants grown at elevated than at ambient CO2, while afternoon values were comparable, The q(N) data suggested that the fixation of external CO2 was enhanced by elevated CO2 in the morning but not in the afternoon when leaf temperature was greater than or equal to 40 degrees C. We found no effect of CO2 levels on leaf N or chlorophyll content, Pineapple dry matter gain was enhanced by elevated CO2, mainly due to increased CO2 dark fixation in environments with day temperatures high enough to suppress C-3 photosynthesis.
he diurnal difference in leaf titratable acidity (H+) at elevated CO2 reached 347 mmol . m(-2), which was up to 42% greater than levels in plants grown in ambiA^6255^Although the response of rice (Oryza sativa L.) to increasing atmospheric CO2 concentration and air temperature has been examined at the greenhouse or growth chamber level, no field studies have been conducted under the tropical, irrigated conditions where the bulk of the world's rice is grown. At the International Rice Research Institute, rice (cv. IR 72) was grown from germination until maturity for the 1994 wet and 1995 dry seasons at three different CO2 concentrations (ambient, ambient + 200, and ambient + 300 mu L L(-1) CO2) and two different air temperatures (ambient and ambient + 4 degrees C) using open-top field chambers. Averaged for both seasons, increases in CO2 concentration alone (+ 200, + 300 mu L L(-1)) resulted in a significant increase in total plant biomass (+ 31%, + 40%) and crop yield (+ 15%, + 27%) compared with the ambient control. The increase in crop yield was associated with an increase in the number of panicles per square meter and a greater percentage of filled spikelets. Simultaneous increases in CO2 and air temperature did not alter the biomass at maturity (relative to elevated CO2 alone), but plant development was accelerated at the higher growth temperature regardless of CO2 concentration. Grain yield, however, became insensitive to CO2 concentration at the higher growth temperature. Increasing both CO2 and air temperature also reduced grain quality (e.g., protein content). The combination of CO2 and temperature effects suggests that, in warmer regions (i.e., > 34 degrees C) where rice is grown, quantitative and qualitative changes in rice supply are possible if both CO2 and air temperature continue to increase.

1742^2^Ball,AS^Drake,BG^1997^1^Short-term decomposition of litter produced by plants grown in ambient and elevated atmospheric CO2 concentrations^127^3^1^29-35^^^^^Feb^^^^^6258
1044^310^348^407^429^430^57^664^818^l. The increase in crop yield was associated with an increase in the number of panicles per square meter and a greater percentage of filled spikelets. SiA^6257^The effects of elevated atmospheric CO2 (ambient + 340 mu mol mol(-1)) on above-ground litter decomposition were investigated over a 6-week period using a field-based mesocosm system. Soil respiratory activity in mesocosms incubated in ambient and elevated atmospheric CO2 concentrations were not significantly different (t-test, P > 0.05) indicating that there were no direct effects of elevated atmospheric CO2 on litter decomposition. A study of the indirect effects of CO2 on soil respiration showed that soil mesocosms to which naturally senescent plant litter had been added (0.5% w/w) from the C-3 sedge Scirpus olneyi grown in elevated atmospheric CO2 was reduced by an average of 17% throughout the study when compared to soil mesocosms to which litter from Scirpus olneyi grown in ambient conditions had been added. In contrast, similar experiments using senescent material from the C-4 grass Spartina patens showed no difference in soil respiration rates between mesocosms to which litter from plants grown in elevated or ambient CO2 conditions had been added. Analysis of the C:N ratio and lignin content of the senescent material showed that, while the C:N ratio and lignin content of the Spartina patens litter did not vary with atmospheric CO2 conditions, the C:N ratio (but not the lignin content) of the litter from Scirpus olneyi was significantly greater (t-test; P < 0.05) when derived from plants grown under elevated CO2 (105:1 compared to 86:1 for litter derived from Scirpus olneyi grown under ambient conditions). The results suggest that the increased C:N ratio of the litter from the C-3 plant Scirpus olneyi grown under elevated CO2 led to the lower rates of biodegradation observed as reduced soil respiration in the mesocosms. Further longterm experiments are now required to determine the effects of elevated CO2 on C partitioning in terrestrial ecosystems.
nescent material from the C-4 grass Spartina patens showed no difference in soil respiration rates between mesocosms to which litter from plants grow1743^3^Berry,SC^Varney,GT^Flanagan,LB^1997^1^Leaf delta C-13 in Pinus resinosa trees and understory plants: Variation associated with light and CO2 gradients^2^109^4^499-506^^^^^Feb^^^^^6260
2094^243^2699^2700^2701^2702^2703^344^348^539^ CO2 conditions, the C:N ratio (but not the lignin content) of the litter from Scirpus olneyi was significantly greater (t-test; P < 0.05) when derived from plants grown under elevated CO2 (105:1 compared to 86:1 for litter derived from Scirpus olneyi grown under ambient conditions). The results suggest that the increased C:N ratio of the litter from the C-3 plant Scirpus olneyi grown under elevated CO2 led to the lower rates of biodegradation observed as reduced soil respiration in the mesocosms. Further longterm experiments are now required to determine the effects of elevated CO2 on C partitioning in terrestrial ecosystems.
nescent material from the C-4 grass Spartina patens showed no difference in soil respiration rates between mesocosms to which litter from plants growA^6259^Our objective was to evaluate the relative importance of gradients in light intensity and the isotopic composition of atmospheric CO2 for variation in leaf carbon isotope ratios within a Pinus resinosa forest. In addition, we measured photosynthetic gas exchange and leaf carbon isotope ratios on four understory species (Dryopteris carthusiana, Epipactus helleborine, Hieracium floribundum, Rhamnus frangula), in order to estimate the consequence of the variation in the understory light microclimate for carbon gain in these plants. During midday, CO2 concentration was relatively constant at vertical positions ranging from 15 m to 3 m above ground. Only at positions below 3 m was CO2 concentration significantly elevated above that measured at 15 m. Based on the strong linear relationship between chan in CO2 concentration and delta(13)C values for air samples collected during a diurnal cycle, we calculated the expected vertical profile for the carbon isotope ratio of atmospheric CO2 within the forest. These calculations indicated that leaves at 3 m height and above were exposed to CO2 of approximately the same isotopic composition during daylight periods. There was no significant difference between the daily mean delta(13)C values at 15 m (- 7.77 parts per thousand) and 3 m (-7.89 parts per thousand), but atmospheric CO2 was significantly depleted in C-13 closer to the ground surface, with daily average delta(13)C values of -8.85 parts per thousand at 5 cm above ground. The light intensity gradient in the forest was substantial, with average photosynthetically active radiation (PAR) on the forest floor approximately 6% of that received at the top of the canopy. In contrast, there were only minor changes in air temperature, and so it is likely that the leaf-air vapour pressure difference was relatively constant from the top of the canopy to the forest floor. For red pine and elm tree samples, there was a significant correlation between leaf delta(13)C value and the height at which the leaf sample was collected. Leaf tissue sampled near the forest floor, on average, had lower delta(13)C values than samples collected near the top of the canopy. We suggest that the average light intensity gradient through the canopy was the major factor influencing vertical changes in tree leaf delta(13)C values. In addition, there was a wide range of variation (greater than 4 parts per thousand) among the four understory plant species for average leaf delta(13)C values. Measurements of leaf gas exchange, under natural light conditions and with supplemental light, were used to estimate the influence of the light microclimate on the observed variation in leaf carbon isotope ratios in the understory plants. Our data suggest that one species, Epipactus helleborine, gained a substantial fraction of carbon during sunflecks.

1744^1^Bunce,JA^1997^1^Variation in growth stimulation by elevated carbon dioxide in seedlings of some C-3 crop and weed species^127^3^1^61-66^^^^^Feb^^^^^6262
349^d the height at which the leaf sample was collectedA^6261^Seven C-3 crop and three C-3 weed species were grown from seed at 360 and at 700 cm(3) m(-3) carbon dioxide concentrations in a controlled environment chamber to compare dry mass, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and photosynthetic acclimation at ambient and elevated carbon dioxide. The dry mass at the final harvest at elevated carbon dioxide relative to that at ambient carbon dioxide was highly correlated with the RGR at the lower carbon dioxide concentration. This relationship could be quite common, because it does not require that species differ in the response of RGR or photosynthesis to elevated carbon dioxide, and holds even when species differ moderately in these responses. RGR was also measured for a limited period at the end of the experiment to determine relationships with leaf gas exchange measured at this time. Relative increases in RGR at elevated carbon dioxide at this time were more highly correlated with the relative increase in NAR at elevated carbon dioxide than with the response of LAR. The amount of acclimation of photosynthesis was a good predictor of the relative increase in NAR at elevated carbon dioxide, and the longterm increase in photosynthesis in the growth environment. No differences between crops and weeds or between cool and warm climate species were found in the responses of growth or photosynthetic acclimation to elevated carbon dioxide.

1745^3^Bunce,JA^Wilson,KB^Carlson,TN^1997^1^The effect of doubled CO2 on water use by alfalfa and orchard grass: Simulating evapotranspiration using canopy conductance measurements^127^3^1^81-87^^^^^Feb^^^^^6264
256^312^372^374^385^639^674^92^dioxide, and holds even when species differ moderately in these responses. RGR was also measured for a limited period at the end of the experiment to determine relationships with leaf gas exchange measured at this time. Relative increases in RGR at elevated carbon dioxide at this time were more highly correlated with the relative increase in NAR at elevA^6263^Alfalfa and orchard grass crops were grown at ambient and twice ambient carbon dioxide concentrations in field plots for several years in Beltsville, MD, using semiopen chambers. Canopy conductances throughout many days were determined from water vapour exchange measurements, and indicated significant reductions in canopy conductance to water vapour at elevated carbon dioxide in both species. However, recognizing that the artificial ventilation in the chambers made direct comparisons of evapotranspiration rates questionable, we used a soil- vegetation-atmosphere model to determine what field-scale evapotranspiration rates would have been with natural ventilation. Unlike the 'omega' approach, the model used allowed feedbacks between the canopy and the atmosphere, such that, for example, canopy conductance responses affected profiles of temperature and water vapour. Simulations indicated that although canopy conductances were lower at elevated carbon dioxide by as much as 20% in alfalfa and 60% in orchard grass, evapotranspiration rates never differed by more than 3% in alfalfa or 8% in orchard grass. Daily totals of evapotranspiration were only 1-2% lower at elevated carbon dioxide in alfalfa, and 2-5% lower in orchard grass. The results are partly explained by the fact that aerodynamic conductances to water vapour were generally smaller than the stomatal conductance, and also by canopy-atmosphere feedback processes which largely compensated for the lower conductance at elevated carbon dioxide by increasing the gradient for evaporation.

1746^1^Bytnerowicz,A^1996^1^Physiological aspects of air pollution stress in forests^262^36^3^15-22^^^^^^^^^^6266
1102^2704^425^57^673^981^he 'omega' approach, the model used allowed feedbacks between the canopy and the atmosphere, such that, for example, canopy conductance responses affected profiles of temperature and water vapour. Simulations indicated that although canopy conductances were lower at elevated carbon dioxide by as much as 20% in alfalfa and 60% in orchaA^6265^Air pollutants, such as ozone, sulfur dioxide, nitrogen compounds and others, affect health of forests in Europe and North America. Gaseous air pollutants enter plants mainly through stomata, although transcuticular transport can also be important for some pollutants. Toxic effects of pollutants depend on their effective dose that is proportional to pollutant ambient concentration and plant stomatal conductance. Mechanisms of air pollution toxicity are very complex and depend on various physiological and biochemical properties of plants. These mechanisms (including formation of free radicals) are still poorly understood. In addition, physiological responses of forest plants to air pollution stress can be modified by various biotic (e.g., insects, pathogens, mycorrhizae associations, genetic variation) and abiotic (e.g., increasing CO2 concentrations, ultraviolet-B radiation, nitrogen deposition, nutrient deficiencies, drought) factors. An example of air pollution effects on forest trees may be responses of ponderosa pine seedlings to elevated concentrations of ozone in the Sierra Nevada. Various physiological changes caused by ozone (e.g., lowered net photosynthesis, altered carbon allocation, deterioration of photosynthetic pigments, etc.) have led to the reduced growth and biomass of the seedlings.

1747^5^Daymond,AJ^Wheeler,TR^Hadley,P^Ellis,RH^Morison,JIL^1997^1^The growth, development and yield of onion (Allium cepa L) in response to temperature and CO2^174^72^1^135-145^^^^^Jan^^^^^6268
230^243^264^312^344^376^400^402^57^58^of plants. These mechanisms (including formation of free radicals) are still poorly understood. In addition, physiological responses of forest plants to air pollution stress can be modified by various biotic (e.g., insects, pathogens, mycorrhizae associations, genetic variation) and abiotic (e.g., increasing CO2 concentrations, ultraviolet-B radiation, nitrogen deposition, nutrient deficiencies, drought) factors. An example of air pollution effects on forest trees may be responsA^6267^Stands of two cultivars (cv. Hysam and Site) of onion (Allium cepa L.) were grown in the held within polyethylene-covered tunnels along which a temperature adient was imposed. Pairs of tunnels were maintained at either 374 or 532 mu mol mol(-1) CO2. The rates of progress from transplanting to bulbing, and from bulbing to harvest maturity, were positive linear functions of mean temperature for each cultivar. At a given temperature, the time of bulbing was earlier, but the duration of bulb growth longer, at elevated compared with normal CO2. Canopy architecture was not affected by CO2, temperature or cultivar; an estimate of 0.25 for the canopy light extinction coefficient was common to all treatment combinations. Radiation use efficiency was greater at elevated compared with normal CO2 in the period up to bulbing, but was the same at both CO2 concentrations during subsequent bulb growth. Total crop dry weight at bulbing was increased by 32-44% due to elevated CO2. Bulb yields at harvest maturity declined with progressively warmer temperatures and to a greater extent in cv. Site than cv. Hysam. Enrichment with CO2 increased bulb yields by 29-37% and by 35-51% in cvs Hysam and Site, respectively. From comparison of the temperature rise needed to offset entirely the yield increases of each cultivar due to elevated CO2, it is concluded that current estimates of climate change should be beneficial for bulb onion production, particularly for long- season cultivars.

1748^4^Delucia,EH^Callaway,RM^Thomas,EM^Schlesinger,WH^1997^1^Mechanisms of phosphorus acquisition for ponderosa pine seedlings under high CO2 and temperature^52^79^2^111-120^^^^^Feb^^^^^6270
1334^179^2012^2530^2705^2706^312^417^733^791^reatment combinations. Radiation use efficiency was greater at elevated compared with normal CO2 in the period up to bulbing, but was the same at both CO2 concentrations during subsequent bulb growth. Total crop dry weight at bulbing was increased by 32-44% due to elevated CO2. Bulb yields at harvest maturity declinA^6269^To test the hypothesis that elevated atmospheric CO2 and elevated temperature, simulating current and predicted future growing season conditions, act antagonistically on phosphorus acquisition of ponderosa pine, seedlings were grown in controlled-environment chambers in a two temperature (25/10 degrees C and 30/15 degrees C)xtwo CO2 (350 and 700 mu l(-1)) experimental design. Mycorrhizal seedlings were watered daily with a nutrient solution with P added in organic form as inositol hexaphosphate (64ppm P). Thus seedlings were challenged to use active forms of P acquisition. Elevated CO2 increased the relative growth rate by approx. 5% which resulted in an approx. 33% increase in biomass after 4 months. There was no main effect of temperature on growth. Increased growth under elevated CO2 and temperature was supported by increases in specific absorption rate and the specific utilization rate of P. The contribution of mycorrhizae to P uptake may have been greater under simulated future conditions, as elevated CO2 increased the number of mycorrhizal roots. There was no main effect of temperature on root phosphatase activity, but elevated CO2 caused a decrease in activity. The inverse pattern of root phosphatase activity and mycorrhizal infection across treatments suggests a physiological coordination between these avenues of P acquisition. The concentration of oxalate in the soil increased under elevated CO2 and decreased under elevated temperature. This small molecular weight acid solubilizes inorganic P making it available for uptake. Increased mycorrhizal infection and exudation of oxalate increased P uptake in ponderosa pine seedlings under elevated CO2, and there was no net negative effect of increased temperature. The increased carbon status of pine under elevated CO2 may facilitate uptake of limiting P in native ecosystems. (C) 1997 Annals of Botany Company.
 the specific utilization rate of P. The contribution of mycorrhizae to P uptake may have been greater under simulated future conditions, as ele1749^5^Docherty,M^Wade,FA^Hurst,DK^Whittaker,JB^Lea,PJ^1997^1^Responses of tree sap-feeding herbivores to elevated CO2^127^3^1^51-59^^^^^Feb^^^^^6272
2533^2707^2708^2709^2710^312^417^797^798^92^oot phosphatase activity and mycorrhizal infection across treatments suggests a physiological coordination between these avenues of P acquisition. The concentration of oxalate in the soil increased under elevated CO2 and decreased under elevated temperature. This small molecular weight acid solubilizes inorganic P making it available for uptake. Increased mycorrhizal infection and exudation of oxalate increased P uptake in ponderosa pine seedlings under elevated CO2, and there was no net negative effect of increased temperature. The increased carbon status of pine under elevated CO2 may facilitate uptake of limiting P in native ecosystems. (C) 1997 Annals of Botany Company.
 the specific utilization rate of P. The contribution of mycorrhizae to P uptake may have been greater under simulated future conditions, as eleA^6271^Five species of sap-feeding homoptera were studied on Fagus sylvatica and Acer pseudoplatanus and exposed to elevated concentrations of carbon dioxide (600 mu L L(-1)). The concentration of total soluble amino acids in foliage of F. sylvatica was unaffected by growing saplings in elevated atmospheric CO2 concentrations. Although experiments on individual aphids indicated poorer performance of Phyllaphis fagi (fewer, smaller nymphs produced), resultant populations did not differ from those in ambient (350 mu L L(-1)) conditions. The area of beech foliage stippled by the leafhopper Fagocyba cruenta was similar at ambient and elevated CO2 concentrations. The concentration of total amino acids and that of serine of A. pseudoplatanus foliage were significantly lower at elevated CO2 concentrations. However, the relative growth rates of two aphid species Drepanosiphum platanoidis and Periphyllus testudinaceus and one leafhopper Ossiannilssonola callosa were not significantly different in elevated CO2. No evidence was found that, under the conditions of these experiments, populations of aphids and leafhoppers will change as concentrations of CO2 increase.

1750^3^Dugas,WA^Prior,SA^Rogers,HH^1997^1^Transpiration from sorghum and soybean growing under ambient and elevated CO2 concentrations^107^83^1-2^37-48^^^^^Jan^^^^^6274
1307^2711^2712^2713^341^344^399^434^442^643^phids indicated poorer performance of Phyllaphis fagi (fewer, smaller nymphs produced), resultant populations did not differ from those in ambient (350 mu L L(-1)) conditions. The area of beech foliage stippled by the leafhopper Fagocyba cruenta was similar at ambient and elevated CO2 concentrations. The concentration of total amino acids and that of serine of A. pseudoplatanus foliage were significantly lower at elevated CO2 concentrations. However, the relative growth rates of two aphid species Drepanosiphum platanoidis and Periphyllus testudinaceus and one leafhopper Ossiannilssonola callosa were not significantly different in elevated CO2. No eviA^6273^The increasing concentration of carbon dioxide in the atmosphere ([CO2]) has several direct effects on plants and these effects may be different for C-3 and C-4 plants. Our objective was to measure hourly and daily whole-plant transpiration rates from the C-4 plant grain sorghum (Sorghum bicolor (L.) Moench) and the C-3 plant soybean (Glycine max (L.) Merr.) grown under ambient (359 mu molCO(2) mol(-1) dry atmospheric air) and elevated (705 mu molmol(-1)) [CO2] values. Transpiration measurements were made for 22 days in August 1994 at Auburn, Alabama, USA, using stem flow gauges on plants growing in open top chambers, n = 8 for each [CO2] and species. Leaf area averaged slightly more than 0.1m(2) per plant for sorghum and about 0.2 m(2) per plant for soybean, Averages (15 min and daily) of transpiration, per unit leaf area, were consistently greater from plants growing under the ambient [CO2,] for both sorghum and soybean. Average daily transpiration from plants growing under the elevated [CO2] was significantly smaller (P = 0.05) on all but 2 days for soybean and on 9 of the 22 days of measurements for sorghum. Average daily sorghum transpiration was 1128 gm(-2) day(-1) and 772 gm(-2) day(-1) from plants growing under an ambient and elevated [CO2], respectively. Corresponding soybean averages were 731 gm(-2) day(-1) and 416 gm(-2) day(-1). The transpiration reduction under elevated [CO2] was greater for the C-3 plant soybean than for the C-4, plant sorghum. These results support previous studies showing that transpiration, per unit leaf area, from sorghum and soybean will both be reduced if atmospheric [CO2] continues to increase, although the reduction may be greater for C-3, plants.

1751^2^During,H^Harst,M^1996^1^Stomatal behaviour, photosynthesis and photorespiration of in vitro-grown grapevines: Effects of light and CO2^334^35^4^163-167^^^^^Dec^^^^^6276
1491^1886^2714^348^he ambient [CO2,] for both sorghum and soybean. Average daily transpiration from plants growing under the elevated [CO2] was siA^6275^To improve photosynthesis and growth of grapevines cultivated in vitro (Seyval blanc and SO 4) effects of light intensity, spectral irradiance and CO2 concentration on stomatal behaviour, CO2 fixation and photorespiration were studied. Stomata were shown to respond to changes of light intensity but, unlike photosynthesis, their reactions were delayed and stomatal closure was incomplete in the dark. In contrast, alterations of the CO2 concentration in the headspace (50-2200 ppm) did not cause stomatal reactions. Photosynthesis vs, light intensity relationships indicated lower light compensation points, higher quantum yield and higher rates of light- saturated photosynthesis with ''Fluora'' lamps (maximal spectral irradiance al 460 and 680 nm) compared to ''projector'' lamps (maximal spectral irradiance at 620 nm). Photosynthesis vs. intercellular CO2 concentration relationships indicated varietal differences, the carboxylation efficiency and rates of photosynthesis at CO2 saturation being distinctly higher in the more vigorous variety SO 4 compared to Seyval blanc. Under the usual light conditions of our in vitro culture (50-60 mu mol quanta . m(-2). s(-1), Fluora) the headspace CO2 concentration ranged from 145 to 155 ppm while at the end of a 10-hour dark period it increased to values >3000 ppm. Rates of photorespiration were high (>50 % of photosynthesis) due to the relative low CO2 concentrations and, presumably, due to elevated O-2 concentrations in the headspace. It is concluded that the often observed low rates of photosynthesis of in vitro plantlets are mainly due to low light intensity and CO2 concentration in the headspace, the latter depending on the low rates of gas diffusion between ambient air and headspace.

1752^2^Heath,J^Kerstiens,G^1997^1^Effects of elevated CO2 on leaf gas exchange in beech and oak at two levels of nutrient supply: Consequences for sensitivity to drought in beech^9^20^1^57-67^^^^^Jan^^^^^6278
243^2715^312^344^361^374^399^417^669^92^at CO2 saturation being distinctly hiA^6277^Beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L,) were grown from seed for two whole seasons at two CO, concentrations (ambient and ambient + 250 mu mol mol(-1)) with two levels of soil nutrient supply, Measurements of net leaf photosynthetic rate (A) and stomatal conductance (g(s)) of well-watered plants were taken over both seasons; a drought treatment was applied in the middle of the second growing season to a separate sample of beech drawn from the same population, The net leaf photosynthetic rate of well-watered plants was stimulated in elevated CO2 by an average of 75% in beech and 33% in oak; the effect continued through both growing seasons at both nutrient levels, There were no interactive effects of CO2 concentration and nutrient level on A or g(s) in beech or oak, Stomatal conductance was reduced in elevated CO2 by an average of 34% in oak, but in beech there were no significant reductions in g(s) except under cloudy conditions (-22% in elevated CO2), During drought, there was no effect of CO2 concentration on g(s) in beech grown with high nutrients, but for beech grown with low nutrients, g(s) was significantly higher in elevated CO2, causing more rapid soil drying, With high nutrient supply, soil drying was more rapid at elevated CO2 due to increased leaf area, It appears that beech may substantially increase whole-plant water consumption in elevated CO2, especially under conditions of high temperature and irradiance when damage due to high evaporative demand is most likely to occur, thereby putting itself at risk during periods of drought.

1753^5^Hungate,BA^Chapin,FS^Zhong,H^Holland,EA^Field,CB^1997^1^Stimulation of grassland nitrogen cycling under carbon dioxide enrichment^2^109^1^149-153^^^^^Jan^^^^^6280
1781^179^20^2716^344^374^433^547^600^672^n beech or oak, Stomatal conductance was reduced in elevated CO2 by an average of 34% in oak, but in beech there were no significant reductions in g(s) except under cloudy conditions (-22% in elevated CO2), During drought, there wA^6279^Nitrogen (N) limits plant growth in many terrestrial ecosystems, potentially constraining terrestrial ecosystem response to elevated CO2. In this study, elevated CO2 stimulated gross N mineralization and plant N uptake in two annual grasslands. In contrast to other studies that have invoked increased C input to soil as the mechanism altering soil N cycling in response to elevated CO2, increased soil moisture, due to decreased plant transpiration in elevated CO2, best explains the changes we observed. This study suggests that atmospheric CO2 concentration may influence ecosystem biogeochemistry through plant control of soil moisture.

1754^3^Iwasaki,I^Kurano,N^Miyachi,S^1996^1^Effects of high-CO2 stress on photosystem II in a green alga, Chlorococcum littorale, which has a tolerance to high CO2^335^36^3^327-332^^^^^Dec^^^^^6282
188^243^2717^493^519^age of 34% in oak, but in beech there were no significant reductions in g(s) except under cloudy conditions (-22% in elevated CO2), During drought, there wA^6281^A green alga, Chlorococcum littorale, is known to have a tolerance to high CO2 conditions. By a sudden change from stir to high CO2, PSII activity of C. littorale decreased temporarily and then recovered, while PSI activity showed the opposite change (Pesheva et al., Plant Cell Physiol, 35 (1994) 379-387). To investigate the efficiency of energy captured by open PSII reaction centers, the quenching of chlorophyll fluorescence of intact cells of C. littorale was analyzed. The data obtained are compared with those obtained with cells of Stichococcus bacillaris which has little tolerance to high CO2. Activities of photosynthetic oxygen evolution of the intact cells and DCIP photoreduction with the crude membrane fraction of C. littorale decreased within 1-2 days, and after about 4 days both activities recovered and/or were elevated to higher levels than those in the air conditions. During this temporal decrease in these activities, the effective quantum yield of PSII also lowered to about 50% of that in air. The values of F- v/F-m transiently decreased indicating photoinhibition in PSII. Such fluorescence quenching parameters recovered after about 4 days. On the other hand, the activities of PSII and other photosynthetic characteristics did not recover in S. bacillaris.

1755^1^Kottke,I^1997^1^Fungal adhesion pad formation and penetration of root cuticle in early stage mycorrhizas of Picea abies and Laccaria amethystea^336^196^1-2^55-64^^^^^^^^^^6284
1079^2718^2719^2720^2721^2722^2723^2724^2725^322^ompared with those obtained with cells of Stichococcus bacillaris which has little tolerance to high CO2. Activities of photosynthetic oxygen evolution of the intact cells and DCIP photoreduction with the crude membrane fraction of C. littorale decreased within 1-2 days, and after about 4 days both activities recovered and/or were elevated to higher levels than those in the air conditions. During this temporal decrease in these activities, the effective quantum yield of PSII also lowered to about 50% of that in A^6283^Primary events during the establishment of the fungus-root symbiosis in ectomycorrhizas are still little understood. No attention has been paid so far to the adhesion of hyphae to the root cuticle and penetration of this barrier, although the importance of the cuticle has been shown for pathogen-plant interactions. Early developmental stages of in vitro mycorrhization of Laccaria amethystea on Picea abies after short periods of incubation in growth chambers under elevated CO2 concentrations were studied by light and transmission electron microscopy. No structural changes in mycorrhization related to elevated CO2 were found, but fine roots and mycorrhizas developed faster. Adhesion pad formation was observed at hyphal tips in contact with the root cuticle. The adhesion pad was connected to the outer cell wall layer of the hypha and reacted positively to the Swift reaction for cysteine rich proteins. Although the reaction cannot be considered as totally specific, findings are discussed in respect to hydrophobins, which have recently been found to be expressed during early steps in ectomycorrhizal development. The root cuticle was dissolved and penetrated by fungal tips of the fingerlike branching mycelium attached to the root surface. The findings are compared with well documented pathogenic fungus- plant interactions at the cuticle. The possibility of restriction of hyphal attack to that part of the cuticle covering cell junctions is discussed.

1756^4^Lawler,IR^Foley,WJ^Woodrow,IE^Cork,SJ^1997^1^The effects of elevated CO2 atmospheres on the nutritional quality of Eucalyptus foliage and its interaction with soil nutrient and light availability^2^109^1^59-68^^^^^Jan^^^^^6286
1086^1661^1725^2726^2727^2728^2729^374^417^57^tips in contact with the root cuticle. The adhesion pad was connected to the outer cell wall layer of the hypha and reacted positively to the Swift reaction for cysteine rich proteins. Although the reaction cannot be considered as totally specific, findings are discussed in respect to hydA^6285^Seedlings of Eucalyptus tereticornis (Smith) were grown under two levels of availability each of CO2 (352 and 793 mu mol mol(-1)), soil nutrients (1/24 and 1/4 Hoagland's solution) and light (full and 30% sunlight). Low soil nutrient availability or high light increased the C:N ratio of leaves, leading to lower leaf nitrogen concentrations, higher leaf specific weights and higher levels of both total phenolics and condensed tannins. These results were consistent with other studies of the effect of environmental resource availability on foliage composition. Similar results were observed when the C:N ratio of leaves was increased under elevated CO2. The changes in leaf chemistry induced by the treatments affected the performance of 4th-instar larvae of Chrysophtharta flaveola (Chapuis) fed on the leaves. Increased C:N ratios of leaves reduced digestive efficiencies and pupal body sizes and increased mortality. Below a threshold nitrogen concentration of approximately 1% dry mass, severe reductions in the performance of larvae were recorded. Such changes may have significant consequences for herbivores of Eucalyptus, particularly in view of projected increases in atmospheric CO2.

1757^2^Leech,RM^Marrison,JL^1996^1^Immunofluorescent quantitation of chloroplast proteins^209^10^6^1169-1175^^^^^Dec^^^^^6288
130^2405^2730^2731^372^948^oncentrations, higher leaf specific weights and higher levels of both total phenolics and condensed tannins. These results were consistent with other studies of the effect of environmental resource availability on foliage composition. Similar results were observed when the C:N ratio of leaves was increased under elevated CO2. The changes in leaf chemistry induced by the treatments affected the performance of 4th-instar larvae of Chrysophtharta flaveola (Chapuis) fed on the leaves. Increased C:N ratios of leaves reduced digestive efficiencies and pupal body sizes and increased mortality. Below a threshold nitrogen concentration of approximately 1% dry mass, severe reductions in thA^6287^Using scanning light microscopy software to detect and measure immunofluorescence in leaf sections Rubisco concentration in situ in chloroplasts has been accurately determined throughout development. The fluorescence measurements were calibrated by comparison with values for Rubisco accumulation obtained from rocket immunoelectrophoresis profiles of soluble protein from isolated cells and from chloroplasts using a purified sample of Rubisco as the standard. It has been shown that in situ immunofluorescence can be used for cytoquantitation of proteins within individual chloroplasts to a sensitivity of 1fg and also for the comparison of the protein levels in adjacent chloroplasts and cells. Several important applications of this new technique are discussed.

1758^4^Markkola,AM^Ohtonen,A^AhonenJonnarth,U^Ohtonen,R^1996^1^Scots pine responses to CO2 enrichment .1. Ectomycorrhizal fungi and soil fauna^35^94^3^309-316^^^^^^^^^^6290
1096^2426^2732^372^377^384^417^680^692^738^ry mass, severe reductions in thA^6289^Ectomycorrhizal Scots pine seedlings were grown in unfertilized forest soil at ambient and double (ca 700 ppm) atmospheric concentrations of CO2. The biomass of seedlings and fungal biomass both in the roots and in the soil and the numbers of certain groups of soil animals were measured under summer conditions and after an artificial winter acclimation period No biomass parameter showed any significant change due to CO2 elevation. Increases were found during the winter acclimation period in total and fine root biomasses, fungal biomass in the soil and total fungal biomass both in the roots and in the soil, while the ratio of needle biomass:fungal biomass and the shoot:root ratio decreased. The N concentration in previous- year needles was lower in the double CO2 environment than with ambient CO2. Enchytraeids almost disappeared in the double CO2 environment during winter acclimation, while the numbers of nematodes increased at the same time in both treatments. (C) 1997 Elsevier Science Ltd.
ons in th1759^3^McKee,IF^Bullimore,JF^Long,SP^1997^1^Will elevated CO2 concentrations protect the yield of wheat from O-3 damage?^9^20^1^77-84^^^^^Jan^^^^^6292
243^2733^312^374^376^435^447^529^73^92^
A^6291^This study investigated the interacting effects of carbon dioxide and ozone concentrations on the growth and yield of spring wheat (Triticum aestivum L, cv, Wembley), Plants were exposed from time of sowing to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO2] at 350 or 700 mu mol mol(-1), and [O-3] at <5 or 60 nmol mol(-1), Records of leaf emergence, leaf duration and tillering were taken throughout leaf development, At harvest, biomass, yield and partitioning were analysed. Our data showed that elevated [CO2] fully protected against the detrimental effect of elevated [O-3] on biomass, but not yield.
 in the double CO2 environment during winter acclimation, while the numbers of nematodes increased at the same time in both treatments. (C) 1997 Elsevier Science Ltd.
ons in th1760^6^Mulholland,BJ^Craigon,J^Black,CR^Colls,JJ^Atherton,J^Landon,G^1997^1^Effects of elevated carbon dioxide and ozone on the growth and yield of spring wheat (Triticum aestivum L)^78^48^306^113-122^^^^^Jan^^^^^6294
1262^1811^1828^243^2733^2734^349^57^673^771^ and ozone concentrations on the growth and yield of spring wheat (Triticum aestivum L, cv, Wembley), Plants were exposed from time of sowing to harvest to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO2] at 350 or 700 mu mol mol(-1), and [O-3] at <5 or 60 nmol mol(-1), Records of leaf emergence, leaf duration and tillering were taken throughout leaf development, At harvest, biomass, yield and partitioning were analysed. Our data showed that elevated [CO2] fully protected against the detrimental effect of elevated [O-3] on biomass, but not yield.
 in the double CO2 environment during winter acclimation, while the numbers of nematodes increased at the same time in both treatments. (C) 1997 Elsevier Science Ltd.
ons in thA^6293^Spring wheat cv. Minaret was grown under three carbon dioxide (CO2) and two ozone (O-3) concentrations from seedling emergence to maturity in open-top chambers. Under elevated CO2 concentrations, the green leaf area index of the main shoot was increased, largely due to an increase in green leaf area duration. Biomass increased linearly in response to increasing CO2 (ambient, 550 and 680 ppm). At anthesis, stem and ear dry weights and plant height were increased by up to 174%, 5% and 9 cm, respectively, and biomass at maturity was 23% greater in the 680 ppm treatment as compared to the ambient control. Grain numbers per spikelet and per ear were increased by 0.2 and 5 grains, respectively, and this, coupled with a higher number of ears bearing tillers, increased grain yield by up to 33%. Exposure to a 7 h daily mean O-3 concentration of 60 ppb induced premature leaf senescence during early vegetative growth (leaves 1-7) under ambient CO2 concentrations. Damage to the main shoot and possible seedling mortality during the first 3 weeks of exposure altered canopy structure and increased the proportion of tillers 1 and 2 which survived to produce ears at maturity was increased; as a result, grain yield was not significantly affected. In contrast to the older leaves, the flag leaf (leaf 8) sustained no visible O-3 damage, and mean grain yield per ear was not affected. Interactions between elevated CO2 and O-3 influenced the severity of visible leaf damage (leaves 1-7), with elevated CO2 apparently protecting against O-3-induced premature senescence during early vegetative growth. The data suggest that the flag leaf of Minaret, a major source of assimilate during grain fill, may be relatively insensitive to O-3 exposure. Possible mechanisms involved in damage and/or recovery are discussed.

1761^2^Nijs,I^Impens,I^1997^1^An analysis of the balance between root and shoot activity in Lolium perenne cv Melvina. Effects of CO2 concentration and air temperature^84^135^1^81-91^^^^^Jan^^^^^6296and possible seedling mo1304^1486^243^312^314^374^376^385^423^738^e altered canopy structure and increased the proportion of tillers 1 and 2 which survived to produce ears at maturity was increased; as a result, grain yield was not significantly affected. In contrast to the older leaves, the flag leaf (leaf 8) sustained no visible O-3 damage, and mean grain yield per ear was not affected. Interactions between elevated CO2 and O-3 influenced the severity of visible leaf damage (leaves 1-7), with elevated CO2 apparently protecting against O-3-induced premature senescence during early vegetative growth. The data suggest that the flag leaf of Minaret, a major source of assimilate during grain fill, may be relatively insensitive to O-3 exposure. Possible mechanisms involved in damage and/or recovery are discussed.

1761^2^Nijs,I^Impens,I^1997^1^An analysis of the balance between root and shoot activity in Lolium perenne cv Melvina. Effects of CO2 concentration and air temperature^84^135^1^81-91^^^^^Jan^^^^^6296and possible seedling moA^6295^This study investigated the mechanisms which control the partitioning between roots and shoots in plants subjected to changes in environment. Two types of analyses were used: firstly, an examination of the cost and revenue associated with investment in different plant parts, and secondly, a test of the principle of functional equilibrium between roots and shoots, i.e. whether root dry matter x root specific activity balances shoot dry matter x shoot specific activity. Measurements were made on individual plants of Lolium perenne in sunlit controlled environments, grown from germination to canopy closure under optimal nitrogen supply. At the final harvest, increased air temperature (+4 degrees C above ambient) reduced whole-plant dry matter by 12% relative to the control, whereas elevated CO2 mole fraction (700 mu mol mol(-1)) led to a 38% gain. The combined treatment yielded an intermediate result (+19%). Plants grown at +4 degrees C maintained balanced activity between roots and shoots throughout the experimental period, irrespective of CO2 concentration. This required enhanced allocation to roots in young plants to compensate for a strong negative effect of higher temperature on root specific activity, which suggests that plants conserve balanced activity by adjusting dry matter partitioning. The extra cost involved with the adjustment at +4 degrees C significantly enhanced the cost:revenue ratio of plant investment. In ambient temperature, the balance between roots and shoots departed from equilibrium, slightly at ambient but substantially at elevated CO2: the plants accumulated excess carbon relative to nitrogen, and this imbalance increased with plant age. At elevated CO2, the cost:revenue ratio increased in young plants but this was later reversed owing to loss of root specific activity, which explains the gradually declining CO2 stimulation with time. The strategies in equilibrating root and shoot functioning observed in the different treatments are discussed in the light of whole plant performance.

1762^1^Overdieck,D^1996^1^CO2 gas exchange and mass production during germination of radish at elevated atmospheric CO2 concentration^292^70^5-6^205-210^^^^^Dec^^^^^6298
130^1404^376^389^417^441^92^ity, which suggests that plants conserve balanced activity by adjusting dry matter partitioning. The extra cost involved with the adjustment at +4 degrees C significantly enhanced the cost:revenue ratio of plant investment. In ambient temperature, the balance between roots and shoots departed from equilibrium, slightly at ambient but substantially at elevated CO2: the plants accumulated excess carbon relative to nitrogen, and this imbalance increased with plant age. At elevated CO2, the cost:revenue ratio increased in young plants but this was later reversed owing to loss of root specific activity, which explains the gradually declining CO2 stimulation with time. The strategies in equilibrating root and shoot functioning observed in the different treatments are discussed in the light of whole plant performancA^6297^The influence of elevated CO2 concentration (similar to 700 mu mol mol(-1)) on dry mass accumulation and CO2 net assimilation of germinating Raphanus sativus L.-seeds was investigated during growth over 10 days at low light during the day (16 h, photosynthetic photon flux density (PPFD: 20-70 mu mol m(-2)s(- 1)) and at darkness (8 h). Investigations at similar to 360 (unchanged ambient air) and at similar to 400 mu mol CO2 mol-L served as controls. At germination and development in a WALZ- mini-cuvette (part of CMS 400) with constant microclimatic conditions (20 degrees C, PPFD during day: 20-60 mu mol m(-2) s(-1), vapor pressure deficit: similar to 0.5 kPa) dry mass decreased by 14% in the course of the experiment without measurable influence of CO2 concentration. In a subsequent experiment with continuous CO2 gas exchange measurements on groups of 10 germinating radishes over 10 days at similar to 360 (n = 6) and at similar to 700 mu mol CO2 mol(-1) (n = 5) and, except for PPFD (70 mu mol m(-2) s(-1)), under unchanged microclimatic conditions no measurable CO2 effect on dark respiration (R(d)) could be found. In light and in both CO2 treatments maximum respiration was reached at day 3 or 4; whereas during darkness its level remained unchanged until the 10(th) day. At 700 mu mol CO2 mol(-1) during the day compensation of respiratory CO2 losses by photosynthetic gains was reached one day earlier than in the control. CO2 net assimilation during the light phase of the 10(th) day was enhanced by the elevated CO2 supply by a factor of 2.2 relative to the control. Results of CO2 gas exchange measurements on groups of 10 germinating radish seeds taken day by day from phytotron chambers with the same microclimatic conditions as before (similar to 400 and similar to 700 mu mol CO2 mol(-1), n = 3/day and CO2 concentration) again showed no CO2 effect on dark respiration; however, a positive effect on CO2 net assimilation clearly occurred once more in light (with an enhancement factor after 10 days of similar to 1.5). The mean dry mass balance - calculated by means of all CO2 gas exchange rates and the C-content [%] of seeds and seedlings of the last experiment - resulted after 10 days in a photosynthetically not yet compensated loss of 8.7% from the starting seed dry mass at 400 mu mol CO2 mol(-1) and of only 3.3% at 700 mu mol CO2 mol(- 1). The reported positive CO2 effect on growth and net production of radish reported in literature could, therefore, be explained at least in the germinating phase by enhanced CO2 net assimilation with unchanging CO2 losses by simultaneous dark respiration.

1763^2^Paul,MJ^Driscoll,SP^1997^1^Sugar repression of photosynthesis: The role of carbohydrates in signalling nitrogen deficiency through source:sink imbalance^9^20^1^110-116^^^^^Jan^^^^^6300
1116^130^1538^2000^360^372^384^448^786^788^on) again showed no CO2 effect on dark respiration; however, a positive effect on CO2 net assimilation clearly occurred once more in light (with an enhancement factor after 10 days of similar to 1.A^6299^The aim of this work was to examine whether carbohydrates are involved in signalling N deficiency through source:sink imbalance. Photosynthetic metabolism in tobacco was studied over 8 d during the withdrawal of N from previously N- sufficient plants in which the source:sink ratio was manipulated by shading leaves on some of the plants, In N- sufficient plants over this timescale, there was a small decline in photosynthetic rate, Rubisco protein and amino acid content, with a larger decrease in carbohydrate content, Withdrawal of N from the growing medium induced a large decrease in the rate of photosynthesis (35% reduction after 8 d under the growing conditions, with a reduction also apparent at high and low measuring CO2), which was caused by a large decrease in the amount of Rubisco protein (62% after 8 d) and Rubisco activity, Higher amounts of hexoses preceded the loss of photosynthetic activity and sucrose and starch accumulation, Reduction of the source:sink ratio by shading prevented the loss of photosynthetic activity and the increase in hexoses and other carbohydrates, These data indicate that the reduction of photosynthesis that accompanies N deficiency in intact plants has the characteristics of sugar repression of photosynthesis observed in model systems, but that the accumulation of hexose prior to the decline in photosynthesis is small, The possibility that sugar repression of photosynthesis under physiological conditions depends more crucially on the C:N status of leaves than the carbohydrate status alone is discussed.

1764^3^Polley,HW^Johnson,HB^Mayeux,HS^1997^1^Leaf physiology, production, water use, and nitrogen dynamics of the grassland invader Acacia smallii at elevated CO2 concentrations^13^17^2^89-96^^^^^Feb^^^^^6302
1298^1514^1783^243^2735^360^376^377^384^92^isco protein (62% after 8 d) and Rubisco activity, Higher amounts of hexoses preceded the loss of photosynthetic activity and sucrose and starch accumulation, Reduction of the source:sink ratio by shading prevented the loss A^6301^Invasion by woody legumes can alter hydrology, nutrient accumulation and cycling, and carbon sequestration on grasslands. The rate and magnitude of these changes are likely to be sensitive to the effects of atmospheric CO2 enrichment on growth and water and nitrogen dynamics of leguminous shrubs. To assess potential effects of increased atmospheric CO2 concentrations on plant growth and acquisition and utilization of water and nitrogen, seedlings of Acacia smallii Isely (huisache) were grown for 13 months at CO2 concentrations of 385 (ambient), 690, and 980 mu mol mol(-1). Seedlings grown at elevated CO2 concentrations exhibited parallel declines in leaf N concentration and photosynthetic capacity; however, at the highest CO2 concentration, biomass production increased more than 2.5-fold as a result of increased leaf photosynthetic rates, leaf area, and N-2 fixation. Measurements of leaf gas exchange and aboveground biomass production and soil water balance indicated that water use efficiency increased in proportion to the increase in atmospheric CO2 concentration. The effects on transpiration of an accompanying decline in leaf conductance were offset by an increase in leaf area, and total water loss was similar across CO2 treatments. Plants grown at elevated CO2 fixed three to four times as much N as plants grown at ambient CO2 concentration. The increase in N-2 fixation resulted from an increase in fixation per unit of nodule mass in the 690 mu mol mol(-1) CO2 treatment and from a large increase in the number and mass of nodules in plants in the 980 mu mol mol(-1) CO2 treatment. Increased symbiotic Nz fixation by woody invaders in response to CO2 enrichment may result in increased N deposition in litterfall, and thus increased productivity on many grasslands.
increased more than 2.5-fold as a result of increased leaf photosynthetic rates, leaf area, and N-2 fixation. Measurements of leaf gas exchange and aboveground biomass production and soil water balance indicated that water use efficiency increase1765^4^Read,JJ^Morgan,JA^Chatterton,NJ^Harrison,PA^1997^1^Gas exchange and carbohydrate and nitrogen concentrations in leaves of Pascopyrum smithii (C-3) and Bonteloua gracilis (C-4) at different carbon dioxide concentrations and temperatures^52^79^2^197-206^^^^^Feb^^^^^6304
243^2736^360^372^417^474^632^739^890^92^wn at ambient CO2 concentration. The increase in N-2 fixation resulted from an increase in fixation per unit of nodule mass in the 690 mu mol mol(-1) CO2 treatment and from a large increase in the number and mass of nodules in plants in the 980 mu mol mol(-1) CO2 treatment. Increased symbiotic Nz fixation by woody invaders in response to CO2 enrichment may result in increased N deposition in litterfall, and thus increased productivity on many grasslands.
increased more than 2.5-fold as a result of increased leaf photosynthetic rates, leaf area, and N-2 fixation. Measurements of leaf gas exchange and aboveground biomass production and soil water balance indicated that water use efficiency increaseA^6303^Pascopyrum smithii (C-3) and Bouteloua gracilis (C-4) are important forage grasses native to the Colorado shortgrass steppe. This study investigated photosynthetic responses of these grasses to long-term CO2 enrichment and temperature in relation to leaf nonstructural carbohydrate (TNC) and [N]. Glasshouse-grown seedlings were transferred to growth chambers and grown for 49 d at two CO2 concentrations (380 and 750 mu mol mol(-1)) al 20 and 35 degrees C, and two additional temperatures (25 and 30 degrees C) at 750 mu mol mol(-1) CO2. Leaf CO2 exchange rate (CER) was measured at a plant's respective growth temperature and at two CO2 concentrations of approx. 380 and 700 mu mol mol(-1). Long-term CO2 enrichment stimulated CER in both species, although the response was greater in the CER P. smithii. Doubling the [CO2] from 380 to 750 mu mol mol(-1) stimulated CER of P. smithii slightly more in plants grown and measured al 30 degrees C compared to plants grown at 20, 25 or 35 degrees C. CO2-enriched plants sometimes exhibited lower CER when compared to ambient-grown controls measured at the same [CO2], indicating photosynthetic acclimation to CO2 growth regime. In P. smithii, such reductions in CER were associated with increases in TNC and specific leaf mass, reductions in leaf [N] and, in one instance, a reduction in leaf conductance compared to controls. In B. gracilis, photosynthetic acclimation was observed more often, but significant changes in leaf metabolite levels from growth at different [CO2] were generally less evident. Temperatures considered optimal for growth (C-3: 20 degrees C; C-4: 35 degrees C) sometimes led to CO2-induced accumulations of TNC in both species, with starch accumulating in the leaves of both species, and fructans accumulating only in P. smithii. Photosynthesis of both species is likely to be enhanced in future CO2-enriched and warmer environments, although responses will sometimes be attenuated by acclimation. (C) 1997 Annals of Botany Company.
5 degrees C. CO2-enriched plants1766^3^Reuveni,J^Gale,J^Zeroni,M^1997^1^Differentiating day from night effects of high ambient [CO2] on the gas exchange and growth of Xanthium strumarium L exposed to salinity stress^52^79^2^191-196^^^^^Feb^^^^^6306
130^1666^2242^243^2737^376^398^417^507^520^ductions in leaf [N] and, in one instance, a reduction in leaf conductance compared to controls. In B. gracilis, photosynthetic acclimation was observed more often, but significant changes in leaf metabolite levels from growth at different [CO2] were generally less evident. Temperatures considered optimal for growth (C-3: 20 degrees C; C-4: 35 degrees C) sometimes led to CO2-induced accumulations of TNC in both species, with starch accumulating in the leaves of both species, and fructans accumulating only in P. smithii. Photosynthesis of both species is likely to be enhanced in future CO2-enriched and warmer environments, although responses will sometimes be attenuated by acclimation. (C) 1997 Annals of Botany Company.
5 degrees C. CO2-enriched plantsA^6305^Sodium chloride, at a concentration of 88 mol m(-3) in half strength Hoagland nutrient solution, increased dry weight per unit area of Xanthium strumarium L. leaves by 19%, and chlorophyll by 45% compared to plants grown without added NaCl at ambient (350 mu mol mol(-1)) CO2 concentration. Photosynthesis, per unit leaf area, was almost unaffected. Even so, over a 4-week period, growth (dry weight increment) was reduced in the salt treatment by 50%. This could be ascribed to a large reduction in leaf area ( >60%) and to an approx. 20% increase in the rate of dark respiration (Rd). Raising ambient [CO2] from zero to 2000 mu mol mol(-1) decreased Rd in both control and salinized plants (by 20% at 1000, and by 50% at 2000 mu mol mol(-1) CO2 concentration) compared to Rd in the absence of ambient CO2. High night-time [CO2] had no significant effect on growth of non-salinized plants, irrespective of day-time ambient [CO2]. Growth reduction caused by salt was reduced from 51% in plants grown in 350 mu mol mol(-1) throughout the day, to 31% in those grown continuously in 900 mu mol mol(-1) [CO2]. The effect of [CO2] at night on salinized plants depended on the daytime CO2 concentration. Under 350 mu mol mol(-1) day-time [CO2], 900 mu mol mol(-1) at night reduced growth over a 4-week period by 9% (P <0.05) and 1700 mu mol mol(-1) reduced it by 14% (P <0.01). However, under 900 mu mol mol(-1) day-time [CO2], 900 vs. 350 mu mol mol(-1) [CO2] at night increased growth by 17% (P <0.01). It is concluded that there is both a functional and an otiose (functionless) component to Rd, which is increased by salt. Under conditions of low photosynthesis (such as here, in the low day-time [CO2] regime) the otiose component is small and high night-time [CO2] partly suppresses functional Rd, thereby reducing salt tolerance. In plants growing under conditions which stimulate photosynthesis (e.g. with increased daytime [CO2]), elevated [CO2] at night suppresses mainly the otiose component of respiration, thus increasing growth. Consequently, in regions of adequate water and sunlight, the predicted further elevation of the world atmospheric [CO2] may increase plant salinity tolerance. (C) 1997 Annals of Botany Company.

1767^3^Righetti,B^Reid,DM^Thorpe,TA^1996^1^Growth and tissue senescence in Prunus avium shoots grown in vitro at different CO2/O-2 ratios^267^32^4^290-294^^^^^Oct-Dec^^^^^6308
1132^2370^2738^2739^2740^312^349^451^962^989^50 mu mol mol(-1) [CO2] at night increased growth by 17% (P <0.01). It is concluded that there is both a functional and an otiose (functionless) component to Rd, which is increased by salt. Under conditions of low photosynthesis (such as here, in the low day-time [CO2] regime) the otiose component is small and high night-time [CO2] partly suppresses functional Rd, thereby reducing salt tolerance. In plants growing under conditions which stimulate photosynthesis (e.g. with increased daytime [CO2]), elevated [CO2] at night suppresses mainly the otiose component of respiration, thus increasing growth. CoA^6307^The rate of metabolism and biosynthetic processes make in vitro cultures very sensitive to environmental changes, and therefore subject to physiological and morphological alterations leading to senescence in the short term. The effects of three different calibrated atmospheric compositions were studied during in vitro culture of Prunus avium shoots. At 0.034% CO2-21% O-2 (vol/vol), which stimulate the natural atmosphere, the highest growth rate and chlorophyll content were recorded. When grown at 0.09% CO2-8% O-2 (vol/vol), a favorable condition for photosynthesis and growth, cultures showed a higher percentage of dry matter and elevated ethylene production, but total chlorophyll was lower. These shoots were also highly lignified and fibrous with red pigmentation along the leaves and stems. At 0% CO2-21% O-2 (vol/vol), in contrast, growth and ethylene formation were inhibited; chlorophyll content was lowest in comparison with the other two environmental conditions, hut regreening of tissues was observed after the first half of the culture period. Senescence symptoms, as indicated by decreased chlorophyll, appeared after about 18 d of culture for tissues grown in CO2-containing atmospheres. These experiments provided evidence that in CO2-enriched cultures biomass production steadily increased even when chlorophyll decreased. A possible role of CO2 in promoting tissue-senescence through activation of photooxidative events and ethylene synthesis is discussed.

1768^7^Robinson,CH^Michelsen,A^Lee,JA^Whitehead,SJ^Callaghan,TV^Press,MC^Jonasson,S^1997^1^Elevated atmospheric CO2 affects decomposition of Festuca vivipara (L) Sm litter and roots in experiments simulating environmental change in two contrasting arctic ecosystems^127^3^1^37-49^^^^^Feb^^^^^6310
1044^137^179^312^57^600^669^750^874^99^tems. At 0% CO2-21% O-2 (vol/vol), in contrast, growth and ethylene formation were inhibited; chlorophyll content was lowest in comparison with the other two environmental conditions, hut regreening of tissues was observA^6309^Mass loss, together with nitrogen and carbon loss, from above- ground material and roots of Festuca vivipara were followed for 13 months in a high Arctic polar semidesert and a low Arctic tree-line dwarf shrub heath. Festuca vivipara for the study was obtained from plants cultivated at two different CO2 concentrations (350 and 500 mu L L(-1)) in controlled environment chambers in the UK. Each of the four resource types (shoots or roots from plants grown in elevated or ambient CO2 concentrations) was subsequently placed in an experiment simulating aspects of environmental change in each Arctic ecosystem. Air, litter and soil temperatures were increased using open-topped polythene tents at both sites, and a 58% increase in summer precipitation was simulated at the high Arctic site. Mass loss was greatest at the low Arctic site, and from the shoot material, rather than the roots. Shoots grown under an elevated CO2 concentration decomposed more slowly at the high Arctic site, and more quickly at the low Arctic one, than shoots grown at ambient CO2. After 13 months, greater amounts of C and N remained in above-ground litter from plants grown under elevated, rather than ambient, CO2 at the polar semi-desert site, although lower amounts of C remained in elevated CO2 litter at the low Arctic ecosystem. In the high Arctic, roots grown in the 500 mu L L(-1) CO2 concentration decomposed significantly more slowly than below-ground material derived from the ambient CO2 chambers. Elevated CO2 concentrations significantly increased the initial C:N ratio, % soluble carbohydrates and alpha-cellulose content, and significantly decreased the initial N content, of the above- ground material compared to that derived from the ambient treatment. Initially, the C:N ratio and percentage N were similar in both sets of roots derived from the two different CO2 treatments, but soluble carbohydrate and or-cellulose concentrations were higher, and percentage lignin lower, in the elevated CO2 treatments. The tent treatments significantly retarded shoot decomposition in both ecosystems, probably because of lower litter bag moisture contents, although the additional precipitation treatment had no effect on mass loss from the above-ground material. The results suggest that neither additional summer precipitation (up to 58%), nor soil temperature increase of 1 degrees C, which may occur by the end of the next century as an effect of a predicted 4 degrees C rise in air temperature, had an appreciable effect on root decomposition in the short term in a high Arctic soil. However, at the low Arctic site, greater root decomposition, and a lower pool of root N remaining, were observed where soil temperature was increased by 2 degrees C in response to a 4 degrees C rise in air temperature. These results suggest that decomposition below-ground in this ecosystem would increase as an effect of predicted climate change. These data also show that there is a difference in the initial results of decomposition processes between the two Arctic ecosystems in response to simulated environmental change.

1769^5^Rudorff,BFT^Mulchi,CL^Lee,EH^Rowland,R^Pausch,R^1996^1^Effects of enhanced O-3 and CO2 enrichment on plant characteristics in wheat and corn^35^94^1^53-60^^^^^^^^^^6312
1279^1364^1962^2374^2733^2741^397^398^435^436^ecipitation (up to 58%), nor soil temperature increase of 1 degrees C, which may occur by the end of the next century as an effect of a predicted 4 degrees C rise in air temperature, had an appreciable effect on root decomposition in the short term in a high Arctic soil. However, at the low Arctic site, greater root decomposition, and a lower pool of root N remaining, were observed where soil temperature was increased by 2 degrees C in response to a 4 degrees C rise in air temperature. These results suggest that decomposition below-ground in this ecosystem would increase as an effect of predicted climate change. These data also show that there is a difference in the initial results of decomposition processes between the two Arctic ecosystems in A^6311^The effects of CO2 enrichment and O-3 induced stress on wheat (Triticum aestivum L.) and corn (Zea mays L.) were studied in field experiments using open-top chambers to simulate the atmospheric concentrations of these two gases that are predicted to occur during the coming century. The experiments were conducted at Beltsville, MD, during 1991 (wheat and corn) and 1992 (wheat). Crops were grown under char coal filtered (CF) air or ambient air +40 nl liter(-1) O-3 (7 h per day, 5 days per week) having ambient CO2 concentration (350 mu l liter(-1) CO2) or +150 mu l liter(-1) CO2 (12 h per day). Averaged over O-3 treatments, the CO2-enriched environment had a positive effect on wheat grain yield (26% in 1991 and 15% in 1992) and dry biomass (15% in 1991 and 9% in 1992). Averaged over CO2 treatments, high O-3 exposure had a negative impact on wheat grain yield (-15% in 1991 and -11% in 1992) and drill biomass (-11% in 1991 and -9% in 1992). Averaged over CO2 treatments, high O-3 exposure decreased corn grain yield by 9%. No significant interactive effects were observed for either crop. The results indicated that CO2 enrichment had a beneficial effect in wheat (C-3 crop) but not in corn (C-4 crop). It is likely that the O-3-induced stress will be diminished under increased atmospheric CO2 concentrations; however, maximal benefits in crop production in wheat in response to CO2 enrichment will not be materialized under concomitant increases in tropospheric O-3 concentration. Copyright (C) 1996 Elsevier Science Ltd.

1770^3^Schenk,U^Jager,HJ^Weigel,HJ^1997^1^The response of perennial ryegrass/white clover swards to elevated atmospheric CO2 concentrations .1. Effects on competition and species composition and interaction with N supply^84^135^1^67-79^^^^^Jan^^^^^6314
1262^1958^1960^229^2742^2743^312^506^507^975^h O-3 exposure had a negative impact on wheat grain yield (-15% in 1991 and -11% in 1992) and drill biomass (-11% in 1991 and -9% in 1992). Averaged over CO2 treatments, high O-3 exposure decreased corn graA^6313^The effects of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at two levels of nitrogen (N) supply (no additional N and 200 kg N ha(-1)) and at season- long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations, in open-top chambers. Stands were cut four times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measured. In addition, plant height of both species at harvest dates and during several regrowth periods was monitored. Results indicate that both species made demand on different resources and profited from growth in a mixed sward. CO2-related yield increase amounted to 16-42% for white clover whereas the effect of high CO2 on ryegrass yield ranged between -33% and +9% depending on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was significantly enhanced by CO2 enrichment at many harvests in both N supply treatments. Without additional N supply, shoot competition for light was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petioles grew longer and ryegrass was shorter at elevated CO2. With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilization treatments, the suppression of ryegrass in mixed swards could only be observed under low N conditions. Generally, the effect of N fertilization on competitive interference between both species was much greater than the effect of CO2 enrichment and it is suggested that the effect of elevated CO2 on the balance of species and the outcome of competition in a grass/clover sward is mainly dependent on the N status.

1771^2^Sicher,RC^Kremer,DF^1996^1^Rubisco activity is altered in a starchless mutant of Nicotiana sylvestris grown in elevated carbon dioxide^173^36^4^385-391^^^^^Dec^^^^^6316
1548^243^2744^344^348^353^360^528^665^competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilizaA^6315^Dry matter and net photosynthesis of a wild type and a starchless mutant NS 458 of Nicotiana sylvestris (Speg. et Comes) were studied after 25 d of CO2 enrichment. Plants were grown from seed in controlled environment chambers and treatments of either ambient (35 Pa) or twice ambient (70 Pa) CO2 were initiated when plants were 3-4 weeks old. Photosynthetic rates measured at 35 and 70 Pa CO2 and at 900 mu mole quanta m(-2) s(-1) were unaffected (P>0.05) by 25 d of CO2 enrichment. However, a CO2-by-genotype interaction was observed indicating that photosynthetic rates of the wild type but not the mutant at 35 Pa CO2 differed in response to CO2 enrichment. Photosynthetic enhancement was greater (P < 0.001) in the wild type than in the mutant when the measurement CO2 was doubled. Total biomass and leaf areas of the mutant and wild type also were unaffected by CO2 enrichment, although specific leaf weight increased 27% and 13% (P<0.001) for the wild type and mutant lines, respectively. Neither chlorophyll nor soluble leaf protein were affected by CO, enrichment. Starch, sucrose, glucose and fructose in wild type and mutant leaf samples were also unaffected by CO2 enrichment. Rubisco protein levels of the wild type and mutant were about 20% lower in elevated compared to ambient CO2-grown plants. Initial and total Rubisco activities of wild type and mutant leaf samples were not significantly different (P>0.05) between CO2 environments. However, initial Rubisco activity was more than 30% lower in mutant than than in wild type samples when results from ambient and elevated CO2-grown plants were combined. Ribulose 1,5- bisphosphate and 3-phosphoglycerate were 280% and 28% greater in the mutant than in the wild type, respectively. These findings suggested that photosynthesis rates of the mutant were limited by Rubisco activity at 35 Pa CO2 and that end product synthesis rates limited photosynthesis of the mutant at 70 Pa CO2.
 and 13% (P<0.001) for the wild type and mutant lines, respectively. Neither chlorophyll 1772^3^Tissue,DT^Megonigal,JP^Thomas,RB^1997^1^Nitrogenase activity and N-2 fixation are stimulated by elevated CO2 in a tropical N-2-fixing tree^2^109^1^28-33^^^^^Jan^^^^^6318
361^376^377^420^421^506^672^704^708^92^mutant were about 20% lower in elevated compared to ambient CO2-grown plants. Initial and total Rubisco activities of wild type and mutant leaf samples were not significantly different (P>0.05) between CO2 environments. However, initial Rubisco activity was more than 30% lower in mutant than than in wild type samples when results from ambient and elevated CO2-grown plants were combined. Ribulose 1,5- bisphosphate and 3-phosphoglycerate were 280% and 28% greater in the mutant than in the wild type, respectively. These findings suggested that photosynthesis rates of the mutant were limited by Rubisco activity at 35 Pa CO2 and that end product synthesis rates limited photosynthesis of the mutant at 70 Pa CO2.
 and 13% (P<0.001) for the wild type and mutant lines, respectively. Neither chlorophyll A^6317^Seeds of Gliricidia sepium, a fast-growing woody legume native to seasonal tropical forests of Central America, were inoculated with N-2-fixing Rhizobium bacteria and grown in environmentally controlled glasshouses for 67-71 days under ambient CO2 (35 Pa) and elevated CO2 (70 Pa) conditions. Seedlings were watered with an N-free, but otherwise complete, nutrient solution such that bacterial N-2 fixation was the only source of N available to the plant. The primary objective of our study was to quantify the effect of CO2 enrichment on the kinetics of photosynthate transport to nodules and determine its subsequent effect on N-2 fixation. Photosynthetic rates and carbon storage in leaves were higher in elevated CO2 plants indicating that more carbon was available for transport to nodules. A (CO2)-C-14 pulse-chase experiment demonstrated that photosynthetically fixed carbon was supplied by leaves to nodules at a faster rate when plants were grown in elevated CO2. Greater rates of carbon supply to nodules did not affect nodule mass per plant, but did increase specific nitrogenase activity (SNA) and total nitrogenase activity (TNA) resulting in greater N-2 fixation. In fact, a 23% increase in the rate of carbon supplied to nodules coincided with a 23% increase in SNA for plants grown in elevated CO2, suggesting a direct correlation between carbon supply and nitrogenase activity. The improvement in plant N status produced much larger plants when grown in elevated CO2. These results suggest that Gliricidia, and possibly other N-2-fixing trees, may show an early and positive growth response to elevated CO2, even in severely N- deficient soils, due to increased nitrogenase activity.

1773^2^VanderKooij,TAW^DeKok,LJ^1996^1^Impact of elevated CO2 on growth and development of Arabidopsis thaliana L^262^36^2^173-184^^^^^^^^^^6320
243^2601^2745^310^312^344^360^374^376^423^y fixed carbon was supplied by leaves to nodules at a faster rate when plants were grown in elevated CO2. Greater rates of carbon supply to nodules dA^6319^After germination, Arabidopsis thaliana L (cv. Landsberg) was grown at 350 mu l l(-1) (control) or 700 mu l l(-1) (elevated) CO2. Total shoot biomass at the end of the vegetative growth period was increased by 56% due to a short transient stimulation of the relative growth rate by elevated CO2 at the onset of the exposure. Thereafter the relative growth rate was comparable for both CO2 levels during the remaining vegetative part of the life cycle (0.42 g g(-1) day(-1)). Flowering architecture was not affected by elevated CO2, but seed production was 51% higher. Starch content of the shoot was substantially increased upon exposure to elevated CO2, while the soluble sugar content remained unaffected. Total nitrogen content, on a dry mass basis, was decreased at elevated CO2 mainly as a result of the increased starch content. Photosynthesis wag stimulated at elevated CO2 and no acclimation of the photosynthesis at elevated CO2 was observed. Even though the stimulation of relative growth rate was only temporary, elevated CO2 resulted in an increased fitness of Arabidopsis thaliana by an increased reproductive output.

1774^4^Vu,JCV^Allen,LH^Boote,KJ^Bowes,G^1997^1^Effects of elevated CO2 and temperature on photosynthesis and Rubisco in rice and soybean^9^20^1^68-76^^^^^Jan^^^^^6322
188^244^310^348^360^377^417^448^562^92^xposure. Thereafter the relative growth rate was comparable for both CO2 levels during the remaining vegetative part of the life cycle (0.42 g g(-1) day(-1)). Flowering architecture was not affected by elevated CO2, but seed production was 51% higher. Starch content of the shoot was substantially increased upon exposure to elevated CO2, while the soluble sugar content remained unaffected. Total nitrogen content, on a dry mass basis, was decreased at elevated CO2 mainly as a result of the increased starch content. Photosynthesis wag stimulated at elevated CO2 and no acclimation of the photosynthesis at elevated CO2 was observed. Even though the stimulation of relative growth rate was only temA^6321^Rice (Oryza sativa L. cv. IR-72) and soybean (Glycine max L. Merr. cv. Bragg), which have been reported to differ in acclimation to elevated CO2, were grown for a season in sunlight at ambient and twice-ambient [CO2], and under daytime temperature regimes ranging from 28 to 40 degrees C. The objectives of the study were to test whether CO2 enrichment could compensate for adverse effects of high growth temperatures on photosynthesis, and whether these two C-3 species differed in this regard. Leaf photosynthetic assimilation rates (A) of both species, when measured at the growth [CO2], were increased by CO2 enrichment, but decreased by supraoptimal temperatures. However, CO2 enrichment more than compensated for the temperature-induced decline in A. For soybean, this CO2 enhancement of A increased in a linear manner by 32-95% with increasing growth temperatures from 28 to 40 degrees C, whereas with rice the degree of enhancement was relatively constant at about 60%, from 32 to 38 degrees C. Both elevated CO2 and temperature exerted coarse control on the Rubisco protein content, but the two species differed in the degree of responsiveness. CO2 enrichment and high growth temperatures reduced the Rubisco content of rice by 22 and 23%, respectively, but only by 8 and 17% for soybean. The maximum degree of Rubisco down-regulation appeared to be limited, as in rice the substantial individual effects of these two variables, when combined, were less than additive. Fine control of Rubisco activation was also influenced by both elevated [CO2] and temperature. In rice, total activity and activation were reduced, but in soybean only activation was lowered. The apparent catalytic turnover rate (K-cat) of rice Rubisco was unaffected by these variables, but in soybean elevated [CO2] and temperature increased the apparent K-cat by 8 and 22%, respectively. Post-sunset declines in Rubisco activities were accelerated by elevated [CO2] in rice, but by high temperature in soybean, suggesting that [CO2] and growth temperature influenced the metabolism of 2-carboxyarabinitol-1-phosphate, and that the effects might be species-specific. The greater capacity of soybean for CO2 enhancement of A at supraoptimal temperatures was probably not due to changes in stomatal conductance, but may be partially attributed to less down- regulation of Rubisco by elevated [CO2] in soybean than in rice. However, unidentified species differences in the temperature optimum for photosynthesis also appeared to be important. The responses of photosynthesis and Rubisco in rice and soybean suggest that among C-3 plants species-specific differences will be encountered as a result of future increases in global [CO2] and air temperatures.

1775^3^Wand,SJE^Midgley,GF^Musil,CF^1996^1^Growth, phenology and reproduction of an arid-environment winter ephemeral Dimorphotheca pluvialis in response to combined increases in CO2 and UV-B radiation^35^94^3^247-254^^^^^^^^^^6324
1208^243^2746^372^376^377^417^568^673^740^bean, suggesting that [CO2] and growth temperature inA^6323^The winter ephemeral Dimorphotheca pluvialis was grown in open- top chambers in ambient or elevated CO2 (350 or 650 mu mol mol(-1)), combined with ambient (2.39 to 7.59 kJ m(-2) d(-1)) or increased (4.94 to 11.13 kJ m(-2) d(-1)) UV-B radiation. Net CO2 assimilation rate and leaf water use efficiency increased in elevated CO2, but increased UV-B did not affect gas exchange. Leaf biomass was greater under increased UV-B, but vegetative biomass was unaffected in elevated CO2. initiation of reproduction was delayed, and proportional investment in reproductive biomass at harvest was reduced in elevated CO2. increased UV-B stimulated reproduction, particularly in ambient CO2, but also in elevated CO2 at a later stage. Changes in reproductive phenology and prolonged development in elevated CO2 during the stressful late season could indirectly be detrimental to reproductive success of D. pluvialis, but stimulation of reproduction by enhanced UV-B may to some extent mitigate this. (C) 1997 Elsevier Science Ltd.

1776^4^Alberto,AMP^Ziska,LH^Cervancia,CR^Manalo,PA^1996^1^The influence of increasing carbon dioxide and temperature on competitive interactions between a C3 crop, rice (Oryza sativa) and a C-4 weed (Echinochloa glabrescens)^92^23^6^795-802^^^^^^^^^^6326
376^409^417^436^57^92^ leaf water use efficiency increased in elevated CO2, but increased UV-B did not affect gas exchange. Leaf biomass was greater under increased UV-B, but vegetative biomass was unaffected in elevated CO2. initiation of reproduction was delayed, and proportional investment in reproductive biomass at harvest was reduced in elevated CO2. increased UV-B stimulated reproduction, particularly in ambient CO2, but also in elevated CO2 at a later stage. Changes in reproductive phenology and prolonged development in elevated CO2 during the stressful late season could indirectly be detrimental to reproductive success of D. pluvialis, but stimulation of reproduction by enhanced UV-B may to some extent mitigate this. (C) 1997 Elsevier Science LtdA^6325^Many of the most troublesome weeds in agricultural systems are C-4 plants. As atmospheric CO2 increases it is conceivable that competitive ability of these weeds could be reduced relative to C-3 crops such as rice. At the International Rice Research Institute (IRRI) in the Philippines, rice (IR72) and one of its associated C-4 weeds, Echinochloa glabrescens, were grown from seeding to maturity using replacement series mixtures (100:0, 75:25, 50:50, 25:75, and 0:100, % rice:%weed) at two different CO2 concentrations (393 and 594 mu L L(-1)) in naturally sunlit glasshouses. Since increasing CO2 may also result in elevated growth temperatures, the response of rice to each CO2 concentration was also examined at day/night temperatures of 27/21 and 37/29 degrees C. At 27/21 degrees C, increasing the CO2 concentration resulted in a significant increase in above ground biomass (+47%) and seed yield (+55%) of rice when averaged over all mixtures. For E. glabrescens, the C-4 species, no significant effect of CO2 concentration on biomass or yield was observed. When grown in mixture, the proportion of rice biomass increased significantly relative to that of the C- 4 weed at all mixtures at elevated CO2. Evaluation of changes in competitiveness (by calculation of plant relative yield (PRY) and replacement series diagrams) of the two species demonstrated that, at elevated CO2, the competitiveness of rice was increased relative to that of E. glabrescens. However, at the higher growth temperature (37/29 degrees C), growth and reproductive stimulation of rice by elevated CO2 was reduced compared to the lower growth temperature. This resulted in a reduction in the proportion of rice:weed biomass present in all mixtures relative to 27/21 degrees C and a greater reduction in PRY in rice relative to E. glabrescens. Data from this experiment suggest that competitiveness could be enhanced in a C-3 crop (rice) relative to a C-4 weed (E. glabrescens) with elevated CO2 alone, but that simultaneous increases in CO2 and temperature could still favour a C-4 species.

1777^4^Brooks,JR^Flanagan,LB^Varney,GT^Ehleringer,JR^1997^1^Vertical gradients in photosynthetic gas exchange characteristics and refixation of respired CO2 within boreal forest canopies^13^17^1^1-12^^^^^Jan^^^^^6328
1234^130^256^2747^2748^361^362^417^431^539^ series diagrams) of the two species demonstrated that, at elevated CO2, the competitiveness of rice was increased relative to that of E. glabrescens. However, at the higher growth temperature (37/29 degrees C), growth and reproductive stimulation of rice by elevated CO2 was reduced compared to the lower growth temperature. This resulted in a reduction in the proportion of rice:weed biomass present in all mixtures relative to 27/21 degrees C and a greater reduction in PRY in rice relative to E. glabrescens. Data from this experiment suggest that competitiveness could be enhanced in a C-3 crop (rice) relative to a C-4 weed (E. glabrescens) with elevated CO2 alone, but that simultaneous increases in CO2 and temperatureA^6327^We compared vertical gradients in leaf gas exchange, CO2 concentrations, and refixation of respired CO2 in stands of Populus tremuloides Michx., Pinus banksiana Lamb. and Picea mariana (Mill.) B.S.P. at the northern and southern boundaries of the central Canadian boreal forest. Midsummer gas exchange rates in Populus tremuloides were over twice those of the two conifer species, and Pinus banksiana rates were greater than Picea mariana rates. Gas exchange differences among the species were attributed to variation in leaf nitrogen concentration. Despite these differences, ratios of intercellular CO2 to ambient CO2 (c(i)/c(a)) were similar among species, indicating a common balance between photosynthesis and stomatal conductance in boreal trees. At night, CO2 concentrations were high and vertically stratified within the canopy, with maximum concentrations near the soil surface. Daytime CO2 gradients were reduced and concentrations throughout the canopy were similar to the CO2 concentration in the well-mixed atmosphere above the canopy space. Photosynthesis had a diurnal pattern opposite to the CO2 profile, with the highest rates of photosynthesis occurring when CO2 concentrations and gradients were lowest. After accounting for this diurnal interaction, we determined that photosynthesizing leaves in the understory experienced greater daily CO2 concentrations than leaves at the top of the canopy. These elevated CO2 concentrations were the result of plant and soil respiration. We estimated that understory leaves in the Picea mariana and Pinus banksiana stands gained approximately 5 to 6% of their carbon from respired CO2.

1778^6^Faria,T^Wilkins,D^Besford,RT^Vaz,M^Pereira,JS^Chaves,MM^1996^1^Growth at elevated CO2 leads to down-regulation of photosynthesis and altered response to high temperature in Quercus suber L seedlings^78^47^304^1755-1761^^^^^Nov^^^^^6330
1121^1247^1347^1584^2083^348^360^493^705^845^ere reduced and concentrations throughout the canopy were similar to the CO2 concentration in the well-miA^6329^The effects of growth at elevated CO2 on the response to high temperatures in terms of carbon assimilation (net photosynthesis, stomatal conductance, amount and activity of Rubisco, and concentrations of total soluble sugars and starch) and of photochemistry (for example, the efficiency of excitation energy captured by open photosystem II reaction centres) were studied in cork oak (Quercus suber L.). Plants grown in elevated CO2 (700 ppm) showed a down-regulation of photosynthesis and had lower amounts and activity of Rubisco than plants grown at ambient CO2 (350 ppm), after 14 months in the greenhouse. At that time plants were subjected to a heat- shock treatment (4 h at 45 degrees C in a chamber with 80% relative humidity and 800-1000 mu mol m(-2) s(-1) photon flux density). Growth in a CO2-enriched atmosphere seems to protect cork oak leaves from the short-term effects of high temperature. Elevated CO2 plants had positive net carbon uptake rates during the heat shock treatment whereas plants grown at ambient CO2 showed negative rates. Moreover, recovery was faster in high CO2-grown plants which, after 30 min at 25 degrees C, exhibited higher net carbon uptake rates and lower decreases in photosynthetic capacity (A(max) as well as in the efficiency of excitation energy captured by open photosystem II reaction centres (F-v/F-m) than plants grown at ambient CO2. The stomata of elevated CO2 plants were also less responsive when exposed to high temperature.

1779^2^Finlayson,SA^Reid,DM^1996^1^The effect of CO2 On ethylene evolution and elongation rate in roots of sunflower (Helianthus annuus) seedlings^37^98^4^875-881^^^^^Dec^^^^^6332
1188^2525^2749^2750^310^312^416^417^451^92^5 degrees C in a chamber with 80% relative humidity and 800-1000 mu mol m(-2) s(-1) photon flux density). Growth in a CO2-enriched atmosphere seems to protect cork oak leaves from the short-term effects of high temperature. Elevated CO2 plants had positive net carbon uptake rates during the heat shock treatment whereas plants grown A^6331^Both carbon dioxide and ethylene can affect the rate of root elongation. Carbon dioxide can also promote ethylene biosynthesis by enhancing the activity of 1-aminocylopropane-1- carboxylic acid (ACC) oxidase. Since the amount of CO2 in the soil air, and in the atmosphere surrounding roots held in enclosed containers, is known to vary widely, we investigated the effects of varying CO2 concentrations on ethylene production by excised and intact sunflower roots (Helianthus annuus L. cv. Dahlgren 131). Seedlings were germinated in an aeroponic system in which the roots hung freely in a chamber and were misted with nutrient solution. This allowed for treatment, manipulation and harvest of undamaged and minimally disturbed roots. While exposure of excised roots to 0.5% CO2 could produce a small increase in ethylene production (compared to roots in ambient CO2), CO2 concentrations of 2% and above always inhibited ethylene evolution. This inhibition of ethylene production by CO2 was attributed to a reduction in the availability of ACC; however, elevated CO2 had no effect on ACC oxidase activity. ACC levels in excised roots were depressed by CO2 at a concentration of 2% (as compared to ambient CO2), but n-malonyl-ACC (MACC) levels were not affected. Treating intact roots with 2% CO2 inhibited elongation by over 50%. Maximum inhibition of elongation occurred 1 h after the CO2 treatment began, but elongation rates returned to untreated values by 6 h. Supplying these same intact roots with 2% CO2 did not alter ethylene evolution. Thus, in excised sunflower roots 2% CO2 treatment reduces ethylene evolution by lowering the availability of ACC. Intact seedlings respond differently in that 2% CO2 does not affect ethylene production in roots. These intact roots also temporarily exhibit a significantly reduced rate of elongation in response to 2% CO2.

1780^2^Gorny,JR^Kader,AA^1996^1^Regulation of ethylene biosynthesis in climacteric apple fruit by elevated CO2 and reduced O-2 atmospheres^259^9^3^311-323^^^^^Dec^^^^^63341068^1678^1864^2077^312^519^owever, elevated CO2 had no effect on ACC oxidase activity. ACC levels in excised roots were depressed by CO2 at a concentration of 2% (as compared to ambient CO2), but n-malonyl-ACC (MACC) levels were not affected. Treating intact roots with 2% CO2 inhibited elongation by over 50%. Maximum inhibition of elongation occurred 1 h after the CO2 treatment began, but elongation rates returned to untreated values by 6 h. Supplying these same intact roots with 2% CO2 did not alter ethylene evolution. Thus, in excised sunflower roots 2% CO2 treatment reduces ethylene evolution by lowering the availability of ACC. Intact seedlings respond differently in that 2% CO2 does not affect ethylene production in roots. These intact roots also temporarily exhibit a significantly reduced rate of elongation in response to 2% CO2.

1780^2^Gorny,JR^Kader,AA^1996^1^Regulation of ethylene biosynthesis in climacteric apple fruit by elevated CO2 and reduced O-2 atmospheres^259^9^3^311-323^^^^^Dec^^^^^6334A^6333^Autocatalytic (System II) C2H4 biosynthesis in climacteric 'Golden Delicious' apples (Malus domestica Borkh) was effectively inhibited at 20 degrees C by atmospheres of 20% CO2-enriched air (17% O-2 + 63% N-2) or 0.25% O-2 (balance N- 2). In vitro 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACC-S) activity of apples held in atmospheres of air + 20% CO2 or 0.25% O-2 was significantly inhibited when compared to apples kept in air, and correlated well with fruit C2H4 production rates. In vivo and in vitro ACC oxidase (ACC-O) activity of fruit held in atmospheres of air, air + 20% CO2 or 0.25% O-2 were similar when the assays were performed under standard assay conditions (i.e., in vivo assay performed in air, in vitro assay performed in air + 6% CO2). However, if the in vivo or in vitro ACC-O enzyme activity assays were performed in an atmosphere of 0.25% O-2, ACC-O catalytic competency and activity were significantly reduced. When the in vivo or in vitro ACC-O enzyme activity assays were performed in an atmosphere of air + 20% CO2, ACC-O enzyme activity was actually stimulated. These data indicate that elevated levels of CO2 do not inhibit ACC-O catalytic competency. Western blot analysis revealed that ACC-O protein abundance was not significantly affected by any of the treatments tested, and only the 0.25% O- 2 atmosphere significantly inhibited ACC-O activity. ACC-S activity was significantly reduced by atmospheres of air + 20% CO2 or 0.25% O-2 but not via direct inhibition of ACC-S catalytic competency.

1781^2^Greaves,AJ^Buwalda,JG^1996^1^Observations of diurnal decline of photosynthetic gas exchange in kiwifruit and the effect of external CO2 concentration^199^24^4^361-369^^^^^Dec^^^^^6336
1007^2072^264^2751^2752^348^665^92^ormed in air + 6% CO2). However, if the in vivo or in vitro ACC-O enzyme activity assays were performed in an atmosphere of 0.25% O-2, ACC-O catalytic competency and activity were significantly reduced. When the in vivo or in vitro ACC-O enzyme activity assays were perfoA^6335^The prevalence of diurnal decline of photosynthesis in field- grown kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa 'Hayward') and the effects of elevated CO2 concentration during decline were studied. During the seasonal period from soon after fruit set to harvest, marked diurnal reductions of photosynthesis rate were found that could not be correlated with levels of photosynthetically active radiation (PAR), temperature, and transpiration. Declines of photosynthesis were observed only on clear days characterised by benign environmental conditions other than sustained irradiance at saturating or near saturating levels. Elevation of CO2 concentration to 200 mu mol/mol above ambient during photosynthesis decline overcame the decline effect, allowing photosynthesis to track irradiance levels throughout the day. Possible mechanisms generating the diurnal decline and the alleviation by elevation of CO2 concentration are discussed.
C-O enzyme activity assays were perfo1782^8^Habash,DZ^Parry,MAJ^Parmar,S^Paul,MJ^Driscoll,S^Knight,J^Gray,JC^Lawlor,DW^1996^1^The regulation of component processes of photosynthesis in transgenic tobacco with decreased phosphoribulokinase activity^91^49^2^159-167^^^^^Aug^^^^^6338
1121^164^2753^348^384^448^493^635^653^989^r fruit set to harvest, marked diurnal reductions of photosynthesis rate were found that could not be correlated with levels of photosynthetically active radiation (PAR), temperature, and transpiration. Declines of photosynthesis were observed only on clear days characterised by benign environmental conditions other than sustained irradiance at saturating or near saturating levels. Elevation of CO2 concentration to 200 mu mol/mol above ambient during photosynthesis decline overcame the decline effect, allowing photosynthesis to track irradiance levels throughout the day. Possible mechanisms generating the diurnal decline and the alleviation by elevation of CO2 concentration are discussed.
C-O enzyme activity assays were perfoA^6337^Tobacco plants (Nicotiana tabacum L.) transformed with an inverted cDNA encoding ribulose 5-phosphate kinase (phosphoribulokinase,PRK;EC 2.7.1.19) were employed to study the in vivo relationship between photosynthetic electron transport and the partitioning of electron transport products to major carbon metabolism sinks under conditions of elevated ATP concentrations and limited ribulose 1,5-bisphosphate (RuBP) regeneration. Simultaneous measurements of room temperature chlorophyll fluorescence and CO2 gas exchange were conducted on intact leaves. Under ambient CO2 concentrations and light intensities above those at which the plants were grown, transformants with only 5% of PRK activity showed 'down- regulation' of PS II activity and electron transport in response to a decrease in net carbon assimilation when compared to wild-type. This was manifested as a decline in the efficiency of PS II electron transport (Phi(PS II)), an increase in dissipation of excess absorbed light in the antennae of PS II and a decline in : total linear electron transport (J(1)), electron transport dedicated to carbon assimilation (J(A)) and electron transport allocated to photorespiration (J(L)). The transformants showed no alteration in the Rubisco specificity factor measured in vitro and calculated in vivo but had a relatively smaller ratio of RuBP oxygenation to carboxylation rates (v(o)/v(c)), due to a higher CO2 concentration at the carboxylation site (C-c). The relationship between Phi(PS II) and Phi(CO2) was similar in transformants and wild-type under photorespiratory conditions demonstrating no change in the intrinsic relationship between PS II function and carbon assimilation, however, a novel result of this study is that this similar relationship occurred at different values of quantum flux, J(1), J(A), J(L) and v(o)/v(c) in the transformant. For both wild-type and transformants, an assessment was made of the possible presence of a third major sink for electron transport products, beside RuBP oxygenation and carboxylation, the data provided no evidence for such a sink.

1783^3^Hattenschwiler,S^Schweingruber,FH^Korner,C^1996^1^Tree ring responses to elevated CO2 and increased N deposition in Picea abies^9^19^12^1369-1378^^^^^Dec^^^^^6340
1998^2401^2754^312^417^56^668^669^778^92^and calculated in vivo but had a relatively smaller ratio of RuBP oxygenation to carboxylation rates (v(o)/v(c)), due to a higher CO2 concentration at the carboxylation site (C-c). The relationship between Phi(PS II) and Phi(CO2) was similar in transformants and wild-type under photorespiratory conditions demonstrating no change in the intrinsic relationship between PS II function and carbon assimilation, however, a novel result of this study is that this similar relationship occurred at different values of quantum flux, J(1), J(A), J(L) and v(o)/v(c) in the transformant. For both wild-type and transformants, an assessment was made of the possible presence of a third major sink for electron transport products, beside RuBP oxygenation and carboxyA^6339^Four- to seven-year-old spruce trees (Picea abies) were exposed to three CO2 concentrations (280, 420 and 560 cm(3) m(-3)) and three rates of wet N deposition (0, 30 and 90 kg ha(-1) year(- 1)) for 3 years in a simulated montane forest climate, Six trees from each of six clones were grown in competition in each of nine 100 x 70 x 36 cm model ecosystems with nutrient-poor natural forest soil, Stem discs were analysed using X-ray densitometry, The radial stem increment was not affected by [CO2] but increased with increasing rates of N deposition, Wood density was increased by [CO2], but decreased by N deposition, Woodstarch concentration increased, and wood nitrogen concentration decreased with increasing [CO2], but neither was affected by N deposition, The lignin concentration in wood was affected by neither [CO2] nor N deposition, Our results suggest that, under natural growth conditions, rising atmospheric [CO2] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition will, and in some regions is probably already doing so, Elevated [CO2], however, will lead to denser wood unless this effect is compensated by massive atmospheric N deposition, It can be speculated that greater wood density under elevated [CO2] may alter the mechanical properties of wood, and higher ratios of C/N and lignin/N in wood grown at elevated [CO2] may affect nutrient cycles of forest ecosystems.

1784^2^Haxeltine,A^Prentice,IC^1996^1^A general model for the light-use efficiency of primary production^43^10^5^551-561^^^^^Oct^^^^^6342
137^1386^2068^256^273^2755^2756^344^372^417^CO2], but decreased by N deposition, Woodstarch concentration increased, and wood nitrogen concentration decreased with increasing [CO2], but neither was affected by N deposition, The lignin concentration in wood was affected by neither [CO2] nor N deposition, Our results suggest that, under natural growth conditions, rising atmospheric [CO2] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition willA^6341^1. Net primary production (NPP) by terrestrial ecosystems appears to be proportional to absorbed photosynthetically active radiation (APAR) on a seasonal and annual basis. This observation has been used in 'diagnostic' models that estimate NPP from remotely sensed vegetation indices. In 'prognostic' process-based models carbon fluxes are more commonly integrated with respect to leaf area index assuming invariant leaf photosynthetic parameters. This approach does not lead to a proportional relationship between NPP and APAR. However, leaf nitrogen content and Rubisco activity are known to vary seasonally and with canopy position, and there is evidence that this variation takes place in such a way as to nearly optimize total canopy net photosynthesis. 2. Using standard formulations for the instantaneous response of leaf net photosynthesis to APAR, we show that the optimized canopy net photosynthesis is proportional to APAR. This theory leads to reasonable values for the maximum (unstressed) light-use efficiency of gross and net primary production of C-3 plants at current ambient CO2, comparable with empirical estimates for agricultural crops and forest plantations. 3. By relating the standard formulations to the Collatz-Farquhar model of photosynthesis, we show that a range of observed physiological responses to temperature and CO2 can be understood as consequences of the optimization. These responses include the CO2 fertilization response and stomatal closure in C-3 plants, the increase of leaf N concentration with decreasing growing season temperature, and the downward acclimation of leaf respiration and N content with increasing ambient CO2. The theory provides a way to integrate diverse experimental observations into a general framework for modelling terrestrial primary production.

1785^1^Hodge,A^1996^1^Impact of elevated CO2 on mycorrhizal associations and implications for plant growth^263^23^4^388-398^^^^^Nov^^^^^6344
2586^2757^377^384^474^545^595^680^685^708^r the maximum (unstressed) light-use effA^6343^The impact of increasing concentrations of atmospheric CO2 upon plant physiology has been widely investigated. Plant, and in particular root, growth is nearly always enhanced as a direct consequence of CO2 enrichment, with C-3 species generally more responsive than C-4 species. Such alterations in plant productivity will have consequence for below-ground processes and increased carbon allocation to the roots may favour symbiotic relationships. This paper discusses the current information available for the consequences of these changes upon mycorrhizal relationships. Generally mycorrhizal plants grown under CO2 enrichment show enhanced phosphorus uptake but nitrogen uptake is unaffected. This increased nutrient uptake is not correlated with increased mycorrhizal colonization of the roots. Similarly root exudation does not increase under CO2 enrichment but qualitative differences have yet to be assessed. However, it is predicted that total rhizodeposition of materials will increase as will litter inputs, although mineral and biochemical alterations to these plant derived inputs may occur. The consequences of such changes within the rhizosphere are discussed and future research priorities identified.

1786^2^Hughes,L^Bazzaz,FA^1997^1^Effect of elevated CO2 on interactions between the western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae) and the common milkweed, Asclepias syriaca^2^109^2^286-290^^^^^Jan^^^^^6346
1142^1997^374^417^489^490^580^628^764^92^current information available for the consequences of these changes upon mycorrhizal relationships. Generally mycorrhizal plants grown under CO2 enrichment show enhanced phosphorus uptake but nitrogen uptake is unaffected. This increased nutrient uptake is not correlated with increased mycorrhizal colonization of the roots. Similarly root exudation does not increase under CO2 enrichment but qualitative differences have yet to be assessed. However, it is predicted that total rhizodeposition of materials will increase as will litter inputsA^6345^We measured the effect of elevated CO2 on populations of the western flower thrips, Frankliniella occidentalis and on the amount of leaf damage inflicted by the thrips to one of its host plants, the common milkweed, Asclepias syriaca. Plants grown at elevated CO2 had significantly greater aboveground biomass and C:N ratios, and significantly reduced percentage nitrogen. The number of thrips per plant was not affected by CO2 treatment, but the density of thrips (numbers per gram aboveground biomass), was significantly reduced at high CO2. Consumption by thrips, expressed as the amount of damaged leaf area per capita, was significantly greater at high CO2, and the amount of leaf area damaged by thrips was increased by 33%. However overall leaf area at elevated CO2 increased by 62%, more than compensating for the increase in thrips consumption. The net outcome was that plants at elevated CO2 had 3.6 times more undamaged leaf area available for photosynthesis than plants at ambient CO2, even though they had only 1.6 times the overall amount of leaf area. This study highlights the need for measuring the effects of herbivory at the whole-plant level and also the importance of taking herbivory into account when predicting plant responses to elevated CO2.

1787^3^Hungate,BA^Canadell,J^Chapin,FS^1996^1^Plant species mediate changes in soil microbial N in response to elevated CO2^11^77^8^2505-2515^^^^^Dec^^^^^6348
1044^2102^2758^312^344^429^56^669^672^92^density of thrips (numbers per gram aboveground biomass), was significantly reduced at high CO2. Consumption by thrips, expressed as the amount of damaged leaf area per capita, was significantly greater at high CO2, and the amount of leaf area damaged by thrips was increased by 33%. However overall leaf area at elevated CO2 increased by 62%, more than compensating for the increase in thrips consumption. The net outcome was that plants at elevated CO2 had 3.6 times more undamaged leaf area available for photosynthesis than plants at ambient CO2, even though they hA^6347^The effect of elevated CO2 on plant-microbial interactions and nitrogen (N) cycling is critical to predicting plant growth responses to elevated CO2, because plant growth is often N- limited. We investigated whether the effects of elevated CO2 on plant-microbial N dynamics differed among six annual plant species: three European grasses that have invaded California grasslands, and one grass and two forbs native to California serpentine grassland. Elevated CO2 altered plant N pools and (NH4+)-N-15 uptake, but the direction and magnitude of the changes were species dependent. The introduced grasses showed increased plant N pools and (NH4+)-N-15 uptake, whereas the native species showed smaller increases or even decreases in plant N pools and N-15(4)+ uptake. Under nutrient enrichment, soil microbial N and (NH4+)-N-15 uptake differed among soils with different plant species, but they were not affected by elevated CO2. At low nutrients, elevated CO2 altered soil microbial N and (NH4+)-N-15 uptake, but the direction and magnitude of the changes were species dependent. The changes in soil microbial N were positively correlated with changes in the plant N pool, suggesting that there was no trade-off in N uptake between plants and microbes. These results also suggest that plant species composition will partly determine the direction of changes in soil N cycling in response to elevated CO2.

1788^4^Kim,HY^Horie,T^Nakagawa,H^Wada,K^1996^1^Effects of elevated CO2 concentration and high temperature on growth and yield of rice^160^65^4^634-643^^^^^Dec^^^^^6350
1528^312^360^cies dependent. The introduced grasses showed increased plant N pools and (NH4+)-N-15 uptake, whereas the native species showed smaller increases or even decreases in plant N pools and N-15(4)+ uptake. Under nutrient enrichment, soil microbial N and (NH4+)-N-15 uptake differed among soils with different plant species, but they were not affected by elevated CO2. At low nutrients, elevated CO2 altered soil microbial N and (NH4+)-N-15 uptake, but the A^6349^Phenological development, biomass production and the related growth characteristics of rice (cv Akihikari) in canopy were measured over the entire growth period under different CO2 concentrations and air temperature regimes in temperature gradient chambers (TGCs), in order to clarify the effects of anticipated global climate change on rice production. The TGC is a plastic tunnel with the dimensions of 26m in length, 2. 05m in width and 1.7m in height in which air was ventilated at varying rates to created a 4 degrees C temperature gradient along its longitudinal axis. Two TGCs were used for this experiment;one was kept at ambient CO2 (congruent to 350 mu LL(-1)) concentration and the other at 690 mu LL(-1) throughout the entire growth period. CO2 x temperature treatmets were applied to potted rice plants displaced in TGC at the density of 20 hills m(-2) in 1991, and on transplanted plants on soil bed in TGC at 25 hills m(-2) in 1992. In both years, a sufficient amount of nutrition was applied in split. The nearly doubled CO2 concentration (690 mu LL(-1)) accelerated phenological development of rice toward heading with more pronounced effects at higher temperatures. The number of days to heading of elevated CO2 plants at 30 degrees C was 11% less than that of ambient CO2 plants. The elevated CO2 concentration remarkably promoted both total and productive tiller numbers, whereas it gave a negligibly small effect on plant height. Also, the elevated CO2 concentration gave minor effects on leaf area index except at the initial growth stage, coinciding with the previous workers' results. The elevated CO2 concentration markedly promoted crop dry matter production, on which temperature appeared to give negligibly small effects. The relative enhancement rate by the doubled CO2 on crop dry weight at maturity was estimated to be 24% as average over the entire temperature range (26 similar to 30 degrees C) in both years. The insensitive temperature response in the enhancement rate was contrary to previous workers' results. This is considered to be due to previous workers' results being based on largely isolated plants where radiation might less limit the growth than in the present experiment in the canopy condition.

1789^4^Kim,HY^Horie,T^Nakagawa,H^Wada,K^1996^1^Effects of elevated CO2 concentration and high temperature on growth and yield of rice .2. The effect on yield and its components of Ahihikari rice^160^65^4^644-651^^^^^Dec^^^^^6352
1528^312^elevated CO2 concentration gave minor effects on leaf area index except at the initial growth stage, coinciding with the previous workers' results. The elevated CO2 concentration markedly promoted crop dry matter production, on which temperature appeared to give negligibly small effects. The relative enhancement rate by the doubled CO2 on crop dry weight at maturity was estimated to be 24% as average over the entire temperature range (26 similar to 30 degrees C) in both years. The insensitive temperature response in the enhancement rate was contrary to previous workers' rA^6351^Yield and its component organs of rice (cv. Akihikari) were examined for populations grown under two different CO2 concentrations (350 and 690 mu LL(-1)) x four temperature regimes in temperature gradient chambers (TGCs) in two cropping seasons of 1991 and 1992. The temperature treatments ranged 27.2 similar to 31.1 degrees C in 1991 and 26.0 similar to 29.3 degrees C in 1992 on average over the entire growth period. The relative yield increases by nearly doubling the CO2 concentration under the lowest temperature conditions were 40% and 22% in 1991 and 1992, respectively. These yield increases were mainly attributable to the increased spikelet number per unit area by elevated CO2, whereas the CO2 effects on ripening percentage and weight of single grain mass were relatively small. The difference in the CO2 enhancement rate in the spikelet number and hence in the yield between the two years was considered to reflect the difference in the nitrogen (N) application rate, as total amounts of N applied were 24 g m(-2) in 1991 and 12 g m(-2) in 1992. With the increase in temperature, yields at ambient and elevated CO2 concentrations decreased drastically with a more pronounced reduction with elevated CO2, resulting in no CO2 enrichment effect on rice yield at higher temperatures. The yield decline at higher temperatures was primarily due to an increase in the number of sterile spikelets and slightly due to the increase in imperfectly ripened grains. The spikelet sterility was most closely related to the daily maximum temperature averaged over the flowering period.

1790^4^Kinney,KK^Lindroth,RL^Jung,SM^Nordheim,EV^1997^1^Effects of CO2 and NO3- availability on deciduous trees: Phytochemistry and insect performance^11^78^1^215-230^^^^^Jan^^^^^6354
1087^1997^229^344^372^374^417^57^690^92^all. The difference in the CO2 enhancement rate in the spikelet number and hence in the yield between the two years was considered to reflect the difference in the nitrogen (N) application rate, as total amounts of N applied werA^6353^Increasing concentrations of atmospheric CO2 will interact with other environmental factors to influence the physiology and ecology of trees. This research evaluated how plant phytochemical responses to enriched atmospheric CO2 are affected by the availability of soil nitrate (NO3-) and how these chemical changes, in turn, alter the performance of a tree-feeding folivore. Seedlings of three deciduous tree species-quaking aspen (Populus tremuloides), red oak (Quercus rubra), and sugar maple (Acer saccharum)-were grown in ambient (355 mu L/L) or elevated (650 mu L/L) CO2 in combination with low (1.25 mmol/L) or high (7.5 mmol/L) soil NO3- availability. After 60 d, foliage was analysed for changes in nutrients and allelochemicals likely to be influenced by the availability of CO2 and NO3-. Penultimate gypsy moth larvae (Lymantria dispar) were reared on foliage (aspen and maple) to determine how performance would be affected by host chemical changes. Using the framework of carbon-nutrient balance (CNB) theory, we tested three hypotheses regarding the impact of CO2 and NO3- availability on plant chemistry and insect performance: (1) nitrogen-based compounds will decrease, and carbon-based compounds will increase in response to elevated CO2 and/or low NO3-; (2) aspen will exhibit the greatest change in C:N ratios, and maple the least; and (3) phytochemical changes will influence gypsy moth performance, with larvae fed aspen being affected more than those fed maple. Concentrations of nitrogen and soluble protein decreased, whereas concentrations of starch, condensed tannins, and ellagitannins increased, in response to elevated CO2 and/or low NO3-. Responses of simple carbohydrates and phenolic glycosides were variable, however, suggesting that foliar accumulations of ''dynamic metabolites'' do not follow the predictions of CNB theory as well as do those of stable end products. With respect to Hypothesis 2, we found that absolute (net) changes in foliar C:N ratios were greatest for aspen and least for oak, whereas relative (proportional) changes were greatest for maple and least for aspen. Thus, Hypothesis 2 was only partially supported by the data. Considering Hypothesis 3, we found that elevated CO2 treatments had little effect on gypsy moth development time, growth rate, or larval mass. Larvae reared on aspen foliage grown under elevated CO2 exhibited increased consumption but decreased conversion efficiencies. Gypsy moth responses to NO3- were strongly host specific: the highest consumption and food digestibility occurred in larvae on high-NO3- aspen, whereas the fastest growth rates occurred in larvae on high-NO3- maple. In short, our results again only partially supported the predicted pattern, They indicate, however, that the magnitude of insect response elicited by resource-mediated shifts in host chemistry will depend on how levels of compounds with specific importance to insect fitness (e.g., phenolic glycosides in aspen) are affected. Overall, we observed relatively few true interactions (i.e,, nonadditive) between carbon and nitrogen availability vis a vis foliar chemistry and insect performance. Tree species, however, frequently interacted with CO2 and/or NO3- availability to affect both sets of parameters. These results suggest that the effects of elevated atmospheric CO2 on terrestrial plant communities will not be homogeneous, but will depend on species composition and soil nutrient availability.

1791^4^Lin,WH^Ziska,LH^Namuco,OS^Bai,K^1997^1^The interaction of high temperature and elevated CO2 on photosynthetic acclimation of single leaves of rice in situ^37^99^1^178-184^^^^^Jan^^^^^6356
312^344^374^376^400^639^In short, our results again only partially supported the predicted pattern, They indicate, however, that the magnitude of insect response elicited by resource-mediated shifts in host chemistry will depend on how levels of compounds with specific importance to insect fitness (e.g., phenolic glycosides in aspen) are affected. Overall, we observed relatively few true interactions (i.e,, nonadditiA^6355^Rice (Oryza sativa L. cv. IR72) was grown at three different CO2 concentrations (ambient, ambient + 200 mu mol mol(-1), ambient + 300 mu mol mol(-1)) at two different growth temperatures (ambient, ambient + 4 degrees C) from sowing to maturity to determine longterm photosynthetic acclimation to elevated CO2 with and without increasing temperature. Single leaves of rice showed a cooperative enhancement of photosynthetic rate with elevated CO2 and temperature during tillering, relative to the elevated CO2 condition alone. However, after flowering, the degree of photosynthetic stimulation by elevated CO2 was reduced for the ambient + 4 degrees C treatment, This increasing insensitivity to CO2 appeared to be accompanied by a reduction in ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco) activity and/or concentration as evidenced by the reduction in the assimilation (A) to internal CO2, C-1) response curve. The reproductive response (e.g. percent filled grains, panicle weight) was reduced at the higher growth temperature and presumably reflects a greater increase in floral sterility. Results indicate that while CO2 and temperature could act synergistically at the biochemical level, the direct effect of temperature on floral development with a subsequent reduction in carbon utilization may change sink strength so as to limit photosynthetic stimulation by elevated CO2, concentration.

1792^3^Lovelock,CE^Kyllo,D^Winter,K^1996^1^Growth responses to vesicular-arbuscular mycorrhizae and elevated CO2 in seedlings of a tropical tree, Beilschmiedia pendula^43^10^5^662-667^^^^^Oct^^^^^6358
2601^2759^2760^310^344^427^669^672^849^ ambient + 4 degrees C treatment, This increasing insensitivity to CO2 appeared to be accompanied by a reduction in ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco) activity and/or concentration as evidenced by the reduction in the assimilation (A) to internal CO2, C-1) response curve. The reproductive response (e.g. percent filled grains, panicle weight) was reduced at the hA^6357^1. Vesicular-arbuscular (VA) mycorrhizae increased relative growth rates (RGR) of the shade-tolerant tropical tree species Beilschmiedia pendula at both ambient and doubled CO2 concentrations. 2. RGR was correlated with the net assimilation rate (NAR) of plants. Within this general correlation, in plants with similar RGR, NAR was decreased in VA-mycorrhizal plants compared with non-mycorrhizal plants. As RGR is the product of NAR and the leaf area ratio (LAR, the ratio of leaf area to plant mass), increases in RGR in VA-mycorrhizal plants were the results of increased LAR. Thus, VA-mycorrhizae increased growth rates of B. pendula by altering the morphology of the seedlings. 3. Under elevated CO2 the amount of fungus within roots increased in VA-mycorrhizal plants compared with those grown under ambient CO2 and this was associated with a greater post-inoculation depression in leaf growth. Post- inoculation depressions in leaf growth and the lower NAR (in plants with similar RGR) of VA-mycorrhizal plants indicate there is increased carbon transfer to soils under elevated CO2.

1793^1^Mathooko,FM^1996^1^Regulation of respiratory metabolism in fruits and vegetables by carbon dioxide^259^9^3^247-264^^^^^Dec^^^^^6360
1085^1558^1861^2177^2761^454^497^655^874^967^ plants. Within this general correlation, in plants with similar RGR, NAR was decreased in VA-mycorrhizal plants compared with non-mycorrhizal plants. As RGR is the product of NAR and the leaf area ratio (LAR, the ratio of leaf area to plant mass), increases in RGR in VA-mycorrhizal plants were the results of increased LAR. Thus, VA-mycorrhizae increased growth rates of B. pendula by altering the morphology of the seedlings. 3. Under elevated CO2 the amount of fungus within roots increased in VA-mycorrhizal plants compared with those grown under ambient CO2 and this was associated with a greater post-inoculation depression in leaf growth. Post- inoculation depressions in leaf growth and the lower NAR (in plants with similar RGR) of VA-mycorrhizal plantA^6359^The respiratory rate of fruits and vegetables can be used as an indicator for designing storage conditions to maximize the longevity of these commodities. One postharvest technique that has been used to prolong the storage life of some of these commodities is the use of a controlled atmosphere. The modulation of respiratory metabolism of such commodities held in controlled atmospheres containing reduced oxygen and/or elevated carbon dioxide levels has been thought of as the primary reason for the beneficial effects on the commodities. However, the mechanism by which elevated carbon dioxide influences the regulation of respiratory metabolism is still obscure and several hypotheses have been proposed for its mode(s) of action. The regulation may be directed towards the glycolytic pathway, the fermentative metabolism, the tricarboxylic acid cycle or the electron transport system, presumably through its influence on the synthesis, degradation, inactivation and/or activation of the respective enzymes. It may also be through the antagonistic effects of carbon dioxide on ethylene action as well as its influence on secondary metabolism through an alteration in cell pH. This article discusses the recent developments on the biochemical and physiological fronts as well as the possible mode(s) of action of elevated carbon dioxide in the regulation of respiratory metabolism in fruits and vegetables.

1794^2^Niklaus,PA^Korner,C^1996^1^Responses of soil microbiota of a late successional alpine grassland to long term CO2 enrichment^206^184^2^219-229^^^^^^^^^^6362
1146^1781^312^344^372^57^738^ carbon dioxide influences the regulation of respiratory metabolism is still obscure and several hypotheses have been proposed for its mode(s) of action. The regulation may be directed towards the glycolytic pathway, the fermentative metabolism, the tricarboxylic acid cycle or the electron transport system, presumably through its influence on the synthesis, degradation, inactivation and/or activation of the respective enzymes. It mA^6361^We investigated microbial responses in a late successional sedge-dominated alpine grassland to four seasons of CO2 enrichment. Part of the plots received fertilizer equivalent to 4.5g N m(-2) a(-1). soil basal respiration (R(mic)), the metabolic quotient for CO2 (qCO(2) = R(mic)/C-mic), microbial C and N (C-mic and N-mic) as well as total soil organic C and N showed no response to CO2 enrichment alone. However, when the CO2 treatment was combined with fertilizer addition R(mic) and qCO(2) were statistically significantly higher under elevated CO2 than under ambient conditions (+57% and +71%, respectively). Fertilizer addition increased microbial N pools by 17%, but this was not influenced by elevated CO2. Microbial C was neither affected by elevated CO2 nor fertilizer. The lack of a CO2-effect in unfertilized plots was surprising in the light of our evidence (based on C balance) that enhanced soil C inputs must have occurred under elevated CO2 regardless of fertilizer treatment. Based on these data and other published work we suggest that microbial responses to elevated CO2 in such stable, late-successional ecosystems are limited by the availability of mineral nutrients and that results obtained with fertile or heavily disturbed substrates are unsuitable to predict future microbial responses to elevated CO2 in natural systems. However, when nutrient limitation is removed (e.g. by wet nitrogen deposition) microbes make use of the additional carbon introduced into the soil system. We believe that the response of natural ecosystems to elevated CO2 must be studied in situ in natural, undisturbed systems.

1795^2^Pachepsky,LB^Acock,B^1996^1^A model 2DLEAF of leaf gas exchange: Development, validation, and ecological application^81^93^1-3^1-18^^^^^16 Dec^^^^^6364
1208^243^348^372^465^543^757^980^ffect in unfertilized plots was surprising in the light of our evidence (based on C balance) that enhanced soil C inputs must have occurred under elevated CO2 regardless of fertilizer treatment. Based on these data anA^6363^A two-dimensional model (2DLEAF) of leaf photosynthesis and transpiration has been developed that explicitly accounts for gas diffusion through the boundary layer and the intercellular space as well as for stomatal regulation. The model has been validated for tomato. It was used to study the effect of stomatal density on photosynthesis and transpiration rate. It has been demonstrated by varying stomatal density in the model that the stomatal density measured on tomato leaves provides the maximal photosynthesis rate for both 300 and 600 mu l l(-1) [CO2]. The transpiration rate varied in direct proportion to stomatal density at all values of stomatal aperture, but transpiration efficiency (photosynthesis rate/transpiration rate) was higher at 600 mu l l(-1) [CO2] with a normal stomatal density than at 300 mu l l(-1) [CO2] with a stomatal density reduced 25%, Such calculations with 2DLEAF can be useful for analysis of contradicting data presented in publications on possible changes in stomatal density in a future high [CO2] atmosphere.

1796^5^Prior,SA^Rogers,HH^Runion,GB^Torbert,HA^Reicosky,DC^1997^1^Carbon dioxide-enriched agroecosystems: Influence of tillage on short-term soil carbon dioxide efflux^204^26^1^244-252^^^^^Jan-Feb^^^^^6366
1262^1298^1510^1617^2762^2763^372^456^534^57^ to study the effect of stomatal density on photosynthesis and transpiration rate. It has been demonstrated by varying stomatal density in the model that the stomatal density measured on tomato leaves provides the maximal photosynthesis rate for both 300 and 600 mu l l(-1) [CO2]. The transpiration rate varied in direct proportion to stomatal density at all values of stomatal aperture, but transpiration efficiency (photosynthesis rate/transpiration rate) was higher at 600 mu l l(-1) [CO2] with a normal stomatal density than at 300 mu l l(-1) [CO2] with a stomatal density reduced 25%, Such calculations with 2DLEAF can be useful for analysis of contradicting data presented in publications on possible changes in stomatal density inA^6365^Increasing atmospheric carbon dioxide (CO2) concentration can increase biomass production that may influence carbon (C) dynamics in terrestrial ecosystems. Soil CO2 efflux as affected by crop residues from high CO2 environments managed under different tillage systems has not been explored. This study examined the effects of tillage systems in a legume {soybean [Glycine max (L.) Merr.]} and nonlegume {grain sorghum [Sorghum bicolor] (L.) Moench.} CO2-enriched agroecosystem on the rates of short-term CO2 evolution from a Blanton loamy sand (loamy siliceous, thermic Grossarenic Paleudults). In the spring of 1993, CO2 efflux observations initiated within 5 s after a tillage event were compared to no-tillage conditions for 8 d in plots where both crop species had been grown in open top field chambers under two CO2 conditions (ambient and twice ambient) for two seasons (1992 and 1993). Added CO2 increased yields, residue, and root biomass; higher percent ground cover was also observed in CO2-enriched plots prior to the tillage treatment. Differences in C/N ratio of the residue may have influenced CO2 efflux rates; C/N ratio was highest for sorghum and was increased by elevated CO2. Efflux patterns were characterized by flushes of CO2 following initial tillage and rainfall events. Species x tillage and CO2 x species interactions were noted on several days and for total CO2 efflux values. Our results suggest that short-term CO2 fluxes may be greater for tilled soybean and for soybean grown under elevated CO2; however, short-term flux rates in the sorghum crop were affected by tillage, but not by CO2 level. These short-term results should be viewed with caution when predicting long-term C turnover in agroecosystems.

1797^2^Roumet,C^Roy,J^1996^1^Prediction of the growth response to elevated CO2: A search for physiological criteria in closely related grass species^84^134^4^615-621^^^^^Dec^^^^^6368
130^2346^243^2764^341^348^417^57^738^740^iomass; higher percent ground cover was also observed in CO2-enriched plots A^6367^Using 11 closely related grass species, we tested the capacity of physiological criteria to predict the growth response to elevated CO2 and to categorize the species with regard to their CO2 response. A growth analysis was conducted under productive conditions both at ambient (350 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) CO2. The relative growth rate stimulation was regressed against each of the growth rate components measured at ambient CO2. Growth response to CO2 was positively correlated with specific leaf area (SLA, the leaf surface area per unit of leaf weight), leaf area ratio (the leaf area per unit of total plant dry weight) and negatively correlated with net assimilation rate and leaf nitrogen concentration, both per unit of leaf area. We suggest that SLA has a predominant role in these relationships. Different hypotheses are proposed and discussed in order to explain why species with low SLA are less responsive to elevated CO2. Neither biomass allocation, relative growth rate, shoot or root specific activities per unit of mass, nor chemical composition were significantly correlated with growth response to CO2. The four predictive criteria mentioned above coherently differentiate the five wild annual species (higher SLA, stronger growth response to CO2) from the four wild perennials. The two perennial crop species, with the highest SLA, were more responsive than the wild species.

1798^5^Schwanz,P^Kimball,BA^Idso,SB^Hendrix,DL^Polle,A^1996^1^Antioxidants in sun and shade leaves of sour orange trees (Citrus aurantium) after long-term acclimation to elevated CO2^78^47^305^1941-1950^^^^^Dec^^^^^6370
1064^1633^1676^1998^2173^2473^2765^2766^2767^364^elated with net assimilation rate and leaf nitrogen concentration, both per unit of leaf area. We suggest that SLA has a predominant role in these relationships. Different hypotheses are proposed and discussed in order to explain why species with low SLA are less responsive to elevated CO2. Neither biomass allocation, relative growth rate, shootA^6369^Antioxidative systems and the contents of pigments, malondialdehyde, soluble protein, and carbohydrate were investigated in sun- and shade-acclimated leaves of sour orange (Citrus aurantium) trees that had been grown for 7.5 years under ambient and elevated (+300 mu mol mol(-1)) atmospheric CO2 concentrations. Sun-acclimated leaves contained higher ascorbate, glutathione and soluble carbohydrate contents and higher catalase activities than shade-acclimated leaves. The activities of superoxide dismutases, which belonged to the family of Cu/Zn-isozymes, were similar in sun- and shade- acclimated leaves and decreased in response to enhanced CO2. In shade-acclimated leaves, none of the other parameters studied was affected by elevated CO2. In sun-acclimated leaves elevated CO2 caused increases in carbohydrate and ascorbate contents. There was no evidence for enhanced lipid peroxidation as assessed from the determination of the malondialdehyde contents under either conditions.
 relative growth rate, shoot1799^2^Slafer,GA^Rawson,HM^1997^1^CO2 effects on phasic development, leaf number and rate of leaf appearance in wheat^52^79^1^75-81^^^^^Jan^^^^^6372
1173^130^2597^2768^341^344^372^435^724^92^tium) trees that had been grown for 7.5 years under ambient and elevated (+300 mu mol mol(-1)) atmospheric CO2 concentrations. Sun-acclimated leaves contained higher ascorbate, glutathione and soluble carbohydrate contents and higher catalase activities than shade-acclimated leaves. The activities of superoxide dismutases, which belonged to the family of Cu/Zn-isozymes, were similar in sun- and shade- acclimated leaves and decreased in response to enhanced CO2. In shade-acclimated leaves, none of the other parameters studied was affected by elevated CO2. In sun-acclimated leaves elevated CO2 caused increases in carbohydrate and ascorbate contents. There was no evidence for enhanced lipid peroxidation as assessed from the determination of the malondialdehyde contents under either conditions.
 relative growth rate, shootA^6371^It has been predicted that the concentration of CO2 in the air could double during the 21st century. Though it is recognized that CO2-doubling could increase yield through its effects on plant photosynthesis and stomatal behaviour, it is unclear whether CO2-doubling will change phasic development in wheat. A phytotron study was conducted with two contrasting cultivars of wheat, Condor (spring) and Cappelle Desprez (winter), to determine whether development is affected by a season-long exposure to 360 and 720 ppmv CO2. Plants were vernalized for 50 d (8/4 degrees C, s h photoperiod) before their exposure to the CO2 treatments. There were significant differences between cultivars in the duration of different phenophases as well as in the final number of leaves. However, CO2 concentration had no effect in either cultivar on the duration of the early developmental phase to terminal spikelet initiation, or on the final number of leaves, though CO2-doubling did slightly increase the later phase from terminal spikelet initiation to heading in Cappelle Desprez. Condor and Cappelle Desprez also differed markedly in the dynamics of leaf appearance. While the former had a constant rate of leaf appearance throughout development, the latter had a fast rate initially (between leaves 1 and 7), similar to that of Condor, which was followed by a slower rate after the appearance of leaf 7. Overall, CO2- doubling did not significantly affect the rates of leaf appearance nor the shape of the relationship. Phyllochron for the first seven leaves was the same for both CO2 concentrations. However, the change in phyllochron associated with CO2-doubling for leaves 7-12 in Cappelle Desprez, although quite small (4%), accounts for part of the slightly increased duration of the phase from terminal spikelet initiation to heading under high CO2 concentration in that cultivar. We conclude that CO2 concentration does not influence development in wheat to a degree relevant to agronomy. (C) 1997 Annals of Botany Company
hase from termina1800^2^Thornley,JHM^Cannell,MGR^1996^1^Temperate forest responses to carbon dioxide, temperature and nitrogen: A model analysis^9^19^12^1331-1348^^^^^Dec^^^^^6374
137^2769^372^545^605^749^751^857^890^975^ut development, the latter had a fast rate initially (between leaves 1 and 7), similar to that of Condor, which was followed by a slower rate after the appearance of leaf 7. Overall, CO2- doubling did not significantly affect the rates of leaf appearance nor the shape of the relationship. Phyllochron for the first seven leaves was the same for both CO2 concentrations. However, the change in phyllochron associated with CO2-doubling for leaves 7-12 in Cappelle Desprez, although quite small (4%), accounts for part of the slightly increased duration of the phase from terminal spikelet initiation to heading under high CO2 concentration in that cultivar. We conclude that CO2 concentration does not influence development in wheat to a degree relevant to agronomy. (C) 1997 Annals of Botany Company
hase from terminaA^6373^The ITE Edinburgh Forest Model, which describes diurnal and seasonal changes in the pools and fluxes of C, N and water in a fully coupled forest-soil system, was parametrized to simulate a managed conifer plantation in upland Britain, The model was used to examine (i) the transient effects on forest growth of an IS92a scenario of increasing [CO2] and temperature over two future rotations, and (ii) the equilibrium (sustainable) effects of all combinations of increases in [CO2] from 350 to 550 and 750 mu mol mol(-1), mean annual temperature from 7.5 to 8.5 and 9.5 degrees C and annual inputs of 20 or 40 kg N ha(- 1), Changes in underlying processes represented in the model were then used to explain the responses, Eight conclusions were supported by the model for this forest type and climate. (1) Increasing temperatures above 3 degrees C alone may cause forest decline owing to water stress. (2) Elevated [CO2] can protect trees from water stress that they may otherwise suffer in response to increased temperature. (3) In N-limiting conditions, elevated [CO2] can increase allocation to roots with little increase in leaf area, whereas in N-rich conditions elevated [CO2] may not increase allocation to roots and generally increases leaf area. (4) Elevated [CO2] can decrease water use by forests in N-limited conditions and increase water use in N-rich conditions. (5) Elevated [CO2] can increase forest productivity even in N-limiting conditions owing to increased N acquisition and use efficiency. (6) Rising temperatures (along with rising [CO2]) may increase or decrease forest productivity depending on the supply of N and changes in water stress. (7) Gaseous losses of N from the soil can increase or decrease in response to elevated [CO2] and temperature. (8) Projected increases in [CO2] and temperature (IS92a) are likely to increase net ecosystem productivity and hence C sequestration in temperate forests.
evated [CO2] can protect trees from water stress that they may otherwise suffer in response to increased temp1801^3^Wand,SJE^Midgley,GF^Musil,CF^1996^1^Physiological and growth responses of two African species, Acacia karroo and Themeda triandra, to combined increases in CO2 and UV-B radiation^37^98^4^882-890^^^^^Dec^^^^^6376
1030^1206^1376^2162^312^344^372^376^421^685^rease water use by forests in N-limited conditions and increase water use in N-rich conditions. (5) Elevated [CO2] can increase forest productivity even in N-limiting conditions owing to increased N acquisition and use efficiency. (6) Rising temperatures (along with rising [CO2]) may increase or decrease forest productivity depending on the supply of N and changes in water stress. (7) Gaseous losses of N from the soil can increase or decrease in response to elevated [CO2] and temperature. (8) Projected increases in [CO2] and temperature (IS92a) are likely to increase net ecosystem productivity and hence C sequestration in temperate forests.
evated [CO2] can protect trees from water stress that they may otherwise suffer in response to increased tempA^6375^The interactive effects of increased carbon dioxide (CO2) concentration and ultraviolet-B (UV-B, 280-320 nm) radiation on Acacia karroo Hayne, a C-3 tree, and Themeda triandra Forsk., a C-4 grass, were investigated. We tested the hypothesis that A. karroo would show greater CO2-induced growth stimulation than T. triandra, which would partially explain current encroachment of A. karroo into C-4 grasslands, but that increased UV-B could mitigate this advantage. Seedlings were grown in open-top chambers in a greenhouse in ambient (360 mu mol mol(-1)) and elevated (650 mu mol mol(-1)) CO2, combined with ambient (1.56 to 8.66 kJ m(-2) day(-1)) or increased (2.22 to 11.93 kJ m(-2) day(-1)) biologically effective (weighted) UV-B irradiances. After 30 weeks, elevated CO2 had no effect on biomass of A. karroo, despite increased net CO2 assimilation rates. Interaction between UV-B and CO2 on stomatal conductance was found, with conductances decreasing only where elevated CO2 and UV-B were supplied separately. Increases in water use efficiencies, foliar starch concentrations, root nodule numbers and total nodule mass were measured in elevated CO2. Elevated UV-B caused only an increase in foliar carbon concentrations. In T. triandra, net CO2 assimilation rates were unaffected in elevated CO2, but stomatal conductances and foliar nitrogen concentrations decreased, and water use efficiencies increased. Biomass of all vegetative fractions, particularly leaf sheaths, was increased in elevated CO2, and was accompanied by increased leaf blade lengths and individual leaf and leaf sheath masses. However, tiller numbers were reduced in elevated CO2. Significantly moderating effects of elevated UV-B were apparent only in individual masses of leaf blades and sheaths, and in total sheath and shoot biomass. The direct CO2-induced growth responses of the species therefore do not support the hypothesis of CO2-driven woody encroachment of C-4 grasslands. Rather, differential changes in resource use efficiency between grass and woody species, or morphological responses of grass species, could alter the competitive balance. Increased UV-B radiation is unlikely to substantially alter the CO2 response of these species.

1802^1^Wolf,J^1996^1^Effects of nutrient (NPK) supply on faba bean response to elevated atmospheric CO2^179^44^3^163-178^^^^^Nov^^^^^6378
179^312^376^542^57^92^reased, and water use efficiencies increased. Biomass of all vegetative fractions, particularly leaf sheaths, was increased in elevated CO2, and was accompanied by increased leaf blade lengths and individual leaf and leaf sheath masses. However, tiller numbers were reduced in elevated CO2. Significantly moderating effects of elevated UV-B were apparent only in individual masses of leaf blades and sheaths, and in total sheath and shoot biomass. The direct CO2-induced growth responses of the species therefore do not support the hypothesis of CO2-driven woody encroachment of C-4 grasslands. Rather, differential changes in resource use efficiency between grass and woodA^6377^The effects of increased atmospheric CO2 on crop growth and dry matter allocation may change if nutrient supply becomes insufficient for maximal growth. Increased atmospheric CO2 may also cause changes in maximum dilution of nutrients in plant tissue and hence, in the minimum nutrient concentration levels and the maximum yield-nutrient uptake ratios of crops. To study these effects for faba bean, pot experiments have been carried out in two glass houses at ambient and doubled CO2 concentration. Bean plants were grown at different supplies of N, P or K. Doubling of atmospheric CO2 resulted in a strong increase (+100%) in total yield. This CO2 effect disappeared rapidly with increasing nitrogen, phosphorus or potassium shortage. Doubling of atmospheric CO2 resulted in no change in minimum nitrogen concentration and a nil to slight decrease in minimum phosphorus concentration in crop residues. Nutrient requirements to attain a certain yield level might change with a future increase in atmospheric CO2. However, such conclusions cannot yet be drawn because nutrient concentrations in seeds were not available.

1803^1^Wolf,J^1996^1^Effects of nutrient supply (NPK) on spring wheat response to elevated atmospheric CO2^206^185^1^113-123^^^^^^^^^^6380
230^312^376^542^57^ce, in the minimum nutrient concentration levels and the maximum yield-nutrient uptake ratios of crops. To study these effects for faba bean, pot experiments have been carried out in two glass houses at ambient and doubled CO2 concentration. Bean plants were grown at different supplies of N, P or K. Doubling of atmospheric CO2 resulted in a strong increase (+100%) in total yield. This CO2 effect disappeared rapidly with increasing nitrogen, phosphorus or potassium shortage. Doubling of atmospheric CO2 resulted in no change in minimum nitrogen concentration and a nil to slight decrease in minimum phosphorus concentration in crop residues. Nutrient requirements to attain a certain yield level might change with a future increase in atmospheric CO2. HoA^6379^The effects of increased atmospheric CO2 on crop growth and dry matter allocation may change if nutrient supply becomes insufficient for maximal growth. Increased atmospheric CO2 may also cause changes in minimum nutrient concentration in plant tissue and hence in the nutrient use efficiency or yield- nutrient uptake ratios of crops. To study these effects for spring wheat, pot experiments have been carried out in two glass houses at ambient and doubled CO2 concentration. Wheat plants were grown at different supplies of N, P or K. Doubling of ambient CO2 resulted in a large increase in total biomass (+70%) and grain yield when the nutrient supply was optimum. With strong N and K limitation this CO2 effect was about halved and with strong P limitation it became almost nil. Doubling of ambient CO2 resulted in a 10% lower minimum N concentration in plant tissue and in no change in the minimum P concentration.
ents to attain a certain yield level might change with a future increase in atmospheric CO2. Ho1804^2^Diaz,S^Cabido,M^1997^1^Plant functional types and ecosystem function in relation to global change^42^8^4^463-474^^^^^Sep^^^^^6382
1019^1721^268^2695^2770^332^349^374^673^778^CO2 may also cause changes in minimum nutrient concentration in plant tissue and hence in the nutrient use efficiency or yield- nutrient uptake ratios of crops. To study these effects for spring wheat, pot experiments have been carried out in two glass houses at ambient and doubled CO2 concentration. Wheat plants were grown at different supplies of N, P or K. Doubling of ambient CO2 resulted in a large increase in total biomass (+70%) and grain yield when the nutrient supply was optimum. With strong N and K limitation this CO2 effect was about halved and with strong P limitation it became almost nil. Doubling of ambient CO2 resulted in a 10% lower minimum N concentration in plant tissue and in no change in the minimum P concentration.
ents to attain a certain yield level might change with a future increase in atmospheric CO2. HoA^6381^Plant functional types (PFTs) bridge the gap between plant physiology and community and ecosystem processes, thus providing a powerful tool in climate change research. We aimed at identifying PFTs within the flora of central-western Argentina, and to explore their possible consequences for ecosystem function. We analyzed 24 vegetative and regenerative traits of the 100 most abundant species along a steep climatic gradient. Based on plant traits and standard multivariate techniques, we identified eight PFTs. Our results confirmed, over a wide range of climatic conditions, the occurrence of broad recurrent patterns of association among plant traits reported for other floras; namely trade-offs between high investment in photosynthesis and growth on the one hand, and preferential allocation to storage and defence on the other. Regenerative traits were only partially coupled with vegetative traits. Using easily-measured plant traits and individual species cover in 63 sites, we predicted main community- ecosystem processes along the regional gradient. We hypothesized likely impacts of global climatic change on PFTs and ecosystems ill situ, and analysed their probabilities of migrating in response to changing climatic conditions. Finally, we discuss the advantages and limitations of this kind of approach in predicting changes in plant distribution and in ecosystem processes over the next century.

1805^2^Glenn,DM^Welker,WV^1997^1^Effects of rhizosphere carbon dioxide on the nutrition and growth of peach trees^170^32^7^1197-1199^^^^^Dec^^^^^6384
1020^244^310^361^374^407^416^417^456^977^ccurrence of broad recurrent patterns of association among plant traits reported for other floras; namely trade-offs between high investment in photosynthesis and growth on the one hand, and preferential allocation to storage and defence on the other. Regenerative traits were only partially coupled with vegetative traits. Using easily-measured plant traits and individual species cover in 63 sites, we predicted main community- ecoA^6383^Our objectives in this study were to measure the effects of low levels of root system carbon dioxide on peach tree growth (Prunus persica L. Batsch) and nutrient uptake. Using soil and hydroponic systems, we found that increased root CO2: 1) increased root growth without increasing shoot growth, 2) increased leaf P concentration, 3) decreased leaf N concentration, and 4) reduced water use relative to air injection or no treatment.

1806^4^Ning,B^Kubo,Y^Inaba,A^Nakamura,R^1997^1^Physiological responses of Chinese pear 'Yali' fruit to CO2- enriched and/or O-2-reduced atmospheres^180^66^3-4^613-620^^^^^Dec^^^^^6386
1068^560^874^n among plant traits reported for other floras; namely trade-offs between high investment in photosynthesis and growth on the one hand, and preferential allocation to storage and defence on the other. Regenerative traits were only partially coupled with vegetative traits. Using easily-measured plant traits and individual species cover in 63 sites, we predicted main community- ecoA^6385^Respiration and ethylene production rates of Chinese pear 'Yali' fruit (Pyrus ussuriensis Maxim. var. sinensis Kikuchi) stored in CO2-enriched and/or O-2-reduced atmospheres. In addition, several types of polyethylene film packaging were also applied to the long-term storage of 'Yali' fruit. 1. Oxygen uptake and ethylene production in 'Yali' fruit at 20 degrees C decreased with increasing CO2 concentration up to 40%. Ethylene production under 60% CO2 was markedly inhibited, whereas O-2 uptake was promoted; a physiological disorder in the flesh developed. 2. Under the same storage condition, oxygen uptake and ethylene production consistently decreased with decreasing O-2 concentration. However, when O-2 was decreased to less than 5%, CO2 output exceeded O-2 uptake, suggesting that anaerobic respiration was occurring. 3. Respiration was inhibited in fruit kept at 10 or 20 degrees C under 5% CO2 + 3% O-2 during the first 4 days of storage and then increased suddenly thereafter accompanied by the development of a physiological disorder. 4. The storage life of the fruit packed in a film with soda lime at 10 degrees C, in which O-2 became to about 8%, was prolonged by about a month, as compared to that of those packed in a perforated bag. The gas concentration higher than 5% CO2 and/or lower than 5% O-2 within a plastic bag caused an accumulation of ethanol and the development of disorder in flesh, thus shortening storage life of fruit. Our results suggest that 'Yali' fruit is sensitive to both CO2-enriched and O-2-reduced atmospheres, and that 2% CO2 and 8% O-2 are about optimal for its long-term storage.

1807^2^Papadopoulos,AP^Hao,XM^1997^1^Effects of three greenhouse cover materials on tomato growth, productivity, and energy use^165^70^2-3^165-178^^^^^Jul^^^^^6388
1673^2771^349^434^607^874^923^respiration was occurring. 3. Respiration was inhibited in fruit kept at 10 or 20 degrees C under 5% CO2 + 3% O-2 during the first 4 days of storage and then increased suddenly thereafter accompanied by the developmA^6387^Effects of single-layered glass (glass), double inflated polyethylene film (D-poly), and rigid-twin wall acrylic panels (acrylic), as greenhouse covers on tomato (Lycopersicon esculentum Mill) growth, productivity and energy use were investigated over two spring seasons in 1993 and 1994. There was no significant difference in early marketable yield (harvested until April 30) between the D-poly and glass houses. Early marketable yield in the acrylic houses was similar to that in the glass houses, but higher than that in the D-poly houses in 1994. Mid-season yield in the D-poly houses was lower than in the glass houses. Final marketable yield in the D-poly and acrylic houses was similar to that in the glass houses. Fruit size during the early and mid-season in the D-poly houses was smaller than in the glass or acrylic houses. This reduction in fruit size shifted 6-12% of grade #1 fruit from extra large to large. Fruit size in the glass and acrylic houses was similar. In 1993, there was a higher BER (blossom-end rot) incidence in the glass houses than in D-poly or acrylic houses, but a higher percentage of grade #1 fruit in the D-poly houses than in the glass or acrylic houses. The D-poly and acrylic houses saved 30% in heating energy compared to the glass houses. (C) 1997 Elsevier Science B.V.

1808^1^Idso,SB^1997^1^The poor man's biosphere, including simple techniques for conducting CO2 enrichment and depletion experiments on aquatic and terrestrial plants^173^38^1^15-38^^^^^Jul^^^^^6390
130^344^92^but higher than that in the D-poly houses in 1994. Mid-season yield in the D-poly houses was lower than in the glass houses. Final marketable yield in the D-poly and acrylic houses was similar to that in the glass houses. Fruit size during the early and mid-season in the D-poly houses was smaller than in the glass or acrylic houses. This reduction in fruit size shifted 6-12% of grade #1 fruit from extra large to large. Fruit size in the glass and acrylic houses was similar. In 1993, there was a higher BER (bloA^6389^This paper reports the results of a 3-year experimental program designed to develop an inexpensive, low-technology approach for conducting atmospheric CO2 enrichment and depletion studies of aquatic and terrestrial plants. It begins by demonstrating the effectiveness of a number of simple techniques for creating a wide range of sub-and supra-ambient atmospheric CO2 concentrations in a set of low-cost experimental enclosures. It then describes the utilization of this approach in a variety of experiments that lead to the derivation of CO2-growth response relationships for a common terrestrial plant and for both a submerged and a floating aquatic species. Finally, it provides a description of a simple procedure for obtaining accurate assessments of atmospheric CO, concentrations in such experiments. (C) 1997 Elsevier Science B.V.

1809^2^Santruckova,H^Simek,M^1997^1^Effect of soil CO2 concentration on microbial biomass^263^25^3^269-273^^^^^Sep^^^^^6392
2772^2773^310^312^1993, there was a higher BER (bloA^6391^The effect of increasing soil CO2 concentration was studied in six different soils. The soils were incubated in ambient air (0.05 vol.% CO2) or in air enriched with CO2 (up to 5.0 vol.% CO2). Carbon dioxide evolution, microbial biomass, growth or death rate quotients and glucose decay rate were measured at 6, 12 and 24 h of CO2 exposure. The decrease in soil respiration ranged from 7% to 78% and was followed by a decrease in microbial biomass by 10-60% in most cases. High CO2 treatments did not affect glucose decay rate but the portion of C-gluc mineralized to CO2 was lowered and a larger portion of C-gluc remained in soils. This carbon was not utilized by soil microorganisms.

1810^3^VanHenten,EJ^Bontsema,J^VanStraten,G^1997^1^Improving the efficiency of greenhouse climate control: an optimal control approach^179^45^1^109-125^^^^^Jul^^^^^6394
2774^2775^2776^349^662^ct of soil CO2 concentration on microbial biomass^263^25^3^269-273^^^^^Sep^^^^^6392
2772^2773^310^312^1993, there was a higher BER (bloA^6393^In this paper a method to improve the efficiency of greenhouse climate control is described. This method is based on the framework of optimal control theory. By exploiting a dynamic model of the greenhouse crop production process, information of the auction price, the operating costs of the climate conditioning equipment and the outdoor climate conditions, the optimal greenhouse climate control scheme balances on a purely objective basis costs against revenues of operating the climate conditioning equipment. Though optimal control of greenhouse climate has received considerable attention in the literature, until now little evidence supported by experimental work has been reported as to the possible improvement in efficiency which can be realised using this approach during a whole growing period. This paper reports a first exploration of this matter for a lettuce crop. In a greenhouse experiment the behaviour of conventional greenhouse climate control supervised by the grower was measured. Then, in simulation experiments, optimal control strategies were calculated for the same conditions (outdoor climate, auction price, energy price). The results obtained support the conclusion that a considerable improvement in the efficiency of greenhouse climate management is possible. This improvement may well exceed 15%.

1811^2^Vuorinen,AH^Kaiser,WM^1997^1^Dark CO2 fixation by roots of willow and barley in media with a high level of inorganic carbon^4^151^4^405-408^^^^^Oct^^^^^6396
1340^2262^2777^2778^417^433^g equipment. Though optimal control of greenhouse climate has received considerable attention in the literature, until now little evidence supported by experimental work has been reported as to the possible improvement in efficiency which can be realised using this approach during a whole growing period. This paper reports a first exploration of this matter for a lettuce crop. In a greenhouse experiment the behaviour of conventional greenhouse climate control supervised by the grower was measured. Then, in simA^6395^Willow (Salix cv. Aquatica gigantea) and barley (Hordeum vulgare L.) plants were grown in a nutrient solution (pH 7) enriched with HCO3- or gaseous CO2. The initial and potential in vivo rates of dark CO2 fixation in the roots were measured using 0.015 mmol/L and 0.74 mmol/L (HCO3-)-C-14 as substrates of phosphoenolpyruvate carboxylase (PEPC). Enrichment of the nutrient solution with HCO3- or CO2 increased the initial rate of dark CO2 fixation in roots of both willow and barley compared with the corresponding control roots. In plants grown with NO3- the initial activity of PEPC was 38 and 89% higher than in control willow and barley, respectively, after the addition of HCO3-. When the nutrient solutions were enriched with CO2 the initial activity of PEPC increased 52% in willows and 58% in barley, compared with the controls. The supply of HCO3- into NH4+ media increased the initial activity of PEPC in the roots of willows and barley by 50% and 17%, respectively. The amount of soluble protein in the roots was also higher in plants grown with inorganic carbon than in the control plants.

1812^3^Goodfellow,JE^Eamus,D^Duff,GA^1997^1^The impact of CO2 enrichment on assimilation, stomatal conductance and growth in a long-term study of Mangifera indica in the wet-dry tropics of Australia^8^114^3^480^^^^^Jul

1813^6^Malmstrom,CM^Thompson,MV^Juday,GP^Los,SO^Randerson,JT^Field,CB^1997^1^Interannual variation in global-scale net primary production: Testing model estimates^137^11^3^367-392^^^^^Sep^^^^^6399
130^1356^1659^2182^2337^2779^2780^2781^2782^377^with NO3- the initial activity of PEPC was 38 and 89% higher than in control willow and barley, respectively, after the addition of HCO3-. When the nutrient solutions were enriched with CO2 the initial activity of PEPC increased 52% in willows and 58% in barley, compared with the controls. The supply of HCO3- into NH4+ media increased the initial activity of PEPC in the roots of willows and barley by 50% and 17%, respectively. The amount of soluble protein in the roA^6398^Testing estimates of year-to-year variation in global net primary production (NPP) poses some challenges. Large-scale, multiyear records of production are not readily available for natural systems but are for agricultural systems, We use records of agricultural yields at selected sites to test NPP estimates produced by CASA, a global-scale production model driven by both meteorological data and the satellite-derived normalized difference vegetation index (NDVI). We also test estimates produced by the Miami model, which has underlain several analyses of biosphere response to interannual changes in climate. In addition, we test estimates against tree ring data for one boreal site for which data from both coniferous and deciduous species were available. The agricultural tests demonstrate that CASA can reasonably estimate interannual variation in production. The Miami model estimates variation more poorly. However, differences in NDVI-processing algorithms substantially affect CASA's estimates of interannual variation. Of the four versions tested, the FASIR NDVI most closely reproduced yield data and showed the least correlation with changes in equatorial crossing time of the National Oceanic and Atmospheric Administration satellites, One issue raised is the source of the positive trends evident in CASA's NDVI-based estimates of global NPP. The existence of these trends is consistent with potential stimulation of terrestrial production by factors such as CO2 enrichment, N fertilization, or temperature warming, but the magnitude of the global trends seen is significantly greater than suggested by constraints imposed by atmospheric fluxes.

1814^7^Nakazawa,T^Murayama,S^Toi,M^Ishizawa,M^Otonashi,K^Aoki,S^Yamamoto,S^1997^1^Temporal variations of the CO2 concentration and its carbon and oxygen isotopic ratios in a temperate forest in the central part of the main island of Japan^257^49^4^364-381^^^^^Sep^^^^^6401
1483^1853^2783^2784^2785^2786^362^376^529^673^rithms substantially affect CASA's estimates of interannA^6400^Using discrete air sampling, values of delta(13)C and delta(18)O in atmospheric CO2, as well as its concentration, were measured in a forest in the central part of the main island of Japan during the period from June 1994 to June 1996 to examine the biospheric contribution to their temporal variations. delta(13)C shows a prominent diurnal variation with high values in the daytime and low values in the nighttime, especially during the warm season. delta(13)C also vary seasonally, showing a maximum in summer and a minimum in spring. The diurnal and seasonal variations of delta(13)C are opposite in phase with those of the CO2 concentration. The rate of change in delta(13)C with respect to the CO2 concentration is found to be approximately -0.05 parts per thousand/ppmv. This suggests that the diurnal and seasonal variations of the CO2 concentration are produced primarily by diurnally-and seasonally-dependent photosynthetic-respiratory processes of the biosphere near the observation site, respectively. In the warm season, delta(18)O also increases in the daytime and decreased in the nighttime, which is similar to the diurnal variation of delta(13)C, but opposite to that of the CO2 concentration. The diurnal delta(18)O variation is thought to be caused by the release of isotopically heavy CO2 during photosynthesis, and light CO2 during respiration. However, an interpretation of the seasonal delta(18)O variation is found to be much more difficult than those of delta(13)C and the CO2 concentration. This is likely due to complicated combinations of different seasonally varying fluxes of biospheric CO2 into the atmosphere, as well as to various weather-dependent factors governing the delta(18)O composition in CO2.

1815^2^Sa,T^Israel,DW^1997^1^Effect of phosphorus deficiency on response of symbiotic N-2 fixation of soybean to atmospheric CO2 enrichment^8^114^3^484^^^^^Jul
marily by diurnally-and seasonally-dependent photosynthetic-respiratory processes of the biosphere near the observation site, respectively. In 1816^3^Simard,SW^Durall,DM^Jones,MD^1997^1^Carbon allocation and carbon transfer between Betula papyrifera and Pseudotsuga menziesii seedlings using a C-13 pulse-labeling method^206^191^1^41-55^^^^^Apr^^^^^6404
1427^174^243^2562^417^92^ to be caused by the release of isotopically heavy CO2 during photosynthesis, and light CO2 during respiration. However, an interpretation of the seasonal delta(18)O variation is found to be much more difficult than those of delta(13)C and the CO2 concentration. This is likely due to complicated combinations of different seasonally varying fluxes of biospheric CO2 into the atmosphere, as well as to various weather-dependent factors governing the delta(18)O composition in CO2.

1815^2^Sa,T^Israel,DW^1997^1^Effect of phosphorus deficiency on response of symbiotic N-2 fixation of soybean to atmospheric CO2 enrichment^8^114^3^484^^^^^Jul
marily by diurnally-and seasonally-dependent photosynthetic-respiratory processes of the biosphere near the observation site, respectively. In A^6403^Here we describe a simple method for pulse-labeling tree seedlings with (CO2(gas)-C-13), and then apply the method in two related experiments: (i) comparison of carbon allocation patterns between Betula papyrifera Marsh. and Pseudotsuga menziesii (Mirb.) France, and (ii) measurement of one-way belowground carbon transfer from B. papyrifera to Fl menziesii. Intraspecific carbon allocation patterns and interspecific carbon transfer both influence resource allocation, and consequently development, in mixed communities of B. papyrifera and P. menziesii. In preparation for the two experiments, we first identified the appropriate (CO2(gas)-C-13) pulse-chase regime for labeling seedlings: a range of pulse (100-mL and 200-mL 99 atom% (CO2(gas)-C-13)) and chase (0, 3 and 6 d) treatments were applied to one year-old B. papyrifera and P. menziesii seedlings. The amount of (CO2)-C-13 fixed immediately after 1.5 h exposure was greatest for both B. papyrifera (40.8 mg excess C-13) and P. menziesii (22.9 mg excess C-13) with the 200-mL pulse, but higher C-13 loss and high sample variability resulted in little difference in excess C-13 content between pulse treatments after 3 d for either species. The average excess C-13 root/shoot ratio of B. papyrifera and P. menziesii changed from 0.00 immediately following the pulse to 0.61 and 0.87 three and six days later, which reflected translocation of 75% of fixed isotope out of foliage within 3 d following the pulse and continued enrichment in fine roots over 6 d. Based on these results, the 100-mL CO2(gas) and 6-d chase were considered appropriate for the carbon allocation and belowground transfer experiments. In the carbon allocation experiment, we found after 6 d that B. papyrifera allocated 49% (average 9.5 mg) and P. menziesii 41% (average 5.8 mg) of fixed isotope to roots, of which over 55% occurred in fine roots in both species. Species differences in isotope allocation patterns paralleled differences in tissue biomass distribution. The greater pulse labeling efficiency of B. papyrifera compared to P. menziesii was associated with its two-fold and 13-fold greater leaf and whole seedling net photosynthetic rates, respectively, 53% greater biomass, and 35% greater root/shoot ratio. For the carbon transfer experiment, B. papyrifera and P. menziesii were grown together in laboratory rootboxes, with their roots intimately mingled. A pulse of 100 mL (CO2(gas)-C- 13) was applied to paper birch and one-way transfer to neighboring P. menziesii was measured after 6 d. Of the excess C-13 fixed by B. papyrifera, 4.7% was transferred to neighboring P. menziesii, which distributed the isotope evenly between roots and shoots. Of the isotope received by P. menziesii, we estimated that 93% was taken up through belowground pathways, and the remaining 7% taken up by foliage as (CO2(gas)-C-13) respired by B. papyrifera shoots. These two experiments indicate that B. papyrifera fixes more total carbon and allocates a greater proportion to its root system than does Il menziesii, giving it a competitive edge in resource gathering; however, below-ground carbon sharing is of sufficient magnitude that it may help ensure co-existence of the two species in mixed communities.





1818^2^Beerling,DJ^Woodward,FI^1997^1^Changes in land plant function over the Phanerozoic: Reconstructions based on the fossil record^337^124^2^137-153^^^^^Jun^^^^^6408
243^2787^348^349^374^385^539^665^668^745^ 13) was applied to paper birch and one-way transfer to neighboring P. menziesii was measured after 6 d. Of the excess C-13 fixed by B. papyrifera, 4.7% was transferred to neighboring P. menziesii, which distributed the isotope evenly between roots and shoots. Of the isotope received by P. menziesii, we estimated that 93% was taken up through belowground pathways, and the remaining 7% taken up by foliage as (CO2(gas)-C-13) respired by B. papyrifera shoots. These two experiments indicate that B. papyrifera fixes more total carbon and allocates a greater proportion to its root system than does Il menziesii, giving it a comA^6407^Major fluctuations in the concentrations of atmospheric CO2 and O-2 are predicted by historical long-term carbon and oxygen cycle models of atmospheric evolution and will have impacted directly on past climates, plant function and evolutionary processes. Here, palaeobotanical evidence is presented from the stomatal density record of fossil leaves spanning the past 400 Myr supporting the predicted changes in atsmopheric CO2. Evidence from experiments on plants exposed to long-term high CO2 environments and the newly assembled fossil data indicate the potential for genetic modification of stomatal characters. The influence of tile changes in fossil stomatal characteristics and atmospheric composition on the rates of leaf gas exchange over the course of land plant evolution has been investigated through modelling. Three contrasting cras of plant water economies emerge in the Devonian (high), Carboniferous (low) and from the Upper Jurassic to the present- day (high but declining). These patterns of change result from structural changes of the leaves and the impact of atmospheric CO2 and O-2 concentrations on RuBisCO function and are consistent with the fossil evidence of sequential appearances of novel plant anatomical changes. The modelling approach is tested by comparing predicted leaf stable carbon isotope ratios with those measured on fossil plant and organic material. Viewed in a geological contest, current and future increases in the concentration of atmospheric CO2 might be considered as restoring-plant function to that more typically experienced by plants over the majority of their evolutionary history. (C) 1997 The Linnean Society of London.

1819^2^Cao,WX^Tibbitts,TW^1997^1^Starch concentration and impact on specific leaf weight and element concentrations in potato leaves under varied carbon dioxide and temperature^166^20^7-8^871-881^^^^^^^^^^6410
1372^349^374^409^57^576^92^an (high), Carboniferous (low) and from the Upper Jurassic to the present- day (high but declining). These patterns of changeA^6409^Foliar concentrations of starch and major elements, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg), along with specific leaf weight (SLW) were determined in the potato (Solanum tuberosum L.) cvs 'Denali', 'Norland', and 'Russet Burbank' grown for 35 days under CO2 concentrations of 500, 1,000, 1,500 and 2,000 mu mol . mol(-1) at both 16 degrees C and 20 degrees C air temperature. The starch concentration, pooled from the three cultivars, increased with increasing CO, concentration at both 16 degrees C and 20 degrees C and was consistently higher at 16 degrees C than at 20 degrees C. The SLW (g . m(-2)) was positively related to the foliar starch concentration on the basis of leaf area or dry weight. The concentrations of N, P, Ca, and Mg in leaves were negatively related to starch concentration under approximate to 14% starch on a dry weight basis. Above 14% starch, there was no significant relationship between element and starch concentrations. Similar patterns were seen when the SLW and element concentrations were expressed on a starch-free basis. In contrast, the leaf concentration of K was not closely related to the starch concentration because the K concentration was similar at varied CO2 levels. The results of this study indicate that the changes in SLW and concentrations of N, P, Ca, and Mg in potato leaves only partially resulted from the changed starch concentration.

1820^5^ElMaayar,M^Singh,B^Andre,P^Bryant,CR^Thouez,JP^1997^1^The effects of climatic change and CO2 fertilisation on agriculture in Quebec^107^85^3-4^193-208^^^^^Jul^^^^^6412
130^2788^312^376^409^413^434^662^771^92^ SLW (g . m(-2)) was positively related to the foliar starch concentration on the basis of leaf area or dry weight. The concentrations of N, P, Ca, and Mg in leaves were negatively related to starch concentration under approximate to 14% starch on a dry weight basis. Above 14% starch, there was no significant relationship between element and starch concentrations. Similar patterns were seeA^6411^The agricultural sector forms an important part of the economy of Quebec. The risk of global increase of atmospheric CO2 concentration and associated climatic change and their influence on agriculture need to be assessed. Although many studies have been conducted on the effect of climate change on agriculture in various parts of the world, fewer studies have focused on the combined effects of climatic change and CO2 fertilisation on agriculture. This study, using the outputs of the Canadian Climate Centre (CCC) general circulation model coupled with the Food and Agricultural Organization (FAG) crop model, attempts to assess the response of agricultural productivity to both direct (or fertilisation) and indirect (or climatic) effects of increased atmospheric CO2 concentration, for a variety of crops including C-3 and C-4 cereals, legumes, vegetables and special crops grown in Quebec. It appears that C-4 cereal (corn and sorghum) crops would benefit by climate change but would be least favoured by CO2 fertilisation effect. (C) 1997 Published by Elsevier Science B.V.

1821^4^Ghannoum,O^vonCaemmerer,S^Barlow,EWR^Conroy,JP^1997^1^The effect of CO2 enrichment and irradiance on the growth, morphology and gas exchange of a C-3 (Panicum laxum) and a C-4 (Panicum antidotale) grass (vol 24, pg 227, 1997)^92^24^3^U2^

1822^2^Jiang,GM^Lin,GH^1997^1^Changes of photosynthetic capacity of some plant species under very high CO2 concentrations in Biosphere 2^338^42^10^859-864^^^^^May
344^374^376^
1823^7^Kloppenburg,WD^Wolthers,BG^Stellaard,F^Elzinga,H^Tepper,T^deJong,PE^Huisman,RM^1997^1^Determination of urea kinetics by isotope dilution with [C- 13]urea and gas chromatography isotope ratio mass spectrometry (GC-IRMS) analysis^339^93^1^73-80^^^^^Jul^^^^^6416
2789^314^mospheric CO2 concentration, for a variety of crops including C-3 and C-4 cereals, legumes, vegetables and special crops grown in Quebec. It appears that C-4 cereal (corn and sorghum) crops would benefit by climate change but would be least favoured by CO2 fA^6415^1. Stable urea isotopes can be used to study urea kinetics in humans, The use of stable urea isotopes far studying urea kinetic parameters in humans on a large scale is hampered by the high costs of the labelled material, We devised a urea dilution for measurement of the distribution volume, production rate and clearance of urea in healthy subjects and renal failure patients using the inexpensive single labelled [C- 13]urea isotope with subsequent analysis by headspace chromatography-isotope ratio MS (GC-IRMS) of the [C-13]urea enrichment, 2. The method involves measurement of the molar percentage excess of [C-13]urea in plasma samples taken over a 4 h period after an intravenous bolus injection of [C-13]urea, During the sample processing procedure, the plasma samples together with calibration samples containing a known molar percentage excess of [C-13]urea are acidified with phosphoric acid to remove endogenous CO2, and are subsequently incubated with urease to convert the urea present in the plasma samples into CO2. The C-13 enrichment of the generated CO2 is analysed by means of GC-IRMS, This method allows measurement of the molar percentage excess of [C-13]urea to an accuracy of 0.02%. 3. Reproducibility studies showed that the sample processing procedure [within-run coefficient of variation (CV) <2.8% and between-run CV <8.8%] and the GC-IRMS analysis (within-day CV <1.3% and between-day CV <1.3%) could be repeated with good reproducibility, 4. In clinical urea kinetic studies in a healthy subject and in a renal failure patient without residual renal function, reproducible values of the distribution volume, production rate and clearance of urea were determined using minimal amounts of [C-13]urea (25-50 mg). 5. because only low [C-13]urea enrichments are needed in this urea dilution method using GC-IRMS analysis, the costs of urea kinetic studies are reduced considerably, especially in patients with renal failure.
 and are subsequently incubated with urease to convert the urea present in the plasma 1824^2^Kontak,DJ^Kerrich,R^1997^1^An isotopic (C, O, Sr) study of vein gold deposits in the Meguma terrane, Nova Scotia: Implication for source reservoirs^340^92^2^161-180^^^^^Mar-Apr^^^^^6418
2790^2791^2792^2793^2794^2795^2796^2797^2798^908^processing procedure [within-run coefficient of variation (CV) <2.8% and between-run CV <8.8%] and the GC-IRMS analysis (within-day CV <1.3% and between-day CV <1.3%) could be repeated with good reproducibility, 4. In clinical urea kinetic studies in a healthy subject and in a renal failure patient without residual renal function, reproducible values of the distribution volume, production rate and clearance of urea were determined using minimal amounts of [C-13]urea (25-50 mg). 5. because only low [C-13]urea enrichments are needed in this urea dilution method using GC-IRMS analysis, the costs of urea kinetic studies are reduced considerably, especially in patients with renal failure.
 and are subsequently incubated with urease to convert the urea present in the plasma A^6417^Vein quartz, carbonate, and tourmaline from 19 Meguma gold deposits in the Meguma terrane of Nova Scotia have been analyzed for stable (delta(18)O, delta(13)C) and radiogenic (Sr-87/Sr-86) isotopes in order to assess the nature and origin of the vein-forming fluids. hs with other mesothermal gold provinces, the Meguma gold deposits are well suited to such a study because carbonate is the next most abundant phase after quartz in these mesothermal lode gold deposits. All vein types have been sampled for quartz and carbonate and, in addition, all compositional and textural varieties of carbonate have been sampled. Vein quartz is of uniform isotopic composition with most delta(18)O values between 10.2 to 17.6 per mil (avg ca. 14 parts per thousand), except for one deposit (West Gore Sb-Au) where values go to 19.4 per mil. There is no systematic variation for quartz within a deposit or position within the Meguma Group stratigraphy. Vein carbonate delta(18)O values range from 11.8 to 27.5 per mil, with most in the 13 to 16 per mil range. The relatively O-18-enriched carbonates reflect exchange with low-temperature fluids based on analyses of quartz-carbo;late pairs that indicate disequilibrium fractionation (Delta(quartz-carbonate) less than or equal to 0); this is best illustrated by the strong negative correlation between delta(18)O(carbonate) and Delta(quartz-carbonate). The delta(18)O(water) is estimated at 10 +/- 3 per mil for a temperature of vein formation of 350 degrees to 400 degrees C and using the appropriate mineral-water fractionation equations. Whereas delta(water)(18) values partly overlap the field for magmatic fluids, the values are wholly consistent with a metamorphic fluid, and it is considered unlikely that a primary magmatic fluid signature has been substantially modified due to wall-rock influences given that mesothermal gold systems are sites of high fluid/rock ratios. Vein carbonate has delta(13)C values of -13.1 to -25.9 per mil, but a slight negative correlation between delta(13)C(carbonate) and Delta(quartz-carbonate) suggests that the primary values lie in the range -20 to -25 per mil. Thus, the delta(13)C values indicate a reduced, biogenic source for the carbon. Oxidation of the reduced carbon, as indicated by CO2 in fluid inclusions, may have occurred via hydrolysis of graphite or dissolution of carbonate minerals, both of which occur in the wall-rock lithologies of the Meguma Group, the latter of which has the appropriate isotopic composition. The initial Sr-87/Sr-66 of the vein fluid, estimated from the analyses of 52 vein carbonates (17 deposits) and four tourmalines (three deposits), ranges from 0.70118 to 0.72284 and within deposits considerable variation is observed. There is insufficient data to quantify the extent of the low-temperature overprint which has modified the C and O isotope data, although it is likely that some influence is present. Nevertheless, the data cannot be reconciled by a source confined exclusively to the Meguma Group, which suggests, therefore, involvement of another reservoir(s). The isotopic heterogeneity can be explained by variable amounts of contamination of a primary fluid with radiogenic Sr derived from Meguma Group lithologies by interaction along the fluid path or at the site of vein formation concomitant with wall-rock alteration; as discussed above, a dominantly magmatic source is not considered feasible. This fluid source is suggested to be within the structural basement to the Meguma Group, and the Liscomb gneisses are the favored source based on the combined results of the Sr isotope data presented herein and previously published Pb isotope data. Collectively, the data indicate that a primary fluid of metamorphic origin has had its isotopic signature variably modified due to interaction with different reservoirs. The most affected isotopic systems are C and S (based on earlier work on delta(35)S values) which are abundant as graphite carbonate and sulfides in the Meguma wall rock, respectively. The range in Sr-87/Sr-86 values of the fluid also reflects contamination, but this was quite variable. The uniform delta(18)O(water) value for the fluid indicates that this was the least affected isotopic system, except for the later exchange of carbonate at low temperatures.

1825^2^Lindqvist,K^Lignell,R^1997^1^Intracellular partitioning of (CO2)-C-14 in phytoplankton during a growth season in the northern Baltic^311^152^1-3^41-50^^^^^^^^^^6420
1578^2070^243^2799^2800^2801^2802^2803^57^711^uma Group, and the Liscomb gneisses are the favored source based on the combined results of the Sr isotope data presented herein and previously published Pb isotope data. Collectively, the data indicate that a primary fluid of metamorphic origin has had its isotopic signature variably modified due to interaction with different reservoirs. The most affected isotopic systems are C and S (based on earlier work on delta(35)S values) which are abundant as graphite carbonate and sulfides in the Meguma wall rock, respectively. The range in Sr-87/Sr-86 values of the fluid alsA^6419^During the phytoplankton succession in the northern Baltic in 1988, the distribution of (CO2)-C-14 assimilated by algae into the main molecular groups [proteins, polysaccharides, lipids and low molar mass compounds (LMC)] after in situ Light (6 h) and Light to dark (20 h from ca 11:00 to 07:00 h) incubations at 2 m depth (just below maximum (CO2)-C-14 fixation) was studied. By early May, the high winter levels of mineral nutrients were depleted from the water column, and in middle May the spring bloom predominated by large dinoflagellates (diatoms subdominant) peaked. The proportion of C-14 lipids was usually ca 15% of total (CO2)-C-14 fixation, but it showed a distinct peak of 40% in middle May. The C-14-Lipid peak probably reflected nutrient stress of the algae, since nutrient (N+P) enrichment decreased this peak by 15 percentage points in 100 l enclosures. During the decline of the spring bloom, the proportion of C-14 proteins increased despite low ambient mineral N concentrations. In summer, the phytoplankton community (mainly small flagellates) consistently exhibited remarkable channelling of (CO2)-C-14 into proteins (50 to 60%), which conformed to the low particulate organic C:N ratios of ca 7 (mol/mol). Summer upwellings, which introduced nutrients into the mixed layer, seemed to be accompanied by the highest proportions of C-14 proteins. The proportion of C-14 polysaccharides was usually ca 20%. After 6 h incubations, this proportion was significantly (on average 10 percentage points) higher than after 20 h, while the inverse was true with C-14 proteins, which reflected continuous nocturnal synthesis of proteins (enzymes) at the expense of polysaccharide storage products. In con elusion, the high proportions of algal C-14 proteins in summer suggest that phytoplankton is usually not physiologically N limited in our study area and provides N- sufficient food for herbivores, hence enabling high efficiency of algal C transfer to higher trophic levels.
bient mineral N concentrations. In summer, the p1826^8^Liu,YT^Karnauchow,TM^Jarrell,KF^Balkwill,DL^Drake,GR^Ringelberg,D^Clarno,R^Boone,DR^1997^1^Description of two new thermophilic Desulfotomaculum spp., Desulfotomaculum putei sp. nov, from a deep terrestrial subsurface, and Desulfotomaculum luciae sp. nov, from a hot spring^341^47^3^615-621^^^^^Jul^^^^^6422
130^2384^2804^2805^2806^416^92^960^. The proportion of C-14 polysaccharides was usually ca 20%. After 6 h incubations, this proportion was significantly (on average 10 percentage points) higher than after 20 h, while the inverse was true with C-14 proteins, which reflected continuous nocturnal synthesis of proteins (enzymes) at the expense of polysaccharide storage products. In con elusion, the high proportions of algal C-14 proteins in summer suggest that phytoplankton is usually not physiologically N limited in our study area and provides N- sufficient food for herbivores, hence enabling high efficiency of algal C transfer to higher trophic levels.
bient mineral N concentrations. In summer, the pA^6421^Six strains of thermophilic, endospore-forming, sulfate- reducing bacteria were enriched and isolated from 2.7 km below the earth's surface in the Taylorsville Triassic Basin in Virginia, The cells of these strains were motile rods that were 1 to 1.1 mu m in diameter and 2 to 5 mu m long. The cells grew by oxidizing H-2, formate, methanol (weakly), lactate (incompletely, to acetate and CO2), or pyruvate (incompletely) while reducing sulfate to sulfide; acetate did not serve as a catabolic substrate, Thiosulfate or sulfite could replace sulfate as an electron acceptor, The results of a phylogenetic analysis of the 16S rRNA gene indicated that these strains belong to the genus Desulfotomaculum, but are distinct from previously described Desulfotomaculum species, Thus, we propose a new species, Desulfotomaculum putei, for them, with strain TH-11 (= SMCC W459) as the type strain, The results of our phylogenetic analysis also indicated that strain SLTT, which was isolated from a hot spring and has been described previously (T. M. Karnauchow, S. F. Koval, and K. F. Jarrell, Syst. Appl. Microbiol, 15:296-310, 1992), is also a member of the genus Desulfotomaculum and is distinct from other species in this genus, We therefore propose the new species Desulfotomaculum luciae for this organism; strain SLT (= SMCC W644) is the type strain of D. luciae.

1827^3^Manninen,P^Pakarinen,J^Kallio,H^1997^1^Large-scale supercritical carbon dioxide extraction and supercritical carbon dioxide countercurrent extraction of cloudberry seed oil^321^45^7^2533-2538^^^^^Jul^^^^^6424
lectron acceptor, The results of a phylogenetic analysis of the 16S rRNA gene indicated that these strains belong to the genus Desulfotomaculum, but are distinct from previously described Desulfotomaculum species, Thus, we propose a new species, Desulfotomaculum putei, for them, with strain TH-11 (= SMCC W459) as the type strain, The results of our phylogenetic analysis also indicated that strain SLTT, which was isolated from a hot spring and has been desA^6423^Dried press residue of cloudberry [Rubus chamaemorus (Rosaceae)] was extracted with carbon dioxide at pressures of 90-300 bar and at a temperature of 40 or 60 degrees C using a pilot-scale or a production-scale plant. The yield of the extract at the highest pressure was approximately 15% less than that obtained with Soxhlet extraction using diethyl ether as solvent. The extracts were either solids or viscous oils depending on the amount of neutral lipids, which increased with increasing pressure. No significant differences in the composition of the major constituent fatty acids in any of the extracts were found. The color of the extracts was clearly dependent an the amount of carotenes, which consisted mainly of beta-carotene. The content of carotenes in the extracts did not increase at pressures higher than 150 bar. The amount of tocopherols in the extracts obtained at highest pressure was found to be approximately 3 times less than that at lower pressures. Countercurrent CO2 extraction of the cloudberry oil extracted at 300 bar and 40 degrees C resulted in enrichment of tocopherols in the extracts and a decrease in the amount of carotenes. The concentrations of tocopherols and carotenes in all of the CO2 extracts, the countercurrent extracts, and the raffinates were found to be clearly higher than those in the edible part of fresh cloudberry reported by other authors.

1828^4^Mayeux,HS^Johnson,HB^Polley,HW^Malone,SR^1997^1^Yield of wheat across a subambient carbon dioxide gradient^127^3^3^269-278^^^^^Jun^^^^^6426
243^2807^344^376^423^436^529^593^751^92^r constituent fatty acids in any of the extracts were found. The color of the extracts was clearly dependent an the amount of carotenes, which consisted mainly of beta-carotene. The content of carotenes in the extracts did not increase at pressures higher than 150 bar. The amount of tocopherols in the extracts obtained at highest pressure was found to be approximately 3 times less than that at lower pressures. Countercurrent CO2 extraction of the cloudbA^6425^Yields and yield components of two cultivars of day-neutral spring wheat (Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO2) concentrations from about 200 to near 350 mu mol CO2 (mol air)(-1) in a 38 m-long controlled environment chamber. The range in CO2 concentration studied approximates that of Earth's atmosphere since the last ice age. This 75% rise in CO2 concentration increased grain yields more than 200% under well-watered conditions and by 80- 150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO2 from the pre-industrial level of 150 years ago (275 mu mol mol(-1)) to near the current concentration (350 mu mol mol(-1)) increased grain yields of 'Yaqui 54' and 'Seri M82' spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO2 concentration, resulting in improved water use efficiency as CO2 rose. Data suggest that rising CO2 concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades.

1829^3^Mohanraju,R^Rajagopal,BS^Daniels,L^1997^1^Isolation and characterization of a methanogenic bacterium from mangrove sediments^342^5^2-3^147-152^^^^^^^^^^6428
244^2808^2809^2810^2811^2812^2813^2814^2815^ields more than 200% under well-watered conditions and by 80- 150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO2 from the pre-industrial level of 150 years ago (275 mu mol mol(-1)) to near the current concentration (350 mu mol mol(-1)) increased grain yields of 'Yaqui 54' and 'Seri M82' spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased littA^6427^A methanogenic bacterium was enriched with trimethylamine and isolated from mangrove sediments. The isolate was a non-spore- forming regular to slightly irregular coccus (0.4-1 mm in diameter). The isolate required sodium chloride for growth with maximal methanogenesis at 420 mM NaCl at 30 degrees C. The optimal growth temperature was 30-35 degrees C with maximal methane production at 30 degrees C. The maximum growth rate was between pH 6.6 and 7.2 with maximum methane production at pH 6.8. The growth requirement of sulfide was 10-15 mM with maximum methane production at 10 mM at 30 degrees C. Mono-, di- , and trimethylamine or methanol were substrates for the methanogen; sodium acetate and H-2:CO2 were not. The DNA base content is consistent with the type descriptions of Methanoccoides methylutens, a methylotrophic methanogen isolated from submarine sediments. The isolate was found to utilize methylamines that are found in mangroves without having to compete with sulfate-reducing bacteria for H-2.
t1830^2^Napolitano,R^Juarez,MP^1997^1^Entomopathogenous fungi degrade epicuticular hydrocarbons of Triatoma infestans^343^344^1^208-214^^^^^1 Aug^^^^^6430
2816^2817^2818^2819^2820^2821^m in diameter). The isolate required sodium chloride for growth with maximal methanogenesis at 420 mM NaCl at 30 degrees C. The optimal growth temperature was 30-35 degrees C with maximal methane production at 30 degrees C. The maximum growth rate was between pH 6.6 and 7.2 with maximum methane production at pH 6.8. The growth requirement of sulfide was 10-15 mM with maximum methane production at 10 mM at 30 degrees C. Mono-, di- , and trimethylamine or methanol were substrates for the methanogen; sodium acetate and H-2:CO2 were not. The DNA base content is consistent with the type descriptions of Methanoccoides methylutens, a methylotrophic methanogen isolated from submarine sediments. The isolate was found to utilize methylamines that are found in mangroves without having to compete with sulfate-reducing bacteria for H-2.
tA^6429^Studies were undertaken to analyze the ability of entomopathogenous fungi to degrade insect hydrocarbons. Strains of Beauveria bassiana and Metarhizium anisopliae pathogenic to the blood-sucking bug Triatoma infestans were grown on hydrocarbon and non-hydrocarbon insect lipid extracts and on synthetic hydrocarbon-enriched media as the sole carbon source. Entomopathogenous fungi were shown to utilize hydrocarbons as the only carbon source for their growth. Insect-derived hydrocarbons served more efficiently as metabolic fuel rather than synthetic compounds of similar structure. [H-3]n- Pentacosane, [11,12-H-3]3,11-dimethylnonacosane, and [C-14]n- hexadecane were catabolized into different amounts of polar lipids, free fatty acids, and acylglycerols. In experiments using the branched alkane, labeled hydrocarbons of different chain length than the precursor were also synthesized. Evidence of complete catabolism was obtained by a significant release of (CO2)-C-14 from [1-C-14]n-hexadecane. (CO2)-C-14 production might be used as a simple method to compare hydrocarbon utilization by fungal strains. These data demonstrate that entomopathogenous fungi are able to transform a variety of hydrocarbon structures into different lipid products, part of which may be subsequently utilized for energy production and for the biosynthesis of cellular components. These data are the first evidence of hydrocarbon catabolism and synthesis in entomopathogenous fungi. (C) 1997 Academic Press.

1831^4^Panina,LI^Motorina,IV^Mamedov,MN^Makhmudov,SA^1997^1^Physicochemical conditions of the development of the tertiary trachybasalt-phonolite formation in the Talysh zone (Azerbaijan)^344^38^4^730-739^^^^^^^^^^6432
fferent amounts of polar lipids, free fatty acids, and acylglycerols. In experiments using the branched alkane, labeled hydrocarbons of different chain length than the precursor were also synthesized. Evidence of complete catabolism was obtained by a significant release of (CO2)-C-14 from [1-C-14]n-hexadecane. (CO2)-C-14 prodA^6431^It has been established by mineral thermobarogeochemistry that the magmas initial of the trachybasalt-phonolite series in the Talysh zone were crystallized according to Bowen's scheme at the following temperatures and order of phenocryst formation: O1 (>1350 degrees C) --> Cpx (1280-1170 degrees C) --> Ap (1240-1030 degrees C) --> P1 (1190-1035 degrees C). The fluid phase at the time of olivine phenocryst crystallization was composed of 90 mol. % CO2 and 10 mol. % N-2, while at the stage of pyroxene and plagioclase formation it was 100 mol. % N-2. A drastic change in fluid composition is related to a discontinuity in time and place of phenocryst formation: olivine crystallization in deep-seated conditions, and formation of pyroxene and plagioclase in shallow depth of the Earth's crust. A microprobe study of silicate melt inclusions has shown that the evolution of the initial magma proceeded by means of differentiation and fractionation of minerals. In the process of crystallization the derivative melts were enriched in SiO2 (up to 64%), Al2O3 (up to 21%), alkalies (up to 10-11 wt.%) and were depleted in femic components (totalled to few per cent). Residual rhyolite-dacite alkali-enriched melts (67- 73% SiO2, 14-17% Al2O3, 4-8% alkalies) appeared in the final stages of magma evolution. The presence of alkalies brings us back to the problem of the mantle, <<basalt>>, origin of some siliceous rocks, as well as of the possibility to overcome an <<impassable>> barrier between quartz-normative acid melts and alkaline leucite-bearing rocks.

1832^5^Patterson,BW^Zhang,XJ^Chen,YP^Klein,S^Wolfe,RR^1997^1^Measurement of very low stable isotope enrichments by gas chromatography mass spectrometry: Application to measurement of muscle protein synthesis^305^46^8^943-948^^^^^Aug^^^^^6434
2584^2822^rust. A microprobe study of silicate melt inclusions has shown that the evolution of the initial magma proceeded by means of differentiation and fractionation of minerals. In the process of crystallization the derivative meltA^6433^Measurement of muscle protein synthesis using stable isotopically labeled tracers usually requires isotope ratio mass spectrometry (IRMS) because of the need to measure very low enrichments of stable isotopically labeled tracers (tracer to tracee ratio [TTR], 0.005% to 0.10%). This approach is laborious, requiring purification of the metabolite of interest and combustion to a gas for IRMS analysis, and is best suited for use with C-13 tracers. We have developed an approach whereby low enrichments can be conveniently measured by a conventional gas chromatography/mass spectrometry (GC/MS) instrument. The approach includes three critical elements: (1) use of a highly substituted tracer containing three or more labeled atoms, to measure enrichment above a very low natural abundance of highly substituted isotopomers; (2) use of a highly substituted natural abundance isotopomer as a base ion for comparison rather than the most abundant m + 0 isotopomer, to reduce the dynamic range of the isotopomer ratio measurement; and (3) a sensitive mass spectrometric analysis that measures the natural abundance of the isotopomer used as a tracer with a high signal to noise ratio (> 100:1). This approach was used to measure the rate of synthesis of muscle protein following a primed continuous infusion of L-[C-13(6)]- phenylalanine (PHE) in eight fasted dogs and L-[H-2(3)]-leucine in five fasted human subjects. Values for [C-13(6)]-PHE enrichment by GC/MS rates were virtually identicalthose obtained by a conventional approach using high-performance liquid chromatography (HPLC) to isolate PHE, combustion to CO2, and measurement of (CO2)-C-13 enrichment by IRMS (IRMS enrichment = 0.9988 x GC/MS enrichment, R-2 = .891), resulting in identical values for muscle fractional synthesis rates ([FSRs] mean +/- SEM: 2.7 +/- 0.2 and 2.5 +/- 0.2%/d for GC/MS and IRMS, respectively). Human muscle synthesis rates measured by GC/MS analysis of [H-2(3)]-leucine enrichment (1.90 +/- 0.17%/d) were similar to published values based on IRMS analysis using a 1-C-13-leucine tracer. We conclude that compared with the IRMS approach, the GC/MS approach offers faster throughput, has a lower sample requirement, and is suitable for a wider variety of tracers such as H-2. The principles outlined here should be applicable to the measurement of low enrichments by GC/MS in a wide variety of stable isotope tracer applications. Copyright (C) 1997 by W.B. Saunders Company.

1833^4^Pearson,S^Wheeler,TR^Hadley,P^Wheldon,AE^1997^1^A validated model to predict the effects of environment on the growth of lettuce (Lactuca sativa L): Implications for climate change^174^72^4^503-517^^^^^Jul^^^^^6436
1055^1158^130^174^312^376^434^720^800^ enrichment, R-2 = .891), resulting in identical values for muscle fractional synthesis rates ([FSRs] mean +/- SEM: 2.7 +/- 0.2 and 2.5 +/- 0.2%/d for GC/MS and IRMS, respectively). Human muscle synthesis rates measured by GC/MS analysis of [H-2(3)]-leucine enrichment (1.90 +/- 0.17%/d) were similar to published values based on IRMS anaA^6435^A mechanistic model is described that predicts the effects of changes to the environment on the growth, yield and maturity of lettuce. The model assumes that lettuce has structural and storage carbon pools. The storage pool is supplied by photosynthesis and depleted by respiratory losses and the conversion of assimilate to the structural pool. The model incorporated both instantaneous effects of temperature and CO2, and long term effects of thermal time on photosynthetic rate. The rate of structural dry-matter production was related to a simple temperature dependent partitioning coefficient. The model was calibrated on eight separate crops of lettuce and validated With independent data from seven sources. The validated model was then used to simulate changes in head weight and time to maturity with systematic changes in temperature (-2 to +5 degrees C in 1K steps) and carbon dioxide (350 to 700 ppm in 50 ppm steps) superimposed on baseline meteorological data from Rothamsted (1984-1995). These predicted that changes to temperature of up to +3 degrees C would reduce the production time from about 96 to 79 d for April plantings, and from 63 to 52 d for August plantings. Head weight would increase by approximately 32% with an increase in CO2 of from 350 to 700 ppm, whilst the magnitude of this response varied little with planting date. For any sowing date, increasing temperature was predicted to have little effect on final head weight, however, head weight was predicted to decrease with later transplanting. The potential effects of changes to climate on lettuce production are discussed.

1834^2^Riis,T^SandJensen,K^1997^1^Growth reconstruction and photosynthesis of aquatic mosses: Influence of light, temperature and carbon dioxide at depth^12^85^3^359-372^^^^^Jun^^^^^6438
131^1721^2823^2824^2825^2826^2827^2828^621^701^nges in temperature (-2 to +5 degrees C in 1K steps) and carbon dioxide (350 to 700 ppm in 50 ppm steps) superimposed on baseline meteorological data from Rothamsted (1984-1995). These predictA^6437^1 The mosses Sphagnum subsecundum and Drepanocladus exannulatus dominate the vegetation in the oligotrophic, softwater Lake Grane Langso, Denmark, even at great depths where light and temperature are low. We used seasonal changes in morphology to reconstruct the annual growth and the longevity of the mosses and measurements of photosynthesis and respiration to evaluate the importance of light, temperature and CO2 for the growth patterns at depth in the lake. 2 The reconstruction technique revealed that the mosses had a relatively fast growth rate (90- 250 mm shoot(-1) year(-1)) and were short lived (0.7-2.9 years). The shoots of both moss species grew faster in deep than in shallow water. Growth experiments in summer confirmed that Sphagnum grew more slowly and decayed more rapidly in shallow than in deep water. 3 Fast growth of mosses in deep waters can be accounted for by lower temperature, extensive CO2 supersaturation and nutrient enrichment in the hypolimnion during summer stratification. Maximum rate of light-saturated photosynthesis in July was 3.3-fold higher and of dark respiration 1.3-fold lower in Sphagnum from 9.5m incubated at the ambient 8 degrees C than in Sphagnum from 0.7m incubated at 20 degrees C. The net daily carbon fixation was greater in deep than in shallow water despite the much lower irradiance at depth. Extensive CO2 supersaturation stimulated photosynthesis several-fold relative to the rates observed in air-saturated water. Tissues of Sphagnum were richer in nitrogen in deep than in shallow water during summer, but the importance of nutrient availability to annual moss growth remains unclear. 4 Reconstruction techniques are recommended for comparative studies on annual and interannual growth patterns of mosses within lakes and among lakes of different altitude, latitude and water chemistry. This information can be based on just a single collection and can therefore include remote sites with adverse climate.
t enrichment in the hypolimnion during summer stratification. Maximum1835^2^Wang,YX^Shpeyzer,GM^1997^1^Genesis of thermal groundwaters from Siping'an district, China^345^12^4^437-445^^^^^Jul^^^^^6440
ubated at the ambient 8 degrees C than in Sphagnum from 0.7m incubated at 20 degrees C. The net daily carbon fixation was greater in deep than in shallow water despite the much lower irradiance at depth. Extensive CO2 supersaturation stimulated photosynthesis several-fold relative to the rates observed in air-saturated water. Tissues of Sphagnum were richer in nitrogen in deep than in shallow water during summer, but the importance of nutrient availability to annual moss growth remains unclear. 4 Reconstruction techniques are recommended for comparative studies on annual and interannual growth patterns of mosses within lakes and among lakes of different altitude, latitude and water chemistry. This information can be based on just a single collection and can therefore include remote sites with adverse climate.
t enrichment in the hypolimnion during summer stratification. MaximumA^6439^Thermal groundwaters (40-52 degrees C, pH = 7.4-7.8, Eh = 210- 245 mV) from Siping' an district, Shanxi Province, northwestern China, are hydrogeochemically unique. Their occurrence is controlled by faulted structures in Precambrian host rocks. Their hydrochemical type (5 springs and 2 wells) is mainly Cl- SO4-Na, with TDS values around 1.0 g/l. Some minor elements such as Si, Pr, Sr, and Li, as well as neutral and acid bituminous substances are so enriched that the thermal waters can also be regarded as mineral waters. Their origin is meteoric, as indicated by 3 lines of geochemical evidence: (1) their delta D and delta(18)O compositions are very close to the Craig meteoric line; (2) their dissolved gas compositions are N-2-dominated, with less O-2 and CO2; and (3) the He-3/He-4 ratios are low (0.028). Geochemical processes responsible for the genesis of the hydrochemical features of the waters include dissolution, mixing, and oxidation. The most important water- rock interaction is dissolution or hydrolysis of alumino- silicate minerals in the magmatic and metamorphic host rocks, since the waters are still undersaturated with respect to albite, anorthite, K-spar, and chlorite, as shown by saturation indices. The tritium contents of some thermal waters (46-53 TU), higher than the tritium concentration of local meteoric water, result from the mixing of thermal waters with cold, shallow-lying groundwaters that are from the 1960s. The predominant species of Fe in the thermal waters is Fe(OH)(3), as a result of oxidation processes under aerobic conditions of the aquifers. (C) 1997 Elsevier Science Ltd.

1836^4^Betts,RA^Cox,PM^Lee,SE^Woodward,FI^1997^1^Contrasting physiological and structural vegetation feedbacks in climate change simulations^36^387^6635^796-799^^^^^19 Jun^^^^^6442
2773^2829^314^633^669^783^812^ochemical processes responsible for the genesis of the hydrochemical features of the waters include dissolution, mixing, and oxidation. The most important water- rock interaction is dissolution or hyA^6441^Anthropogenic increases in the atmospheric concentration of carbon dioxide and other greenhouse gases are predicted to cause a warming of the global climate by modifying radiative forcing(1). Carbon dioxide concentration increases may make a further contribution to warming by inducing a physiological response of the global vegetation-a reduced stomatal conductance, which suppresses transpiration(2). Moreover, a CO2-enriched atmosphere and the corresponding change in climate may also alter the density of vegetation cover, thus modifying the physical characteristics of the land surface to provide yet another climate feedback(3-6). But such feedbacks from changes in vegetation structure have not yet been incorporated into general circulation model predictions of future climate change. Here we use a general circulation model iteratively coupled to an equilibrium vegetation model to quantify the effects of both physiological and structural vegetation feedbacks on a doubled- CO2 climate. On a global scale, changes in vegetation structure are found to partially offset physiological vegetation-climate feedbacks in the long term, but overall vegetation feedbacks provide significant regional-scale effects.

1837^3^Carey,EV^Callaway,RM^DeLucia,EH^1997^1^Stem respiration of ponderosa pines grown in contrasting climates: Implications for global climate change^2^111^1^19-25^^^^^Jun^^^^^6444
130^174^2830^2831^2832^360^423^427^520^605^riched atmosphere and the corresponding change in climate may also alter the density of vegetation cover, thus modifying the physical characteristics of the land surface to provide yet another climate feedback(3-6). But such feedbacks from changes in vegetation structure have not yet been incorporated into general circulation model predictions of future climate change. Here we use a general circulation model iteratively coupled to an equilibrium vegetation model to quantify the effects of both physiological and structural vegetation feedbacks on a doubled- CO2 climate. On a global scale, A^6443^We examined the effects of climate and allocation patterns on stem respiration in ponderosa pine (Pinus ponderosa) growing on identical substrate in the cool, moist Sierra Nevada mountains and the warm, dry, Great Basin Desert. These environments are representative of current climatic conditions and those predicted to accompany a doubling of atmospheric CO2, respectively, throughout the range of many western north American conifers. A previous study found that trees growing in the desert allocate proportionally more biomass to sapwood and less to leaf area than montane trees. We tested the hypothesis that respiration rates of sapwood are lower in desert trees than in montane trees due to reduced stem maintenance respiration (physiological acclimation) or reduced construction cost of stem tissue (structural acclimation). Maintenance respiration per unit sapwood Volume at 15 degrees C did not differ between populations (desert: 6.39 +/- 1.14 SE mu mol m(- 3) s(-1), montane: 6.54 +/- 1.13 SE mu mol m(-3) s(-1), P = 0.71) and declined with increasing stem diameter (P = 0.001). The temperature coefficient of respiration (Q(10)) varied seasonally within both environments (P = 0.05). Construction cost of stem sapwood was the same in both environments (desert: 1.46 +/- 0.009 SE g glucose g(-1) sapwood, montane: 1.48 +/- 0.009 SE glucose g(-1) sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees. Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic rates may be partially offset by increases in maintenance respiration in large trees growing in CO2-enriched atmospheres.

1838^3^DolcetSanjuan,R^Claveria,E^Huerta,A^1997^1^Androgenesis in Capsicum annuum L - Effects of carbohydrate and carbon dioxide enrichment^154^122^4^468-475^^^^^Jul^^^^^6446
1085^2471^2833^2834^2835^2836^2837^2838^2839^417^48 +/- 0.009 SE glucose g(-1) sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees. Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic rates may be partially offset by incrA^6445^A new and simple protocol for androgenesis in bell pepper is described. The initial medium, a modification of Nitsch and Nitsch's H medium, consisted of a two-phase system of semi- solid and liquid medium and contained maltose as carbon source. The total number of embryos formed was greater with maltose at 40 g . L-1, but embryos developed better at 10 to 20 g . L-1. Depending on the genotype, the number of embryos and plants recovered ranged from 3 to 750 and 0.25 to 8, respectively, per 100 flowers. Further increases in the number of embryos (up to 3561 per 100 flowers) and plants (up to 23 per 100 flowers) could be attained by flushing cultures with air enriched with CO2 at 900 mu L . L-1. The ploidy level and the microspore origin of the recovered plants were determined by flow cytometry and zymograms for isocitrate dehydrogenase. Nearly 65% of the acclimated plants had undergone spontaneous doubling of the chromosome number, as confirmed by flow cytometry of leaf nuclei. Isocitrate dehydrogenase zymograms demonstrated that plants originated from microspores and that the two parental alleles were equally represented among the haploid and dihaploid plants.

1839^2^Endo,M^Ikushima,I^1997^1^Effects of CO2 enrichment on yields and preservability of cut flowers in Phalaenopsis^180^66^1^169-174^^^^^Jun^^^^^6448
243^385^1, but embryos developed better at 10 to 20 g . L-1. Depending on the genotype, the number of embryos and plants recovered ranged from 3 to 750 and 0.25 to 8, respectively, per 100 flowers. Further increases in the number of embryos (up to 3561 per 100 flowers) and plants (up to 23 per 100 flowers) could be attained by flushing cultures with air enriched with CO2 at 900 mu L . L-1. The ploidy level and the microspore origin of the recovered plants were determined by flow cytometry and zymograms for isocitrate dehydrogenase. Nearly 65% of the acclimated plants had undergone spontaneous doubling of the chromosome number, as confirmed by flow cytometry of leaf nuclei. Isocitrate dehydrogenase A^6447^The effect of CO2 enrichment on Phalaenopsis cut flower production was examined for 30 months throughout five flowering cycles. The plant was cultured in three greenhouses with different CO2 levels of (A) : control, daily mean of ambient air = 438 ppm; (B) : 700 ppm; and (C) : 1000 ppm. 1. The fresh weight of cut flowers, the numbers of inflorescence and flowers per 20 plants varied, depending on the CO2 concentration for each flowering cycle. 2. The preservability (vase life) of cut flowers always improved under higher CO2 levels. Organic acid contents of plants were also higher under higher CO2 levels. The malic acid content in the flowers was higher than in the younger leaf and flower stalk at 1:00 PM and 10:00 PM; and it was also higher in the younger leaf than in the flower stalk at 10:00 PM, but lower at 1:00 PM. The pH value of plants was always lower at higher ambient CO2 levels, and lower in the younger leaf and flower stalk at 1:00 PM than at 10:00 PM, wheras at those same times the sugar content at the higher ambient CO2 levels reached its maximum.

1840^2^Endo,M^Ikusima,I^1997^1^Effects of CO2 enrichment by complete combustion of liquid petroleum gas on growth of Doritaenopsis^180^66^1^163-168^^^^^Jun^^^^^6450
188^374^417^
A^6449^The effects of increasing ambient CO2 levels on the growth of developing Doritaenopsis plants in a greenhouse were studied for 840 days. Leaf area, dry weight, and content of total carbon and total nitrogen in dry matter were measured every three months, and the time course of the relative growth rate (RGR) was investigated. Leaf area and dry weight increased with increasing CO2 concentration from 438 ppm to 946 ppm in the atmosphere. In an initial growth stage when plants were transplanted from flasks to pots, RGR increased as the CO2 level increased. RGR during a later vegetative growth stage was not affected by the CO2 concentration, and its value was 0.006/day. The value of RGR was less than that of the other C- 3, C-4, and CAM plants.




ame times the sugar co1842^4^Paustian,K^Elliott,ET^Peterson,GA^Killian,K^1996^1^Modelling climate, CO2 and management impacts on soil carbon in semi-arid agroecosystems^206^187^2^351-365^^^^^^^^^^6454
2840^32^344^376^429^51^534^848^962^979^^^6450
188^374^417^
A^6449^The effects of increasing ambient CO2 levels on the growth of developing Doritaenopsis plants in a greenhouse were studied for 840 days. Leaf area, dry weight, and content of total carbon and total nitrogen in dry matter were measured every three months, and the time course of the relative growth rate (RGR) was investigated. Leaf area and dry weight increased with increasing CO2 concentration from 438 ppm to 946 ppm in the atmosphere. In an initial growth stage when plants were transplanted from flasks to pots, RGR increased as the CO2 level increased. RGR during a later vegetative growth stage was not affected by the CO2 concentration, and its value was 0.006/day. The value of RGR was less than that of the other C- 3, C-4, and CAM plants.




ame times the sugar coA^6453^In agroecosystems, there is likely to be a strong interaction between global change and management that will determine whether soil will be a source or sink for atmospheric C. We conducted a simulation study of changes in soil C as a function of climate and CO2 change, for a suite of different management systems, at four locations representing a climate sequence in the central Great Plains of the US. Climate, CO2 and management interactions were analyzed for three agroecosystems: a conventional winter wheat-summer fallow rotation, a wheat-corn- fallow rotation and continuous cropping with wheat. Model analyses included soil C responses to changes in the amount and distribution of precipitation and responses to changes in temperature, precipitation and CO2 as projected by a general circulation model for a 2xCO(2) scenario. Overall, differences between management systems at all the sites were greater than those induced by perturbations of climate and/or CO2. Crop residue production was increased by CO2 enrichment and by a changed climate. Where the frequency of summer fallowing was reduced (wheat-corn-fallow) or eliminated (continuous wheat), soil C increased under all conditions, particularly with increased (640 mu L L-1) CO2. For wheat-fallow management, the model predicted declines in soil C under both ambient conditions and with climate change alone. Increased CO2 with wheat-fallow management yielded small gains in soil C at three of the sites and reduced losses at the fourth site. Our results illustrate the importance of considering the role of management in determining potential responses of agroecosystems to global change. Changes in climate will determine changes in management as farmers strive to maximize profitability. Therefore, changes in soil C may be a complex function of climate driving management and management driving soil C levels and not be a simple direct effect of either climate or management.
nduced by perturbations of climate and/or CO2. Crop residue production was increased by CO2 1843^3^Prior,LD^Eamus,D^Duff,GA^1997^1^Seasonal and diurnal patterns of carbon assimilation, stomatal conductance and leaf water potential in Eucalyptus tetrodonta saplings in a wet-dry savanna in northern Australia^182^45^^241-258^^^^^^^^^^6456
130^1627^174^243^2841^348^374^376^674^923^n soil C under both ambient conditions and with climate change alone. Increased CO2 with wheat-fallow management yielded small gains in soil C at three of the sites and reduced losses at the fourth site. Our results illustrate the importance of considering the role of management in determining potential responses of agroecosystems to global change. Changes in climate will determine changes in management as farmers strive to maximize profitability. Therefore, changes in soil C may be a complex function of climate driving management and management driving soil C levels and not be a simple direct effect of either climate or management.
nduced by perturbations of climate and/or CO2. Crop residue production was increased by CO2 A^6455^Seasonal and diurnal trends in carbon assimilation, stomatal conductance and leaf water potential were studied using 1-3 m tall saplings of Eucalyptus tetrodonta (F.Muell.). The study site was in an unburnt savanna near Darwin, where rainfall is strongly seasonal. Mean daily maximum assimilation rates ranged from 14.5 mu mol m(-2) s(-1) in May to 4.8 mu mol m(-2) s(-1) in October. There was a linear relationship between daily maximum assimilation rates and pre-dawn leaf water potential (r = 0.62, n = 508) and a log-log linear relationship between daily maximum stomatal conductance and pre-dawn leaf water potential (r = 0.68, n = 508). Assimilation rates and stomatal conductance were always higher in the morning than in the afternoon, irrespective of season. Stomatal conductance responded more strongly to leaf-to-air vapour pressure difference when pre-dawn leaf water potentials were moderately low (-0.5 to -1.5 MPa) than when they were very low (< -1.5 MPa) or high (> -0.5 MPa). Assimilation decreased sharply when temperature exceeded 35 degrees C. Seasonal trends in assimilation rate could be attributed primarily to stomatal closure, but diurnal trends could not. High leaf temperatures were a major cause of lower assimilation rates in the afternoon. Approximately 90% of leaves were lost by the end of the dry season, and above-ground growth was very slow. It is hypothesised that E. tetrodonta saplings allocate most photosynthate to root and lignotuber growth in order to tolerate seasonal drought and the high frequency of fire in northern Australian savannas.

1844^2^Wheeler,RM^Tibbitts,TW^1997^1^Influence of changes in daylength and carbon dioxide on the growth of potato^52^79^5^529-533^^^^^May^^^^^6458
1129^1170^130^1372^188^1953^2842^885^spective of season. Stomatal conductance responded more strongly to leaf-to-air vapour pressure difference when pre-dawn leaf water potentials were moderately low (-0.5 to -1.5 MPa) than when they were very low (< -1.5 MPa) or high (> -0.5 MPa). Assimilation decreasedA^6457^Potatoes (Solanum tuberosum L.) are highly productive in mid- to high-latitude areas where photoperiods change significantly throughout the growing season. To study the effects of changes in photoperiod on growth and tuber development of potato cv. Denali, plants were grown for 112 d with 400 mu mol m(-2) s(-1) photosynthetic photon flux (PPF) under a 12-h photoperiod (short days, SD), a 24-h photoperiod (long days, LD), and combinations where plants were moved between the two photoperiods 28, 56, or 84 d after planting. Plants given LD throughout growth received the greatest total daily PPF and produced the greatest tuber yields. At similar levels of total PPF, plants given SD followed by LD yielded greater tuber dry mass (DM) than plants given IID followed by SD. Stem DM per plant, leaf DM, and total plant DM all increased with an increasing proportion of LD and increasing daily PPF, regardless of the daylength sequence. When studies were repeated, but at an enriched (1000 mu mol mol(-1)) CO2 concentration, overall growth trends were similar, with high CO2 resulting in greater stem length, stem DM, leaf DM, and total plant DM; but high CO2 did not increase tuber DM. (C) 1997 Annals of Botany Company.

1845^2^Bacanamwo,M^Harper,JE^1997^1^Response of a hypernodulating soybean mutant to increased photosynthate supply^330^124^2^119-129^^^^^16 May^^^^^6460
1461^1809^2843^2844^2845^2846^2847^2848^312^859^eriod (long days, LD), and combinations where plants were moved between the two photoperiods 28, 56, or 84 d after planting. Plants given LD throughout growth received the greatest total daily PPF and produced the greatest tuber yields. At similar levels of total PPF, plants given SD followed by LD yielded greater tuber dry mass (DM) than plants given IID followed by SD. Stem DM per plant, leaf DM, and total plant DM all increased with an increasing proportion of LD and increasing daily PPF, regardless of the daylength sequence. When studies were repeated, but at an enriched (1000 mu mol mol(-1)) CO2 concenA^6459^Growth chamber studies were conducted to determine if increased photoassimilate supply, through light enhancement and CO2 enrichment, could reverse the deleterious plant growth and enhance nodule function traits of NOD1-3, a hypernodulating mutant of Williams. Both light enhancement and CO2 enrichment increased nodule number, acetylene reduction activity plant(-1) (but not specific activity) and dry matter accumulation in all tissues in both genotypes. Total biomass and specific nitrogenase activity were always less in the mutant than in Williams 82, indicating that the inferiority of the mutant may not be reversed by enhanced photoassimilate supply. Under all growth conditions, the mutant allocated relatively more photosynthate to nodules and less photosynthate to roots, compared to the control. Despite this, the decreased growth of the mutant relative to the control was not solely attributable to excessive nodulation of the mutant, since decreased growth was observed even on uninoculated plants. It is suggested that light enhancement and CO2 enrichment may have stimulated nodulation through increased photosynthate supply, independent of the nodulation autoregulatory signal. (C) 1997 Elsevier Science Ireland Ltd.

1846^2^Chen,K^Lenz,F^1997^1^Responses of strawberry to doubled CO2 concentration and phosphorus deficiency .1. Distribution of dry matter, macronutrients, and carbohydrates^172^62^1^30-37^^^^^Jan-Feb^^^^^6462
312^344^376^417^434^757^92^otypes. Total biomass and specific nitrogenase activity were always less in the mutant than in Williams 82, indicating that the inferiority of the mutant may not be reversed by enhanced photoassimilate supply. Under all growth conditions, the mutant allocated relatively more photosynthate to nodules and less photosynthate to roots, compared to the control. Despite this, the decreased growth of the mutant relative to the control was not solely attributable to excessive nodulation of the mutant, since decreased growth was observed even on uninoculated plants. It A^6461^One-year-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants grown in controlled environmental chambers were supplied with a modified P-sufficient (0.5 mmol P l(-1)) or P-deficient (0.05 mmol P l(-1)) Hoagland nutrient solution and acclimatized by an ambient CO2 (340 +/- 20 ppm) or doubled CO2 (680 +/- 20 ppm) concentration for one month. Doubled CO2 concentration promoted plant vegetative growth and dry matter assimilation, especially in leaf area enlargement, leaf dry weight, and runner extending growth. The plant responses to doubled CO2 concentration were more pronounced under P- sufficient than P-deficient conditions. P deficiency not only moderated the above plant responses to CO2 enrichment, but also accelerated premature leaf senescence and aggravated P- deficient symptoms at doubled CO2 concentration. The mean increment in total dry matter of the plants in virtue of doubled CO2 concentration and P-sufficiency were 25-63 % and 123-191 %, respectively. Doubled CO2 concentration reduced N level in the plant organs, particularly in both new and old leaves and runners, while increased the contents of starch, glucose, fructose, sucrose, and total non-structural carbohydrates in most organs; but not particularly affected contents of P, K, Ca, and Mg. P deficiency decreased contents of N, P, K, Mg, and soluble carbohydrates, while increased root : shoot ratio and starch level in roots, stems, runners, and leaves whether at the ambient CO2 or at doubled CO2 condition. Neither doubled CO2 nor P deficiency definitely altered Ca content in the plant organs.
n were more pronounced under P- sufficient than P-deficient conditions. P deficiency not only moderated the above plant responses to CO2 enrichment, but also accelerated premature leaf senescence and aggravated P- deficient symptoms at doubled CO2 concentration. The mean increment in total dry matter of the plants in virtue of doubled CO2 concentration and P-sufficiency were 25-63 % and 123-191 %, respectively. Doubled CO2 concentration redu1847^35^Grime,JP^Thompson,K^Hunt,R^Hodgson,JG^Cornelissen,JHC^Rorison,IH^Hendry,GAF^Ashenden,TW^Askew,AP^Band,SR^Booth,RE^Bossard,CC^Campbell,BD^Cooper,JEL^Davison,AW^Gupta,PL^Hall,W^Hand,DW^Hannah,MA^Hillier,SH^Hodkinson,DJ^Jalili,A^Liu,Z^Mackey,JML^Matthews,N^Mowforth,MA^Neal,AM^Reader,RJ^Reiling,K^RossFraser,W^Spencer,RE^Sutton,F^Tasker,DE^Thorpe,PC^Whitehouse,J^1997^1^Integrated screening validates primary axes of specialisation in plants^15^79^2^259-281^^^^^Jun^^^^^6464
1074^1159^1696^2849^2850^2851^349^423^540^673^efinitely altered Ca content in the plant organs.
n were more pronounced under P- sufficient than P-deficient conditions. P deficiency not only moderated the above plant responses to CO2 enrichment, but also accelerated premature leaf senescence and aggravated P- deficient symptoms at doubled CO2 concentration. The mean increment in total dry matter of the plants in virtue of doubled CO2 concentration and P-sufficiency were 25-63 % and 123-191 %, respectively. Doubled CO2 concentration reduA^6463^Standardised procedures have been used to measure 67 traits in 43 common plants of the British flora. This paper provides an interpretation of the most consistent patterns in the resulting matrix by means of correlation, ordination and classification analyses. Only a weak coupling was observed between attributes of the regenerative and established phases of the life history. However, within each phase, attributes were strongly aggregated into sets and a high proportion of the variation between species coincided with a single axis. Attributes of the established phase displayed remarkably consistent trends, with a strong 'Axis 1' being identified by three different multivariate methods. There was a marked correlation between foliar concentrations of N, P, K, Ca and Mg, high concentrations of which coincided with the capacity for rapid growth in productive conditions and an inability to sustain yield under limiting supplies of nutrients. A diverse array of other traits, less immediately involving mineral nutrients, were also entrained in Axis 1; these included life history, root and shoot foraging, the morphology, longevity, tensile strength and palatability of leaves, and the decomposition rate of leaf litter. This pattern occurred in both monocotyledons and dicotyledons and appeared to reflect a tradeoff between attributes conferring an ability for high rates of resource acquisition in productive habitats and those responsible for retention of resource capital in unproductive conditions. The second axis of variation evident in the established phase was related to phylogeny and distinguished between monocotyledons and dicotyledons on the basis of a diverse set of traits including genome size, cell size, root and shoot foraging characteristics and vascular tissues. A third axis was detected in which ephemerals and perennials were separated by differences in attributes such as breeding system, leaf decomposition rate and a set of traits reflecting the small stature of many short-lived plants. In the regenerative phase, the leading axis was clearly related to the widely recognised tradeoff between seed size and seed number and was consistent with current understanding of seed banks, and with modern theories explaining species coexistence in terms of complementary responses to temporal and spatial variation in vegetation gap dynamics. The data provide strong evidence of functional integration between evolutionary specialisations in root and shoot and support Donald's unified theory of competitive ability. The data are not consistent with theories of functional types based upon evolutionary tradeoffs in allocation between root and shoot. We suggest that the evidence assembled here and elsewhere in the current literature points to the existence of primary functional types, including those recognised by Ramenskii and Grime. These functional types can be reconciled with the individuality of plant ecologies in the field and provide an effective basis For interpretation and prediction at various scales from the plant community to regional floras. There are particular opportunities for prediction of successional trajectories, the role of herbivores in vegetation succession and the response of vegetation to eutrophication and extreme climatic events. It is also suggested that aspects of this investigation may provide a Darwinian underpinning for Odum's theory of ecosystem maturation.

1848^2^Hunt,R^Cornelissen,JHC^1997^1^Components of relative growth rate and their interrelations in 59 temperate plant species^84^135^3^395-417^^^^^Mar^^^^^6466
1721^2069^2073^2184^2852^312^349^385^750^803^evolutionary tradeoffs in allocation between root and shoot. We suggest that the evidence assembled here and elsewhere in the current literature points to the existence of primary functional types, including those recognised by Ramenskii and Grime. These functional types can be reconciled with the individuality of plant ecologies in the field and provide an effective basis For interpretation and prediction at various scales from the plant cA^6465^Three groups of species (21 herbaceous monocotyledons, 22 herbaceous dicotyledons and 16 woody dicotyledons), including representatives of a wide range of natural habitats and life forms in inland Britain, were grown in the seedling phase in a resource-rich controlled environment and assessed over a 14-day period (21 d in the case of woody species). Mean values of relative growth rate (RGR), Unit leaf rate (ULR), leaf area ratio (LAR), leaf weight fraction (LWF), specific leaf area (SLA), and the root-shoot allometric coefficient were derived. In herbaceous species, the grand mean RGR was 0.20 d(-1), comparable to values previously recorded. For woody species, the mean was 0.09 d(-1). An existing assumption linking high RGR to high allocation to photosynthetic biomass was upheld by comparisons made between groups. Within groups, however, no pattern of this kind could be demonstrated. When photosynthetically active radiation was increased from 125 to 250 mu mol m(-2) s(-1), ULR was increased almost pro rata. The parallel response in RGR was only slight, being offset by considerable reductions in LAR. The apparent mean quantum yield for photosynthesis in herbaceous species (whole-plant d. wt basis) was 0.60 g mol(-1). There was no significant dependence of RGR on ULR in any of the three groups of species, although the absolute magnitude of ULR declined in the order: herbaceous monocotyledons > herbaceous dicotyledons > woody dicotyledons. In all three groups, RGR was strongly dependent upon LAR but no differences emerged in absolute scale of LAR. The absolute scale of mean LWF decreased from herbaceous to woody species, but the dependence of LAR on LWF strengthened. Groups showed no systematic differences in magnitude of SLA, but the correlation of LAR with SLA was strong throughout. Multiple regression showed that the leading determinants of RGR were ULR and SLA in herbaceous species and LWF in woody species. Principal components analyses (PCA) on each of the three groups explained at least 77% of variation and agreed closely with an optimal (non-hierarchical) classification. Only six cluster 'types' were recognized out of the 16 theoretically possible combinations of 'high' or 'low' values of the four growth parameters. Strong evidence of evolutionary trade-offs emerged, most strikingly in that high RGR was never seen in combination with low SLA. The morphological/physiological types identified by an all-groups PCA separated woody from the herbaceous species, but dicotyledons were almost congruent with the monocotyledons. The non-growth-analytical attributes most strongly correlated with mean RGR were percentage yield at a low level of mineral nutrients, leaf nitrogen concentration, and seed weight. It was concluded that mean RGR plays a central role in the identification of pathways of evolutionary specialization in herbaceous species.
ts of RGR were ULR and SLA in herbaceous species and LWF in woody species. Principal components analyses (PCA) on each of the three groups explained at least 77% of variati1849^5^Sallanon,H^Isaka,H^Dimon,B^Ravel,C^Chagvardieff,P^1997^1^CO2 exchanges and nutrient uptake during multiplication and rooting of micropropagated Juglans regia plantlets^330^124^1^107-116^^^^^18 Apr^^^^^6468
1869^243^376^561^610^781^92^olutionary trade-offs emerged, most strikingly in that high RGR was never seen in combination with low SLA. The morphological/physiological types identified by an all-groups PCA separated woody from the herbaceous species, but dicotyledons were almost congruent with the monocotyledons. The non-growth-analytical attributes most strongly correlated with mean RGR were percentage yield at a low level of mineral nutrients, leaf nitrogen concentration, and seed weight. It was concluded that mean RGR plays a central role in the identification of pathways of evolutionary specialization in herbaceous species.
ts of RGR were ULR and SLA in herbaceous species and LWF in woody species. Principal components analyses (PCA) on each of the three groups explained at least 77% of variatiA^6467^CO2 gas exchanges in light and dark, PEPC and Rubisco activities and consumption of sugar and mineral nutrients (K+, Ca2+ Mg2+: NH4+, NO3-, PO43-, SO42-) were measured during multiplication and rooting stages of in vitro-cultivated Juglans regia. CO2 gas exchanges in light and dark, and PEPC and Rubisco activities varied with plantlet age during a growth cycle. They were higher during the first part of the exponential stage of growth (defined in terms of dry weight increase). Respiratory gas exchanges were always higher than photosynthetic ones. The differences between the two stages of growth were reflected in respiration/photosynthesis and total Rubisco activity/initial Rubisco activity ratios, which were higher in the rooting than in the multiplication stage. This work underlines the need to consider the wide variations in photosynthetic and respiratory gas exchanges related to the plantlet development stage. Mineral absorption also displayed variations, both in the quantity and selectivity of the inorganic nutrients supplied. During the multiplication stage, fast exhaustion of PO43- and NH4(+) occurred, whereas depletion of Ca2+, NH4+, PO43- and SO42- were observed throughout the rooting stage. The inhibition of photosynthetic activity may be linked to the presence of sugar in the medium and also to ion deficiencies during the multiplication stage. Hence, this work also highlights the importance of mineral elements, suggesting a need to review nutrient medium compositions. (C) 1997 Elsevier Science Ireland Ltd.

1850^1^Tajiri,T^1997^1^Studies on the cultivation and storage quality of bean sprouts .13. Growth and quality of thick bean sprouts cultivated with a CO2-enriched rotary method^346^44^4^332-339^^^^^^^^^^6470
he rooting than in the multiplication stage. This work underlines the need to consider the wide variations in photosynthetic and respiratory gas exchanges related to the plantlet development stage. Mineral absorption also displayed variations, both in the quantity and selectivity of the A^6469^Thick bean sprouts cultivated using a rotary box (rotary cultivation, RC) have a decreased yield and inferior quality, although the growth of sprouts from the beans is promoted and the nutrient content of the sprouts is improved(1)2)). Because exposure to high levels of carbon dioxide was useful for promoting the growth of the hypocotyl and increasing the quantity of harvested sprouts(3)), we combined the rotary box method with the CO2-enriched method(1)). Herein the usefulness of this combination method for improving the physical properties and the yield of bean sprouts by controlling hypocotyl growth were examined.

1851^4^Baker,JT^Allen,LH^Boote,KJ^Pickering,NB^1997^1^Rice responses to drought under carbon dioxide enrichment .1. Growth and yield^127^3^2^119-128^^^^^Apr^^^^^6472
1760^349^409^439^629^634^ wide variations in photosynthetic and respiratory gas exchanges related to the plantlet development stage. Mineral absorption also displayed variations, both in the quantity and selectivity of the A^6471^Projections of future climate change include a strong likelihood of a doubling of current atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Drought stress is a major environmental limitation for crop growth and yield and is common in rainfed rice production systems. This study was conducted to determine the growth and grain yield responses of rice to drought stress under [CO2] enrichment. Rice (cv. IR-72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 mu mol CO2 mol(-1) air. In both [CO2], water management treatments included continuously hooded (CF) controls, flood water removed and drought stress imposed at panicle initiation (PI), anthesis (ANT), and both panicle initiation and anthesis (PI & ANT). The [CO2] enrichment increased growth, panicles plant(-1) and grain yield. Drought accelerated leaf senescence, reduced leaf area and above-ground biomass and delayed crop ontogeny. The [CO2] enrichment allowed 1-2 days more growth during drought stress cycles. Grain yields of the PI and PI & ANT droughts were similar to the CF control treatments while the ANT drought treatment sharply reduced growth, grain yield and individual grain mass. We conclude that in the absence of air temperature increases, future global increases in [CO2] should promote rice growth and yield while providing a modest reduction of near 10% in water use and so increase drought avoidance.





1853^2^Loaiza,J^Cantwell,M^1997^1^Postharvest physiology and quality of cilantro (Coriandrum sativum L)^170^32^1^104-107^^^^^Feb^^^^^6476
1000^348^454^560^ts included continuously hooded (CF) controls, flood water removed and drought stress imposed at panicle initiation (PI), anthesis (ANT), and both panicle initiation and anthesis (PI & ANT). The [CO2] enrichment increased growth, panicles plant(-1) and grain yield. Drought accelerated leaf senescence, reduced leaf area and above-ground biomass and delayed crA^6475^Respiration rates of freshly harvested cilantro were moderately high (CO2 at 15 to 20 mu L . g(-1). h(-1)) and ethylene production rates were low (<0.2 nL . g(-1). h(-1)) at 5 degrees C and were typical of green leafy tissues. Cilantro stored in darkness at a range of temperatures in air or controlled atmospheres was evaluated periodically for visual quality, decay, aroma, off-odor, color, and chlorophyll content. Cilantro stored in air at 0 degrees C had good visual quality for 18 to 22 days, while at 5 and 7.5 degrees C good quality was maintained for about 14 and 7 days, respectively. An atmosphere of air plus 5% or 9% CO2 extended the shelf-life of cilantro stored at 7.5 degrees C to about 14 days. Quality of cilantro stored in 3% O(2)plus CO2 was similar to that stored in air plus CO2. Atmospheres enriched with 9% to 10% CO2 caused dark lesions after 18 days; 20% CO2 caused severe injury after 7 days. Although visual quality could be maintained for up to 22 days, typical cilantro aroma decreased notably after 14 days, regardless of storage conditions.

1854^2^Murchie,EH^Horton,P^1997^1^Acclimation of photosynthesis to irradiance and spectral quality in British plant species: Chlorophyll content, photosynthetic capacity and habitat preference^9^20^4^438-448^^^^^Apr^^^^^6478
1240^2033^2048^2287^2346^2853^348^411^567^635^uated periodically for visual quality, decay, aroma, off-odor, color, and chlorophyll content. Cilantro stored in air at 0 degrees C had good visual quality for 18 to 22 days, while at 5 and 7.5 degrees C good quality was maintained for about 14 and 7 days, respectively. An atmosphere of air plus 5% or 9% CO2 extended the shelf-life of cilantro stored at 7.5 degrees C to about 14 days. Quality of cilantro stored in 3% O(2)plus CO2 was similar to that stored in air plus CO2. Atmospheres enriched with 9% to 10% CO2 caused dark lesions after 18 days; 20% CO2 caused severe injury after 7 days. Although visual quality could be maintained for up to 22 days, typical cilantro aroma decreased A^6477^Twenty-two common British angiosperms were examined for their ability to acclimate photosynthetically to sun and shade conditions, Plants were grown under low irradiance, far-red enriched light (50 mu mol m(-2) s(-1)), selected to mimic as closely as possible natural canopy shade, and moderately high light of insufficient irradiance to induce photoinhibitory or photoprotective responses (300 mu mol m(-2) s(-1)), Light- and CO2-saturated photosynthetic rates of m s oxygen evolution (P- max) and chlorophyll content were measured, Large variation was found in both parameters, and two 'strategies' for long-term acclimation were identified: firstly a change in chlorophyll per unit leaf area which was found to correlate positively with photosynthetic capacity, and secondly changes in chlorophyll a/b ratio and P-max, indicative of alterations at the chloroplast level, which were not associated with a change in chlorophyll content per unit leaf area, Combinations of these two strategies may occur, giving rise to the observed diversity in photosynthetic acclimation, The extent and nature of photosynthetic acclimation were compared with an index of shade association, calculated from the association each species has with woodland, It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in 'sun' species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level, A framework for explaining the variation between plant species in leaf-level photosynthetic capacity, in relation to the natural light environment, is presented, This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.




ere not associated with a change in chlorophyll content per unit leaf area, Combinations of these two strategies may occur, giving rise1856^3^Reddy,KR^Hodges,HF^McKinion,JM^1997^1^Modeling temperature effects on cotton internode and leaf growth^164^37^2^503-509^^^^^Mar-Apr^^^^^6482
1332^2011^312^348^434^from the association each species has with woodland, It was found that the greatest flexibility for change at the chloroplast level was found in those species possessing an intermediate shade association, whilst acclimation in 'sun' species proceeded by a change in chlorophyll content; obligate shade species showed little capacity for acclimation at either the chloroplast or leaf level, A framework for explaining the variation between plant species in leaf-level photosynthetic capacity, in relation to the natural light environment, is presented, This is the first time the potential for light acclimation of photosynthesis in different plant species has been satisfactorily linked to habitat distribution.




ere not associated with a change in chlorophyll content per unit leaf area, Combinations of these two strategies may occur, giving riseA^6481^Cotton (Gossypium hirsutum L.) is grown commercially in temperatures that vary greatly during the season. The purpose of this study was to develop potential growth and developmental rates of cotton leaves and internodes as a function of temperature in a temperature-limiting environment. That information may be used with growth duration and appropriate stress factors to develop a crop canopy development model. Plants were grown in sunlit plant growth chambers in five temperatures, 20/12 degrees C to 40/32 degrees C (day/night), at ambient (350 mu L L-1 CO2) and twice ambient carbon dioxide levels in well-watered and fertilized conditions. Plants were monitored daily for leaf unfolding dates, areas of leaves, and lengths of internodes at leaf unfolding, and growth of leaves and internodes. Durations of leaf and internode expansion were also determined. Leaf unfolding interval rates of both mainstem and fruiting branches increased as temperature increased; the rate of mainstem leaf unfolding interval increased more than the rate of branch leaf unfolding. Irrespective of sizes, leaves, and internodes fit a single relationship of relative expansion rates and age for each temperature condition. Enriching CO2 to twice the ambient level did not change these relationships. Increasing temperature increased maximum growth rate, decreased the decay in the rate of expansion due to age, and reduced growth duration of both leaves and internodes. Internodes typically took less time than leaves to elongate at all temperatures. Leaf area and internode length at leaf unfolding increased as temperature increased to 27 to 30 degrees C, then decreased at higher temperatures.

1857^1^Sultemeyer,D^1997^1^Changes in the CO2 concentrating mechanism during the cell cycle in Dunaliella tertiolecta^118^110^1^55-61^^^^^Feb^^^^^6484
1020^1085^1453^2244^243^2854^528^543^573^958^ined. Leaf unfolding interval rates of both mainstem and fruiting branches increased as temperature increased; the rate of mainstem leaf unfolding interval incA^6483^Synchronised cells of Dunaliella tertiolecta were used to investigate the expression of the CO2 concentrating mechanism over the cell cycle during growth in either ambient air (low Ci cells) or air enriched with 5% CO2 (high Ci cells). The cultures were analysed for extracellular carbonic anhydrase activity, affinity of photosynthesis for inorganic carbon (Ci) and the ability to accumulate Ci. In high Ci cells, carbonic anhydrase activity changed between 2-4 units mg(-1) Chl during the light-dark rhythm showing no clear periodicity. Similarly, the apparent affinity for Ci remained rather constant over the cell cycle. This was judged from the Ci concentrations required for half maximum rate of photosynthesis (K-1/2(Ci)) of 72-80 mu M. In the same cells the accumulation ratio of internal Ci versus external Ci ranged between 5 and 9.5 without a clear rhythm. In contrast, these parameters showed distinct periodical changes in synchronised low Ci cells. Carbonic anhydrase activity changed from 10 to 350 units mg(-1) Chl with maximum and minimum activities occurring in the middle and at the end of the light period, respectively. The K-1/2(Ci) values showed similar periodicity ranging between 13-36 mu M. In addition the accumulation ratio increased up to 30 in the middle of illumination and decreased to its lowest level of 12 at the end of the light period. These results indicate the presence of a common step in regulating the induction of the measured parameters and that light is not an absolute requirement for the induction of the CO2 concentrating mechanism in synchronous low CO2 grown cells of Dunaliella tertiolecta.

1858^3^Weltzin,JF^Archer,S^Heitschmidt,RK^1997^1^Small-mammal regulation of vegetation structure in a temperate Savanna^11^78^3^751-763^^^^^Apr^^^^^6486
1770^2855^2856^2857^2858^2859^2860^429^751^956^nged between 5 and 9.5 without a clear rhythm. In contrast, these parameters showed distinct periodical changes in synchronised low Ci cells. Carbonic anhydrase activity changed from 10 to 350 unA^6485^Explanations for documented increases in woody plant dominance in grasslands and savannas of North America include atmospheric CO2 enrichment and changes in climate, livestock grazing, and fire regimes. However, tree/shrub encroachment has also coincided with the eradication of a once widespread native herbivore, the black-tailed prairie dog (Cynomys ludovicianus). We used field experiments and repeat aerial photography to demonstrate that prairie dogs, and the herbivores and granivores associated with their colonies, probably maintained grassland and savanna by preventing woody species such as Prosopis glandulosa (honey mesquite) from establishing or attaining dominance. Prosopis seed and pod disappearance was 3- 99 times greater within prairie dog colonies. Ants were the primary agent of seed removal, whereas prairie dogs and associated vertebrates were the primary agents of pod removal. Survival of Prosopis seedlings protected from vertebrate herbivory was similar on and off prairie dog colonies (approximate to 60%), whereas survival of unprotected seedlings was 3 times greater off- than on-colony. On-colony, prairie dogs and associated herbivores girdled and destroyed all Prosopis saplings within 2 d of planting; survival of 1-yr-old seedlings was reduced by 50% after 3 mo of exposure to on- colony herbivores. Despite high levels of woody plant seed disappearance and seedling herbivory, on-colony ''seedling'' reserves were substantial (950 plants/ha). Thus, prairie dogs and the fauna that occur on their colonies suppressed rather than eliminated Prosopis from the colony site. Removal of prairie dogs led to rapid development of Prosopis stands. Repeat aerial photography showed that Prosopis canopy cover on a colony eradicated in 1950 (27%) increased to a level (61%) comparable to that of off-colony Prosopis stands (65%) within 23 yr. These data illustrate how transitions from grassland to woodland vegetation can be mediated by a rodent herbivore. They further demonstrate how purposeful or inadvertent removal of native herbivores can have unforeseen effects on plant species composition and landscape physiognomy. Investigations of environmental constraints on vegetation distribution and abundance should take into account the historical role of herbivores in shaping the present system. Inconsistencies among historic accounts of woody plant distribution and abundance in semiarid western North America may be resolved by considering population dynamics of prairie dogs. Widespread eradication of this formerly abundant rodent has eliminated a significant constraint to woody plant establishment on many semiarid grassland and savanna landscapes and has thereby facilitated transitions to shrubland and woodland states. Past land management designed to remove one perceived impediment to livestock production appears to have contributed significantly to development of another management problem that is now a major detriment to sustainable livestock production.
e. They further demonstrate how purposeful or inadvertent 1859^3^Hertstein,U^Fangmeier,A^Jager,HJ^1996^1^ESPACE-wheat (European Stress Physiology and Climate Experiment-project 1: Wheat): Objectives, general approach, and first results^292^70^5-6^172-180^^^^^Dec^^^^^6488
2734^312^344^417^447^673^962^f herbivores in shaping the present system. Inconsistencies among historic accounts of woody plant distribution and abundance in semiarid western North America may be resolved by considering population dynamics of prairie dogs. Widespread eradication of this formerly abundant rodent has eliminated a significant constraint to woody plant establishment on many semiarid grassland and savanna landscapes and has thereby facilitated transitions to shrubland and woodland states. Past land management designed to remove one perceived impediment to livestock production appears to have contributed significantly to development of another management problem that is now a major detriment to sustainable livestock production.
e. They further demonstrate how purposeful or inadvertent A^6487^The ''European Stress Physiology and Climate Experiment - project 1: wheat'' (acronym: ESPACE-wheat) is funded by the EU since 1994. In the present paper the projects goals, the general methodological approach, and a summary of the experimental work performed in 1994 and 1995 are described. Main objectives of the project are 1) to investigate experimentally the sensitivity of wheat growth, development and productivity to changes in CO2 concentration, climatic variables and other physiological stresses, 2) to use experimental data for extension, improvement and validation of process-based wheat growth simulation models, and 3) to use models for assessments of the influences on crops of climatic change, increasing CO2 concentration and additional physiological stresses in Europe. Most experimental investigations are being performed by means of open-top chambers (OTC's) according to a common standard protocol to meet specific data requirements for model construction and validation. ESPACE-wheat OTC-experiments in 1994 and 1995 are summarized and the principal methods of data evaluation are presented by analyzing responses of grain yield and aboveground biomass of spring wheat, cv. Minaret, to CO2 enrichment and other factors varied in experiments at different sites. The mean observed CO2-doubling responses was about 1.4, i.e. grain yield and biomass production were increased by about 40% compared to growth in ambient CO2 concentration. However, there was a large variability of responses between sites and years. Results are discussed with respect to modeling attempts.

1860^4^Hungate,BA^Jordan,TE^Jackson,RB^Drake,BG^1997^1^Atmospheric nitrogen deposition^32^275^5301^739-740^^^^^7 Feb
312^349^417^420^92^
1861^3^Martinez,I^Orus,MI^Marco,E^1997^1^Carboxysome structure and function in a mutant of Synechococcus that requires high levels of CO2 for growth^184^35^2^137-146^^^^^Feb^^^^^6491
1545^1856^243^2786^2861^2862^2863^2864^448^570^data requirements for model construction and validation. ESPACE-wheat OTC-experA^6490^The high CO2-requiring mutant N1 of Synechococcus sp. PCC 7942 possesses aberrant carboxysomes and is unable to utilize the internal inorganic carbon pool for photosynthesis. Normal carboxysomal carbonic anhydrase (EC 4.2.1.1) and ribulose 1,5 bisphosphate carboxylase/oxygenase (EC 4.1.1.39) activities were obtained under saturated substrate concentrations, but limiting concentrations of inorganic carbon resulted in a lower Rubisco activity compared to the wild type. The polypeptidic pattern of carboxysome-enriched fractions showed no differences between wild type and mutant N1, suggesting that the putative gene product inactivated in the mutant does not constitute a polypeptide of the carboxysome shell, but could play an important role in the process of carboxysome assembly. Data obtained are discussed in relation to the proposed quantitative model of the inorganic carbon concentrating mechanism of cyanobacteria.
48^570^data requirements for model construction and validation. ESPACE-wheat OTC-exper1862^4^Mitchell,CA^Chun,CH^Brandt,WE^Nielsen,SS^1997^1^Environmental modification of yield and nutrient composition of 'Waldmann's Green' leaf lettuce^214^20^1^73-80^^^^^Jan^^^^^6493
1507^188^2865^92^ carbonic anhydrase (EC 4.2.1.1) and ribulose 1,5 bisphosphate carboxylase/oxygenase (EC 4.1.1.39) activities were obtained under saturated substrate concentrations, but limiting concentrations of inorganic carbon resulted in a lower Rubisco activity compared to the wild type. The polypeptidic pattern of carboxysome-enriched fractions showed no differences between wild type and mutant N1, suggesting that the putative gene product inactivated in the mutant does not constitute a polypeptide of the carboxysome shell, but could play an important role in the process of carboxysome assembly. Data obtained are discussed in relation to the proposed quantitative model of the inorganic carbon concentrating mechanism of cyanobacteria.
48^570^data requirements for model construction and validation. ESPACE-wheat OTC-experA^6492^Leaf number, dry weight, and nutrient composition of Lactuca sativa L. cv. 'Waldmann's Green leaves were compared following 9 days of treatment in a controlled environment room under various combinations of photosynthetic photon flux (PPF:350 vs 800 mu mol m(-2) s(-1)), atmospheric CO2 level (ambient vs 1500 mu mol mol(-1)), and single-strength (1X:15 mM) vs double- strength (2X:30 mM nitrogen (N) as NO3- alone or as NH4+ + NO3- (1:5 molar ratio). CO2 enrichment greatly enhanced leaf number under all PPF and N conditions, but increased leaf dry weight only at high PPF . Conditions favoring high photosynthesis enhanced leaf starch content 3-fold, and protein content increased as much as 64% with 2X NH4++NO3-. Free sugar content was 6 to 9% of leaf dry weight for all treatment combinations, while fat was 1.5 to 3.5%. Ash content varied from 15 to 20% of leaf dry weight. Modified controlled environments can be used to enhance the nutritional content as well as the yield of crops to be used for life support in space-deployed, self- sustaining human habitats. Leaf lettuce is a useful model crop for demonstrating the potential of nutritional value added by environmental manipulation.

1863^2^Pedersen,O^SandJensen,K^1997^1^Transpiration does not control growth and nutrient supply in the amphibious plant Mentha aquatica^9^20^1^117-123^^^^^Jan^^^^^6495
1020^2866^2867^2868^2869^983^ngth (2X:30 mM nitrogen (N) as NO3- alone or as NH4+ + NO3- (1:5 molar ratio). CO2 enrichment greatly enhanced leaf number under all PPF and N conditions, but increased leaf dry weight only at high PPF . Conditions favoring high photosynthesis enhanced leaf starch content 3-fold, and protein content increased as much as 64% with 2X NH4++NO3-. Free sugar content was 6 to 9% of leaf dry weight for all treatment combinations, while fat was 1.5 to 3.5%. Ash content varied from 15 to 20% of leaf dry weight. Modified controlled environments can be used to enhance the nutritional content as well as the yield of crops to be used for life suppoA^6494^Mentha aquatica L. was grown at different nutrient availabilities in water and in air at 60% RH, The plants were kept at 600 mmol m(-3) free CO2 dissolved in water (40 times air equilibrium) and at 30 mmol m(-3) CO2 in air to ensure CO2 saturation of growth in both environments, We quantified the transpiration-independent water transport from root to shoot in submerged plants relative to the transpiration stream in emergent plants and tested the importance of transpiration in sustaining nutrient flux and shoot growth. The acropetal water flow was substantial in submerged Mentha aquatica, reaching 14% of the transpiration stream in emergent plants, The transpiration-independent mass flow of water from the roots, measured by means of tritiated water, was diverted to leaves and adventitious shoots in active growth, The plants grew well and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in fertile sediments, Restricted O-2 supply to the roots of submerged plants may account for the smaller nutrient concentrations, though these exceeded the levels required to saturate growth, In hydroponics, the root medium was aerated and circulated between submerged and emergent plants to minimize differences in medium chemistry, and here the two growth forms behaved similarly and could fully exploit nutrient enrichment. It is concluded that the lack of transpiration from leaf surfaces in a vapour- saturated atmosphere, or under water, is not likely to constrain the transfer of nutrients from root to shoot in herbaceous plants, Nutrient deficiency under these environmental conditions is more likely to derive from restricted development and function of the roots in waterlogged anoxic soils or from low porewater concentrations of nutrients.
ell and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in fer1864^3^RossKarstens,GS^Ebert,G^Ludders,P^1996^1^Influence of CO2 concentration, light intensity, and sucrose concentration on net photosynthesis of citrus plantlets during in vitro propagation^292^70^5-6^188-193^^^^^Dec^^^^^6497
1852^312^376^561^781^92^ubmerged and emergent plants to minimize differences in medium chemistry, and here the two growth forms behaved similarly and could fully exploit nutrient enrichment. It is concluded that the lack of transpiration from leaf surfaces in a vapour- saturated atmosphere, or under water, is not likely to constrain the transfer of nutrients from root to shoot in herbaceous plants, Nutrient deficiency under these environmental conditions is more likely to derive from restricted development and function of the roots in waterlogged anoxic soils or from low porewater concentrations of nutrients.
ell and at the same rates in water and air, but nutrient fluxes to the shoot were greater in plants grown in air than in those that were submerged when they were rooted in ferA^6496^Light curves of the CO2 gas exchange of irt vitro plantlets of citrus (Citrus limonia Osb. (Rutaceae)) were measured continuously in an open system using different CO2 concentrations (350, 1000, and 2000 mu l l(-1) CO2). The plantlets were grown in media with sucrose concentrations from 0 to 5% under light intensities of 60, 100, and 260 mu mol m(- 2) l(-1). Before starting the measurements the plantlets were pretreated with 1000 mu l l(-1) CO2 for several weeks. Control plantlets were grown for the same period in gas tight vessels. CO2 concentration of the gas atmosphere inside the plant vessels had a stronger influence on CO2 gas exchange of citrus plantlets than sucrose concentration of the medium. Net photosynthesis of plantlets grown under various light intensities differed only little when using the same CO2 concentration for measurement as used for growing. After pretreatment with 1000 mu l l(-1) CO2 during growth, net photosynthesis of plantlets measured under 350 Cll l(-1) CO2 was higher compared to control plantlets.

1865^2^Solarova,J^Pospisilova,J^1997^1^Effect of carbon dioxide enrichment during in vitro cultivation and acclimation to ex vitro conditions^261^39^1^23-30^^^^^^^^^^6499
1126^1491^1855^243^349^781^92^e plantlets were grown in media with sucrose concentrations from 0 to 5% under light intensities of 60, 100, and 260 mu mol m(- 2) l(-1). Before starting the measurements the plantlets were pretreated with 1000 mu l l(-1) CO2 for several weeks. Control plantlets were grown for the same period in gas tight vessels. CO2 concentration of the gas atmosphere inside the plant vessels had a stronger influence on CO2 gas exchange of citrus plantlets than sucrose concentration of the medium. Net photosynthesis of plantlets grown under various light intensities differed only little when using the same CO2 concentration for measurement as used for growing. After pretreatment with 1000 mu l l(-1) CO2 during growth, net photosynthesis of plantlets measured under 350 Cll l(-1) CO2 was higher compA^6498^Tobacco and carnation plantlets were grown in vitro on Murashige and Skoog's medium with 2% saccharose. Carnation plantlets were also grown fully photoautotrophically on a medium without saccharose. The ambient CO2 concentration was increased from 0.6 to 10 or 40 g m(-3) during the last 3 weeks of in vitro cultivation or during the first 3 weeks of acclimation to ex vitro condition (plantlets transplanted to pots with sand and nutrient solution) or during both growth phases. CO2 enrichment during in vitro cultivation markedly stimulated growth of tobacco plantlets, and also of carnation plantlets, both with and without saccharose. CO2 enrichment during the acclimation period promoted plant growth more effectively in plantlets grown in vitro at a CO2 concentration of 0.6 g m(-3) than in plantlets grown in either growth phase at higher CO2 concentrations.
 growing. After p