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