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