746^1^Vitousek,PM^1994^1^Beyond global warming - ecology and global change^11^75^7^1861-1876^^^^^Oct^^^^^4303
137^1597^1598^1599^1600^344^396^49^539^741^deling global vegetation patterns and terrestrial carbon storage at the last glacial maximum^175^3^3^67-76^^^^^May^^^^^4301
1079^1133^1251^1594^1595^1596^227^344^593^
A^4300^Global patterns of potential natural vegetation were simulated for present and last glacial maximum (LGM) climates. The LGM simulation showed good agreement with available evidence, most importantly in the humid tropics. Simple calculations based on these simulations indicate that terrestrial carbon storage increased by 300-700 Pg C after the LGM. The range is due to uncertainties in the mean carbon storage values for different biomes, and in the amount of carbon in boreal peats. These results are consistent with the global change in ocean delta-C- 13, inferred from measurements on benthic foraminifera, reflecting the increased storage of isotopically light carbon on land.
sing. Such iA^4302^While ecologists involved in management or policy often are advised to learn to deal with uncertainty, there are a number of components of global environmental change of which we are certain-certain that they are going on, and certain that they are human-caused. Some of these are largely ecological changes, and all have important ecological consequences. Three of the well-documented global changes are: increasing concentrations of carbon dioxide in the atmosphere; alterations in the biogeochemistry of the global nitrogen cycle; and ongoing land use/land cover change. Human activity-now primarily fossil fuel combustion-has increased carbon dioxide concentrations from similar to 280 to 355 mu L/L since 1800; the increase is unique, at least in the past 160 000 yr, and several lines of evidence demonstrate unequivocally that it is human-caused. This increase is likely to have climatic consequences-and certainly it has direct effects on biota in all Earth's terrestrial ecosystems. The global nitrogen cycle has been altered by human activity to such an extent that more nitrogen is fixed annually by humanity (primarily for nitrogen fertilizer, also by legume crops and as a byproduct of fossil fuel combustion) than by all natural pathways combined. This added nitrogen alters the chemistry of the atmosphere and of aquatic ecosystems, contributes to eutrophication of the biosphere, and has effects on biological diversity in the most affected areas. Finally, human land use/land cover change has transformed one-third to one-half of Earth's ice-free surface. This in and of itself probably represents the most important component of global change now and will for some decades to come; it has profound effects on biological diversity on land and on ecosystems downwind and downstream of affected areas. Overall, any clear dichotomy between pristine ecosystems and human-altered areas that may have existed in the past has vanished, and ecological research should account for this reality. These three and other equally certain components of global environmental change are the primary causes of anticipated changes in climate, and of ongoing losses of biological diversity. They are caused in turn by the extraordinary growth in size and resource use of the human population. On a broad scale, there is little uncertainty about any of these components of change or their causes. However, much of the public believes the causes-even the existence-of global change to be uncertain and contentious topics. By speaking out effectively, we can help to shift the focus of public discussion towards what can and should be done about global environmental change.

747^5^Alagusundaram,K^Jayas,DS^White,NDG^Muir,WE^Sinha,RN^1995^1^Controlling cryptolestes-ferrugineus (stephens) adults in wheat stored in bolted-metal bins using elevated carbon-dioxide^250^37^3^217-223^^^^^Jul-Sep^^^^^4305
1601^human-altered areas that may have existed in the past has vanished, and ecological research should account for this reality. These three and other equally certaiA^4304^Experiments were conducted in two 5.56 m-diameter farm bins to determine the mortality of caged adult rusty grain beetles, Cryptolestes ferrugineus (Stephens) (Coleoptera: cucujidae), under elevated carbon dioxide (CO2) concentrations. The bins were filled with wheat to a depth of 2.5 m. Dry ice was used to create high CO2 concentrations in the wheat bulks. Two different modes of application of dry ice were used: (i) pellets on the grain surface and in the aeration duct and (ii) pellets on the grain surface and blocks in insulated boxes on the grain surface. The pellets exposed to the ambient conditions on the grain surface and in the aeration duct sublimated quickly and had to be replenished at frequent intervals. Dry ice blocks in insulated boxes, however, maintained high CO2 concentrations without replenishment for over 15 d. In both modes of application, the observed CO2 concentrations in the intergranular gas were about 15% and 30% (all the CO2 concentrations given in this article are on a volume basis) at 2.05 m and 0.55 m above the floor, respectively. At 0.55 m above the floor, the mortality of rusty grain beetle adults was more than 90% while in the top portions of the bulk (2.05 m above the floor) the mortality was only 30%. On an average about two thirds of the insects were killed. The use of controlled atmosphere treatment within an integrated pest management context is outlined.

748^8^Bainbridge,G^Madgwick,P^Parmar,S^Mitchell,R^Paul,M^Pitts,J^Keys,AJ^Parry,MAJ^1995^1^Engineering rubisco to change its catalytic properties^78^46^^1269-1276^^^^^Sep^^^^^4307
1265^1602^1603^1604^1605^1606^1607^355^356^e grain surface and in the aeration duct sublimated quickly and had to be replenished at frequent intervals. Dry ice blocks in insulated boxes, however, maintained high CO2 concentrations without replenishment for over 15 d. In both modes of application, the observed CO2 concentrations in the intergranular gas were about 15% and 30% (all the CO2 concentrations given in this article are on a volumeA^4306^The initial steps of carbon assimilation and photorespiration are catalysed by ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39). Natural variation in the kinetic properties of the enzyme suggest that it is possible to alter the enzyme to favour the carboxylation activity relative to oxygenation, Mutagenesis in vitro of the gene encoding the large subunit of the enzyme from Anacystis nidulans has been used to modify catalytic properties. Residues at the C-terminal end of loop 6 of the beta/alpha barrel structure of the large subunit influence specificity towards the gaseous substrates, CO2 and O-2. None of the residues altered by mutagenesis appear to interact directly with the transition state analogue and their effect on the reaction of the enediolate intermediate with the gaseous substrates and stabilization of the resulting transition state intermediates by lysine 334 must be indirect. Interactions with other parts of the enzyme must also be important in determining substrate specificity, Backbone carbonyl groups close to lysine 334 interact with lysine 128; mutation of lysine 128 to residues of less positive polarity reduces enzyme activity and favours oxygenation relative to carboxylation, the likely effects on assimilation rates of altering the kinetic properties of Rubisco have been modelled. A leaf with cyanobacterial Rubisco may out-perform a higher plant Rubisco at elevated CO2 and cool temperatures.

749^2^Behboudian,MH^Lai,R^1995^1^Partitioning of photoassimilates in virosa tomatoes under elevated co2 concentration^4^147^1^43-47^^^^^Oct^^^^^4309
1608^348^376^711^820^strates, CO2 and O-2. None of the residues altered by mutagenesis appear to interact directly with the transition state analogue and their effect on the reaction of the enediolate intermediate with the gaseous substrates and stabilization of the resulting transition state intermediates by lysine 334 must be indirect. Interactions with other parts of the enzyme must also be important in determining substrate specificiA^4308^The effect of CO2 enrichment on the distribution of assimilates in tomato plants, Lycopersicon esculentum Mill. cv. 'Virosa', was studied using C-14-label. Plants were defoliated except for leaves 8, 9, and 10 (numbered acropetally). Depending on the experiment, truss 1 or trusses 1 and 2 were maintained on the plant. Within a 24-h period, the labelled leaf (leaf 10) retained high levels of C-14 in both control and CO2-enriched plants. Truss 1 was the dominant sink for both CO2 treatments, drawing on a considerable supply of C-14 re-exported from leaf 8 and leaf 9. The stem and root were transitory sinks and had the capacity to re-export C-14 at different rates during the light and dark periods. Pattern of photoassimilate partitioning was not affected by CO2 treatment.

750^2^Farnsworth,EJ^Bazzaz,FA^1995^1^Inter-generic and intra-generic differences in growth, reproduction, and fitness of 9 herbaceous annual species grown in elevated co2 environments^2^104^4^454-466^^^^^Dec^^^^^4311ubstrate specifici1380^1609^1610^1611^1612^312^376^417^423^740^tribution of assimilates in tomato plants, Lycopersicon esculentum Mill. cv. 'Virosa', was studied using C-14-label. Plants were defoliated except for leaves 8, 9, and 10 (numbered acropetally). Depending on the experiment, truss 1 or trusses 1 and 2 were maintained on the plant. Within a 24-h period, the labelled leaf (leaf 10) retained high levels of C-14 in both control and CO2-enriched plants. Truss 1 was the dominant sink for both CO2 treatments, drawing on a considerable supply of C-14 re-exported from leaf 8 and leaf 9. The stem and root were transitory sinks and had the capacity to re-export C-14 at different rates during the light and dark periods. Pattern of photoassimilate partitioning was not affected by CO2 treatment.

750^2^Farnsworth,EJ^Bazzaz,FA^1995^1^Inter-generic and intra-generic differences in growth, reproduction, and fitness of 9 herbaceous annual species grown in elevated co2 environments^2^104^4^454-466^^^^^Dec^^^^^4311ubstrate specificiA^4310^In assessing the capacity of plants to adapt to rapidly changing global climate, we must elucidate the impacts of elevated carbon dioxide on reproduction, fitness and evolution. We investigated how elevated CO2 influenced reproduction and growth of plants exhibiting a range of floral morphologies, the implications of shifts in allocation for fitness in these species, and whether related taxa would show similar patterns of response. Three herbaceous, annual species each of the genera Polygonum, Ipomoea, and Cassia were grown under 350 or 700 ppm CO2. Vegetative growth and reproductive output were measured non-destructively throughout the full life span, and vegetative biomass was quantified for a subsample of plants in a harvest at first flowering. Viability and germination studies of seed progeny were conducted to characterize fitness precisely. Early vegetative growth was often enhanced in high- CO2 grown plants of Polygonum and Cassia (but not Ipomoea). However, early vegetative growth was not a strong predictor of subsequent reproduction. Phenology and production of floral buds, flowers, unripe and abscised fruits differed between CO2 treatments, and genera differed in their reproductive and fitness responses to elevated CO2. Polygonum and Cassia species showed accelerated, enhanced reproduction, while Ipomoea species generally declined in reproductive output in elevated CO2. Seed ''quality'' and fitness (in terms of viability and percentage germination) were not always directly correlated with quantity produced, indicating that output alone may not reliably indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO2 than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductive output under global change, but fitness and prognoses of population persistence and evolutionary performance can be inferred only rarely from examination of vegetative characters alone.

751^9^Galtier,N^Foyer,CH^Murchie,E^Alred,R^Quick,P^Voelker,TA^Thepenier,C^Lasceve,G^Betsche,T^1995^1^Effects of light and atmospheric carbon-dioxide enrichment on photosynthesis and carbon partitioning in the leaves of tomato (lycopersicon-esculentum L) plants over-expressing sucrose- phosphate synthase^78^46^^1335-1344^^^^^Sep^^^^^4313
1012^1116^204^360^372^441^448^550^632^92^ly indicate fitness or evolutionary potential. Species within genera typically responded more consistently to CO2 than unrelated species. Cluster analyses were performed separately on suites of vegetative and reproductive characters. Some species assorted within genera when these reproductive responses were considered, but vegetative responses did not reflect taxonomic affinity in these plants. Congeners may respond similarly in terms of reproductiveA^4312^Photosynthetic carbon assimilation, carbon partitioning and foliar carbon budgets were measured in the leaves of transformed tomato plants expressing a maize sucrose-phosphate synthase (SPS) gene in addition to the native enzyme, and in untransformed controls. The maize SPS gene was expressed under control of either the promoter of the small subunit of ribulose 1,5-bisphosphate carboxylase (rbcS promoter; lines 2, 9 and 18) or the 35S promoter from cauliflower mosaic virus (CaMV promoter; line 13). The rate of sucrose synthesis was increased relative to that of starch and sucrose/starch ratios were higher throughout the photoperiod in the leaves of all plants expressing high SPS activity. The leaf carbon budget over the day/night cycle in air at low irradiance (180 mu mol photon m(- 2) s(-1)) was similar in all plants. Net photosynthesis measured in air and at elevated CO2 (800-1500 mu l I-1) on whole plants grown in air at 400 mu mol m(-2) s(-1) irradiance was significantly increased in the high SPS expressors compared to the untransformed controls and was highest where SPS activity was greatest. At high CO2 the stimulation of photosynthesis was more pronounced, We conclude that SPS activity is a major point of control of photosynthesis particularly under saturating light and CO2.

752^5^Habash,DZ^Paul,MJ^Parry,MAJ^Keys,AJ^Lawlor,DW^1995^1^Increased capacity for photosynthesis in wheat grown at elevated co2 - the relationship between electron-transport and carbon metabolism^6^197^3^482-489^^^^^Oct^^^^^4315
264^348^384^386^422^493^528^713^ased relative to that of starch and sucrose/starch ratios were higher throughout the photoperiod in the leaves of all plants expressing high SPS activity. The leaf carbon budget over the day/night cycle in air at low irradiance (180 mu mol photon m(- 2) s(-1)) was similar in all plants. Net photosynthesis measured in air and at elevated CO2 (800-1500 mu l I-1) on whole plants grown in air at 400 mu mol m(-2) s(-1) irradiance was significantly increased in the high SPS A^4314^Spring wheat (Triticum aestivum L.) was grown under optimal nutrition for six weeks at 700 and 350 mu mol . mol(-1) CO2 and simultaneous measurements of photosystem-II (PSII) chlorophyll fluorescence and gas exchange were conducted on intact attached leaves. Plants grown at elevated CO2 had double the concentration of CO2 at the carboxylation site (C-c) despite a lowered stomatal (g(s)) and mesophyll (g(m)) conductance compared with ambient-grown plants. Plants grown at elevated CO2 had a higher relative quantum yield of PSII electron transport (Phi(PSII)) and a higher relative quantum yield of CO2 fixation (Phi CO2). The higher Phi(PSII) was due to a larger proportion of open PSII centres, estimated by the coefficient of photochemical quenching of fluorescence (q(p)), with no change in the efficiency of light harvesting and energy transduction by open PSII centres (F'(v)/F'(m)). Analysis of the relationship between Phi(PSII) and Phi(CO2) conducted under various CO2 and O-2 concentrations showed that the higher Phi(CO2) for a given Phi(PSII) in leaves developed under elevated CO2 was similar to that obtained in leaves upon a partial reduction in photorespiration. Calculation of the allocation of photosynthetic electron-transport products to CO2 and O-2 showed that for leaves developed in elevated CO2, there was an increase in both total linear electron flow and electron flow to CO2 and a decrease in electron flow to O-2. Plants developed under elevated CO, showed positive acclimation manifested by a higher Phi(CO2) when measured under ambient CO2 and higher assimilation rates in A/C-i curves. Initial and to tal activity of ribulose-1,5- bisphosphate carboxylase- oxygenase (Rubisco EC 4.1.1.39) measured in vitro increased by 16 and 15% respectively in leaves from plants grown in elevated CO2, which was in agreement with a 15% higher in vivo carboxylation efficiency. It is concluded that growth of spring wheat at elevated CO2 enhances photosynthesis due to a change in the balance of component processes manifested as an increased capacity for carbon fixation, total electron transport and Rubisco activity, and a concomitant partial reduction of photorespiration.

753^4^Ham,JM^Owensby,CE^Coyne,PI^Bremer,DJ^1995^1^Fluxes of co2 and water-vapor from a prairie ecosystem exposed to ambient and elevated atmospheric co2^107^77^1-2^73-93^^^^^Nov^^^^^4317
1146^312^374^529^662^687^tron flow to CO2 and a decrease in electron flow to O-2. Plants developed under elevated CO, showed positive acclimation manifested by a higher Phi(CO2) when measured under ambient CO2 and higher assimilation rates in A/C-i curves. Initial and to tal activity of ribulose-1,5- bisphosphate carboxylase- oxygenase (Rubisco EC 4.1.1.39) measured in vitro increased by 16 and 15% respectively in leaves from plants grown in elevated CO2, which was in agreement with a 15% higher in vivo carboxylation efficiency. It is concluded that growth of spring wheat at elevated CO2 enhances photosynthesis due to a change in the balance of component processes manA^4316^Increasing concentrations of atmospheric CO2 may alter the carbon and water relations of prairie ecosystems. A C-4- dominated tallgrass prairie near Manhattan, KS, was exposed to 2x ambient CO2 concentrations using 4.5 m-diameter open-top chambers. Whole-chamber net CO2 exchange (NCE) and evapotranspiration (ET) were continuously monitored in CO2- enriched and ambient (no enrichment) plots over a 34-d period encompassing the time of peak biomass in July and August, 1993. Soil-surface CO2 fluxes were measured with a portable surface chamber, and sap flow (water transport in xylem) in individual grass culms was monitored with heat balance techniques. Environmental measurements were used to determine the effect of CO2 on the surface energy balance and canopy resistances to vapor flux. In 1993, frequent rainfall kept soil water near field capacity and minimized plant water stress. Over the 34-d measurement period, average daily NCE (canopy photosynthesis - soil and canopy respiration) was 9.3 g CO2 m(-2) in the ambient treatment and 11.4 g CO2 m(-2) under CO2 enrichment. However, differences in NCE were caused mainly by delayed senescence in the CO2-enriched plots at the end of the growing season. At earlier stages of growth, elevated CO2 had no effect on NCE. Soil-surface CO2 fluxes typically ranged from 0.4 to 0.66 mg CO2 m(-2) s(-1), but were slightly greater in the CO2-enriched chambers. CO2 enrichment reduced daily ET by 22%, reduced sap flow by 18%, and increased canopy resistance to vapor flux by 24 s m(-1). Greater NCE and lower ET resulted in higher daytime water use efficiency (WUE) under CO2 enrichment vs. ambient (9.84 vs. 7.26 g CO2 kg(-1) H2O). However, record high precipitation during the 1993 season moderated the effect of WUE on plant growth, and elevated CO2 had no effect on peak aboveground biomass. CO2-induced stomatal closure also affected the energy balance of the surface by reducing latent heat flux (LE), thereby causing a consequent change in sensible heat flux (H). The daytime Bowen ratio (H/LE) for the study period was near zero for the ambient treatment and 0.21 under CO2 enrichment.

754^3^Holland,EA^Townsend,AR^Vitousek,PM^1995^1^Variability in temperature regulation of co2 fluxes and n mineralization from 5 hawaiian soils - implications for a changing climate^127^1^2^115-123^^^^^Apr^^^^^4319
1234^312^314^673^893^947^e slightly greater in the CO2-enriched chambers. CO2 enrichment reduced daily ET by 22%, reduced sap flow by 18%, and increased canopy resistance to vapor flux by 24 s m(-1). Greater NCE and lower ET resulted in higher daytime water use efficiency (WUE) under CO2 enrichment vs. ambient (9.84 vs. 7.26 g CO2 kg(-1) H2O). However, record high precipitation during the 1993 season moderated the effect of WUE on plant growth, and elevated CO2 had no effect on peak aboveground biomass. CO2-induced stomatal closure also affected the energy balance of the surface by reducing latent heat flux (LE), thereby causing a consequent change in sensible heat flux (H). The daytime Bowen A^4318^We examined the possibility that microbial adaptation to temperature could affect rates of CO2, N2O and CH4 release from soils. Laboratory incubations were used to determine the functional relationship between temperature and CO2, N2O and CH4 fluxes for five soils collected across an elevational range in Hawaii. Initial rates of CO2 production and net N mineralization increased exponentially from 15 degrees C to 55 degrees C; initial rates of CH4 and N2O release were more complex. No optimum temperature (in which rates decline at higher and lower temperatures) was apparent for any of the gases, but respiration declined with time at higher temperatures, suggesting rapid depletion of readily available substrate. Mean Q(10)s for respiration varied from 1.4 to 2.0, a typical range for tropical soils. The functional relationship between CO2 production and temperature was consistent among all five soils, despite the substantial differences in mean annual temperature, soils, and land-use among the sites. Temperature responses of N2O and CH4 fluxes did not follow simple Q(10) relationships suggesting that temperature functions developed for CO2 release from heterotrophic respiration cannot be simply extrapolated. Expanding this study to tropical heterotrophic respiration, the flux is more sensitive to changes in Q(10) than to changes in temperature on a per unit basis: the partial derivative with respect to temperature is 2.4 Gt C . degrees C- 1, with respect to Q(10) it is 3.5 Gt C . Q(10) unit(-1). Therefore, what appears to be minor variability might still produce substantial uncertainty in regional estimates of gas exchange.

755^5^Jongen,M^Jones,MB^Hebeisen,T^Blum,H^Hendrey,G^1995^1^The effects of elevated co2 concentrations on the root-growth of lolium-perenne and trifolium-repens grown in a face system^127^1^5^361-371^^^^^Oct^^^^^4321
224^312^344^349^373^374^423^436^547^57^istent among all five soils, despite the substantial differences in mean annual temperature, soils, and land-use among the sites. TemA^4320^Lolium perenne and Trifolium repens were grown in a Free Air CO2 Enrichment (FACE) system at elevated (600 mu mol mol(-1)) and ambient (340 mu mol mol(-1)) carbon dioxide concentrations during a whole growing season. Using a root ingrowth bag technique the extent to which CO2 enrichment influenced the growth of L. perenne and T. repens roots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of both L. perenne and T. repens increased under elevated CO2 conditions. In L. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but for T. repens the root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made for T. repens. These showed an increase under elevated CO2 concentrations. Root decomposition appeared to decrease under elevated CO2 concentrations. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon:nitrogen ratio in roots of L. perenne at elevated CO2 concentrations.

756^1^Kennedy,AD^1995^1^Antarctic terrestrial ecosystem response to global environmental-change^27^26^^683-704^^^^^^^^^^4323
1435^1613^1614^1615^1616^189^209^312^344^509^. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It was also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of both L. perenne and T. repens increased under elevated CO2 conditions. In L. perenne, root ingrowth decreased with increasing nutrient fertilizer level, but for T. repens the root ingrowth was not affected by the nutrient application rate. Besides biomass measurements, root length estimates were made for T. repens. These showed an increase under elevated CO2 concentrations. Root decomposition appeared to decreA^4322^Geographical isolation and climatic constraints are responsible for the low biodiversity and structural simplicity of the antarctic terrestrial ecosystem Under projected scenarios of global change, both limiting factors may be released. Alien species immigration is likely to be facilitated as modified ocean and atmospheric circulation introduce exotic water- and air-borne propagules from neighboring continents. Elevated temperature, UV radiation, CO2, and precipitation will combine additively and synergistically to favor new trajectories of community development. It can be predicted that existing patterns of colonization, recruitment, succession, phenology and mortality will be perturbed with concomitant effects for ecosystem function through changes in biomass, trophodynamics, nutrient cycling, and resource partitioning. Soil propagule banks will play an important role through founder effects. Uniquely in Antarctica, many of the short-term consequences of global change will depend on the ecophysiological relationships of cryptogamic plants. However, in the long term, climatic warming will favor an increase in phanerogamic biomass since these species are currently excluded by the low cumulative degree-days > 0 degrees C. It has been suggested that antarctic communities may be particularly vulnerable to global change: Their slow rate of development and restricted gene flow limit response to new conditions. However, vulnerability must be defined with respect to both the direction and rate of change and it is likely that some perturbations will enhance the complexity and productivity of the biota, with negative feedback to the global carbon cycle. The chapter concludes with a discussion of institutional issues surrounding this topic.

757^4^Kerstiens,G^Townend,J^Heath,J^Mansfield,TA^1995^1^Effects of water and nutrient availability on physiological- responses of woody species to elevated co2^251^68^4^303-315^^^^^^^^^^4325
1144^1342^312^344^345^376^384^417^685^92^lobal change will depend on the ecophysiologA^4324^The growth responses to elevated CO2 found in experiments are highly variable and depend on other experimental parameters such as irrigation, fertilization, light regime, etc. As yet, the strength or even the sign of most interactions is all but impossible to predict from first principles. Experiments in ambient and CO2-enriched ambient air (+250 p.p.m.) have been conducted in specially adapted greenhouses (Solardomes) at Lancaster University for the past four seasons on Sitka spruce (Picea sitchensis (Bong.) Carr.), wild cherry (Prunus avium L.), beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.). These experiments are reviewed together with other published studies on interactive effects of elevated CO2 and water and nutrient supply on physiological processes, in particular gas exchange, in tree species. It is often assumed that drought tolerance will increase in elevated CO2 because of a suppression of stomatal conductance and an increase in instantaneous water use efficiency. There is, however, some evidence that such effects could be more than offset in beech by CO2-induced increases in leaf area. It is tentatively suggested that in beech, drought tolerance could already have been reduced by the increase in atmospheric CO2 over the last century.

758^1^King,DA^1995^1^Equilibrium-analysis of a decomposition and yield model applied to pinus-radiata plantations on sites of contrasting fertility^81^83^3^349-358^^^^^15 Dec^^^^^4327
32^416^57^58^669^738^791^908^92^945^ruce (Picea sitchensis (Bong.) Carr.), wild cherry (Prunus avium L.), beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.). These experiments are reviewed together with other published studies on interactive effects of elevated CO2 and water and nutrient supply on physiological processes, in particular gas exchange, in tree species. It is often assumed that drought tolerance will increase in elevated CO2 because of a suppression of stomatal conductance and an increase in instantaneous water use efficiency. There iA^4326^Recent models of growth and nutrient cycling relate forest productivity to canopy photosynthesis, as influenced by the effect of nutrient cycling on foliar nitrogen concentration. A useful approach for analysing the impact of elevated CO2 or altered nitrogen inputs on production is to consider model solutions where recycling leaves, fine roots, litter and soil organic pools of intermediate turnover time are in equilibrium, while tree stems and recalcitrant humus are accumulating or releasing carbon and nitrogen. This equilibrium analysis, employed by the Generic Decomposition and Yield (G'DAY) model, was applied to Pinus radiata plantations growing on an infertile site in Australia and a fertile site in New Zealand. Predicted productivities and foliar nitrogen concentrations were substantially lower than observed for the young (12-year- old) stands, particularly for the fertile site. The model predictions were closer to values expected for older stands late in the commercial rotation cycle when reduced wood production rates reduce the net nitrogen requirements for growth. These results underscore the importance of the net release of nitrogen from soil organic matter early in the life of a stand and suggest that care should be taken in using equilibrium analyses to estimate the impacts of elevated [CO2] on forest production.

759^4^Lethiec,D^Dixon,M^Loosveldt,P^Garrec,JP^1995^1^Seasonal and annual variations of phosphorus, calcium, potassium and manganese contents in different cross-sections of picea-abies (L) karst needles and quercus-rubra L leaves exposed to elevated co2^252^10^2^55-62^^^^^Dec^^^^^4329
s applied to Pinus radiata plantations growing on an infertile site in Australia and a fertile site in New Zealand. Predicted productivities and foliar nitrogen concentrations were substantially lower than observed for the young (12-year- old) stands, particularly for the fertile site. The model predictions were closer to values expected for older stands late in the commercial rotation cycle when reduceA^4328^Norway spruce and red oak trees were planted directly into the soil and enclosed in open-top chambers. For 2 years the trees were exposed to both ambient and elevated CO2 concentrations (700 mu mol mol(-1)) and during this time variations in nutrient concentrations were studied. CO2-treated plants had decreases in global leaf concentrations of nitrogen, potassium, calcium and manganese for both species. When different areas of the foliage were analysed however, the response showed much variability between the respective sites and between species. Furthermore the nutrient concentrations changed differently as the plant material aged and this change showed inter-treatment differences. These results show how it may be important to analyse plant material of different ages and at different cell sites when studying nutrient levels.

760^2^Manderscheid,R^Weigel,HJ^1995^1^Do increasing atmospheric co2 concentrations contribute to yield increases of german crops^161^175^2^73-82^^^^^Sep^^^^^4331cle when reduce312^372^374^376^388^409^417^92^ trees were planted directly into the soil and enclosed in open-top chambers. For 2 years the trees were exposed to both ambient and elevated CO2 concentrations (700 mu mol mol(-1)) and during this time variations in nutrient concentrations were studied. CO2-treated plants had decreases in global leaf concentrations of nitrogen, potassium, calcium and manganese for both species. When different areas of the foliage were analysed however, the response showed much variability between the respective sites and between species. Furthermore the nutrient concentrations changed differently as the plant material aged and this change showed inter-treatment differences. These results show how it may be important to analyse plant material of different ages and at different cell sites when studying nutrient levels.

760^2^Manderscheid,R^Weigel,HJ^1995^1^Do increasing atmospheric co2 concentrations contribute to yield increases of german crops^161^175^2^73-82^^^^^Sep^^^^^4331cle when reduceA^4330^The global atmospheric CO2-concentration is increasing and there has been an increase in Germany of about 30 ppm from 340 ppm to 370 ppm CO2 during the last two decades. The hectare yield of many crops has also increased during this time period. The objective of the present study was to estimate whether the past and future change in the atmospheric composition significantly contributes to the increase in hectare yield. Different crop species (beans, Phaseolus vulgaris, cv Pfalzer Juni; spring barley, Hordeum vulgare L., cvs. Alexis and Arena; spring wheat, Triticum aestivum L., cvs. Star and Turbo; maize, Zea mays L., cvs. Bonny and Boss) were grown at ambient (372 ppm) and at slightly elevated CO2-concentrations (459 ppm and 539 ppm) in open-top chambers and the effect of the different CO2-concentrations on the growth and yield of the plants was measured. The past and future CO2-effect was estimated from the slope of a linear CO2-yield curve (percentage increase in yield per ppm CO2, 100 % at 370 ppm) fitted to the data and those from previous studies on wheat and maize. The percentage increase in yield per ppm CO2 is insignificant for beans, of borderline significance for silage maize (0.06 % per ppm), and 0.35 % per ppm and 0.26 % per ppm for barley and wheat, respectively. The CO2-elevation primarily decreases the tiller dieback of the cereals. Considering the increase in CO2 of 30 ppm and in the hectare yield of 25 % (barley) and 28 % (wheat) from 1970 to 1990, the contribution of CO2 to the increase in the agricultural production is estimated to be one fourth up to one half of the increase in hectare yield of spring cereals. Given a recent yearly increase of 2 ppm the future CO2-related increase in hectare yield is estimated to be about 0.5-0.7 % per year.

761^3^McGuire,AD^Melillo,JM^Joyce,LA^1995^1^The role of nitrogen in the response of forest net primary production to elevated atmospheric carbon-dioxide^27^26^^473-503^^^^^^^^^^4333
1342^1344^349^419^431^546^595^765^966^975^O2, 100 % at 370 ppmA^4332^We review experimental studies to evaluate how the nitrogen cycle influences the response of forest net primary production (NPP) to elevated CO2. The studies in our survey report that at the tissue level, elevated CO2 reduces leaf nitrogen concentration an average 21%, but that it has a smaller effect on nitrogen concentrations in stems and fine roots. In contrast, higher soil nitrogen availability generally increases leaf nitrogen concentration. Among studies that manipulate both soil nitrogen availability and atmospheric CO2, photosynthetic response depends on a linear relationship with the response of leaf nitrogen concentration and the amount of change in atmospheric CO2 concentration. Although elevated CO2 often results in reduced tissue respiration rate per unit biomass, the link to changes in tissue nitrogen concentration is not well studied.

762^1^Miao,SL^1995^1^Acorn mass and seedling growth in quercus-rubra in response to elevated co2^42^6^5^697-700^^^^^Oct^^^^^4335
5^O2, 100 % at 370 ppmA^4334^In order to explore whether seed size affects plant response to elevated CO2 plants grown from red oak (Quercus rubra L.) acorns were studied for differences in their first year response to CO2 concentrations of 350 and 700 ul/l. Overall, at final harvest, total biomass of plants grown in elevated CO2 were 47 % larger than that of plants grown in ambient CO2. There were significant interactions between CO2 treatments and initial acorn mass for total biomass, as well as for root, leaf, and stem biomass. Although total biomass increased with increasing initial acorn mass for both high and ambient CO2 plants, high CO2 plants exhibited a greater increase than ambient CO2 plants, as indicated by a steeper slope in high CO2 plants. However, CO2 levels did not affect biomass partitioning traits, such as root/shoot ratio, leaf, stem, and root weight ratios, and leaf area ratio. These results suggest that variation in seed size or initial plant size can cause intraspecific variation in response to elevated CO2.

763^4^Navas,ML^Guillerm,JL^Fabreguettes,J^Roy,J^1995^1^The influence of elevated co2 on community structure, biomass and carbon balance of mediterranean old-field microcosms^127^1^5^325-335^^^^^Oct^^^^^4337
1239^1617^189^245^344^362^378^417^740^92^al harvest, total biomass of plants grown in elevated CO2 were 47 % larger than that of plants grown in ambient CO2. There were significant interactions between CO2 treatments and initial acorn mass for total biomass, as well as for root, leaf, and stem biomass. Although total biomass increased with increasing initial acorn mass for both high and ambient CO2 plants, high CO2 plants exhibited a greater increase than ambient CO2 plants, as indicated by a steeper slope in high CO2 plants. However, CO2 levels did not affect biomass partitioning traits, such as root/shoot ratio, leaf, stem, and root weight ratios, and leaf area ratio. These results suggest that variation in seed size or initial plant size can cause intraspecific variation in response to elevated CO2A^4336^We studied the effects of a doubling of atmospheric CO2 concentration on intact monoliths of Mediterranean grassland in growth chambers where climatic field conditions were simulated. During the six month growing season, changes in community structure were monitored by quantifying species richness and cover. The CO2 exchange of microcosms was measured continuously and the resulting quantity and quality of biomass were evaluated. Species richness and cover did not respond to elevated C02. After one month of treatment, CO2 exchange measured during the day did not differ between CO2 levels but the night respiration was two-fold higher under elevated CO2. Stimulations of both day and night CO2 flux by short-term CO2 enrichment were recorded several times during the growing season. These results suggest that despite some downward adjustment of photosynthesis, net canopy photosynthesis was stimulated by elevated CO2, but this stimulation was compensated for by an increased respiration. The 20% stimulation of final phytomass under elevated CO2 was not significant: it resulted from unchanged live plant matter but a significant, 100% increase in litter accumulation. These results suggest that in low-productivity Mediterranean herbaceous systems, the greatest effect of CO2 is not on the storage of carbon in biomass but on the turnover of the carbon in the plants.

764^1^Nielsen,MV^1995^1^Photosynthetic characteristics of the coccolithophorid emiliania-huxleyi (prymnesiophyceae) exposed to elevated concentrations of dissolved inorganic carbon^249^31^5^715-719^^^^^Oct^^^^^4339
1618^1619^1620^1621^1622^188^362^92^t respiration was two-fold higher under elevated CO2. Stimulations of both day and night CO2 flux by short-term CO2 enrichment were recorded several times during the growing season. These results suggest that despite some downward adjustment of photosynthesis, net canopy photosynthesis was stimulated by elevated CO2, but this stimulation was compensated for by an increased respiration. The 20% stimulation oA^4338^Light-saturated photosynthesis (P-max) of Emiliania huxleyi (Lohmann) Hay et Mohler is known to be carbon-limited at natural concentrations of dissolved inorganic carbon (DIC). In the present study, light-limited and light-saturated photosynthetic rates of E. huxleyi were studied at three concentrations of DIC (2.4, 7.4, and 12.4 mM) for high-calcite (C-in/C-tot = 0.48) and low-calcite (C-in/C-tot = 0.08) cells of the same strain. The photosynthetic efficiency (alpha) and the maximum quantum yield (Phi(max)) increased by more than a factor of 2 from the lowest to the highest DIC level. P-max, alpha, and Phi(max) were always higher for the high-calcite than for the low-calcite cells at identical DIC levels. This may indicate that the calcification process acts as an extra supplier of CO2 for photosynthesis making the CO2 shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of Phi(max) on DIC has not previously been shown for marine phytoplankton. Phi(max) is a key parameter in recent biooptical models of phytoplankton productivity, and the results from the present study are therefore important for modeling the productivity of E. huxleyi.

765^3^Norton,LR^Firbank,LG^Watkinson,AR^1995^1^Ecotypic differentiation of response to enhanced co2 and temperature levels in arabidopsis-thaliana^2^104^3^394-396^^^^^Nov^^^^^4341
376^ low-calcite (C-in/C-tot = 0.08) cells of the same strain. The photosynthetic efficiency (alpha) and the maximum quantum yield (Phi(max)) increased by more than a factor of 2 from the lowest to the highest DIC level. P-max, alpha, and Phi(max) were always higher for the high-calcite than for the low-calcite cells at identical DIC levels. This may indicate that the calcification process acts as an extra supplier of CO2 for photosynthesis making the CO2 shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of Phi(max) on DIC has not previously been shown for marine phytoplanktonA^4340^Five ecotypes of Arabidopsis thaliana, from widely dispersed origins, were grown under combinations of ambient and elevated atmospheric CO2 concentrations and ambient and elevated temperatures within solardomes. Total above-ground plant biomass was measured when the majority of plants across all ecotypes and treatments had formed seed pods. There were substantial differences in biomass between the ecotypes across all treatments. Temperature had no effect on biomass whilst CO2 had a significant effect both alone and in interaction with ecotype. The CO2 x ecotype interaction was mostly due to the enhancement of a single ecotype from the Cape Verde Islands.

766^1^Patterson,DT^1995^1^Weeds in a changing climate^253^43^4^685-700^^^^^Oct-Dec^^^^^4343
1456^1623^1624^1625^1626^230^343^398^399^456^photosynthesis making the CO2 shortage at natural DIC levels a little smaller for high-calcite than for low-calcite E. huxleyi. A dependency of Phi(max) on DIC has not previously been shown for marine phytoplanktonA^4342^Current and projected increases in the concentrations of CO2 and other radiatively-active gases in the Earth's atmosphere lead to concern over possible impacts on agricultural pests, All pests would be affected by the global warming and consequent changes in precipitation, wind patterns, and frequencies of extreme weather events which may accompany the ''greenhouse effect.'' However, only weeds are likely to respond directly to the increasing CO2 concentration, Higher CO2 will stimulate photosynthesis and growth in C-3 weeds and reduce stomatal aperture and increase water use efficiency in both C-3 and C-4 weeds, Respiration, and photosynthate composition, concentration, and translocation may be affected, Perennial weeds may become more difficult to control, if increased photosynthesis stimulates greater production of rhizomes and other storage organs, Changes in leaf surface characteristics and excess starch accumulation in the leaves of C-3 weeds may interfere with herbicidal control, Global warming and other climatic changes will affect the growth, phenology, and geographical distribution of weeds, Aggressive species of tropical and subtropical origins, currently restricted to the southern U.S., may expand northward. Any direct or indirect consequences of the CO2 increase that differentially affect the growth or fitness of weeds and crops will alter weed-crop competitive interactions, sometimes to the detriment of the crop and sometimes to its benefit.

767^2^Saebo,A^Mortensen,LM^1995^1^Growth and regrowth of phleum-pratense, lolium-perenne, trifolium-repens and trifolium-pratense at normal and elevated co2 concentration^169^55^1^29-35^^^^^Aug^^^^^4345
130^312^344^376^409^434^57^961^tion may be affected, Perennial weeds may become more difficult to control, if increased photosynthesis stimulates greater production of rhizomes and other storage organs, Changes in leaf surface characteristics and excess starch accumulation in the leaves of C-3 weeds may interfere with herbicidal control, Global warmingA^4344^The effect of elevated CO2 concentration (680 +/- 52 mu mol mol(-1)) on growth of three cultivars of Phleum pratense, two of Lolium perenne and one of Trifolium repens and Trifolium pratense each, was studied during one growth season including three harvests. The study was performed in ten 9 m(2) field chamber units in a cool maritime climate under long days (15-18 h), on the southwest coast of Norway (59 degrees N, 6 degrees E). Tillering in P. pratense and L. perenne was not significantly affected in the first harvest (June/July), but was increased by 30% in the third harvest (September) in response to elevated CO2 concentrations. The plant height was reduced by 16-24% in P. pratense and by 25-29% in L. perenne at high CO2. The dry weight yield of the two grass species was negatively affected by elevated CO2 in the two first harvests, however, no effect was found in the last harvest. The total harvestable dry matter was decreased by 18% in P. pratense and 13% in L. perenne. The dry matter of the stubble was increased at elevated CO2, by 18% in P. pratense and 26% in L. perenne, leaving more of the yield in the meadow after harvest. Raising the CO2 concentration increased the dry weight by 30% in both clover species. The results are discussed in relation to the climatic conditions during the season.

768^1^Sage,RF^1995^1^Was low atmospheric co2 during the pleistocene a limiting factor for the origin of agriculture^127^1^2^93-106^^^^^Apr^^^^^4347
137^178^229^398^417^685^742^766^91^975^icantly affected in the first harvest (June/July), but was increased by 30% in the third harvest (September) in response to elevated CO2 concentrations. The plant height was reduced by 16-24% in P. pratense and by 25-29% in L. perenne at high CO2. The dry weight yield of the two grass species was negatively affected by elevated CO2 in the two first harvests, however, no effect was found in the last harvest. The total harvestable dry matter was decreased by 18% in P. pratense and 13% in L. perenne. The dry matter of the stuA^4346^Agriculture originated independently in many distinct regions at approximately the same time in human history. This synchrony in agricultural origins indicates that a global factor may have controlled the timing of the transition from foraging to food- producing economies. The global factor may have been a rise in atmospheric CO:! from below 200 to near 270 mu mol mol(-1) which occurred between 15,000 and 12,000 years ago. Atmospheric CO2 directly affects photosynthesis and plant productivity, with the largest proportional responses occurring below the current level of 350 mu mol mol(-1). In the late Pleistocene, CO2 levels near 200 mu mol mol(-1) may have been too low to support the level of productivity required for successful establishment of agriculture. Recent studies demonstrate that atmospheric CO2 increase from 200 to 270 mu mol mol(-1) stimulates photosynthesis and biomass productivity of C-3 plants by 25% to 50%, and greatly increases the performance of C-3 plants relative to weedy C-4 competitors. Rising CO2 also stimulates biological nitrogen fixation and enhances the capacity of plants to obtain limiting resources such as water and mineral nutrients. These results indicate that increases in productivity following the late Pleistocene rise in CO2 may have been substantial enough to have affected human subsistence patterns in ways that promoted the development of agriculture. Increasing CO2 may have simply removed a productivity barrier to successful domestication and cultivation of plants. Through effects on ecosystem productivity rising CO2 may also have been a catalyst for agricultural origins by promoting population growth, sedentism, and novel social relationships that in turn led to domestication and cultivation of preferred plant resources.

769^6^Taylor,G^Gardner,SDL^Bosac,C^Flowers,TJ^Crookshanks,M^Dolan,L^1995^1^Effects of elevated co2 on cellular mechanisms, growth and development of trees with particular reference to hybrid poplar^251^68^4^379-390^^^^^^^^^^4349e to weedy C-4 compe1344^243^312^360^374^417^803^867^
A^4348^Growth is often stimulated when C-3 plants, including trees, are exposed to elevated CO2, although evidence from the literature suggests that the responsiveness of trees to CO2 varies, depending on species. This paper explores some of the cellular mechanisms which underlie increased growth, using both the authors' own data and information from the literature. Mechanisms include photosynthetic fixation of CO2 and the role of Rubisco, the link between carbon fixation and growth, in particular, how increased carbon is thought to influence the process of plant cell expansion and cell production and finally the consequences of cellular effects for the growth and development of whole planes. Data are presented for the growth and development of hybrid poplars in elevated CO2, following both field (open-top chambers) and laboratory experiments which suggest that this type of tree with indeterminate, rapid growth may be favoured by the CO2 concentrations of the next century.
770^2^Vanoosten,JJ^Besford,RT^1995^1^Some relationships between the gas-exchange, biochemistry and molecular-biology of photosynthesis during leaf development of tomato plants after transfer to different carbon-dioxide concentrations^9^18^11^1253-1266^^^^^Nov^^^^^4351
1584^310^348^360^363^372^374^448^556^845^lie increased growth, using both the authors' own data and information from the literature. Mechanisms include photosynthetic fixation of CO2 and the role of Rubisco, the link between carbon fixation and growth, in particular, how increased carbon is thought to influence the process of plant cell expansion and cell production and finally the consequences of cellular effects for the growth and development of whole planes. Data are presented for the growth and development of hybrid poplars in elevated CO2, following both field (open-top chambers) and laboratory experiments which suggest that this type of tree with indeterminate, rapid growth may be favoured by the CO2 concentrations of the next century.
A^4350^Tomato plants were exposed to four concentrations of CO2 (350, 700, 1050 or 1400 mu mol CO2 mol(-1)) for 31 d. The light- saturated rate of photosynthesis (A) of the unshaded fifth leaf was measured at either an ambient CO2 concentration of 350 mu mol CO2 mol(-1) [A (350)] or at the level of CO2 at which the plants were grown. The chloroplast protein composition and the level of transcripts of nuclear or plastid photosynthesis- associated genes (PAGs), as well as the main carbohydrate content of the fifth leaf maintained horizontal and unshaded, were also measured during leaf development. At 60 and 95 % leaf expansion, the A of high CO2-grown plants measured at growth CO2 was higher than the A (350) of the plants grown at ambient CO2. However, in the fully mature leaves, A (growth CO2) declined linearly as growth CO2 concentration increased. The A (350) of plants exposed to elevated CO2 up to 60% leaf expanion had not acclimated to high CO2. At 95% leaf expansion, A (350) was lower in plants grown at high CO2. A versus CO2 (C-i) for mature leaves showed that A of the plants grown at high CO2 was lower over the entire range than that for plants grown at present ambient CO2 concentration. Lines fitted to the linear part of the A/C-l curves were concurrent at a C-i of 49 mu mol CO2 mol(-1) and A=-1.21 mu mol CO2 m(-2)s(-1). This C-i value is close to Gamma* (46 mu mol CO2 mol(-1)), the compensation point at 27 degrees C calculated from the equation described in Brooks & Farquhar (1985, Planta 165, 397-406). This A is an estimate of respiration in the light (R(1)) and was not affected by acclimation to elevated CO2. Thylakoid proteins (photosystem I core protein, D-1 and D-2 of the photosystem II core complex, cytochrome f) were all reduced by elevated CO2 only in the fully mature leaves (310 exposure), whereas the large and small subunits of Rubisco and Rubisco activase proteins had already declined after 22 d exposure. Transcript levels of the plastid-encoded FAG (rbcL, psbA, psaA-B) were reduced in the mature leaves by elevated CO2 when expressed on a total RNA basis, but they were not sensitive to elevated CO2 when expressed on a chloroplast 16S rRNA basis. However, rbcS, rca and cab mRNA transcripts were lower in the plants grown at high CO2 than in control plants after 22 d exposure when expressed on a nuclear rRNA basis. The loss of these nuclear PAGs was correlated with an accumulation of soluble sugars and starch.

771^4^Walker,RF^Geisinger,DR^Johnson,DW^Ball,JT^1995^1^Enriched atmospheric co2 and soil p effects on growth and ectomycorrhizal colonization of juvenile ponderosa pine^45^78^1-3^207-215^^^^^Oct^^^^^4353
341^372^374^416^419^610^680^757^ protein, D-1 and D-2 of the photosystem II core complex, cytochrome f) were all reduced by elevated CO2 only in the fully mature leaves (310 exposure), whereas the large and small subunits of Rubisco and Rubisco activase proteins had already declined after 22 d exposure. Transcript levels of the plastid-encoded FAG (rbcL, psbA, psaA-B) were reduced in the maA^4352^Interactive effects of atmospheric CO2 enrichment and soil P fertility on above- and below-ground development of juvenile ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were examined. Seedlings were reared from seed in atmospheres with 700 mu l l(-1), 525 mu l l(-1), or ambient CO2 concentrations, and in a potting mix with 68, 43, or 18 mu g g(-1) soil P, and all were inoculated with the mycobiont Pisolithus tinctorius (Pers.) Coker and Couch shortly after emergence. At 4-month intervals over the 1-year duration of the study, three whole seedlings of each combination of CO2 and P treatments were harvested to permit detailed assessment of shoot and root growth and ectomycorrhizal colonization. After 4 months, shoot volume, root dry weight, and total root length of seedlings grown in 700 mu l(-1) CO2 were greater than those of seedlings grown in the other atmospheres regardless of P treatment, and shoot/root ratios decreased as the CO2 concentration increased within each P treatment as well. After 8 months, the smallest shoot volumes and root weights and lengths within each P treatment were those of seedlings grown in ambient CO2. Root weight and total length increased as the CO2 concentration increased in high soil P, but the greatest root weights and lengths within the medium and low P treatments were those of seedlings reared in the 525 mu l(-1) CO2 atmosphere. Nevertheless, shoot/root ratios decreased with increasing CO2 in both high and medium soil P at the second harvest, and the highest shoot/root ratio in low P was that of seedlings grown in ambient CO2. After 1 year, the largest shoot and root volumes within the high and medium P treatments were those of seedlings grown in intermediate CO2, while the reverse was true in low P. The effects of CO2 concentration on dry weights, total root length, and shoot/root ratio at the final harvest were nonsignificant. As proved true with seedling growth, CO2 effects on ectomycorrhizal colonization varied temporally, as mycorrhizal development was not affected by the atmospheric treatments after 4 months, while seedlings grown in ambient CO2 exhibited the highest percent infections within each P treatment at the second harvest but those grown in 700 mu l l(-1) CO2 had the highest percentages after 1 year. These results suggest that elevated CO2 exerts stimulatory effects on shoot and root development of juvenile ponderosa pine which may be dependent on P availability to some degree, but these effects are somewhat transient and vary in magnitude over time.

772^2^Wayne,PM^Bazzaz,FA^1995^1^Seedling density modifies the growth-responses of yellow birch maternal families to elevated carbon-dioxide^127^1^5^315-324^^^^^Oct^^^^^4355
1627^384^417^456^540^57^634^669^672^740^ reverse was true in low P. The effects of CO2 concentration on dry weights, total root length, and shoot/root ratio at the final harvest were nonsignificant. As proved true with seedling growth, CO2 effects on ectomycorrhizal colonization varied temporally, as mycorrhizal development was not affecteA^4354^We studied seedling growth responses to ambient and elevated CO2 (350 and 700 mu L L(-1)) of three maternal families of yellow birch (Betula alleghaniensis), raised both individually and in high-density stands. Seedlings in competitive, dense stands exhibited markedly lower average CO2-induced growth enhancements than individually grown plants (16% vs. 49%). Maternal families differed in their growth responses to elevated CO2. However, differences among families were contingent upon density; families which exhibited the greatest CO2-induced growth at low density exhibited the least CO2- responsiveness at high density. These data are discussed in two separate contexts; the reliability of estimates of the CO2 fertilization potential of forest species based solely on individually grown plants, and the potential evolutionary consequences of rising CO2 on regenerating forest tree populations.
 growth, CO2 effects on ectomycorrhizal colonization varied temporally, as mycorrhizal development was not affecte773^3^Wilks,DS^Wolfe,DW^Riha,SJ^1995^1^Simple carbon assimilation response functions from atmospheric co2, and daily temperature and shortwave radiation^127^1^5^337-346^^^^^Oct^^^^^4357
243^314^362^372^528^635^665^92^Seedlings in competitive, dense stands exhibited markedly lower average CO2-induced growth enhancements than individually grown plants (16% vs. 49%). Maternal families differed in their growth responses to elevated CO2. However, differences among families were contingent upon density; families which exhibited the greatest CO2-induced growth at low density exhibited the least CO2- responsiveness at high density. These data are discussed in two separate contexts; the reliability of estimates of the CO2 fertilization potential of forest species based solely on individually grown plants, and the potential evolutionary consequences of rising CO2 on regenerating forest tree populations.
 growth, CO2 effects on ectomycorrhizal colonization varied temporally, as mycorrhizal development was not affecteA^4356^A global 'CO2 fertilizer effect' multiplier is often used in crop or ecosystem models because of its simplicity. However, this approach does not take into account the interaction between CO2, temperature and light on assimilation. This omission can lead to significant under- or overestimation of the magnitude of beneficial effects from elevated CO2, depending on environmental conditions. We use a mechanistic model of the biochemistry of photosynthesis to represent the response of net assimilation to different levels of CO2, temperature and radiation, on the daily time scale. Instantaneous assimilation rates for an idealized canopy model are integrated through diurnal cycles of environmental variables derived from historical climate data at three locations in North America. The calculated CO2 fertilizer effect is greatest at high light and warm temperatures. The results are summarized by assimilation response surfaces specified by the CO2 concentration, the canopy leaf area index, and by daily values of temperature and radiation available from climatic records. These summary functions are suitable for incorporation into crop or ecosystem models for predicting carbon assimilation or biomass production on a daily time step. An example application of the function reveals that for a relatively cool, high latitude location, the beneficial effects from a CO2 doubling would be negligible during the early spring, even assuming a + 4 degrees C global warming scenario. In contrast, the beneficial effects from increasing CO2 at a relatively warm, lower latitude location are greatest in the spring, but decline in late summer because of excessively warm temperatures with a + 4 degrees C global warming.

774^2^Woodward,FI^Kelly,CK^1995^1^The influence of co2 concentration on stomatal density^84^131^3^311-327^^^^^Nov^^^^^4359
1628^344^348^372^374^376^399^400^634^92^eratures. The results are summarized by assimilation response surfaces specified by the CO2 concentration, the canopy leaf area index, and by daily values oA^4358^A survey of 100 species and 122 observations has shown an average reduction in stomatal density of 14.3% (SE+/-2.2%) with CO2 enrichment, with 74% of the cases exhibiting a reduction in stomatal density. A sign test demonstrated that stomatal density decreases, in response to CO2, significantly more often than expected by chance. Repeated observations on the same species indicated a significant repeatability in the direction of the stomatal response. Analyses which removed the potential effect of taxonomy on this data set showed no significant patterns in the dependency of the degree of stomatal change on growth form (woodiness vs. non-woodiness; trees vs. shrubs), habitat (cool vs. warm) or stomatal distribution on the leaf (amphi- vs. hypostomatous). Forty-three of the observations had been made in controlled environments and under a typical range in CO2 enrichment of 350-700 mu mol mol(-1). For these cases the average stomatal density declined by 9% (SE+/-3.3%) and 60% of the cases showed reductions in stomatal density. When analyses were restricted to these 43 observations, amphistomatous samples more frequently had greater changes in stomatal density than did hypostomatous samples. The degree of reduction in stomatal density with increasing CO2 increases with initial stomatal density, after the influence of taxonomy is removed using analyses of independent contrasts. When the data were examined for patterns that might be due explicitly to the effects of relatedness, the subclasses of the Hamamelidae and the Rosidae showed highly significant reductions in stomatal density with CO2 (87% of the species studied in the Hamamelidae and 80% of the species in the Rosidae showed reduction with CO2 enrichment) and correlations between initial stomatal density and degree of reduction in stomatal density. The species sampled in the Hamamelidae were dominantly trees, whereas herbs dominated the species in the Rosidae. There were insufficient species studied at lower taxonomic levels to warrant further statistical analyses. This problem results from experimental and observational data being most often restricted to one species per taxonomic level, typically up to the level of order, a feature which can severely limit the extraction of taxonomically-related and ecologically-related plant responses.

775^2^Ackerly,DD^Bazzaz,FA^1995^1^Plant-growth and reproduction along co2 gradients - nonlinear responses and implications for community change^127^1^3^199-207^^^^^Jun^^^^^4361
1629^342^344^345^372^376^505^540^611^957^ae and the Rosidae showed highly significant reductions in stomatal density with CO2 (87% of the species studied in the Hamamelidae and 80% of the species in the Rosidae showed reduction with CO2 enrichment) and correlations between initial stomatal density and degree of reduction in stomatal density. The species sampled in the Hamamelidae were dominantly trees, whereas herbs dominated the species in the Rosidae. There were insufficient species studied at lower taxonomic levels to warrant further statisticaA^4360^The effects of rising atmospheric CO2 concentrations on natural plant communities will depend upon the cumulative responses of plant growth and reproduction to gradual, incremental changes in climatic conditions. We analysed published studies of plant responses to elevated CO2 to address whether reproductive and total biomass exhibit similar enhancement to elevated vs. ambient CO2 concentrations, and to assess the patterns of plant response along gradients of CO2 concentrations. In six annual plant species, mean enhancement at double ambient vs. ambient CO2 was 1.13 for total biomass and 1.30 for reproductive biomass. The two measures were significantly correlated, but there was considerable scatter in the relationship, indicating that reproductive responses cannot be consistently predicted from enhancement of total biomass. Along experimental CO2 gradients utilizing three concentrations, there was a great diversity of response patterns, including positive, negative, non-monotonic and non-significant (nat) responses. The distribution of response patterns differed for plants grown in stands compared to those grown individually. Positive responses were less frequent in competitive environments, and non- monotonic responses were more frequent. These results emphasize that interpolation of plant response based on enhancement ratios measured at elevated vs. ambient CO2 concentrations is not sufficient to predict community responses to incremental changes in atmospheric conditions. The consequences of differential response patterns were assessed in a simulation of community dynamics for four species of annual plants. The model illustrates that the final community composition at a future point in time depends critically on both the magnitude and the rate of increase of atmospheric CO2.

776^1^Amthor,JS^1995^1^Terrestrial higher-plant response to increasing atmospheric [co2] in relation to the global carbon-cycle^127^1^4^243-274^^^^^Aug^^^^^4363
1290^372^384^399^448^458^685^698^745^900^onic and non-significant A^4362^Terrestrial higher plants exchange large amounts of CO2 with the atmosphere each year; c. 15% of the atmospheric pool of C is assimilated in terrestrial-plant photosynthesis each year, with an about equal amount returned to the atmosphere as CO2 in plant respiration and the decomposition of soil organic matter and plant litter. Any global change in plant C metabolism can potentially affect atmospheric CO2 content during the course of years to decades. In particular, plant responses to the presently increasing atmospheric CO2 concentration might influence the rate of atmospheric CO2 increase through various biotic feedbacks. Climatic changes caused by increasing atmospheric CO2 concentration may modulate plant and ecosystem responses to CO2 concentration. Climatic changes and increases in pollution associated with increasing atmospheric CO2 concentration may be as significant to plant and ecosystem C balance as CO2 concentration itself. Moreover, human activities such as deforestation and livestock grazing can have impacts on the C balance and structure of individual terrestrial ecosystems that far outweigh effects of increasing CO2 concentration and climatic change. In short-term experiments, which in this case means on the order of 10 years or less, elevated atmospheric CO2 concentration affects terrestrial higher plants in several ways. Elevated CO2 can stimulate photosynthesis, but plants may acclimate and (or) adapt to a change in atmospheric CO2 concentration. Acclimation and adaptation of photosynthesis to increasing CO2 concentration is unlikely to be complete, however. Plant water-use efficiency is positively related to CO2 concentration, implying the potential for more plant growth per unit of precipitation or soil moisture with increasing atmospheric CO2 concentration. Plant respiration may be inhibited by elevated CO2 concentration, and although a naive C balance perspective would count this as a benefit to a plant, because respiration is essential for plant growth and health, an inhibition of respiration can be detrimental. The net effect on terrestrial plants of elevated atmospheric CO2 concentration is generally an increase in growth and C accumulation in phytomass. Published estimations, and speculations about, the magnitude of global terrestrial- plant growth responses to increasing atmospheric CO2 concentration range from negligible to fantastic. Well-reasoned analyses point to moderate global plant responses to CO2 concentration. Transfer of C from plants to soils is likely to increase with elevated CO2 concentrations because of greater plant growth, but quantitative effects of those increased inputs to soils on soil C pool sizes are unknown. Whether increases in leaf-level photosynthesis and short-term plant growth stimulations caused by elevated atmospheric CO2 concentration will have, by themselves, significant long-term (tens to hundreds of years) effects on ecosystem C storage and atmospheric CO2 concentration is a matter for speculation, not firm conclusion. Longterm field studies of plant responses to elevated atmospheric CO2 are needed. These will be expensive, difficult, and by definition, results will not be forthcoming for at least decades. Analyses of plants and ecosystems surrounding natural geological CO2 degassing vents may provide the best surrogates for long-term controlled experiments, and therefore the most relevant information pertaining to long-term terrestrial-plant responses to elevated CO2 concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO2 concentrations near vents is limited. On the whole, terrestrial higher-plant responses to increasing atmospheric CO2 concentration probably act as negative feedbacks on atmospheric CO2 concentration increases, but they cannot by themselves stop the fossil-fuel-oxidation-driven increase in atmospheric CO2 concentration. And, in the very long-term, atmospheric CO2 concentration is controlled by atmosphere-ocean C equilibrium rather than by terrestrial plant and ecosystem responses to atmospheric CO2 concentration.

777^2^Arnone,JA^Korner,C^1995^1^Soil and biomass carbon pools in model communities of tropical plants under elevated co2^2^104^1^61-71^^^^^Sep^^^^^4365
189^245^344^362^376^378^540^57^740^92^ best surrogates for long-term controlled experiments, and therefore the most relevant information pertaining to long-term terrestrial-plant responses to elevated CO2 concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO2 concentrations near vents is limited. On the whole, terrestrial higher-plant responses to increasing atmospheric CO2 concentration probably act as negative feedbacks on atmospheric CO2 concentration increases, but they cannot by themselves stop the fossil-fuel-oxidation-driven increase in atmospheric CO2 concentration. And, in the very long-term, atmospheric CO2 concentration is controlled by atmosphere-ocean C equilibrium rather than by teA^4364^The experimental data presented here relate to the question of whether terrestrial ecosystems will sequester more C in their soils, litter and biomass as atmospheric CO2 concentrations rise. Similar to our previous study with relatively fertile growth conditions (Korner and Arnone 1992), we constructed four rather nutrient-limited model communities of moist tropical plant species in greenhouses (approximately 7 m(2) each). Plant communities were composed of seven species (77 individuals per community) representing major taxonomic groups and various life forms found in the moist tropics. Two ecosystems were exposed to 340 mu l CO2 l(-1) and two to 610 mu l l(-1) for 530 days of humid tropical growth conditions. In order to permit precise determination of C deposition in the soil, plant communities were initially established in C-free unwashed quartz sand. Soils were then amended with known amounts of organic matter (containing C and nutrients). Mineral nutrients were also supplied over the course of the experiment as timed-release full-balance fertilizer pellets. Soils represented by far the largest repositories for fixed C in all ecosystems. Almost 5 times more C (ca. 80% of net C fixation) was sequestered in the soil than in the biomass, but this did not differ between CO2 treatments. In addition, at the whole-ecosystem level we found a remarkably small and statistically non-significant increase in C sequestration (+4%; the sum of C accretion in the soil, biomass, litter and necromass). Total community biomass more than quadrupled during the experiment, but at harvest was, on average, only 8% greater (i.e. 6% per year; n.s.) under elevated CO2, mainly due to increased root biomass (+15%, P = 0.12). Time courses of leaf area index of all ecosystems suggested that canopy expansion was approaching steady state by the time systems were harvested. Net primary productivity (NPP) of all ecosystems - i.e. annual accumulation of biomass, necromass, and leaf litter (but not plant-derived soil organic matter) - averaged 815 and 910 g m(-2) year(-1) at ambient and elevated CO2, respectively. These NPPs are remarkably similar to those of many natural moist tropical forested ecosystems. At the same time net productivity of soil organic matter reached 7000 g dry matter equivalent per m(2) and year (i.e. 3500 g C m(-2) year(-1)). Very slight yet statistically significant CO2- induced shifts in the abundance of groups of species occurred by the end of the experiment, with one group of species (Elettaria cardamomum, Ficus benjamina, F: pumila, Epipremnum pinnatum) gaining slightly, and another group (Ctenanthe lubbersiana, Heliconia humilis, Cecropia peltata) losing. Our results show that: (1) enormous amounts of C can be deposited in the ground which are normally not accounted for in estimates of NPP and net ecosystem productivity; (2) any enhancement of C sequestration under elevated atmospheric CO2 may be substantially smaller than is believed will occur (yet still very important), especially under growth conditions which permit close to natural NPP; and (3) species dominance in plant communities is likely to change under elevated CO2, but that changes may occur rather slowly.

778^5^Arnone,JA^Zaller,JG^Ziegler,C^Zandt,H^Korner,C^1995^1^Leaf quality and insect herbivory in model tropical plant- communities after long-term exposure to elevated atmospheric co2^2^104^1^72-78^^^^^Sep^^^^^4367
374^376^423^489^628^669^672^774^92^965^s occurred by the end of the experiment, with one group of species (Elettaria cardamomum, Ficus benjamina, F: pumila, Epipremnum pinnatum) gaining slightly, and another group (Ctenanthe lubbersiana, Heliconia humilis, Cecropia peltata) losing. Our results show that: (1) enormous amounts of C can be deposited in the ground which are normally not accounted for in estimates of NPP and net ecosystem productivity; (2) any enhancement of C sequestration under elevated atmospheric CO2 may be substantially smaller than is believed will occur (yet still very important), especially under growth conditions whicA^4366^Results from laboratory feeding experiments have shown that elevated atmospheric carbon dioxide can affect interactions between plants and insect herbivores, primarily through changes in leaf nutritional quality occurring at elevated CO2. Very few data are available on insect herbivory in plant communities where insects can choose among species and positions in the canopy in which to feed. Our objectives were to determine the extent to which CO2-induced changes in plant communities and leaf nutritional quality may affect herbivory at the level of the entire canopy. We introduced equivalent populations of fourth instar Spodoptera eridania, a lepidopteran generalist, to complex model ecosystems containing seven species of moist tropical plants maintained under low mineral nutrient supply. Larvae were allowed to feed freely for 14 days, by which time they had reached the seventh instar. Prior to larval introductions, plant communities had been continuously exposed to either 340 mu l CO2 l(-1) or to 610 mu l CO2 l(-1) for 1.5 years. No major shifts in leaf nutritional quality [concentrations of N, total non-structural carbohydrates (TNC), sugar, and starch; ratios of: C/N, TNC/N, sugar/N, starch/N; leaf toughness] were observed between CO2 treatments for any of the species. Furthermore, no correlations were observed between these measures of leaf quality and leaf biomass consumption. Total leaf area and biomass of all plant communities were similar when caterpillars were introduced. However, leaf biomass of some species was slightly greater - and for other species slightly less (e.g. Cecropia peltata) - in communities exposed to elevated CO2. Larvae showed the strongest preference for C. peltata leaves, the plant species that was least abundant in all communities, and fed relatively littie on plants species which were more abundant. Thus, our results indicate that leaf tissue quality, as described by these parameters, is not necessarily affected by elevated CO2 under relatively low nutrient conditions. Hence, the potential importance of CO2-induced shifts in leaf nutritional quality, as determinants of herbivory, may be overestimated for many plant communities growing on nutrient-poor sites if estimates are based on traditional laboratory feeding studies. Finally, slight shifts in the abundance of leaf tissue of various species occurring under elevated CO2 will probably not significantly affect herbivory by generalist insects. However, generalist insect herbivores appear to become more dependent on less-preferred plant species in cases where elevated CO2 results in reduced availability of leaves of a favoured plant species, and this greater dependency may eventually affect insect populations adversely.

779^2^Baldocchi,DD^Harley,PC^1995^1^Scaling carbon-dioxide and water-vapor exchange from leaf to canopy in a deciduous forest .2. Model testing and application^9^18^10^1157-1173^^^^^Oct^^^^^4369
130^137^1386^1630^1631^243^256^372^674^711^y affected by elevated CO2 under relatively low nutrient conditions. HenceA^4368^The scaling of CO2 and water vapour transfer from leaf to canopy dimensions was achieved by integrating mechanistic models for physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer, turbulent transfer and surface energy exchanges) processes, The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements, The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere, In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO2) and ecophysiological (photosynthetic capacity) variables on canopy-scale carbon and water vapour fluxes.
levated CO2 under relatively low nutrient conditions. Hence780^3^Barnes,JD^Ollerenshaw,JH^Whitfield,CP^1995^1^Effects of elevated co2 and/or o-3 on growth, development and physiology of wheat (triticum-aestivum L)^127^1^2^129-142^^^^^Apr^^^^^4371
1097^1632^1633^230^377^384^435^446^692^724^eteorological (radiative transfer, turbulent transfer and surface energy exchanges) processes, The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements, The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere, In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO2) and ecophysiological (photosynthetic capacity) variables on canopy-scale carbon and water vapour fluxes.
levated CO2 under relatively low nutrient conditions. HenceA^4370^Two cultivars of spring wheat (Triticum aestivum L. cvs. Alexandria and Hanno) and three cultivars of winter wheat (cvs. Riband, Mercia and Haven) were grown at two concentrations of CO2 [ambient (355 mu mol mol(-1)) and elevated (708 mu mol mol(-1))] under two O-3 regimes [clean air (< 5 nmol mol(-1) O- 3) and polluted air (15 nmol mol(-1) O-3 at night rising to a midday maximum of 75 nmol mol(-1))] in a phytotron at the University of Newcastle-upon-Tyne. Between the two-leaf stage and anthesis, measurements of leaf gas-exchange, non-structural carbohydrate content, visible O-3 damage, growth, dry matter partitioning, yield components and root development were made in order to examine responses to elevated CO2 and/or O-3. Growth at elevated CO2 resulted in a sustained increase in the rate of CO2 assimilation, but after roughly 6 weeks' exposure there was evidence of a slight decline in the photosynthetic rate (c.-15%) measured under growth conditions which was most pronounced in the winter cultivars. Enhanced rates of CO2 assimilation were accompanied by a decrease in stomatal conductance which improved the instantaneous water use efficiency of individual leaves. CO2 enrichment stimulated shoot and root growth to an equivalent extent, and increased tillering and yield components, however, non-structural carbohydrates still accumulated in source leaves. In contrast, long-term exposure to O-3 resulted in a decreased CO2 assimilation rate (c.-13%), partial stomatal closure, and the accumulation of fructan and starch in leaves in the light. These effects were manifested in decreased rates of shoot and root growth, with root growth more severely affected than shoot growth. In the combined treatment growth of O-3-treated plants was enhanced by elevated CO2, but there was little evidence that CO2 enrichment afforded additional protection against O-3 damage. The reduction in growth induced by O-3 at elevated CO2 was similar to that induced by O-3 at ambient CO2 despite additive effects of the individual gases on stomatal conductance that would be expected to reduce the O-3 flux by 20%, and also CO2-induced increases in the provision of substrates for detoxification and repair processes. These observations suggest that CO2 enrichment may render plants more susceptible to O-3 damage at the cellular level. Possible mechanisms are discussed.

781^2^Beerling,DJ^Quick,WP^1995^1^A new technique for estimating rates of carboxylation and electron-transport in leaves of C-3 plants for use in dynamic global vegetation models^127^1^4^289-294^^^^^Aug^^^^^4373
1386^1634^227^509^539^553^812^92^951^eased rates of shoot and root growth, with root growth more severely affected than shoot growth. In the combined treatment growth of O-3-treated plants was enhanced by elevated CO2, but there was little evidence that CO2 enrichment afforded additional protection against O-3 damage. The reduction in growth induced by O-3 at elevated CO2 was similar to that induced by O-3 at ambient CO2 despite additive effects of the individual gases oA^4372^The possible responses of the terrestrial biosphere to future CO2 increases and associated climatic change are being investigated using dynamic global vegetation models (DGVMs) which include the Farquhar ef al. (1980) biochemical model of leaf assimilation as the primary means of carbon capture. This model requires representative values of the maximum rates of Rubisco activity, V-max, and electron transport, J(max), for different vegetation types when applied at the global scale. Here, we describe an approach for calculating these values based on measurements of the maximum rate of leaf photosynthesis (A(max)) and C-13 discrimination. The approach is tested and validated by comparison with measurements of Rubisco activity assayed directly on wild-type and transgenic Nicotiana tabacum (tobacco) plants with altered Rubisco activity grown under ambient and elevated CO2 mole fractions with high and low N-supply. V-max and J(max) values are reported for 18 different vegetation types with global coverage. Both variables were linearly related reinforcing the idea of optimal allocation of resources to photosynthesis (light harvesting vs. Rubisco) at the global scale. The reported figures should be of value to the further development of vegetation and ecosystem models employing mechanistic DGVMs.

782^3^Ceulemans,R^Vanpraet,L^Jiang,XN^1995^1^Effects of co2 enrichment, leaf position and clone on stomatal index and epidermal-cell density in poplar (populus)^84^131^1^99-107^^^^^Sep^^^^^4375
130^1635^344^610^634^92^980^oach for calculating these values based on measurements of the maximum rate of leaf photosynthesis (A(max)) and C-13 discrimination. The approach is tested and validated by comparison with measurements of Rubisco activity assayed directly on wild-type and transgenic Nicotiana tabacum (tobacco) plants with altered Rubisco activity grown under ambient and elevated CO2 mole fractions with high and low N-supply. V-max and J(max) values are reported for 18 different vegetation types with global coverage. BA^4374^The effects of CO2 enrichment and leaf position on stomatal characteristics (stomatal density, stomatal index and stomatal pore length) and epidermal cell density were examined for two different Populus clones, Beaupre and Robusta, grown from cuttings in open-top chambers under ambient and elevated atmospheric CO2 conditions. Both clones had amphistomatous leaves, and stomatal density was significantly larger on the abaxial leaf surface than on the adaxial. Significant interactions between CO2 enrichment, leaf position and clone were observed for most stomatal and epidermal characteristics. A significant reduction of the number of stomata mm(-2) under elevated CO2 was observed in expanding leaves near the upper portion of the plant for both leaf surface sides and in both clones. For the abaxial leaf side only, this reduction under elevated CO2 was accompanied by a similar reduction of the stomatal index in both clones. In mature leaves on the middle and lower portion of the plants, there was no significant effect of the CO2 treatment on stomatal density. In young, expanding leaves near the upper part of the plant there were significant interactions between the CO2 treatment and leaf surface side for epidermal cell density. The latter increased under elevated CO2 at the abaxial leaf surface, but decreased at the adaxial surface on the upper part of the plant. Total epidermal cell numbers of mature, fully expanded leaves increased under elevated CO2 in both clones. The observation that interactions with leaf age and/or leaf position significantly confound the CO2 treatment effect on stomatal and epidermal cell densities, might contribute to the elucidation of the problem of the phenomenon of stomatal density reduction under elevated atmospheric CO2.

783^2^Christ,RA^Korner,C^1995^1^Responses of shoot and root gas-exchange, leaf blade expansion and biomass production to pulses of elevated co2 in hydroponic wheat^78^46^292^1661-1667^^^^^Nov^^^^^4377
130^1636^264^310^341^348^417^434^724^92^here was no signifA^4376^Short-term effects of elevated CO2 during the early life phase of plants may have long lasting consequences for growth and biomass in later periods. We exposed hydroponically grown wheat seedlings to 5 d pulses of elevated CO2 while leaf expansion growth as well as shoot and root gas exchange were measured simultaneously and continuously. Shoot photosynthesis, night- time shoot respiration and below-ground respiration (largely by roots) roughly doubled when atmospheric CO2 concentration was doubled. An interruption of CO2 enrichment caused CO2 assimilation and respiration to return to control levels, However, while the response of photosynthesis was immediate, that of respiration showed a hysteresis of about 3 d. Since shoot biomass increased at elevated CO2 (with no change in allocation pattern) equal fluxes per shoot or root system after a return to control CO2 concentrations indicate substantial downward adjustment of the capacity for CO2 fixation and release in high-CO2 grown plants. Leaf expansion growth was completely unaffected by CO2 enrichment, whereas tiller initiation was significantly increased (doubled in 18 d). We conclude that leaf growth in these wheat plants was already carbon-saturated at ambient CO2 concentration at optimum mineral nutrient supply. The stimulation of growth of whole plants was exclusively due to enhanced tillering during this very early part of the life of these wheat plants.

784^5^Ellsworth,DS^Oren,R^Huang,C^Phillips,N^Hendrey,GR^1995^1^Leaf and canopy responses to elevated co2 in a pine forest under free-air co2 enrichment^2^104^2^139-146^^^^^Oct^^^^^4379
243^341^361^384^465^546^705^742^748^92^ photosynthesis was immediate, that of respiration showed a hysteresis of about 3 d. Since shoot biomass increased at elevated CO2 (with no change in allocation pattern) equal fluxes per shoot or root system after a return to control CO2 concentrations indicate substantial downward adjustment of the capacity for CO2 fixation and release in high-CO2 grown plants. Leaf expansioA^4378^Physiological responses to elevated CO2 at the leaf and canopy- level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO2 using a free-air CO2 enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO2 over an 8-day exposure period was similar to that of trees exposed to current ambient CO2 under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO2-exposed trees showed minor (less than or equal to 7%) but significant reductions in relative sap flux density compared to trees under ambient CO2 conditions. Short-term (minutes) direct stomatal responses to elevated CO2 were also relatively weak (approximate to 5% reduction in stomatal aperture in response to high CO2 concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO2 for nearly 80 days compared to foliage grown under current ambient CO2 so intrinsic leaf water-use efficiency at elevated CO2 was enhanced primarily by direct responses of photosynthesis to CO2. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO2 (A(net)-C-i curves) for Pinus taeda foliage grown under elevated CO2 (550 mu mol mol(-1)) for 50-80 days compared to those for foliage grown under current ambient CO2 from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 mu mol mol(-1) CO2 was enhanced by approximately 65% compared to the rate at ambient CO2 (350 mu mol mol(-1)). A similar level of enhancement under elevated CO2 was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO2 during the study period appears to be primarily attributable to direct photosynthetic responses to CO2 in the pine forest, longer-term CO2 responses and feedbacks remain to be evaluated.
 compared to foliage grown under current ambient CO2 so intrinsic leaf water-use efficiency at elevated 785^3^Field,CB^Jackson,RB^Mooney,HA^1995^1^Stomatal responses to increased co2 - implications from the plant to the global-scale^9^18^10^1214-1225^^^^^Oct^^^^^4381
243^344^384^398^400^465^546^674^92^968^Pinus taeda foliage grown under elevated CO2 (550 mu mol mol(-1)) for 50-80 days compared to those for foliage grown under current ambient CO2 from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 mu mol mol(-1) CO2 was enhanced by approximately 65% compared to the rate at ambient CO2 (350 mu mol mol(-1)). A similar level of enhancement under elevated CO2 was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO2 during the study period appears to be primarily attributable to direct photosynthetic responses to CO2 in the pine forest, longer-term CO2 responses and feedbacks remain to be evaluated.
 compared to foliage grown under current ambient CO2 so intrinsic leaf water-use efficiency at elevated A^4380^Increased atmospheric CO2 Often but not always leads to large decreases in leaf conductance, Decreased leaf conductance has important implications for a number of components of CO2 responses, from the plant to the global scale, All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO2. The list of potentially sensitive processes includes soil evaporation, run- off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities, Experimental evidence concerning ecosystem-scale consequences of the effects of CO2 on water use is only beginning to accumulate, but the initial indication is that, in water-limited areas, the effects of CO2- induced changes in leaf conductance are comparable in importance to those of CO2-induced changes in photosynthesis, Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotranspiration to increased CO2. While some components of these processes tend to amplify the sensitivity of evapotranspiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance, The effects of increased CO2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances, Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance, Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation, The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO2.
dulate the response of canopy or r786^7^Friedlingstein,P^Fung,I^Holland,E^John,J^Brasseur,G^Erickson,D^Schimel,D^1995^1^On the contribution of co2 fertilization to the missing biospheric sink^137^9^4^541-556^^^^^Dec^^^^^4383
1637^1638^227^314^372^374^377^51^57^672^f canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance, The effects of increased CO2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances, Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one-fourth as large as decreases in canopy conductance, Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation, The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO2.
dulate the response of canopy or rA^4382^A gridded biospheric carbon model is used to investigate the impact of the atmospheric CO2 increase on terrestrial carbon storage. The analysis shows that the calculated CO2 fertilization sink is dependent not just on the mathematical formulation of the ''beta factor'' but also on the relative controls of net primary productivity (NPP), carbon residence times, and resource availability. The modeled evolution of the biosphere for the period 1850-1990 shows an increasing lag between NPP and the heterotrophic respiration. The time evolution of the modeled biospheric sink (i.e., difference between enhanced NPP and enhanced respiration) does not match that obtained by deconvolution of the ice core CO2 time series. Agreement between the two is reasonable for the first half of the period, but during the recent decades the deconvoluted CO2 increase is much too fast to be explained by the CO2 fertilization effect only. Therefore other mechanisms than CO2 fertilization should also contribute to the missing sink. Our results suggest that about two thirds to three fourths of the 1850-1990 integrated missing sink is due to the CO2 greening of the biosphere. The remainder may be due to the increased level of nitrogen deposition starting around 1950.

787^3^Gardner,SDL^Taylor,G^Bosac,C^1995^1^Leaf growth of hybrid poplar following exposure to elevated co2^84^131^1^81-90^^^^^Sep^^^^^4385
1267^1383^1384^1639^1640^361^376^377^434^664^ biosphere for the period 1850-1990 shows an increasing lag between NPP and the heterotrophic respiration. The time evolution of the modeled biospheric sink (i.e., difference between enhanced NPP and enhanced respiration) does not match that obtained by deconvolution of the ice core CO2 time series. Agreement between the two is reasonable for the first half of the period, but during the recent decades the deconvoluted CO2 increase is much too fast to be explained by the CO2 fertilization effect only. Therefore other mechanisms than CO2 fertilization should also contribute to the missing sinkA^4384^Leaf extension was stimulated following exposure of three interamerican hybrid poplar clones (Populus trichocarpa x P. deltoides); 'Unal', 'Boelare', and 'Beaupre' and a euramerican clone 'Primo' (Populus nigra x P. deltoides) to elevated CO2 in controlled environment chambers. For all three interamerican clones the evidence suggests that this was the result of increased leaf cell expansion associated with enhanced cell wall extensibility (WEx), measured as tensiometric increases in cell wall plasticity. For the interamerican clone 'Boelare', there was also a significant increase in cell wall elasticity following exposure to elevated CO2 (P less than or equal to 0.001). The effect of elevated CO2 in stimulating cell wall extensibility was confirmed in a detailed spatial analysis of extensibility made across the lamina of expanding leaves of the clone 'Boelare'. For two of the interamerican hybrids, 'Unal' and 'Beaupre', both leaf cell water potential (psi) and turgor pressure (P) were lower in elevated than in ambient CO2 By contrast, no significant effects on the cell wall properties or leaf water relations for the euramerican hybrid 'Primo' were observed following exposure to elevated CO2, suggesting that the mechanism for increased leaf extension in elevated CO2 differed, depending on clone. The cumulative total length of leaves of 'Boelare' grown in elevated CO2 was significantly increased (P less than or equal to 0.05) and since leaf number was not significantly increased in any inter-american clone it is hypothesized that final leaf size was stimulated in elevated CO2 for these clones. By contrast, there was no significant effect of CO2 on cumulative total leaf length for the euramerican clone 'Primo', but leaf number was significantly increased by elevated CO2. The measurements suggest that total tree leaf area was stimulated for a range of poplar hybrids exposed to elevated CO2. Given the short rotation of a coppiced crop, it is likely that increased leaf areas will result in enhanced stemwood production when hybrid poplars are grown in the CO2 concentrations predicted for the next century.

788^3^Greer,DH^Laing,WA^Campbell,BD^1995^1^Photosynthetic responses of 13 pasture species to elevated co2 and temperature^92^22^5^713-722^^^^^^^^^^4387
1345^310^360^377^434^506^58^692^792^92^on clone. The cumulative total length of leaves of 'Boelare' grown in elevated CO2 was significantly increased (P less than or equal to 0.05) and since leaf number was not significantly increased in any inter-american clone it is hypothesized that final leaf size was stimulated in elevated CO2 for these clones. By contrast, there was no significant effect of CO2 on cumulative total leaf length for the euramerican clone 'Primo', but leaf number was significantly increased by elevated CO2. The measurements suggest that total tree leaf area was stimulated for a range of poplar hybrids exposed to elevated CO2. Given the short rotation of a coppiced crop, it is likely that increased leaf areas will result in enhanced stemwood prA^4386^Thirteen common pasture species, (eleven C-3 and two C-4), were grown in controlled environments at 12/7, 18/13 and 28/23 degrees C and at 350 and 700 ppm CO2 to evaluate the effects of elevated CO2 on their photosynthetic responses. Photosynthesis was measured at the growth temperatures and at both 350 and 700 ppm CO2. In C-3 species, short-term (within minutes) increases in CO2 had the greatest effect on photosynthesis, with an average of 50-60% higher rates in plants exposed to 700 ppm CO2 at each temperature. However, there was a continuum of response between the C-3 species whereas C-4 species were unaffected by short-term changes in CO2 There was also a long-term (4-8 weeks) response to high CO2, with an average of about 40-50% higher rates of photosynthesis, with some response by C-4 species. Both short- and long-term responses were negatively correlated with the photosynthetic rate of each species at 350 ppm CO2 and all species were less efficient at converting photosynthate to dry matter at elevated CO2. These data show clearly that photosynthesis of these cool temperate pasture species can respond to elevated CO2, especially at low temperatures. This will have consequences for predicting the potential effects of climate change, accompanied by rising CO2, on pasture ecosystems.

789^4^Hutchin,PR^Press,MC^Lee,JA^Ashenden,TW^1995^1^Elevated concentrations of co2 may double methane emissions from mires^127^1^2^125-128^^^^^Apr^^^^^4389
1377^1641^1642^59^99^ in plants exposed to 700 ppm CO2 at each temperature. However, there was a continuum of response between the C-3 species whereas C-4 species were unaffected by short-term changes in CO2 There was also a long-term (4-8 weeks) response to high CO2, with an average of about 40-50% higher rates of photosynthesis, with some response by C-4 species. Both short- and long-term responses were negatively correlated with the photosynthetic rate of each species at 350 ppm CO2 and all species were less efficient at converting photosynthate to dry matter at eA^4388^The potential impact of an increase in methane emissions from natural wetlands on climate change models could be very large. We report a profound increase in methane emissions from cores of mire peat and vegetation as a direct result of increasing the CO2 concentration from 355 to 550 mu mol mol(-1) (a 60% increase). Increased CH4 fluxes were observed throughout the four month period of study. Seasonal variation in CH4 flux, consistent with that seen in the field, was observed under both ambient and elevated CO2. Under ambient CO2 methane fluxes rose from 0.02 mu mol m(-2) s(-1) in May to 0.11 mu mol m(-2) s(-3) in July before declining again in August. Under elevated CO2, methane fluxes were at least 100% greater throughout the experiment, rising from 0.05 mu mol m(-2) s(-1) in May to a peak of 0.27 mu mol m(-2) s(-1) in July. The stimulation of CH4 emissions was accompanied by a 100% increase in rates of photosynthesis from 4.6 (+/- 0.3) under ambient CO2 to 9.3 (+/- 0.7) mu mol m(-2) s(-1). Root and shoot biomass were unaffected.

790^4^Jones,MB^Brown,JC^Raschi,A^Miglietta,F^1995^1^The effects on arbutus-unedo L of long-term exposure to elevated co2^127^1^4^295-302^^^^^Aug^^^^^4391
243^344^348^360^376^384^417^634^705^745^rect result of increasing the CO2 concentration from 355 to 550 mu mol mol(-1) (a 60% increase). Increased CH4 fluxes were observed throughout the four month period of study. Seasonal variation in CH4 flux, consistent with that seen in the field, was observed under both ambient and elevated CO2. Under ambient CO2 methane fluxes rose from 0.02 mu mol m(-2) s(-1) in May to 0.11 mu mol m(-2) s(-3) in July before declining again in August. Under elevated CO2, methane fluxes were at least 100% greater throughout the experiment, rising from 0.05 mu mol m(-2) s(-1) in May to a peak of 0.27 mu mol m(-2) s(-1) in July. The stimulation of CH4 emissions was accompanied by a 100% increase in rates of photosynthesis from 4.6 (+/- 0.3) under ambient CO2 to 9.3 (+/- 0.7) mu mol m(-2) s(-1). Root anA^4390^Arbutus unedo is a sclerophyllous evergreen, characteristic of Mediterranean coastal scrub vegetation. In Italy, trees of A. unedo have been found close to natural CO2 vents where the mean atmospheric carbon dioxide concentration is about 2200 mu mol mol(-1). Comparisons were made between trees growing in elevated and ambient CO2 concentrations to test for evidence of adaptation to long-term exposure to elevated CO2. Leaves formed at elevated CO2 have a lower stomatal density and stomatal index and higher specific leaf area than those formed at ambient CO2, but there was no change in carbon to nitrogen ratios of the leaf tissue. Stomatal conductance was lower at elevated CO2 during rapid growth in the spring. In mid-summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO2 increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO2 was higher than the leaves at elevated CO2, increasing instantaneous water use efficiency at elevated CO2. Chlorophyll fluorescence measurements suggested that elevated CO2 provided some protection against photoinhibition in mid- summer. Analysis of A/C-i curves showed that there was no evidence of either upward or downward regulation of photosynthesis at elevated CO2. It is therefore anticipated that A. unedo will have higher growth rates as the ambient CO2 concentrations increase.

791^1^Korner,C^1995^1^Towards a better experimental basis for upscaling plant- responses to elevated co2 and climate warming^9^18^10^1101-1110^^^^^Oct^^^^^4393
312^344^361^507^540^672^685^705^740^92^as lower at elevated CO2 during rapid growth in the spring. In mid-summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO2 increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO2 was higher than the leaA^4392^Few of the most common assumptions used in models of responses of plants and ecosystems to elevated CO2 and climate warming have been tested under realistic life conditions, It is shown that some unexpected discrepancies between predictions and experimental findings exist, suggesting that a better empirical basis is required for predictions, The following ten suggestions may improve our potential to scale up from experimental scales to the real world, (1) Experiments should be timed to account for non-linearity in system responsiveness, asynchrony of responses and developmental differences, (2) By altering mineral nutrient supply, a wide range of CO2 responses can be 'produced', thus requiring realistic soil conditions, (3) Distinctions should be made between 'doubling CO2 supply' and biologically effective degrees of CO2 enrichment. (4) Because of the non-linearity of plant responses to CO2, studies of at least three instead of two CO2 concentrations are necessary to describe future trends adequately, (5) Edge effects, in particular unscreened side light, may lead to allometric anomalies, strongly constraining up-scaling to stand-scale CO2 responses, (6) Variables such as growth, yield, net primary production and C turnover are often confused with carbon pools, carbon sequestration or net ecosystem production, (7) Mono- and interspecific interactions between individuals may lead to completely unpredictable CO2 responses, (8) Experiments with seedlings benefit from the absence of prehistory effects but are likely to be irrelevant for the responses of larger trees which, on the other hand, may be constrained by carryover effects, Tree ring research indicates immediate sensitivity of large trees to environmental changes, supporting their usefulness in short-term CO2-enrichment experiments, (9) In predicting temperature responses, acclimation deserves more attention, (10) The significance of developmental responses is largely under-represented in experimental research, although these responses may overrule many of the other effects of atmospheric change, Results of more realistic experiments which account for these problems will provide a better basis for modelling the future of the biosphere.

792^2^Krapfenbauer,A^Wriessnig,K^1995^1^Anthropogenic environmental-pollution - the share of agriculture^254^46^3^269-283^^^^^Aug^^^^^4395
nterspecific interactions between individuals may lead to completely unpredictable CO2 responses, (8) Experiments with seedlings benefit from the absence of prehistory effects but are likely to be irrelevant for the responses of larger trees which, on the other hand, may be constrained by carryover effects, Tree ring research indicates immediate sensitivity of large trees to environmental changes, supporting their usefulness in short-term CO2-enrichment experiments, (9) In predicting temperature responses, acclimation deserves more attention, (10) The significance of developmental responses is largely under-represented in experimental research, although these responses may overrule A^4394^The increase of environmental pollution is in direct relation to the consumption of fossil coal, gas and oil and the progressive growth of the world population. Since 1950 these issues increased considerably and they will continue to increase in the future. At the moment the population increases by 1.9 %, the consumption of energy between 2 and 3 % and the environmental pollution up to 3.5 % annually. With the progressive growth of the world population and the increase in prosperity in the developed countries the demand for food increased also progressively and therewith the productivity index of the units of arable land, by growing consumption of fertilizers and the installation of irrigation systems. At the same time the pollution of air, water and soil caused by agriculture also grew progressively. But up to date there is still a shortcoming of reliable statistical facts and figures. A higher productivity index of the units of arable land in the different ecoclimatic zones of the earth leads to higher production and consumption by an inevitably higher turnover of plant nutrients and diverse gaseous substances, for example carbon mono- and dioxide, diverse compounds of nitrogen etc. At the same time an excess of the ''critical loads'' for soil, air and water must be expected. The main items of the emissions produced by an intensified agriculture are, besides carbon mono- and dioxide, methane, nitric and nitrous oxide, ammonia and diverse hydrocarbons. A higher productivity index is consequently related to a higher consumption. This also leads to an intensified turnover of carbon dioxide. There is consequently a progressive input of carbon dioxide resulting from the emissions of burning fossil fuel in the recently produced and consumed biomass. This inevitably leads to a higher level of carbon dioxide in the air. A main source of emissions of methane and ammonia is animal breeding. In Austria at this time from each of the 3,508.000 hectars of land used by agriculture annual emissions of 63 kg methane and 11 kg ammonia are resulting theoretically. The use of organic and inorganic fertilizers, the growing cultivation of legumes and the emissions of nitrogen compounds resulting from burning processes elevate likewise the pool and the annual turnover of nitrogen compounds by production and consumption of biomass. Inevitably related to it is a growing amount of the annual input of nitrogen compounds to the air, the soil and the water. A rough approximation says that at present agriculture contributes to the global anthropogenic pollution of the environment (air, soil and water) 85 % of the ammonia, 81 % of the nitrous oxide, 35 % of nitric mono- and dioxide, 70 % of the methane, 52 % of the carbon monoxide and 21 % of the carbon dioxide. Not considered in the figure for carbon dioxide is the inevitable increase of the level of CO2 in the air by the elevated turnover of biomass. The world population growth in the future leads to an increasing contribution of agriculture to the anthropogenic environmental pollution. For the developed countries this is an obligatory challenge to avoid surplus production. On a global scale there must be a sensible reduction of animal breeding to reduce the high emissions of methane and ammonia from this sector of agriculture. It must also be considered, that by feeding animals with vegetable food stuff, which also could be used for direct nutrition of man, the efficiency of it is lowered by a factor of 1:10. In spite of a growing crisis to maintain the alimentation of the growing world population in many countries the nutrition of man must rapidly be centered on vegetable food stuff rich in protein. At the same time an essential reduction of the environmental pollution resulting from animal breeding could be realized. Beside of it and other reducing issues a continuous growth of the world population, the energy consumption and environmental pollution will make it necessary to observe the development and reactions in the environment by monitoring and phenological observations. The results must be used to counteract finally by looking for adaptation strategies. Considering the realities it must be realized that by all means to mobilize for counteracting the environmental pollution directly, a certain climate change will be inevitable. The consequences will also be an outstanding challenge for the agriculture.

793^4^Kwa,SH^Wee,YC^Lim,TM^Kumar,PP^1995^1^Establishment and physiological analyses of photoautotrophic callus-cultures of the fern platycerium-coronarium (koenig) desv under co2 enrichment^78^46^291^1535-1542^^^^^Oct^^^^^4397
1643^1644^243^372^92^948^tered on vegetable food stuff rich in protein. At the same time an essential reduction of the environmental pollution resulting from animal breeding could be realized. Beside of it and other reducing issues a continuous growth of the world population, the energy consumption and environmental pollution will make it necessary to observe the development and reactions in the environment by monitoring and phenological observations. The resuA^4396^Gametophyte-derived callus cultures of Platycerium coronarium could be maintained under photoautotrophic conditions on Murashige and Skoog medium supplemented with 2 mu M 2,4- dichlorophenoxyacetic acid (2,4-D) and with CO2 enrichment. Progressive reduction of sucrose from the medium resulted in a reduction in growth, but an increase in total chlorophyll content. When subculturing was delayed beyond 2 weeks, callus cells differentiated into gametophytes on the medium with less than or equal to 0.2% sucrose and no CO2 enrichment. Enriching the photoautotrophic cultures on 2 mu M 2,4-D with 1% CO2 resulted in about 1.7-fold increase in fresh weight within 42 d. Total chlorophyll content was generally higher with 1% CO2 enrichment than with 10%. F-v/F-m ratio was higher for callus on low levels of sucrose (less than or equal to 0.5%) than that on sucrose greater than or equal to 1.0%. An increase in autofluorescence of chloroplasts, but not the size, was observed with decreasing sucrose levels in the medium. Autofluorescence decreased with increase in CO2 from 0.03%. Our data are in agreement with the view that long-term exposure to high levels of CO2 can cause a decrease in photosynthetic capacity.

794^3^Liang,N^Maruyama,K^Huang,Y^1995^1^Interactions of elevated co2 and drought stress in gas-exchange and water-use efficiency in 3 temperate deciduous tree species^79^31^4^529-539^^^^^^^^^^4399
1234^1645^243^312^374^376^409^417^434^92^tiated into gametophytes on the medium with less than or equal to 0.2% sucrose and no CO2 enrichment. Enriching the photoautotrophic cultures on 2 mu M 2,4-D with 1% CO2 resulted in about 1.7-fold increase in fresh weight within 42 d. Total chlorophyll content was generally higher with 1% CO2 enrichment than with 10%. F-v/F-m ratio was higher for callus on low levels of sucrose (less than or equal to 0.5%) than that on sucrose greater than or equal to 1.0%. An increase in autofluorescence of chloroplasts, but not the size, was observed with decreasing sucrose levels in the medA^4398^The effect of CO2 increase on gas exchange and water-use efficiency (WUE) in three temperate deciduous species (Fagus crenata, Ginkgo biloba and Alnus firma) under gradually- developing drought-stress was assessed. Seedlings were grown within transparent open-top cabinets and maintained for 4 months at mean CO2 concentrations of either 350 (ambient; C- 350) Or 700 mu mol mol(-1) (elevated; C-700) and combined with five water regimes [leaf water potential, Psi(w), higher than - 0.3 (well-watered), -0.5 and -0.8 (moderate drought), -1.0 and fewer than -1.2 MPa (serious drought-stress)]. Increase in CO2 concentration induced a 60 % average increase in net photosynthetic rate (P-N) under well-watered conditions. The effect of C-700 became more pronounced with drought stress established, with an 80 % average increase in P-N at Psi(w), as low as -0.8 MPa; leaf conductance to water vapour transfer (g(s)) and transpiration rate (E), however, were significantly decreased. Consequently, WUE increased under drought, through drought stress affected potential E sooner than potential P-N. The interaction of CO2 x drought stress on WUE was significant in that P-N was stimulated while E in C-700 enriched plants resembled that of C-350 plants under drought. Hence if a doubling of atmospheric CO2 concentration occurs by the mid 21(st) century, then greater P-N in F. crenata, G. biloba and A. firma may be expected and the drought susceptibility of these species will be substantially enhanced.

795^5^Martin,CA^Stutz,JC^Kimball,BA^Idso,SB^Akey,DH^1995^1^Growth and topological changes of citrus-limon (L) burm f eureka in response to high-temperatures and elevated atmospheric carbon-dioxide^154^120^6^1025-1031^^^^^Nov^^^^^4401
1386^1646^1647^243^310^361^376^384^528^58^ounced with drought stress established, with an 80 % average increase in P-N at Psi(w), as low as -0.8 MPa; leaf conductance to water vapour transfer (g(s)) and transpiration rate (E), however, were significantly decreased. Consequently, WUE increased under drouA^4400^Growth and topological indices of 'Eureka' lemon were measured after 6 months in well-watered and well-fertilized conditions and factorial combinations of moderate (29/21C day/night) or high (42/32C day/night) temperatures and ambient (350 to 380 mu mol . mol(-1)) or elevated (constant 680 mu mol . mol(-1)) CO2. In high temperatures, plants were smaller and had higher levels of leaf chlorophyll alpha than in moderate temperatures. Moreover, plants in high temperatures and elevated CO2 had about 15% higher levels of leaf chlorophyll alpha than those in high temperatures and ambient CO2. In high temperatures, plant growth in elevated CO2 was about 87% more than in ambient CO2. Thus, high CO2 reduced the negative effect of high temperature on shoot growth, In moderate temperatures, plant growth in elevated CO2 Was only about 21% more than in ambient CO2. Irrespective of temperature treatments, shoot branch architecture in elevated CO2 was more hierarchical than those in ambient CO2. Specific shoot extension, a topological measure of branch frequency, was not affected by elevated CO2 in moderate temperatures, but was increased by elevated CO2 enrichment in high temperatures-an indication of decreased branch frequency and increased apical dominance, In moderate temperatures, plants in elevated CO2 had fibrous root branch patterns that were less hierarchical than at ambient CO2. The lengths of exterior and interior fibrous roots between branch points and the length of second-degree adventitious lateral branches were increased >50% by high temperatures compared with moderate temperatures, Root length between branch points was not affected by CO2 levels.

796^3^McKee,IF^Farage,PK^Long,SP^1995^1^The interactive effects of elevated co2 and o-3 concentration on photosynthesis in spring wheat^91^45^2^111-119^^^^^Aug^^^^^4403
130^1364^1648^264^344^355^417^444^553^73^Irrespective of temperature treatments, shoot branch architecture in elevated CO2 was more hierarchical than those in ambient CO2. Specific shoot extensA^4402^This study investigated the interacting effects of carbon dioxide and ozone on photosynthetic physiology in the flag leaves of spring wheat (Triticum aestivum L. cv. Wembley), at three stages of development. Plants were exposed throughout their development to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO2] at 350 or 700 mu mol mol(-1), [O-3] at < 5 or 60 nmol mol(-1). Gas exchange analysis, coupled spectrophotometric assay for RuBisCO activity, and SDS-PAGE, were used to examine the relative importance of pollutant effects on i) stomatal conductance, ii) quantum yield, and iii) RuBisCO activity, activation, and concentration. Independently, both elevated [CO2] and elevated [O-3] caused a loss of RuBisCO protein and V-cmax. In combination, elevated [CO2] partially protected against the deleterious effects of ozone. It did this partly by reducing stomatal conductance, and thereby reducing the effective ozone dose. Elevated [O-3] caused stomatal closure largely via its effect on photoassimilation.

797^27^Melillo,JM^Borchers,J^Chaney,J^Fisher,H^Fox,S^Haxeltine,A^Janetos,A^Kicklighter,DW^Kittel,TGF^McGuire,AD^McKeown,R^Neilson,R^Nemani,R^Ojima,DS^Painter,T^Pan,Y^Parton,WJ^Pierce,L^Pitelka,L^Prentice,C^Rizzo,B^Rosenbloom,NA^Running,S^Schimel,DS^Sitch,S^Smith,T^Woodward,I^1995^1^Vegetation ecosystem modeling and analysis project - comparing biogeography and biogeochemistry models in a continental-scale study of terrestrial ecosystem responses to climate-change and co2 doubling^137^9^4^407-437^^^^^Dec^^^^^4405
130^1649^243^529^58^633^660^669^697^700^ductance, ii) quantum yield, and iii) RuBisCO activity, activation, and concentration. Independently, both elevated [CO2] and elevated [O-3] caused a loss of RuBisCO protein and V-cmax. In combination, elevated [CO2] partially protected against the deleterious effects of ozone. It did this partly by reducing stomatal conductance, and thereby reducing the effective ozone dose. Elevated [O-3] caused stomatal closure largely via its effecA^4404^We compare the simulations of three biogeography models (BIOME2, Dynamic Global Phytogeography Model (DOLY), and Mapped Atmosphere-Plant Soil System (MAPSS)) and three biogeochemistry models (BIOME-BGC (BioGeochemistry Cycles), CENTURY, and Terrestrial Ecosystem Model (TEM)) for the conterminous United States under contemporary conditions of atmospheric CO2 and climate. We also compare the simulations of these models under doubled CO2 and a range of climate scenarios. For contemporary conditions, the biogeography models successfully simulate the geographic distribution of major vegetation types and have similar estimates of area for forests (42 to 46% of the conterminous United States), grasslands (17 to 27%), savannas (15 to 25%), and shrublands (14 to 18%). The biogeochemistry models estimate similar continental-scale net primary production (NPP; 3125 to 3772 x 10(12) gC yr(-1)) and total carbon storage (108 to 118 x 10(15) gC) for contemporary conditions. Among the scenarios of doubled CO2 and associated equilibrium climates produced by the three general circulation models (Oregon State University (OSU), Geophysical Fluid Dynamics Laboratory (GFDL), and United Kingdom Meteorological Office (UKMO)), all three biogeography models show both gains and losses of total forest area depending on the scenario (between 38 and 53% of conterminous United States area). The only consistent gains in forest area with all three models (BIOME2, DOLY, and MAPSS) were under the GFDL scenario due to large increases in precipitation. MAPSS lost forest area under UKMO, DOLY under OSU, and BIOME2 under both UKMO and OSU, The variability in forest area estimates occurs because the hydrologic cycles of the biogeography models have different sensitivities to increases in temperature and CO2. However, in general, the biogeography models produced broadly similar results when incorporating both climate change and elevated CO2 concentrations. For these scenarios, the NPP estimated by the biogeochemistry models increases between 2% (BIOME-BGC with UKMO climate) and 35% (TEM with UKMO climate). Changes in total carbon storage range from losses of 33% (BIOME-BGC with UKMO climate) to gains of 16% (TEM with OSU climate). The CENTURY responses of NPP and carbon storage are positive and intermediate to the responses of BIOME-BGC and TEM. The variability in carbon cycle responses occurs because the hydrologic and nitrogen cycles of the biogeochemistry models have different sensitivities to increases in temperature and CO2. When the biogeochemistry models are run with the vegetation distributions of the biogeography models, NPP ranges from no response (BIOME-BGCwith all three biogeography model vegetations for UKMO climate) to increases of 40% (TEM with MAPSS vegetation for OSU climate). The total carbon storage response ranges from a decrease of 39% (BIOME-BGC with MAPSS vegetation for UKMO climate) to an increase of 32% (TEM with MAPSS vegetation for OSU and GFDL climates). The UKMO responses of BIOME-BGC with MAPSS vegetation are primarily caused by decreases in forested area and temperature-induced water stress, The OSU and GFDL responses of TEM with MAPSS vegetations are primarily caused by forest expansion and temperature-enhanced nitrogen cycling.

798^6^Mitchell,RJ^Runion,GB^Prior,SA^Rogers,HH^Amthor,JS^Henning,FP^1995^1^Effects of nitrogen on pinus-palustris foliar respiratory responses to elevated atmospheric co2 concentration^78^46^291^1561-1567^^^^^Oct^^^^^4407
1259^1260^137^1650^240^312^389^595^752^92^re and CO2. When the biogeochemistry models are run with the vegetation distributions of the biogeography models, NPP ranges from no response (BIOME-BGCwith all three biogeography model vegetations for UKMO climate) to increases of 40% (TEM with MAPSS vegetation for OSU climate). The total carbon storage response ranges from a decrease of 39% (BIOME-BGC with MAPSS vegetation for UKMO climate) to an increase of 32% (TEM with MAPSS vegetation for OSU and GFDL climates). The UKMO responses of BIOME-BGC with MAPSS vegetation are primarilyA^4406^Indirect effects of atmospheric CO2 concentration [CO2], on longleaf pine (Pinus palustris Mill.) foliage respiration were studied by growing trees in a factorial arrangement of low and high [CO2] (369 and 729 mu mol CO2 mol(-1)) and low and high N (40 and 400 kg ha(-1) yr(-1)). Direct effects of [CO2] on leaf respiration were tested by measuring respiration rates of foliage from all treatments at two CO2 levels (360 and 720 mu mol CO2 mol(-1)) at the time of measurement. Elevated CO2 did not directly or indirectly affect leaf respiration when expressed on a leaf area or mass basis, but a significant increase in respiration per unit leaf N was observed in trees grown in elevated [CO2] (indirect response to elevated [CO2]). The lack of a [CO2] effect on respiration, when analysed on an area or mass basis, may have resulted from combined effects of [CO2] on factors that increase respiration (e.g. greater availability of non-structural carbohydrates stimulating growth and carbon export from leaves) and on factors that decrease respiration (e.g. lower N concentration leading to lower construction costs and maintenance requirements). Thus, [CO2] affected factors that influence respiration, but in opposing ways.

799^4^Norby,RJ^Wullschleger,SD^Gunderson,CA^Nietch,CT^1995^1^Increased growth efficiency of quercus-alba trees in a co2- enriched atmosphere^84^131^1^91-97^^^^^Sep^^^^^4409
312^349^361^372^374^407^664^O2 levels (360 and 720 mu mol CO2 mol(-1)) at the time of measurement. Elevated CO2 did not directly or indirectly affect leaf respiration when expressed on a leaf area or mass basis, but a significant increase in respiration per unit leaf N was observed in trees grown in elevated [CO2] (indirect response to elevated [CO2]). The lack of a [CO2] effect on respiration, when analysed on an area or mass basis, may have resulted from combined effects of [CO2] on factors that increase respiration (e.g. greater availability of non-structural carbohydrates stimulating growth and carbon export from leaves) and oA^4408^Forests have a prominent role in the global carbon cycle, but their response to a changing atmosphere cannot be measured directly. Experimental observations of small trees in CO2- enriched atmospheres must be interpreted carefully if they are to be relevant to the potential responses of forest trees. We grew white oak (Quercus alba L.) saplings for four complete growing seasons in open-top chambers with different partial pressures of atmospheric CO2. White oak saplings produced 58% more dry mass in 50 Pa CO2 and 135% more in 65 Pa, compared with plants in ambient (35 Pa) CO2. Although this result might suggest a substantial potential for increased carbon storage in forests, the large difference in growth rate could be attributed to a stimulation of growth very early in the experiment. There was not a sustained effect of CO2 on relative growth rate after the first year, and the increased absolute growth rate could persist only so long as leaf area could increase, a condition that would not occur indefinitely in a forest. Nevertheless, annual stem wood production per unit area (growth efficiency) was 37% greater in elevated CO2. This increase in growth efficiency, a response that is consistent across diverse studies, implies a potential increase in carbon sequestration by forests, subject to critical assumptions about forest canopy development in a CO2-enriched atmosphere.

800^5^Parton,WJ^Scurlock,JMO^Ojima,DS^Schimel,DS^Hall,DO^1995^1^Impact of climate-change on grassland production and soil carbon worldwide^127^1^1^13-22^^^^^Feb^^^^^4411
1649^314^454^56^57^979^ent (35 Pa) CO2. Although this result might suggest a substantial potential for increased carbon storage in forests, the large difference in growth rate could be attributed to a stimulation of growth very early in the experiment. There was not a sustained effect of CO2 on relative growth rate after the first year, and the increased absolute growth rate could persist only so long as leaf area could increase, a condition that would not occur indefiA^4410^The impact of climate change and increasing atmospheric CO2 was modelled for 31 temperate and tropical grassland sites, using the CENTURY model. Climate change increased net primary production, except in cold desert steppe regions, and CO2 increased production everywhere. Climate change caused soil carbon to decrease overall, with a loss df 4 Pg from global grasslands after 50 years. Combined climate change and elevated CO2 increased production and reduced global grassland C losses to 2 Pg, with tropical savannas becoming small sinks for soil C. Detection of statistically significant change in plant production would require a 16% change in measured plant production because of high year to year variability in plant production. Most of the predicted changes in plant production are less than 10%.

801^2^Pearson,M^Brooks,GL^1995^1^The influence of elevated co2 on growth and age-related-changes in leaf gas-exchange^78^46^292^1651-1659^^^^^Nov^^^^^4413
1651^243^312^344^360^374^399^528^674^829^ occur indefiA^4412^Rumex obtusifolius plants were grown far several months in daylit environment chambers (Solardomes) force-ventilated with air containing 350 or 600 mu mol mol(-1) CO2. Elevated CO2 was found to accelerate the natural ontogenic decline in photosynthesis, but did not reduce leaf duration, In both CO2 treatments photosynthetic rates declined progressively with increasing leaf age, the decline being greater for plants grown in elevated CO2 such that rates became lower than in ambient CO2. The degree of CO2-induced photosynthetic down-regulation as determined by A/C-I analysis was found to be dependent on leaf age, The major contribution to the decline in photosynthesis was likely to be a reduction in Rubisco activity as changes in stomatal and mesophyll limitations were small. Instantaneous water use efficiency (WUE(i)) was greater for plants in elevated CO2, but these values declined rapidly with leaf age, whereas in ambient CO2 values were always lower, but were maintained for longer. Growth analysis indicated an increased root: shoot ratio for plants grown in elevated CO2, this occurring almost entirely as a result of increased root growth. Greater root proliferation and increased WUE(i) are characteristics which should give this persistent and troublesome weed an increased competitive under projected conditions of climate change.

802^3^Reddy,KR^Hodges,HF^McKinion,JM^1995^1^Carbon-dioxide and temperature effects on pima cotton development^48^87^5^820-826^^^^^Sep-Oct^^^^^4415
372^374^376^417^92^ree of CO2-induced photosynthetic down-regulation as determined by A/C-I analysis was found to be dependent on leaf age, The major contribution to the decline in photosynthesis was likely to be a reduction in Rubisco activity as changes in stomatal and mesophyll limitations were small. Instantaneous water use efficiency (WUE(i)) was greater for plants in elevated CO2, but these values declined rapidly with leaf age, whereas in ambient CO2 values were always lower, but were maintained for longer. Growth analysis inA^4414^Predicting plant responses to changing atmospheric CO2 and to the possible global warming are important concerns. Effects of CO2 on developmental events are poorly documented, as is the interaction of CO2 and other major climate variables on crop development. The objective of this experiment was to determine the effects of an altered CO2 environment and interactions of CO2 and temperature on pima cotton developmental rates. Pima cotton (Gossypium barbadense L. cv. S-6) was grown from seed in sun-lit plant growth chambers. Air temperatures were controlled from 20/12 to 40/32 degrees C (day/night) in 5-degree increments. Daytime CO2 was maintained at 350 or 700 mu L L(- 1). In a second experiment, the temperature was maintained at 30/22 degrees C day/night and the plants were grown in 350, 450, or 700 mu L L(-1) CO2. Days required to develop nodes on the mainstem, days from emergence to first square, number of vegetative and fruiting branches, number of fruiting sites produced, number of bells and squares produced, and number of bells and squares retained by the plants were determined. Rates of mainstem node formation and the time required to produce the first square and first flower were not sensitive to atmospheric CO2, but were very sensitive to temperature. Prefruiting branch nodal positions required longer to develop than nodes with fruiting branches. Carbon dioxide levels did not affect the time required to produce nodes. Number of branches produced was sensitive to both temperature and CO2. The larger number of bells set on the lower branches of plants grown at high CO2 provided a larger sink for photosynthate than plants grown at low CO2. This may be the reason for the observed reduction in number of fruit at the upper nodes of high-CO2-grown plants. More bells and squares were produced and retained on plants grown in high-CO2 environments, except that none were produced in either CO2 environment at 40/32 degrees C. Our results indicate that high-temperature-tolerant cotton cultivars would be more productive in the present-day CO2 world, and they would be essential in the future if global temperature increases.

803^1^Reining,F^1995^1^The effect of elevated co2 concentrations on the competition between lamium-galeobdolon and stellaria-holostea^79^31^4^501-508^^^^^^^^^^4417
312^376^417^505^869^92^957^962^r to develop than nodes with fruiting branches. Carbon dioxide levels did not affect the time required to produce nodes. Number of branches produced was sensitive to both temperature and CO2. The larger number of bells set on the lower branches of plants grown at high CO2 provided a larger sink for photosynthate than plants grown at low CO2. This may be the reason for the observed reduction in number of fruit at the upper nodes of high-CO2-grown plants. More bells and squares were produced and retained on plants grown in high-CO2 environments, except that none were produced in either CO2 environment at 40/32 degrees C. Our results indicate that high-temperature-tolerant cotton cultivars would be more A^4416^The effect of enhanced air CO2 concentrations (c(520) and c(650) = 520 and 650 cm(3) m(-3)) on the growth of Lamium galeobdolon and Stellaria holostea and on the competition between the two species was examined. After five months growth under CO2 enrichment the dry masses of both species increased when the plants were grown in monoculture, but the increase in biomass was much more pronounced in Stellaria. When the plants were grown together in competition, the measured shoot masses of Stellaria were again higher under c(520) and c(650) than at ambient CO2 concentration (c(390) = 390 cm(3) m(-3)), while the shoot masses of lamium strongly decreased at c(650) The effect of CO2 enrichment on the two plant species in monoculture differed significantly from that observed in mixed cultures. In terms of plant relative yield. Stellaria benefitted slightly but insignificantly from competition, while Lamium was significantly suppressed under c(650). Total community production of the mixed culture was optimum at c(520), while that of the monocultures was highest at c(650) At c(390) and c(520), growth of Stellaria depended strongly on irradiance in all types of culture. At c(650) no such dependence could be demonstrated.

804^2^Roth,SK^Lindroth,RL^1995^1^Elevated atmospheric co2 effects on phytochemistry, insect performance and insect parasitoid interactions^127^1^3^173-182^^^^^Jun^^^^^4419
1652^1653^417^57^690^705^829^When the plants were grown together in competition, the measured shoot masses of Stellaria were again higher under c(520) and c(650) than at ambient CO2 concentration (c(390) = 390 cm(3) m(-3)), while the shoot masses of lamium strongly decreased at c(650) The effect of CO2 enrichment on the two plant species in monoculture differed significantly from that observed in mixed cultures. In terms of plant relative yield. Stellaria benefitted slightly but insignificantly from competition, while Lamium was significantly suppressed under c(650). Total community production of the mixed culture was optimum atA^4418^This study was conducted to examine the effects of CO2-mediated changes in tree chemistry on the performance of the gypsy moth (Lymantria dispar L.) and the parasitoid Cotesia melanoscela (Ratz.). We used carbon-nutrient balance theory to develop hypotheses regarding changes in tree chemistry and the performance of both insects under elevated CO2. As predicted, levels of foliar nitrogen declined and concentrations of carbon-based compounds (e.g. starch and phenolics) increased under elevated CO2. Gypsy moth performance (e.g. growth, development) was altered by CO2-mediated changes in foliar chemistry, but the magnitude was small and varied across tree species. Larvae feeding on high CO2 aspen exhibited the largest reduction in performance, relative to larvae feeding on birch, oak, or maple. Parasitism by C. melanoscela significantly prolonged gypsy moth development and reduced growth rates. Overall, the effect of parasitism on gypsy moth performance did not differ between CO2 treatments. Altered gypsy moth performance on high CO2 foliage in turn affected parasitoid performance, but the response was variable: parasitoid mortality increased and adult female size declined slightly under high CO2, while development time and adult male size were unaffected. Our results suggest that CO2-induced changes in plant chemistry were buffered to the extent that effects on third trophic level interactions were weak to non-existent for the system examined in this study.

805^3^Salt,DT^Brooks,GL^Whittaker,JB^1995^1^Elevated carbon-dioxide affects leaf-miner performance and plant-growth in docks (rumex spp)^127^1^2^153-156^^^^^Apr^^^^^4421
1601^174^434^varied across tree species. Larvae feeding on high CO2 aspen exhibited the largest reduction in performance, relative to larvae feeding on birch, oak, or maple. Parasitism by C. melanoscela significantly prolonged gypsy moth development and reduced growth rates. Overall, the effect of parasitism on gypsy moth performance did not differ between CO2 treatments. Altered gypsyA^4420^Exposure of R. crispus and R. obtusifolius to elevated CO2 (600 ppm) resulted in an increased C:N ratio of leaf tissue and greater leaf areas. Larvae of P. nigritarsis mining leaves of X. obtusifolius during exposure produced significantly bigger mines in elevated than in ambient (350 ppm) conditions. There were no significant treatment effects on pupal weight although in both host species mean weight was greater in ambient than in elevated conditions. These results are consistent with the hypothesis that insect herbivores compensate for increased C:N ratios by increased food consumption This response by herbivores may partially offset predicted increases in plant biomass in a future high CO2 environment.

806^1^Schimel,DS^1995^1^Terrestrial ecosystems and the carbon-cycle^127^1^1^77-91^^^^^Feb^^^^^4423
1103^1466^1617^1654^1655^362^372^454^738^975^moth development and reduced growth rates. Overall, the effect of parasitism on gypsy moth performance did not differ between CO2 treatments. Altered gypsyA^4422^The terrestrial biosphere plays an important role in the global carbon cycle. In the 1994 Intergovernmental Panel Assessment on Climate Change (IPCC), an effort was made to improve the quantification of terrestrial exchanges and potential feedbacks from climate, changing CO2, and other factors; this paper presents the key results from that assessment, together with expanded discussion. The carbon cycle is the fluxes of carbon among four main reservoirs: fossil carbon, the atmosphere, the oceans, and the terrestrial biosphere. Emissions of fossil carbon during the 1980s averaged 5.5 Gt y(-1). During the same period, the atmosphere gained 3.2 Gt C y(-1), and the oceans are believed to have absorbed 2.0 Gt C y(-1). The regrowing forests of the Northern Hemisphere may have absorbed 0.5 Gt C y(-1) during this period. Meanwhile, tropical deforestation is thought to have released an average 1.6 Gt C y(-1) over the 1980s. While the fluxes among the four pools should balance, the average 1980s values lead to a 'missing sink' of 1.4 Gt C y(-1). Several processes, including forest regrowth, CO2 fertilization of plant growth (c. 1.0 Gt C y(-1)), N deposition (c. 0.6 Gt C y(-1)), and their interactions, may account for the budget imbalance. However, it remains difficult to quantify the influences of these separate but interactive processes. Uncertainties in the individual numbers are large, and are themselves poorly quantified. This paper presents detail beyond the IPCC assessment on procedures used to approximate the flux uncertainties. Lack of knowledge about positive and negative feedbacks from the biosphere is a major limiting factor to credible simulations of future atmospheric CO2 concentrations. Analyses of the atmospheric gradients of CO2 and (CO2)-C-13 concentrations provide increasingly strong evidence for terrestrial sinks, potentially distributed between Northern Hemisphere and tropical regions, but conclusive detection in direct biomass and soil measurements remains elusive. Current regional-to-global terrestrial ecosystem models with coupled carbon and nitrogen cycles represent the effects of CO2 fertilization differently, but all suggest long-term responses to CO2 that are substantially smaller than potential leaf- or laboratory whole plant-level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO2 concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere. Critical areas for future research are continued measurements and analyses of atmospheric data (CO2 and (CO2)-C-13) to serve as large-scale constraints, process studies of the scaling from the photosynthetic response to CO2 to whole-ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.
ct biomass and soil measurements remains elusive. Current regional-to-global te807^2^Vandasselaar,AV^Lantinga,EA^1995^1^Modeling the carbon-cycle of grassland in the netherlands under various management strategies and environmental-conditions^179^43^2^183-194^^^^^Jun^^^^^4425
130^1656^179^428^429^51^534^57^600^672^plant-level responses. Analyses of emissions and biogeochemical fluxes consistent with eventual stabilization of atmospheric CO2 concentrations are sensitive to the way in which biospheric feedbacks are modeled by c. 15%. Decisions about land use can have effects of 100s of Gt C over the next few centuries, with similarly significant effects on the atmosphere. Critical areas for future research are continued measurements and analyses of atmospheric data (CO2 and (CO2)-C-13) to serve as large-scale constraints, process studies of the scaling from the photosynthetic response to CO2 to whole-ecosystem carbon storage, and rigorous quantification of the effects of changing land use on carbon storage.
ct biomass and soil measurements remains elusive. Current regional-to-global teA^4424^A simulation model of the carbon cycle of grassland (CCGRASS) was developed to evaluate the long-term effects of different management strategies and various environmental conditions on carbon sequestration in the soil. The results presented here refer to permanent grassland on a young sedimentary loam soil in the Netherlands. The model predicted that the rate of increase in the amount of soil organic carbon will be highest at low to moderate application rates of nitrogen (100 - 250 kg N ha(-1) yr(-1)). This is due to the fact that the annual gross photosynthetic uptake of CO2 in permanent grassland is hardly influenced by the level of N supply. Since N shortage stimulates the growth of the unharvested plant parts (roots and stubble) the carbon supply to the soil is highest at low to moderate N application rates. The rate of increase in the amount of soil organic carbon will be higher under grazing than under mowing as a result of a greater amount of carbon added to the soil. Increase of atmospheric CO2 concentration may induce an increase in decomposition rate of soil organic matter due to simultaneously increased temperatures. At the same time: plant productivity and thus carbon supply to the soil will be stimulated due to the CO2-fertilization effect. Under the assumption of a temperature increase of 3 degrees C if the present atmospheric CO2 concentration doubles, the model predicted that the combined effect of elevated CO2 and temperature will slightly reduce the rate of increase in the amount of organic carbon in grassland soils compared to that under unchanged environmental conditions. There was 2% less carbon sequestration by grassland at the end of a period of 100 years as a result of these changes in environmental conditions. The separate effects of increased temperature or elevated CO2 were 10% less and 10% more carbon storage at the end of a period of 100 years, respectively.
nder grazing than under mowing as a result of a greater amount of carbon added to the soil. Increase of atmospheric CO808^4^Vandestaaij,JWM^Huijsmans,R^Ernst,WHO^Rozema,J^1995^1^The effect of elevated uv-b (280-320 nm) radiation-levels on silene vulgaris - a comparison between a highland and a lowland population^35^90^3^357-362^^^^^^^^^^4427
1657^1658^360^374^417^441^673^694^860^92^assumption of a temperature increase of 3 degrees C if the present atmospheric CO2 concentration doubles, the model predicted that the combined effect of elevated CO2 and temperature will slightly reduce the rate of increase in the amount of organic carbon in grassland soils compared to that under unchanged environmental conditions. There was 2% less carbon sequestration by grassland at the end of a period of 100 years as a result of these changes in environmental conditions. The separate effects of increased temperature or elevated CO2 were 10% less and 10% more carbon storage at the end of a period of 100 years, respectively.
nder grazing than under mowing as a result of a greater amount of carbon added to the soil. Increase of atmospheric COA^4426^Highland (altitude 1600 m above sea level) and lowland (altitude -2 m below sea level) populations of the perennial herb Silene vulgaris (Moench) Garcke, were tested on their response to elevated levels of UV-B radiation. Highland populations typically receive high natural UV-B fluxes, whereas lowland populations receive a lower natural UV-B dose. Adaptation to high UV-B levels of the highland population is to be expected. Experimental comparison of growth rates, gas exchange rates, transpiration and biochemical parameters using adult plants as well as seedlings did not show a difference in the response to elevated UV-B levels between the two populations. Individuals of both populations were relatively insensitive to elevated UV-B radiation. The response of alpine and lowland populations of Silene vulgaris is discussed in relation to the dispersal of this species after the last ice age.
r grazing than under mowing as a result of a greater amount of carbon added to the soil. Increase of atmospheric CO809^2^Vogel,CS^Curtis,PS^1995^1^Leaf gas-exchange and nitrogen dynamics of n-2-fixing field- grown alnus-glutinosa under elevated atmospheric co2^127^1^1^55-61^^^^^Feb^^^^^4429
130^1339^137^240^243^312^376^421^441^865^adiation. Highland populations typically receive high natural UV-B fluxes, whereas lowland populations receive a lower natural UV-B dose. Adaptation to high UV-B levels of the highland population is to be expected. Experimental comparison of growth rates, gas exchange rates, transpiration and biochemical parameters using adult plants as well as seedlings did not show a difference in the response to elevated UV-B levels between the two populations. Individuals of both populations were relatively insensitive to elevated UV-B radiation. The response of alpine and lowland populations of Silene vulgaris is discussed in relation to the dispersal of this species after the last ice age.
r grazing than under mowing as a result of a greater amount of carbon added to the soil. Increase of atmospheric COA^4428^Few studies have investigated the effects of elevated CO2 on the physiology of symbiotic N-2-fixing trees. Tree species grown in low N soils at elevated CO2 generally show a decline in photosynthetic capacity over time relative to ambient CO2 controls. This negative adjustment may be due to a reallocation of leaf N away from the photosynthetic apparatus, allowing for more efficient use of limiting N. We investigated the effect of twice ambient CO2 on net CO2 assimilation (A), photosynthetic capacity, leaf dark respiration, and leaf N content of N-2- fixing Alnus glutinosa (black alder) grown in field open top chambers in a low N soil for 160 d. At growth CO2, A was always greater in elevated compared to ambient CO2 plants. Late season A vs. internal leaf p(CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, but unaffected by CO2 on a mass or N basis. In elevated CO2 plants, leaf N content (mu g N cm(- 2)) increased 50% between Julian Date 208 and 264. Leaf N content showed little seasonal change in ambient CO2 plants. A single point acetylene reduction assay of detached, nodulated root segments indicated a 46% increase in specific nitrogenase activity in elevated compared to ambient CO2 plants. Our results suggest that N-2-fixing trees will be able to maintain high A with minimal negative adjustment of photosynthetic capacity following prolonged exposure to elevated CO2 on N-poor soils.

810^3^Woodward,FI^Smith,TM^Emanuel,WR^1995^1^A global land primary productivity and phytogeography model^137^9^4^471-490^^^^^Dec^^^^^4431
137^1659^1660^1661^256^659^665^696^697^714^CO2) response curves indicated no negative adjustment of photosynthesis in elevated CO2 plants. Rather, elevated CO2 plants had 16% greater maximum rate of CO2 fixation by Rubisco. Leaf dark respiration was greater at elevated CO2 on an area basis, A^4430^A global primary productivity and phytogeography model is described. The model represents the biochemical processes of photosynthesis and the dependence of gas exchange on stomatal conductance, which in turn depends on temperature and soil moisture. Canopy conductance controls soil water loss by evapotranspiration. The assignment of nitrogen uptake to leaf layers is proportional to irradiance, and respiration and maximum assimilation rates depend on nitrogen uptake and temperature. Total nitrogen uptake is derived from soil carbon and nitrogen and depends on temperature. The long-term average annual carbon and hydrological budgets dictate canopy leaf area. Although observations constrain soil carbon and nitrogen, the distribution of vegetation types is not specified by an underlying map. Variables simulated by the model are compared to experimental results. These comparisons extend from biochemical processes to the whole canopy, and the comparisons are favorable for both current and elevated CO2 atmospheres. The model is used to simulate the global distributions of leaf area index and annual net primary productivity. These distributions are sufficiently realistic to demonstrate that the model is useful for analyzing vegetation responses to global environmental change.

811^3^Tschaplinski,TJ^Stewart,DB^Norby,RJ^1995^1^Interactions between drought and elevated co2 on osmotic adjustment and solute concentrations of tree seedlings^84^131^2^169-177^^^^^Oct^^^^^4433
1662^1663^1664^376^377^386^664^91^ogen uptake is derived from soil carbon and nitrogen and depends on temperature. The long-term average annual carbon and hydrological budgets dictate canopy leaf area. Although observations constrain soil carbon and nitrogen, the distribution of vegetation types is not specified by an underlying map. Variables simulated by the model are compared to experimental results. These comparisons extend from biochemical processes to the whole canopy, and the comparisons are favorable for both current and elevated CO2 atmosA^4432^Although drought tolerance of tree species is a critical determinant of forest composition, how elevated CO2 affects drought tolerance is uncertain. Interactions between elevated CO2 and drought on osmotic potential and osmotic adjustment of American sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.), and sugar maple (Acer saccharum Marsh.) were investigated using l-yr-old seedlings, planted in 81 pots and grown in four open-top chambers, containing either ambient air or ambient air enriched with 300 mu mol mol(-1) CO2. A well-watered treatment with plants watered daily and a droughted treatment in which plants were subjected to a series of drought cycles were included within each chamber. Sugar maple and sweetgum seedlings completed a total of seven drying cycles, whereas sycamore seedlings, because of their greater leaf area and plant size, completed 11 cycles. The mean soil water potential at re-watering for droughted seedlings in ambient CO2 was -0.5, -0.7, and -1.8 MPa for sugar maple, sweetgum and sycamore, respectively, compared with -0.2, -0.7, and -1.2 MPa, respectively, under elevated CO2. By contrast, all well-watered plants were maintained at soil water potential >-0.1 MPa. Drought under ambient CO2 reduced osmotic potential at saturation for leaves of sycamore and sweetgum by 0.30 MPa and 0.61 MPa, respectively, but leaves of sugar maple did not display osmotic adjustment to drought. Elevated CO2 increased osmotic potential at turgor loss for leaves of sugar maple by 0.33 MPa under well-watered conditions, and 0.48 MPa under drought. This response was not evident in the other species and might be related to the rapid growth of sugar maple causing a depletion of solutes. Whereas drought reduced the total solute concentration in roots of sugar maple, primarily the result of a reduction in K, elevated CO2 did not alter the concentration of total solutes in roots of any of the three species. Elevated CO2 has differing effects on drought tolerance among tree species, and thus might alter the competitive relations between species.

812^5^Baxter,R^Bell,SA^Sparks,TH^Ashenden,TW^Farrar,JF^1995^1^Effects of elevated co2 concentrations on 3 montane grass species .3. Source leaf metabolism and whole-plant carbon partitioning^78^46^289^917-929^^^^^Aug^^^^^4435
1116^1665^310^346^347^360^363^650^721^92^nd 0.61 MPa, respectively, but leaves of sugar maple did not display osmotic adjustment to drought. Elevated CO2 increased osmotic potential at turgor loss for leaves of sugar maple by 0.33 MPa under well-watered conditions, and 0.48 MPa under drought. This response was not evident in the other species and might be related to the rapid growth of sugar maple causing a depletion of solutes. Whereas drought reduced the total solute concentration in roots of sugar maple, primarily the result of a reduction in K, elevated CO2 did not alter the concentration of total solutes in roots of any of the three species. Elevated CO2 has differing effects on drought tolerance among tree species, and tA^4434^Agrostis capillaris L.(5), Festuca vivipara L. and Poa alpina L. were grown in outdoor open-top chambers at either ambient (340 +/- 3 mu mol mol(-1)) or elevated (680 +/- 4 mu mol mol(- 1)) concentrations of atmospheric carbon dioxide (GO,) for periods from 79-189 d. Photosynthetic capacity of source leaves of plants grown at both ambient and elevated CO2 concentrations was measured at saturating light and 5% CO2. Dark respiration of leaves was measured using a liquid phase oxygen electrode with the buffer solution in equilibrium with air (21% O-2, 0.034% CO2). Photosynthetic capacity of P. alpina was reduced by growth at 680 mu mol mol(-1) CO2 by 105 d, and that of F. vivipara was reduced at 65 d and 189 d after CO2 enrichment began, suggesting down-regulation or acclimation. Dark respiration of successive leaf blades of all three species was unaltered by growth at 680 relative to 340 mu mol mol(-1) CO2. In F. vivipara, leaf respiration rate was markedly lower at 189 d than at either 0 d or 65 d, irrespective of growth CO2 concentration. There was a significantly lower total non- structural carbohydrate (TNC) concentration in the leaf blades and leaf sheaths of A. capillaris grown at 680 mu mol mol(-1) CO2. TNC of roots of A. capillaris was unaltered by CO2 treatment. TNC concentration was increased in both leaves and sheaths of P. alpina and F. vivipara after 105 d and 65 d growth, respectively. A 4-fold increase in the water-soluble fraction (fructan) in P. alpina and in all carbohydrate fractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosynthetic capacity and leaf carbohydrate concentration was such that there was a strong positive correlation between photosynthetic capacity and total leaf N concentration (expressed on a per unit structural dry weight basis), and total nitrogen concentration of successive mature leaves reduced with time, Multiple regression of leaf photosynthetic capacity upon leaf nitrogen and carbohydrate concentrations further confirmed that leaf photosynthetic capacity was mainly determined by leaf N concentration. In P. alpina, leaf photosynthetic capacity was mainly determined by leaf CHO concentration. Thus there is evidence for downregulation of photosynthetic capacity in P. alpina resulting from increased carbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positively correlated in P. alpina and F. vivipara. Leaf dark respiration and soluble carbohydrate concentration of source leaves were positively correlated in A. capillaris. Changes in source leaf photosynthetic capacity and carbohydrate concentration of plants grown at ambient or elevated CO, are discussed in relation to plant growth, nutrient relations and availability of sinks for carbon.

813^4^Bazzaz,FA^Jasienski,M^Thomas,SC^Wayne,P^1995^1^Microevolutionary responses in experimental populations of plants to co2-enriched environments - parallel results from 2 model systems^255^92^18^8161-8165^^^^^29 Aug^^^^^44371208^1666^349^361^398^540^57^672^740^975^tic capacity was mainly determined by leaf N concentration. In P. alpina, leaf photosynthetic capacity was mainly determined by leaf CHO concentration. Thus there is evidence for downregulation of photosynthetic capacity in P. alpina resulting from increased carbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positively correlated in P. alpina and F. vivipara. Leaf dark respiration and soluble carbohydrate concentration of source leaves were positively correlated in A. capillaris. Changes in source leaf photosynthetic capacity and carbohydrate concentration of plants grown at ambient or elevated CO, are discussed in relation to plant growth, nutrient relations and availability of sinks for carbon.

813^4^Bazzaz,FA^Jasienski,M^Thomas,SC^Wayne,P^1995^1^Microevolutionary responses in experimental populations of plants to co2-enriched environments - parallel results from 2 model systems^255^92^18^8161-8165^^^^^29 Aug^^^^^4437A^4436^Despite the critical role that terrestrial vegetation plays in the Earth's carbon cycle, very little is known about the potential evolutionary responses of plants to anthropogenically induced increases in concentrations of atmospheric CO2. We present experimental evidence that rising CO2 concentration may have a direct impact on the genetic composition and diversity of plant populations but is unlikely to result in selection favoring genotypes that exhibit increased productivity in a CO2-enriched atmosphere. Experimental populations of an annual plant (Abutilon theophrasti, velvetleaf) and a temperate forest tree (Betula alleghaniensis, yellow birch) displayed responses to increased CO2 that were both strongly density-dependent and genotype-specific. In competitive stands, a higher concentration of CO2 resulted in pronounced shifts in genetic composition, even though overall CO2-induced productivity enhancements were small, For the annual species, quantitative estimates of response to selection under competition were 3 times higher at the elevated CO2 level. However, genotypes that displayed the highest growth responses to CO2 when grown in the absence of competition did not have the highest fitness in competitive stands. We suggest that increased CO2 intensified interplant competition and that selection favored genotypes with a greater ability to compete for resources other than CO2. Thus, while increased CO2 may enhance rates of selection in populations of competing plants, it is unlikely to result in the evolution of increased CO2 responsiveness or to operate as an important feedback in the global carbon cycle, However, the increased intensity of selection and drift driven by rising CO2 levels may have an impact on the genetic diversity in plant populations.

814^2^Boese,SR^Wolfe,DW^1995^1^Elevated-temperatures limit sink development and photosynthetic benefit from elevated co2^8^108^2^26^^^^^Jun
y enhancements were small, For the annual species, quantitative estimates of response to selection under 815^2^Burton,PJ^Cumming,SG^1995^1^Potential effects of climatic-change on some western canadian forests, based on phenological enhancements to a patch model of forest succession^94^82^1-2^401-414^^^^^May^^^^^4440
1167^1263^1667^174^427^633^705^905^ed CO2 intensified interplant competition and that selection favored genotypes with a greater ability to compete for resources other than CO2. Thus, while increased CO2 may enhance rates of selection in populations of competing plants, it is unlikely to result in the evolution of increased CO2 responsiveness or to operate as an important feedback in the global carbon cycle, However, the increased intensity of selection and drift driven by rising CO2 levels may have an impact on the genetic diversity in plant populations.

814^2^Boese,SR^Wolfe,DW^1995^1^Elevated-temperatures limit sink development and photosynthetic benefit from elevated co2^8^108^2^26^^^^^Jun
y enhancements were small, For the annual species, quantitative estimates of response to selection under A^4439^We enhanced the forest patch model, Zelig, to explore the implications of 2xCO(2) climate change scenarios on several forest regions in British Columbia and Alberta, Canada. In addition to the processes and phenomena commonly represented in individual-based models of forest stand dynamics, we added some species-specific phenology and sire-specific frost events. The consideration of bud-break heat sum requirements, growing season limits, and chilling requirements for the induction of dormancy and cold hardiness slightly improved the ability of Zelig to predict the present composition of B.C. forests. Simulations of the predicted effects of future climatic regimes (based on the averaged predictions of four general circulation models) include some major shifts in equilibrial, forest composition and productivity. Lowland temperate coastal forests are predicted to be severely stressed because indigenous species will no longer have their winter chilling requirements met. High-elevation coastal forests are expected to increase in productivity, while interior subalpine forests are expected to remain stable in productivity but will gradually be replaced by species currently characteristic of lower elevations. Dry, interior low-elevation forests in southern B.C. are likely to persist relatively unchanged, while wet interior forests are expected to support dramatic increases in yield, primarily by western hemlock. Northern interior sub-boreal forests are likewise expected to increase in productivity through enhanced growth of lodgepole pine. Conversely, the precipitous collapse of spruce stands in the true boreal forests of northeastern B.C. is expected to be associated with reduced productivity as they are replaced by pine species. Boreal-Cordilleran and Moist Boreal Mixedwood forests in Alberta are less likely to undergo compositional change, while becoming somewhat more productive. We believe these model enhancements to be a significant improvement over existing formulations, but the resulting predictions must still be viewed with caution. Model limitations include: (1) the current inability of climate models to predict future variation in monthly temperature and precipitation; (2) sparse information on the phenological behaviour of several important tree species; and (3) a poor understanding of the degree to which growth is constrained by different suboptimal climatic events.

816^2^Cardon,ZG^Jckson,RB^1995^1^Root acid-phosphatase-activity in bromus-hordeaceus and avena- barbata remains unchanged under elevated [co2]^8^108^2^148^^^^^Jun

817^3^Eamus,D^Berryman,CA^Duff,GA^1995^1^The impact of co2 enrichment on water relations in maranthes- corymbosa and eucalyptus-tetrodonta^182^43^3^273-282^^^^^^^^^^4443
312^344^361^372^386^610^92^984^al-Cordilleran and Moist Boreal Mixedwood forests in Alberta are less likely to undergo compositional change, while becoming somewhat more productive. We believe these model enhancements to be a significant improvement over existing formulations, but the resulting predictions must sA^4442^Seeds of Maranthes corymbosa Blume and Eucalyptus tetrodonta F.Muell were sown under ambient or CO2 enriched conditions (two replicate tents per treatment) in tropical Australia and allowed to grow, rooted in the ground, for 20 months. For both species, periodic measurements of leaf water potential, stomatal conductance and leaf temperature were made on four replicate leaves on each of four replicate trees within each tent. Measurements were made in November (M. corymbosa) and June (E. tetrodonta). At the same time, atmospheric wet and dry bulb temperatures were recorded and hence leaf-to-air vapour presure difference (LAVPD) calculated. Measurements of pre-dawn leaf water potential were also made on E. tetrodonta. Leaves were also taken to the laboratory, rehydrated to full turgor and pressure-volume analyses undertaken. For M. corymbosa, leaf water potential was lower throughout the day for control leaves compared to leaves growing in CO2 enriched air. Similarly, pre dawn leaf water potential was lower for control E. tetrodonta trees than for trees grown with CO2 enrichment. However, mid- morning and mid-afternoon values of leaf water potential for E. tetrodonta were slightly lower for plants growing in CO, enriched air compared to control plants. In both species, stomatal conductance was consistently lower for trees grown in CO2 enriched air than for controls. Whole plant hydraulic conductivity of both species was significantly lower for trees grown in CO2 enriched air than for control trees. For both species, maximum turgor and bulk volumetric elastic modulus increased and osmotic potential at zero turgor decreased for trees grown in CO2 enriched air.

818^2^Fiscus,EL^Reid,CD^1995^1^Pollutant ozone does not affect stomatal limitation to photosynthesis in soybean in ambient or elevated co2^8^108^2^63^^^^^Jun

819^5^Hew,CS^Hin,SE^Yong,JWH^Gouk,SS^Tanaka,M^1995^1^In-vitro co2 enrichment of cam orchid plantlets^174^70^5^721-736^^^^^Sep^^^^^4446
424^781^92^ Similarly, pre dawn leaf water potential was loA^4445^Increased growth of an in vitro-propagated CAM orchid hybrid Mokara 'White' was obtained using a novel method of COP enrichment in an optimized photoautotrophic open system compared with the conventional closed system of culture. The optimization process for the open system involved the manipulation of external CO2 concentrations (0.03%, 1% and 10%), sucrose requirements, light intensities (80 and 200 mu mol m(-2) s(-1)) and the venting of headspace ethylene from the culture vessels. The physiological basis for increased growth in these CAM orchid plantlets after three months was attributed to the direct effects of elevated CO2 resulting in higher CAM activity for the plantlets and to the elevated CO2 present in the system which might interact with the ethylene present thereby reducing the inhibition of growth of plantlets due to ethylene.
k,SS^Tanaka,M^1995^1^In-vitro co2 enrichment of cam orchid plantlets^174^70^5^721-736^^^^^Sep^^^^^4446
424^781^92^ Similarly, pre dawn leaf water potential was lo820^5^Houpis,JLJ^Pushnik,J^Anschel,D^Anderson,P^Demaree,R^1995^1^Intraspecific variability of photosynthetic traits of pinus- ponderosa subjected to long-term exposure to elevated co2^8^108^2^62^^^^^Jun

821^3^Jones,P^Collins,LM^Ingram,KT^1995^1^Open-top chambers for field studies of crop response to elevated co2 and temperature^256^38^4^1195-1201^^^^^Jul-Aug^^^^^4449
1668^174^312^417^73^881^ies (80 and 200 mu mol m(-2) s(-1)) and the venting of headspace ethylene from the culture vessels. The physiological basis for increased growth in these CAM orchid plantlets after three months was attributed to the direct effects of elevated CO2 resulting in higher CAM activity for the plantlets and to the elevated CO2 present in the system which might interact with the ethylene present thereby reducing the inhibition of growth of plantlets due to ethylene.
k,SS^Tanaka,M^1995^1^In-vitro co2 enrichment of cam orchid plantlets^174^70^5^721-736^^^^^Sep^^^^^4446
424^781^92^ Similarly, pre dawn leaf water potential was loA^4448^A new design for Open Top Chambers (OTCs) is described. In addition to providing CO2 controls as do several other existing OTCs, the system is designed to provide elevated temperature control. To provide a more natural vertical microclimate profile, the newly designed system pulls air down through the chamber and out the bottom rather than injecting air at the bottom and venting it out the top of the chamber. A prototype was constructed and performance tests were conducted. Over a 24-h test period with a CO2 concentration setpoint of 660 ppm, individual measurements of concentration taken every 5 min averaged 660.5 ppm with a standard deviation of 26.6 ppm. Temperature controls were rested over 24-h periods for two different setpoints-ambient +4 degrees C and ambient +6 degrees C. For the two test periods the average chamber temperature measurements were 3.98 degrees and 5.99 degrees C above ambient, respectively. Twenty chambers based on the prototype design were constructed and installed at the International Rice Research Institute, Los Banos, Philippines. As intended, the chambers are currently being used to conduct research on rice crop response to elevated CO2 and temperature.

822^4^King,AW^Emanuel,WR^Wullschleger,SD^Post,WM^1995^1^In search of the missing carbon sink - a model of terrestrial biospheric response to land-use change and atmospheric co2^257^47^4^501-519^^^^^Sep^^^^^4451
1637^209^417^454^661^672^862^905^ was constructed and performance tests were conducted. Over a 24-h test period with a CO2 concentration setpoint of 660 ppm, individual measurements of concentration taken every 5 min averaged 660.5 ppm with a standard deviation of 26.6 ppm. Temperature controls were rested over 24-h periods for two different setpoints-ambient +4 degrees C and ambient +6 degrees C. For the two test periods the average chamber temperature measurements were 3.98 degrees and 5.99 degrees C above ambient, respectively. Twenty chambers based on the prototype design were constructed and installed at the InteA^4450^Estimates of the net exchange of carbon between the terrestrial biosphere and the atmosphere may be too large because the models of carbon release from changes in land use do not allow for enhanced carbon assimilation by the terrestrial biosphere in response to increasing atmospheric CO2. We address this deficiency with a model of terrestrial biosphere that includes both ecosystem response to land-use perturbation and vegetation response to atmospheric CO2. Model inputs specify the areas affected by land-use change since 1700. The carbon dynamics of the affected areas are described by an area distribution function for vegetation carbon density and a compartment model of carbon in vegetation, litter, and soil. Vegetation growth is modeled as the difference between net primary production (NPP) and mortality. NPP, the net flux of carbon from atmosphere to vegetation, is a logistic function of vegetation carbon density. The response of NPP to atmospheric CO2 is modeled with three response functions: a logarithmic, a rectangular- hyperbolic, and a response function derived from a biochemical model of C-3 photosynthesis. The response functions are parameterized by ecosystem type with data from CO2 exposure experiments. Elevated CO2 affects the NPP of both undisturbed and recovering ecosystems. We use the model to test the hypothesis that the CO2 enhancement of terrestrial NPP explains the historical missing carbon sink of the the global carbon cycle budget. Our estimates of the biosphere's CO2 enhanced carbon flux are much smaller than the reconstructed missing carbon sink. We conclude that our model results do not support the hypothesis.

823^4^Manderscheid,R^Bender,J^Jager,HJ^Weigel,HJ^1995^1^Effects of season long co2 enrichment on cereals .2. Nutrient concentrations and grain quality^169^54^3^175-185^^^^^Jul^^^^^4453
204^341^344^372^374^422^436^683^724^92^ vegetation, is a logistic function of vegetation carbon density. The response of NPP to atmospheric CO2 is modeled with three response functions: a logA^4452^Two cultivars each of spring wheat (Triticum aestivum L., cv. Star and cv. Turbo) and spring barley (Hordeum vulgare L., cv. Alexis and cv. Arena) were exposed season-long to ambient (384 p.p.m.) and above ambient CO2 concentrations (551, 718 p.p.m.) in open-top chambers. Plant samples were taken at the booting stage and at maturity. Concentrations (grams per gram dry weight) of macro (Ca, K, Mg, N, P, S) and micronutrients (Fe, Mn, Zn) were measured in stems, leaves, ears and grains, and the amino acid composition of the grain protein was determined. For most nutrients studied the sequence and size of the response of the four cereal plants to the CO, enrichment was cv. Arena < cv. Alexis < cv. Turbo < cv. Star. The CO2 enrichment usually produced a decrease in nutrient concentrations, which was already detectable at the booting stage and was further enhanced until plant maturity. Nutrient concentrations of straw were more affected than those of grains. The decrease in concentration was greatest for N followed by Mg, Ca and K, and the maximum decrease as compared with ambient CO2 amounted to 43%, 35%, 33% and 21% for straw, and 30%, 13%, 28% and - 6% for grains. Concentrations of micronutrients were also found to be partially decreased by about 10-30%. At 718 p.p.m. CO, grain protein concentrations were 96% (cv. Arena), 85% (cv. Alexis), 72% (cv. Turbo) and 70% (cv. Star) of the ambient CO2 value, however, the index of essential amino acids was increased. Overall, the CO2 enrichment did not decrease the nutrient harvest index of all nutrients except of sulphur. Nutrient use efficiency increased by high CO2 levels for cv. Star and cv. Turbo and decreased for cv. Arena.

824^2^McElwain,JC^Chaloner,WG^1995^1^Stomatal density and index of fossil plants track atmospheric carbon-dioxide in the paleozoic^52^76^4^389-395^^^^^Oct^^^^^4455
349^ge and was further enhanced until plant maturity. Nutrient concentrations of straw were more affected than those of grains. The decrease in concentration was greatest for NA^4454^It has been demonstrated that the leaves of a range of forest tree species have responded to the rising concentration of atmospheric CO2 over the last 200 years by a decrease in both stomatal density and stomatal index. This response has also been demonstrated experimentally by growing plants under elevated CO2 concentrations. Investigation of Quaternary fossil leaves has shown a corresponding stomatal response to changing CO2 concentrations through a glacial-interglacial cycle, as revealed by ice core data. Tertiary leaves show a similar pattern of stomatal density change, using palynological evidence of palaeo-temperature as a proxy measure of CO2 concentration. The present work extends this approach into the Palaeozoic fossil plant record. The stomatal density and index of Early Devonian, Carboniferous and Early Permian plants has been investigated, to test for any relationship that they may show with the changes in atmospheric CO2 concentration, derived from physical evidence, over that period. Observed changes in the stomatal data give support to the suggestion from physical evidence, that atmospheric CO2 concentrations fell from an Early Devonian high of 10-12 times its present value, to one comparable to that of the present day by the end of the Carboniferous. These results suggest that stomatal density of fossil leaves has potential value for assessing changes in atmospheric CO2 concentration through geological time. (C) 1995 Annals of Botany Company

825^4^Newbery,RM^Wolfenden,J^Mansfield,TA^Harrison,AF^1995^1^Nitrogen, phosphorus and potassium uptake and demand in agrostis-capillaris - the influence of elevated co2 and nutrient supply^84^130^4^565-574^^^^^Aug^^^^^4457
243^312^376^417^423^436^437^439^787^92^aeozoic fossil plant record. The stomatal density and index of Early Devonian, Carboniferous and Early Permian plants has been investigated, to test for any relationship that they may show with the changes in atmospheric CO2 concentration, derived from physical evidence, over that period. ObA^4456^Responses to elevated CO2 have been studied using Agrostis capillaris L., an upland grass which is abundant on nutrient- poor soils. Plants were grown in sand culture with a wide range of nitrogen, phosphorus and potassium concentrations, and the impact of CO2 on the demand for nutrients was determined using isotopic root bioassays. Plants grown with the smallest concentrations of N and P showed typical foliar symptoms associated with deficiency of these elements. However, even when supplies of N and P were limiting to growth, additional CO2 (250 ppm above ambient) influenced neither total N nor total P in above-ground tissues, nor nutrient demands as indicated by the bioassay. The estimates of the demand of the plants for K from the Rb-86 bioassay indicated an appreciable increase when plants were raised in elevated CO2. For plants of the same size with the same nutrient supply, those grown in elevated CO2 consistently displayed an increased internal demand for K. Uptake of K was not, however, enhanced by elevated CO2 even in non-limiting conditions and it might therefore be limited by a factor other than K supply. The overall conclusion from the experiments is that when A. capillaris is grown in elevated CO2, uptake of N, P and K fails to increase proportionally with dry mass. This was true even when nutrient supplies were adequate, and it appears that nutrient-use-efficiency might increase to enable the plants to maintain growth in elevated CO2.

826^4^Nie,GY^Hendrix,DL^Long,SP^Webber,AN^1995^1^The effect of elevated co2 concentration throughout the growth of a wheat crop in the field on the expression of photosynthetic genes in relation to carbohydrate accumulation^8^108^2^92^^^^^Jun

827^2^Nowak,EJ^Martin,CE^1995^1^Effect of elevated co2 on nocturnal malate accumulation in the cam species tillandsia-ionantha and crassula-arborescens^79^31^3^441-444^^^^^^^^^^4460
1669^1670^1671^417^92^rown in elevated CO2 consistently displayed an increased internal demand for K. Uptake of K was not, however, enhancA^4459^The effect of elevated CO2 on overnight malate accumulation in the CAM epiphyte Tillandsia ionantha and the CAM terrestrial species Crassula arborescens was compared. Both species showed an increase in nocturnal accumulation of malate with increasing CO2 concentrations. This study is the first to show an increase in nighttime malate accumulation with increasing levels of CO2 at near-ambient concentrations in a CAM plant. The results indicate that some CAM plants can respond to increasing levels of CO2 in the atmosphere, potentially leading to an increase in productivity.

828^4^Pennanen,AH^Vu,JCV^Allen,LH^Bowes,G^1995^1^Elevated co2 and temperature effects on enzymes of sucrose and starch synthesis in soybean^8^108^2^90^^^^^Jun

829^4^Penuelas,J^Biel,C^Save,R^Estiarte,M^1995^1^Detrimental effects of fluctuating high co2 concentrations on peppers^79^31^3^361-370^^^^^^^^^^4463
1628^1672^1673^312^374^376^417^434^618^632^y displayed an increased internal demand for K. Uptake of K was not, however, enhancA^4462^Plants of pepper (Capsicum annuum L.) were grown in controlled environment chambers at ambient (360 mu mol mol(-1)) and fluctuating pulse-enriched CO2 concentrations (700 mu mol mol(- 1) daily average, ranging from 500 to 3500 mu mol mol(-1) = ECO(2)) under two water regimes. A decrease in plant growth and yield together with frequent visual injuries was found in plants growing under ECO(2). Root/shoot ratio was greater, chlorophyll concentration and respiration rates were lower, and stomatal conductance and relative importance of alternative pathway respiration were higher under ECO(2). The negative effects of ECO(2) were more intense under high water availability. The symptoms produced by ECO(2) were similar to those of resource limitation, and were alleviated with increased nutrient supply. Constant elevated CO2 concentrations (700 mu mol mol(-1)) increased pepper production and did not produce any of the injuries described for this erratic ECO(2) treatment. Thus, it is probably the erratic nature of the CO2 concentration and not the gas itself that was causing the injury.

830^4^Perezsoba,M^Dueck,TA^Puppi,G^Kuiper,PJC^1995^1^Interactions of elevated co2, nh3 and o-3 on mycorrhizal infection, gas-exchange and n-metabolism in saplings of scots pine^206^176^1^107-116^^^^^Sep^^^^^4465
1674^1675^360^361^374^377^386^447^586^92^th frequent visual injuries was found in plants growing under ECO(2). Root/shoot ratio was greater, chlorophyll concentration and respiration rates were lower, and stomatal conductance and relative importance of alternative pathway respiration were higher under ECO(2). The negative effects of ECO(2) were more intense under high water availability. The symptoms produced by ECO(2) were similar to those of resource limitation, and were alleviated with increased nutrient supply. Constant elevated CO2 concentrations (700 mu mol mol(-1)) increased pepper production and did not produce any of the injuries described for this erratic ECO(2) treatment. Thus, it is probably the erratic nature A^4464^Four-year-old saplings of Scots pine (Pinus sylvestris L.) were exposed for 11 weeks in controlled-environment chambers to charcoal-filtered air, or to charcoal-filtered air supplemented with NH3 (40 mu g m(-3)), O-3 (110 mu g m(-3) during day/ 40 mu g m(-3) during night) or NH3 + O-3. All treatments were carried out at ambient (350 mu L L(-1)) and at elevated CO2 concentration (700 mu L L(-1)). Total tree biomass, mycorrhizal infection, net CO2 assimilation (P-n), stomatal conductance (g(s)), transpiration of the shoots and NH3 metabolization of the needles were measured. In ambient CO2 (1) gaseous NH3 decreased mycorrhizal infection, without significantly affecting tree biomass or N concentration and it enhanced the activity of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in one-year-old needles; (2) ozone decreased mycorrhizal infection and the activity of GS in the needles, while it increased the activity of GDH; (3) exposure to NH3 + O-3 lessened the effects of single exposures to NH3 and O-3 on reduction of mycorrhizal infection and on increase in GDH activity. Similar lessing effects on mycorrhizal infection as observed in trees exposed to NH3 + O-3 at ambient CO2, were measured in trees exposed to NH3 + O-3 at elevated CO2. Exposure to elevated CO2 without pollutants did not significantly affect any of the parameters studied, except for a decrease in the concentration of soluble proteins in the needles. Elevated CO2 + NH3 strongly decreased root branching and mycorrhizal infection and temporarily stimulated P-n and g(s). The exposure to elevated CO2 + NH3 + O-3 also transiently stimulated P-n. The possible mechanisms underlying and integrating these effects are discussed. Elevated CO2 clearly did not alleviate the negative effects of NH3 and O-3 on mycorrhizal infection. The significant reduction of mycorrhizal infection after exposure to NH3 or O-3, observed before significant changes in gas exchange or growth occurred, suggest the use of mycorrhizal infection as an early indicator for NH3 and O-3 induced stress.

831^2^Piastuch,WC^Stryjewski,EC^1995^1^Arabidopsis-thaliana growth, morphology and ultrastructure at elevated and super-elevated co2 concentrations^8^108^2^62^^^^^Jun

832^3^Rao,MV^Hale,BA^Ormrod,DP^1995^1^Amelioration of ozone-induced oxidative damage in wheat plants grown under high-carbon dioxide - role of antioxidant enzymes^8^109^2^421-432^^^^^Oct^^^^^4468
1102^1347^1676^1677^372^376^446^461^504^509^O2 + NH3 strongly decreased root branching and mycorrhizal infection and temporarily stimulated P-n and g(s). The exposure to elevated CO2 + NH3 + O-3 also transiently stimulated P-n. The possible mechanisms underlying and integrating these effects are discussed. Elevated CO2 clearly did not alleviate the negative effects of NH3 and O-3 on mycorrhizal infection. The significant reduction of mycorrhizal infection after exposure to NH3 or O-3, observed before significant changes in gas exchange or growth occurred, suggest the use of mycorrhizal infection as an early indicatoA^4467^O-3-induced changes in growth, oxidative damage to protein, and specific activities of certain antioxidant enzymes were investigated in wheat plants (Triticum aestivum L. cv Roblin) grown under ambient or high CO2. High CO2 enhanced shoot biomass of wheat plants, whereas O-3 exposure decreased shoot biomass. The shoot biomass was relatively unaffected in plants grown under a combination of high CO2 and O-3. O-3 exposure under ambient CO2 decreased photosynthetic pigments, soluble proteins, and ribulose-1,5-bisphosphate carboxylase/oxygenase protein and enhanced oxidative damage to proteins, but these effects were not observed in plants exposed to O-3 under high CO2. O-3 exposure initially enhanced the specific activities of superoxide dismutase, peroxidase, glutathione reductase, and ascorbate peroxidase irrespective of growth in ambient or high CO2. However, the specific activities decreased in plants with prolonged exposure to O-3 under ambient CO2 but not in plants exposed to O-3 under high CO2. Native gels revealed preferential changes in the isoform composition of superoxide dismutase, peroxidases, and ascorbate peroxidase of plants grown under a combination of high CO2 and O-3. Furthermore, growth under high CO2 and O-3 led to the synthesis of one new isoform of glutathione reductase. This could explain why plants grown under a combination of high CO2 and O-3 are capable of resisting O-3-induced damage to growth and proteins compared to plants exposed to O-3 under ambient CO2.

833^3^Reuveni,J^Mayer,AM^Gale,J^1995^1^High ambient carbon-dioxide does not affect respiration by suppressing the alternative, cyanide-resistant pathway^52^76^3^291-295^^^^^Sep^^^^^4470
130^1678^240^348^372^376^389^441^756^92^ecific activities of superoxide dismutase, peroxidase, glutathione reductase, and ascorbate peroxidase irrespective of growth in ambient or high CO2. However, the specific activities decreased in plants with prolonged exposure to O-3 under ambient CO2 but not in plants exposed to O-3 under high CO2. NaA^4469^Total dark respiration (v(t)), cytochrome pathway (v(eyt)), alternative pathway (v(alt)) and residual (v(res)) respiration were measured in Lemna gibba plants, by the use of pathway inhibitors. NaCN was used to inhibit v(eyt) and SHAM (salicylhydroxamic acid) to inhibit v(alt). Residual respiration (v(res)) was about 5% of v(t). The effect of high (100 Pa) and low (0 Pa) carbon dioxide partial pressure ([CO2) on v(t), v(cyt) and v(alt) was determined from both CO2 efflux and O(2)uptake measurements. The higher [CO2] suppressed v(t) by about 30%. When respiration operated through the cytochrome pathway only. in the absence of v(alt), it was suppressed by about 12% as measured by the O-2 uptake of submerged Lemna fronds or by about 40% as measured by CO2 efflux from Boating fronds. The higher [CO2] treatment had only a small effect oil respiration, when v(alt) alone operated. There was no evidence of a specific suppression of the v(alt) pathway by high [CO2]. Succinic dehydrogenase activity of the mitochondria of roots of Medicago sativum was reduced by 18%, when the mitochondria were pre-treated with 120 as compared to 34 Pa [CO2]. There was no such effect on cytochrome c oxidase activity of mitochondria under the same conditions. It is concluded that there is no evidence for the hypothesis that the high [CO2] suppression of respiration is a result of a CO2 effect on the non- phosphorylating alternative respiration pathway. (C) 1995 Annals of Botany Company

834^3^Ross,DJ^Tate,KR^Newton,PCD^1995^1^Elevated co2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an endoaquept soil^206^176^1^37-49^^^^^Sep^^^^^4472
1016^1679^1680^1681^1682^344^362^466^56^600^ submerged Lemna fronds or by about 40% as measured by CO2 efflux from Boating fronds. The higher [CO2] treatment had only a small effect oil respiration, when v(alt) alone operated. There was no evidence of a specific suppression of the v(alt) pathway by high [CO2]. Succinic dehydrogenase activity of the mitocA^4471^Effects of elevated CO2 (700 mu L L(-1)) and a control (350 mu L L(-1) CO2) on the productivity of a 3-year-old rye- grass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 mu L L(-1) CO2 and a temperature 6 degrees C higher throughout than in the other treatments, was included. Under the same temperature conditions, overall herbage yields in the '700 mu L L(-1) CO2' treatment were ca. 7% greater than in the control at the end of the 'summer' period. Root mass (to ca 25 cm depth) in the '700 mu L L(-1) CO2' treatment was then about 50% greater than in the control, but in the '700 mu L L(- 1) CO2 + 6 degrees C' treatment it was 6% lower than in the control. Based on decomposition results, herbage from the '700 mu L L(-1) + 6 degrees C' treatment probably contained the highest proportion of readily decomposable components. Elevated CO2 had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials. Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long- term experiments are required to determine the overall effect of elevated CO2 on the soil C balance.

835^6^Saurer,M^Maurer,S^Matyssek,R^Landolt,W^Gunthardtgoerg,MS^Siegenthaler,U^1995^1^The influence of ozone and nutrition on delta-C-13 in betula- pendula^2^103^4^397-406^^^^^Sep^^^^^4474
1683^174^383^384^417^444^539^729^912^92^rature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials. Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long- term experiments are required to determine the overall effect of elevated CO2 on the soil CA^4473^In the cellulose of stems and leaves, delta(13)C was investigated in a birch clone (Betula pendula), which was exposed throughout the growing season to either <3 (control) or 90/40 nl O-3 1(-1) (day/night). Each regime was split into plants under high or low nutrient supply. delta(13)C was increased (becoming less negative), in stems rather than leaves, by both high nutrition (+2 parts per thousand) and O-3 stress (+1 parts per thousand). Whereas high nutrition raised the water-use efficiency (WUE) while lowering the CO2 concentration in the inner leaf air space (c(i)), WUE decreased and c(i) increased under O-3 stress. Therefore, only the nutritional effect on the carbon isotope fractionation was reproduced by the model of Farquhar et al. (1982) which estimates WUE by means of delta(13)C based on C-i, C-i was not biased by 'patchiness' in respect to stomatal opening. The latter was verified by microscopical analysis and the complete water infiltration of the birch leaves through the stomata, independent of the diurnal course of the leaf conductance for water vapour. Under low nutrient supply, the activity of phosphoenol pyruvate carboxylase (PEPC) was roughly doubled by ozone to about 1.3% of the total carboxylation capacity (by PEPC + rubisco), and was increased to 1.7% under high nutrition. The fractionation model, extended to account for varying activities of the carboxylating enzymes, indicated that stimulated PEPC was the cause of elevated delta(13)C, although c(i) was increased under O-3 stress. The stimulation of PEPC and, as a consequence, elevated delta(13)C are discussed as part of a whole-plant acclimation to O-3 stress.

836^4^Schenk,U^Manderscheid,R^Hugen,J^Weigel,HJ^1995^1^Effects of co2 enrichment and intraspecific competition on biomass partitioning, nitrogen-content and microbial biomass carbon in soil of perennial ryegrass and white clover^78^46^289^987-993^^^^^Aug^^^^^4476
1290^130^1684^243^310^385^547^733^792^92^te water infiltration of the birch leaves through the stomata, independA^4475^Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina) grown at five different plant densities were exposed to ambient (390 ppm) and elevated (690 ppm) CO2 concentrations, After 43 d the effects of CO2 enrichment and plant density on growth of shoot and root, nitrogen concentration of tissue, and microbial biomass carbon (C-mic) in soil were determined, CO2 enrichment of Lolium perenne increased shoot growth on average by 17% independent of plant density, while effects on root biomass ranged between -4% and +107% due to an interaction with plant density, Since tiller number per plant was unaffected by elevated CO2, the small response of shoot growth to CO2 enrichment was attributed to low sink strength. A significant correlation between nitrogen concentration of total plant biomass and root fraction of total plant dry matter, which was not changed by CO2 enrichment, indicates that nitrogen status of the plant controls biomass partitioning and the effect of CO2 enrichment on root growth. Effects of elevated CO2( )and plant density on shoot and root growth of Trifolium repens were not significantly interacting and mean CO2 related increase amounted to 29% and 66%, respectively, However, growth enhancement due to elevated CO2 was strongest when leaf area index was lowest. Total amounts of nitrogen in shoots and roots were bigger at 690 ppm than at 390 ppm CO2. There was a significant increase in C-mic in experiments with both species whereas plant density had no substantial effect.

837^1^Sicher,R^1995^1^Diurnal amylolytic activity in soybean leaves grown at ambient and elevated co2^8^108^2^55^^^^^Jun

838^2^Stryiewski,EC^Vieglais,DA^1995^1^Changes in leaf structure of 3 native florida plant-species grown in elevated co2 concentrations^8^108^2^63^^^^^Jun

839^2^Tomlinson,PT^Anderson,PD^1995^1^Elevated co2 compensates for water-stress in red oak^8^108^2^36^^^^^Jun
chment, indicates that nitrogen status of the plant controls biomass partitioning and 840^3^Torbert,HA^Prior,SA^Rogers,HH^1995^1^Elevated atmospheric carbon-dioxide effects on cotton plant residue decomposition^110^59^5^1321-1328^^^^^Sep-Oct^^^^^4481
349^57^mean CO2 related increase amounted to 29% and 66%, respectively, However, growth enhancement due to elevated CO2 was strongest when leaf area index was lowest. Total amounts of nitrogen in shoots and roots were bigger at 690 ppm than at 390 ppm CO2. There was a significant increase in C-mic in experiments with both species whereas plant density had no substantial effect.

837^1^Sicher,R^1995^1^Diurnal amylolytic activity in soybean leaves grown at ambient and elevated co2^8^108^2^55^^^^^Jun

838^2^Stryiewski,EC^Vieglais,DA^1995^1^Changes in leaf structure of 3 native florida plant-species grown in elevated co2 concentrations^8^108^2^63^^^^^Jun

839^2^Tomlinson,PT^Anderson,PD^1995^1^Elevated co2 compensates for water-stress in red oak^8^108^2^36^^^^^Jun
chment, indicates that nitrogen status of the plant controls biomass partitioning and A^4480^Assessing the impact of elevated atmospheric CO2 concentration on the global environment is hampered due to a lack of understanding of global C cycling. Carbon fixed within plant biomass ultimately enters the soil via plant residues, but the effects of elevated-CO2-grown plant material on decomposition rates and long-term soil C storage are unknown. The objective of this study was to determine the decomposition rate of plant residues grown under an elevated CO2 environment as affected by soil type. Cotton (Gossypium hirsuturn L. 'Delta Pine 77') samples were collected from a free-air CO2 enrichment (550 mu L L(-1)) experiment. The plant residues were incubated under ambient CO2 conditions to determine decomposition rates of leaves, stems, and roots and potential N and P mineralization- immobilization in three soil series: a Blanton loamy sand (loamy siliceous, thermic Grossarenic Paleudult), a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult), and a Houston clay loam (very fine, montmorillonitic Typic Chromudert). No significant difference was observed between plant residue grown under CO2 enrichment vs. ambient CO2 conditions for soil respiration or P mineralization- immobilization. Significantly greater net N immobilization was observed during the incubation in all soil types for plant residue grown at elevated CO2. These results indicate that while decomposition of plant residue may not be reduced by CO2 enrichment, N dynamics may be markedly changed.

841^2^Townend,J^Dickinson,AL^1995^1^A comparison of rooting environments in containers of different sizes^206^175^1^139-146^^^^^Aug^^^^^4483
1685^312^361^372^546^685^811^92^999^ues were incubated under ambient CO2 conditions to determine decomposition rates of leaves, stems, and roots and potential N and P mineralization- immobilization in three soil series: a Blanton loamy sand (loamy siliceous, thermic Grossarenic Paleudult), a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudult), and a Houston clay loam (very fine, montmorA^4482^Experiments on plants are often carried out in growth chambers or greenhouses which necessitate the use of an artificial rooting environment, though this is seldom characterized in detail. Measurements were made to compare the rooting environment in large boxes (0.25 m(3)) with that in small pots (0.19, 0.55 and 1.90 dm(3)) in naturally lit chambers. Diurnal temperature fluctuations of 14.6, 11.6 and 7.7 degrees C occurred in the pots compared with only 1.9 degrees C in the boxes. Soil drying to a matric potential of -50 kPa was approximately 25 times faster in the pots. The mean heights of 2 year old Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings grown throughout their second growing season in the three sizes of pots were 38, 62 and 92% of the mean height of those grown in the boxes. Soil solution nutrient concentrations in the boxes were considerably increased by soil drying, an aspect which seems to have received little attention in experiments involving artificially imposed drought. An alternative system of constraining the roots of individual plants within nylon fabric bags, embedded in larger volumes of soil, to facilitate harvesting of complete root systems is described. The importance of the rooting environment in determining the outcome of physiological experiments is also briefly discussed.

842^6^Vose,JM^Elliott,KJ^Johnson,DW^Walker,RF^Johnson,MG^Tingey,DT^1995^1^Effects of elevated co2 and n fertilization on soil respiration from ponderosa pine (pinus-ponderosa) in open-top chambers^155^25^8^1243-1251^^^^^Aug^^^^^4485
130^1686^1687^1688^1689^524^672^711^782^946^heights of 2 year old Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings grown throughout their second growing season in the three sizes of pots were 38, 62 and 92% of the mean height of those grown in the boxes. Soil solution nutrient concentrations in the boxes were considerably increased by soil drying, an aspect which seems to have received little attention in experiments involving artificially imposed drought. An alA^4484^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 determine regulating mechanisms. Elevated CO2 treatments were applied in open-top chambers containing 3-year- old ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings. Nitrogen 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 sulfate). Soils were irrigated to maintain soil moisture at >25%. Soil CO2 evolution was measured over diurnal periods (20-22 h) in April, June, and October 1993 using a flow-through, infrared gas analyzer measurement system. To examine regulating mechanisms, we linked our results with other studies measuring root biomass with destructive sampling and root studies using minirhizotron techniques. Significantly higher soil CO2 evolution was observed in the elevated CO2 treatments in April and October; N effects were not significant. In October, integrated daily values for CO2 evolution ranged from 3.73 to 15.68 g CO2 . m(- 2)day(-1) for the ambient CO2 + 0 N and 525 mu L . L(-1) CO2 + 20 g . m(-2) N, respectively. Soil CO2 flux among treatments was correlated with coarse root biomass (r(2) = 0.40; p >F = 0.0380), indicating that at least some of the variation observed among treatments was related to variation in root respiration. Across ail sample periods and treatments, there was a significant correlation (r(2) = 0.63; p >F = 0.0001) between soil CO2 evolution acid percent fungal hyphae observed in minirhizotron tubes. Hence, some of the seasonal and treatment variation was also related to differences in heterotrophic activity.

843^2^Ziska,LH^Bunce,JA^1995^1^Growth and photosynthetic response of 3 soybean cultivars to simultaneous increases in growth temperature and co2^37^94^4^575-584^^^^^Aug^^^^^4487
1097^245^344^348^376^687^evA^4486^Three soybean (Glycine max L. Merr.) cultivars (Maple Glen, Clark and CNS) were exposed to three CO2 concentrations (370, 555 and 740 mu mol mol(-1)) and three growth temperatures (20/15 degrees, 25/20 degrees and 31/26 degrees C, day/night) to determine intraspecific differences in single leaf/whole plant photosynthesis, growth and partitioning, phenology and final biomass. Based on known carboxylation kinetics, a synergistic effect between temperature and CO2 on growth and photosynthesis was predicted since elevated CO2 increases photosynthesis by reducing photorespiration and photorespiration increases with temperature. Increasing CO2 concentrations resulted in a stimulation of single leaf photosynthesis for 40-60 days after emergence (DAE) at 20/15 degrees C in all cultivars and for Maple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO2 concentrations. Despite the season-long stimulation of single leaf photosynthesis, elevated CO2 concentrations did not increase whole plant photosynthesis except at the highest growth temperature in Maple Glen and CNS, and there was no synergistic effect on final biomass. Instead, the stimulatory effect of CO2 on growth was delayed by higher temperatures. Data from this experiment suggest that: (1) intraspecific variation could be used to select for optimum soybean cultivars with future climate change; and (2) the relationship between temperature and CO2 concentration may be expressed differently at the leaf and whole plant levels and may not solely reflect known changes in carboxylation kinetics.

844^3^Ziska,LH^Weerakoon,W^Hong,LW^1995^1^Photosynthetic acclimation of field-grown rice to elevated co2^8^108^2^92^^^^^Jun
aple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO2 concentrations. Despite the845^7^Clifford,SC^Black,CR^Roberts,JA^Stronach,IM^Singletonjones,PR^Mohamed,AD^Azamali,SN^1995^1^The effect of elevated atmospheric co2 and drought on stomatal frequency in groundnut (arachis-hypogaea (L))^78^46^288^847-852^^^^^Jul^^^^^4490
1208^374^376^634^stimulatory effect of CO2 on growth was delayed by higher temperatures. Data from this experiment suggest that: (1) intraspecific variation could be used to select for optimum soybean cultivars with future climate change; and (2) the relationship between temperature and CO2 concentration may be expressed differently at the leaf and whole plant levels and may not solely reflect known changes in carboxylation kinetics.

844^3^Ziska,LH^Weerakoon,W^Hong,LW^1995^1^Photosynthetic acclimation of field-grown rice to elevated co2^8^108^2^92^^^^^Jun
aple Glen and CNS at all temperatures. For Clark, however, the onset of flowering at warmer temperatures coincided with the loss of stimulation in single leaf photosynthesis at elevated CO2 concentrations. Despite theA^4489^The effects of elevated atmospheric CO2, alone or in combination with water stress, on stomatal frequency in groundnut (Arachis hypogaea (L.) cv. Kadiri-3) were investigated. CO2 exerted significant effects on stomatal frequency only in irrigated plants. The effects of drought on leaf development outweighed the smaller effects of CO2 concentration, although reductions in stomatal frequency induced by elevated atmospheric CO2 were still observed. When stands of groundnut were grown under irrigated conditions with unrestricted root systems, an increase in atmospheric CO2 from 375 to 700 ppmv decreased stomatal frequency on both leaf surfaces by up to 16%; in droughted plants, stomatal frequency was reduced by 8% on the adaxial leaf surface only, Elevated atmospheric CO2 promoted larger reductions in leaf conductance than the changes in stomatal frequency, indicating partial stomatal closure. As a result, the groundnut stands grown at elevated CO2 utilized the available soil moisture more slowly than those grown under ambient CO2, thereby extending the growing period. Despite the large variations in cell frequencies induced by drought, there was no treatment effect on either stomatal index or the adaxial/abaxial stomatal frequency ratio. The data suggest that the effects of future increases in atmospheric CO2 concentration on stomatal frequency in groundnut are likely to be small, especially under conditions of water stress, but that the combination of associated reductions in leaf conductance and enhanced assimilation at elevated CO2 will be important in semi-arid regions.

846^3^Eamus,D^Duff,GA^Berryman,CA^1995^1^Photosynthetic responses to temperature, light flux-density, co2 concentration and vapor-pressure deficit in eucalyptus tetrodonta crown under co2 enrichment^35^90^1^41-49^^^^^^^^^^4492
1690^1691^256^312^360^361^372^528^550^92^ stomatal frequency, indicating partial stomatal closure. As a result, the groundnut stands grown at elevated CO2 utilized the available soil moisture more slowly than thoA^4491^Seeds of Eucalyptus tetrodonta were sown under ambient or CO2 enriched (700 mu l litre(-1)) conditions in tropical Australia. Four sets of measurements were made, the first two after 12 months, on trees growing either in pots or planted in the ground. The third and fourth set were made after 18 and 30 months exposure to CO2 enrichment, on trees growing in the ground After 12 months exposure to CO2 enrichment, the rate of light-saturated assimilation (A(max)) of plants growing in the ground was determined. Responses of CO2 assimilation to variations in leaf temperature, leaf-to-air vapour,pressure deficit (LAVPD), Eight flux density and CO2 concentration were also measured in the laboratory using plants growing in large pots. There was no significant difference in A(max) between pot and ground located plants. Assimilation of E. tetrodonta was relatively insensitive to changes in LAVPD for both ambient and CO2 enriched plants but the temperature optimum of assimilation was increased in plants grown and measured under CO2 enrichment. Plants grown with CO2 enrichment had an increased rate of light-saturated assimilation and apparent quantum yield I-vas significantly inn eased by CO2 enrichment. rn contrast, carboxylation efficiency was decreased significantly by CO2 enrichment. After 18 months growth with CO2 enrichment, there was no sign of a decline in assimilation I ate compared to measurements undertaken after 12 months, At low LAVPD values, assimilation rate was not influenced by CO2 treatment but at moderate to high LAVPD, plants grown under CO2 enrichment exhibited a larger assimilation rate than control plants. Specific leaf area and chlorophyll contents decreased in response to CO2 enrichment, whilst foliar soluble protein contents and chlorophyll a/b ratios were unaffected by CO2 treatment. Changes in soluble protein and chlorophyll contents in response to CO2 enrichment did not account for changes in assimilation between treatments. After 30 months exposure to CO2 enrichment, the rate of light-saturated assimilation was approximately 50% larger than controls and this enhancement was larger than that observed after 18 months exposure to CO2 enrichment.

847^2^Fredeen,AL^Field,CB^1995^1^Contrasting leaf and ecosystem co2 and h2o exchange in avena- fatua monoculture - growth at ambient and elevated co2^91^43^3^263-271^^^^^Mar^^^^^4494
243^29^312^344^374^399^417^787^e compared to measurements undertaken after 12 months, At low LAVPD values, assimilation rate was not influenced by CO2 treatment but at moderate to high LAVPD, plants grown under CO2 enrichment exhibited a larger assimilation rate than control plants. Specific leaf area and chlorophyll contents decreased in response to CO2 enrichment, whilst foliar soluble protein contents and chlorophyll a/b ratios were unaffected by CO2 treatment. Changes in soluble protein and chlorophyll contents in response to CO2 enrichment did not account for changes in assimilation between treatments. After 30 months exposure to CO2 enrichment, the rate of light-satA^4493^Elevated CO2 (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by similar to 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO2 uptake (A) per unit of leaf area and a 65% increase in average A at the 'ecosystem' level per unit of ground area. Elevated CO2 also increased 'ecosystem' A per unit of biomass. However, the products of total leaf area and light- saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO2 treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is similar to 10-fold greater than the 'ecosystem' rate. 'Ecosystem' respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from -20 (at day 19) to -18 (at day 40) mu mol m(-2) s(-1) for both elevated and ambient CO2 Avena. 'Ecosystem' below-ground respiration at the time of seedling emergence was similar to -10 mu mol m(-2) s(- 1), while that occuring after shoot removal at the termination of the experiment ranged from -5 to -6 mu mol m(-2) s(-1). Hence, no significant differences between elevated and ambient CO2 treatments were found in any respiration measure on a ground area basis, though 'ecosystem' respiration on a shoot biomass basis was clearly reduced by elevated CO2. Significant differences existed between leaf and 'ecosystem' water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while 'ecosystem' rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO2, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, 'ecosystem' evapotranspiration (ET) was significantly decreased by elevated CO2 on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the 'ecosystem' level) were increased by elevated CO2. Increases were due to both increased A at leaf and 'ecosystem' level and decreased leaf E and 'ecosystem' ET.

848^7^Grant,RF^Kimball,BA^Pinter,PJ^Wall,GW^Garcia,RL^Lamorte,RL^Hunsaker,DJ^1995^1^Carbon-dioxide effects on crop energy-balance - testing ecosys with a free-air co2 enrichment (face) experiment^48^87^3^446-457^^^^^May-Jun^^^^^4496
1692^1693^1694^230^256^399^614^642^687^977^riment, possibly in response to leaf aging, while 'ecosystem' rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO2, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, 'ecosystem' evapotranspiration (ET) was significantly decreased by elevated CO2 on 5 out of 8 measA^4495^Elevated CO2 concentrations (C-e) have been observed to decrease short-term plant water use under controlled conditions by increasing stomatal resistance. The extent to which this decrease occurs over a growing season in the held is uncertain, however, because stomatal resistance is only one of many mechanisms that control water use. In this study, we tested the ecosystem simulation model ecosys, which reproduces an hourly energy balance through soil-vegetation systems under defined atmospheric boundary renditions, using energy exchange data measured as part of the Free-Air CO2 Enrichment (FACE) experiment at C-e = 550 vs. 370 mu mol mol(-1). The model reproduced reductions in measured upward latent heat fluxes that varied from -10 to +40 W m(-2), depending on atmospheric conditions. In the model, the primary effect of elevated C-e on latent heat fluxes was through canopy stomatal conductance. This effect was largely offset by secondary effects through canopy temperature that enabled the model to reproduce measured changes in sensible heat fluxes. The total effect simulated by ecosys of C-e = 550 vs. 370 mu mol mol(-1) on evapotranspiration during the entire PACE experiment was a reduction of 7%. This reduction compares with one of 11% estimated from accumulated daily measurements of latent heat flux. In the model, the different effects of C-e on plant water use depend on atmosphere and soil boundary conditions, and are highly dynamic. Consequently the simulated C-e-water use relationship is likely to be site-specific. The use of models such as ecosys allows site-specific boundary conditions to be considered in the study of C-e effects on plant growth and water use.

849^4^Groninger,JW^Seiler,JR^Zedaker,SM^Berrang,PC^1995^1^Effects of elevated co2, water-stress, and nitrogen level on competitive interactions of simulated loblolly-pine and sweetgum stands^155^25^7^1077-1083^^^^^Jul^^^^^4498
1144^264^312^345^374^376^417^836^92^ by secondary effects through canopy temperature that enabled the model to reprA^4497^Loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) were grown in mixed stands and in monocultures at 2.54 X 2.54 cm spacing in controlled-environment chambers. Treatments consisted of present (ambient) and projected future (ambient + 400 ppm) carbon dioxide (CO2) concentrations, drought-stressed, and well-watered conditions, and low (20 kg N/ha) and high (474 kg N/ha) nitrogen application rates. After two accelerated growing cycles, total biomass of both species was significantly greater under elevated CO2. No significant interactions between CO2 concentration and water availability, nitrogen availability, or stand type were observed. Competitive interactions between loblolly pine and sweetgum were strongly influenced by water availability, but not CO2 concentration. Assessment of species response to CO2 was dependent upon growth in monoculture or mixture. Under low water availability, data from monocultures suggested that sweetgum had a stronger growth response to elevated CO2 concentrations than loblolly pine. In contrast, results from mixed-species stands showed that the competitive status of loblolly pine and sweetgum did not change under the high CO2 concentration. These results underscore the value of growing co-occurring species in mixed stands under varying levels of multiple resources for the determination of relative performance under future environments.

850^6^Hadley,P^Batts,GR^Ellis,RH^Morison,JIL^Pearson,S^Wheeler,TR^1995^1^Temperature-gradient chambers for research on global environment change .2. a twin-wall tunnel system for low- stature, field-grown crops using a split heat-pump^9^18^9^1055-1063^^^^^Sep^^^^^4500
174^d. Competitive interactions between loblolly pine and sweetgum were strongly influenced by water availability, but not CO2 concentration. Assessment of species response to CO2 was dependent upon growth in monoculture or mixture. Under low water availability, data from monocultures suggested that sweetgum had a stronger growth response to elevated CO2 cA^4499^A temperature gradient chamber (TGC) is described which enables elevated CO2 concentrations and a dynamic temperature gradient to be imposed on field crops throughout their life cycle under standard husbandry. Air is circulated through two double-walled polyethylene-covered tunnels connected to a split heat pump system to give a near-linear temperature gradient along each tunnel, Solar energy gain along each tunnel and exchange with outer tunnel air flow contribute to the temperature gradient and also produce diurnal and seasonal temperature fluctuations corresponding to ambient conditions, Mean temperature gradients of between 3 and 5 degrees C have been recorded throughout the growing seasons of crops of lettuce, carrot, cauliflower and winter wheat, Elevated or present CO2 concentrations are maintained in each of two pairs of tunnels throughout the cropping season using pure CO2 injected through motorized needle valves. This system can realistically simulate aspects of the effects of projected future environmental change on crop growth, development and yield, and in particular the possible interaction of the effects of increased CO2 and temperature.

851^5^Horie,T^Nakagawa,H^Nakano,J^Hamotani,K^Kim,HY^1995^1^Temperature-gradient chambers for research on global environment change .3. a system designed for rice in kyoto, japan^9^18^9^1064-1069^^^^^Sep^^^^^4502
312^374^each tunnel, Solar energy gain along each tunnel and exchange with outer tunnel air flow contribute to the temperature gradient and also produce diurnal and seasonal temperature fluctuations corresponding to ambient conditions, Mean temperature gradients of between 3 and 5 degrees C have been recorded throughout the growing seasons of crops of lettuce, carrot, cauliflower and winter wheat, Elevated or present CO2 concentrations are maintained in each of two pairs of tunnels throughout the cropping season using pure CO2 injected through motorized needle valves. This system can realistically simulate aspects of the effects of projected futuA^4501^Synthesis and validation of crop models for assessment of of the impact of elevated atmospheric CO2 concentration and anticipated global warming on crop production require crop response data obtained under field-like conditions, The temperature gradient chamber (TGC) with the facility for CO2 enrichment allows the creation of various CO2 and temperature regimes for crops over the entire growth period with relatively inexpensive construction and running costs, The TGC develops a temperature gradient along its longitudinal axis using solar energy during the day and heating at night while maintaining the natural diurnal cycle, The temperature gradient and the CO2 concentration in the TGC are regulated by computer control of the air ventilation rate through the TGC and of the CO2 release rate, Longitudinal gradients of CO2 concentration and water vapour pressure deficit of air in the TGC were generally less than 5% and +/-0.2 kPa, respectively. A CO2 enrichment experiment on rice in the TGC showed that a doubling of the CO2 concentration markedly enhanced crop dry matter production, Temperature had less effect on dry matter production, although panicle dry weight was greatly decreased at higher temperature as a result of high-temperature-induced sterility of rice spikelets, Since rice spikelets are most sensitive to high temperature at the moment of flowering, and their flowering habit is highly synchronized with the diurnal courses of environmental conditions, the TGC is a useful tool in understanding rice responses to changes in atmosphere and temperature.

852^2^Humphries,SW^Long,SP^1995^1^Wimovac - a software package for modeling the dynamics of plant leaf and canopy photosynthesis^258^11^4^361-371^^^^^Aug^^^^^4504
245^312^372^374^434^ilation rate through the TGC and of the CO2 release rate, Longitudinal gradients of CO2 concentration and water vapour pressure deficit of air in the TGC were generally less than 5% and +/-0.2 kPa, respectively. A CO2 enrichment experiment on rice in the TGC showed that a A^4503^The ability to predict net carbon exchange and production of vegetation in response to predicted atmospheric and climate change is critical to assessing the potential impacts of these changes. Mathematical models provide an important tool in the study of whole plant, canopy and ecosystem responses to global environmental change. Because this requires prediction beyond experience, mechanistic rather than empirical models are needed. The uniformity and strong understanding of the photosynthetic process, which is the primary point of response of plant production to global atmospheric change, provides a basis for such an approach. Existing modelling systems have been developed primarily for expert modellers and have not been easily accessible to experimentalists, managers and students. Here we describe a modular modelling system operating within Winnows to provide this access. WIMOVAC (Windows Intuitive Model of Vegetation response to Atmosphere and Climate Change) is designed to facilitate the modelling of various aspects of plant photosynthesis with particular emphasis on the effects of global climate change. WIMOVAC has been designed to run on IBM PC-compatible computers running Microsoft Windows. The package allows the sophisticated control of the simulation processes for photosynthesis through a standardized Windows user interface and provides automatically formatted results as either tabulated data or as a range of customizable graphs. WIMOVAC has been written in Microsoft Visual Basic, to facilitate the rapid development of user-friendly modules within the familiar Windows framework, while allowing a structured development. The highly interactive nature of controls adopted by WIMOVAC makes it suitable for research, management and educational purposes.

853^3^Jacob,J^Greitner,C^Drake,BG^1995^1^Acclimation of photosynthesis in relation to rubisco and nonstructural carbohydrate contents and in-situ carboxylase activity in scirpus-olneyi grown at elevated co2 in the field^9^18^8^875-884^^^^^Aug^^^^^4506 245^348^356^363^374^376^417^430^451^735^s with particular emphasis on the effects of global climate change. WIMOVAC has been designed to run on IBM PC-compatible computers running Microsoft Windows. The package allows the sophisticated control of the simulation processes for photosynthesis through a standardized Windows user interface and provides automatically formatted results as either tabulated data or as a range of customizable graphs. WIMOVAC has been written in Microsoft Visual Basic, to facilitate the rapid development of user-friendly modules within the familiar Windows framework, while allowing a structured development. The highly interactive nature of controls adopted by WIMOVAC makes it suitable for research, management and educational purposes.

853^3^Jacob,J^Greitner,C^Drake,BG^1995^1^Acclimation of photosynthesis in relation to rubisco and nonstructural carbohydrate contents and in-situ carboxylase activity in scirpus-olneyi grown at elevated co2 in the field^9^18^8^875-884^^^^^Aug^^^^^4506 A^4505^Stands of Scirpus olneyi, a native saltmarsh sedge with C-3 photosynthesis, had been exposed to normal ambient and elevated atmospheric CO2 concentrations (C-a) in their native habitat since 1987, The objective of this investigation was to characterize the acclimation of photosynthesis of Scirpus olneyi stems, the photosynthesizing organs of this species, to long-term elevated C-a treatment in relation to the concentrations of Rubisco and non-structural carbohydrates, Measurements were made on intact stems in the field under existing natural conditions and in the laboratory under controlled conditions on stems excised in the field early in the morning, Plants grown at elevated C-a had a significantly higher (30-59%) net CO2 assimilation rate (A) than those grown at ambient C-a when measurements were performed on excised stems at the respective growth C-a. However, when measurements were made at normal ambient C-a, A was smaller (45-53%) in plants grown at elevated C-a than in those grown at ambient C- a. The reductions in A at normal ambient C-a, carboxylation efficiency and in situ carboxylase activity were caused by a decreased Rubisco concentration (30-58%) in plants grown at elevated C-a; these plants also contained less soluble protein (39-52%). The Rubisco content was 43 to 58% of soluble protein, and this relationship was not significantly altered by the growth CO2 concentrations. The Rubisco activation state increased slightly, but the in situ carboxylase activity decreased substantially in plants grown at elevated C-a. When measurements were made on intact stems in the field, the elevated C-a treatment caused a greater stimulation of A (100%) and a smaller reduction in carboxylation efficiency (which was not statistically significant) than when measurements were made on excised stems in the laboratory. The possible reasons for this are discussed. Plants grown at elevated C-a contained more non-structural carbohydrates (25-53%) than those grown at ambient C-a. Plants grown at elevated C-a appear to have sufficient sink capacity to utilize the additional carbohydrates formed during photosynthesis. Overall, our results are in agreement with the hypothesis that elevated C-a leads to an increased carbohydrate concentration and the ensuing acclimation of the photosynthetic apparatus in C-3 plants results in a reduction in the protein complement, especially Rubisco, which reduces the photosynthetic capacity in plants grown at elevated C-a, relative to plants grown at normal ambient C-a. Nevertheless, when compared at their respective growth C-a, Scirpus olneyi plants grown at elevated C-a in their native habitat maintained a substantially higher rate of photosynthesis than those grown at normal ambient C-a even after 8 years of growth at elevated C-a.

854^3^Jifon,JL^Friend,AL^Berrang,PC^1995^1^Species mixture and soil-resource availability affect the root- growth response of tree seedlings to elevated atmospheric co21^155^25^5^824-832^^^^^May^^^^^4508
1144^1342^1695^312^345^376^417^540^672^711^a appear A^4507^The effects of CO2 enrichment on root proliferation of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) seedlings were studied under varied water and nitrogen (N) regimes and in competitive interaction. Seedlings of each species were grown from seed as monocultures or as 50:50 pine- sweetgum mixtures in 22-L pots filled with forest soil. Seedlings were exposed to either ambient (400 ppm) or CO2- enriched (ambient plus 400 ppm) air for 32 weeks in continuously stirred tank reactors. Detailed sampling of very fine roots (<0.5 mm diam.) showed a general increase (up to 2- fold) in root length density (RLD, cm . cm(-3)) with elevated CO2; however, the effects of CO2 on RLD differed according to species, culture type, water, and N availability. In monoculture, low water with low N conditions produced the largest RLD responses to elevated CO2: 75% increase for sweetgum and 31% increase for pine. In mixed culture, by contrast, the largest RLD responses to CO2 were observed under high water, high N regimes: pine showed a 110% increase and sweetgum a 96% increase. The total RLD of the standing crop in mixture under elevated CO2, high water, and high N was 2.6 cm . cm(-3) compared with 1.6 cm . cm(-3) in ambient CO2, with sweetgum accounting for >75% of the total RLD in both cases. These findings suggest that resource-rich rather than resource- poor soil environments could be the circumstances under which belowground interference from sweetgum would intensify in pine- sweetgum mixtures with rising atmospheric CO2.

855^1^Loehle,C^1995^1^Anomalous responses of plants to co2 enrichment^15^73^2^181-187^^^^^Jun^^^^^4510
1304^1315^1696^1697^229^341^344^372^803^92^ effects of CO2 on RLD differed according to species, culture type, water, and N availability. In monoculture, low water with low N conditions produced the largest RLD responses to elevated CO2: 75% increase for sweetgum and 31% increase for pine. In mixed culture, by contrast, the largest RLD responses to CO2 were observed under high A^4509^A number of unexplained responses of plants to CO2 enrichment have been observed. These anomalies can be explained on the basis of growth analysis of whole plants. Some plants may fail to respond to enrichment because they are long-lived and have conservative growth responses or come from impoverished habitats. Apparent (but not real) acclimation to CO2 enrichment might be observed if only part of the growth curve over the life of a perennial is studied. The apparent increased efficiency of nitrogen use may merely be an increase in storage of nonstructural carbohydrate. A model analysis of these effects is presented. Discrepancies among species in relative responses of different plant parts are argued to be largely a function of where the plant typically stores nonstructural carbohydrates, which itself is a function of plant growth stage. Thus, a closer consideration of plant growth strategies and growth partitioning is needed to properly interpret results of CO2 enrichment studies.
erved under high 856^3^Marek,MV^Kalina,J^Matouskova,M^1995^1^Response of photosynthetic carbon assimilation of norway spruce exposed to long-term elevation of co2 concentration^79^31^2^209-220^^^^^^^^^^4512
1290^130^344^356^360^376^384^441^451^92^re long-lived and have conservative growth responses or come from impoverished habitats. Apparent (but not real) acclimation to CO2 enrichment might be observed if only part of the growth curve over the life of a perennial is studied. The apparent increased efficiency of nitrogen use may merely be an increase in storage of nonstructural carbohydrate. A model analysis of these effects is presented. Discrepancies among species in relative responses of different plant parts are argued to be largely a function of where the plant typically stores nonstructural carbohydrates, which itself is a function of plant growth stage. Thus, a closer consideration of plant growth strategies and growth partitioning is needed to properly interpret results of CO2 enrichment studies.
erved under high A^4511^Young (12 years old) Norway spruce (Picea abies [L.] Karst.) trees were exposed to ambient CO2 or ambient + 350 mu mol(CO2) mol(-1) continuously over 2 growing seasons in open-top chambers, under field conditions of a mountain stand. Comprehesive analysis of CO2 assimilation was performed after 4 and 22 weeks of the second growing season to evaluate the influence of elevated atmospheric CO2. A combination of gas exchange and a mathematical mo del of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity was used. After 4 weeks of exposure no statistically significant stimulation of the radiant energy and CO2 saturated rate of CO2 uptake (P-Nsat) by the elevated CO2 concentration was found. Yet after 24 weeks a statistically significant depression of P-Nsat (38 %) and carboxylation efficiency (32 %) was observed. Depression of photosynthetic activity by elevated CO2 resulted from a decrease in the RuBPCO carboxylation rate. The electron transport rate was also modified similarly to the rate of RuBP formation. An accompanying decrease in nitrogen content of the needles (by 12 %) together with an increase in total saccharides (by 34 %) was observed after 24 weeks of exposure to enhanced CO2.

857^6^Mitchell,RAC^Lawlor,DW^Mitchell,VJ^Gibbard,CL^White,EM^Porter,JR^1995^1^Effects of elevated co2 concentration and increased temperature on winter-wheat - test of arcwheat1 simulation-model^9^18^7^736-748^^^^^Jul^^^^^4514
1584^1698^243^273^434^435^720^92^951^-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity was used. After 4 weeks of exposure no statistically significant stimulation of the radiant energy and CO2 saturated rate of CO2 uptake (P-Nsat) by the elevated CO2 concentration was found. Yet after 24 weeks a statistically significant depression of P-Nsat (38 %) and carboxylation efficiency (32 %) was observed. Depression of photosynthetic activity by elevated CO2 resulted from a decrease in the RuBPCO carboxylation rate. The electron transport rate was also modified similarly to the rate A^4513^Winter wheat (Triticum aestivum L., cv, Mercia) was grown in a controlled-environment facility at two CO2 concentrations (targets 350 and 700 mu mol mol(-1)), and two temperature regimes (tracking ambient and ambient + 4 degrees C), Observations of phenology, canopy growth, dry matter production and grain yield were used to test the ARCWHEAT1 simulation model, Dry-matter production and grain yield were increased at elevated CO2 concentration (27 and 39%, respectively) and reduced at increased temperature (-16 and -35%, respectively), ARCWHEAT1 substantially underestimated canopy growth for all treatments, However, differences in the facility environment from field conditions over the winter, indicated by the unusually rapid canopy growth observed in this period, meant that empirical model relationships were being used outside the conditions for which they were developed, The ARCWHEAT1 productivity submodel, given observed green area indices as inputs, overestimated the effect of CO2 on productivity, An alternative, more mechanistic submodel of productivity, based on the SUCROS87 and Farquhar and von Caemmerer models, simulated observed crop biomass very closely, When these productivity simulations were inputed into the ARCWHEAT1 partitioning and grain-fill submodels, grain yield was predicted poorly, mainly as a result of the assumption that the number of grains is proportional to total growth during a short preanthesis phase, While yield was not correlated with growth in this phase, it was correlated with growth in longer preanthesis phases, indicating that ARCWHEAT1 could be improved by taking into account the contribution of earlier growth in determining yield.

858^1^Mortensen,LM^1995^1^Diurnal carbon-dioxide exchange-rates of greenhouse roses under artificial-light as compared with daylight conditions in summer^200^45^2^148-152^^^^^Jun^^^^^4516
349^92^ were developed, The ARCWHEAT1 productivity submodel, given observed green area indices as inputs, overestimated the effect of CO2 on productivity, AA^4515^Carbon dioxide exchange rates (CER) of greenhouse roses (cut flowers) were measured under daylight conditions in a greenhouse in July, and under artificial light only (300 mu mol m(-2) s(-1) PPFD in 18 h day(-1)) at two CO2 concentrations (350 and 700 mu mol mol(-1)). The daily CER varied considerably from day to day owing to the large variation in solar radiation. Light saturation of CER seemed not to be reached even on clear days, and a light dose (PAP = number of photosynthetic active photons) produced by variable light over one week in summer gave the same total CER as a similar PAP produced by a constant PPFD. CER at constant PPFD increased rapidly during the first two hours of the photoperiod, followed by a slight increase during the subsequent hours, before CER slightly decreased towards the end of the photoperiod. Raising the CO2 concentration significantly increased CER during the entire photoperiod, and by 32% as a mean for the whole photoperiod. Elevated CO2 decreased the night respiration of the plants by 30%. As a total of the light and dark period, CO2 enrichment increased CER by 38%.

859^5^Nie,GY^Hendrix,DL^Webber,AN^Kimball,BA^Long,SP^1995^1^Increased accumulation of carbohydrates and decreased photosynthetic gene transcript levels in wheat grown at an elevated co2 concentration in the field^8^108^3^975-983^^^^^Jul^^^^^4518
1699^1700^312^343^348^360^363^448^632^845^n of CER seemed not to be reached even on clear days, and a light dose (PAP = number of photosynthetic active photons) produced by variable light over one week in summer gave the same total CER as a similar PAP produced by a constant PPFD. CER at constant PPFD increased rapidly during the first two hours of the photoperiod, followed by a slight increase during the subsequent hours, before CER slightly decreased towards the end of the photoperiod. Raising the CO2 concentration significantly increased CER during the entire photoperiod, and by 32% as a mean for the whole photoperiod. Elevated CO2 decreased the night respiration A^4517^Repression of photosynthetic genes by increased soluble carbohydrate concentrations may explain acclimation of photosynthesis to elevated CO2 concentration. This hypothesis was examined in a field crop of spring wheat (Triticum aestivum L.) grown at both ambient (approximately 360 mu mol mol(-1)) and elevated (550 mu mol mol(-1)) atmospheric CO2 concentrations using free-air CO2 enrichment at Maricopa, Arizona. The correspondence of steady-state levels of mRNA transcripts (coding for the 83-kD photosystem I apoprotein, sedoheptulose-1,7-bisphosphatase, phosphoribulokinase, phosphoglycerokinase, and the large and small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase) with leaf carbohydrate concentrations (glucose-6-phosphate, glucose, fructose, sucrose, fructans, and starch) was examined at different stages of crop and leaf development and through the diurnal cycle. Overall only a weak correspondence between increased soluble carbohydrate concentrations and decreased levels for nuclear gene transcripts was found. The difference in soluble carbohydrate concentration between leaves grown at elevated and current ambient CO2 concentrations diminished with crop development, whereas the difference in transcript levels increased. In the flag leaf, soluble carbohydrate concentrations declined markedly with the onset of grain filling; yet transcript levels also declined. The results suggest that, whereas the hypothesis may hold well in model laboratory systems, many other factors modified its significance in this field wheat crop.

860^8^Nie,GY^Long,SP^Garcia,RL^Kimball,BA^Lamorte,RL^Pinter,PJ^Wall,GW^Webber,AN^1995^1^Effects of free-air co2 enrichment on the development of the photosynthetic apparatus in wheat, as indicated by changes in leaf proteins^9^18^8^855-864^^^^^Aug^^^^^4520
348^360^363^372^374^430^448^607^914^92^rop and leaf development and through the diurnal cycle. Overall only a weak correspondence between increased soluble carbohydrate concentrations and decreased levels for nuclear geneA^4519^A spring wheat crop was grown at ambient and elevated (550 mu mol mol(-1)) CO2 concentrations under free-air CO2 enrichment (FACE) in the field, Four experimental blocks, each comprising 21-m-diameter FACE and control experimental areas, were used, CO2 elevation was maintained day and night from crop emergence to final grain harvest, This experiment provided a unique opportunity to examine the hypothesis that CO2 elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and to assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age, Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS-PAGE, For leaves at completion of emergence of the blade, growth at the elevated CO2 concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined, Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3-4 further leaves formed above with continued development of the crop, By 35 d following completion of blade emergence, leaf 5 was in shade, At this point, the chlorophyll alb ratio had declined by 26% both in plants grown at the control CO2 concentration and in those grown at the elevated CO2 concentration, which is indicative of shade acclimation. The ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO2 concentration, The light- harvesting complex of photosystem II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag-leaf blade, the elevated-CO2 treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d, From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated- CO2 treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%, At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2 concentration treatment relative to the control, By 52 d, all of these proteins showed a significant decline relative to the control, This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated-CO2 treatment, but that this was preceded by a CO2-concentration-dependent decline in Rubisco.
ct of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag-leaf blade, the elevated-CO2 treatment inhibited the further accumulat861^3^Pearson,M^Davies,WJ^Mansfield,TA^1995^1^Asymmetric responses of adaxial and abaxial stomata to elevated co2 - impacts on the control of gas-exchange by leaves^9^18^8^837-843^^^^^Aug^^^^^4522
1167^243^360^465^618^92^ment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%, At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2 concentration treatment relative to the control, By 52 d, all of these proteins showed a significant decline relative to the control, This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated-CO2 treatment, but that this was preceded by a CO2-concentration-dependent decline in Rubisco.
ct of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag-leaf blade, the elevated-CO2 treatment inhibited the further accumulatA^4521^The response of adaxial and abaxial stomatal conductance in Ruiner obtusifolius to growth at elevated atmospheric concentrations of CO2 (250 mu mol mol(-1) above ambient) was investigated over two growing seasons, The conductance of both the adaxial and abaxial leaf surfaces was found to be reduced by elevated concentrations of CO2. Elevated CO2 caused a much greater reduction in conductance for the adaxial surface than for the abaxial surface, The absence of effects upon stomatal density indicated that the reductions were probably the result of changes in stomatal aperture, Partitioning of gas exchange between the leaf surfaces revealed that increased concentrations of CO2 caused increased rates of photosynthesis only via the abaxial surface, Additionally, leaf thickness was found to increase during growth at elevated concentrations of CO2. The tendency for these amphistomatous leaves to develop a distribution of conductance approaching that of hypostomatous leaves clearly reduced their maximum photosynthetic potential. This conclusion was supported by measurements of stomatal limitation, which showed greater values for the adaxial surfaces, and greater values at elevated CO2. This reduction in photosynthesis may in part be caused by higher diffusive limitations imposed because of increased leaf thickness, in an uncoupled canopy, asymmetrical stomatal responses of the kind identified here may appreciably reduce transpiration, Species which show symmetrical responses are less likely to show reduced transpirational rates, and a redistribution of water loss between species may occur. The implications of asymmetrical stomatal responses for photosynthesis and canopy transpiration are discussed.

862^6^Reece,CF^Krupa,SV^Jager,HJ^Roberts,SW^Hastings,SJ^Oechel,WC^1995^1^Evaluating the effects of elevated levels of atmospheric trace gases on herbs and shrubs - a prototype dual array field exposure system^35^90^1^25-31^^^^^^^^^^4524
1510^376^aching that of hypostomatous leaves clearly reduced their maximum photoA^4523^In the context of global climate change, an understanding of the long-term effects of increasing concentrations of atmospheric trace gases (carbon dioxide, CO2, ozone, O-3, oxides of nitrogen, NOx etc.) on both cultivated and native vegetation is of utmost importance. Over the years, under field conditions, various trace gas-vegetation exposure methodologies with differing advantages and disadvantages have been used. Because of these variable criteria, with elevated O-3 or CO2 levels, at the present time the approach of free-air experimental-release of the gas into study plots is attracting much attention. However, in the case of CO2, this approach (using 15 m diameter study plot with a single circular array of vent pipes) has proven to be cost prohibitive (about $59000- 98000/year/replicate) due to the consumption of significant quantities of the gas to perform the experiment (CO2 level elevated to 400 ppm above the ambient). Therefore, in this paper, we present a new approach consisting of a dual concentric exposure array of vertical risers or vent pipes. The purpose of the outer array (17 m diameter) is to vent ambient air outward and toward the incoming wind thus providing an air curtain to reduce the velocity of that incoming wind to simulate the mode or the most frequently occurring wind speed at the study site. The inner array (15 m diameter) vents the required elevated levels of trace gases (CO2, O-3, etc.) into the study plot. This dual array system is designed to provide spatial homogeneity (shown through diffusion modeling) of the desired trace-gas levels within the study plot and to also reduce its consumption. As an example, while in the single- array free-air CO2-release system the consumption of CO2 to elevate its ambient concentration by 400 ppm is calculated to be about 980 tons/year/replicate, it is estimated that in the dual array system it would be approximately 590 tons/year/replicate. Thus, the dual array system may provide substantial cost savings ($24000-39000/year/replicate) in the CO2 consumption ($60-100/ton of CO2) alone. Similarly, benefits in the requirements of other trace gases (O-3, NOx, etc.) are expected, in future multivariate studies on global climate change.

863^4^Seneweera,SP^Basra,AS^Barlow,EW^Conroy,JP^1995^1^Diurnal regulation of leaf blade elongation in rice by co2 - is it related to sucrose-phosphate synthase activity^8^108^4^1471-1477^^^^^Aug^^^^^4526
243^348^417^427^57^92^nto the study plot. This dual array system is designed to provide spatial homogeneity (shown through diffusion modeling) of the desired trace-gas levels within the study plot and to also reduce its consumption. As an example, while in the single- array free-air CO2-release system the consumption of CO2 to elevate its ambient concentration by 400 ppm is calculated to be about 980 tons/year/replicate, it is estimated that in the dual array system it would be approximately 590 tons/year/replicate. Thus, the dual array system may provide substantial cost savings ($24000-39000/year/replicate) in tA^4525^The relationship between leaf blade elongation rates (LER) and sucrose-phosphate synthase (SPS) activity was investigated at different times during ontogeny of rice (Oryza safiva L. cv Jarrah) grown in flooded soil at either 350 or 700 mu L CO2 L(- 1). High CO2 concentrations increased LER of expanding blades and in vivo activity (V-limiting) SPS activity of expanded blades during the early vegetative stage (21 d after planting [DAP]), when tiller number was small and growing blades were strong carbohydrate sinks. Despite a constant light environment, there was a distinct diurnal pattern in LER, V- limiting SPS activity, and concentration of soluble sugars, with an increase in the early part of the light period and a decrease later in the light period. The strong correlation (r = 0.65) between LER and V-limiting SPS activity over the diurnal cycle indicated that SPS activity played an important role in controlling blade growth. The higher V-limiting SPS activity at elevated CO, at 21 DAP was caused by an increase in the activation state of the enzyme rather than an increase in V- max. Fructose and glucose accumulated to a greater extent than sucrose at high CO2 and may have been utilized for synthesis of cell-wall components, contributing to higher specific leaf weight. By the mid-tillering stage (42 DAP), CO2 enrichment enhanced V-limiting and V-max activities of source blades. Nevertheless, LER was depressed by high CO2, probably because tillers were stronger carbohydrate sinks than growing blades.

864^1^Townend,J^1995^1^Effects of elevated co2, water and nutrients on picea- sitchensis (bong) carr seedlings^84^130^2^193-206^^^^^Jun^^^^^4528
1291^1304^1701^229^342^345^377^595^692^975^ly part of the light period and a decrease later in the light period. The strong correlation (r = 0.65) between LER and V-limiting SPS activity over the diurnal cycle indicated that SPS activity played an important role in controlling blade growth. The higher V-limiting SPS activity at elevated CO, at 21 DAP was caused byA^4527^Sitka spruce (Picea sitchensis (Pong.) Carr.) seedlings were grown from seed for one year in naturally lit growth chambers with either ambient or ambient + 250 ppm concentrations of CO2. In the following year the plants were grown in the same CO2 treatments for the whole growing season at two concentrations of nutrients and were either well-watered or subjected to a long-term, gradually increasing drought. Elevated CO2 increased significantly growth in all treatments except the well-watered, unfertilized treatment. The relative increases in end-of-year biomass in the elevated CO2 treatment compared with the ambient treatment were: well-watered, fertilized + 52%, well-watered, unfertilized + 19%, droughted, fertilized + 44%, and droughted, unfertilized + 49%. Growth analysis revealed that treatment effects on both unit leaf rates and leaf area duration were important in determining the final masses of the plants. Plants growing in elevated CO2 had increased relative growth rates in the first half of the growing season but only slightly increased or even slightly decreased relative growth rates in the later part of the growing season in all water x nutrient treatments. Overall there was a significant CO2 x water x nutrient interaction on end-of-year biomass. A combination of small nutrient concentration and adequate water supply led to the smallest growth response to elevated CO2.

865^3^Vanoosten,JJ^Wilkins,D^Besford,RT^1995^1^Acclimation of tomato to different carbon-dioxide concentrations - relationships between biochemistry and gas- exchange during leaf development^84^130^3^357-367^^^^^Jul^^^^^4530
1302^1702^243^355^363^372^448^550^650^749^red, fertilized + 52%, well-watered, unfertilized + 19%, droughted, fertilized + 44%, and droughted, unfertilized + 49%. Growth analysis revealed that treatment effects on both unit leaf rates and leaf area duration were important in determining the final masses of the plants. Plants growing in elevated CO2 had increased relative growth rates in the first half of thA^4529^Tomato plants were transferred to different CO2 mole fractions (350, 700, 1050 and 1400 mu mol CO2 mol(-1)) 31 d after sowing (2% of full expansion) and the light saturated rate of photosynthesis (P-max) of the unshaded 5th leaf was measured at either an ambient CO2 mole fraction, C-a of 350 mu mol CO2 mol(-1) [P-max (350)] or at the mole fraction of CO2 at which the plants were grown. At 60% and 95% leaf expansion, P-max of high CO2 grown plants measured at growth CO2, was greater than the P-max (350) of the ambient CO2 grown plants. However, by leaf maturity, P-max (growth CO2) declined linearly as growth CO2 concentration increased. P-max (350) of plants exposed to elevated CO2 up to 60% leaf expansion had not acclimated to high CO2. At 95% leaf expansion, P-max (350) was smaller in the high CO2 grown plants. P-max (350) was predicted from Rubisco in vitro carboxylation capacity using tomato Rubisco kinetic constants. By 95% leaf expansion, high CO2 grown plants showed similarities to the response of plants to low nitrogen supply, in terms of Rubisco and chlorophyll content. The observed and theoretical relationships between the initial slopes of the P- max/C-i responses and Rubisco activity were statistically equivalent. Both short-term and long-term effects of elevated CO2 on dark respiration (R(n)) were also investigated at two stages of leaf development (50 and 100% expansion). R(a) (growth CO2) was smaller for the high CO2 grown plants compared with the control plants, whereas R(n) (350) was either equal or greater for the plants grown in high CO2.

866^4^Walker,RF^Geisinger,DR^Johnson,DW^Ball,JT^1995^1^Interactive effects of atmospheric co2 enrichment and soil n on growth and ectomycorrhizal colonization of ponderosa pine- seedlings^49^41^3^491-500^^^^^Aug^^^^^4532
341^372^374^416^419^610^757^rown plants. P-max (350) was predicted from Rubisco in vitro carboxylation capacity using tomato Rubisco kinetic constants. By 95% leaf expansion, high CO2 grown plants showed similarities to the response A^4531^Interactive effects of elevated atmospheric CO2 and soil N fertility on above- and belowground development of juvenile ponderosa pine (Pinus ponderosa Dougl, ex Laws.) were examined. Seedlings were grown from seed in atmospheres containing 700 mu l l(-1), 525 mu l l(-1), or ambient CO2. Medium and high soil N treatments were created by adding sufficient (NH4)(2)SO4 to the potting mix to increase total N by 100 mu g g(-1) and 200 mu g g(-1), respectively, while unamended mix, which had a total N concentration of approximately 300 mu g g(-1), served as the low N treatment. Three whole-seedling harvests at 4-month intervals permitted assessment of shoot and root growth and ectomycorrhizal formation resulting from inoculation with Pisolithus tinctorius (Pers.) Coker and Couch. After 4 months, CO2 enrichment increased shoot volume and dry weight of seedlings grown in high soil N, but this result was not evident in the other N treatments and did not persist to the second harvest. Root weight, however, increased, and shoot/root ratio decreased as the CO2 concentration increased within all three N treatments at the first harvest. At the second harvest, root weights within the high and intermediate N treatments were lowest in seedlings grown in ambient CO2 and shoot/root ratios decreased as CO2 increased in these two N treatments as well. Although the ectomycorrhizal infection percentage of seedlings grown in 700 mu l l(-1) CO2 was highest among the seedlings grown in high N after 4 months, mycorrhizal colonization was variable overall at the first and second harvests. After 1 yr, the 525 mu l l(-1) CO2 concentration stimulated above- and belowground growth more than the high CO2 atmosphere in both high and medium soil N. These seedlings also had relatively extensive ectomycorrhizal formation, but colonization was again variable. Results presented here suggest the response of juvenile ponderosa pine to CO2 enrichment is ephemeral, with the effects on roots more pronounced and persistent overall than those on shoots, and that the response is dependent on N availability.

867^4^Williams,M^Shewry,PR^Lawlor,DW^Harwood,JL^1995^1^The effects of elevated-temperature and atmospheric carbon- dioxide concentration on the quality of grain lipids in wheat (triticum-aestivum L) grown at 2 levels of nitrogen application^9^18^9^999-1009^^^^^Sep^^^^^4534
137^230^243^360^434^724^741^848^nfection percentage of seedlings grown in 700 mu l l(-1) CO2 was highest among the seedlings grown in high N after 4 months, mycorrhizal colonization was variable overall at the first and second harvests. After 1 yr, the 525 mu l l(-1) CO2 concentration stimulated above- and belowground growth more than the high CO2 atmosphere in both high and medium soil N. These seedlings also had relatively extensive ectomycorrhizal formation, but colonization was again variable. Results presented here suggest the response of juvenile ponderosa pine to CO2 enrichment is ephemeral, with the effects on roots more pronounced and persistent overall than those on shooA^4533^Wheat plants were cultivated under growth regimes combining two temperatures (ambient and 4 degrees C above ambient temperature) with two concentrations of carbon dioxide (350 and 700 mu mol mol(-1)) and two nitrogen fertilizer applications (high and low), The aim of this study was to define any changes in the acyl lipid composition of wheat grains which could result from alterations in the growth conditions, Qualitative and quantitative changes were observed in both non-starch and starch lipid fractions, Temperature was by far the most influential growth factor, although interactions between all three growth conditions occurred, as confirmed by analysis of variance, Growth at elevated temperatures had the general effect of reducing the amounts of accumulated lipids, particularly non-polar lipids (1322mg fatty acids per 100g fresh weight at ambient temperatures as opposed to 777mg fatty acids per 100 g fresh weight at 4 degrees C above ambient temperatures), There were changes in the proportions of the major non-starch as well as the starch lipids, In the former category, non-polar lipids (principally triacylglycerols), the membrane glycosylglycerides and phosphatidylcholine were the main constituents, whereas in the starch lipids, lysophosphatidylcholine and lysophosphatidylethanolamine represented over 70% of the total, Depending on the growth conditions, the percentages of lipids such as monogalactosyldiacylglycerol, digalactosyldiacylglycerol and phosphatidylcholine (non-starch) or the starch lysophosphatidylethanolamine varied 2-fold or more, Significant changes in the acyl composition of individual lipids were also observed, most often in the proportions of palmitate, oleate and linoleate, The observed alterations in wheat lipids are likely to affect the properties of any flours derived from grain grown under climate change conditions.

868^2^Wolfenden,J^Diggle,PJ^1995^1^Canopy gas-exchange and growth of upland pasture swards in elevated co2^84^130^3^369-380^^^^^Jul^^^^^4536n the proportions of th130^1345^137^189^240^243^376^377^57^740^lipids, In the former category, non-polar lipids (principally triacylglycerols), the membrane glycosylglycerides and phosphatidylcholine were the main constituents, whereas in the starch lipids, lysophosphatidylcholine and lysophosphatidylethanolamine represented over 70% of the total, Depending on the growth conditions, the percentages of lipids such as monogalactosyldiacylglycerol, digalactosyldiacylglycerol and phosphatidylcholine (non-starch) or the starch lysophosphatidylethanolamine varied 2-fold or more, Significant changes in the acyl composition of individual lipids were also observed, most often in the proportions of palmitate, oleate and linoleate, The observed alterations in wheat lipids are likely to affect the properties of any flours derived from grain grown under climate change conditions.

868^2^Wolfenden,J^Diggle,PJ^1995^1^Canopy gas-exchange and growth of upland pasture swards in elevated co2^84^130^3^369-380^^^^^Jul^^^^^4536n the proportions of thA^4535^Vegetation monoliths (450 x 450 mm) from two contrasting upland grassland communities were grown in Solardomes in either ambient air or ambient air enriched with 250 ppm CO2. During the first two growing seasons measurements of canopy gas exchange showed that rates of photosynthesis of limestone swards were enhanced by growth in elevated CO2, by approx. 50% during spring and early summer. Although canopy respiration was also greater in elevated CO2, the overall effect was an average increase of 33% in net CO2 assimilation. Enhanced respiration rates persisted into the autumn, whereas the effect on photosynthesis diminished through the growing season, so that in September swards growing in high CO2 had net photosynthesis rates similar to, or even lower than those in ambient air. This response varied between swards of differing species composition. In acidic grassland no significant effects of CO2 on respiration or net CO2 uptake rates were detected at any time. The above ground productivity of limestone grassland was measured in several harvests throughout both seasons, and was not affected by CO2 concentration at any time. Similarly, the acidic grassland, harvested at the end of the second season, showed no significant effect of CO2 on above-ground biomass. The results suggest that increasing atmospheric CO2 concentration is unlikely to cause large changes in net primary productivity in these grasslands.

869^4^Balaguer,L^Barnes,JD^Panicucci,A^Borland,AM^1995^1^Production and utilization of assimilates in wheat (triticum- aestivum L) leaves exposed to elevated o-3 and/or co2^84^129^4^557-568^^^^^Apr^^^^^4538
137^1633^1703^312^384^446^447^520^692^728^n, so that in September swards growing in high CO2 had net photosynthesis rates similar to, or even lower than those in ambient air. This response varied between swards of differing species composition. In acidic grassland no significant effects of CO2 on respiration or net CO2 uptake rates were detected at any time. The above ground productivity of limestonA^4537^This study examined the effects of elevated ozone (O-3) and/or carbon dioxide (CO2) on the diel allocation of photosynthetically fixed carbon in fully expanded leaves of young (growth stages 4-5) spring wheat (Triticum aestivum L. cv. Hanno). Plants were grown in controlled environment chambers and exposed to two O-3 regimes ['non-polluted' air (CF), < 5 nmol mol(-1); 'polluted' air, CF + 75 nmol mol(-1) 7 h d(-1)] and two CO2 treatments ('ambient', 354 mu mol mol(-1); 'elevated', 700 mu mol mol(-1)) over a 30 d period. Neutral sugars (predominantly sucrose) were found to be the most abundant form of carbohydrate accumulated by leaves during the day, but significant quantities of starch and high degree of polymerization (d.p.) fructans were also present. Elevated concentrations of O-3 and/or CO2 were found to have marked effects on diel patterns of export, storage and respiration, whilst the proportions of fixed carbon allocated to each of these processes were broadly similar. O-3 depressed the rate of net CO2 assimilation (-20%) and reduced stomatal conductance (- 19%). This was reflected in a reduced amount of carbohydrate accumulated in, and exported by, source tissue during the day. Effects of O-3 on the rate of CO2 fixation were aggravated by an increased demand for carbon by dark respiratory processes. In contrast, doubling the atmospheric concentration of CO2 enhanced the rate of net CO2 assimilation (+ 47%) and reduced the proportion of fixed carbon retained in the leaf blade, increasing the rate of export. The favourable carbon balance of CO2 enriched leaves was further enhanced by a decrease in the cost of maintenance respiration, whilst simultaneous measurements of CO2 efflux and O-2 uptake at night suggested a shift in the substrates metabolized at high CO2. Effects of elevated CO2 and O-3 on the carbon balance of individual leaf blades over a single 24 h light/dark cycle were entirely consistent with the cumulative effects of the gases on plant growth over a 30 d period. O-3 reduced the rate of plant growth (-10%), but there were differential effects of O-3 on the growth of root and shoot which exacerbated the decrease in assimilate availability induced by O-3. In contrast the favourable effects of CO2 enrichment on the carbon balance of individual source leaves was reflected in the enhanced accumulation of dry matter in existing sinks, and the initiation of new sinks (i.e. increased tillering). In the combined treatment (elevated CO2 + O-3), O-3 counteracted the favourable effects of CO2 enrichment on the carbon balance of individual leaves, and the combined effects of the individual gases on the diel partitioning of photosynthetically fixed carbon in fully expanded leaf blades was reflected in a decreased rate of plant growth at elevated CO2, a situation further exacerbated by O-3-induced shifts in the relative partitioning of carbon between root and shoot. There was no evidence that CO2 enrichment afforded additional protection against O-3 damage: the extent of the O-3-induced reduction in photosynthesis, carbohydrate availability and growth observed at elevated CO2 was similar to that induced by O-3 in ambient air, despite additive effects of the gases on stomatal conductance that would reduce the effective dose of O-3 by approximate to 30%. The wider ecological significance of interactions between elevated CO2 and O-3 is discussed in the light of other recent findings.

870^5^Bettarini,I^Calderoni,G^Miglietta,F^Raschi,A^Ehleringer,J^1995^1^Isotopic carbon discrimination and leaf nitrogen-content of erica-arborea L along a co2 concentration gradient in a co2 spring in italy^13^15^5^327-332^^^^^May^^^^^4540
1262^243^348^372^745^881^lly fixed carbon in fully expanded leaf blades was reflected in a decreased rate of plant growth at elevated CO2, a situation further exacerbated by O-3-induced shifts in the relative partitioning of carbon between root and shoot. There was no evidence that CO2 enrichment afforded additional protection against O-3 damage: the extent of the O-3-induced reduction in pA^4539^We studied a Mediterranean species (Erica arborea L.) growing in a CO2 spring in Italy that was naturally exposed for generations to a gradient of atmospheric CO2 concentrations. The CO2 concentration gradient to which different individual plants were exposed was determined by an indirect method based on radioisotope analysis. The stable carbon isotope ratio of sampled leaves was determined by mass spectrometry, and isotopic discrimination was then calculated. Leaf nitrogen, specific leaf area, total soil nitrogen, soil organic matter content and soil pH were also measured. In one group of plants, grown on a homogeneous soil and exposed to moderate CO2 enrichment, isotopic discrimination was significantly reduced in response to increasing CO2 concentrations, whereas the intercellular CO2 concentration and leaf nitrogen content were almost unaffected. In a second group of plants, grown along a gradient of CO2 concentration and soil nitrogen content, leaf nitrogen content was reduced when nitrogen availability was limiting. However, when soil nitrogen was available in excess, even very high CO2 concentrations did not result in increased discrimination or reduced leaf nitrogen content in the long term. The results are discussed with respect to current theories about the long-term CO2 response of plants based on several years of experimentation with elevated atmospheric CO2 concentrations under controlled conditions.

871^4^Bosac,C^Gardner,SDL^Taylor,G^Wilkins,D^1995^1^Elevated co2 and hybrid poplar - a detailed investigation of root and shoot growth and physiology of populus-euramericana, primo^45^74^1-3^103-116^^^^^Jun^^^^^4542
1272^1704^1705^243^360^376^377^465^514^692^otopic discrimination was significantly reduced in response to increasing CO2 concentrations, whereas the intercellular CO2 concentration and leaf nitrogen content were almost unaffected. In a second group of plants, grown along a gradient of CO2 concentration and soil nitrogen content, leaf nitrogen content was reduced when nitrogen availA^4541^Exposure of the hybrid poplar clone 'Primo' (Populus deltoides X Populus nigra) to 580 mu l 1(-1) carbon dioxide for just 68 days significantly (P less than or equal to 0.05) increased stem height by 13% compared with trees grown in ambient CO2 concentrations. The stem diameter was significantly (P less than or equal to 0.05) increased and both total biomass and woody stem biomass also showed higher values (38% and 31% increases respectively) in elevated CO2. Trees in elevated CO2 had more leaves and a greater total leaf area, whilst the specific leaf area was decreased in elevated CO2 on four out of five occasions and was significantly (P less than or equal to 0.05) lower after 68 days, an effect indicating that leaves were thicker and/or heavier. Rates of photosynthesis (A) measured after 49 and 67 days of exposure revealed that trees in the elevated CO2 treatment had lower values of A when measured at either 350 or 580 mu l 1(-1) CO2. Sequential harvests at intervals during the study in which the root and shoot components were analysed separately allowed the construction of root:shoot ratios and allometric coefficients; there was no significant effect on the allometric coefficient and the root:shoot ratio was significantly increased on only one occasion. However, measurements of the 'apparent' root length suggested that root lengths were greater in the CO2 treatment. There was a significant increase in the number of fine root tips visible down the surface of specially designed rooting tubes (P less than or equal to 0.05), indicating more fine roots or an increase in fine root branching. The growth rates of individual fine or large roots over 24 h were unaffected, again suggesting that increases in biomass may be due to more root segments rather than longer individual roots. Root water relations were also examined and showed a tendency towards solute accumulation and increases in turgor pressure (P) and effective tugor (P-e) at times when root growth was stimulated, although these were not consistent. Cell wall plasticity of the tips of large roots was significantly (P less than or equal to 0.01) reduced in elevated CO2, possibly indicating a greater tendency to divert resources to the formation of root branches. The results of the study are discussed in the light of the possible consequences of changes in poplar growth and physiology for forestry practice in an increased CO2 environment.

872^3^Ceulemans,R^Jiang,XN^Shao,BY^1995^1^Growth and physiology of one-year-old poplar (populus) under elevated atmospheric co2 levels^52^75^6^609-617^^^^^Jun^^^^^4544
1705^1706^312^342^345^374^376^384^400^546^owth rates of individual fine or large roots over 24 h were unaffected, again suggesting that increases in biomass may be due to more root segments rather than longer individual roots. Root water relations were also examined and showed a tendency towards solute accumulation and increases in turgor pressure (P) and effective tugor (P-e) at times when root growth was stimulated, although these were not consistent. A^4543^The effects of elevated atmospheric CO2 concentrations on the ecophysiological responses (gas exchange, chlorophyll a fluorescence, Rubisco activity, leaf area development) as well as on the growth and biomass production of two poplar clones (i.e. Populus trichocarpa x P. deltoides clone Beaupre and P. x euramericana clone Robusta) were examined under open top chamber conditions. The elevated CO2 treatment (ambient + 350 mu mol mol-1) stimulated above-ground biomass of clones Robusta and Beaupre after the first growing season by 55 and 38 %, respectively. This increased biomass production under elevated CO2 was associated with a significant increase in plant height, the latter being the result of enhanced internode elongation rather than an increased production of leaves or internodes. Both an increased leaf area index (LAI) and a stimulated net photosynthesis per unit leaf contributed to a significantly higher stem biomass per unit leaf area, and thus to the increased above-ground biomass production under the elevated CO2 concentrations in both clones. The larger LAI was caused by a larger individual leaf size and leaf growth rate; the number of leaves was not altered by the elevated CO2 treatment. The higher net leaf photosynthesis was the result of an increase in the photochemical (maximal chlorophyll fluorescence Fm and photochemical efficiency Fv/Fm) as well as in the biochemical (increased Rubisco activity) process capacities. No significant differences were found in dark respiration rate, neither between clones nor between treatments, but specific leaf area significantly decreased under elevated CO2 conditions. (C) 1995 Annals of Botany Company

873^2^Cotrufo,ME^Ineson,P^1995^1^Effects of enhanced atmospheric co2 and nutrient supply on the quality and subsequent decomposition of fine roots of betula- pendula roth and picea-sitchensis (bong) carr^206^170^2^267-277^^^^^Mar^^^^^4546
32^374^376^398^425^534^57^669^672^92^ss per unit leaf area, and thus to the increased above-ground biomass production A^4545^Fine root litter derived from birch (Betula pendula Roth.) and Sitka spruce (Picea sitchensis (Bong.) Carr.) plants grown under two CO2 atmospheric concentrations (350 ppm and 600 ppm) and two nutrient regimes was used for decomposition studies in laboratory microcosms. Although there were interactions between litter type, CO2/fertiliser treatments and decomposition rates, in general, an increase in the C/N ratio of the root tissue was observed for roots of both species grown under elevated CO2 in unfertilized soil. Both weight loss and respiration of decomposing birch roots were significantly reduced in materials derived from enriched CO2, whilst the decomposition of spruce roots showed no such effect. A parallel experiment was performed using Betula pendula root litter grown under different N regimes, in order to test the relationship between C/N ratio of litter and root decomposition rate. A highly significant (p < 0.001) negative correlation between C/N ratio and root litter respiration was found, with an r(2) = 0.97. The results suggest that the increased C/N ratio of plant tissues induced by elevated CO2 can result in a reduction of decomposition rate, with a resulting increase in forest soil C stores.

874^4^Firbank,LG^Watkinson,AR^Norton,LR^Ashenden,TW^1995^1^Plant-populations and global environmental-change - the effects of different temperature, carbon-dioxide and nutrient regimes on density-dependence in populations of vulpia-ciliata^43^9^3^432-441^^^^^Jun^^^^^4548
1110^1707^1708^227^349^372^422^51^512^692^ Both weight loss and respiration of decomposing birch roots were significantly reduced in materials derived from enriched CO2, whilst the decomposition of spruce roots showed no such effect. A parallel experiment was performed using Betula pendula root litter grown under different N regimes, in order to test the relationship between C/N ratio of litter and root decomposition rate. A highly significant (p < 0.001) negative correlation between C/N ratio and root litter respiration was found,A^4547^1. Monocultures of Vulpia ciliata spp. ambigua were subjected to a range of temperatures, CO2, nutrient and density regimes in a factorial design housed within solar-domes. Temperature treatments were imposed at ambient and +3 degrees C levels, CO2 at ambient and +340 ppm, and there were three levels of nutrients and eight levels of densities ranging from 156 to 31250 seeds m(-2). The abiotic treatments were imposed after emergence. 2. There was little mortality and this was unrelated to the treatments. Plants grew more quickly at the high temperature, high nutrient and low density regimes, and flowering was earlier at the high temperature regime. 3. At seed set, biomass per plant and seed production per plant were analysed by analysis of variance and by fitting mean yield- density models expanded to account for different environmental conditions. Biomass and fecundity were greatest at high temperature, high nutrient and low density regimes. Allocation of biomass to shoots was greater at the high temperatures, as were seed number/shoot biomass ratios. Any effects of CO2 were negligible. The parameter b describing the nature of the relationship between seed production per plant and density was always less than unity but was greater at the higher temperature regime. The response to density was therefore undercompensating in all conditions, implying that populations would display monotonic damping to equilibrium densities. 4. Under proposed future environmental regimes, V. ciliata has the capacity for more rapid population growth from low levels and for a northwards range shift. However, if open ground is not maintained, its habitat may become dominated by species that are more competitive or that have a higher rate of increase.

875^4^Hibbs,DE^Chan,SS^Castellano,M^Niu,CH^1995^1^Response of red alder seedlings to co2 enrichment and water- stress^84^129^4^569-577^^^^^Apr^^^^^4550
1709^372^377^421^423^92^ture, high nutrient and low density regimes. Allocation of biomass to shoots was greater at the high tempA^4549^Red alder (Alnus rubra Bong.) is a nitrogen-fixing pioneer tree species of the Pacific Northwest of North America. We investigated the response of different seed sources of red alder to elevated atmospheric CO2 and to varied levels of water stress. Seeds were stratified, germinated and grown for up to 147 d under ambient (350 mu l l(-1)) or elevated (700 mu l l(- 1)) CO2. There were no significant interactions of seed source latitude with either treatment, although seedlings from more northerly sources were larger. Elevated CO2 and low moisture stress resulted in larger plants with more leaf area; effects of the two factors appeared additive. Effects of both factors on biomass allocation, including root:shoot ratios, were small or nonsignificant. Elevated CO2 decreased specific nitrogenase activity and generally increased photosynthesis (A) and stomatal conductance (g). The ratio A:g, potential water use efficiency, also increased when plants were under water stress. Elevated CO2 appears to improve drought tolerance in red alder. Overall, these results indicate that red alder would benefit in total plant growth from increased ambient CO2 and could tolerate changes in precipitation.

876^3^Ineichen,K^Wiemken,V^Wiemken,A^1995^1^Shoots, roots and ectomycorrhiza formation of pine-seedlings at elevated atmospheric carbon-dioxide^9^18^6^703-707^^^^^Jun^^^^^4552
376^417^705^740^741^92^e were no significant interactions of seed source latitude with either treatment, although seedlings from more northerly sources were larger. Elevated CO2 and low moisture stress resulted in larger plants with more leaf area; effects of the two factors appeared additive. Effects of both factors on biomass allocation, including root:shoot ratios, were small or nonsignificant. Elevated CO2 decreased specific nitrogenase activity and generally increased photosynthesis (A) and stomatal conductance (g). The ratio A:g, potential water use efficiency, also increased when plants were under water stress. Elevated CO2 appears to improve drA^4551^The effect of elevated atmospheric CO2 concentration on the growth of shoots, roots, mycorrhizas and extraradical mycorrhizal mycelia of pine (Pinus silvestris L.) was examined, Two and a half-month-old seedlings were inoculated axenically with the mycorrhizal fungus Pisolithus tinctorius (Pers,) by a method allowing rapid mycorrhiza formation in Petri dishes, The plants were then cultivated for 3 months in growth chambers with daily concentrations of 350 and 600 mu mol mol(-1) CO2 during the day, Whereas plants harvested after 1 and 2 months did not differ appreciably between ambient and increased CO2 concentrations, after 3 months they developed a considerably higher root biomass (+57%) at elevated CO2, but did not increase significantly in root length, The mycorrhizal fungus Pisolithus tinctorius, which depended entirely on the plant assimilates in the model system, grew much faster at increased CO2: 3 times more mycorrhizal root clusters were formed and the extraradical mycelium produced had twice the biomass at elevated as at ambient CO2. No difference in shoot biomass was found between the two treatments after 91d, However, since the total water consumption of seedlings was similar in the two treatments, the water use efficiency was appreciably higher for the seedlings at increased CO2 because of the higher below- ground biomass.

877^3^Johnson,DW^Walker,RF^Ball,JT^1995^1^Lessons from lysimeters - soil n release from disturbance compromises controlled environment study^56^5^2^395-400^^^^^May^^^^^4554
398^669^672^ested after 1 and 2 months did not differ appreciably between ambient and increased CO2 concentrations, after 3 months they developed a considerably higher root biomass (+57%) at elevated CO2, but did not increase significantly in root length, The mycorrhizal fungus Pisolithus tinctorius, which depended entirely on the plant assimilates in the model system, grew much faster at increased CO2: 3 times more mycorrhizal root clusters were formed and the extraradical mycelium produced had twiceA^4553^A controlled environment study of the effects of carbon dioxide (CO2) and nitrogen (N) on growth of ponderosa pine seedlings produced results contradictory to those obtained in the field with the same species, soil, and treatments. In the controlled environment study, there was a significant negative growth response to N fertilization, whereas in the field there was a significant positive response to N. The difference was due to high rates of native N mineralization after soil disturbance during potting. This was evident from soil solution NO3- concentrations that peaked at approximate to 5000 mu mol/L in the unfertilized pots and 20 000 mu mol/L in the fertilized pots. These concentrations are orders of magnitude greater than those typically observed in the field. The effects of soil disturbance on N mineralization and nitrification need to be carefully considered before initiating controlled environment studies. The results of this study show that excessive N mineralization caused by soil disturbance can seriously compromise the results of controlled environment studies

878^2^Larsen,M^Watkins,CB^1995^1^Firmness and concentrations of acetaldehyde, ethyl-acetate and ethanol in strawberries stored in controlled and modified atmospheres^259^5^1-2^39-50^^^^^Jan^^^^^4556
1460^1539^454^874^875^ant negative growth response to N fertilization, whereas in the field there was a significant positive response to N. The difference was due to high rates of native N mineralization after soil disturbance during potting. This was evident from soil solution NO3- concentrations that peaked at approximate to 5000 mu mol/L in the unfertilized pots and 20 000 mu mol/L in the fertilized pots. These concentrations are orders of magnitude greater than those typically observed in the field. The effects of soil disturbance on N mineralization and nitrification need to be carefully considered before initiating controlled environment studies. The results of this study show that excessive N mineralization caused by soil disturbancA^4555^'Pajaro' strawberries (Fragaria x ananassa Duch.) were stored at 0 degrees C in a range of controlled atmosphere (CA) conditions with CO2 concentrations up to 24%, O-2 concentrations down to 1%, or a combination of 10% CO2 and 2% O-2 Elevated CO2 concentrations resulted in firmer fruit, while low O-2 did not affect texture. Off-flavours developed after 3 days of storage at 20% CO2, but decreased when fruit was subsequently held for 24 h at 20 degrees C. However, off- flavours were persistent after CA storage for 7 days or more. Off-flavours were related to increases in ethyl acetate and ethanol concentrations but not to acetaldehyde. Beneficial atmospheres of close to 10% CO2 and 2% O-2 resulted in a firmer texture and delayed ripening with no off-flavour development. However, fruit quality was poor when similar atmospheres were developed in modified atmosphere (MA)-producing polythene bags. Rapid imposition of CA resulted in better quality fruit than when MAs around the fruit were developed gradually.

879^4^Lenssen,GM^Vanduin,WE^Jak,P^Rozema,J^1995^1^The response of aster-tripolium and puccinellia-maritima to atmospheric carbon-dioxide enrichment and their interactions with flooding and salinity^159^50^2^181-192^^^^^May^^^^^4558
1710^1711^224^245^372^378^57^778^881^92^d in firmer fruit, while low O-2 did not affect texture. Off-flavours developed after 3 days of storage at 20% CO2, but decreased when fruit was subsequently held for 24 h at 20 degrees C. However, off- flavours were persistent after CA storage for 7 days or more. Off-flavours were related to increases in ethyl acetate and ethanol concentrations but not to acetaldehyde. Beneficial atmospheres of close to 10% CO2 and 2% O-2 resulted in a firmer texture and delayed ripening with no off-flavour development. However, fruit quality was poor when similar atmospheres were developed in modified atmosphere (MA)-producing polythene bags. Rapid imposition of CA resulted in better quality fruit than when MAs around the fruit were developed graduallyA^4557^The effects of 380 and 720 mumol mol-1 atmospheric CO2 on growth, dry matter allocation, net leaf photosynthesis and stomatal conductance of the C3 salt marsh species Aster tripolium L. and Puccinellia maritima (Hudson) Parl. were studied. Plants were grown in pots under combinations of low (50-250 mM NaCl) or high (450-550 mM NaCl) salinity and non- flooded or flooded salt marsh soil. High salinity reduced growth of both species, while flooding increased biomass production of A. tripolium. Root weight of A. tripolium and total plant weight of P. maritima was increased by atmospheric CO2 enrichment when the soil was flooded. Under non-flooded conditions, the effect of elevated CO2 on growth was small (P. maritima) or absent (A. tripolium). The relative increase in total plant weight of both species by elevated CO2 was higher under saline conditions. Dry matter allocation between root, stem and leaf, as reflected in leaf weight ratio and shoot to root ratio, was not changed by elevated CO2, while specific leaf area was slightly decreased by CO2 enrichment. Elevated CO2 stimulated net leaf photosynthesis of both species, while stomatal conductance decreased. These effects were not changed by salinity or flooding treatment.

880^1^Leverenz,JW^1995^1^Shade shoot structure of conifers and the photosynthetic response to light at 2 co2 partial pressures^43^9^3^413-421^^^^^Jun^^^^^4560
1034^1712^361^372^605^607^727^748^92^h of both species, while flooding increased biomass production of A. tripolium. Root weight of A. tripolium and total plant weight of P. maritima was increased by atmospheric CO2 enrichment when the soil was flooded. Under non-flooded conditions, the effect of elevated CO2 on growth was small (P. maritima) or absent (A. tripolium). The relative increase in total plant weight of both species by elevated CO2 was higher under saline conditions. Dry matter allocation between root, stem and leaf, as reflected in leaf weight ratio and shoot to root ratio, was not changed by elevated CO2, while speciA^4559^1. The response of net photosynthesis to irradiance was measured for shade-adapted shoots of different conifer species. Shoots were illuminated unidirectionally or in a light integrating sphere to study the effects of shoot structure. 2. Shoot structure was quantified as R(max) the ratio of the shoot-silhouette area to the leaf-silhouette area. 3. The initial slopes and the convexities (rate of bending) of the light response curves were strongly affected by R(max) during unilateral illumination. There was also a strong positive effect of R(max) on the maximum efficiency of net photosynthesis and a strong negative effect of R(max) on the light compensation point. 4. Increasing atmospheric CO2 partial pressure (C-a) from 35 to 70 Pa did not affect the convexity of the light response curves nor rates of dark respiration. 5. Increasing C-a affected the initial slope, the light compensation point, the maximum rate of photosynthesis and the efficiency of net photosynthesis. 6. Except for the maximum rate of net photosynthesis, the responses to C-a were controlled by shoot structure. 7. Studies of the effect of atmospheric CO2 on photosynthesis and growth in conifers need to consider variations in shoot structure.

881^2^Liu,SY^Teskey,RO^1995^1^Responses of foliar gas-exchange to long-term elevated co2 concentrations in mature loblolly-pine trees^13^15^6^351-359^^^^^Jun^^^^^4562
1706^256^312^344^361^400^511^546^685^92^ light response curves were strongly affected by R(max) during unilateral illumination. There was also a strong positive effect of R(max) on the maximum efficiency of net photosynthesis and a strong negative effect of R(max) on the light compensation point. 4. Increasing atmospheric CO2 partial pressure (C-a) from 35 to 70 Pa did not affect the convexity of the light response curves nor rates of dark respiration. 5. Increasing C-a affected the initial slope, the light compensation point, the maximum rate of photosynthesis and the efficiency of net photosynthesis. 6. Except for the maximum rate ofA^4561^Branches of field-grown mature loblolly pine (Pinus taeda L.) trees were exposed for 2 years (1992 and 1993) to ambient or elevated CO2 concentrations (ambient + 165 mu mol mol(-1) or ambient + 330 mu mol mol(-1) CO2). Exposure to elevated CO2 concentrations enhanced rates of net photosynthesis (P-n) by 53-111% compared to P-n of foliage exposed to ambient CO2. At the same CO2 measurement concentration, the ratio of intercellular to atmospheric CO2 concentration (C-i/C-a) and stomatal conductance to water vapor did not differ among foliage grown in an ambient or enriched CO2 concentration. Analysis of the relationship between P-n and C-i indicated no significant change in carboxylation efficiency of ribulose-1,5- bisphosphate carboxylase/oxygenase during growth in elevated CO2 concentrations. Based on estimates derived from P-n/C-i curves, there were no apparent treatment differences in dark respiration, CO2 compensation point or P-n at the mean C-i. In 1992, foliage in the three CO2 treatments yielded similar estimates of CO2-saturated P-n (P-max), whereas in 1993, estimates of P-max were higher far branches grown in elevated CO2 than in ambient CO2. We conclude that field-grown loblolly pine trees do not exhibit downward acclimation of leaf-level photosynthesis in their long-term response to elevated CO2 concentrations.

882^4^Mathooko,FM^Kubo,Y^Inaba,A^Nakamura,R^1995^1^Induction of ethylene biosynthesis and polyamine accumulation in cucumber fruit in response to carbon-dioxide stress^259^5^1-2^51-65^^^^^Jan^^^^^4564
1068^1412^1678^1713^1714^1715^1716^1717^451^454^iched CO2 concentration. Analysis of the relationship between P-n and C-i indicated no significant change in carboxylation efficiency of ribulose-1,5- bisphosphate carboxylase/oxygenase during growth in elevated CO2 concentrations. Based on estimates derived from P-n/C-i curves, there were no apparent treatment differences in dark respiration, CO2 compensation point or P-n at the mean C-i. In 1992, foliage in the three CO2 treatments yieldeA^4563^Carbon dioxide stress-induced ethylene biosynthesis, respiration and polyamine accumulation in cucumber fruit (Cucumis sativus L, cv. Sharp-1) held at 25 degrees C was investigated. Control fruit produced little ethylene and the respiration rate decreased with increase in incubation time while polyamine levels decreased. Elevated CO2 induced ethylene production, respiration and polyamine accumulation. Putrescine and spermidine levels increased in response to CO2 treatment, whereas spermine levels were not significantly affected. No cadaverine was detected in all treatments. The increase in ethylene production paralleled increases in 1- aminocyclopropane-1-carboxylic acid (ACC) and the activities of both ACC synthase and in vitro ACC oxidase. Infiltration of the fruit with aminooxyacetic acid, a potent inhibitor of the conversion of S-adenosylmethionine (AdoMet) to ACC completely blocked CO2 stress-induced ethylene production. Similarly, cycloheximide, an inhibitor of nucleocytoplasmic protein synthesis effectively blocked CO2 stress induction of polyamine accumulation, ethylene production, ACC formation and the development of ACC synthase. Withdrawal of CO2 gas caused cessation of increases in ethylene production, respiration, ACC, putrescine and the activities of ACC synthase and ACC oxidase, but caused increase in spermidine and spermine levels. These data indicate that CO2 induces de novo synthesis of ACC synthase thereby causing accumulation of ACC and increase in ethylene production and suggest that the conversion of AdoMet to ACC is the rate-limiting step in CO2 stress-induced ethylene biosynthesis. The induction, however, requires continuous presence of the stimulus. The results also suggest that protein synthesis might be required for the CO2 stress induction of polyamine biosynthesis. The results further suggest that in cucumber fruit under CO2 stress, at least, the ethylene and polyamine biosynthetic pathways are not competitive.
ycloheximide, an inhibitor of nucleocytoplasmic protein synthesi883^6^Micallef,BJ^Haskins,KA^Vanderveer,PJ^Roh,KS^Shewmaker,CK^Sharkey,TD^1995^1^Altered photosynthesis, flowering, and fruiting in transgenic tomato plants that have an increased capacity for sucrose synthesis^6^196^2^327-334^^^^^May^^^^^4566
130^1718^348^349^360^372^384^388^434^92^ ACC oxidase, but caused increase in spermidine and spermine levels. These data indicate that CO2 induces de novo synthesis of ACC synthase thereby causing accumulation of ACC and increase in ethylene production and suggest that the conversion of AdoMet to ACC is the rate-limiting step in CO2 stress-induced ethylene biosynthesis. The induction, however, requires continuous presence of the stimulus. The results also suggest that protein synthesis might be required for the CO2 stress induction of polyamine biosynthesis. The results further suggest that in cucumber fruit under CO2 stress, at least, the ethylene and polyamine biosynthetic pathways are not competitive.
ycloheximide, an inhibitor of nucleocytoplasmic protein synthesiA^4565^Photosynthesis, leaf assimilate partitioning, flowering, and fruiting were examined in two lines of Lycopersicon esculentum Mill. transformed with a gene coding for sucrose-phosphate synthase (SPS) (EC 2.3.1.14) from Zea mays L. expressed from a tobacco ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit promoter. Plants were grown at either 35 or 65 Pa CO2 and high light (1000 mu mol photons . m(-2). s(-1)). Limiting and maximum SPS activities were significantly greater (up to 12 times) in the leaves of SPS-transformed lines for all treatments. Partitioning of carbon into sucrose increased 50% for the SPS transformants. Intact leaves of the control lines exhibited CO2-insensitivity of photosynthesis at high CO2 levels, whereas the SPS transformants did not exhibit CO2-insensitivity. The O-2-sensitivity of photosynthesis was also greater for the SPS-transformed lines compared to the untransformed control when measured at 65 Pa CO2. These data indicate that the SPS transformants had a reduced limitation on photosynthesis imposed by end-product synthesis. Growth at 65 Pa CO2 resulted in reduced photosynthetic capacity for control lines but not for SPS-transformed lines. When grown at 65 Pa CO2, SPS transformed lines had a 20% greater photosynthetic rate than controls when measured at 65 Pa CO2 and a 35% greater rate when measured at 105 Pa CO2. Photosynthetic rates were not different between lines when grown at 35 Pa CO2. The time to 50% blossoming was reduced and the total number of inflorescences was significantly greater for the SPS transformants when grown at either 35 or 65 Pa CO2. At 35 Pa CO2, the total fruit number of the SPS transformants was up to 1.5 times that of the controls, the fruit matured earlier, and there was up to a 32% increase in total fruit dry weight. Fruit yield was not significantly different between the lines when grown at 65 Pa CO2. Therefore, there was not a strict relationship between yield and leaf photosynthesis rate. Flowering and fruit development of the SPS-transformed lines grown at 35 Pa CO2 showed similar trends to the controls grown at 65 Pa CO2. Incidences of bios som-end rot were also reduced in the SPS-transformed lines. These data indicate that altering starch/sucrose partitioning by increasing the capacity for sucrose syn thesis can affect acclimation to elevated CO2 partial pressure and flowering and fruiting in tomato.

884^6^Pregitzer,KS^Zak,DR^Curtis,PS^Kubiske,ME^Teeri,JA^Vogel,CS^1995^1^Atmospheric co2, soil-nitrogen and turnover of fine roots^84^129^4^579-585^^^^^Apr^^^^^4568
312^374^417^664^formants when grown at either 35 or 65 Pa CO2. At 35 Pa CO2, the total fruit number of the SPS transformants was up to 1.5 times that of the controls, the fruit matured earlier, and there was up to a 32% increase in total fruit dry weight. Fruit yield was not significantly different between the lines when grown at 65 Pa CO2. Therefore, there was not a strict relationship between yield and leaf photosynthesis rate. Flowering and fruit development of tA^4567^In most natural ecosystems a significant portion of carbon fixed through photosynthesis is allocated to the production and maintenance of fine roots, the ephemeral portion of the root system that absorbs growth-limiting moisture and nutrients. In turn, senescence of fine roots can be the greatest source of C input to forest soils. Consequently, important questions in ecology entail the extent to which increasing atmospheric CO2 may alter the allocation of carbon to, and demography of, fine roots. Using microvideo and image analysis technology, we demonstrate that elevated atmospheric CO2 increases the rates of both fine root production and mortality. Rates of root mortality also increased substantially as soil nitrogen availability increased, regardless of CO2 concentration. Nitrogen greatly influenced the proportional allocation of carbon to leaves vs. fine roots. The amount of available nitrogen in the soil appears to be the most important factor regulating fine root demography in Populus trees.
 t885^3^Reddy,KR^Hodges,HF^McKinion,JM^1995^1^Carbon-dioxide and temperature effects on pima cotton growth^169^54^1-2^17-29^^^^^Jun^^^^^4570
1719^372^374^ts, the ephemeral portion of the root system that absorbs growth-limiting moisture and nutrients. In turn, senescence of fine roots can be the greatest source of C input to forest soils. Consequently, important questions in ecology entail the extent to which increasing atmospheric CO2 may alter the allocation of carbon to, and demography of, fine roots. Using microvideo and image analysis technology, we demonstrate that elevated atmospheric CO2 increases the rates of both fine root production and mortality. Rates of root mortality also increased substantially as soil nitrogen availability increased, regardless of CO2 concentration. Nitrogen greatly influenced the proportional allocation of carbon to leaves vs. fine roots. The amount of available nitrogen in the soil appears to be the most important factor regulating fine root demography in Populus trees.
 tA^4569^Temperature and CO2 are major environmental variables that affect plant growth and development. Limited information is available concerning how these factors affect plants, as well as specific interactions between the two. We conducted two experiments in controlled environmental chambers were temperature and CO2 were controlled and other environmental factors were not limiting. The purpose was to determine how cotton grew and responded to a range of temperatures and CO2 concentrations. During vegetative development, stem growth was quite sensitive to CO2 resulting in more effective early-season light capture. Plants did not develop more nodes when exposed to additional CO2, while node number increased more at higher temperatures. Individual leaf growth was about 18% greater at optimum temperature in 450 mul 1(-1) than in 350 mul 1(-1) CO2, but did not increase from 450 mul 1(-1) CO2 to 700 mul 1(-1) CO2. However, the time required for a leaf to reach mature size was not influenced by CO2. Leaf area, on the whole plant basis, was about 33% greater on plants grown at optimum temperature in high CO2 than in ambient CO2. The greater leaf area on a whole plant basis was achieved by a combination of larger leaves and additional leaves produced primarily on the branches. There was a 28% increase in number of bolls produced at 700 mul 1(-1) CO2 at optimum temperature compared with bolls produced at 350 mul 1(-1) CO2. There was not, however, an increase in boll size due to high CO2. At 35.5-degrees-C, little growth response to high CO2 environments occurred at 700 mul 1(-1) CO2 compared with 350 mul 1(-1) CO2, but approximately a 45% increase occurred in the plants grown at 18.9-26.9-degrees-C. Less total biomass was produced at 35.5- degrees-C than at 26.9-degrees-C and no bolls were produced in either CO2 environment at the higher temperature. The most important response to temperature and CO2 occurred at high temperatures where the effects of elevated CO2 on plant growth were masked by apparent high-temperature injury that limited growth of all plant organs, particularly, reproductive growth.

886^6^Robertson,EJ^Williams,M^Harwood,JL^Lindsay,JG^Leaver,CJ^Leech,RM^1995^1^Mitochondria increase 3-fold and mitochondrial proteins and lipid change dramatically in postmeristematic cells in young wheat leaves grown in elevated co2^8^108^2^469-474^^^^^Jun^^^^^4572
1720^243^310^312^376^with bolls produced at 350 mul 1(-1) CO2. There was not, however, an increase in boll size due to high CO2. At 35.5-degrees-C, little growth response to high CO2 environments occurred at 700 mul 1(-1) CO2 compared with 350 mul 1(-1) CO2, but approximately a 45% increase occurred in the plants grown at 18.9-26.9-degrees-C. Less total biomass was produced at 35.5- degrees-C than at 26.9-degrees-C and no bolls were produced in either CO2 environment at the higher temperature. The most important response to temperature and CO2 occurred at high temperatures where the effects of elevated CO2 on plant growth were masked by apparent high-temperaturA^4571^A dramatic stimulation in mitochondrial biogenesis during the very early stages of leaf development was observed in young wheat plants (Triticum aestivum cv Hereward) grown in elevated CO2 (650 mu L L(-1)). An almost 3-fold increase in the number of mitochondria was observed in the very young leaf cells at the base of the first leaf of a 7-d-old wheat plant. In the same cells large increases in the accumulation of a mitochondrial chaperonin protein and the mitochondrial 2- oxoglutarate dehydrogenase complex and pyruvate dehydrogenase complex were detected by immunolabeling. Furthermore, the basal segment also shows a large increase in the rate of radiolabeling of diphosphatidylglycerol, a lipid confined to the inner mitochondrial membrane. This dramatic response in very young leaf cells to elevated CO2 suggests that the numerous documented positive effects of elevated CO2 on wheat leaf development are initiated as early as 12 h postmitosis.
 CO2 on plant growth were masked by apparent high-temperatur887^3^Wang,ZM^Lechowicz,MJ^Potvin,C^1995^1^Responses of black spruce seedlings to simulated present versus future seedbed environments^155^25^4^545-554^^^^^Apr^^^^^4574
1617^1721^1722^243^372^377^57^58^672^92^)). An almost 3-fold increase in the number of mitochondria was observed in the very young leaf cells at the base of the first leaf of a 7-d-old wheat plant. In the same cells large increases in the accumulation of a mitochondrial chaperonin protein and the mitochondrial 2- oxoglutarate dehydrogenase complex and pyruvate dehydrogenase complex were detected by immunolabeling. Furthermore, the basal segment also shows a large increase in the rate of radiolabeling of diphosphatidylglycerol, a lipid confined to the inner mitochondrial membrane. This dramatic response in very young leaf cells to elevated CO2 suggests that the numerous documented positive effects of elevated CO2 on wheat leaf development are initiated as early as 12 h postmitosis.
 CO2 on plant growth were masked by apparent high-temperaturA^4573^We investigated the effects of nitrogen availability and present versus future atmospheric environments (i.e., climate) on the seedling performance of 16 open-pollinated maternal families of Picea mariana (Mill.) B.S.P. over two simulated growing seasons. Diurnal and seasonal patterns of temperature, relative humidity, photoperiod, and light intensity were simulated. The simulated future climate included both elevated CO2 and seasonally appropriate increases in mean monthly temperatures. Compared with the present, the future climate increased seedling survival, total and root dry mass, rate of winter bud development, net photosynthetic rate, and water and nitrogen use efficiencies; decreased needle nitrogen content; and altered biomass allocation patterns. Greater nitrogen availability greatly improved seedling performance and changed biomass allocation patterns. Climate and nitrogen level interacted synergistically to promote seedling growth (branch number and root dry mass), survival, and bud development. The future climate increased seedling survival, rate of bud development, and nitrogen use efficiency much more in the low than in the high nitrogen regime. Seedling performance in the second season was dependent on initial seed mass, but less than in the 1st year. Some of the differences among the families and in their interactions with the climate and (or) nitrogen fertilization suggest that families selected for rapid growth under present conditions may not do well in the future, at least in terms of early establishment. Forest managers and tree breeders should take this possibility into consideration in their tree improvement and reforestation programs.

888^3^White,NDG^Jayas,DS^Muir,WE^1995^1^Toxicity of carbon-dioxide at biologically producible levels to stored-product beetles^238^24^3^640-647^^^^^Jun^^^^^4576
1723^1724^1725^1726^314^409^llocation patterns. Climate and nitrogen level interacted synergistically to promote seedling growth (branch number and root dry mass), survival, and bud develoA^4575^The effect of concentrations of carbon dioxide (CO2) that can be produced by biological respiration (7.5-19.2%) on oviposition of adult Tribolium castaneum (Herbst), Cryptolestes pusillus (Schonherr), or C. ferrugineus (Stephens) was determined. Relative to controls, T. castaneum , C. pusillus , and C. ferrugineus , exposed to 7.5% CO2 for 1 wk, had numbers of offspring reduced by 43, 94, and 50%, respectively, and the total population at 6 wk was reduced 53, 84, and 19%, respectively. With levels of greater than or equal to 17.1% CO2 for 1 wk, no offspring were produced and exposed adults had high mortality. Eggs and subsequent immatures of Tribolium confusum J. du Val, T. castaneum, or C. ferrugineus were exposed for 3 wk to elevated levels of CO2 at 22 degrees C. Insect development was similar at 7.5 and 8.6% CO2 with mean mortality 43, 62, and 30% greater than controls for T. confusum, T. castancum, and C. ferrugineus, respectively. Also, mean levels of 5.8-8.3% CO2 for 7 wk reduced, on all sampling dates, populations of T. confusum by 85%, T. castaneum by 99%, C. pusillus by 68%, and C. ferrugineus by 54%. Although T. castaneum had a greater oviposition rate than C. pusillus at 7.5% CO2, immature mortality was greater for T. castaneum. Based on long-term exposure to levels of CO2 which can be produced by biological activity that affects oviposition and immature development, species in increasing order of sensitivity to CO2 are C. ferrugineus, C. pusillus, T. confusum, and T. castaneum.

889^2^Zhang,J^Lechowicz,MJ^1995^1^Responses to co2 enrichment by 2 genotypes of arabidopsis- thaliana differing in their sensitivity to nutrient availability^52^75^5^491-499^^^^^May^^^^^4578
1305^1727^1728^341^372^386^417^423^57^92^r 3 wk to elevated levels of CO2 at 22 degrees C. Insect development was similar at 7.5 and 8.6% CO2 with mean mortality 43, 62, and 30% greater than controls for T. confusum, T. castancum, and C. ferrugineus, respectively. Also, mean levels of 5.8-8.3% CO2 for 7 wk reduced, on all sampliA^4577^The responses of two genotypes of Arabidopsis thaliana, which differ in their sensitivities to nutrients to present and predicted future CO2 concentration were determined under rich vs. poor nutrient regimes on the basis of both single traits and the whole plant. Based on individual traits, the two genotypes responded similarly to CO2 enrichment for all the traits measured except for rate of increase in crown diameter, for which a decrease was observed in the less nutrient- sensitive genotype grown at increased CO2. Based on the overall response of the whole plant, by analysing groups of plant traits using multivariate analysis, the two genotypes differed substantially from one another and both responded more strongly to nutrient availability than to CO2 concentration, especially for traits measured at harvest that related to reproductive fitness. The less nutrient-sensitive genotype also showed a weaker overall response to CO2, and the pattern of the overall response was strikingly similar at different nutrient Supply. In contrast, the more nutrient-sensitive genotype responded more strongly to CO2 than the less nutrient-sensitive genotype, and responded differently to CO2 at low vs. high nutrient availability.

890^8^Akin,DE^Kimball,BA^Windham,WR^Pinter,PJ^Wall,GW^Garcia,RL^Lamorte,RL^Morrison,WH^1995^1^Effect of free-air co2 enrichment (face) on forage quality of wheat^260^53^1^29-43^^^^^May^^^^^4580
1141^1704^1729^672^or which a decrease was observed in the less nutrient- sensitive genotype grown at increased CO2. Based on the overall response of the whole plant, by analysing groups of plant traits using multivariate analysis, the two genotypes differed substantially from one another and both responded more strongly to nutrient availability than to CO2 concentration, especially for traits measured at harvest that related to reproductive fitness. The less nutrient-sensitive genotype also showed a weaker overall response to CO2, and the pattern of the overall response was strikingly similar at differeA^4579^Wheat (Triticum aestivum L., cultivar 'Yecora rojo') was grown in ambient (370 mu mol mol(-1)) or enriched (550 mu mol mol(- 1)) concentrations of CO2 in the free-air CO2 enrichment (FACE) project, and components were analyzed for in vitro digestibility, fiber constituents, and crude protein. Four replicated plots of each CO2 treatment were split for irrigation: 'wet' regions received 60 cm of water and 'dry' regions received 30 cm of water through underground tubes. Enriched CO2 concentrations had no effect on in vitro digestion of intact sections of young (26-32-day-old plants) leaf blades except at 24-27 h incubation, at which time enriched leaves were lower in digestibility than control ones. Enriched CO2 concentrations increased the content of acid detergent fiber (ADF) and cellulose of young wet leaves, Sections of main shoots at 26 days tended to have increased digestibility with elevated CO2 levels. Enriched CO2 concentrations did not alter the digestibility of flag leaves from 105-day-old plants or of flag leaves, uppermost stems, and sheaths from plants at full grain maturity, Enriched CO2 levels reduced the acid detergent lignin (ADL) and tended to reduce the protein of leaves from 105-day-old plants. For mature leaf blades, neutral detergent fiber, ADF, and cellulose were, or tended to be, higher while protein content tended to be lower in elevated CO2-grown plants; for both CO2 treatments, 'dry' leaves were higher in digestibility and lower in ADL than 'wet' samples. Mature stems plus sheaths had lower protein contents in plants grown in elevated CO2. Results indicated that enriched CO2 concentrations to 550 mu mol mol(-1) did not substantially alter wheat in vitro digestibility, regardless of irrigation treatment. Elevated CO2 altered fiber components and protein, but these were not consistent among parts and harvests.
s at 26 days tended to have increased digestibility with elevated CO2 levels. Enriched CO2 concentrations did not alter the digestibility of flag leaves from 105-day-old pla891^2^Boerner,REJ^Rebbeck,J^1995^1^Decomposition and nitrogen release from leaves of 3 hardwood species grown under elevated o-3 and/or co2^206^170^1^149-157^^^^^Mar^^^^^4582
1627^1730^243^312^344^361^374^447^461^874^r mature leaf blades, neutral detergent fiber, ADF, and cellulose were, or tended to be, higher while protein content tended to be lower in elevated CO2-grown plants; for both CO2 treatments, 'dry' leaves were higher in digestibility and lower in ADL than 'wet' samples. Mature stems plus sheaths had lower protein contents in plants grown in elevated CO2. Results indicated that enriched CO2 concentrations to 550 mu mol mol(-1) did not substantially alter wheat in vitro digestibility, regardless of irrigation treatment. Elevated CO2 altered fiber components and protein, but these were not consistent among parts and harvests.
s at 26 days tended to have increased digestibility with elevated CO2 levels. Enriched CO2 concentrations did not alter the digestibility of flag leaves from 105-day-old plaA^4581^Elevated concentrations of O-3 and CO2 have both been shown to affect structure, nutrient status, and deposition of secondary metabolites in leaves of forest trees. While such studies have produced robust models of the effects of such air pollutants on tree ecophysiology and growth, few have considered the potential for broader, ecosystem-level effects after these chemically and structurally altered leaves fall as leaf litter and decay. To determine the effects of elevated O-3 and/or CO2 on the subsequent decomposition and nutrient release from the leaves grown in such altered atmospheres, we grew seedlings of three widespread North American forest trees, black cherry (Prunus serotina) (BC), sugar maple (Acer saccharum) (SM), and yellow-poplar (Liriodendron tulipifera) (YP) for two growing seasons in charcoal-filtered air (CF-air=approximately 25% ambient O-3), ambient O-3 (1X) or twice-ambient O-3 (2X) in outdoor open-top chambers. We then assayed the loss of mass and N from the litter derived from those seedlings through one year litterbag incubations in the forest floor of a neighboring forest stand. Mass loss followed linear functions and was not affected by the O-3 regime in which the leaves were grown. Instantaneous decay rates (i.e. k values) averaged SM:-0.707 y(-1), BC:-0.613 y(-1), and YP:-0.859 y(-1). N loss from ambient (1X) O-3-grown SM leaves was significantly greater than from CF-air leaves; N loss from BC leaves did not differ among treatments. Significantly less N was released from CF-air-grown YP leaves than from 1X or 2X O-3-treated leaves. YP leaves from plants grown in pots at 2X O-3 and 350 ppm supplemental CO2 in indoor pollutant fumigation chambers (CSTRs or Continuously Stirred Tank Reactors) loss 40% as much mass and 27% as much N over one year as did leaves from YP grown in CF-air or 2X O-3. Thus, for leaves from plants grown in pots in controlled environment fumigation chambers, the concentrations of both O-3 and CO2 can affect N release from litter incubated in the field whereas mass loss rate was affected only by CO2. Because both mass loss and N release from leaves grown at elevated CO2 were reduced significantly (at least for yellow-poplar), forests exposed to elevated CO2 may have significantly reduced N turnover rates, thereby resulting in increased N limitation of tree growth, especially in forests which are already N-limited.

892^2^Brakke,M^Allen,LH^1995^1^Gas-exchange of citrus seedlings at different temperatures, vapor-pressure deficits, and soil-water contents^154^120^3^497-504^^^^^May^^^^^4584
1731^243^312^348^374^674^705^92^923^s from plants grown in pots at 2X O-3 and 350 ppm supplemental CO2 in indoor pollutant fumigation chambers (CSTRs or Continuously Stirred Tank Reactors) loss 40% as much mass and 27% as much N over one year as did leaves from YP grown in CF-air or 2X O-3. Thus, for leaves from plants grown in pots in controlled environment fumigation chambers, the concentrations of both O-3 and CO2 can affect N release from litter incubated in the field wherA^4583^Midday reductions of stomatal conductance and carbon dioxide assimilation rates (A(CO2)) in Citrus are typically attributed to large leaf-to-air vapor-pressure differences or high atmospheric vapor-pressure deficits (VPD). This study investigated air temperature (T-a) and available soil water (ASW) level as corollary factors of atmospheric VPD that influence midday reduction of net gas exchange in citrus leaves. The influence of elevated atmospheric CO2 under conditions that inhibit net canopy A(CO2) was also investigated. Net canopy A(CO2) and evapotranspiration rates of Carrizo citrange [Poncirus trifoliata Raf x Citrus sinensis (L.) Osbeck] and Swingle citrumelo (P. trifoliata Raf x C. paradisii Macf.) seedlings grown in outdoor controlled- environment growth chambers were measured under two levels of T-a with concomitant changes in VPD and two levels of atmospheric CO2 concentration, which were changed in steps over time. Cyclical depletion of ASW was allowed to occur at each set of T-a/VPD and CO2 combinations. Highest net canopy A(CO2) rates at ambient CO2 concentration (330 mu mol . mol(-1)) were obtained at the low T-a/VPD level (29C/2.4 kPa) and ASW >50%. Diurnal canopy CO2 uptake rates decreased at the high T-a/VPD level (37C/3.6 kPa), and midday depression of canopy A(CO2) was observed at ASW levels <50%. Net canopy A(CO2) decreased at higher levels of ASW under the high T-a/VPD treatment than at the low T-a/VPD treatment. At the elevated CO2 concentration (840 mu mol . mol(-1)) net canopy CO2 uptake rates were double those that occurred at ambient CO2 levels and they did not exhibit midday reduction. Our data indicate that, when soil water is not readily available, citrus seedlings are more sensitive to high levels of T-a and VPD which results in reduction of CO2 uptake. The inhibitory effects of elevated VPD and reduced ASW on citrus net A(CO2) were lessened at the elevated atmospheric CO2 level.
n steps over time. Cyclical depletion of ASW was allowed to occur at each set of T-a/VPD and CO893^1^Bunce,JA^1995^1^The effect of carbon-dioxide concentration on respiration of growing and mature soybean leaves^9^18^5^575-581^^^^^May^^^^^4586
1035^240^349^372^389^441^722^782^92^uptake rates decreased at the high T-a/VPD level (37C/3.6 kPa), and midday depression of canopy A(CO2) was observed at ASW levels <50%. Net canopy A(CO2) decreased at higher levels of ASW under the high T-a/VPD treatment than at the low T-a/VPD treatment. At the elevated CO2 concentration (840 mu mol . mol(-1)) net canopy CO2 uptake rates were double those that occurred at ambient CO2 levels and they did not exhibit midday reduction. Our data indicate that, when soil water is not readily available, citrus seedlings are more sensitive to high levels of T-a and VPD which results in reduction of CO2 uptake. The inhibitory effects of elevated VPD and reduced ASW on citrus net A(CO2) were lessened at the elevated atmospheric CO2 level.
n steps over time. Cyclical depletion of ASW was allowed to occur at each set of T-a/VPD and COA^4585^Soybean plants were grown continuously at 350 and 700cm(3)m(-3) CO2 at constant temperature, Respiration rates of third trifoliolate leaves were measured at the growth CO2 concentration for the whole dark period from 5d before through to 5d after full area expansion, The short-term response of respiration rate to the measurement CO2 concentration was also determined at each age, Respiration rates per unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO2. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO2 concentrations, The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO2 treatments, The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respiration from total respiration was negative in rapidly growing leaves for both CO2 treatments, This indicates that CO2 efflux in the dark does not accurately reflect the average 24h rate of energy expenditure on growth and maintenance for soybean leaves.

894^1^Bunce,JA^1995^1^Effects of elevated carbon-dioxide concentration in the dark on the growth of soybean seedlings^52^75^4^365-368^^^^^Apr^^^^^4588
130^310^r unit of dry mass declined with age and were significantly less at a given age or RGR in leaves grown and measured at the elevated CO2. The difference in respiration rate was largest in mature leaves and resulted from the different measurement CO2 concentrations, The respiratory costs of the tissue synthesis, estimated from the elemental composition of the tissue, did not differ substantially between CO2 treatments, The response of respiration rate to carbon dioxide concentration was not strongly affected by the form of nitrogen supplied. Maintenance respiration calculated by subtracting growth respirationA^4587^Previous work has shown that elevated carbon dioxide (CO2) concentrations in the dark reversibly reduce the rate of CO2 efflux from soybeans. Experiments were performed exposing soybean plants continually to concentrations of 350 or 700 cm(3) m(-3) for 24 h d(-1), or to 350 during the day and 700 cm(3) m(-3) at night, in order to determine the importance of the reduced rate of dark CO2 efflux for plant growth. High CO2 applied only at night conserved carbon and increased dry mass during initial growth compared with the constant 350 cm(3) m-3 treatment. Long-term net assimilation rate was increased by high CO2 in the dark, without any increase in daytime leaf photosynthesis. However, leaf area ratio was reduced by the dark CO2 treatment to values equal to those of plants continually exposed to the higher concentration. From days 14- 21, leaf area was less for the elevated night-time CO2 treatment than for either the constant 350 or 700 cm(3) m(-3) treatments. For the day 7-21-period, relative growth rate was significantly reduced by the high night CO2 treatment compared with the 350 cm(3) m(-3) continuous treatment. The results indicate that some functionally significant component of respiration was reduced by the elevated CO2 concentration in the dark.

895^3^Carter,GA^Rebbeck,J^Percy,KE^1995^1^Leaf optical-properties in liriodendron-tulipifera and pinus- strobus as influenced by increased atmospheric ozone and carbon-dioxide^155^25^3^407-412^^^^^Mar^^^^^4590
1732^1733^1734^348^372^374^57^864^965^growth compared with the constant 350 cm(3) m-3 treatment. Long-term net assimilation rate was increased by high CO2 in the dark, without any increase in daytime leaf photosynthesis. However, leaf area ratio was reduced by the dark CO2 treatment to values equal to those of plants continually exposed to the higher concentration. From days 14- 21, leaf area was less for the elevated night-time CO2 treatment than for either the constant 350 or 700 cm(3) m(-3) treatments. For the day 7-21-period, relative growth raA^4589^Seedlings of Liriodendron tulipifera L. and Pinus strobus L. were grown in open-top chambers in the field to determine leaf optical responses to increased ozone (O-3) or O-3 and carbon dioxide (CO2). In both species, seedlings were exposed to charcoal-filtered air, air with 1.3 times ambient O-3 concentrations (1.3X), or air with 1.3 times ambient O-3 and 700 mu L . L(-1) CO2 (1.3X + CO2). Exposure to 1.3X increased reflectance in the 633-697 nm range in L. tulipifera. Also, 1.3X decreased transmittance within the 400-420 nm range, increased transmittance at 686-691 nm, and decreased absorptance at 655-695 nm. With 700 mu L . L(-1) CO2, O-3 did not affect reflectance in L. tulipifera, but decreased transmittance and increased absorptance within the 400-421 nm range and increased transmittance and decreased absorptance in the 694-697 nm range. Under 1.3X, reflectance in P. strobus was not affected. However, 1.3X + CO2 increased pine reflectance in the 538-647, 650, and 691-716 nm ranges. Transmittances and absorptances were not determined for P. strobus. Reflectance in both species, and transmittance and absorptance in L. tulipifera, were most sensitive to O-3 near 695 nm. Reflectance at 695 nm, but particularly the ratio of reflectance at 695 nm to reflectance at 760 nm, was related closely to ozone-induced decreases in leaf chlorophyll contents, particularly chlorophyll a (r(2) = 0.82).

896^2^Ceulemans,R^Mousseau,M^1995^1^Effects of elevated atmospheric co2 on woody-plants (vol 12m, pg 425, 1995)^84^129^3^535^^^^^Mar

897^3^Chen,XM^Begonia,GB^Hesketh,JD^1995^1^Soybean stomatal acclimation to long-term exposure to co2- enriched atmospheres^79^31^1^51-57^^^^^^^^^^4593
312^349^426^ifera, but decreased transmittance and increased absorptance within the 400-421 nm range and increased transmittance and decreased absorptance in the 694-697 nm range. Under 1.3X, reflectance in P. strobus was not affected. However, 1.3X + CO2 increased pine reflectance in the 538-647, 650, and 691-716 nm ranges. TransmittancesA^4592^Soybean [Glycine max (L.) cv. Jack] grown in open top chambers under controlled laboratory and field conditions was used to study the acclimation of leaf gas exchange processes to CO2 enrichment. Air inside the open top chambers was maintained at either 700-800 or 350-400 mu mol(CO2) mol(-1)(air). Leaf gas exchange rates were measured for some plants switched between treatments. When measured in the CO2-enriched atmosphere, stomatal conductances (g(s)) were higher in leaves grown in CO2-enriched atmospheres than in those grown under ambient conditions, and the lower g(s) values for plants in the CO2- enriched atmospheres were limiting to leaf net photosynthetic CO2 exchange rates (P-N). P-N of enriched leaves was higher than those of the ambient controls when measured at elevated CO2 levels in both controlled environment and field studies, while it was depressed in enriched leaves when measured under ambient CO2 conditions, and this drop in P-N did not recover until 6-15 d after plants were placed back in ambient conditions.

898^4^Ellis,RH^Craufurd,PQ^Summerfield,RJ^Roberts,EH^1995^1^Linear relations between carbon-dioxide concentration and rate - of development towards flowering in sorghum, cowpea and soybean^52^75^2^193-198^^^^^Feb^^^^^4595
130^1735^1736^1737^227^349^372^434^92^CO2) mol(-1)(air). Leaf gas exchange rates were measured for some plants switched between treatments. When measured in the CO2-enriched atmosphere, stomatal conductances (g(s)) were higher in leaves grown in CO2-enriched atmospheres than in those grown under ambient conditions, and the lower g(s) values for plants in the CO2- enriched atmospheres were limiting to leaf net photosynthetic CO2 exchange rates (P-N). P-N of enriched leaves was higher than those of the ambient controls when measured at elevated CO2 levels in both controlled environment and field studies, while it was depressed in enriched leaves when measured under ambient CO2 conditions, and this drop in P-N did not recover until 6-15 d after plants were placed bacA^4594^Negative linear relations were detected (P < 0.005) between the rate of progress from sowing to panicle initiation and CO2 concentration (210-720 mu mol CO2 mol(-1) air) for two genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relations between CO2 concentration and the rate of progress from sewing to first flowering were also negative in soyabean [Glycine max (L). Merrill] (P < 0.025), but positive in cowpea [Vigna unguiculata (L.) Walp.] (P < 0.025), albeit that in both grain legumes sensitivity was much less than in sorghum. Thus CO2 elevation does not delay flowering in all short-day species. The considerable effect of CO2 concentration on times to panicle initiation resulted in large differences among the sorghum plants at this developmental stage; with increase in CO2 concentration, plants were taller with slightly more leaves and more pronounced apical extension. At the same time after sowing however, sorghum plants were heavier (P < 0.05) at 210 than at 360 mu mol CO2 mol(-1) air. In contrast, relations between the dry masses of the soyabean and cowpea plants and CO2 concentration were positive and curvilinear (P < 0.05). It is suggested that the impact of global environmental change could be severe for sorghum production in the semi-arid tropics.

899^1^Ericsson,T^1995^1^Growth and shoot - root ratio of seedlings in relation to nutrient availability^206^169^^205-214^^^^^Jan-Feb^^^^^4597
1344^1360^1443^1738^1739^243^372^639^820^953^] (P < 0.025), albeit that in both grain legumes sensitivity was much less than in sorghum. Thus CO2 elevation does not delay flowering in all short-day species. The considerable effect of CO2 concentration on times to panicle initiation resulted in large differences among the sorghum plants at this developmental stage; with increase in CO2 concentration, plants were taller with slightly more leaves and more pronounced apical extension. At the same time after sowing however, sorghum plants were heavier (P < 0.05) at 210 than at 360 mu mol CO2 mol(-1) air. In contraA^4596^The influence of mineral nutrient availability, light intensity and CO2 on growth and shoot:root ratio in young plants is reviewed. Special emphasis in this evaluation is given to data from laboratory experiments with small Betula pendula plants, in which the concept of steady-state nutrition has been applied. Three distinctly different dry matter allocation patterns were observed when growth was limited by the availability of mineral nutrients: 1, Root growth was favoured when N, P or S were the major growth constraints. 2, The opposite pattern obtained when K, Mg and Mn restricted growth. 3, Shortage of Ca, Fe and Zn had almost no effect on the shoot:root ratio. The light regime had no effect on dry matter allocation except at very low photon flux densities (< 6.5 mol m(-2) day(-1)), in which a small decrease in the root fraction was observed. Shortage of CO2 on the other hand, strongly decreased root development, while an increase of the atmospheric CO2 concentration had no influence on dry matter partitioning. An increased allocation of dry matter to below- ground parts was associated with an increased amount of starch in the tissues. Depletion of the carbohydrate stores occurred under all conditions in which root development was inhibited. It is concluded that the internal balance between labile nitrogen and carbon in the root and the shoot system determines how dry matter is being partitioned in the plant. The consistency of this statement with literature data and existing models for shoot:root regulation is examined.

900^1^Hanninen,H^1995^1^Effects of climatic-change on trees from cool and temperate regions - an ecophysiological approach to modeling of bud burst phenology^188^73^2^183-199^^^^^Feb^^^^^4599
1173^1263^1740^1741^1742^1743^1744^361^417^586^s (< 6.5 mol m(-2) day(-1)), in which a small decrease in the root fraction was observed. Shortage of CO2 on the other hand, strongly decreased root development, while an increase of the atmospheric CO2 concentration had no influence on dry matter A^4598^A framework is presented for meddling bud burst phenology of trees from the cool and temperate regions. Three ecophysiological aspects affecting the timing of bud burst are considered: (i) effects of environmental factors on the rest status of the bud, (ii) effect of rest status on the ability for bud burst, and (iii) direct effect of air temperature on the rate of development towards bud burst. Any model for bud burst phenology can be presented within the framework with three submodels, each of them addressing one of the corresponding three ecophysiological aspects. A total of 96 hypothetical models were synthesized by combining submodels presented in the literature. The models were tested in two experiments with saplings of Pinus sylvestris L. growing in experimental chambers at their natural site in eastern Finland. In the first experiment, air temperature and (or) concentration of atmospheric CO2 was elevated. Elevation of the air temperature hastened bud burst, whereas elevation of the concentration of CO2 did not affect it. Several models accurately predicted the timing of bud burst for natural conditions but too early for bud burst at the elevated temperatures. This finding suggests that (i) the risk of a premature bud burst with subsequent frost damage, as a result of climatic warming, was overestimated in a recent simulation study, and (ii) bud burst observations in natural conditions alone are not sufficient for the testing of these mechanistic models. Several models did predict the timing of bud burst accurately for all treatments, but none of them obtained sufficiently strong support from the findings to stand out as superior or uniquely correct. In the second experiment a photoperiod submodel for rest break was tested by exposing the saplings to short-day conditions. The short-day treatment had only a minor effect on the timing of bud burst. These results demonstrated the importance of the concept of model realism: the accuracy of a model can be lost in new conditions (e.g., global warming), unless the model correctly addresses the essential ecophysiological aspects of the regulation of timing of bud burst.

901^4^Hunt,R^Hand,DW^Hannah,MA^Neal,AM^1995^1^Temporal and nutritional influences on the response to elevated co2 in selected british grasses^52^75^2^207-216^^^^^Feb^^^^^4601
1745^1746^230^312^361^376^57^705^803^999^on study, and (ii) bud burst observations in natural conditions alone are not sufficient for the testing of these mechanistic models. Several models did predict the timing of bud burst accurately for all treatments, but none of them obtained sufficiently strong support from the findings to stand out as superior or uniquely correct. In the second experiment a photoperiod submodel for rest break was tested by exposing the saplings to short-day conditions. The short-day treatment had only a minor effect on the timing of bud burst. These results demonstrated the importance of the concept of model realism: the accuracy of a model can be lost in new conditions (e.g., global warming),A^4600^To investigate the duration of the CO2 response and its interaction with mineral nutrition, CO2-enrichment experiments were performed on four British grasses of differing ecology and functional type: Arrhenatherum elatius (L.) Beauv., Festuca ovina L., Festuca rubra L. and Poa annua L. Naturally-lit, glasshouse cabinets were used, with a non-limiting water supply and a daytime mean temperature of 18 degrees C. Two CO2 treatments were maintained at nominal concentrations of 350 and 700 vpm and were combined factorially with two levels of balanced mineral nutrition at conductivities of 0.1 and 1 mS cm(-1). Harvests took place at planting-out, and at 16, 37 and 58 d thereafter. Fitted curves were used to derive instantaneous values of total dry weight, relative growth rate (RGR), shoot weight fraction (SWF) and unit shoot rate (USR) for all combinations of species, CO2 level, nutrient level and time of harvesting. At the higher nutrient level there was a reasonably close agreement with previous estimates of the CO2 response in the four species. The response, if any, most often arose from an increase in USR being accompanied by a less than proportionate decline in SWF. Responses were sustained throughout the period studied. At the lower nutrient level, all species showed a CO2 response initially, but this declined at a rate which was inversely related to the CO2- responsiveness of the species at the higher nutrient level. The underlying ontogenetic drift appeared to be markedly towards adjustment in SWF and away from that of USR. However, this drift was retarded, suspended or even reversed by low-nutrient conditions and/or by high CO2 responsiveness in the species itself.

902^3^Johnson,DW^Ball,T^Walker,RF^1995^1^Effects of elevated co2 and nitrogen on nutrient-uptake in ponderosa pine-seedlings^206^169^^535-545^^^^^Jan-Feb^^^^^4603
1747^344^362^376^392^407^512^666^669^672^evel, nutrient level and time of harvesting. At the higher nutrient level there was a reasonably close agreement with previous estimatesA^4602^This paper reports on the results of a controlled-environment study on the effects of CO2 (370, 525, and 700 mu mol mel(-1)) and N [0, 200, and 400 mu g N g soil(-1) as (NH4)SO4] on ponderosa pine (Pinus ponderosa) seedlings. Based upon a review of the literature, we hypothesized that N limitations would not prevent a growth response to elevated CO2. The hypothesis was not supported under conditions of extreme N deficiency (no fertilizer added to a very poor soil), but was supported when N limitations were less severe but still suboptimal (lower rate of fertilization), The growth increases in N-fertilized seedlings occurred mainly between 36 and 58 weeks without any additional N uptake. Thus, it appeared that elevated CO2 allowed more efficient use of internal N reserves in the previously-fertilized seedlings, whereas internal N reserves in the unfertilized seedlings were insufficient to allow this response, Uptake rates of other nutrients were generally proportional to growth. Nitrogen treatment caused reductions in soil exchangeable K+, Ca2+, and Mg2+ (presumably because of nitrification and NO3- leaching) but increases in extractable P (presumably due to stimulation of phosphatase activity). The results of this and other seedling studies show that elevated CO2 causes a reduction in tissue N concentration, even under N- rich conditions. The unique response of N is consistent with the hypothesis that the efficiency of Rubisco increases with elevated CO2. These results collectively have significant implications for the response of mature, N-deficient forests to elevated CO2.

903^1^Kennedy,AD^1995^1^Temperature effects of passive greenhouse apparatus in high- latitude climate-change experiments^43^9^2^340-350^^^^^Apr^^^^^4605
1615^1668^1748^1749^30^372^374^672^691^92^erves in the previously-fertilized seedlings, whereas internal N reserves in the unfertilized seedlings were insufficient to allow this response, Uptake rates of other nutrients were generally proportional to growth. Nitrogen treatment causA^4604^1. Passive greenhouse apparatus is commonly used to investigate the in situ biological response of terrestrial communities to global warming. 2. Although close conformity of greenhouse treatment effects to general circulation model (GCM) scenarios is widely claimed, no proof of such a relationship has yet been published. 3. Here, the relationship between passive greenhouse thermal environment and future climate conditions is considered using temperature data collected from within and without greenhouses deployed in the maritime Antarctic. It is revealed that in terms of thermal extremes, diel and annual variation, and overall distribution across the temperature spectrum, such apparatus achieves only poor simulation of GCM forecasts. 4. During summer, greenhouses induce an amplified daily range of temperatures, elevated maxima and accelerated rates of change. 5. During spring and autumn, diel temperature variation continues inside the greenhouses while snow cover protects the controls. 6. During winter, an inverse treatment effect occurs, in which the relative depth of snow cover causes lower temperatures in greenhouses than in controls. 7. These treatment effects differ significantly from GCM climate predictions. Changes recorded in the composition, structure and function of greenhouse biota may thus be artefacts of the methodology. 8. Thorough a priori testing of greenhouse treatment effects is recommended for future climate change studies that are to be conducted in environments subject to seasonal snowfall, solar elevation and day length.

904^1^Kerstiens,G^1995^1^Cuticular water permeance of european trees and shrubs grown in polluted and unpolluted atmospheres, and its relation to stomatal response to humidity in beech (fagus-sylvatica L)^84^129^3^495-503^^^^^Mar^^^^^4607
1750^1751^312^348^386^447^466^467^674^798^ed maxima and accelerated rates of change. 5. During spring and autumn, diel temperature variation continues inside the greenhouses while snow cover protects the controls. 6. During winterA^4606^Cuticular water permeance (P) of astomatous adaxial surfaces of intact leaves was determined in Acer pseudoplatanus L., Betula pubescens Ehrh., Corylus avellana L., Fagus sylvatica L. and Prunus avium L. Water evaporating from the stomata-bearing abaxial leaf surface could not reach the moisture analyzer and the values of P presented here are therefore free from errors that often arise from unintentional inclusion of residual stomatal transpiration. Plants were exposed from before bud- break for several months to 20-50 ppb SO2 (Fagus), a combination of 50-60 ppb SO2 and 50-60 ppb NO2 (Betula), 300- 400 ppb NO (Acer, Corylus, Fagus), regular ozone episodes of up to 120 ppb (Fagus, Prunus), or an elevated level of CO2 (600 ppm for 2 yr; Acer, Fagus). Permeances were in the range 0.6- 2.9 x 10(-5) m s-1 and were unaffected by most treatments. In Prunus, P increased slightly but significantly in the NO treatment. In Corylus and Fagus, P was sometimes found to be reduced by fumigation with NO, but not always. Betula leaves grown under elevated SO2 and NO2 showed higher values of P only if they were visibly damaged. Minimum conductances (g(min) estimated from water loss rates of both sides of detached hypostomatous leaves were higher than P, and were more strongly affected by treatments. In these cases, the most probable explanation is some damage to stomatal function resulting in a reduced ability to close after leaf excision. Effects of growing conditions and time of year on P were found, which allowed a hypothetical interaction between P and stomatal sensitivity to air humidity to be tested in beech. No unambiguous indication of such a relationship was found.

905^1^Koike,T^1995^1^Effects of co2 in interaction with temperature and soil fertility on the foliar phenology of alder, birch, and maple seedlings^188^73^2^149-157^^^^^Feb^^^^^4609
1114^1344^1752^342^345^372^376^385^708^92^significantly in the NO treatment. In Corylus and Fagus, P was sometimes found to be reduced by fumigation with NO, but not alwaA^4608^The foliar phenology of potted 1-year-old seedlings of alder (Alnus hirsuta Turcz.), maple (Acer mono Maxim.), and birch (Betula platyphylla Sukatch, var. japonica Hara) was observed from May to September in eight growth environments: factorial combinations of temperatures (light:dark, 30:20 degrees C and 26:16 degrees C), CO2 level (70 and 36 Pa), and nutrient regime (high versus low levels of fertilization). Seedlings grown at high fertility always had more leaves, and under high CO2, shed leaves slightly later than seedlings grown at low fertility. Except for maple, production of newly formed shoots and leaves was accelerated by high CO2. In maple, high CO2 only increased the number of flushes of the leader shoot. Alder and birch accelerated sylleptic shoot and leaf production at high CO2 in fertile conditions. The production of new leaves by alder grown at high CO2 and low fertility was almost the same as that grown under normal CO2 at high fertility. At high CO2, the timing of winter bud formation of monopodial alder and maple was delayed, while that of sympodial birch was almost the same as at ambient CO2.

906^3^Korner,C^Pelaezriedl,S^Vanbel,AJE^1995^1^Co2 responsiveness of plants - a possible link to phloem loading^9^18^5^595-600^^^^^May^^^^^4611
130^348^374^376^398^442^92^:dark, 30:20 degrees C and 26:16 degrees C), CO2 level (70 and 36 Pa), and nutrient regime (high versus low levels of fertilization). Seedlings grown at high fertility always had more leaves, and under high CO2, shed leaves slightly later than seedlings grown at low fertility. Except for maple, production of newly formed shoots and leaves was accelerated by high CO2. In maple, high CO2 only increased the number of flushes of the leader shoot. Alder and birch accelerated sylleptic shoot and leaf production at high CO2 in fertile conditions. The production of new leaves by alder grown at high CO2 and low fertility was almost the same as that grown under normal CO2 at high fertility. At high CO2, the timing of winter bud formatioA^4610^Of the many responses of plants to elevated CO2, accumulation of total non-structural carbohydrates (TNC in % dry weight) in leaves is one of the most consistent, Insufficient sink activity or transport capacity may explain this obvious disparity between CO2 assimilation and carbohydrate dissipation and structural investment, If transport capacity contributes to the problem, phloem loading may be the crucial step, It has been hypothesized that symplastic phloem loading is less efficient than apoplastic: phloem loading, and hence plant species using the symplastic pathway and growing under high light and good water supply should accumulate more TNC at any given CO2 level, but particularly under elevated CO2. We tested this hypothesis by carrying out CO2 enrichment experiments with 28 plant species known to belong to groups of contrasting phloem loading type. Under current ambient CO2 symplastic loaders were found to accumulate 36% TNC compared with only 19% in apoplastic loaders (P = 0.0016), CO2 enrichment to 600 mu mol mol(-1) increased TNC in both groups by the same absolute amount, bringing the mean TNC level to 41% in symplastic loaders (compared to 25% in apoplastic loaders), which may be close to TNC saturation (coupled with chloroplast malfunction), Eight tree species, ranked as symplastic loaders by their minor vein companion cell configuration, showed TNC responses more similar to those of apoplastic herbaceous loaders, Similar results are obtained when TNC is expressed on a unit leaf area basis, since mean specific leaf areas of groups were not significantly different, We conclude that phloem loading has a surprisingly strong effect on leaf tissue composition, and thus may translate into alterations of food webs and ecosystem functioning, particularly under high CO2.

907^3^Lindroth,RL^Arteel,GE^Kinney,KK^1995^1^Responses of 3 saturniid species to paper birch grown under enriched co2 atmospheres^43^9^2^306-311^^^^^Apr^^^^^4613
57^ared with only 19% in apoplastic loaders (P = 0.0016), CO2 enricA^4612^1. Interactions between trees and tree-feeding insects are likely to shift under conditions of enriched atmospheric CO2 owing to changes in foliar chemical composition. This study addressed the effects of CO2-mediated changes in leaf chemistry on performance of three silkmoth (Saturniidae) species: cecropia (Hyalophora cecropia), luna (Actias luna) and polyphemus (Antheraea polyphemus polyphemus). 2. Growth under elevated CO2 atmospheres decreased nitrogen concentrations (23%) but tripled starch and doubled condensed tannin concentrations, resulting in a marked increase in foliar carbon:nitrogen ratio. 3. Survival of first stadium larvae was marginally reduced when reared on high CO2 leaves. 4. Development rates were prolonged, growth rates tended to decline, consumption increased and food processing efficiencies decreased for fourth stadium larvae reared on high CO2 leaves. The magnitude of responses varied among species. 5. Overall performance of these saturniid species, at least when feeding on birch, is predicted to decline under atmospheric CO2 conditions anticipated for the next century.

908^1^Murray,DR^1995^1^Plant-responses to carbon-dioxide^5^82^5^690-697^^^^^May^^^^^4615
1345^1753^1754^389^399^436^506^733^745^92^
A^4614^The average atmospheric concentration of CO2 will probably double before the end of next century. Many of the consequences for plant growth can and should be determined now. In this review the effects of [CO2] on a variety of plant processes are summarized: stomatal opening and closing; stomatal density; respiration; root morphogenesis; and flowering. The effects of growth under elevated [CO2] on crop yield and seed composition are also discussed. Adverse effects on the composition of C-3 cereal grains are clearly indicated.

909^3^Nicolussi,K^Bortenschlager,S^Korner,C^1995^1^Increase in tree-ring width in sub-alpine pinus-cembra from the central alps that may be co2-related^252^9^4^181-189^^^^^Apr^^^^^4617
l performance of these saturniid species, at least when feeding on birA^4616^It has been suggested many times that elevated atmospheric CO2 levels should stimulate radial increment of stem growth. However, interpretation of dendrochronologies with respect to a CO2 signal is a difficult task, since a multitude of environmental and tree factors influence the growth of stems. Here we provide a data set from subalpine stone pine which covers the period from 1750 to 1988, and from which growth rings of the 80- to 90-year age class were analysed. The most common climatological effects are taken into consideration. We found a steady and significant increase of mean ring width for the considered age class from approximately 1 mm per year in the middle of the last century to about 1.4 mm per year at present. Selected periods of equal mean summer temperatures in the last century and in more recent decades still yield a mean stimulation of about 25% for which atmospheric CO2 enrichment appears to be the most plausible explanation. The recent dramatic increase of atmospheric N-deposition could confound this interpretation, but chronologies of the last 2 decades during which wet and dry deposition of N-compounds showed the most dramatic increase exhibit no deviation from the long term trend. In contrast to the so far conflicting evidence of tree- ring responses to atmospheric changes the clear signal obtained here may be explained as follows: (1) stone pine produces little late season wood and moisture is never a limiting factor (particularly not in the early season); (2) comparatively good climatic records permitted the selection of thermally comparable periods; (3) trees grew under little spatial competition, (4) cores were collected well below the upper altitudinal range-limit of stone pine, leaving enough physiological leeway under episodic climatic stress, but (5) trees grew at altitudes high enough so that the reduction of the partial pressure of CO2 could be expected to cause CO2 to become relatively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition 910^1^Pajari,B^1995^1^Soil respiration in a poor upland site of scots pine stand subjected to elevated-temperatures and atmospheric carbon concentration^206^169^^563-570^^^^^Jan-Feb^^^^^4619
174^314^362^672^n contrast to the so far conflicting evidence of tree- ring responses to atmospheric changes the clear signal obtained here may be explained as follows: (1) stone pine produces little late season wood and moisture is never a limiting factor (particularly not in the early season); (2) comparatively good climatic records permitted the selection of thermally comparable periods; (3) trees grew under little spatial competition, (4) cores were collected well below the upper altitudinal range-limit of stone pine, leaving enough physiological leeway under episodic climatic stress, but (5) trees grew at altitudes high enough so that the reduction of the partial pressure of CO2 could be expected to cause CO2 to become relatively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition A^4618^Soil respiration rates under elevated temperature and atmospheric CO2 concentrations were studied in eastern Finland (62 degrees 47'N, 30 degrees 58'E, 144 m.a.s.l.) around naturally regenerated 20 - 30 years old Scots pine trees, enclosed in open top chambers. The production of CO2 varied spatially and temporally, but clearly followed the changes in temperature measured at the soil surface. However, soil respiration in the open control was higher than that in chambers; i.e. the chamber itself changed the conditions by increasing the temperature, altering the movement of water, and thereby soil moisture, Nevertheless, an elevation in the concentration of atmospheric CO2 raised soil respiration and brought it nearer to the level in the open control. An increase in temperature seemed to inhibit this rise, possibly because of an imbalance between temperature and moisture.
 be expected to cause CO2 to become relatively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition 911^3^Penuelas,J^Biel,C^Estiarte,M^1995^1^Growth, biomass allocation, and phenology responses of pepper to elevated co2 concentrations and different water and nitrogen supply^79^31^1^91-99^^^^^^^^^^4621
130^1628^229^341^344^400^417^434^442^962^d in open top chambers. The production of CO2 varied spatially and temporally, but clearly followed the changes in temperature measured at the soil surface. However, soil respiration in the open control was higher than that in chambers; i.e. the chamber itself changed the conditions by increasing the temperature, altering the movement of water, and thereby soil moisture, Nevertheless, an elevation in the concentration of atmospheric CO2 raised soil respiration and brought it nearer to the level in the open control. An increase in temperature seemed to inhibit this rise, possibly because of an imbalance between temperature and moisture.
 be expected to cause CO2 to become relatively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition A^4620^Fifty-day old plants of Capsicum annuum L. with two developed leaves were placed into controlled environment chambers at atmospheric (350 cm(3) m(-3), ACO(2)) and elevated (700 cm(3) m(-3), ECO(2)) CO2 concentrations under different nitrogen and water supply. Plant response to ECO(2) and the modulating effect of the availability of nitrogen and water were evaluated. CO2 effects were significant only after 40 d of treatment. An increase in plant growth and yield was found in ECO(2) plants only under a good supply of both water (HW) and nitrogen (HN). Chlorophyll concentration responded only to N supply. Root/shoot ratio was higher under ECO(2) only under low N (LN) and low water (LW) supply. Leaf area and specific leaf area decreased under ECO2. Flowering and fructification took place earlier in ECO(2) under HN and HW. Thus, all CO2 effects were modulated by the N and water supply and the duration of exposure.
ively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition 912^3^Polley,HW^Johnson,HB^Mayeux,HS^1995^1^Nitrogen and water requirements of C3 plants grown at glacial to present carbon-dioxide concentrations^43^9^1^86-96^^^^^Feb^^^^^4623
1755^1756^1757^1758^344^372^374^384^437^672^s under different nitrogen and water supply. Plant response to ECO(2) and the modulating effect of the availability of nitrogen and water were evaluated. CO2 effects were significant only after 40 d of treatment. An increase in plant growth and yield was found in ECO(2) plants only under a good supply of both water (HW) and nitrogen (HN). Chlorophyll concentration responded only to N supply. Root/shoot ratio was higher under ECO(2) only under low N (LN) and low water (LW) supply. Leaf area and specific leaf area decreased under ECO2. Flowering and fructification took place earlier in ECO(2) under HN and HW. Thus, all CO2 effects were modulated by the N and water supply and the duration of exposure.
ively more limiting than at low elevations.
 dramatic increase of atmospheric N-deposition A^4622^1. Nitrogen- and water-use efficiencies in biomass production were determined for three C3 plant species at carbon dioxide concentrations ([CO2]) that spanned glacial to present atmospheric levels [200-350 mumol CO2 (mol air)-1]. The species were annual grasses Bromus tectorum and Triticum aestivum (two cultivars) and a woody perennial Prosopis glandulosa (alone and in mixtures with the C4 grass, Schizachyrium scoparium). 2. Changes in nitrogen- and water- use efficiencies were used to investigate effects of increasing [CO2] on the relative requirements of C3 plants for these frequently limiting resources. 3. Water-use efficiency (biomass produced/evapotranspiration; WUE) increased at higher [CO2] in all species but relative responses to [CO2] varied among species, cultivars and watering regimes. 4. Intrinsic WUE (net assimilation/stomatal conductance to water), calculated from stable carbon isotopes in plants, increased by about the same relative amount as did [CO2] in all species. 5. Nitrogen-use efficiency (biomass produced/plant N; NUE) rose at higher [CO2] only in well-watered B. tectorum and in P. glandulosa grown alone. 6. The more consistent increase in WUE than NUE in these species at higher [CO2] implies that rising [CO2] may have reduced the amount of water relative to nitrogen that some C3 plants require and thereby altered the composition and function of terrestrial ecosystems.

913^1^Rawson,HM^1995^1^Yield responses of 2 wheat genotypes to carbon-dioxide and temperature in-field studies using temperature-gradient tunnels^92^22^1^23-32^^^^^^^^^^4625
1173^1759^1760^230^243^372^386^416^456^58^ces. 3. Water-use efficiency (biomass produced/evapotranspiration; WUE) increased at higher [CO2] in all species but relative responses to [CO2] varied among species, cultivars and watering regimes. 4. Intrinsic WUE (net assimilation/stomatal conductance to water), calculated from stable carbon isotopes in plants, increased by about the same relative amount as did [CO2] in all species. 5. Nitrogen-use efA^4624^Clear, plastic-coated, temperature gradient tunnels (TGTs), 8 X 1.25 X 1.25 m were designed and built to examine how temperature and CO2 affect the yield of wheat in the field. Each of the three modules of each TGT was maintained at a different temperature above the ambient temperature using solar heating during the day and electric heating at night. The maximum day-time increment above ambient for the warmest module was 5 degrees C and full-season averages were close to 2 degrees C. TGTs were paired, with air in one being enriched to 700 mu L L(-1) CO2, and in the other being maintained at ambient CO2. Crops were planted in the TGTs at two sites in either summer (December) or winter (April and July) and they remained there until maturity. CO2 enrichment increased the yield in summer plantings by up to 36%. In winter plantings, with mean temperatures between sowing and anthesis of around 10 degrees C, the responses to CO2 were small averaging only 7% (range 1-12%). Though yield declined with increasing temperature in the TGTs in summer, there was a clear trend for an increasing response to CO2 at these higher temperatures, i.e. yield declined less. In summer, there was no convincing evidence for a different relative response to CO2 in two isolines which differed in maturity date, though the later line yielded more under the highest temperature regime (mean of 22- 24 degrees C between sowing and anthesis). In winter there was a strong trend for the isoline requiring less vernalisation to respond more to CO2. It is suggested that early progress towards flowering might predispose wheat to a greater CO2 response. Overall, the data indicated that the positive response to CO2 in grain yield is likely to increase at approximately 1.8% per 1 degrees C in wheat crops that are not limited by water. Extrapolation indicated that the temperature at which there was no response to CO2 was 5 degrees C. All yield responses reflected biomass responses as harvest index was unchanged by CO2.
h yield declined with increasin914^1^Reich,PB^1995^1^Phenology of tropical forests - patterns, causes, and consequences^188^73^2^164-174^^^^^Feb^^^^^4627
1314^1761^1762^1763^1764^1765^338^394^484^705^s no convincing evidence for a different relative response to CO2 in two isolines which differed in maturity date, though the later line yielded more under the highest temperature regime (mean of 22- 24 degrees C between sowing and anthesis). In winter there was a strong trend for the isoline requiring less vernalisation to respond more to CO2. It is suggested that early progress towards flowering might predispose wheat to a greater CO2 response. Overall, the data indicated that the positive response to CO2 in grain yield is likely to increase at approximately 1.8% per 1 degrees C in wheat crops that are not limited by water. Extrapolation indicated that the temperature at which there was no response to CO2 was 5 degrees C. All yield responses reflected biomass responses as harvest index was unchanged by CO2.
h yield declined with increasinA^4626^Leaf phenology of tropical forests is distinct from other biomes. Unlike the marked temperature-related periodicity of temperate forests, development tends to be continuous in aseasonal lowland tropical rain forests and becomes more episodic in response to increasing annual drought in tropical dry forests. Hence, in tropical rain forests, foliar development (production, senescence, and longevity) is largely under internal rather than environmental control. In contrast, tropical forests with marked annual dry seasons display associated seasonality of leaf production and shedding. This developmental seasonality can be explained by overlaying the influence of seasonality on trees' internally regulated development and appears to be controlled by acclimative physiological processes and not by sensitivity to photo-, thermo-periodic, or direct environmental cues. Consequences of tropical phenology stem from both the variety of leaf and species ecophysiological types common to a given moisture regime and their relative synchrony of development, and include the following: larger diversity of ecophysiological species types in rain than dry forests; differential rates of herbivory in dry than wet seasons and for synchronous versus asynchronous leaf flushes; ecosystems with greater canopy foliar mass per hectare in rain than dry forests; and several leaf adaptations perhaps unique to tropical forests, such as delayed greening and seasonal leaf phenotypes. Tropical forests may vary in sensitivity to predicted climate change. Phenology of rain forests should change little unless water balance changes markedly, and developmental events in rain forests may be relatively insensitive to moderate changes in CO2 or temperature. Phenology of dry forests could be more sensitive, and in opposite directions, to elevated CO2 and temperatures. Elevated CO2 might delay the onset of leaf shedding and stimulate longer life span if stand level transpiration is reduced, whereas higher temperatures could lead to more rapid water depletion, longer leafless periods, and more strongly synchronized phenology.

915^2^Reinert,RA^Ho,MC^1995^1^Vegetative growth of soybean as affected by elevated carbon- dioxide and ozone^35^89^1^89-96^^^^^^^^^^4629
130^1766^1767^243^264^349^374^542^57^73^ecosystems with greater canopy foliar mass per hectare in rain than dry forests; and several leaf adaptations perhaps unique to tropical forests, such as delayed greening and seasonal leaf phenotypes. Tropical forests may vary in sensitivity to predicted climate change. Phenology of rain forests should change little unless water balance changes markedly, and developmental events in rain forests may be relatively insensitive to moderate changes in CO2 or temperature. Phenology of dry forests could be more sensitive, and in opposite directions, to elevated CO2 and temperatures. Elevated CO2 might delay the onset of leaf shedding and stimulate longer life span if stand level transpiration is reduced, whereas higher temperatures could lead to more rapid water depletA^4628^The effects of elevated carbon dioxide (CO2) and ozone (O-3) on soybean (Glycine max (L.) Merr. cv. Centennial) growth and biomass partitioning were evaluated under greenhouse conditions. Soybeans were exposed to CO2 concentrations at 350 (ambient), 450, 550, and 650 mu l liter(-1) (ppm) for 24 h day(-1) for 5 weeks. Ozone treatments of 0 and 120 nl liter(-1) (ppb) for 6 h day(-1) for 5 days week-1 for 5 weeks were added in combination with the CO2 treatments. Plant dry weight and biomass partitioning were assessed each week. Dry weight of leaf, stem, and root, as well as the total plant dry weight increased with exposure to increasing levels of CO2. Dry weight of leaf, root and total plant were suppressed significantly by the O-3 treatment. Stem dry weight was not affected by O-3. Suppression of root dry weight due to O-3 at each weekly harvest was significantly dependent on the CO2 concentration. Root growth was enhanced by CO2 at 650 mu l liter(-1) compared with ambient CO2 (350 mu l liter(-1)) at 5 weeks of age. At ambient CO2 in the presence of O3 the roots were only about 63% of the weight of the root grown in the absence of O-3. At 550 and 650 mu l liter(-1) CO2 the biomass of soybean roots in the presence of 120 nl liter(-1) O-3 was 88.2 and 88.4% of the control, respectively. Thus, CO2 limited the amount of root growth suppression caused by O-3. The partitioning of leaf, stems and root dry weight in relation to total plant dry weight remained relatively constant across each CO2 concentration. Thus, CO2 did not affect biomass partitioning among leaves, stems and roots of soybean.

916^1^Reining,E^1994^1^Acclimation of C-3 photosynthesis to elevated co2 - hypotheses and experimental-evidence^79^30^4^519-525^^^^^^^^^^4631
204^343^355^376^377^384^417^550^632^92^ affected by O-3. Suppression of root dry weight due to O-3 at each weekly harvest was significantly dependent on the CO2 concentration. Root growth was enhanced by CO2 at 650 mu l liter(-1) compared with ambient CO2 (350 mu l liter(-1)) at A^4630^Acclimation of the photosynthesis of C-3 plants to elevated atmospheric CO2 concentrations is frequently observed. Some hypotheses frequently proposed to explain this phenomenon are: (1) stomatal closure; (2) inhibition of photosynthesis by starch accumulation, and (3) reduced activity or concentration of ribulose-1,5-bisphosphate carboxylase/oxygenase. These hypotheses are compared with experimental evidence from the literature.

917^3^Samarakoon,AB^Muller,WJ^Gifford,RM^1995^1^Transpiration and leaf-area under elevated co2 - effects of soil-water status and genotype in wheat^92^22^1^33-44^^^^^^^^^^4633
1163^230^374^376^386^430^434^722^740^998^elevated co2 - hypotheses and experimental-evidence^79^30^4^519-525^^^^^^^^^^4631
204^343^355^376^377^384^417^550^632^92^ affected by O-3. Suppression of root dry weight due to O-3 at each weekly harvest was significantly dependent on the CO2 concentration. Root growth was enhanced by CO2 at 650 mu l liter(-1) compared with ambient CO2 (350 mu l liter(-1)) at A^4632^Transpiration rate, leaf area expansion, water use and water- use efficiency (WUE) of spaced plants of wheat (cvv. Matong and Quarrion), were examined at ambient and twice ambient CO2 concentrations in wet and drying soil regimes. A hypothesis tested was that both stomatal conductance (g(s)) and leaf area development are so regulated by the plant in relation to soil water status that the reduction of approximately 40% in g(s) in high CO2 has no permanent impact on whole-plant water use. Whereas, during a soil drying cycle, leaf area increase under elevated CO2 counterbalanced closely for reduced g(s) in terms of soil water depletion as reported elsewhere, this counterbalance was neither exact at all times, nor did it apply when the soil was continuously wet. In wet soil, leaf area was not enhanced much by elevated CO2, probably because, under the high radiation and nutritional conditions used, the tillering rate was almost maximal anyway. Quarrion, having a 40% lower g(s) than Matong genetically, did not counterbalance a reduced transpiration rate with a larger leaf area under either drying or wet soil conditions. These results support rejection, for wheat, of the hypothesis posed; elevated CO2 increased leaf area mainly by virtue of the direct photosynthetic increase rather than changed soil water status. In wet soil, low g(s) Quarrion had a higher CO2 effect on WUE (+ 73 to 82%) than did Matong (+ 54 to 65%). In drying soil, both cultivars had a similar increase in WUE at high CO2 (+ 60 to 68%).

918^2^Silvola,J^Ahlholm,U^1995^1^Combined effects of co2 concentration and nutrient status on the biomass production and nutrient-uptake of birch seedlings (betula-pendula)^206^169^^547-553^^^^^Jan-Feb^^^^^4635
1277^130^243^312^372^374^376^439^496^92^ntinuously wet. In wet soil, leaf area was not enhanced much by elevated CO2, probably because, under the high radiation and nutritional conditions used, the tillering rate was almost maximal anyway. Quarrion, having a 40% lower g(s) than Matong genetically, did A^4634^Birch seedlings (Betula pendula) were grown for four months in a greenhouse at three nutrient levels (fertilization of 0, 100 and 500 kg ha(-1) monthly) and at four CO2 concentrations (350, 700, 1050 and 1400 ppm). The effect of CO2 concentration on the biomass production depended on the nutrient status. When mineralization of the soil material was the only source of nutrients (0 kg ha(-1)), CO2 enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha(-1), being over 100% between 350 and 700 ppm CO2. At 500 kg ha(-1) the production increase was smaller, and the production decreased beyond a CO2 concentration of 700 ppm. The CO2 concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO2 concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO2 concentration had no effect on the growth rhythm and higher CO2 reduced the nutrient concentrations.

919^1^Teskey,RO^1995^1^A field-study of the effects of elevated co2 on carbon assimilation, stomatal conductance and leaf and branch growth of pinus-taeda trees^9^18^5^565-573^^^^^May^^^^^4637
1291^1768^243^310^343^361^374^384^966^968^neralization of the soil material was the only source of nutrients (0 kg ha(-1)), CO2 enhancement reduced the biomass production slightly, whereas the highest production increase occurred at a fertilization of 100 kg ha(-1), being over 100% between 350 and 700 ppm CO2. At 500 kg ha(-1) the production increase was smaller, and the production decreased beyond a CO2 concentration of 700 ppm. The CO2 concentration had a slight effect on the biomass distribution, the leaves accounting for the highest proportion at the lowest CO2 concentration (350 ppm). An increase in nutrient status led to a longer growth period and increased the nutrient concentrations in the plants, but the CO2 concentration had A^4636^A study was conducted in 21-year-old loblolly pine (Pinus taeda L.) trees growing in plantation in north central Georgia, USA, The experiment used branch chambers to impose treatments of ambient, ambient+165 and ambient+ 330 mu mol mol(-1) CO2. After one growing season there was no indication of acclimation to elevated CO2. In August and September, carbon assimilation, measured by two different methods, was twice as high at ambient +330 mu mol mol(-1) CO2 than at ambient, Dark respiration was suppressed by 6% at ambient+l65 and by 14% at ambient+330 mu mol mol(-1) CO2. This suppression was immediate, and not an effect of exposure to elevated CO2 during growth, since respiration was reduced by the same amount in all treatments when measured at a high CO2 concentration, Elevated CO2 increased the growth of foliage and woody tissue, It also increased instantaneous transpiration efficiency, but it had no effect on stomatal conductance, Since the soil at the study site had low to moderate fertility, these results suggest that the growth potential of forests on many sites may be enhanced by global increases in atmospheric CO2 concentration.

920^3^Wang,KY^Kellomaki,S^Laitinen,K^1995^1^Effects of needle age, long-term temperature and co2 treatments on the photosynthesis of scots pine^13^15^4^211-218^^^^^Apr^^^^^4639
1769^310^348^360^372^374^384^430^92^999^, carbon assimilation, measured by two different methods, was twice as high at ambient +330 mu mol mol(-1) CO2 than at ambient, Dark respiration was suppressed by 6% at ambient+l65 and by 14% at ambient+330 mu mol mol(-1) CO2. This suppression was immediate, and not an effect of exposure to elevated CO2 during growth, since respiration was reduced by the same amount in all treatments when measured at a high CO2 concentration, Elevated CO2 increased the growth of foliage and woody tissue, It also increased instantaneous transpiration efficiency, but it had no effect on stomatal conductance, Since the soil at the study site had low to moderate fertility, these A^4638^Naturally regenerated 20-25-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers in the presence of an elevated temperature or CO2 concentration, or both. The elevated temperature treatment was administered year- round for 3 years. The CO2 treatment was applied between April 15 and September 15 for 2 years. The photosynthetic responses of 1- and 2-year-old needles to varying photon flux densities (0-1500 mu mol m(-2) s(-1)) and CO2 concentrations (350, 700 and 1400 mu mol mol(-1)) during measurement were determined. The CO2 treatment alone increased maximum photosynthetic rate and light-use efficiency, but decreased dark respiration rate, light compensation and light saturation regardless of needle age. In contrast, the temperature treatment decreased maximum photosynthetic rate and photosynthetic efficiency, but increased dark respiration rate, light compensation and light saturation. The aging of needles affected the photosynthetic performance of the shoots; values of all parameters except photosynthetic efficiency were less in 2- than in I-year-old needles. The CO2 treatment decreased and the temperature treatment enhanced the reduction in maximum photosynthesis due to needle aging.

921^2^Acock,B^Wall,GW^1995^1^A simple conductimetric co2 analyzer with automatic recalibration .1. Design, implementation, and functionality^48^87^1^70-75^^^^^Jan-Feb^^^^^4641
eedles to varying photon flux densities (0-1500 mu mol m(-2) s(-1)) and CO2 concentrations (350, 700 and 1400 mu mol mol(-1)) during measurement were determined. The CO2 treatment alone increased maximum photosynthetic rate and light-use efficiency, but decreased dark respiration rate, light compensation and light saturation regardless of needle age. In contrast, the temperature treatment decreased maximum photosynthetic rate and photosynthetic efficiency, but increased dark respiration rate, light compensation and light saturation. The aging of needles affected the photosynthetic performance of the shoots; values of all A^4640^Controlled-environment plant growth cabinets may be used to investigate the long-term effect of elevated carbon dioxide concentration ([CO2]) on plant growth. Infrared gas analyzers (IRGAs) are normally used to monitor and control [CO2] in plant cabinets. With many cabinets in use, however, it soon becomes impractical to purchase an individual IRGA for each cabinet, A more economical method of monitoring and controlling [CO2] relies on the change in electrical conductivity when CO2 is dissolved in demineralized water, This work describes the design, implementation, and functionality of an inexpensive conductimetric system for controlling [CO2] in plant growth cabinets, Regressing electrical conductivity against [CO2] over the range 0 to 1000 mu L L(-1) yields a quadratic response. Calibration drift inherent in the conductimetric CO2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosures to within 10 to 15 mu L L(-1) of the set point, The [CO2] control system is robust enough to maintain this accuracy regardless of the desired [CO2] set point or the mass of plant material within the plant growth cabinet, In this approach, only one IRGA is required to control [CO2] in many plant growth cabinets if each cabinet has a dedicated conductimetric CO2 analyzer.

922^3^Archer,S^Schimel,DS^Holland,EA^1995^1^Mechanisms of shrubland expansion - land-use, climate or co-2^50^29^1^91-99^^^^^Jan^^^^^4643
1770^1771^1772^312^344^372^458^672^751^92^sign, implementation, and functionality of an inexpensive conductimetric system for controlling [CO2] in plant growth cabinets, Regressing electrical conductivity against [CO2] over the range 0 to 1000 mu L L(-1) yields a quadratic response. Calibration drift inherent in the conductimetric CO2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosurA^4642^Encroachment of trees and shrubs into grasslands and the 'thicketization' of savannas has occurred worldwide over the past century. These changes in vegetation structure are potentially relevant to climatic change as they may be indicative of historical shifts in climate and as they may influence biophysical aspects of land surface-atmosphere interactions and alter carbon and nitro en cycles. Traditional explanations offered to account for the historic displacement of grasses by woody plants in many arid and semi-arid ecosystems have centered around changes in climatic, livestock grazing and fire regimes. More recently, it has been suggested that the increase in atmospheric CO2 since the industrial revolution has been the driving force. In this paper we evaluate the CO2 enrichment hypotheses and argue that historic, positive correlations between woody plant expansion and atmospheric CO2 are not cause and effect.
ecalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosur923^1^Beerling,DJ^1994^1^Modeling palaeophotosynthesis - late cretaceous to present^190^346^1318^421-432^^^^^29 Dec^^^^^4645
130^137^1773^1774^1775^243^312^344^372^417^ructure are potentially relevant to climatic change as they may be indicative of historical shifts in climate and as they may influence biophysical aspects of land surface-atmosphere interactions and alter carbon and nitro en cycles. Traditional explanations offered to account for the historic displacement of grasses by woody plants in many arid and semi-arid ecosystems have centered around changes in climatic, livestock grazing and fire regimes. More recently, it has been suggested that the increase in atmospheric CO2 since the industrial revolution has been the driving force. In this paper we evaluate the CO2 enrichment hypotheses and argue that historic, positive correlations between woody plant expansion and atmospheric CO2 are not cause and effect.
ecalibrating with an IRGA every 900 s gave control of the [CO2] within the plant enclosurA^4644^This paper presents an attempt to reconstruct potential changes in the photosynthetic rates of terrestrial C3 leaves over the past 120 Ma. The approach has been to couple palaeoatmospheric reconstructions of O-2, CO2 and temperature from geochemical modelling, and an independent estimate of ancient CO2 changes from fossil porphyrins, with a mechanistic biochemical model of C3 photosynthesis. The model accounts for the effect of each of these palaeoenvironmental changes, at the biochemical level, to predict leaf photosynthesis and has been parametrized for a typical gymnosperm and angiosperm. The results indicate clear potential for increased photosynthetic C3 fixation in the warm Cretaceous for both angiosperms and gymnosperms, despite the increased O-2 content of the atmosphere prevailing at the time. Photosynthetic rates are then predicted to progressively decline into the Tertiary, as a result of global cooling. The model simulations also point towards some leaf-level ecophysiological explanations for the rise in angiosperm dominance and the concomitant decline in gymnosperms from the late Cretaceous onwards, at mid-latitudes, which have not been considered previously. This work provides a basis for scaling up to the canopy level to predict the primary productivity of ancient ecosystems and their possible feedback on atmospheric composition and climate.

924^5^Catsky,J^Pospisilova,J^Solarova,J^Synkova,H^Wilhelmova,N^1995^1^Limitations on photosynthesis under environment-simulating culture in-vitro^261^37^1^35-48^^^^^^^^^^4647
nd has been parametrized for a typical gymnosperm and angiosperm. The results indicate clear potential for increased photosynthetic C3 fixation in the warm Cretaceous for both angiosperms and gymnosperms, despite the increased O-2 content of the atmosphere prevailing at the time. Photosynthetic rates are then predicted to progressively decline into the Tertiary, as a result of global cooling. The model simulations also point towards some leaf-level ecophysiological explanations A^4646^Limitations on photosynthesis, characterized by leaf CO2 exchange, chlorophyll fluorescence, and thylakoid structure, were studied under environmental conditions simulating culture in vitro. These were simulated by growing Phaseolus vulgaris plants in nutrient solution under high relative humidity of air (> 90%), and CO2 concentrations (c(a)) that decreased with the development of photosynthetic activities during plant ontogeny (1200 to 300 mg m-3). The ontogeny of such model plants was more rapid, primary leaves reached photosynthetic maturity 2 to 3 d earlier and their life span was 7 to 14 d shorter than in control plants. Their photosynthetic activity in situ was limited, after reaching ''photosynthetic maturity'', similarly to plants grown in vitro. When measured under optimal conditions, however, 50 to 70% higher net photosynthetic rate (P(N)) were found in leaves of different ages as compared with plants grown under c(a) of 700 mg m-3 and a lower air humidity (30 - 35%). This increase in P(N) was associated with a high conductance for CO2 transfer by adaxial and abaxial epidermes. In model plants, the dark respiration rate (R(D)) was almost twice that in the control, while the photorespiration rates were similar to controls; CO2 compensation concentration was about 50% of that in controls. The ratios P(N)/R(D) were similar in control and in model plants. Chlorophyll a+b content in leaves of the model plants was lower than that in the control plants. Grana extent increased with plant age in the model plants while it decreased in the control ones. In both the stomal and granal membranes of the chloroplasts in model plants, a marked accumulation of carotenoids occurred independent of age. The ratio of variable to maximal fluorescence, F(v)/F(m), did not differ in the model and the control plants. In the control plants, photochemical quenching (qp) slightly increased with plant age and was not affected by CO2 concentration present during measurement. In the model plants, qp increased with elevated CO2 concentration in young plants and decreased in saturating CO2 concentrations in older plants. Nonphotochemical quenching (q(NP)) was lower in the model plants and increased under CO2 saturating conditions. Vitality index, Rfd, was markedly lower in the model plants than in the control ones and a decline was found in saturating CO2 concentration.

925^4^Clark,H^Newton,PCD^Bell,CC^Glasgow,EM^1995^1^The influence of elevated co2 and simulated seasonal-changes in temperature on tissue turnover in pasture turves dominated by perennial ryegrass (lolium-perenne) and white clover (trifolium-repens)^39^32^1^128-136^^^^^Feb^^^^^4649
1776^1777^1778^1779^243^344^385^430^778^914^occurred independent of age. The ratio of variable to maximal fluorescence, F(v)/F(m), did not differ in the model and the control plants. In the control plants, photochemical quenching (qp) slightly increased with plant age and was not affected by CO2 concentration present during measurement. In the model plants, qp increased with elevated CO2A^4648^1. Tissue turnover, leaf morphology and population dynamics of perennial ryegrass and white clover were studied in pasture turves grown at ambient (350 mu molmol(-1)) or double ambient (700 mu molmol(-1)) CO2 concentrations for 217 days in controlled environment rooms. The turves were subjected sequentially to three day/night temperature regimes; 10/4 degrees C, 16/10 degrees C and 22/16 degrees C and harvested at 3-week intervals. The photoperiod was 12 hours for all of the temperature treatments with a mean photon flux density of 480 mu E m(-2) s(-1). 2. Ryegrass leaf extension and leaf death rates did not differ between CO2 treatments and there was no effect of CO2 on rates of leaf appearance in white clover. Weight per unit length of ryegrass laminae was unaffected by elevated CO but lamina weight per unit area, lamina area and petiole weight per unit length in white clover showed a small positive response, especially at the two higher temperatures. Rates of growth and senescence per ryegrass tiller were therefore similar between CO2 treatments, but rates of growth per white clover growing point were increased by 4, 23 and 13% at 10/4 degrees C, 16/10 degrees C and 22/16 degrees C, respectively, at elevated CO2. Responses to CO2 could not be attributed to any consistent change in morphological characteristics in either species and exposure to elevated concentrations of CO2 did not appear to change the relationship between growth and senescence per meristem. 3. Total grass tiller populations were similar at both CO2 concentrations, but ryegrass tiller densities more than halved in both CO2 treatments as the temperature was increased. The fall was most severe at 700 mu mol mol(-1) and at the end of the experiment ryegrass tiller densities in this treatment were only 47% of those found at 350 mu molmol(-1). There was no consistent effect of CO2 concentration on clover growing point numbers and they increased from 800 m(-2) to over 3000 m(-2) in both treatments with maximum densities occurring at 22/16 degrees C. 4. The results imply that, in plant communities dominated by ryegrass and white clover, exposure to elevated CO2 concentrations will alter the species composition in favour of white clover. Responses in above-ground dry matter yield to elevated CO2 will be a balance between the positive response shown by white clover and the negative response of perennial ryegrass. Temperature will have a major influence on the magnitude of this response since both the response of white clover to CO2 and the ratio of white clover growing points to ryegrass tillers are temperature-dependent.

926^5^Conroy,JP^Seneweera,S^Basra,AS^Rogers,G^Nissenwooller,B^1994^1^Influence of rising atmospheric co2 concentrations and temperature on growth, yield and grain quality of cereal crops^92^21^6^741-758^^^^^^^^^^4651
1163^1780^230^243^372^430^57^665^698^91^fect of CO2 concentration on clover growing point numbers and they increased from 800 m(-2) to over 3000 m(-2) in both treatments with maximum densities occurring at 22/16 dA^4650^A possible scenario for the end of the 21st century is that the atmospheric CO2 concentration will be in the range of 510-760 mu L L(-1) and that the mean global temperature will be 1.5-4.5 degrees C higher. Further, there may be greater incidences of extreme climatic events, which together with the CO2 and temperature changes will influence development, growth and grain yield of cereals such as rice and wheat. For these C-3, plants, the driving force for the growth response to elevated CO2 is higher leaf CO2 assimilation rates (4). However, the response of A to CO2 depends on temperature with maximum absolute increases occuring at temperatures which do not cause flower abortion, while negligible increases are observed at low temperatures. At high temperatures, where A is reduced because of partial inactivation of photosynthetic enzymes, the increase in A due to CO2 enrichment is still observed. Other factors, such as changes in shoot water relations or hormone concentrations, may influence growth at elevated CO2 concentrations. Wheat and rice development is accelerated by high temperature and consequently grain yield is reduced because there is less time for radiation to be intercepted during the vegetative phase. Although high CO2 also accelerates development in rice and, to a lesser extent in wheat, the extra carbohydrate produced by increases in A results in at least a 40% increase in grain yield at temperatures which do not cause flower abortion. This is due mainly to increased tiller numbers rather than increases in the number or weight of individual grains. However, the yield enhancement due to high CO2 will not necessarily compensate for decreases in yield caused by accelerated development at high temperatures. As predicted by the response of A to high CO2, the relative increase in yield, due to rising CO2 concentrations, is smaller at lower temperatures. Elevated atmospheric CO2 may improve the tolerance of plants to heat-induced drought stress by facilitating the maintenance of cell volume and photosynthetic function in the leaves. Increased carbohydrate storage in the stems may also be an advantage during grain filling if the flag leaves senesce prematurely. However, it is unlikely that the effect of very high temperatures on newer abortion will be ameliorated by high CO2. For bread making, the quality of flour produced from grain developed at high temperatures is poorer. High CO2 may also have an effect through a reduction in the protein content of wheat grain. For rice, the amylose content of the grain, a major determinant of cooking quality is increased under elevated CO2.

927^5^Curtis,PS^Vogel,CS^Pregitzer,KS^Zak,DR^Teeri,JA^1995^1^Interacting effects of soil fertility and atmospheric co2 on leaf-area growth and carbon gain physiology in populus X euramericana (dode) guinier^84^129^2^253-263^^^^^Feb^^^^^4653
1290^1781^243^372^376^384^417^436^57^749^ Elevated atmospheric CO2 may improve the tolerance of plants to heat-induced drought stress by facilitating the maintenance of cell volume and A^4652^Two important processes which may limit productivity gains in forest ecosystems with rising atmospheric CO2 are reduction in photosynthetic capacity following prolonged exposure to high CO2 and diminution of positive growth responses when soil nutrients, particularly N, are limiting. To examine the interacting effects of soil fertility and CO2 enrichment on photosynthesis and growth in trees we grew hybrid poplar (Populus x euramericana) for 158 d in the field at ambient and twice ambient CO2 and in soil with low or high N availability. We measured the timing and rate of canopy development, the seasonal dynamics of leaf level photosynthetic capacity, respiration, and N and carbohydrate concentration, and final above- and belowground dry weight. Single leaf net CO2 assimilation (A) increased at elevated CO2 over the majority of the growing season in both fertility treatments. At high fertility, the maximum size of individual leaves, total leaf number, and seasonal leaf area duration (LAD) also increased at elevated CO2, leading to a 49% increase in total dry weight. In contrast, at low fertility leaf area growth was unaffected by CO2 treatment. Total dry weight nonetheless increased 25% due to CO2 effects on A. Photosynthetic capacity (A at constant internal p(CO2), (C-i)) was reduced in high CO2 plants after 100 d growth at low fertility and 135 d growth at high fertility. Analysis of A responses to changing C-i indicated that this negative adjustment of photosynthesis was due to a reduction in the maximum rate of CO2 fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO2. Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid-season and no change (area basis) or reduced (mass basis) respiration late- season in elevated compared to ambient CO2 plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results demonstrate the importance of considering both structural and physiological pathways of net C gain in predicting tree responses to rising CO2 under conditions of suboptimal soil fertility.

928^2^Demothes,MAG^Knoppik,D^1994^1^Effects of long-term enhanced co2 partial-pressure on gas- exchange parameters and saccharide pools of wheat leaves^79^30^3^435-445^^^^^^^^^^4655
130^243^310^312^344^360^372^374^434^639^ging C-i indicated that this negative adjustment of photosynthesis was due to a reduction in the maximum rate of CO2 fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO2. Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid-season and no change (area basis) or reduced (mass basis) respiration late- season in elevated compared to ambient CO2 plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results deA^4654^Wheat plants were cultivated in a growth chamber at normal (35 Pa, c35 plants) and enhanced (70 Pa, c70 plants) CO2 partial pressure. In C35 plants the net photosynthetic rate (P(N)) of flag leaves and the concentrations of saccharides such as sucrose, glucose, fructose and starch were increased. The c70 plants possessed higher chlorophyll (Chl) a and Chl b contents. The CO2 response of P(N) at saturating photosynthetically active radiation (PAR) was very similar for both variants. At the highest CO2 concentration saccharides accumulated in both variants as a consequence of decreased export rate. The response of P(N) to PAR at saturating CO2 concentrations was similar in the two variants. On the other hand, the response of water vapour pressure conductance (gH2O) to PAR in c35 plants followed a hyperbolic response to PAR, while in the c70 plants it was linearly related to PAR up to the mean PAR used for growth. In this variant gH2O seemed to change parallelly to changes in the mesophyll demand for CO2 caused by PAR.

929^3^Dixon,M^Lethiec,D^Garrec,JP^1995^1^The growth and gas-exchange response of soil-planted norway spruce [picea-abies (L) karst] and red oak (quercus-rubra L) exposed to elevated co2 and to naturally-occurring drought^84^129^2^265-273^^^^^Feb^^^^^4657
1206^243^361^376^546^634^666^745^861^70 plants possessed higher chlorophyll (Chl) a and Chl b contents. The CO2 response of P(N) at saturating photosynthetically active radiation (PAR) was very similar for both variants. At the highest CO2 concentration saccharides accumulated in both variants as a consequence of decreased export rate. The response of P(N) to PAR at saturating CO2 concentrations was similar in the two variants. On the other hand, the response of water vapour pressure conductance (gH2O) to PAR in c35 plants followed a hyperbolic response to PAR, while in the c70 plants it was linearly related to PAR up to the mean PAR used for growth. In this variant gH2O seemed to change parallelly to changes in the mesophyll demand for CO2A^4656^Norway spruce and red oak trees were planted directly into the soil and exposed to 700 mu mol mol(-1) CO2 in open-top chambers. There were large inter-specific differences in response to naturally occurring drought during the second pear of exposure to elevated CO2. Both species had decreased assimilation rates. CO2-treated red oak had no loss of photosynthetic enhancement when undroughted, whereas CO2- treated Norway spruce showed a relative increase in assimilation rates only when droughted. The effect of CO2 on radial growth of both species was less marked in the second growing season, but this may have been a result of different biomass partitioning as Norway spruce shoot extension had a different pattern of growth in elevated CO2. Stomatal density and chlorophyll content were largely unaffected by the CO2 treatment. A precise method for measuring Norway spruce needle surface area was also developed.
owth. In this variant gH2O seemed to change parallelly to changes in the mesophyll demand for CO2930^1^Field,CD^1995^1^Impact of expected climate-change on mangroves^232^295^1-3^75-81^^^^^6 Jan^^^^^4659
1262^1782^1783^1784^1785^372^677^92^re large inter-specific differences in response to naturally occurring drought during the second pear of exposure to elevated CO2. Both species had decreased assimilation rates. CO2-treated red oak had no loss of photosynthetic enhancement when undroughted, whereas CO2- treated Norway spruce showed a relative increase in assimilation rates only when droughted. The effect of CO2 on radial growth of both species was less marked in the second growing season, but this may have been a result of different biomass partitioning as Norway spruce shoot extension had a different pattern of growth in elevated CO2. Stomatal density and chlorophyll content were largely unaffected by the CO2 treatment. A precise method for measuring Norway spruce needle surface area was also developed.
owth. In this variant gH2O seemed to change parallelly to changes in the mesophyll demand for CO2A^4658^There is a consensus of scientific opinion that the activities of man will cause a significant change in the global climate over the next hundred years. The rising level of carbon dioxide and other industrial gases in the atmosphere may lead to global warming with an accompanying rise in sea-level. Mangrove ecosystems grow in the intertidal zones in tropical and sub- tropical regions and are likely to be early indicators of the effects of climate change. The best estimates of predicted climate change in the literature are presented. It is suggested that a rise in mean sea-level may be the most important factor influencing the future distribution of mangroves but that the effect will vary dramatically depending on the local rate of sea-level rise and the availability of sediment to support reestablishment of the mangroves. The predicted rise in mean air temperature will probably be of little consequence to the development of mangroves in general but it may mean that the presence of mangroves will move further north and south, though this will depend on a number of additional factors. The effect of enhanced atmospheric CO2 on the growth of mangroves is unknown at this time but that there is some evidence that not all species of mangroves will respond similarly. The socio- economic impacts of the effects of climate change on mangrove ecosystems may include increased risk of flooding, increased erosion of coast lines, saline intrusion and increased storm surges.

931^2^Friend,AD^Cox,PM^1995^1^Modeling the effects of atmospheric co2 on vegetation atmosphere interactions^107^73^3-4^285-295^^^^^Mar^^^^^4661
243^256^264^312^361^372^674^future distribution of mangroves but that the effect will vary dramatically depending on the local rate of sea-level rise and the availability of sediment to support reestablishment of the mangroves. The predicted rise in mean air temperature will probably be of little consequence to the development of mangroves in general but it may mean that the presence of mangroves will move A^4660^The effect of doubling atmospheric CO2 concentration (C-a) on climate and vegetation is investigated using a combined climate-vegetation model. The vegetation model predicts the response of leaf area index, canopy transpiration (E(T)) and whole-plant carbon balance to changes in climate, soil moisture, and atmospheric CO2 forcing. This model has been embedded in the UK Meteorological Office Single Column Model (SCM), which provides the climate feedback to the vegetation. The vegetation model uses an optimisation approach to predict stomatal resistance, a biochemical model to predict photosynthesis and a simple carbon balance model to predict leaf area. Respiration is calculated as a function of leaf area and vegetation height. Clouds are assumed to be radiatively passive in the SCM to avoid unrealistic feedbacks. Simulations were performed with the fully interactive vegetation-climate model for an Amazon location with the present-day value of C-a (1 x CO2), and twice this value (2 x CO2). In addition, two other types of simulation were performed at both CO2 concentrations: one in which the vegetation component was forced only with 1 x CO2, and one using a fixed surface resistance. The latter case is equivalent to simulations using most current general circulation models. In all the simulations, increased atmospheric CO2 caused an increase in surface temperature owing to increased radiative forcing. With a fixed resistance, mean E(T) was increased by 5.6% and sensible heat flux was reduced by 3.8%. The fully interactive model had significant effects on the response of both climate and productivity to C-a. Increased C-a caused stomatal closure, which resulted in a reduction in mean E(T) Of 25%. The effect of C-a on E(T) was amplified by the positive feedback resulting from the effect of increased air humidity deficit on stomatal resistance.

932^3^Gorissen,A^Kuikman,PJ^Vandebeek,H^1995^1^Carbon allocation and water-use in juvenile douglas-fir under elevated co2^84^129^2^275-282^^^^^Feb^^^^^4663n addition,1343^342^345^362^374^376^531^672^685^92^rmed at both CO2 concentrations: one in which the vegetation component was forced only with 1 x CO2, and one using a fixed surface resistance. The latter case is equivalent to simulations using most current general circulation models. In all the simulations, increased atmospheric CO2 caused an increase in surface temperature owing to increased radiative forcing. With a fixed resistance, mean E(T) was increased by 5.6% and sensible heat flux was reduced by 3.8%. The fully interactive model had significant effects on the response of both climate and productivity to C-a. Increased C-a caused stomatal closure, which resulted in a reduction in mean E(T) Of 25%. The effect of C-a on E(T) was amplified by the positive feedback resulting from the effect of increased air humidity deficit on stomatal resistance.

932^3^Gorissen,A^Kuikman,PJ^Vandebeek,H^1995^1^Carbon allocation and water-use in juvenile douglas-fir under elevated co2^84^129^2^275-282^^^^^Feb^^^^^4663n addition,A^4662^In this study the impact of an elevated CO2 level on allocation of assimilates and water use efficiency of Douglas fir [Pseudotsuga menziesii (Mirb.) France] was investigated. Juvenile Douglas firs were exposed to a long-term treatment at 350 and 700 pi l(-1) CO2 for 14 months and subsequently crosswise transferred to phytotrons for a short-term treatment with 350 and 700 mu l l(-1) CO2 for 4 wk in an atmosphere continuously labelled with (CO2)-C-14. No interactive effects on total net uptake of (CO2)-C-14 between long-term treatment and short-term treatment were observed. The short-term treatment with 700 mu l l(-1) CO2 increased the total net uptake of (CO2)-C-14 by 22%, compared with the 350 mu l l(-1) CO2 treatment. The long-term pretreatment did not affect the total net uptake, suggesting that photosynthetic acclimation had not occurred. However, expressed per unit of needle mass a 14% reduction was observed in the trees pretreated at 700 mu l l(-1) CO2. This was not because of a reduced sink strength of the root system. This reduced uptake per unit of needle mass after long-term treatment may have implications for carbon storage in forest ecosystems. The results showed that an initial growth stimulation can eventually be annulled by developing physiological or morphological adaptions. (CO2)-C-14 the root/soil respiration increased in the short-term treatment with 700 mu l l(-1) CO2, indicating a stimulated use of current carbon compounds either by roots or microorganisms. The water use efficiency during the short-term treatment with 700 mu l l(-1) CO2 increased by 32%, but was not affected by the long- term pretreatment. Water use per unit needle mass during the short-term treatment was decreased both by the short-term treatment and by the long-term pretreatment by about 15%. Some of the observed effects appeared to be persistent, such as decreased water use per unit needle mass, whereas others, stimulation of total net (CO2)-C-14 uptake and water use efficiency, were transient.
a reduced sink str933^2^Horn,ME^Widholm,JM^1994^1^Photoautotrophic growth of soybean cells in suspension-culture .3. Characterization of carbon fixation products under high and low co2 levels^177^39^3^239-244^^^^^Dec^^^^^4665
1786^243^244^ually be annulled by developing physiological or morphological adaptions. (CO2)-C-14 the root/soil respiration increased in the short-term treatment with 700 mu l l(-1) CO2, indicating a stimulated use of current carbon compounds either by roots or microorganisms. The water use efficiency during the short-term treatment with 700 mu l l(-1) CO2 increased by 32%, but was not affected by the long- term pretreatment. Water use per unit needle mass during the short-term treatment was decreased both by the short-term treatment and by the long-term pretreatment by about 15%. Some of the observed effects appeared to be persistent, such as decreased water use per unit needle mass, whereas others, stimulation of total net (CO2)-C-14 uptake and water use efficiency, were transient.
a reduced sink strA^4664^A photoautotrophic soybean suspension culture (SB-P) was used to study CO2 assimilation while exposed to elevated or ambient CO2 levels. These studies showed that under elevated CO2 (5% v/v) malate is the dominant fixation product, strongly suggesting that phosphoenolpyruvate carboxylase (PEPCase) is the primary enzyme involved in carbon fixation in these cells under their normal growth conditions. Citrate and [aspartate + glutamate] were also significant fixation products during fifteen minutes of exposure to (CO2)-C-14. During the ten minute unlabeled CO2 chase however, C-14-malate continued to increase while citrate and [aspartate + glutamate] declined. Fixation of (CO2)-C-14 under ambient CO2 levels (0.037%) showed a very different product pattern as 3-phosphoglycerate was very high in the first one to two minutes followed by increases in [serine + glycine] and [aspartate + glutamate]. Hexose phosphates were also quite high initially but then declined relatively rapidly. Thus, the carbon fixation pattern at ambient CO2 levels resembles somewhat that seen in C3 leaf cells while that seen at elevated CO2 levels more closely resembles that of a C-4 plant. The initial fixation product of C-3 plants, 3-PGA, was never detectable under high CO2 conditions. These data suggest that an in vitro photoautotrophic system would be suitable for studying carbon fixation physiology during photosynthetic and non- photosynthetic growth.

934^3^Muller,M^Grill,D^Guttenberger,H^1994^1^The effects of interactions between ozone and co2 on the chromosomes of norway spruce root-meristems^262^34^2^321-335^^^^^^^^^^4667
o increase while citrate and [aspartate + glutamate] declined. Fixation of (CO2)-C-14 under ambient CO2 levels (0.037%) showed a very different product pattern as 3-phosphoglycerate was very high in the first one to two minutes followed by increases in [serine + glycine] and [aspartate + glutamate]. Hexose phosphates were also quite high initially but then declined relatively rapidly. Thus, the carbon fixation A^4666^A Norway spruce (Picea abies (L.) Karsten) test system was used to study the immediate and after effects of increased ozone or elevated CO2 or both, on root tip chromosomes. Five-year-old potted spruce trees were exposed in environmental chambers to elevated concentrations of ozone (0.1 cm3m-3) for the study of an immediate effect and to elevated concentrations of carbon dioxide (750 cm3m-3) and ozone (0.08 cm3m-3) as single variables or in combination and then transferred to a field for the observation of an after effect. Elevated ozone caused an increased number of chromosomal abnormalities directly after finishing the fumigation and also 21 months later. Elevated CO2 more likely induced a decrease rather than an increase in the number of chromosomal aberrations. The most common abnormalities were chromsome stickiness, in the form of connections, clumped metaphases and amorphous chromatin masses. An increased number of chromosomal aberrations especially chromosome stickiness reflects highly toxic effects, usually of an irreversible type leading to cell death.

935^5^Naeem,S^Thompson,LJ^Lawler,SP^Lawton,JH^Woodfin,RM^1995^1^Empirical-evidence that declining species-diversity may alter the performance of terrestrial ecosystems^190^347^1321^249-262^^^^^28 Feb^^^^^4669
174^1787^398^one (0.1 cm3m-3) for the study of an immediate effect and to elevated concentrations of carbon dioxide (750 cm3m-3) and ozone (0.08 cm3m-3) as single variables or in combination and then transferred to a field for the observation of an after effect. Elevated ozone caused an increased number of chromosomal abnormalities directly after finishing the fumigation and also 21 months later. Elevated CO2 more likely induced a decrease rather than an increase in the number of chromosomal aberrations. The most common abnormalities were chromsome stickiness, in the form of connections, clumped metaphases and amorphous chromatin masses. An increased number of chromosomal aberrations especially chromosome stickiness reflects highly toxic efA^4668^We examined experimentally the association between species diversity and ecosystem processes in a series of terrestrial mesocosms. We developed and maintained 14 mesocosms whose biota were assembled from a single pool of plant and animal species and whose environmental conditions were identically controlled. Each community contained four trophic levels: primary producers (annual herbs), consumers (herbivorous molluscs and phloem sucking insects), secondary consumers (parasitoids) and decomposers (earthworms, Collembola and microbes). All mesocosms received the same diurnal pattern of light, temperature, relative humidity and water. The initial volume of soil, soil structure, composition, nutrient content and inocula of both soil microbes and nematodes were also identical among replicates. The only experimentally manipulated factor was the number of plant and animal species within each trophic level. High, medium and low diversity communities had nine, 15 or 31 plant and animal species, respectively. We measured five ecosystem processes as response variables in these mesocosms over the course of 206 days: (i) community respiration; (ii) productivity; (iii) decomposition; (iv) nutrient retention; and (v) water retention. The manipulation of diversity produced communities that differed significantly in their ecosystem processes. Our results provide the first evidence (obtained by a direct manipulation of diversity under controlled environmental conditions) that ecosystem processes may be affected by loss of diversity.

936^3^North,GB^Moore,TL^Nobel,PS^1995^1^Cladode development for opuntia-ficus-indica (cactaceae) under current and doubled co2 concentrations^5^82^2^159-166^^^^^Feb^^^^^4671
1788^1789^348^372^374^376^610^779^92^984^oil microbes and nematodes were also identical among replicates. The only experimentally manipulated factor was the number of plant and animal species within each trophic level. High, medium and low diversity communities had nine, 15 or 31 plant and animal species, respectively. WA^4670^Morphological and anatomical changes for first-order daughter cladodes (flattened stem segments) of a prickly pear cactus, Opuntia ficus-indica, were monitored to determine the effects of a doubled atmospheric CO2 concentration on their development and mature form. For daughter cladodes developing in controlled environment chambers for 60 d, maximal elongation rates were similar under a photosynthetic photon flux density (PPFD) of 6 mol m(-2) d(-1) and a CO2 concentration of 370 mu l liter(-1), an increased PPFD (10 mol m(-2) d(-1)), and an increased PPFD and a doubled CO2 concentration. These maximal rates, however, occurred at 20, 15, and 12 d, respectively. The maximal relative growth rate under the doubled CO2 concentration was about twice that under the other conditions. For cladodes at 60 d as well as after 4 and 16 mo in open-top chambers, doubling the CO2 concentration had no effect on final length or width. At 4 mo, cladodes under doubled CO2 were 27% thicker, perhaps allowing the earlier production of second-order daughter cladodes. The chlorenchyma was then 31% thicker and composed of longer cells. At 16 mo, the difference in cladode thickness diminished, but the chlorenchyma remained thicker under doubled CO2, which may contribute to greater net CO2 uptake for O. ficus-indica under elevated CO2 concentrations. Two other persistent differences were a 20% lower stomatal frequency and a 30% thicker cuticle with more epicuticular wax for cladodes under doubled CO2, both of which may help reduce transpirational water loss.

937^2^Prior,SA^Rogers,HH^1995^1^Soybean growth-response to water-supply and atmospheric carbon- dioxide enrichment^166^18^4^617-636^^^^^^^^^^4673
224^264^349^361^372^386^409^417^434^685^O2 concentration was about twice that under the other conditions. For cladodes at 60 d as well as after 4 and 16 mo in open-top chambers, doubling the CO2 concentration had no effect on final length or width. At 4 mo, cladodes under doubled CO2 were 27% thicker, perhaps allowing the earlier proA^4672^Growth response of soybean [Glycine max (L.) Merr. 'Bragg'] grown in open top field chambers at five carbon dioxide (CO2) concentrations ranging from 349 to 946 mu LL(-1) and under two water regimes was examined. During reproductive growth, plants grown under CO2 enrichment exhibited increases in total leaf area and dry weight. Water stress inhibited growth at all CO2 levels, but the relative enhancement of growth due to CO2 enrichment under water-stressed (WS) conditions was greater than under well-watered (WW) conditions. Water-stressed plants grown under 946 mu LL(-1) CO2 were larger than WW plants grown under 349 mu LL(-1) CO2. Reproductive yield increases were represented by increases in seed number rather than larger seeds. Although water stress reduced yield, the relative increase in seed number in response to elevated CO2 was greater for WS plants. Leaf tissue analysis suggested that a phosphorus deficiency may have restricted the seed dry weight response to elevated CO2. The mean relative growth rate (RGR) and mean net assimilation rate (NAR) increased with CO2 concentration in the first interval (5 to 14 days after planting) and diminished with time thereafter for each CO2 level. At the second interval (14 to 63 days), the direct effect of NAR was offset by lower leaf area ratio (LAR). However, the LAR was greater for WS plants but the response of RGR to CO2 was similar under both water treatments. At the third interval (63 to 98 days), the RGR for WS plants remained constant across CO2 treatments, whereas under WW conditions a level response of NAR coupled with a negative response of LAR resulted in a decrease in RGR under CO2-enriched conditions. The decrease in LAR was attributed to a decrease in specific leaf area. Leaf weight ratio was unaffected by Co-2.

938^2^Rao,MV^Dekok,LJ^1994^1^Interactive effects of high co2 and so2 on growth and antioxidant levels in wheat^262^34^2^279-290^^^^^^^^^^4675
ciency may have restricted the seed dry weight response to elevated CO2. The mean relative groA^4674^The impact of elevated CO2 and/or SO2 on the growth and antioxidant levels of wheat (Triticum aestivum L. cv. Urban) plants has been studied. High CO2 (0.7 ml l-1) significantly enhanced shoot biomass and photosynthetic capacity, while exposure to SO2 (0.14 mul l-1) resulted in a decreased shoot biomass and in an injured photosynthetic aparatus, illustrated by a loss of chlorophyll and a decreased ratio of variable to maximal fluorescence (F(v)/F(m)) and A(max). However, combined exposure of plants to high CO2 and SO2 eliminated the negative effects of SO2. Sulfate accumulation was almost equal in plants exposed to SO2 and, high CO2 and SO2. A significant increase in ascorbate, glutathione and their redox state was observed in plants exposed to high CO2 and SO2, compared to that of plants exposed to solely SO2. The absence of the negative efects of SO2 in the presence of high CO2 might be related to a high redox state of ascorbate and glutathione. Abbreviations: A(max), maximum rate of oxygen evolution at saturated light and CO2 (mumol m-2 s-1); ASA, reduced ascorbic acid; DHA, dehydroascorbic acid; F(m), maximum emission of photosystem-II chlorophyll fluorescence; F(v), variable component of F(m); GSH, reduced glutathione; GSSG, oxidized glutathione.

939^3^Rattray,EAS^Paterson,E^Killham,K^1995^1^Characterization of the dynamics of C-partitioning within lolium-perenne and to the rhizosphere microbial biomass using C-14 pulse-chase^263^19^4^280-286^^^^^Mar^^^^^4677
1096^1790^1791^1792^344^407^409^417^57^975^ CO2 and SO2 eliminated the negative effects of SO2. Sulfate accumulation was almost equal in plants exposed to SO2 and, high CO2 and SO2. A significant increase in ascorbate, glutathione and their redox state was observed in plants exposed to high CO2 and SO2, compared to that of plants exposed to solely SO2. The absence of the negative efects of SO2 in the presence of high CO2 might be related to a high redox state of ascorbate and glutathione. Abbreviations: A(max), maximum rate of oxygen evolutioA^4676^The dynamics of C partitioning with Lolium perenne and its associated rhizosphere was investigated in plant-soil microcosms using C-14 pulse-chase labelling. The CO2(C-14) pulse was introduced into the shoot chamber and the plants allowed to assimilate the label for a fixed period. The microcosm design facilitated independent monitoring of shoot and root/soil respiration during the chase period. Partitioning between above- and below-ground pools was determined between 30 min and 168 h after the pulse, and the distribution was found to vary with the length of the chase period. Initially (30 min after the pulse), C-14 was predominantly (99%) in the shoot biomass and declined thereafter. The results indicate that translocation of recent photoassimilate is rapid, with C-14 detected below ground within 30 min of pulse application. The translocation rate of C-14 below ground was maximal (6.2% h-1) between 30 min and 3h after the pulse, with greatest incorporation into the microbial biomass detected at 3 h. After 3 h, the microbial biomass C-14 pool accounted for 74% of the total C-14 rhizosphere pool. By 24 h, approximately 30% of C-14 assimilate had been translocated below ground; thereafter C-14 translocation was greatly reduced. Partitioning of recent assimilate changed with increasing CO2 concentration. The proportion of C-14 translocated below ground almost doubled from 17.76% at the ambient atmospheric CO2 concentration (450 ppm) to 33.73% at 750 ppm CO2 concentration. More specifically, these changes occurred in the root biomass and the total rhizosphere pools, with two- and threefold C-14 increases at an elevated CO2 concentration compared to ambient, respectively. The pulse- labelling strategy developed in this study provided sufficient sensitivity to determine perturbations in C dynamics in L. perenne, in particular rhizosphere C pools, in response to an elevated atmospheric CO2 concentration.
een 30 min and 3h after the pulse, with greatest incorporation into the microbial biomass detected at 3 h. 940^3^Raveh,E^Gersani,M^Nobel,PS^1995^1^Co2 uptake and fluorescence responses for a shade-tolerant cactus hylocereus-undatus under current and doubled co2 concentrations^37^93^3^505-511^^^^^Mar^^^^^4679
1669^312^348^372^376^401^529^547^779^92^f recent assimilate changed with increasing CO2 concentration. The proportion of C-14 translocated below ground almost doubled from 17.76% at the ambient atmospheric CO2 concentration (450 ppm) to 33.73% at 750 ppm CO2 concentration. More specifically, these changes occurred in the root biomass and the total rhizosphere pools, with two- and threefold C-14 increases at an elevated CO2 concentration compared to ambient, respectively. The pulse- labelling strategy developed in this study provided sufficient sensitivity to determine perturbations in C dynamics in L. perenne, in particular rhizosphere C pools, in response to an elevated atmospheric CO2 concentration.
een 30 min and 3h after the pulse, with greatest incorporation into the microbial biomass detected at 3 h. A^4678^Hylocereus undatus (Haworth) Britton and Rose growing in controlled environment chambers at 370 and 740 mu mol CO2 mol(- 1) air showed a Crassulacean acid metabolism (CAM) pattern of CO2 uptake, with 34% more total daily CO2 uptake under the doubled CO2 concentration and most of the increase occurring in the late afternoon. For both CO2 concentrations, 90% of the maximal daily CO2 uptake occurred at a total daily photosynthetic photon flux density (PPFD) of only 10 mol m(-2) day(-1) and the best day/night air temperatures were 25/15 degrees C. Enhancement of the daily net CO2 uptake by doubling the CO2 concentration was greater under the highest PPFD (30 mol m(-2) day(-1)) and extreme day/night air temperatures (15/5 and 45/35 degrees C). After 24 days of drought, daily CO2 uptake under 370 mu mol CO2 mol(-1) was 25% of that under 740 mu mol CO2 mol(-1). The ratio of variable to maximal chlorophyll fluorescence (F-v/F-m) decreased as the PPFD was raised above 5 mol m(-2) day(-1), at extreme day/night temperatures and during drought, suggesting that stress occurred under these conditions. F-v/F-m was higher under the doubled CO2 concentration, indicating that the current CO2 concentration was apparently limiting for photosynthesis. Thus net CO2 uptake by the shade-tolerant H. undatus, the photosynthetic efficiency of which was greatest at low PPFDs, showed a positive response to doubling the CO2 concentration, especially under stressful environmental conditions.

941^2^Robertson,EJ^Leech,RM^1995^1^Significant changes in cell and chloroplast development in young wheat leaves (triticum-aestivum CV hereward) grown in elevated co2^8^107^1^63-71^^^^^Jan^^^^^4681
188^243^312^344^360^376^385^417^829^962^ air temperatures (15/5 and 45/35 degrees C). After 24 days of drought, daily CO2 uptake under 370 mu mol CO2 mol(-1) was 25% of that under 740 mu mol CO2 mol(-1). The ratio of variable to maximal chlorophyll fluorescence (F-v/F-m) decreased as the PPFD was raised above 5 mol m(-2) day(-1), at extreme day/night A^4680^Cell and chloroplast development were characterized in young Triticum aestivum cv Hereward leaves grown at ambient (350 mu L L(-1)) or at elevated (650 mu L L(-1)) CO2. In elevated CO2, cell and chloroplast expansion was accelerated by 10 and 25%, respectively, in the first leaf of 7-d-old wheat plants without disruption to the leaf developmental pattern. Elevated CO2 did not affect the number of chloroplasts in relation to mesophyll cell size or the linear relationship between chloroplast number or size and mesophyll cell size. No major changes in leaf anatomy or in chloroplast ultrastructure were detected as a result of growth in elevated CO2, but there was a marked reduction in starch accumulation. In leaf sections fluorescently tagged antisera were used to visualize and quantitate the amount of cytochrome f, the alpha- and beta- subunits of the coupling factor 1 in ATP synthase, D1 protein of the photosystem II reaction center, the 33-kD protein of the extrinsic oxygen-evolving complex, subunit II of photosystem I, and ribulose-1,5-bisphosphate carboxylase/oxygenase. A significant finding was that in 10 to 20% of the mesophyll cells grown in elevated CO2 the 33-kD protein of the extrinsic oxygen-evolving complex of photosystem II and cytochrome f were deficient by 75%, but the other proteins accumulated normally.

942^2^Seegmuller,S^Rennenberg,H^1994^1^Interactive effects of mycorrhization and elevated carbon- dioxide on growth of young pedunculate oak (quercus-robur L) trees^206^167^2^325-329^^^^^Dec^^^^^4683
229^349^361^ize. No major changes in leaf anatomy or in chloroplast ultrastructure were detected as a result of growth in elevated CO2, but there was a marked reduction in starch accumulation. In leaf sections fluorescently tagged antisera were used to visualize and quantitate the amount of cytochrome f, the alpha- and beta- subunits of the coupling factor 1 in ATP synthase, D1 protein of the photosystem II reaction center, the 33-kD protein of the extrinsic oxygen-evolving complex, subunit IIA^4682^Pedunculate oak (Quercus robur L.) was germinated and grown at ambient CO2 level and 650 ppmv CO2 in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 6 month under nutrient non-limiting conditions. Mycorrhization and elevated atmospheric CO2 each supported the growth of the trees. Stem height, stem diameter, and dry matter accumulation of pedunculate oak were increased by mycorrhization. Elevated atmospheric CO2 enhanced stem height, stem diameter, fresh weight and dry weight, as well as lateral root formation of the trees. In combination, mycorrhization and elevated atmospheric CO2 had a more than additive, positive effect on tree height and biomass accumulation, and further improved lateral root formation of the trees. From these findings it is suggested that the efficiency of the roots in supporting the growth of the shoot is increased in mycorrhized oak trees at elevated atmospheric CO2.
, the 33-kD protein of the extrinsic oxygen-evolving complex, subunit II943^2^Seligman,NG^Sinclair,TR^1995^1^Global environment change and simulated forage quality of wheat .2. Water and nitrogen stress^207^40^1^29-37^^^^^Jan^^^^^4685
130^1793^204^312^349^434^547^771^92^th under nutrient non-limiting conditions. Mycorrhization and elevated atmospheric CO2 each supported the growth of the trees. Stem height, stem diameter, and dry matter accumulation of pedunculate oak were increased by mycorrhization. Elevated atmospheric CO2 enhanced stem height, stem diameter, fresh weight and dry weight, as well as lateral root formation of the trees. In combination, mycorrhization and elevated atmospheric CO2 had a more than additive, positive effect on tree height and biomass accumulation, and further improved lateral root formation of the trees. From these findings it is suggested that the efficiency of the roots in supporting the growth of the shoot is increased in mycorrhized oak trees at elevated atmospheric CO2.
, the 33-kD protein of the extrinsic oxygen-evolving complex, subunit IIA^4684^Forage crops are frequently subjected to stress conditions resulting from inadequate supplies of water and N. Because forages grown under these stress conditions constitute an important resource in animal agriculture, this study was undertaken to assess possible changes in the nutritive value and productivity of forage crops as a consequence of global environment change. A relatively simple, mechanistic model of wheat was extended to simulate growth and important determinants of feed quality ([N], leaf:stem, dry matter digestibility) in an annual, temperate climate C-3 forage grass. Weather data for a semiarid region and different levels of applied N were used to examine the response of forage productivity to various levels of water and N availability. Not surprisingly, responses to global environment change were highly dependent on the availability of both water and N. When either resource was available at low levels, production of digestible dry matter was nearly unchanged by elevated [CO2] or increased temperature. When compared at equivalent development stages, small increases in forage quality were simulated, mainly because higher temperature resulted in achievement of the initiation of grain fill at an earlier date. As N availability increased, differences in forage characteristics and productivity became more prominent. Elevated ambient [CO2] increased vegetative mass, digestible dry matter, and concentration of digestible dry matter but decreased leaf:stem and [N]. Increased temperature generally had an effect on forage traits that was opposite to the elevated [CO2] response. The combined effects of both factors sometimes cancelled each other, but usually one of the factors was dominant. Negative effects of temperature tended to be aggravated by dry conditions. At crop maturity, positive effects of elevated atmospheric [CO2] on forage productivity and quality were severely decreased by nutrient and physiological constraints. These simulations indicate that when forage crops are grown under irrigation in semiarid regions, there may be substantial and complex changes in productivity and feed quality as a consequence of warmer temperature and elevated atmospheric [CO2]. Under rainfed conditions, these differences could be quite erratic and virtually unpredictable within the current range of interannual variation in forage productivity and quality.

944^2^Sinclair,TR^Seligman,NG^1995^1^Global environment change and simulated forage quality of wheat .1. Nonstressed conditions^207^40^1^19-27^^^^^Jan^^^^^4687
130^312^349^372^434^435^436^57^724^92^posite to the elevated [CO2] response. The combined effects of both factors sometimes cancelled each other, but usually one of the factors was dominant. Negative effects of temperature tended to be aggravated by dry conditions. At crop maturity, positive effects of elevated atmospheric [CO2] on forage productivity and quality were severely decreased by nutrient and physiological constraints. These simulations indicate that when forage crops are grown under irrigaA^4686^Projected changes in the global environment may affect both the quantity and quality of grain and forage mass produced and harvested in that environment. Quality is a major factor in determining the value of a forage crop as feed for ruminants. The objective of this study was to make a preliminary assessment of potential changes in the quantity and quality of forage as measured by [N] and leaf:stem of an annual, temperate climate C-3 forage crop grown under nonstressed conditions. Starting with a relatively simple, well-checked mechanistic model of wheat, adaptations were added to estimate changes in forage attributes. Increased temperature influenced both yield and nutritive value, mainly through changes in ontological development rates. Elevated,atmospheric [CO2] resulted in greater mass accumulation, but with lower leaf:stem and [N]. The combined effect of increased temperature and elevated [CO2] was to decrease slightly forage yield and to increase the forage nutritive value. These compensating effects of higher temperature and elevated [CO2] could be modified by interactions between [CO2] and the chemical composition and cell wall structure of forage plants. Analysis of such subtle interaction requires considerable experimental amplification.

945^3^Sulzman,EW^Poiani,KA^Kittel,TGF^1995^1^Modeling human-induced climatic-change - a summary for environmental managers^264^19^2^197-224^^^^^Mar-Apr^^^^^4689
1637^1794^1795^1796^1797^1798^344^372^430^659^n under nonstressed conditions. Starting with a relatively simple, well-checked mechanistic model of wheat, adaptations were added to estimate changes in forage attributes. Increased temperature influenced both yield and nutritive value, mainly through changes in ontological development rates. Elevated,atmospheric [CO2] resulted in greater mass accumulation, but with lower leaf:stem and [N]. The combined effect of increased temperature and elevated [CO2] was to decrease slightly forage yield and to increase the forage nutritive value. These compensating efA^4688^The rapid increase in atmospheric concentrations of greenhouse gases has caused concern because of their potential to alter the earth's radiation budget and disrupt current climate patterns. While there are many uncertainties associated with use of general circulation models (GCMs), GCMs are currently the best available technology to project changes in climate associated with elevated gas concentrations. Results indicate increases in global temperature and changes in global precipitation patterns are likely as a result of doubled CO2. GCMs are not reliable for use at the regional scale because local scale processes and geography are not taken into account. Comparison of results from five GCMs in three regions of the United States indicate high variability across regions and among models depending on season and climate variable. Statistical methods of scaling model output and nesting finer resolution models in global models are two techniques that may improve projections. Despite the many limitations in GCMs, they are useful tools to explore climate-earth system dynamics when used in conjunction with water resource and ecosystem models. A variety of water resource models showed significant alteration of regional hydrology when run with both GCM-generated and hypothetical climate scenarios, regardless of region or model complexity. Similarly, ecological models demonstrate the sensitivity of ecosystem production, nutrient dynamics, and distribution to changes in climate and CO2 levels. We recommend the use of GCM-based scenarios in conjunction with water resource and ecosystem models to guide environmental management and policy in a ''no-regrets'' framework or as part of a precautionary approach to natural resource protection.

946^1^Suzuki,K^1995^1^Phosphoglycolate phosphatase-deficient mutants of chlamydomonas-reinhardtii capable of growth under air^231^36^1^95-100^^^^^Jan^^^^^4691
1799^1800^resolution models in global models are two techniques that may improve projections. Despite the many limitations iA^4690^Mutants deficient in phosphoglycolate phosphatase (PGPase) require elevated levels of CO2 for growth in the light and cannot grow when photorespiration occurs. Revertants, namely, double mutants capable of growth under air without restoration of the missing PGPase activity, might be expected to have secondary mutations that reduce or eliminate photorespiration. Nineteen revertants were selected from a culture of a PGPase- deficient mutant of Chlamydomonas reinhardtii (pgp-1-18-7F) after a second mutagenesis that involved treatment with 5- fluorodeoxyuridine and ethyl methanesulfonate. There were significant differences in the photosynthetic affinity for CO2 among revertant cells grown under 5% CO2. Eight revertants had five times higher photosynthetic affinity for CO2 than that of wild type 2137 cells grown under 5% CO2, resembling air-adapted wild-type cells, whereas four revertants had less than half the affinity for CO2 of the wild type. In all of the revertant cells with higher affinity grown in 5% CO2, the rates of photosynthesis under levels of CO2 below those in air were apparently higher than that of the wild type, whereas the rates under CO2-saturating conditions were lower than that of wild type, indicating that the efficiency of photosynthesis under air was significantly improved in these revertants. In addition, some revertants had a photosynthetic capacity and a growth rate higher than those of the wild type, without any increased photosynthetic affinity for CO2.

947^4^Tschaplinski,TJ^Stewart,DB^Hanson,PJ^Norby,RJ^1995^1^Interactions between drought and elevated co2 on growth and gas-exchange of seedlings of 3 deciduous tree species^84^129^1^63-71^^^^^Jan^^^^^4693
256^312^342^344^345^374^376^511^546^794^had five times higher photosynthetic affinity for CO2 than that of wild type 2137 cells grown under 5% CO2, resembling air-adapted wild-type cells, whereas four revertants had less than half the affinity for CO2 of the wild type. In all of the revertant cells with higher affinity grown in 5A^4692^Interactions between elevated atmospheric CO2 and drought on growth and gas exchange of American sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.) and sugar maple (Acer saccharum Marsh.) were investigated using 1- yr-old seedlings, planted in 81 pots and grown in four open-top chambers, containing either ambient air or ambient air enriched with 300 mu mol mol(-1) CO2. Two soil moisture regimes were included within each chamber: a 'well-watered' treatment with plants watered daily and a 'drought' treatment in which plants were subjected to a series of drought cycles. Duration and depth of the drought cycles were determined by soil matric potential. Mean soil water potential at rewatering for the water-stressed seedlings under ambient CO2 for sugar maple, sweetgum and sycamore was -0.5, -0.7 and -1.8 MPa, respectively, compared with > -0.1 MPa for all well-watered plants. Elevated CO2 increased relative growth rate of well- watered sugar maple by 181%, resulting in a 4.3-fold increase in total plant dry weight after 81 d, compared with 1.4 and 1.6-fold increases for sweetgum and sycamore, respectively, after 69 d. Although elevated CO2 increased net CO2 assimilation rate of sugar maple by 115 %, there was a 10-fold increase in leaf area which contributed to the growth response. Although drought did not eliminate a growth response of sugar maple to elevated CO2, it greatly reduced the elevated CO2- induced enhancement of relative growth rate. In contrast, relative growth rates of sweetgum and sycamore were not significantly increased by elevated CO2. Drought, under elevated CO2, reduced leaf area of all three species to a greater extent than it reduced net CO2 assimilation rate. The response ranged from no effect in sugar maple to a 40 % reduction in sycamore, with sweetgum exhibiting an intermediate response. Results indicate that drought may alter the growth response, gas exchange and water relations of tree species growing in an elevated CO2 atmosphere. Under high nutrient and water availability, sugar maple may benefit the most (of the three species studied) from a CO2-enriched atmosphere, but productivity gains will be limited if frequent drought is prevalent.

948^4^Vivin,P^Gross,P^Aussenac,G^Guehl,JM^1995^1^Whole-plant co2 exchange, carbon partitioning and growth in quercus-robur seedlings exposed to elevated co2^184^33^2^201-211^^^^^Mar-Apr^^^^^4695
1801^1802^1803^1804^243^310^376^423^57^692^ induced enhancement of relative growth rate. In contrast, relative growth rates of sweetgum and sycamore were not significantly increased by elevated CO2. Drought, under elevated CO2, reduced leaf area of all three species to a greater extent than it reduced net CO2 assimilation rate. The response ranged from no effect in sugar maple to a 40 % reduction in sycamore, with sweetgum exhibiting an intermediate response. Results indicate that drought may alter the growth response, gas exchange and water relations of tree species growing in an elevated CO2 atmosphere. Under high nutrient and waA^4694^Pedunculate oak acorns (Quercus robur L.) were germinated and grown under nonlimiting nutritional and water conditions in controlled-environment greenhouses with ambient (350 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) CO2 concentrations. A semiclosed gas exchange measurements, and (CO2)-C-13 labelling, system (1.5% (CO2)-C-13) was used to simultaneously assess (a) the CO2 exchange of both aerial and below-ground (roots plus soil) compartments of the soil-plant system and (b) the partitioning of the recently photo-assimilated carbon. Measurements were made during the fast aerial growth phase (July 30) and at the end of the growing season (October 15). On July 30, whole-plant dry mass had been increased by 44% since the beginning of the growing season in the elevated CO2 treatment, whereas at the end of the growing season the enhancing effect was only 17%. Elevated CO2 stimulated net CO2 assimilation rate per unit leaf area (A) in July (+40%), whereas in October this stimulation had disappeared. The respiratory CO2 evolution of the root-soil compartment (individual plant basis) was stimulated by 35% under the elevated CO2 conditions on July 30, but not on October 15. In July, relative specific allocation (RSA), a parameter expressing the sink strength, was higher in all compartments under 700 mu mol mol(-1) compared to 350 mu mol mol(-1). Moreover in root tips, the RSA values determined 4 h after the labelling were particularly high (7.8%)with elevated CO2, whereas under ambient CO2 RSA values were close to zero.

949^2^Williams,TG^Colman,B^1995^1^Quantification of the contribution of co2, hco3-, and external carbonic-anhydrase to photosynthesis at low dissolved inorganic carbon in chlorella-saccharophila^8^107^1^245-251^^^^^Jan^^^^^4697
1545^1622^1805^1806^362^441^543^958^treatment, whereas at the end of the growing season the enhancing effect was only 17%. Elevated CO2 stimulated net CO2 assimilation rate per unit leaf area (A) in July (+40%), whereas in October this stimulation had disappeared. TA^4696^An equation has been developed incorporating whole-cell rate constants for CO2 and HCO3- that describes accurately photosynthesis (Phs) in suspensions of unicellular algae at low dissolved inorganic carbon. At pH 8.0 the concentration of CO2 available to the algal cells depends on the rate of supply from, and the loss to, HCO3- and the rate of use by the cells. At elevated cell densities (>30 mg chlorophyll [Chl] L(-1)), at which CO2 use by the cells is high, the slope of a graph of absolute Phs versus Chl concentration approaches the rate of Phs on a milligram of Chl basis because of HCO3- use alone. The slope of a graph of Phs versus HCO3- will be the rate constant for HCO3- and for Chlorella saccharophila it was 0.16 L mg(-1) Chl h(-1). The difference between the constants for dissolved inorganic carbon (measured in cells with external carbonic anhydrase) and HCO3-1 is the constant for CO2, which was 26 L mg(-1) Chl h(-1). This difference causes the half-saturation constant for Phs to increase 5- to 6-fold at high cell densities. The increase in CO2 use as a result of external carbonic anhydrase is described mathematically as a function of cell density.

950^6^Amthor,JS^Mitchell,RJ^Runion,GB^Rogers,HH^Prior,SA^Wood,CW^1994^1^Energy content, construction cost and phytomass accumulation of glycine-max (L) merr and sorghum-bicolor (L) moench grown in elevated co2 in the field^84^128^3^443-450^^^^^Nov^^^^^4699
1035^243^310^312^348^374^376^417^434^57^lls is high, the slope of a graph of absolute Phs versus Chl concentration approaches the rate of Phs on a milligram of Chl basis because of HCO3- use alone. The slope of a graph of Phs versus HCO3- will be the rate constant for HCO3- and for Chlorella saccharophila it was 0.16 L mg(-1) Chl h(-1). The difference between the constants for dissolved inorganic carbon (measured in cells with external carbonic anhydrase) and HCO3-1 is the constant for CO2, which was 26 L mg(-1) Chl h(-1). This difference causes the half-saturation constant for Phs to increase 5- tA^4698^Grain sorghum [Sorghum] bicolor (L.) Moench, a C-4 crop] and soybean [Glycine max (L.) Merr. cv. Stonewall, a C-3 crop] plants were grown in ambient (c. 360 mu l l(-1)) and twice- ambient (c. 720 mu l l(-1)) CO2 levels in open-top chambers in soil without root constriction. Plant dry mass, energy content, composition and construction cost (i.e. amount of carbohydrate required to synthesize a unit of plant dry mass) were assessed at the end of the growing season. Elevated CO2 (a) increased phytomass accumulation (kg per plant) in both species, (b) had little affect on energy concentration (MJ kg(-1) plant) but caused large increases in the amount of plant energy per ground area (MJ m(-2) ground), and (c) did not alter specific growth cost (kg carbohydrate kg(-1) plant growth) but greatly increased growth cost per ground area (kg carbohydrate m(-2) ground) because growth was enhanced. For soybean, twice-ambient CO2 resulted in a 50 % increase in the amount of nitrogen and energy in grain (seed plus pod) per ground area. This response to elevated CO2 has important implications for agricultural productivity during the next century because the rate of human population growth is exceeding the rate of increase of land used for agriculture so that future food demands can only be met by greater production per ground area.

951^2^Carlsson,BA^Callaghan,TV^1994^1^Impact of climate-change factors on the clonal sedge carer bigelowii - implications for population-growth and vegetative spread^122^17^4^321-330^^^^^Dec^^^^^4701
1277^1807^1808^189^30^312^372^374^417^429^ little affect on energy concentration (MJ kg(-1) plant) but caused large increases in the amount of plant energy per ground area (MJ m(-2) ground), and (c) did not alter specific growth cost (kg carbohydrate kg(-1) plant growth) but greatly increased growth cost per ground area (kg carbohydrate m(-2) ground) because growth was enhanced. For soybean, twice-ambient CO2 resulted in a 50 % increase in the amount of nitrogen and energy in grain (seed plus pod)A^4700^Hypothesized life-cycle responses to climate change for the arctic, clonal perennial Carer bigelowii are constructed using a range of earlier observations and experiments together with new information from monitoring and an environmental perturbation study. These data suggest, that under current climate change scenarios, increases in CO2, temperature and nutrient availability would promote growth in a qualitatively similar way. The evidence suggests that both tiller size and daughter tiller production will increase, and be shifted towards production of phalanx tillers which have a greater propensity for flowering. Furthermore, age at tillering as well as tiller life span may decrease, whereas survival of younger age classes might be higher. Mathematical models using experimental data incorporating these hypotheses were used to a) integrate the various responses and to calculate the order of magnitude of changes in population growth rate (lambda), and b) to explore the implications of responses in individual demographic parameters for population growth rate. The models suggest that population growth rate following climate change might increase significantly, but not unrealistically so, with the younger, larger, guerilla tillers being the most important tiller categories contributing to lambda. The rate of vegetative spread is calculated to more than double, while cyclical trends in flowering and population growth are predicted to decrease substantially.

952^4^Chen,DX^Coughenour,MB^Eberts,D^Thullen,JS^1994^1^Interactive effects of co2 enrichment and temperature on the growth of dioecious hydrilla-verticillata^173^34^4^345-353^^^^^Oct^^^^^4703
312^434^509^733^851^881^fe span may decrease, whereas survival of younger age classes might be higher. Mathematical models using experimental data incorporating these hypotheses were used to a) integrate the various responses and to calculate the order of magnitude of changes in population growth rate (lambda), and b) to explore the implications of responses in indiA^4702^Experiments of plant growth responses to different CO2 concentrations and temperatures were conducted in growth chambers to explore the interactive effects of atmospheric CO2 enrichment and temperature on the growth and dry matter allocation of dioecious Hydrilla [Hydrilla verticillata (L.f.) Royle]. Hydrilla plants were exposed to two atmospheric CO2 concentrations (350 and 700 ppm) and three temperatures (15, 25 and 32 degrees C) under a 12-hr photoperiod for about 2 months. The plant growth analysis showed that elevated CO2 appeared to enhance the growth of Hydrilla, and that the percentage of the enhancement is strongly temperature-dependent. Maximum biomass production was achieved at 700 ppm CO2 and 32 degrees C. At 15 degrees C, the total dry matter production was increased about 27% by doubling CO2, due to a 26% enhancement of leaf biomass, a 34% enhancement of stem biomass and 16% enhancement of root biomass. At 25 degrees C, the dry matter production was increased about 46% by doubling CO2, due to a 29% enhancement of leaf biomass, a 27% enhancement of stem biomass and 40% enhancement of root biomass. At 32 degrees C, however, the percentage of the enhancement of total dry matter production by doubling CO2 was only about 7%. The dry matter allocation among different plant parts was influenced by temperature but not by elevated CO2 concentration.

953^1^Crush,JR^1994^1^Elevated atmospheric co2 concentration and rhizosphere nitrogen-fixation in 4 forage plants^167^37^4^455-463^^^^^^^^^^4705
1030^1096^1684^1809^1810^1811^427^541^562^92^nhance the growth of Hydrilla, and that the percentage of the enhancement is strongly temperature-dependent. Maximum biomass production was achieved at 700 ppm CO2 and 32 degrees C. At 15 degrees C, the total dry matter production was increased about 27% by doubling CO2, due to a 26% enhancement of leaf biomass, a 34% enhancement of stem biomass and 16% enhancement of root biomass. At 25 degrees C, the dry matter production was increased about 46% by doubling CO2, dA^4704^Lolium x boucheanum (2n and 4n), Plantago lanceolata, and Pennisetum clandestinum were grown in pots of soil in growth rooms with factorial combinations of 350 or 700 mul/l atmospheric CO2 and day/night temperatures of 28/23-degrees-C or 18/13-degrees-C. Both cultivars of Lolium and P. lanceolata grew faster with elevated CO2 but P. clandestinum was unaffected. Rhizosphere nitrogenase activity, assessed by acetylene reduction, was reduced by the 700 mul/l CO2 treatment in the tetraploid Lolium but otherwise did not vary significantly with CO2 level.

954^4^Curtis,PS^Zak,DR^Pregitzer,KS^Teeri,JA^1994^1^Aboveground and belowground response of populus grandidentata to elevated atmospheric co2 and soil n-availability^206^165^1^45-51^^^^^^^^^^4707
243^312^376^419^57^680^705^increased about 27% by doubling CO2, due to a 26% enhancement of leaf biomass, a 34% enhancement of stem biomass and 16% enhancement of root biomass. At 25 degrees C, the dry matter production was increased about 46% by doubling CO2, dA^4706^Soil N availability may play an important role in regulating the long-term responses of plants to rising atmospheric CO2 partial pressure. To further examine the linkage between above- and belowground C and N cycles at elevated CO2, we grew clonally propagated cuttings of Populus grandidentata in the field at ambient and twice ambient CO2 in open bottom root boxes filled with organic matter poor native soil. Nitrogen was added to all root boxes at a rate equivalent to net N mineralization in local dry oak forests. Nitrogen added during August was enriched with N-25 to trace the flux of N within the plant-soil system. Above- and belowground growth, CO2 assimilation, and leaf N content were measured non- destructively over 142 d. After final destructive harvest, roots, stems, and leaves were analyzed for total N and N-15. There was no CO2 treatment effect on leaf area, root length, or net assimilation prior to the completion of N addition. Following the N addition, leaf N content increased in both CO2 treatments, but net assimilation showed a sustained increase only in elevated CO2 grown plants. Root relative extension rate was greater at elevated CO2, both before and after the N addition. Although final root biomass was greater at elevated CO2, there was no CO2 effect on plant N uptake or allocation. While low soil N availability severely inhibited CO2 responses, high CO2 grown plants were more responsive to N. This differential behavior must be considered in light of the temporal and spatial heterogeneity of soil resources, particularly N which often limits plant growth in temperate forests.

955^4^Dippery,JK^Tissue,DT^Thomas,RB^Strain,BR^1995^1^Effects of low and elevated co2 on C-3 and C-4 annuals .1. Growth and biomass allocation^2^101^1^13-20^^^^^Jan^^^^^4709
1073^1758^243^312^344^361^374^376^417^540^total N and N-15. There was no CO2 treatment effect on leaf area, root length, or net assimilation prior to the completion of N addition. Following the N addition, leaf N content increased in both CO2 tA^4708^In order to study C-3 and C-4 plant growth in atmospheric CO2 levels ranging from past through predicted future levels, Abutilon theophrasti (C-3) and Amaran thus retroflexus (C-4) were grown from seed in growth chambers controlled at CO2 partial pressures of 15 Pa (below Pleistocene minimum) 27 Pa (pre-industrial), 35 Pa (current) and 70 Pa (predicted future). After 35 days of growth, CO2 had no effect on the relative growth rate, total biomass or partitioning of biomass in the C- 4 species. However, the C-3 species had greater biomass accumulation with increasing CO2 partial pressure. C-3 plants grown in 15 Pa CO2 for 35 days had only 8% of the total biomass of plants grown in 35 Pa CO2. In 15 Pa CO2, C-3 plants had lower relative growth rates and lower specific leaf mass than plants grown in higher CO2 partial pressures, and aborted reproduction. C-3 plants grown in 70 Pa CO2 had greater root mass and root-to-shoot ratios than plants grown in lower CO2 partial pressures. These findings support other studies that show C-3 plant growth is more responsive to CO2 partial pressure than C-4 plant growth. Differences in growth responses to CO2 levels of the Pleistocene through the future suggest that competitive interactions of C-3 and C-4 annuals have changed through geologic time. This study also provided evidence that C-3 annuals may be operating near a minimum CO2 partial pressure for growth and reproduction at 15 Pa CO2.

956^4^Epron,D^Godard,D^Cornic,G^Genty,B^1995^1^Limitation of net co2 assimilation rate by internal resistances to co2 transfer in the leaves of 2 tree species (fagus- sylvatica L and castanea-sativa mill)^9^18^1^43-51^^^^^Jan^^^^^4711
1812^1813^1814^256^310^372^384^417^448^493^5 Pa CO2, C-3 plants had lower relative growth rates and lower specific leaf mass than plants grown in higher CO2 partial pressures, and aborted reproduction. C-3 plants grown in 70 Pa CO2 had greater root mass and root-to-shoot ratios than plants grown in lower CO2 partial pressures. These findings support otheA^4710^Using a combination of gas-exchange and chlorophyll fluorescence measurements, low apparent CO2/O-2 specificity factors (1300 mol mol(-1)) were estimated for the leaves of two deciduous tree species (Fagus sylvatica and Castanea sativa), These low values contrasted with those estimated for two herbaceous species and were ascribed to a drop in the CO2 mole fraction between the intercellular airspace (C-i) and the catalytic site of Rubisco (C-c) due to internal resistances to CO2 transfer, C-c was calculated assuming a specificity of Rubisco value of 2560 mol mol(-1). The drop between C-i and C-c was used to calculate the internal conductance for CO2 (g(i)), A good correlation between mean values of net CO2 assimilation rate (A) and g(i) was observed within a set of data obtained using 13 woody plant species, including our own data, We report that the relative limitation of A, which can be ascribed to internal resistances to CO2 transfer, was 24-30%, High internal resistances to CO2 transfer may explain the low apparent maximal rates of carboxylation and electron transport of some woody plant species calculated from A/C-i curves.

957^3^Garcia,RL^Idso,SB^Kimball,BA^1994^1^Net photosynthesis as a function of carbon-dioxide concentration in pine trees grown at ambient and elevated co2^173^34^3^337-341^^^^^Jul^^^^^4713
310^360^376^417^d to a drop in the CO2 mole fraction between the intercellular airspace (C-i) and the catalytic site of Rubisco (C-c) due to internal resistances to CO2 transfer, C-c was calculated assuming a specificity of Rubisco value of 2560 mol mol(-1). The drop between C-i and C-c was used to calculate the internal conductance for CO2 (g(i)), A good correlation between mean values of net CO2 assimilation rate (A) and g(i) was observed within a set of data obtained using 13 woody plant species, including our own data, We report that the relative limitation of A, which can be ascribed to internal resistances to CO2 transfer, was 24-30%, High internal resistances to CO2 transfer may explainA^4712^Pinus eldarica seedlings were grown in a field of Avondale loam at Phoenix, Arizona within transparent open-top enclosures maintained for 15 months at mean CO2 concentrations of 402 and 788 mu l 1(-1), after which whole-tree net photosynthetic rates were measured at a number of CO2 concentrations ranging from ambient (360 mu l 1(-1)) to 3000 mu l 1(-1). Rates of the low- CO2-treatment trees saturated at approximately five times their ambient-concentration value; while rates of the high-CO2- treatment trees rose linearly across the entire CO2 range investigated to more than 10 times their value al 360 mu l 1(- 1). These findings suggest that long-term exposure to elevated CO2 can increase the ability of trees with unrestricted root systems to respond positively to still higher CO2 concentrations.

958^4^Gorissen,A^Vanginkel,JH^Keurentjes,JJB^Vanveen,JA^1995^1^Grass root decomposition is retarded when grass has been grown under elevated co2^130^27^1^117-120^^^^^Jan
1044^312^344^407^57^634^661^y explain959^5^Grieb,B^Gross,U^Pleschka,E^Arnholdtschmitt,B^Neumann,KH^1994^1^Embryogenesis of photoautotrophic cell-cultures of daucus- carota L^177^38^2-3^115-122^^^^^Sep^^^^^4716
1815^1816^1817^1818^243^800^
A^4715^In this paper photoautotrophic carrot (Daucus carota L.) suspension cultures are described which are able to produce somatic embryos. The development of somatic embryos, however, requires a sucrose supplement. Although an elevation of the CO2 concentration up to 2.3% results in the same level of dry weight production as with sucrose in the medium, somatic embryos could not be observed. Results on the influence of sucrose on some aspects of the photosynthetic apparatus of cultured cells are discussed.

960^5^Idso,SB^Idso,KE^Garcia,RL^Kimball,BA^Hoober,JK^1995^1^Effects of atmospheric co2 enrichment and foliar methanol application on net photosynthesis of sour orange tree (citrus- aurantium, rutaceae) leaves^5^82^1^26-30^^^^^Jan^^^^^4718
130^264^372^384^92^0^^^^^Jan
1044^312^344^407^57^634^661^y explainA^4717^Foliar spray applications of 40% aqueous methanol were made to sunlit leaves of sour orange trees that had been grown continuously in clear-plastic-wall open-top enclosures maintained out-of-doors at Phoenix, Arizona, for over 5.5 years in ambient air of approximately 400 mu mol mol(-1) CO2 and in air enriched with CO2 to a concentration of approximately 700 mu mol mol(-1). No unambiguous effects of the methanol applications were detected in net photosynthesis measurements made on foliage in either of the two CO2 treatments. The 75% increase in CO2 however, raised the upper-limiting leaf temperature for positive net photosynthesis by approximately 7 C, which resulted in a 75% enhancement in net photosynthesis at a leaf temperature of 31 C, a 100% enhancement at a leaf temperature of 35 C, and a 200% enhancement at 42 C.
ation on net photosynthesis of sour orange tree (citrus- aurantium, rutaceae) leaves^5^82^1^26-30^^^^^Jan^^^^^4718
130^264^372^384^92^0^^^^^Jan
1044^312^344^407^57^634^661^y explain961^7^Johnson,D^Geisinger,D^Walker,R^Newman,J^Vose,J^Elliot,K^Ball,T^1994^1^Soil pco(2), soil respiration, and root activity in co2- fumigated and nitrogen-fertilized ponderosa pine^206^165^1^129-138^^^^^^^^^^4720
1819^312^344^374^672^835^ars in ambient air of approximately 400 mu mol mol(-1) CO2 and in air enriched with CO2 to a concentration of approximately 700 mu mol mol(-1). No unambiguous effects of the methanol applications were detected in net photosynthesis measurements made on foliage in either of the two CO2 treatments. The 75% increase in CO2 however, raised the upper-limiting leaf temperature for positive net photosynthesis by approximately 7 C, which resulted in a 75% enhancement in net photosynthesis at a leaf temperature of 31 C, a 100% enhancement at a leaf temperature of 35 C, and a 200% enhancement at 42 C.
ation on net photosynthesis of sour orange tree (citrus- aurantium, rutaceae) leaves^5^82^1^26-30^^^^^Jan^^^^^4718
130^264^372^384^92^0^^^^^Jan
1044^312^344^407^57^634^661^y explainA^4719^The purpose of this paper is to describe the effects of CO2 and N treatments on soil pCO(2), calculated CO2 efflux, root biomass and soil carbon in open-top chambers planted with Pinus ponderosa seedlings. Based upon the literature, it was hypothesized that both elevated CO2 and N would cause increased foot biomass which would in turn cause increases in both total soil CO2 efflux and microbial respiration. This hypothesis was only supported in part: both CO2 and N treatments caused significant increases in root biomass, soil pCO(2), and calculated CO2 efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO2 efflux rates indicated that microbial respiration contributes little to total soil CO2 efflux in the field. Measurements of soil pCO(2) and calculated CO2 efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO2 and N treatments.
44^407^57^634^661^y explain962^5^Kemp,PR^Waldecker,DG^Owensby,CE^Reynolds,JF^Virginia,RA^1994^1^Effects of elevated co2 and nitrogen-fertilization pretreatments on decomposition on tallgrass prairie leaf-litter^206^165^1^115-127^^^^^^^^^^4722
1820^1821^1822^1823^1824^344^374^417^672^739^at both elevated CO2 and N would cause increased foot biomass which would in turn cause increases in both total soil CO2 efflux and microbial respiration. This hypothesis was only supported in part: both CO2 and N treatments caused significant increases in root biomass, soil pCO(2), and calculated CO2 efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO2 efflux rates indicated that microbial respiration contributes little to total soil CO2 efflux in the field. Measurements of soil pCO(2) and calculated CO2 efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO2 and N treatments.
44^407^57^634^661^y explainA^4721^Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C-4), Sorghastrum nutans (C-4), and Poa pratensis (C-3) plants that were grown in large open-top chambers under ambient or twice ambient CO2 and with or without nitrogen fertilization (45 kg N ha(-1)). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO2 on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter However, there was a large difference in characteristics of leaf Litter decomposition among the species. Paa leaf fitter had a different initial chemistry and decayed more rapidly than C-4 grasses. We conclude that an indirect effect of CO2 on decomposition and nutrient cycling could occur if CO2 induces changes in the relative aboveground biomass of the prairie species.

963^2^Kerstiens,G^Hawes,CV^1994^1^Response of growth and carbon allocation to elevated co2 in young cherry (prunus-avium L) saplings in relation to root environment^84^128^4^607-614^^^^^Dec^^^^^4724
361^362^417^685^zed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO2 on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter However, there was a large difference in characteristA^4723^The hypothesis that inadequate rooting volume may reduce the growth stimulation by elevated CO2 in potted tree seedlings and saplings was tested experimentally and by surveying the literature. One-year-old cherry saplings were grown for one season in naturally lit growth chambers in eight combinations of CO2 concentration (ambient; ambient + 250 ppm) and root environment (four types). The latter included (1) moderately restrictive pot volume (4 l) in combination with two levels of fertilizer addition (1a, 1b); (2) 10 l pots with total fertilizer content per pot as in treatment 1a, and (3) 20 l pots with five plants sharing five times the space and nutrient resources of treatment 1a. Plants were harvested in April, May, June, August and September. The overall mean effect of high CO2 plant dry mass by the end of the season was +24%. Interactive effects of root environments and CO2 concentrations on dry mass were not significant at the 5% level, but repeated measurements of basal stem diameter of individual plants indicated a significant impact of root environment on the response to CO2. Overall growth enhancement by elevated CO2 did not differ significantly between harvests, but it tended to increase during the season in those root environments which restricted growth in ambient CO2 most strongly (1a and 3). The hypothesis was rejected for this experiment. Leaf area and stem height were not affected by any treatment. The variation of carbon allocation to roots and shoots with plant size was very similar in all treatments. Plants grew faster in elevated CO2 very early in the season, and this resulted in small but significant differences between seasonal patterns of biomass partitioning in ambient and elevated CO2. A survey of 33 studies on growth responses of 47 tree species to elevated CO2 (600-800 ppm) showed that the relative change in biomass was not related to the ratio of plant biomass and pot volume found in either ambient or elevated CO2. We conclude that there is no evidence that inadequate pot volume had a negative impact on the stimulation of growth of tree species in elevated CO2.

964^3^Kleemola,J^Peltonen,J^Peltonensainio,P^1994^1^Apical development and growth of barley under different co2 and nitrogen regimes^161^173^2^79-92^^^^^Sep^^^^^4726
1010^130^312^349^422^435^723^ most strongly (1a and 3). The hypothesis was rejected for this experiment. Leaf area and stem height were not affected by any treatment. The variation of carbon allocation to roots and shoots with plant size was very similar in all treatments. Plants grew faster in elevated CO2 very early in the season, and this resulted in small but significant differences between seasonal patterns of biomass partitioning in ambient and elevated CO2. A survey of 33 studies on growth responses of 47 tree species to elevated CO2 (600-800 ppm) showed that the relative change in biomass was not related to the ratio of plant biomass and pot volume found in either ambient or elevated CO2. We conclude that there is no evidence that inadequate pot volA^4725^Increases in atmospheric carbon dioxide (CO2) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO2. Several studies have addressed the response of C3 cereals to CO2, but the interactive effect of nutrient supply and CO2 on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 mumol CO2mol-1 air) and low (400 mumol mol- 1) levels of atmospheric CO2 on apical development, spikelet set and abortion, and pre- and post-anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot-1 before sowing +0.11 g N pot-1 week-1) and low N (0.3 g N pot-1) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO2 enrichment, and the C+ plants pollinated few days earlier than the C- plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO2]. Barley plants did not tiller when grown in low [CO2] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9% under high N regime and by 21% under low N regime. Under high [CO2] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23% increase in kernel yield under low N regime and 76% increase in kernel yield under high N regime. The rate of N application influenced growth and yield components to a greater extent than CO2 enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 mumol m-2s-1), and at constant temperature of 20-degrees-C high [CO2] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.

965^4^Knapp,AK^Cocke,M^Hamerlynck,EP^Owensby,CE^1994^1^Effect of elevated co2 on stomatal density and distribution in a C-4 grass and a C-3 forb under field conditions^52^74^6^595-599^^^^^Dec^^^^^4728
1298^1825^243^344^374^514^634^711^980^ kernel weight both on main stem and on tiller spikes resulted in a 23% increase in kernel yield under low N rA^4727^Two common tallgrass prairie species, Andropogon gerardii, the dominant C-4 grass in this North American grassland, and Salvia pitcheri, a C-3 forb, were exposed to ambient and elevated (twice ambient) CO2 within open-top chambers throughout the 1993 growing season. After full canopy development, stomatal density on abaxial and adaxial surfaces, guard cell length and specific leaf mass (SLM; mg cm(-2) were determined for plants in the chambers as well as in adjacent unchambered plots. Record high rainfall amounts during the 1993 growing season minimized water stress in these plants (leaf xylem pressure potential was usually > -1.5 MPa in A. gerardii) and also minimized differences in water status among treatments. In A. gerardii, stomatal density was significantly higher (190 +/- 7 mm(-2); mean +/- s.e.) in plants grown outside of the chambers compared to plants that developed inside the ambient CO2 chambers (161 +/- 5 mm(-2)). Thus, there was a significant 'chamber effect' on stomatal density. At elevated levels of CO2, stomatal density was even lower (P < 0.05; 121 +/- 5 mm(- 2)). Most stomata were on abaxial leaf surfaces in this grass, but the ratio of adaxial to abaxial stomatal density was greater at elevated levels of CO2. In S. pitcheri, stomatal density was also significantly lower when plants were grown in the open-top chambers (235 +/- 10 mm(-2) outside vs. 140 +/- 6 mm(-2) in the ambient CO2 chamber). However, stomatal density was greater at elevated CO2 (218 +/- 12 mm(-2)) compared to plants from the ambient CO2 chamber. The ratio of stomata on adaxial vs. abaxial surfaces did not vary significantly in this herb. Guard cell lengths were not significantly affected by growth in the chambers or by elevated CO2 for either species. Growth within the chambers resulted in lower SLM in S. pitcheri, but CO2 concentration had no effect. In A. gerardii, SLM was lower at elevated CO2. These results indicate that stomatal and leaf responses to elevated CO2 are species specific, and reinforce the need to assess chamber effects along with treatment effects (CO2) when using open-top chambers.

966^2^Krapp,A^Stitt,M^1995^1^An evaluation of direct and indirect mechanisms for the sink- regulation of photosynthesis in spinach - changes in gas- exchange, carbohydrates, metabolites, enzyme-activities and steady-state transcript levels after cold-girdling source leaves^6^195^3^313-323^^^^^Jan^^^^^4730
1026^1351^1826^1827^356^372^448^647^650^965^nsity was greater at elevated CO2 (218 +/- 12 mm(-2)) compared to plants from the ambient CO2 chamber. The ratio of stomata on adaxial vs. abaxial surfaces did not vary significantly in this herb. Guard cell lengths were not significantly affected by growth in the chambers or by elevated CO2 for either species. Growth within the chambers resulted in lower SLM in S. pitcheri, but CO2 concentration had no effect. In A. gerardii, SLM was lower at elevated CO2. These results indicate that stomatal and leaf responses to elevated CO2 are species specific, and reinforce the need to A^4729^Mature source leaves of spinach (Spinacia oleracea L.) plants growing hydroponically in a 9 h light (350 mu mol photons.m(- 2).s(-1))/15 h dark cycle at 20 degrees C in a climate chamber were fitted with a cold girdle around the petiole, 2 h into the light period. Samples were taken 1, 3 and 7 h later, and at the end of the photoperiod for the following 4 d. Control samples were taken from ungirdled leaves. in the first 7 h after fitting the cold girdle there was (compared to the control leaves) a two to fivefold accumulation of sucrose, glucose, fructose and starch, a 40-50% increase of hexose-phosphates and ribulose-1,5-bisphosphate, a decrease of glycerate-3-phosphate, a small decrease in sucrose-phosphate synthase activation, an increase of fructose-2,6-bisphosphate, increased activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), but no significant change in photosynthetic rate or stomatal conductance. Steady-state transcript levels for rbcS (small subunit of Rubisco) and atp-D (D-subunit of the thylakoid ATP synthase) decreased 30%, cab (chlorophyll-a-binding protein) decreased by 15% and agp-S (S-isoenzyme of ADP-glucose pyrophosphorylase) and nra (nitrate reductase) rose twofold. On the following days, levels of carbohydrates continued to rise and the changes of metabolites were maintained. Transcripts for rbcS, cab and atpD declined to 20, 70 and 25% of the control values. From day 3 onward the maximum activity of Rubisco declined. This was accompanied by a further increase of Rubisco activation to over 90% and, from day 4 onwards, an inhibition of photosynthesis which was associated with high internal CO2 concentration (c(i)), high ribulose-1,5-bisphosphate, and low glycerate-3-phosphate. When the cold-girdle was removed on day 5 there was a gradual recovery of photosynthesis and decline of c(i) over the next 2 d. Hexose-phosphates levels and transcripts for rbcS, cab and atp-D completely recovered within 2 d, even though the levels of carbohydrates had not fully recovered. Activity of Rubisco only reverted partly after 2 d, and Rubisco activation state and the ribulose-1,5- bisphosphate/glycerate-3-phosphate ratio were still higher than in control leaves. Transcripts for nra and agp-S were also still higher than in control leaves. It is concluded (i) that a reversible modulation of gene expression in response to the export rate plays a central role in the mid-term feedback ''sink'' regulation of photosynthesis, and (ii) that feedback regulation of CO2 fixation by changes of P-i are of little importance in spinach under these conditions. Further (iii) the rapid and reciprocal changes in nra and agpS transcripts, compared to rbcS, provide evidence that gene expression could also contribute to the modulation of nitrate assimilation and carbohydrate storage in conditions of decreased sink demand.

967^2^Krupa,SV^Legge,AH^1995^1^Air-quality and its possible impacts on the terrestrial ecosystems of the north-american great-plains - an overview^35^88^1^1-11^^^^^^^^^^4732
1102^447^. AcA^4731^Over the past several decades, numerous studies have been conducted on the impacts of air pollutants (air quality) on terrestrial ecosystems (crops and forests). Although ambient air is always composed of pollutant mixtures, in determining the relative air quality and its ecosystem impacts at a given geographic location and time, a predominant number of studies have shown that at the present time surface level O-3 is the most important phytotoxic air pollutant. Within the North American Great Plains, the precursors; for surface-level O-3 are mainly anthropogenic NOx and VOCs (volatile organic compounds). Texas and Alberta ta are the top regions of such emissions in the United States and Canada, respectively. This appears to be due mainly to the prevalence of natural gas and/or oil industry in the two regions and the consequent urbanization. Nevertheless, the total emissions of NOx and VOCs within the North American Great Plains represent only about 25- 36% of the corresponding total emissions within the contiguous United States and the whole of Canada. Within the Great Plains many major crop and tree species are known to be sensitive to O-3. This sensitivity assessment, however, is based mainly on our knowledge from univariate (O-3 only) exposure-plant response studies. In the context of global climate change, in almost all similar univariate studies, elevated CO2, concentrations have produced increases in plant biomass (both crop and tree species). The question remains as to whether this stimulation will offset any adverse effects of elevated surface O-3 concentrations. Future research must address this important issue both for the Great Plains and for all other geographic locations, taking into consideration spatial and temporal variabilities in the ambient concentrations of the two trace gases.

968^3^Larigauderie,A^Reynolds,JF^Strain,BR^1994^1^Root response to co2 enrichment and nitrogen supply in loblolly-pine^206^165^1^21-32^^^^^^^^^^4734
204^341^361^417^439^92^rresponding total emissions within tA^4733^This paper examines how elevated CO2 and nitrogen (N) supply affect plant characteristics of loblolly pine (Pinus taeda L.) with an emphasis on root morphology. Seedlings were grown in greenhouses from seeds during one growing season at two atmospheric CO2 concentrations (375 and 710 mu L L(-1)) and two N levels (High and Low). Root morphological characteristics were determined using a scanner and an image analysis program on a Macintosh computer. In the high N treatment, elevated CO2 increased total plant dry weight by 80% and did not modify root to shoot (R/S) dry weight ratio, and leaf and plant N concentration at the end of the growing season. In the low N treatment, elevated CO2 increased total dry weight by 60%. Plant and leaf N concentration declined and R/S ratio tended to increase. Nitrogen uptake rate on both a root length and a root dry weight basis was greater at elevated CO2 in the high N treatment and lower in the low N treatment. We argue that N stress resulting from short exposures to nutrients might help explain the lower N concentrations observed at high CO2 in other experiments; Nitrogen and CO2 levels modified root morphology. High N increased the number of secondary lateral roots per length of first order lateral root and high CO2 increased the length of secondary lateral roots per length of first order lateral root. Number and length of first order lateral roots were not modified by either treatment. Specific root length of main axis, and to a lower degree, of first order laterals, declined at high CO2, especially at high N. Basal stem diameter and first order root diameters increased at high CO2, especially at high N. Elevated CO2 increased the proportion of upper lateral roots within the root system.

969^3^Lewis,JD^Thomas,RB^Strain,BR^1994^1^Effect of elevated co2 on mycorrhizal colonization of loblolly- pine (pinus-taeda L) seedlings^206^165^1^81-88^^^^^^^^^^4736
224^407^417^419^757^791^849^92^wer in the low N treatment. We argue that N stress resulting from short exposures to A^4735^Interactive effects of elevated atmospheric CO2 and phosphorus supply on mycorrhizal colonization rates were investigated using loblolly pine (Pinus taeda L.) seedlings from Florida and coastal North Carolina. Seedlings from both populations were grown in greenhouses maintained at either 35.5 Pa or 71.0 Pa CO2. In both CO2 treatments, seedlings were grown in a full factorial experiment with or without mycorrhizal inoculum and with an adequate or a limiting supply of phosphorus. Seedlings were harvested 60, 90 and 120 days after emergence and at each harvest root subsamples were examined to determine the percent of fine roots that were mycorrhizal. Additionally, root carbohydrate and nutrient levels were measured at each harvest. Root starch, sugar and total non-structural carbohydrate (TNC) concentrations were increased by growth in elevated CO2 and decreased by mycorrhizal colonization. Phosphorus stress decreased root starch concentrations, increased root sugar concentrations and did not significantly affect TNC concentrations. However, despite significant effects on root carbohydrate levels, there were generally no significant treatment effects on mycorrhizal colonization. Additionally, at all harvests, root starch and sugar concentrations were not correlated with percent of fine roots that were mycorrhizal. These results suggest that although elevated CO2 may significantly increase root carbohydrate levels, the increases may not affect the percent of fine roots that are mycorrhizal.

970^4^Monz,CA^Hunt,HW^Reeves,FB^Elliott,ET^1994^1^The response of mycorrhizal colonization to elevated co2 and climate-change in pascopyrum-smithii and bouteloua-gracilis^206^165^1^75-80^^^^^^^^^^4738
245^672^92^vels were measured at each harvest. Root starch, sugar and total non-structural carbohydrate (TNC) concentrations were increased by growth in elevated CO2 and decreased by mycorrhizal colonization. Phosphorus stress decreased root starch concentrations, increased root sugar concentrations and did not significantA^4737^Large intact soil cores of nearly pure stands of Pascopyrum smithii (western wheatgrass, C-3) and Bouteloua gracilis (blue grama, C-4) were extracted from the Central Plains Experimental Range in northeastern Colorado, USA and transferred to controlled environment chambers. Cores were exposed to a variety of water, temperature and CO2 regimes for a total of four annual growth cycles. Root subsamples were harvested after the completion of the second and fourth growth cycles at a time corresponding to late winter, and were examined microscopically for the presence of mycorrhizae. After two growth cycles in the growth chambers, 54% of the root length was colonized in P smithii, compared to 35% in blue grama. Field control plants had significantly lower colonization. Elevation of CO2 increased mycorrhizal colonization in B. gracilis by 46% but had no effect in P. smithii. Temperatures 4 degrees C higher than normal decreased colonization in P. smithii by 15%. Increased annual precipitation decreased colonization in both species. Simulated climate change conditions of elevated CO2, elevated temperature and lowered precipitation decreased colonization in P. smithii but had less effect on B. gracilis. After four growth cycles in P. smithii, trends of treatments remained similar, but overall colonization rate decreased.

971^4^Morgan,JA^Knight,WG^Dudley,LM^Hunt,HW^1994^1^Enhanced root-system C-sink activity, water relations and aspects of nutrient acquisition in mycotrophic bouteloua- gracilis subjected to co2 enrichment^206^165^1^139-146^^^^^^^^^^4740
224^243^386^398^407^417^419^57^778^92^ter two growth cycles in the growth chambers, 54% of the root length was colonized in P smithii, compared to 35% in blue grama. Field control plants had significantly lower colonization. Elevation of CO2 increased mycorrhizal colonization in B. gracilis by 46% but had no effect in P. smithii. Temperatures 4 degrees C higher than normal decreased colonization in P. smithii by 15%. Increased annual precipitation decreased colonA^4739^In order to better elucidate fixed-C partitioning, nutrient acquisition and water relations of prairie grasses under elevated [CO2], we grew the C-4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column- lysimeters in two growth chambers maintained at current ambient [CO2] (350 mu L L(-1)) and twice enriched [CO2] (700 mu L L(- 1)). Once established, plants were deficit irrigated; growth chamber conditions were maintained at day/night temperatures of 25/16 degrees C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root biomass, respectively, and had twice the level of vesicular-arbuscular mycorrhizal (VAM) infection (19.8% versus 10.8%) as plants grown under current ambient [CO2]. The CO2-enriched plants also exhibited greater leaf water potentials and higher plant water use efficiencies. Plant N uptake was reduced by CO2 enrichment, while P uptake appeared little influenced by CO2 regime. Under the conditions of the experiment, CO2 enrichment increased root biomass and VAM infection via stimulated growth and adjustments in C partitioning below-ground.

972^1^Mortensen,LM^1995^1^Effect of carbon-dioxide concentration on biomass production and partitioning in betula-pubescens ehrh seedlings at different ozone and temperature regimes^35^87^3^337-343^^^^^^^^^^4742
174^1828^243^92^rees C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root biomass, respectively, and had twice the level of vesicular-arbuscular mycorrhizal (VAM) infection (19.8% versus 10.8%) as plants grown under current ambient [CO2]. The CO2-enriched plants also exhibited greater leaf water potentials and higher plant water use efficiencies. PA^4741^Seedlings of Betula pubescens were grown at two CO2 concentrations, in combination with either two O3 concentrations or two air temperatures, during 34-35 days at 24 h day-1 photoperiod in growth chambers placed in a greenhouse. Increasing the CO2 concentration from 350 to 560 mumol mol-1 at 17-degrees-C air temperature increased the dry weight of the main leaves, main stem, branches and root. The mean relative growth rate (RGR) was increased 10% by CO2 enrichment, while increasing the O3 concentration from 7 to 62 nmol mol-1 decreased the RGR by 9%. The relative biomass distribution between the different plant components was not significantly affected by the CO2 concentration irrespective of the O3 concentration. No significant interactions between CO2 and O3 concentration were found except on leaf size, which was stimulated more by elevated CO2 concentration at high, compared to low, O3 levels. In another experiment, elevated CO2 (700 mumol mol-1) significantly increased the dry weight of the different plant components, and more at 20-degrees-C than at 15-degrees-C. Raising the CO2 concentration increased the RGR by 5 and 10% at 15 and 20-degrees-C, respectively. CO2 enrichment increased the branch dry weight relatively more than the dry weight of the other plant parts. Increasing the CO2 concentration or temperature increased the plant height and stem diameter, however, no interactions between CO2 and temperature were found.

973^1^Norby,RJ^1994^1^Issues and perspectives for investigating root responses to elevated atmospheric carbon-dioxide^206^165^1^9-20^^^^^^^^^^4744
137^1829^1830^229^349^534^698^857^92^ant components was not significantly affected by the CO2 concentration irrespective of the O3 concentration. No significant interactions between CO2 and O3 concentration were found except on leaf size, which was stimulated more by elevated CO2 concentration at high, compared to low, O3 levels. In another experiment, elevated CO2 (700 mumol mol-1) significantly increased the dry weight of the differA^4743^A thorough assessment of how plants and ecosystems will respond to increasing concentrations of atmospheric CO2 requires that the responses of root systems and associated belowground processes be understood. Static measures of root-to-shoot ratio have not been satisfactory for describing the integrated responses of plants to CO2-enriched atmospheres, but research with a process orientation has suggested that elevated CO2 can stimulate root growth or root activity and provide a positive feedback on plant growth. There are, however, critical questions concerning the relevance of root data from short-term studies with potted plants when scaling to questions about plants in the field. Data on root responses to CO2 enrichment in the field are fragmentary, but they allow us to more clearly define research questions for further investigation. Three perspectives for analyzing the significance of root responses as a component of the overall response of the terrestrial biosphere to increasing atmospheric CO2 are suggested: (1) roots as a platform for nutrient acquisition and a mediator of whole-plant response to CO2; (2) carbon storage in roots as a component of whole-plant carbon storage; and (3) effects of CO2 enrichment on root turnover and the implications for carbon storage as soil organic matter. The relative importance of these different perspectives will vary depending on the ecosystem of interest and the larger-scale issues being considered.

974^1^Oneill,EG^1994^1^Responses of soil biota to elevated atmospheric carbon-dioxide^206^165^1^55-65^^^^^^^^^^4746
1334^1831^1832^1833^349^419^420^429^680^803^-term studies with potted plants when scaling to questions about plants in the field. Data on root responses to CO2 enrichment in the field are fragmentary, but they allow us to more clearly define research questions for further investigation. Three perspectives for analyzing the significance of root responses as a component of the overall response of the terrestrial biosphere to increasing atmospheric CO2 arA^4745^Increasing concentrations of atmospheric CO2 could have dramatic effects upon terrestrial ecosystems including changes in ecosystem structure, nutrient cycling rates, net primary production, C source-sink relationships and successional patterns. All of these potential changes will be constrained to some degree by below ground processes and mediated by responses of soil biota to indirect effects of CO2 enrichment. A review of our current state of knowledge regarding responses of soil biota is presented, covering responses of mycorrhizae, N-fixing bacteria and actinomycetes, soil microbiota, plant pathogens, and soil fauna. Emphasis will be placed on consequences to biota of increasing C input through the rhizosphere and resulting feedbacks to above ground systems. Rising CO2 may also result in altered nutrient concentrations of plant litter, potentially changing decomposition rates through indirect effects upon decomposer communities. Thus, this review will also cover current information on decomposition of litter produced at elevated CO2.

975^3^Owensby,CE^Auen,LM^Coyne,PI^1994^1^Biomass production in a nitrogen-fertilized, tallgrass prairie ecosystem exposed to ambient and elevated levels of co2^206^165^1^105-113^^^^^^^^^^4748
312^374^376^378^417^429^778^92^e potential changes will be constrained to some degree by below ground processes and mediated by responses of soil biota to indirect effects of CO2 enrichment. A review of our current state of knowledge regarding responses of soil biota is presented, covering responses of mycorrhizae, N-fixing bacteria and actinomycetes, soil microbiota, plant pathogens, and soil fauna. Emphasis will be placed on consequences to biota of increasing C input through the rhizosphere and resulting feedbacks to above ground systems. Rising CO2 may also result in altered nutrient concentrations of plant litter, potentially changing decomposition rates through indirect effects upon decomposer communities. Thus, this review will also cover current information on decompositiA^4747^Increased biomass production in terrestrial ecosystems with elevated atmospheric CO2 may be constrained by nutrient limitations as a result of increased requirement or reduced availability caused by reduced turnover rates of nutrients. To determine the short-term impact of nitrogen (N) fertilization on plant biomass production under elevated CO2, we compared the response of N-fertilized tallgrass prairie at ambient and twice-ambient CO2 levels over a 2-year period. Native tallgrass prairie plots (4.5 m diameter) were exposed continuously (24 h) to ambient and twice-ambient CO2 from 1 April to 26 October. We compared our results to an unfertilized companion experiment on the same research site. Above- and belowground biomass production and leaf area of fertilized plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in plants exposed to elevated CO2, but total standing crop N was greater at high CO2. Increased root biomass under elevated CO2 apparently increased N uptake. The biomass production response to elevated CO2 was much greater on N-fertilized than unfertilized prairie, particularly in the dry year. We conclude that biomass production response to elevated CO2 was suppressed by N limitation in years with below-normal precipitation. Reduced N concentration in above-and belowground biomass could slow microbial degradation of soil organic matter and surface litter, thereby exacerbating N limitation in the long term.

976^4^Rice,CW^Garcia,FO^Hampton,CO^Owensby,CE^1994^1^Soil microbial response in tallgrass prairie to elevated co2^206^165^1^67-74^^^^^^^^^^4750
1834^312^314^344^376^429^534^57^672^738^ plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in plants exposed to elA^4749^Terrestrial responses to increasing atmospheric CO2 are important to the global carbon budget. Increased plant production under elevated CO2 is expected to increase soil C which may induce N limitations. The objectives of this study were to determine the effects of increased CO2 on 1) the amount of carbon and nitrogen stored in soil organic matter and microbial biomass and 2) soil microbial activity. A tallgrass prairie ecosystem was exposed to ambient and twice-ambient CO2 concentrations in open-top chambers in the field from 1989 to 1992 and compared to unchambered ambient CO2 during the entire growing season. During 1990 and 1991, N fertilizer was included as a treatment. The soil microbial response to CO2 was measured during 1991 and 1992. Soil organic C and N were not significantly affected by enriched atmospheric CO2. The response of microbial biomass to CO2 enrichment was dependent upon soil water conditions. In 1991, a dry year, CO2 enrichment significantly increased microbial biomass C and N. In 1992, a wet year, microbial biomass C and N were unaffected by the CO2 treatments. Added N increased microbial C and N under CO2 enrichment. Microbial activity was consistently greater under CO2 enrichment because of better soil water conditions. Added N stimulated microbial activity under CO2 enrichment. Increased microbial N with CO2 enrichment may indicate plant production could be limited by N availability. The soil system also could compensate for the limited N by increasing the labile pool to support increased plant production with elevated atmospheric CO2. Longer-term studies are needed to determine how tallgrass prairie will respond to increased C input.

977^4^Singer,A^Eshel,A^Agami,M^Beer,S^1994^1^The contribution of aerenchymal co2 to the photosynthesis of emergent and submerged culms of scirpus-lacustris and cyperus- papyrus^159^49^2-3^107-116^^^^^Aug^^^^^4752
1146^1835^427^733^ upon soil water conditions. In 1991, a dry year, CO2 enrichment significantly increased microbial biomass C and N.A^4751^In this work it was investigated whether sediment-derived aerenchymal CO2 could be utilized for photosynthesis in the culms of the two emergent aquatic macrophytes Scirpus lacustris L. (a C-3 plant) and Cyperus papyrus L. (a C-4 plant). Aerenchymal CO2 concentrations within the submerged parts of the culms were found to be 30 000-50 000, mu l l(-1), and ca. 800 mu l l(-1) in the emergent parts of Scirpus lacustris and 2000 mu l l(-1) in Cyperus papyrus. These concentrations tended to be lower during the day in Cyperus, while no dear diurnal pattern was observed for Scirpus. Photosynthetic rates based on fixation of external or internal CO2 were measured in situ by providing (CO2)-C-14 either externally or from the aerenchyma (by supplying C-14-labelled CO2 through test-tubes attached to excised culms). The results showed that the contribution of aerenchymal CO2 to the total photosynthesis of emergent culms was less than 0.25% in both species. This has a rationale in that photosynthetic rates of both species were saturated at the ambient air CO2 concentration, but it remains unclear why CO2 does not diffuse towards the photosynthesizing tissues. By contrast, internal CO2 appeared to be the only source of inorganic carbon used for photosynthesis of young submerged green culms. It is thus suggested that the aerenchyma, in addition to other functions, is important in providing sediment-derived CO2 for photosynthesis in young shoots or culms if growing submerged, before they reach the water surface.

978^4^Tissue,DT^Griffin,KL^Thomas,RB^Strain,BR^1995^1^Effects of low and elevated co2 on C-3 and C-4 annuals .2. Photosynthesis and leaf biochemistry^2^101^1^21-28^^^^^Jan^^^^^4754
256^312^344^348^356^376^492^550^635^92^ the aerenchyma (by supplying C-14-labelled CO2 through test-tubes attached to excised culms). The results showed that the contribution of aerenchymal CO2 to the total photosynthesis of emergent culms was less than 0.25% in both species. This has a rationale in that photosynthetic rates of both sA^4753^Abutilon theophrasti (C-3) and Amaranthus retroflexus (C-4), were grown from seed at four partial pressures of CO2: 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) in the Duke Phytotron under high light, high nutrient, and well-watered conditions to evaluate their photosynthetic response to historic and future levels of CO2. Net photosynthesis at growth CO2 partial pressures increased with increasing CO2, for C-3 plants, but not C-4 plants. Net photosynthesis of Abutilon at 15 Pa CO2 was 70% less than that of plants grown at 35 Pa CO2, due to greater stomatal and biochemical limitations at 15 Pa CO2. Relative stomatal limitation (RSL) of Abutilon at 15 Pa CO2 was nearly 3 times greater than at 35 Pa CO2. A photosynthesis model was used to estimate ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vc(max)), electron transport mediated RuBP regeneration capacity (J(max)), and phosphate regeneration capacity (PiRC) in Abutilon from net photosynthesis versus intercellular CO2 (A-C-i) curves. All three component processes decreased by approximately 25% in Abutilon grown at 15 Pa compared with 35 Pa CO2. Abutilon grown at 15 Pa CO2 had significant reductions in total rubisco activity (25%), rubisco content (30%), activation state (29%), chlorophyll content (39%), N content (32%), and starch content (68%) compared with plants grown at 35 Pa CO2. Greater allocation to rubisco relative to light reaction components and concomitant decreases in J(max) and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO2. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO2 compared with 35 Pa CO2, suggesting that the rise in CO2 since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in all CO2 treatments. Differences in photosynthetic response to growth over a wide range of CO2 partial pressures suggest chang es in the relative performance of C-3 and C-4 annuals as atmospheric CO2 has fluctuated over geologic time.

979^4^Wheeler,TR^Ellis,RH^Hadley,P^Morison,JIL^1995^1^Effects of co2, temperature and their interaction on the growth, development and yield of cauliflower (brassica-oleracea L botrytis)^165^60^3-4^181-197^^^^^Jan^^^^^4756
131^1836^1837^230^312^376^402^58^662^867^J(max) and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO2. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO2 compared with 35 Pa CO2, suggesting that the rise in CO2 since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in allA^4755^Stands of summer cauliflower were grown within polyethylene- covered tunnels along which a temperature gradient was imposed. Two tunnels were maintained at either normal or elevated CO2 concentrations. At the last harvest (88 days from transplanting) no interaction between CO2 and temperature on total biomass was detected. The total dry weight of plants grown at 531 mu mol mol-L CO2 was 34% greater than those grown at 328 mu mol mol(-1) CO2, whereas a 1 degrees C rise reduced dry weight by 6%. From serial harvests the radiation conversion coefficient was 2.01 g MJ(-1) and 1.42 g MJ(-1) at 531 mu mol mol(-1) CO2 and 328 mu mol mol(-1) CO2, respectively, but was not greatly affected by differences in temperature. No effect of either CO2 or temperature on the canopy light extinction coefficient was detected. The rate of progress towards curd initiation increased to a maximum at 15.5 degrees C, and declined thereafter. Provided the effect of temperature was accounted for, CO2 enrichment did not affect the time of curd initiation. From serial harvests after curd initiation, the logarithm of curd weight or diameter were negative linear functions of mean temperature from initiation. Increases in curd weight and diameter at 531 compared with 328 mu mol mol(- 1) CO2 were greater at warmer temperatures (27% at 13 degrees C compared with 47% at 15 degrees C, 57 days after initiation). Effects of CO2 on curd diameter were less than those on curd dry weight because the curd dry matter content was greater at 531 compared with 328 mu mol mol(-1) CO2. Thus, the effects of elevated CO2 concentrations on fresh weight based yield parameters of cauliflower were less than the increase in total dry matter production.

980^3^Wullschleger,SD^Lynch,JP^Berntson,GM^1994^1^Modeling the belowground response of plants and soil biota to edaphic and climatic-change - what can we expect to gain^206^165^1^149-160^^^^^^^^^^4758
146^372^419^423^427^456^57^680^715^803^fect of temperature was accounted for, CO2 enrichment did not affect theA^4757^As atmospheric CO2 concentrations continue to increase, so too will the emphasis placed on understanding the belowground response of plants to edaphic and climatic change. Controlled- exposure studies that address the significance of an increased supply of carbon to roots and soil biota, and the consequences of this to nutrient cycling will play a prominent role in this process. Models will also contribute to understanding the response of plants and ecosystems to changes in the earth's climate by incorporating experimental results into conceptual or quantitative frameworks from which potential feedbacks within the plant-soil system can be identified. Here we present five examples of how models can be used in this analysis and how they can contribute to the development of new hypotheses in the areas of root biology, soil biota, and ecosystem processes. Two examples illustrate the role of coarse and fine roots in nitrogen and phosphorus uptake from soils, the respiratory costs associated with this acquisition of nutrients, and the significance of root architecture in these relationships. Another example focuses on a conceptual model that has helped raise new ideas about the effects of elevated CO2 on root and microbial biomass, and on nutrient dynamics in the rhizosphere. Difficulties associated with modeling the contribution of mycorrhizal fungi to whole-plant growth are also discussed. Finally several broad-scale models are used to illustrate the importance of root turnover, litter decomposition, and nitrogen mineralization in determining an ecosystem's response to atmospheric CO2 enrichment. We conclude that models are appropriate tools for use both in guiding existing studies and in identifying new hypotheses for future research. Development of models that address the complexities of belowground processes and their role in determining plant and ecosystem function within the context of rising CO2 concentrations and associated climate change should be encouraged.
iratory costs associated with this acqui981^3^Wullschleger,SD^Norby,RJ^Hanson,PJ^1995^1^Growth and maintenance respiration in stems of quercus-alba after 4 years of co2 enrichment^37^93^1^47-54^^^^^Jan^^^^^4760
1627^240^243^348^389^398^441^669^722^782^crobial biomass, and on nutrient dynamics in the rhizosphere. Difficulties associated with modeling the contribution of mycorrhizal fungi to whole-plant growth are also discussed. Finally several broad-scale models are used to illustrate the importance of root turnover, litter decomposition, and nitrogen mineralization in determining an ecosystem's response to atmospheric CO2 enrichment. We conclude that models are appropriate tools for use both in guiding existing studies and in identifying new hypotheses for future research. Development of models that address the complexities of belowground processes and their role in determining plant and ecosystem function within the context of rising CO2 concentrations and associated climate change should be encouraged.
iratory costs associated with this acquiA^4759^Atmospheric CO2 enrichment is increasingly being reported to inhibit leaf and whole-plant respiration. It is not known, however, whether this response is unique to foliage or whether woody-tissue respiration might be affected as well. This was examined for mid-canopy stem segments of white oak (Quercus alba L.) trees that had been grown in open-top field chambers and exposed to either ambient or ambient + 300 mu mol mol(-1) CO2 over a 4-year period. Stem respiration measurements were made throughout 1992 by using an infrared nas analyzer and a specially designed in situ cuvette. Rates of woody-tissue respiration were similar between CO2 treatments prior to leaf initiation and after leaf senescence, but were several fold greater for saplings grown at elevated concentrations of CO2 during much of the growing season. These effects were most evident on 7 July when stem respiration rates for trees exposed to elevated CO2 concentrations were 7.25 compared to 3.44 mu mol CO2 m(-2) s(-1) for ambient-grown saplings. While other explanations must be explored, greater rates of stem respiration for saplings grown at elevated CO2 concentrations were consistent with greater rates of stem growth and more stem-wood volume present at the time of measurement. When rates of stem growth were at their maximum (7 July to 3 August), growth respiration accounted for about 80 to 85% of the total respiratory costs of stems at both CO2 treatments, while 15 to 20% supported the costs of stem-wood maintenance. Integrating growth and maintenance respiration throughout the season, taking into account treatment differences in stem growth and volume, indicated that there were no significant effects of elevated CO2 concentration on either respiratory process. Quantitative estimates that could be used in modeling the costs of woody-tissue growth and maintenance respiration are provided.
July when stem respiration rates for trees exposed to elevated CO2 concentrations were 7.25 compared to 3.44 mu mol CO2 m(-2) s(-1) for ambient-grown sap982^6^Andrews,TJ^Hudson,GS^Mate,CJ^Voncaemmerer,S^Evans,JR^Arvidsson,YBC^1995^1^Rubisco - the consequences of altering its expression and activation in transgenic plants^78^46^^1293-1300^^^^^Sep^^^^^4762
1634^1838^1839^1840^1841^1842^243^355^448^92^ rates of stem growth were at their maximum (7 July to 3 August), growth respiration accounted for about 80 to 85% of the total respiratory costs of stems at both CO2 treatments, while 15 to 20% supported the costs of stem-wood maintenance. Integrating growth and maintenance respiration throughout the season, taking into account treatment differences in stem growth and volume, indicated that there were no significant effects of elevated CO2 concentration on either respiratory process. Quantitative estimates that could be used in modeling the costs of woody-tissue growth and maintenance respiration are provided.
July when stem respiration rates for trees exposed to elevated CO2 concentrations were 7.25 compared to 3.44 mu mol CO2 m(-2) s(-1) for ambient-grown sapA^4761^Transgenic tobacco (Nicotiana tabacum W38) hemizygous for a single antisense gene directed against Rubisco's small subunit had 35% of the Rubisco content of control leaves (15% when homozygous). CO2 assimilation (at 1000 mu mol quanta m(-2) s(- 1) and 350 mu bar CO2) by the hemizygous leaves was reduced to 40% of that of the controls without material effect on stomatal conductance, chlorophyll content or other photosynthetic components. Leaf soluble protein was reduced commensurately with the reduction in Rubisco. CO2 assimilation rate in the hemizygous leaves remained limited by Rubisco activity at all, even very high, CO2 concentrations. This led to a simple, hyperbolic response of photosynthesis to intraplastid CO2 concentration from which the in vivo catalytic properties of Rubisco were inferred and compared with those of isolated Rubisco in vitro. Using a similar approach, the content of Rubisco activase was suppressed by incorporating a partial cDNA for activase into the tobacco genome in the antisense orientation with respect to a cauliflower mosaic virus 35S promoter. The progeny of a primary transformant with two anti- activase inserts had from <1% to 20% of the activase content of control plants. Quite severe suppression of activase, to less than 5% of the amount present in control leaves, was required before effects on photosynthesis and growth became apparent, indicating that one activase tetramer must be able to service, continuously, as many as 200 Rubisco octamers. Plants with lower activase contents could not grow unless the atmosphere was enriched with CO2. Their Rubisco was less carbamylated and they had lower CO2 assimilation rates than the controls. The rate of release of 2'-carboxyarabinitol-1-phosphate from Rubisco after illumi