82451^4^Curtis,PS^Balduman,LM^Drake,BG^Whigham,DF^1990^1^Elevated atmospheric CO2 effects on belowground processes in C3 and C4 estuarine marsh communities^11^71^5^2001-2006^^^^^Oct2^3^Garbutt,K^Williams,WE^Bazzaz,FA^1990^1^Analysis of the differential response of 5 annuals to elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun3^5^Grulke,NE^Riechers,GH^Oechel,WC^Hjelm,U^Jaeger,C^1990^1^Carbon balance in tussock tundra under ambient and elevated atmospheric CO2^2^83^4^485-494^4^3^Kerbel,EL^Kader,AA^Romani,RJ^1990^1^Respiratory and glycolytic response of suspension-cultured passe-crassane pear fruit cells to elevated CO2 concentrations^154^115^1^111-114^^^^^Jan5^1^Meheriuk,M^1990^1^Effects of diphenylamine, gibberellic-acid, daminozide, calcium, high CO2 and elevated-temperatures on quality of stored bartlett pears^146^70^3^887-892^^^^^Jul6^3^Teramura,AH^Sullivan,JH^Ziska,LH^1990^1^Interaction of elevated ultraviolet-b radiation and CO2 on productivity and photosynthetic characteristics in wheat, rice, and soybean^8^94^2^470-475^^^^^Oct7^1^Wong,SC^1990^1^Elevated atmospheric partial-pressure of CO2 and plant-growth .2. Nonstructural carbohydrate content in cotton plants and its effect on growth-parameters^91^23^2^171-180^^^^^Febential response of 5 annuals to elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun8^3^Ziska,LH^Drake,BG^Chamberlain,S^1990^1^Long-term photosynthetic response in single leaves of a C3 and C4 salt-marsh species grown at elevated atmospheric CO2 in Situ^2^83^4^469-472^9^3^Bazzaz,FA^Coleman,JS^Morse,SR^1990^1^Growth-responses of 7 major cooccurring tree species of the northeastern united-states to elevated CO2^155^20^9^1479-1484^^^^^Sep10^3^Acock,B^Acock,MC^Pasternak,D^1990^1^Interactions of CO2 enrichment and temperature on carbohydrate production and accumulation in muskmelon leaves^154^115^4^525-529^^^^^Jul11^5^Allen,LH^Valle,RR^Mishoe,JW^Jones,JW^Jones,PH^1990^1^Soybean leaf gas-exchange responses to CO2 enrichment^156^49^^192-198^12^2^Arnone,JA^Gordon,JC^1990^1^Effect of nodulation, nitrogen-fixation and CO2 enrichment on the physiology, growth and dry mass allocation of seedlings of alnus-rubra bong^84^116^1^55-66^^^^^Sepand its effect on growth-parameters^91^23^2^171-180^^^^^Febential response of 5 annuals to elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun13^4^Barr,AG^King,KM^Thurtell,GW^Graham,MED^1990^1^Humidity and soil-water influence the transpiration response of maize to CO2 enrichment^146^70^4^941-948^^^^^Oct14^4^Conroy,JP^Milham,PJ^Bevege,DI^Barlow,EWR^1990^1^Influence of phosphorus deficiency on the growth-response of 4 families of Pinus radiata seedlings to CO2-enriched atmospheres^45^30^1-4^175-188^^^^^Feb15^4^Conroy,JP^Milham,PJ^Mazur,M^Barlow,EWR^1990^1^Growth, dry-weight partitioning and wood properties of Pinus radiata d don after 2 years of CO2 enrichment^9^13^4^329-337^^^^^May16^4^Conroy,JP^Milham,PJ^Reed,ML^Barlow,EW^1990^1^Increases in phosphorus requirements for CO2-enriched pine species^8^92^4^977-982^^^^^Apr17^3^Cure,JD^Rufty,TW^Israel,DW^1989^1^Alterations in soybean leaf development and photosynthesis in a CO2-enriched atmosphere^20^150^4^337-345^^^^^Dec^1^55-66^^^^^Sepand its effect on growth-parameters^91^23^2^171-180^^^^^Febential response of 5 annuals to elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun18^3^Desjardins,Y^Gosselin,A^Lamarre,M^1990^1^Growth of transplants and invitro-cultured clones of asparagus in response to CO2 enrichment and supplemental lighting^154^115^3^364-368^^^^^May19^3^Dugal,A^Yelle,S^Gosselin,A^1990^1^Influence of CO2 enrichment and its method of distribution on the evolution of gas exchanges in greenhouse tomatoes^146^70^1^345-356^^^^^Jan20^1^Fajer,ED^1989^1^The effects of enriched CO2 atmospheres on plant-insect herbivore interactions- growth-responses of larvae of the specialist butterfly, Junonia coenia (lepidoptera, nymphalidae)^2^81^4^514-520^21^4^Frederick,JR^Alm,DM^Hesketh,JD^Below,FE^1990^1^Overcoming drought-induced decreases in soybean leaf photosynthesis by measuring with co2-enriched air^91^25^1^49-57^^^^^Jul22^3^Guy,M^Granoth,G^Gale,J^1990^1^Cultivation of Lemna gibba under desert conditions .2. the effect of raised winter temperature, CO2 enrichment and shading on productivity^157^23^1^1-11^elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun24^3^Idso,SB^Allen,SG^Kimball,BA^1990^1^Growth-response of water lily to atmospheric CO2 enrichment^159^37^1^87-92^^^^^Jun25^6^Inoue,Y^Kimball,BA^Mauney,JR^Jackson,RD^Pinter,PJ^Reginato,RJ^1990^1^Stomatal behavior and relationship between photosynthesis and transpiration in field-grown cotton as affected by CO2 enrichment^160^59^3^510-517^^^^^Sep26^3^Kubo,Y^Inaba,A^Nakamura,R^1990^1^Respiration and C2H4 production in various harvested crops held in CO2-enriched atmospheres^154^115^6^975-978^^^^^Nov27^2^Margolis,HA^Vezina,LP^1990^1^Atmospheric CO2 enrichment and the development of frost hardiness in containerized black spruce seedlings^155^20^9^1392-1398^^^^^Sep28^2^Marks,S^Clay,K^1990^1^Effects of CO2 enrichment, nutrient addition, and fungal endophyte-infection on the growth of 2 grasses^2^84^2^207-214^29^1^Mohapatra,PK^1990^1^CO2 enrichment and physiology of inflorescence development in wheat^79^24^1^9-15^ctivity^157^23^1^1-11^elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun30^1^Msudoe,NNA^1990^1^2 mutants of Arabidopsis thaliana that become chlorotic in atmospheres enriched with CO2^9^13^6^575-580^^^^^Aug31^2^Radoglou,KM^Jarvis,PG^1990^1^Effects of CO2 enrichment on 4 poplar clones .1. Growth and leaf anatomy^52^65^6^617-626^^^^^Jun32^2^Radoglou,KM^Jarvis,PG^1990^1^Effects of CO2 enrichment on 4 poplar clones .2. Leaf surface- properties^52^65^6^627-632^^^^^Jun33^3^Rey,P^Eymery,F^Peltier,G^1990^1^Effects of CO2-enrichment and of aminoacetonitrile on growth and photosynthesis of photoautotrophic calli of Nicotiana plumbaginifolia^8^93^2^549-554^^^^^Jun34^2^Sasek,TW^Strain,BR^1990^1^Implications of atmospheric CO2 enrichment and climatic-change for the geographical-distribution of 2 introduced vines in the USA^50^16^1^31-51^^^^^Feb35^2^Stuhlfauth,T^Fock,HP^1990^1^Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, digitalis-lanata^161^164^3^168-173^^^^^Aprty^157^23^1^1-11^elevated CO2 during growth^11^71^3^1185-1194^^^^^Jun36^3^Titus,JE^Feldman,RS^Grise,D^1990^1^Submersed macrophyte growth at low ph .1. CO2 enrichment effects with fertile sediment^2^84^3^307-313^37^2^Wallick,K^Zinnen,TM^1990^1^Basil chlorosis - a physiological disorder in CO2-enriched atmospheres^162^74^2^171-173^^^^^Feb38^4^Yelle,S^Beeson,RC^Trudel,MJ^Gosselin,A^1990^1^Duration of CO2 enrichment influences growth, yield, and gas- exchange of 2 tomato species^154^115^1^52-57^^^^^Jan39^1^Arp,WJ^1991^1^Effects of source-sink relations on photosynthetic acclimation to elevated CO2^9^14^8^869-875^^^^^Oct^^^^^2939230^341^342^343^344^345^346^347^348^349^^Strain,BR^1990^1^Implications of atmospheric CO2 enrichment and climatic-change for the geographical-distribution of 2 introduced vines in the USA^50^16^1^31-51^^^^^Feb35^2^Stuhlfauth,T^Fock,HP^1990^1^Effect of whole season CO2 enrichment on the cultivation of a medicinal plant, digitalis-lanata^161^164^3^168-173^^^^^Aprty^157^23^1^1-11^elevated CO2 during growth^11^71^3^1185-1194^^^^^JunA^2938^While photosynthesis of C3 plants is stimulated by an increase in the atmospheric CO2 concentration, photosynthetic capacity is often reduced after long-term exposure to elevated CO2. This reduction appears to be brought about by end product inhibition, resulting from an imbalance in the supply and demand of carbohydrates. A review of the literature revealed that the reduction of photosynthetic capacity in elevated CO2 was most pronounced when the increased supply of carbohydrates was combined with small sink size. The volume of pots in which plants were grown affected the sink size by restricting root growth. While plants grown in small pots had a reduced photosynthetic capacity, plants grown in the field showed no reduction or an increase in this capacity. Pot volume also determined the effect of elevated CO2 on the root/shoot ratio: the root/shoot ratio increased when root growth was not restricted and decreased in plants grown in small pots. The data presented in this paper suggest that plants growing in the field will maintain a high photosynthetic capacity as the atmospheric CO2 level continues to rise.40^1^Ball,AS^1991^1^Degradation by Streptomyces viridosporus t7a of plant-material grown under elevated CO2 conditions^163^84^2^139-142^^^^^15 Nov^^^^^2941350^351^352^353^354^A^2940^The biodegradability of plant material derived from wheat grown under different concentrations of atmospheric CO2 was investigated using the lignocarbohydrate solubilising actinomycete, Streptomyces viridosporus. Growth of S. viridosporus and solubilisation of lignocarbohydrate were highest when wheat grown at ambient CO2 concentrations (350 ppm) was used as C-source. Growth of S. viridosporus and solubilisation were reduced when the plant material was derived from wheat grown at 645 PPM CO2. The results suggest that modifications in plant structure occur when wheat is grown under conditions of elevated atmospheric CO2 which make it more resistant to microbial digestion.resented in this paper suggest that plants gro41^2^Beeson,RC^Graham,MED^1991^1^CO2 enrichment of greenhouse roses affects neither rubisco nor carbonic-anhydrase activities^154^116^6^1040-1045^^^^^Nov^^^^^2943348^355^356^357^358^359^360^361^362^92^der elevated CO2 conditions^163^84^2^139-142^^^^^15 Nov^^^^^2941350^351^352^353^354^A^2940^The biodegradability of plant material derived from wheat grown under different concentrations of atmospheric CO2 was investigated using the lignocarbohydrate solubilising actinomycete, Streptomyces viridosporus. Growth of S. viridosporus and solubilisation of lignocarbohydrate were highest when wheat grown at ambient CO2 concentrations (350 ppm) was used as C-source. Growth of S. viridosporus and solubilisation were reduced when the plant material was derived from wheat grown at 645 PPM CO2. The results suggest that modifications in plant structure occur when wheat is grown under conditions of elevated atmospheric CO2 which make it more resistant to microbial digestion.resented in this paper suggest that plants groA^2942^The effect of prolonged CO2 enrichment on the activities of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and carbonic anhydrase (CA) of greenhouse roses were studied. Plants of Rosa X hybrida 'Red Success' were grown for 2 years at ambient and 900-mu-l CO2/liter during winter and spring with 75-mu-mol.m-2.s-1 photosynthetically active radiation supplemental lighting for 2 years. Measurements of initial and Mg+2-Co2-activated activities of Rubisco and CA were made during shoot development and at different positions within the plant canopy. Generally, there were no significant differences measured in the enzyme activities between the two CO2 concentrations. The results suggest that the photosynthetic capacity did not change and that there were no characteristic adaptations to long-term growth (up to 20 weeks) at elevated C02 concentrations. The maintenance of Rubisco and CA activities with prolonged exposure to C02-enriched atmospheres is proposed as the reason for long-term yield increases in roses when grown in enriched environments.42^1^Bowes,G^1991^1^Growth at elevated CO2 - photosynthetic responses mediated through rubisco^9^14^8^795-806^^^^^Oct^^^^^2945343^355^363^364^365^366^367^368^369^370^ Success' were grown for 2 years at ambient and 900-mu-l CO2/liter during winter and spring with 75-mu-mol.m-2.s-1 photosynthetically active radiation supplemental lighting for 2 years. Measurements of initial and Mg+2-Co2-activated activities of Rubisco and CA were made during shoot development and at different positions within the plant canopy. Generally, there were no significant differences measured in the enzyme activities between the two CO2 concentrations. The results suggest that the photosynthetic capacity did not change and that there were no characteristic adaptations to long-term growth (up to 20 weeks) at elevated C02 concentrations. The maintenance of Rubisco and CA activities with prolonged exposure to C02-enriched atmospheres is proposed as the reason for long-term yield increasesA^2944^The global uptake of CO2 in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco). which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO2 and O2 are substrates; CO2 also activates the enzyme. In C3 plants, rubisco has a low catalytic activity, operates below its K(m) (CO2), and is inhibited by O2. Consequently, increases in the CO2/O2 ratio stimulate C3 photosynthesis and inhibit photorespiration. CO2 enrichment usually enhances the productivity of C3 plants, but the effect is marginal in C4 species. It also causes acclimation in various ways: anatomically. morphologically, physiologically or biochemically. So, CO2 exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO2 enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/P(i)-regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/P(i)-regeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/P(i)-regeneration capacities, or chloroplast disruption. As exemplified by field-grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO2 enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C4 and CAM plants have genetically adapted to a decline in the external CO2/O2 ratio, by the development of mechanisms to concentrate CO2 internally; thus circumventing O2 inhibition of rubisco. Here rubisco affinity for CO2 is less, but its catalytic activity is greater, a situation compatible with a high-CO2 internal environment. In aquatic autotrophs, the CO2 concentrating mechanisms acclimate to the external CO2, being suppressed at high-CO2. It is unclear, whether a doubling in atmospheric CO2 will be sufficient to cause a de-adaptive trend in the rubisco kinetics of future C3 plants, producing higher catalytic activities.43^4^Coleman,JS^Rochefort,L^Bazzaz,FA^Woodward,FI^1991^1^Atmospheric CO2, plant nitrogen status and the susceptibility of plants to an acute increase in temperature^9^14^7^667-674^^^^^Sep^^^^^2947245^371^372^373^374^375^376^92^ble under CO2 enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C4 and CAM plants have genetically adapted to a decline in the external CO2/O2 ratio, by the development of mechanisms to concentrate CO2 internally; thA^2946^Elevated levels of CO2 in the atmosphere are expected to affect plant performance and may alter global temperature patterns. Changes in mean air temperatures that might be induced by rising levels of CO2 and other greenhouse gases could also be accompanied by increased variability in daily temperatures such that acute increases in air temperature may be more likely than at present. Consequently, we investigated whether plants grown in a CO2 enriched atmosphere would be differently affected by a heat shock than plants grown at ambient CO2 levels. Plants of a C3 annual (Abutilon theophrasti), a C3 annual crop (Sinapis alba) and a C4 annual (Amaranthus retroflexus) were grown from seed in growth chambers under either 400 or 700 cm3 m-3 CO2, and were fertilized with either a high or low nutrient regime. Young seedlings of S. alba, as well as plants of all species in either the vegetative or reproductive phase of growth were exposed to a 4-h heat shock in which the temperature was raised an additional 14-23-degrees-C (depending on plant age). Total biomass and reproductive biomass were examined to determine the effect of CO2, nutrient and heat shock treatments on plant performance. Heat shock, CO2, and nutrient treatments, all had some significant effects on plant performance, but plants from both CO2 treatments responded similarly to heat shocks. We also found, as expected, that plants grown under high CO2 had dramatically decreased tissue N concentrations relative to plants grown under ambient conditions. We predicted that high- CO2-grown plants would be more susceptible to a heat shock than ambient-CO2-grown plants, because the reduced N concentrations of high-CO2 grown plants could result in the reduced synthesis of heat shock proteins and reduced thermotolerance. Although we did not examine heat shock proteins, our results showed little relationship between plant nitrogen status and the ability of a plant to tolerate an acute increase in temperature.n which the temperature was raised an additional 14-244^2^Drake,BG^Leadley,PW^1991^1^Canopy photosynthesis of crops and native plant-communities exposed to long-term elevated CO2^9^14^8^853-860^^^^^Oct^^^^^2949130^189^349^376^377^378^379^380^381^92^nd nutrient treatments, all had some significant effects on plant performance, but plants from both CO2 treatments responded similarly to heat shocks. We also found, as expected, that plants grown under high CO2 had dramatically decreased tissue N concentrations relative to plants grown under ambient conditions. We predicted that high- CO2-grown plants would be more susceptible to a heat shock than ambient-CO2-grown plants, because the reduced N concentrations of high-CO2 grown plants could result in the reduced synthesis of heat shock proteins and reduced thermotolerance. Although we did not examine heat shock proteins, our results showed little relationship between plant nitrogen status and the ability of a plant to tolerate an acute increase in temperature.n which the temperature was raised an additional 14-2A^2948^There have been seven studies of canopy photosynthesis of plants grown in elevated atmospheric CO2: three of seed crops, two of forage crops and two of native plant ecosystems. Growth in elevated CO2 increased canopy photosynthesis in all cases. The relative effect of CO2 was correlated with increasing temperature: the least stimulation occurred in tundra vegetation grown at an average temperature near 10-degrees-C and the greatest in rice grown at 43-degrees-C. In soybean, effects of CO2 were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO2 treatment to date, monospecific stands of a C3 sedge, Scirpus olneyi (Grey), and a C4 grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO2 concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO2 exchange per unit green biomass (NCE(b)) increased by an average of 48% throughout the growing season of 1988, the second year of treatment. Elevated CO2 increased net ecosystem carbon assimilation by 88% in the Scirpus olneyi community and 40% in the Spartina patens community.45^1^Eamus,D^1991^1^The interaction of rising CO2 and temperatures with water-use efficiency^9^14^8^843-852^^^^^Oct^^^^^2951230^372^374^376^377^382^383^384^385^386^occurred in tundra vegetation grown at an average temperature near 10-degrees-C and the greatest in rice grown at 43-degrees-C. In soybean, effects of CO2 were greater during leaf expansion and pod fill than at other stages of crop maturation. In the longest running experiment with elevated CO2 treatment to date, monospecific stands of a C3 sedge, Scirpus olneyi (Grey), and a C4 grass, Spartina patens (Ait.) Muhl., have been exposed to twice normal ambient CO2 concentrations for four growing seasons, in open top chambers on a Chesapeake Bay salt marsh. Net ecosystem CO2 exchange per unit green biomass (NCE(b)) increased by an average of 48% throughout the growing seasoA^2950^Recent data concerning the impact of elevated atmospheric CO2 upon water use efficiency (WUE) and the related measure, instantaneous transpiration efficiency (ITE), are reviewed. It is concluded from both short and long-term studies that, at the scale of the individual leaf or plant, an increase in WUE or ITE is generally observed in response to increased atmospheric CO2 levels. However, the magnitude of this increase may decline with time. The opinion that elevated CO2 may substantially decrease transpiration at the regional scale is discussed. The mechanisms by which elevated CO2 may cause a change in these measures are discussed in terms of stomatal conductance, assimilation and respiration responses to elevated CO2. Finally, recent experimental data and model outputs concerning the impact of the interaction of increased temperature with elevated CO2 on WUE, ITE and yield are reviewed. It is concluded that substantially more data is required before reliable predictions about the regional scale response of WUE and catchment hydrology can be made.46^2^Farrar,JF^Williams,ML^1991^1^The effects of increased atmospheric carbon-dioxide and temperature on carbon partitioning, source-sink relations and respiration^9^14^8^819-830^^^^^Oct^^^^^2953230^346^349^372^380^383^387^388^389^390^ant, an increase in WUE or ITE is generally observed in response to increased atmospheric CO2 levels. However, the magnitude of this increase may decline with time. The opinion that elevated CO2 may substantially decrease transpiration at the regional scale is discussed. The mechanisms by which elevated CO2 may cause a change in these measures are discussed in terms of stomatal conductance, assimilation and respiration responses to elevated CO2. Finally, recent experimental data and model outputs concerning the impact of the interaction of increased temperature with elevated CO2 on WUE, ITE and yield are reviewed. It is concluded that substantially more data is required before reliable predictions about the regional scale respA^2952^Herbaceous C3 plants grown in elevated CO2 show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO2-enriched herbaceous plants and decrease for CO2-enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root:shoot ratios due to elevated CO2 show no alteration in the whole-plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold-adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO2-enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented in support.47^3^Hogan,KP^Smith,AP^Ziska,LH^1991^1^Potential effects of elevated CO2 and changes in temperature on tropical plants^9^14^8^763-778^^^^^Oct^^^^^2955137^344^373^391^392^393^394^395^396^91^crease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root:shoot ratios due to elevated CO2 show no alteration in the whole-plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold-adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, inA^2954^Very little attention has been directed at the responses of tropical plants to increases in global atmospheric CO2 concentrations and the potential climatic changes. The available data, from greenhouse and laboratory studies, indicate that the photosynthesis, growth and water use efficiency of tropical plants can increase at higher CO2 Concentrations. However, under field conditions abiotic (light, water or nutrients) or biotic (competition or herbivory) factors might limit these responses. In general, elevated atmospheric CO2 concentrations seem to increase plant tolerance to stress, including low water availability, high or low temperature, and photoinhibition. Thus, some species may be able to extend their ranges into physically less favourable sites, and biological interactions may become relatively more important in determining the distribution and abundance of species. Tropical plants may be more narrowly adapted to prevailing temperature regimes than are temperate plants, so expected changes in temperature might be relatively more important in the tropics. Reduced transpiration due to decreased stomatal conductance could modify the effects of water stress as a cue for vegetative or reproductive phenology of plants of seasonal tropical areas. The available information suggests that changes in atmospheric CO2 concentrations could affect processes as varied as plant/herbivore interactions, decomposition and nutrient cycling, local and geographic distributions of species and community types, and ecosystem productivity. However, data on tropical plants are few, and there seem to be no published tropical studies carried out in the field. Immediate steps should be undertaken to reduce our ignorance of this critical area.48^5^Kirkham,MB^He,H^Bolger,TP^Lawlor,DJ^Kanemasu,ET^1991^1^Leaf photosynthesis and water-use of big bluestem under elevated carbon-dioxide^164^31^6^1589-1594^^^^^Nov-Dec^^^^^2957344^374^376^397^dapted to prevailing temperature regimes than are temperate plants, so expected changes inA^2956^With the atmospheric concentration of CO2 increasing, it is important to know how this will affect crop growth. The objective of the study was to determine the effect of elevated CO2 on big bluestem (Andropogon gerardii Vitman) growing in a tallgrass prairie on a Tully silty clay loam (fine, mixed, mesic Pachic Argiustoll) kept at a high water level (field capacity) or a low water level (half field capacity). Sixteen cylindrical plastic chambers were placed on the prairie to maintain the two levels of CO2 (mean +/- SD: 337 +/- 32 Ind 658 +/- 81-mu-mol mol-1) over a full growing season. Soil-water content was measured weekly with a neutron probe. Photosynthesis, transpiration, stomatal resistance, and intercellular CO2 concentration were determined with a portable leaf Photosynthetic system. Canopy temperature was monitored with an infrared thermometer. Elevated (doubled) CO2 reduced transpiration rate of big bluestem by 25 and 35% under the high- and low-water treatments, respectively. Under both watering regimes, stomatal resistance was greater by almost- equal-to 1.6 s cm-1 with doubled CO2 than with ambient CO2. Plants grown with doubled CO2 at high- and low-water levels had warmer canopy temperatures (average 1.15 and 0.70-degrees-C warmer, respectively) than plants grown at ambient CO2. Carbon- dioxide concentration did not affect the rate of photosynthesis, even though intercellular CO2 concentration was increased under high CO2. Elevated CO2 did not increase the height of plants grown at the high water level, but it did increase the height at the low water level by an average of 9 cm.49^2^Lawlor,DW^Mitchell,RAC^1991^1^The effects of increasing CO2 on crop photosynthesis and productivity - a review of field studies^9^14^8^807-818^^^^^Oct^^^^^2959230^256^344^369^380^398^399^400^401^402^anopy temperature was monitored with an infrared thermometer. Elevated (doubled) CO2 reduced transpiration rate of big bluestem by 25 and 35% under the high- and low-water treatments, respectively. Under both wateA^2958^Only a small proportion of elevated CO2 studies on crops have taken place in the field. They generally confirm results obtained in controlled environments: CO2 increases photosynthesis, dry matter production and yield, substantially in C3 species, but less in C4, it decreases stomatal conductance and transpiration in C3 and C4 species and greatly improves water-use efficiency in all plants. The increased productivity of crops with CO2 enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield-forming structures than in their size. There is little evidence of a consistent effect of CO2 on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO2 in combination with temperature, water and nutrition are essential; they should be related to the development and improvement of mechanistic crop models, and designed to test their predictions.50^2^Muchow,RC^Sinclair,TR^1991^1^Water deficit effects on maize yields modeled under current and greenhouse climates^48^83^6^1052-1059^^^^^Nov-Dec^^^^^2961264^403^404^405^406^407^408^409^410^411^anspiration in C3 and C4 species and greatly improves water-use efficiency in all plants. The increased productivity of crops with CO2 enrichment is also related to the greater leaf area produced. Stimulation of yield is due more to an increase in the number of yield-forming structures than in their size. There is little evidence of a consistent effect of CO2 on partitioning of dry matter between organs or on their chemical composition, except for tubers. Work has concentrated on a few crops (largely soybean) and more is needed on crops for which there are few data (e.g. rice). Field studies on the effects of elevated CO2 in combination with temperature, water and nutrition are essential; they should beA^2960^The availability of water imposes one of the major limits on rainfed maize (Zea mays L.) productivity. This analysis was undertaken in an attempt to quantify the effects of limited water on maize growth and yield by extending a simple, mechanistic model in which temperature regulates crop development and intercepted solar radiation is used to calculate crop biomass accumulation. A soil water budget was incorporated into the model by accounting for inputs from rainfall and irrigation, and water use by soil evaporation and crop transpiration. The response functions of leaf area development and crop gas exchange to the soil water budget were developed from experimental studies. The model was used to interpret a range of field experiments using observed daily values of temperature, solar radiation, and rainfall or irrigation, where water deficits of varying durations developed at different stages of growth. The relative simplicity of the model and its robustness in simulating maize yields under a range of water-availability conditions allows the model to be readily used for studies of crop performance under alternate conditions. One such study, presented here, was a yield assessment for rainfed maize under possible "greenhouse" climates where temperature and atmospheric CO2 concentration were increased. An increase in temperature combined with decreased rainfall lowered grain yield, although the increase in crop water use efficiency associated with elevated CO2 concentration, ameliorated the response to the greenhouse climate. Grain yields for the greenhouse climates as compared to current conditions increased, or decreased only slightly, except when the greenhouse climate was assumed to result in severely decreased rainfall.51^1^Nobel,PS^1991^1^Environmental productivity indexes and productivity for Opuntia ficus-indica under current and elevated atmospheric CO2 levels^9^14^7^637-646^^^^^Sep^^^^^2963130^374^412^413^414^415^416^y of the model and its robustness in simulating maize yields under a range ofA^2962^The productivity of the prickly-pear cactus Opuntia ficus- indica, which is cultivated worldwide for its fruits and stem segments, was predicted based on the responses of its net CO2 uptake to soil water status, air temperature and photosynthetic photon flux density (PPFD). Each of these environmental factors was represented by an index with a maximum value of unity when that factor was not limiting net CO2 uptake over a 24-h period. The water index, the temperature index, and the PPFD index were determined for 87 sites in the contiguous United States using data from 189 weather stations and for 148 sites worldwide using data from 1464 weather stations. The product of these three indices, the environmental productivity index (EPI), was used to predict the productivity of O. ficus-indica under current climatic conditions and under those accompanying a possible increase in the atmospheric CO2 level to 650-mu-mol mol-1. Sites with temperatures always above -10- degrees-C and hence suitable for prickly-pear cultivation numbered 37 in the United States and 110 worldwide; such sites increased by 43 and 5%, respectively, for the global warming accompanying the elevated CO2. Productivity of O. ficus-indica was at least 15 tonnes dry weight hectare-1 year-1, comparable to that of many agronomic crops, for 20 sites with temperatures always above -10-degrees-C in the contiguous United States and for 12 such sites worldwide under current climatic conditions; such sites increased by 85 and 117%, respectively, under the elevated CO2 condition, mainly because of direct effects of the atmospheric CO2 level on net CO2 uptake. In summary, simulations based on EPI indicate that O. ficus-indica may presently be advantageously cultivated over a substantial fraction of the earth's surface, such regions increasing markedly with a future doubling in atmospheric CO2 levels.52^2^Sung,FJM^Chen,JJ^1991^1^Gas-exchange rate and yield response of strawberry to carbon- dioxide enrichment^165^48^3-4^241-251^^^^^Nov^^^^^2965prickly-pe243^372^417^418^92^A^2964^Short-term carbon dioxide (CO2) enrichment (1000-mu-l l-1 for 10 days), starting 2 weeks after initial bloom, enhanced the leaf CO2 exchange rate (CER) in rockwool-cultured strawberry (Fragaria x ananassa). CO2 enrichment throughout the fruiting period stimulated canopy CER, decreased chlorophyll and leaf protein loss, and enhanced fruit set and consequent fruit production.53^5^Thomas,RB^Richter,DD^Ye,H^Heine,PR^Strain,BR^1991^1^Nitrogen dynamics and growth of seedlings of an n-fixing tree (Gliricidia sepium (jacq) walp) exposed to elevated atmospheric carbon-dioxide^2^88^3^415-421^^^^^^^^^^2967349^416^417^419^420^421^422^423^424^425^. ficus-indica may presently be advantageously cultivated over a substantial fraction of the earth's surface, such regions increasing markedly with a future doubling in atmospheric CO2 levels.52^2^Sung,FJM^Chen,JJ^1991^1^Gas-exchange rate and yield response of strawberry to carbon- dioxide enrichment^165^48^3-4^241-251^^^^^Nov^^^^^2965prickly-peA^2966^Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO2 and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO2 partial pressures of 350 and 650-mu-bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO2 when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO2 enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO2. In seedlings supplied with soil N, elevated CO2 increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf delta-N-15). While CO2 enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO2 partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO2 will depend greatly on plant and soil nutrient status.54^4^Tripp,KE^Peet,MM^Willits,DH^Pharr,DM^1991^1^CO2-enhanced foliar deformation of tomato-relationship to foliar starch concentration^154^116^5^876-880^^^^^Sep^^^^^2969343^349^374^426^re supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was litA^2968^Two cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown with ambient or 1000-mu-l CO2/liter during Jan.-June 1987 and 1988. In both years, CO2-enrichment increased foliar deformation and foliar starch, but during the season, foliar starch levels decreased while deformation increased. 'Laura' had more deformation, while 'Michigan-Ohio' had higher foliar starch concentration. During an entire season, there was no significant relationship between foliar starch concentration and deformation severity. Foliar C exchange rates in the lower canopy were not affected by severity of deformation. Data from these experiments do not support the hypothesis that excess foliar starch is responsible for foliar deformation at elevated CO2.55^2^Hall,DO^Scurlock,JMO^1991^1^Climate change and productivity of natural grasslands^52^67^^49-55^^^^^Jun372^378^417^427^428^429^57^26^re supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was lit56^2^Hocking,PJ^Meyer,CP^1991^1^Effects of CO2 enrichment and nitrogen stress on growth, and partitioning of dry-matter and nitrogen in wheat and maize^92^18^4^339-356^^^^^^^^^^2972224^229^230^243^416^430^431^432^433^434^starch, but during the season, foliar starch levels decreased while deformation increased. 'Laura' had more deformation, while 'Michigan-Ohio' had higher foliar starch concentration. During an entire season, there was no significant relationship between foliar starch concentration and deformation severity. Foliar C exchange rates in the lower canopy were not affected by severity of deformation. Data from these experiments do not support the hypothesis that excess foliar starch is responsible for foliar deformation at elevated CO2.55^2^Hall,DO^Scurlock,JMO^1991^1^Climate change and productivity of natural grasslands^52^67^^49-55^^^^^Jun372^378^417^427^428^429^57^26^re supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO2 enrichment but there was litA^2971^Atmospheric CO2 levels are increasing, but little is known about how this will affect tissue concentrations and the partitioning of agriculturally important nutrients such as nitrogen (N) within crop plants. To investigate this, a glasshouse experiment was conducted in which wheat, a C3 species, and maize, a C4 species, were grown for 8 weeks at high CO2 (1500 cm3 m-3) on N supplies ranging from deficient (0.5 mol m-3) to more than adequate for maximum growth (25 mol m-3). Wheat responded to both CO2 enrichment and N supply; maize responded only to N supply. CO2-enriched wheat produced about twice the dry matter of control plants at all levels of N supply. Tiller and ear numbers were increased by CO2 enrichment irrespective of N supply. Enriched wheat plants had a lower Leaf Area Ratio but higher Net Assimilation Rate and Relative Growth Rate than control plants. There was no effect of CO2 enrichment on specific leaf weight. The enriched plants had lower shoot to root dry matter ratios than thecontrols at 6 mol m-3 N and higher. Shoot to root dry matter ratios of both wheat and maize increased with increasing N supply. CO2-enriched wheat plants accumulated more N than the controls but the proportional increase in N content was not as great as that in dry matter, with the result that concentrations of total-N and nitrate-N were lower in all organs of enriched plants, including ears. Nitrate reductase activity was lower in enriched than in control wheat plants. N-use efficiency by wheat was increased by CO2 enrichment. From a practical point of view, the study indicates that critical total-N and NO3-N concentrations used to diagnose the N status of wheat will need to be reassessed as global CO2 levels increase. Elevated CO2 may also reduce the protein content of grain and thus the baking quality of hard wheats.57^2^Hocking,PJ^Meyer,CP^1991^1^Carbon-dioxide enrichment decreases critical nitrate and nitrogen concentrations in wheat^166^14^6^571-584^^^^^^^^^^2974349^407^434^435^436^437^438^439^92^econtrolA^2973^Atmospheric carbon dioxide (CO2) levels are increasing. In a glasshouse experiment with wheat grown at 5 levels of nitrate (NO3) supply, CO2 enrichment (1500 cm3/m3) substantially decreased critical concentrations of NO3-N and total-N in stem bases and leaves. For example, critical NO3-N concentrations in stem bases at Feekes Stages 1.5, 5, and 10.3, were 4.5, 2.0, and 2.0 mg/g dry wt, respectively, for CO2-enriched plants, compared with 7.5, 6.2 and 6.4 mg/g dry wt, respectively, for control plants grown at the ambient level of CO2. However, concentrations of NO3-N in the rooting medium required to produce maximum dry matter accumulation by CO2-enriched plants were similar to those of control plants at the three growth stages. Critical concentrations of NO3-N and total-N declined with time in stem bases and leaves of plants grown at both ambient and elevated CO2 levels, but the decline was greater for CO2-enriched plants. It was concluded that diagnostic criteria based on current critical N concentrations may become invalid as the atmospheric level of CO2 increases.58^2^Idso,SB^Kimball,BA^1991^1^Downward regulation of photosynthesis and growth at high CO2 levels - no evidence for either phenomenon in 3-year study of sour orange trees^8^96^3^990-992^^^^^Jul^^^^^2976377^417^440^441^442^73^A^2975^Numerous photosynthesis and growth measurements of sour orange (Citrus aurantium L.) trees maintained in ambient air and air enriched with an extra 300 microliters per liter of CO2 have revealed the CO2-enriched trees to have consistently sequestered approximately 2.8 times more carbon than the control trees over a period of three full years. Under field conditions in the natural environment, plants may not experience the downward regulation of photosynthetic capacity typically observed in long-term CO2 enrichment experiments with plants growing in pots.and elevated CO2 levels, but the decline was greater for CO2-enriched plants. It was concluded that diagnostic criteria based on current critical N concentra59^4^Kramer,GF^Lee,EH^Rowland,RA^Mulchi,CL^1991^1^Effects of elevated CO2 concentration on the polyamine levels of field-grown soybean at 3 O3 regimes^35^73^2^137-152^^^^^^^^^^2978348^385^386^417^441^443^444^445^446^447^ sour orange trees^8^96^3^990-992^^^^^Jul^^^^^2976377^417^440^441^442^73^A^2975^Numerous photosynthesis and growth measurements of sour orange (Citrus aurantium L.) trees maintained in ambient air and air enriched with an extra 300 microliters per liter of CO2 have revealed the CO2-enriched trees to have consistently sequestered approximately 2.8 times more carbon than the control trees over a period of three full years. Under field conditions in the natural environment, plants may not experience the downward regulation of photosynthetic capacity typically observed in long-term CO2 enrichment experiments with plants growing in pots.and elevated CO2 levels, but the decline was greater for CO2-enriched plants. It was concluded that diagnostic criteria based on current critical N concentraA^2977^Effects of increased ozone (O3) and carbon dioxide (CO2) on polyamine levels were determined in soybean (Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre-1 O3 and CO2 treatments equal to 350, 400 and 500-mu-l litre-1 for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO2 ameliorated the deleterious effects of increased O3. Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O3 at ambient CO2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO2. Elevated CO2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O3-induced increases in Put and Spd at ambient CO2 concentrations. However, increased CO2 levels inhibited this response by blocking the O3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O3 or CO2 effects on polyamine levels. Our results demonstrate that current ambient O3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO2 to protect soybeans from O3 damage, however, does not appear to involve polyamine accumulation.60^4^Rowlandbamford,AJ^Baker,JT^Allen,LH^Bowes,G^1991^1^Acclimation of rice to changing atmospheric carbon-dioxide concentration^9^14^6^577-583^^^^^Aug^^^^^2980ted with CF air, but had no188^243^370^376^448^449^450^451^452^92^hanced O3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O3-induced increases in Put and Spd at ambient CO2 concentrations. However, increased CO2 levels inhibited this response by blocking the O3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O3 or CO2 effects on polyamine levels. Our results demonstrate that current ambient O3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO2 to protect soybeans from O3 damage, however, does not appear to involve polyamine accumulation.60^4^Rowlandbamford,AJ^Baker,JT^Allen,LH^Bowes,G^1991^1^Acclimation of rice to changing atmospheric carbon-dioxide concentration^9^14^6^577-583^^^^^Aug^^^^^2980ted with CF air, but had noA^2979^The effects were studied of season-long (75 and 88 d) exposure of rice (Oryza sativa L. cv. IR-30) to a range of atmospheric CO2 concentrations in outdoor, computer-controlled, environment chambers under natural solar radiation. The CO2 concentrations were maintained at 160, 250, 330, 500, 660 and 900-mu-mol mol-1 air. Photosynthesis increased with increasing growth CO2 concentrations up to 500-mu-mol mol-1, but levelled off at higher CO2 values. Specific leaf area also increased significantly with increasing CO2. Although leaf dry weight and leaf area index increased, the overall response was not statistically significant. Leaf nitrogen content dropped slightly with elevated CO2, but the response was not statistically significant. The specific activity of ribulose bisphosphate carboxylase/oxygenase (rubisco) declined significantly over the CO2 concentration range 160 to 900-mu- mol mol-1. When expressed on a leaf area basis, rubisco activity decreased by 66%. This was accompanied by a 32% decrease in the amount of rubisco protein as a fraction of the total soluble leaf protein, and by 60% on a leaf area basis. For leaves in the dark, the total rubisco activity (CO2/Mg2+- activated) was reduced by more than 60%. This indicates that rice accumulated an inhibitor in the dark, probably 2- carboxyarabinitol 1-phosphate (CA-1-P). However, the inhibitor did not seem to be involved in the acclimation response. The degree of carbamylation of the rubisco enzyme was unchanged by the CO2 growth regime, except at 900-mu-mol mol-1 where it was reduced by 24%. The acclimation of rice to different atmospheric CO2 conditions involved the modulation of both the activity and amount of rubisco protein in the leaf.61^5^Tripp,KE^Peet,MM^Pharr,DM^Willits,DH^Nelson,PV^1991^1^CO2-enhanced yield and foliar deformation among tomato genotypes in elevated CO2 environments^8^96^3^713-719^^^^^Jul^^^^^2982312^374^376^453^454^455^ssed on a leaf area basis, rubisco activity decreased by 66%. This was accompanied by a 32% decrease inA^2981^Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO2 (about 350) or 1000 microliters per liter CO2 were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO2 enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO2. Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH2PO4. Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO2- enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit.62^3^Woodward,FI^Thompson,GB^McKee,IF^1991^1^The effects of elevated concentrations of carbon-dioxide on individual plants, populations, communities and ecosystems^52^67^^23-38^^^^^Jun343^369^373^420^426^436^456^457^458^459^63^3^Atkinson,CJ^Wookey,PA^Mansfield,TA^1991^1^Atmospheric-pollution and the sensitivity of stomata on barley leaves to abscisic-acid and carbon-dioxide^84^117^4^535-541^^^^^Apr^^^^^2985417^460^461^462^463^464^465^466^467^Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolaA^2984^Spring barley (Hordeum vulgare L. cv. Klaxon) plants were exposed to mixtures of SO2 + NO2 (at concentrations of 24-35 nl l-1 of each gas, depending upon fumigation system), or to charcoal-filtered, or unfiltered ambient air during the period in which the second, and subsequent, leaves were emerging. The ability of individual detached leaves to regulate water loss was then examined after terminating the pollutant treatment. Observations of diurnal changes in stomatal resistance of well- watered plants, using a viscous flow porometer, failed to indicate any major alterations which could be attributed to prior exposure to SO2 + NO2. By contrast, when an ABA solution (10(-1) mol m-3) was applied to detached leaves, the stomata of polluted plants were less responsive than plants previously exposed to control air. The dynamics of the observed responses strongly implicated impaired physiology of the guard cells rather than mechanical changes in the epidermis that might, for example, result from damage to the cuticle. Stomatal closure was considerably slower in polluted leaves compared with the controls. This decline in responsiveness to ABA was observed using leaves excised from well-watered plants and in the absence of any externally visible injury. The ability of stomata to respond to a range of CO2 concentrations from 195- 735-mu-mol mol-1 was also examined using individual leaves, attached to the plant, in an environmentally controlled cuvette. Here the stomata of leaves which had been fumigated with SO2 + NO2 behaved in a similar manner to the non-fumigated leaves, both showing closure in elevated CO2 concentrations.64^3^Fajer,ED^Bowers,MD^Bazzaz,FA^1991^1^Performance and allocation patterns of the perennial herb, Plantago lanceolata, in response to simulated herbivory and elevated CO2 environments^2^87^1^37-42^^^^^^^^^^298792^e observed responses strongly implicated impaired physiology of the guard cells rather than mechanical changes in the epidermis that might, for example, result from damage to thA^2986^We tested the prediction that plants grown in elevated CO2 environments are better able to compensate for biomass lost to herbivory than plants grown in ambient CO2 environments. The herbaceous perennial Plantago lanceolata (Plantaginaceae) was grown in either near ambient (380 ppm) or enriched (700 ppm) CO2 atmospheres, and then after 4 weeks, plants experienced either 1) no defoliation; 2) every fourth leaf removed by cutting; or 3) every other leaf removed by cutting. Plants were harvested at week 13 (9 weeks after simulated herbivory treatments). Vegetative and reproductive weights were compared, and seeds were counted, weighed, and germinated to assess viability. Plants grown in enriched CO2 environments had significantly greater shoot weights, leaf areas, and root weights, yet had significantly lower reproductive weights (i.e. stalks + spikes + seeds) and produced fewer seeds, than plants grown in ambient CO2 environments. Relative biomass allocation patterns further illustrated differences in plant responses to enriched CO2 atmospheres: enriched CO2-grown plants only allocated 10% of their carbon resources to reproduction whereas ambient CO2-grown plants allocated over 20%. Effects of simulated herbivory on plant performance were much less dramatic than those induced by enriched CO2 atmospheres. Leaf area removal did not reduce shoot weights or reproductive weights of plants in either CO2 treatment relative to control plants. However, plants from both CO2 treatments experienced reductions in root weights with leaf area removal, indicating that plants compensated for lost above-ground tissues, and maintained comparable levels of reproductive output and seed viability, at the expense of root growth.65^3^Figueira,A^Whipkey,A^Janick,J^1991^1^Increased co2 and light promote invitro shoot growth and development of theobroma-cacao^154^116^3^585-589^^^^^May^^^^^2989468^469^470^471^472^an plants grown in ambient CO2 environments. Relative biomass allocation patterns further illustrated differences in pA^2988^Axillary shoots of cacao (Theobroma cacao L.), induced in vitro with cytokinins (BA or TDZ), elongated and produced leaves only in the presence of cotyledons and/or roots. Detached axillary shoots, which do not grow in vitro under conventional tissue culture protocols, rooted with auxin and developed normally in vivo. Detached axillary shoots from cotyledonary nodes and single-node cuttings from mature plants were induced to elongate and produce normal leaves in the presence of 20,000 ppm CO2 and a photosynthetic photon flux density (PPFD) of 150 to 200-mu-mol.s-1.m-2. Subcultured nodal cuttings continued to elongate and produce leaves under elevated CO2 and light levels, and some formed roots. Subculture of microcuttings under CO2 enrichment could be the basis for a rapid system of micropropagation for cacao. Chemical names used: N- (phenylmethyl)-1H-purin-6-amine (BA); 1H-indole-3-butyric acid (IBA); alpha-naphthaleneacetic acid (NAA); thidiazuron (TDZ).atterns further illustrated differences in p66^10^Hunt,HW^Trlica,MJ^Redente,EF^Moore,JC^Detling,JK^Kittel,TGF^Walter,DE^Fowler,MC^Klein,DA^Elliott,ET^1991^1^Simulation-model for the effects of climate change on temperate grassland ecosystems^81^53^3-4^205-246^^^^^Apr^^^^^2991312^372^431^456^473^474^475^476^477^478^s, rooted with auxin and developed normally in vivo. Detached axillary shoots from cotyledonary nodes and single-node cuttings from mature plants were induced to elongate and produce normal leaves in the presence of 20,000 ppm CO2 and a photosynthetic photon flux density (PPFD) of 150 to 200-mu-mol.s-1.m-2. Subcultured nodal cuttings continued to elongate and produce leaves under elevated CO2 and light levels, and some formed roots. Subculture of microcuttings under CO2 enrichment could be the basis for a rapid system of micropropagation for cacao. Chemical names used: N- (phenylmethyl)-1H-purin-6-amine (BA); 1H-indole-3-butyric acid (IBA); alpha-naphthaleneacetic acid (NAA); thidiazuron (TDZ).atterns further illustrated differences in pA^2990^We studied the responses of temperate grasslands to climate change using a grassland ecosystem model which simulates seasonal dynamics of shoots, roots, soil water, mycorrhizal fungi, saprophytic microbes, soil fauna, inorganic nitrogen, plant residues and soil organic matter. Forty-year simulations were made for several climate change scenarios. The model was driven with observed weather and with combinations of elevated atmospheric CO2, elevated temperature, and either increased or decreased precipitation. Precipitation and CO2 level accounted for most of the variation among climate change treatments in the responses of soil, plants, animals and microbes. Elevated temperature extended the growing season but depressed photosynthesis in the summer, with little net effect on annual primary production. Doubling CO2 (1) caused persistent increases in primary production, in spite of greater nitrogen limitation, and (2) led to greater storage of carbon in plant residues and soil organic matter. The increased carbon storage was not great enough to keep pace with the present rate of increase in atmospheric CO2.67^3^Idso,SB^Kimball,BA^Allen,SG^1991^1^Net photosynthesis of sour orange trees maintained in atmospheres of ambient and elevated CO2 concentration^107^54^1^95-101^^^^^30 Mar^^^^^2993312^376^lations were made for several climate change scenarios. The model was driven with observed weather and with combinations of elevated atmospheric CO2, elevated temperature, and either increased or decreased precipitation. Precipitation and CO2 level accounted for most of the variation among climate change treatments in the responses of soil, plants, animals and microbes. Elevated temperature extended the growing season but depressed photosynthesis in the summer, with little net effect on annual primary production. Doubling CO2 (1) caused persistent increases in primary production, in spite of greater nitrogen limitation, and (2) led to greater storage of carbon in plant residues and soil organic matter. The increasA^2992^Eight sour orange trees planted directly into the ground at Phoenix, Arizona, as small seedlings in July 1987 have been enclosed by four clear-plastic-wall, open-top chambers since November of that year. Half of the trees have been continuously supplied with a CO2-enriched atmosphere consisting of an extra 300 cm3 of CO2 per m3 of air. Data from a comprehensive inventory of all above-ground plant parts at the conclusion of two full years of growth under these conditions have revealed that the net effect of the CO2-enriched air was to more than double the normal production of biomass over that time interval. Here we report net photosynthesis measurements made throughout the last summer of the period, which suggest that the primary impetus for this large growth response was an equivalent enhancement of the net photosynthetic rates of the CO2-enriched trees.68^2^Johnson,DW^Ball,JT^1990^1^Environmental-pollution and impacts on soils and forests nutrition in north-america^94^54^^3-20^^^^^Nov-Dec^^^^^299519^341^349^372^479^480^481^482^483^484^irectly into the ground at Phoenix, Arizona, as small seedlings in July 1987 have been enclosed by four clear-plastic-wall, open-top chambers since November of that year. Half of the trees have been continuously supplied with a CO2-enriched atmosphere consisting of an extra 300 cm3 of CO2 per m3 of air. Data from a comprehensive inventory of all above-ground plant parts at the conclusion of two full years of growth under these conditions have revealed that the net effect of the CO2-enriched air was to more than double the normal production of biomass over that time interval. Here we report net photosynthesis measurements made throughout the last summer of the period, which suggest that the primary impetus for this large growth response was an equivalent enhancement of the net photosynthetic rates of the CO2-enriched trees.68^2^Johnson,DW^Ball,JT^1990^1^Environmental-pollution and impacts on soils and forests nutrition in north-america^94^54^^3-20^^^^^Nov-Dec^^^^^2995A^2994^The effects of acid deposition, excess N deposition, and elevated CO2 on forest soils and nutrition in North America are reviewed. While there remains the possibility that acid deposition and excess N deposition are contributing to declines in red spruce, sugar maple, and southern pines, clear-cut cause and effects are still not evident. Climate is clearly a major factor in red spruce decline in the northeastern U.S., but air pollution may contribute. There is some evidence that soil solution Al may be approaching deleterious levels in southeastern red spruce forests. Lack of proper management may be a major factor in the sugar maple and southern pine declines, but once again, air pollution as a potential contributor cannot be ignored. Nutrient budget analyses and discoveries of soils base cation depletion in certain sites suggest that base cation status is declining in forests of the southeastern U.S., but thus far, base cation deficiences are uncommon. Recent research has revealed that there are more cases of N-saturated forests in North America than was previously suspected. These systems are characterized by high rates of soil N mineralization, high atmospheric N inputs, low uptakes, or some combination of these factors. Soil leaching and Al mobilization in such systems is often dominated by nitrate. However, the geographical extent of these types of systems is limited, and the traditional view that most forest ecosystems are N limited remains valid, especially where forest management is intensive. The limited information available on tree response to CO2 suggests N-deficient plants often grow faster with elevated CO2, whereas P-deficient plants often do not. Research is needed to 1) determine if the differences in response between N- and P-deficient plants is common, 2) the responses of plants deficient in other nutrients to elevated CO2, and 3) the interactions of CO2 increase, nutrient deficiencies, climate change.e cation deficiences are uncommon. Recent research has revealed that there are mor69^2^Johnson,RH^Lincoln,DE^1991^1^Sagebrush carbon allocation patterns and grasshopper nutrition - the influence of CO2 enrichment and soil mineral limitation^2^87^1^127-134^^^^^^^^^^2997372^373^485^486^487^488^489^490^57^92^. Soil leaching and Al mobilization in such systems is often dominated by nitrate. However, the geographical extent of these types of systems is limited, and the traditional view that most forest ecosystems are N limited remains valid, especially where forest management is intensive. The limited information available on tree response to CO2 suggests N-deficient plants often grow faster with elevated CO2, whereas P-deficient plants often do not. Research is needed to 1) determine if the differences in response between N- and P-deficient plants is common, 2) the responses of plants deficient in other nutrients to elevated CO2, and 3) the interactions of CO2 increase, nutrient deficiencies, climate change.e cation deficiences are uncommon. Recent research has revealed that there are morA^2996^Artemisia tridentata seedlings were grown under carbon dioxide concentrations of 350 and 650-mu-l l-1 and two levels of soil nutrition. In the high nutrient treatment, increasing CO2 led to a doubling of shoot mass, whereas nutrient limitation completely constrained the response to elevated CO2. Root biomass was unaffected by any treatment. Plant root/shoot ratios declined under carbon dioxide enrichment but increased under low nutrient availability, thus the ratio was apparently controlled by changes in carbon allocation to shoot mass alone. Growth under CO2 enrichment increased the starch concentrations of leaves grown under both nutrient regimes, while increased CO2 and low nutrient availability acted in concert to reduce leaf nitrogen concentration and water content. Carbon dioxide enrichment and soil nutrient limitation both acted to increase the balance of leaf storage carbohydrate versus nitrogen (C/N). The two treatment effects were significantly interactive in that nutrient limitation slightly reduced the C/N balance among the high-CO2 plants. Leaf volatile terpene concentration increased only in the nutrient limited plants and did not follow the overall increase in leaf C/N ratio. Grasshopper consumption was significantly greater on host leaves grown under CO2 enrichment but was reduced on leaves grown under low nutrient availability. An overall negative relationship of consumption versus leaf volatile concentration suggests that terpenes may have been one of several important leaf characteristics limiting consumption of the low nutrient hosts. Digestibility of host leaves grown under the high CO2 treatment was significantly increased and was related to high leaf starch content. Grasshopper growth efficiency (ECI) was significantly reduced by the nutrient limitation treatment but co-varied with leaf water content.70^4^Kuehny,JS^Peet,MM^Nelson,PV^Willits,DH^1991^1^Nutrient dilution by starch in CO2-enriched chrysanthemum^78^42^239^711-716^^^^^Jun^^^^^2999204^360^422^430^450^453^491^492^92^tlA^2998^Increasing growth irradiance and CO2 generally decreases foliar nutrient concentration on a dry weight basis and increases foliar starch concentration. However, the extent to which starch concentrations 'dilute' foliar nutrient concentrations when the latter are expressed on a dry weight basis is not known. To determine the importance of differential starch accumulation in calculating nutrient concentrations on a dry weight basis, leaf nutrient and starch concentrations were measured in Chrysanthemum x morifolium 'Fiesta' (Ramat.) cuttings grown at three irradiance levels and two CO2 levels for eight weeks in both winter and spring. On a dry weight basis, foliar concentrations of most nutrients were lower in both seasons as a result of the elevated CO2 and irradiance levels, and total dry weights were higher. Per cent starch was greater at the high CO, level in both seasons but was only greater at higher irradiances in the winter experiment. When starch was subtracted from the leaf dry weights, the differences between CO2 and irradiance treatments disappeared with respect to N, P, K, Ca, Mg, S, and B but not for Fe, Mn, Zn, and Cu.71^2^Long,SP^Drake,BG^1991^1^Effect of the long-term elevation of CO2 concentration in the field on the quantum yield of photosynthesis of the C3 sedge, Scirpus olneyi^8^96^1^221-226^^^^^May^^^^^3001348^493^494^495^496^ial starch accumulation in calculating nutrient concentrations on a dry weight basis, leaf nutrient and starch concentrations were measured in Chrysanthemum x morifolium 'Fiesta' (Ramat.) cuttings grown at three irradiance levels and two CO2 levels for eight weeks in both winter and spring. On a dry weight basis, foliar concentrations of most nutrients were lower in both seasons as a result of the elevated CO2 and irradiance levels, and total dry weights were higher. Per cent starch was greater at the high CO, level in both seasons but was only greater at higher irradiances in the winter experiment. When starch was subtracted from the leaf dry weights, the diA^3000^CO2 concentration was elevated throughout 3 years around stands of the C3 sedge Scirpus olneyi on a tidal marsh of the Chesapeake Bay. The hypothesis that tissues developed in an elevated CO2 atmosphere will show an acclimatory decrease in photosynthetic capacity under light-limiting conditions was examined. The absorbed light quantum yield of CO2 uptake (phi- abs and the efficiency of photosystem II photochemistry were determined for plants which had developed in open top chambers with CO2 concentrations in air of 680 micromoles per mole, and of 351 micromoles per mole as controls. An Ulbricht sphere cuvette incorporated into an open gas exchange system was used to determine phi-abs and a portable chlorophyll fluorimeter was used to estimate the photochemical efficiency of photosystem II. When measured in an atmosphere with 10 millimoles per mole O2 to suppress photorespiration, shoots showed a phi-abs of 0.093 +/- 0.003, with no statistically significant difference between shoots grown in elevated or control CO2 concentrations. Efficiency of photosystem II photochemistry was also unchanged by development in an elevated CO2 atmosphere. Shoots grown and measured in 680 micromoles per mole of CO2 in air showed a phi- abs of 0.078 +/- 0.004 compared with O.065 +/- 0.003 for leaves grown and measured in 351 micromoles per mole CO2 in air; a highly significant increase. In accordance with the change in phi-abs, the light compensation point of photosynthesis decreased from 51 +/- 3 to 31 +/- 3 micromoles per square meter per second for stems grown and measured in 351 and 680 micromoles per mole of CO2 in air, respectively. The results suggest that even after 3 years of growth in elevated CO2, there is no evidence of acclimation in capacity for photosynthesis under light-limited conditions which would counteract the stimulation of photosynthetic CO2 uptake otherwise expected through decreased photorespiration. of 0.093 +/- 0.003, with no statistically significant difference between shoots grown in elevated o72^2^Long,SP^Hutchin,PR^1991^1^Primary production in grasslands and coniferous forests with climate change - an overview^56^1^2^139-156^^^^^May^^^^^300335^389^493^497^498^499^500^501^502^503^f CO2 in air showed a phi- abs of 0.078 +/- 0.004 compared with O.065 +/- 0.003 for leaves grown and measured in 351 micromoles per mole CO2 in air; a highly significant increase. In accordance with the change in phi-abs, the light compensation point of photosynthesis decreased from 51 +/- 3 to 31 +/- 3 micromoles per square meter per second for stems grown and measured in 351 and 680 micromoles per mole of CO2 in air, respectively. The results suggest that even after 3 years of growth in elevated CO2, there is no evidence of acclimation in capacity for photosynthesis under light-limited conditions which would counteract the stimulation of photosynthetic CO2 uptake otherwise expected through decreased photorespiration. of 0.093 +/- 0.003, with no statistically significant difference between shoots grown in elevated oA^3002^In energy terms primary production is the driving step of the global carbon cycle. To predict the interaction of ecosystems with the "greenhouse" effect, it is necessary to understand how primary production, consumption, and decomposition will respond to climate change. Most estimates of primary production have been made by extrapolation from measured standing crops. For grasslands we show this approach to be seriously in error. Even where detailed studies of turnover and belowground production have been undertaken, errors are invariably high, severely limiting the value of models based on correlation of climate with measured production. Detailed information is available on the responses of individual plant processes to individual climatic variables at the leaf, plant, and stand level, giving potential for a more mechanistic approach in modelling. This approach is limited by lack of information on multivariate interactions and on some key physiological processes, and by uncertainties in scaling up to populations and communities. Despite this, some important insights to possible community responses, particularly those of C3 and C4 types, may be gained from knowledge of responses at the plant level and below. This review outlines the expected character of climate change in grasslands and coniferous forests. Knowledge of the responses of different physiological processes underlying production to individual aspects of climate change is considered, and its implications for higher levels of organization are discussed. Although feasible, mechanistic models of production compound the errors associated with individual process responses with uncertainties surrounding interaction and scaling up, and result in very large errors in any prediction of response to climate change. We conclude that there is insufficient information to predict accurately the response of primary production to climate change. The key processes for which information is inadequate and the parameters that have meaning at different scales need to be identified. Of particular promise is the approach of predicting production from light interception and conversion efficiency.73^1^Mooney,HA^1991^1^Biological response to climate change - an agenda for research^56^1^2^112-117^^^^^May^^^^^3005372^417^climate change in grasslands and coniferous forests. Knowledge of the responses of different physiological processes underlying production to individual aspects of climate change is considered, and its implications for higher levels of organization are discussed. Although feasible, mechanistic models of production compound the errors associated with individual process responses with uncertainties surrounding interaction and scaling up, and result in very large errors in any prediction of response to climate change. We conclude that there is insufficient information to predict accurately the response of primary production to climate change. The key processes for which information is inadequate and the parameters that have meaning at different scales need tA^3004^Our knowledge of the structure and functioning of terrestrial ecosystems on a global scale is not developed to a sufficient degree to understand - much less predict - the consequences of climate change either on the systems themselves or on subsequent atmospheric interactions. In many regards we have lagged behind the atmospheric scientists, and to a certain degree the oceanographers, in establishing a global understanding of the dynamics of our respective systems. This is due in part to the inherently greater complexity of biotic systems, but also to the lack of appropriate tools to measure regional biotic processes. These tools are now becoming available and with them a better understanding of terrestrial and atmospheric interactions. Even as these capabilities become a reality we must be realistic in recognizing that we have so far to go along the road to understanding that useful predictive capacity may elude us for a long time to come. What we now need to do is act on the recommendations that have been emerging over the past few years and develop a global program to document more precisely the distribution, structure, and quantity of the earth's biotic systems, their principal functional properties, and - most difficult of all - their changing nature. In order to do this we will have to: (1) perfect some of the emerging new tools for assessing these properties, (2) fill some of the gaps in our knowledge about the relevant processes, and (3) establish an international network of long-term observations and large-scale ecosystem manipulations. We have been aware of these needs and shortcomings for some time and we must move from plans to concerted international action.74^1^Newton,PCD^1991^1^Direct effects of increasing carbon-dioxide on pasture plants and communities^167^34^1^1-24^^^^^^^^^^3007372^384^457^504^505^506^507^508^509^510^o go along the road to understanding that useful predictive capacity may elude us for a long time to come. What we now need to do is act on the recommendations that havA^3006^The atmospheric carbon dioxide (CO2) level is rising and is expected to double during the next century. This paper reviews information on the responses of pasture species and communities to elevated CO2. Data for some further non-arable species are included where relevant. The effect of CO2 on yield and on morphological and physiological characteristics are considered together with aspects of particular relevance to pasture, for example, herbivory, plant community relationships, and experimental methods for the exposure of pasture to elevated CO2. At the plant level, physiological responses to CO2 include enhanced net photosynthesis and reduced stomatal conductance; morphological changes include greater leaf areas, shoot production, and root: shoot ratios. Little is known about community responses or about plant-herbivore dynamics at elevated CO2. Changes in herbage quality, tissue turnover, and botanical composition may be expected but confirmation of these responses will only be possible when data are available from long-term studies of grazed pasture at elevated CO2.75^2^Norby,RJ^Oneill,EG^1991^1^Leaf-area compensation and nutrient interactions in CO2- enriched seedlings of yellow-poplar (Liriodendron tulipifera L)^84^117^4^515-528^^^^^Apr^^^^^3009376^377^386^399^450^465^511^512^513^514^on yield and on morphological and physiological characteristics are considered together with aspects of particular relevance to pasture, for example, herbivory, plant community relationships, and experimental methods for the exposure of pasture to elevated CO2. At the plant level, physiological responses to CO2 include enhanced net photosynthesis and reduced stomatal conductance; morphological changes include greater leaf areas, shoot production, and root: shoot ratios. Little is known about community responses or about plant-herbivore dynamics at elevated CO2. Changes in herbage quality, tissue turnover, and botanical composition may be expected but confirmation of these responses will only be possible when data aA^3008^The responses of yellow-poplar (Liriodendron tulipifera L.) seedlings to elevated levels of atmospheric CO2 were investigated to identify attributes governing growth and physiological responses to CO2. Based on the pattern of leaf initiation and nutrient requirements of the species, it was predicted that (1) CO2 enrichment would enhance growth of yellow-poplar seedlings both through accelerated leaf area production and through higher rates of carbon assimilation per unit leaf area; and (2) growth enhancement of yellow-poplar by CO2 enrichment would be reduced by nutrient limitations. The hypotheses were tested in an experiment in which yellow-poplar plants were grown from seed for 24 weeks in controlled- environment chambers. The experimental design comprised three atmospheric CO2 concentrations (371, 493, and 787 cm3 m-3), two levels of mineral nutrients (unfertilized or weekly additions of complete nutrient solution), and three harvests (6, 12, and 24 weeks). Plant growth rate, water use, foliar gas exchange, component dry weights, and nutrient contents were measured. Both hypotheses were rejected. Whole-plant dry weight increased similarly with CO2 enrichment in plants provided with additional mineral nutrients and in unfertilized plants, although the fertilized plants grew 10-fold larger. The increase in dry weight resulting from elevated CO2 occurred only in root systems. Although leaves were produced continuously during the experiment, leaf area was slightly reduced in elevated CO2, and the whole-plant growth response was wholly attributable to an increase in carbon assimilation per unit leaf area. Although the compensation between photosynthesis and leaf area reduced the potential growth response to CO2, the reduction in leaf area ratio was associated with a significant increase in water-use efficiency. This unexpected result demonstrated the importance of feedbacks and interactions between resources in shaping the response of a plant to CO2.nd 24 weeks). Plant growth rate, water use, foliar gas76^4^Palet,A^Ribascarbo,M^Argiles,JM^Azconbieto,J^1991^1^Short-term effects of carbon-dioxide on carnation callus cell respiration^8^96^2^467-472^^^^^Jun^^^^^3011243^244^348^385^497^515^516^517^518^519^ral nutrients and in unfertilized plants, although the fertilized plants grew 10-fold larger. The increase in dry weight resulting from elevated CO2 occurred only in root systems. Although leaves were produced continuously during the experiment, leaf area was slightly reduced in elevated CO2, and the whole-plant growth response was wholly attributable to an increase in carbon assimilation per unit leaf area. Although the compensation between photosynthesis and leaf area reduced the potential growth response to CO2, the reduction in leaf area ratio was associated with a significant increase in water-use efficiency. This unexpected result demonstrated the importance of feedbacks and interactions between resources in shaping the response of a plant to CO2.nd 24 weeks). Plant growth rate, water use, foliar gasA^3010^The addition of potassium bicarbonate to the electrode cuvette immediately stimulated the rate of dark O2 uptake of photomixotrophic and heterotrophic carnation (Dianthus caryophyllus L.) callus, of Elodea canadensis (Michx) leaves, and of other plant tissues. This phenomenon occurred at pH values lower than 7.2 to 7.8, and the stimulation depended on the concentration of gaseous CO2 in the solution. These stimulatory responses lasted several minutes and then decreased, but additional bicarbonate or gaseous CO2 again stimulated respiration, suggesting a reversible effect. Carbonic anhydrase in the solution increased the stimulatory effect of potassium bicarbonate. The CO2/bicarbonate dependent stimulation of respiration did not occur in animal tissues such as rat diaphragm and isolated hepatocytes, and was inhibited by salicylhydroxamic acid in carnation callus cells and E. canadensis leaves. This suggested that the alternative oxidase was engaged during the stimulation in plant tissues. The cytochrome pathway was severely inhibited by CO2/bicarbonate either in the absence or in the presence of the uncoupler carbonyl-cyanide m-chlorophenyl hydrazone. The activity of cytochrome c oxidase of callus tissue homogenates was also inhibited by CO2/bicarbonate. The results suggested that high carbon dioxide levels (mainly free CO2) Partially inhibited the cytochrome pathway (apparently at the oxidase level), and this block in electron transport elicited a large transient engagement of the alternative oxidase when present uninhibited.77^1^Ryan,MG^1991^1^Effects of climate change on plant respiration^56^1^2^157-167^^^^^May^^^^^3013174^389^398^520^521^522^523^524^525^92^te. The CO2/bicarbonate dependent stimulation of respiration did not occur in animal tissues such as rat diaphragm and isolated hepatocytes, and was inhibited by salicylhydroxamic acid in carnation callus cells and E. canadensis leaves. This suggested that the alternative oxidase was engaged during the stimulation in plant tissues. The cytochromA^3012^Plant respiration is a large, environmentally sensitive component of the ecosystem carbon balance, and net ecosystem carbon flux will change as the balance between photosynthesis and respiration changes. Partitioning respiration into the functional components of construction, maintenance, and ion uptake will aid the estimation of plant respiration for ecosystems. Maintenance respiration is the component most sensitive to changes in temperature, CO2, protein concentration and turnover, water stress, and atmospheric pollutants. For a wide variety of plant tissues, maintenance respiration, corrected for temperature, appears to be linearly related to Kjeldahl nitrogen content of live tissue. Total and maintenance respiration may decline under CO2 enrichment, but the mechanism, independence from changes in protein content, and acclimation are unknown. Response of respiration to temperature can be modelled as a Q10 relationship, if corrections for bias arising from daily and annual temperature amplitude are applied. Occurrence and control of the cyanide- resistant respiratory pathway and acclimation of respiration rates to different climates are poorly understood, but may substantially affect the reliability of model estimates of plant respiration.78^2^Smith,WK^Donahue,RA^1991^1^Simulated influence of altitude on photosynthetic CO2 uptake potential in plants^9^14^1^133-136^^^^^Jan^^^^^3015465^526^e component most sensitive to changes in temperature, CO2, protein concentration and turnover, water stress, and atmospheric pollutants. For a wide variety of plant tissues, maintenance respiration, corrected for temperature, appears to be linearly related to Kjeldahl nitrogen content of live tissue. Total and maintenance respiration may decline under CO2 enrichment, but the mechanism, independence from changes in protein content, and acclimation are unknown. Response of respiration to temperature can be modelled as a Q10 relationship, if corrections for bias arising from daily and annual temperature amplitude areA^3014^A simulation of the quantitative influence of altitude on photosynthetic CO2 uptake capability (A(P)) included the effects of predicted changes (1) in air temperature (lapse rate) and (2) leaf temperature, (3) ambient pressure and CO2 concentration, and (4) the diffusion coefficient for CO2 in air. When a dry lapse rate (0.01-degrees-C m-1) in air temperature was simulated, significant declines (up to 14%) in A(P) were predicted from sea level to 4km altitude. A moist lapse rate of 0.003-degrees-C m-1 resulted in less than a 4% decrease in A(P) over the same altitude range. When natural leaf temperatures (predicted from heat balance analyses) were simulated, A(P) was significantly greater (almost-equal-to 20%) than when leaf temperatures were considered equal to air temperature for all lapse conditions. There was virtually no change in A(P) with altitude when predicted leaf temperatures and moist lapse conditions were simulated. There was a significant (almost-equal-to 10%) increase in A(P) with altitude when leaf temperature was held constant at 30-degrees- C (regardless of altitude) under moist lapse conditions. Future studies evaluating the effects of elevation on photosynthesis could benefit from the above considerations of the effects of natural leaf temperature regimes and prevailing lapse conditions on CO2 uptake potential.79^2^Thomas,RB^Strain,BR^1991^1^Root restriction as a factor in photosynthetic acclimation of cotton seedlings grown in elevated carbon-dioxide^8^96^2^627-634^^^^^Jun^^^^^3017130^343^348^363^376^441^527^528^529^530^P) over the same altitude range. When natural leaf temperatures (predicted from heat balance analyses) were simulated, A(P) was significantly greater (almost-equal-to 20%) than when leaf temperatures were considered equal to air temperature for all lapse conditions. There was virtually no change in A(P) with altitude when predicted leaf temperatures and moist lapse conditions were simulated. There was a significant (almost-equal-to 10%) increase in A(P) with altitA^3016^Interactive effects of root restriction and atmospheric CO2 enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO2 partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO2 partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO2. In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars Of CO2 were not significantly different. Plants grown in small pots in 650 microbars Of CO2 produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels Of CO2 was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO2 enrichment occurred only when root growth was restricted suggesting that ribulose-1,5- bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO2 concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1, 5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO2.microbars, but the dry weight gain was found to be primarily an accumulation of le80^4^Vanveen,JA^Liljeroth,E^Lekkerkerk,LJA^Vandegeijn,SC^1991^1^Carbon fluxes in plant-soil systems at elevated atmospheric CO2 levels^56^1^2^175-181^^^^^May^^^^^3019436^531^532^533^534^535^536^537^538^57^A^3018^The flow of carbon from photosynthesizing tissues of higher plants, through the roots and into the soil is one of the key processes in terrestrial ecosystems. An increased level of CO2 in the atmosphere will likely result in an increased input of organic carbon into the soil due to the expected increase in primary production. Whether this will lead to accumulation of greater amounts of organic carbon in soil depends on the flow of carbon through the plant into the soil and its subsequent transformation in the soil by microorganisms. In this paper the major controls of carbon translocation via roots into the soil as well as the subsequent microbial turnover of root-derived carbon are reviewed. We discuss possible consequences of an increased CO2 level in the atmosphere on these processes.ion of le81^2^Wong,SC^Osmond,CB^1991^1^Elevated atmospheric partial-pressure of CO2 and plant-growth .3. Interactions between Triticum aestivum (C3) and Echinochloa frumentacea (C4) during growth in mixed culture under different CO2, N-nutrition and irradiance treatments, with emphasis on belowground responses estimated using the delta-C-13 value of root biomass^92^18^2^137-152^^^^^^^^^^3021178^243^245^431^539^540^541^57^ill likely result in an increased input of organic carbon into the soil due to the expected increase in primary production. Whether this will lead to accumulation of greater amounts of organic carbon in soil depends on the flow of carbon through the plant into the soil and its subsequent transformation in the soil by microorganisms. In this paper the major controls of carbon translocation via roots into the soil as well as the subsequent microbial turnover of root-derived carbon are reviewed. We discuss possible consequences of an increased CO2 level in the atmosphere on these processes.ion of leA^3020^Wheat (Triticum aestivum L.), a C3 species, and Japanese millet (Echinochloa frumentacea Link), a C4 species, were grown in pots in monoculture and mixed culture (2 C3:1 C4 and 1 C3:2 C4) at two ambient partial pressures of CO2 (320 and 640-mu-bar), two photosynthetic photon flux densities (PPFDs) (daily maximum 2000 and 500-mu-mol m-2 s-1) and two levels of nitrogen nutrition (12 mM and 2 mM NO3BAR). Growth of shoots of both components in mixed culture was measured by physical separation, and the proportions of root biomass due to each component were calculated from delta-C-13 value of total root biomass. In air (320-mu-bar CO2) at high PPFD and with high root zone-N, the shoot biomass of C3 and C4 components at the first harvest (28 days) was in proportion to the sowing ratio. However, by the second harvest (36 days) the C4 component predominated in both mixtures. Under the same conditions, but with low PPFD, C3 plants predominated at the first harvest but C4 plants had overtaken them by the time of the second harvest. Elevated atmospheric CO2 (640-mu-bar) stimulated shoot growth of Triticum in 15 of 16 treatment combinations and the stimulation was greatest in plants provided with low NO3BAR. Root growth of the C3 plants was generally stimulated by elevated CO2, but was only occasionally sensitive to the presence of C4 plants in mixed culture. However, growth of the C4 plants was often sensitive to the presence of C3 plants in mixed culture. In mixed cultures, elevated CO2 plants stimulated growth of C4 plants at high PPFD, high-N and in all low-N treatments but this was insufficient to offset a marked decline in shoot growth with increasing proportion of C3 plants in mixed cultures. The unexpected stimulation of growth of C4 plants by elevated CO2 was correlated with more negative delta- C-13 values of C4 root biomass, suggesting a partial failure of the CO2 concentrating mechanism of C4 photosynthesis in Echinochloa under low-N. These experiments show that for these species nitrogen was more important than light or elevated pCO2 in determining the extent of competitive interactions in mixed culture.82^4^Ziska,LH^Hogan,KP^Smith,AP^Drake,BG^1991^1^Growth and photosynthetic response of 9 tropical species with long-term exposure to elevated carbon-dioxide^2^86^3^383-389^^^^^^^^^^3023174^245^348^417^422^he presence of C4 plants in mixed culture. However, growth of the C4 plants was often sensitive to the presence of C3 plants in mixed culture. In mixed cultures, elevated CO2 plants stimulated growth of C4 plants at high PPFD, high-N and in all low-N treatments but this was insufficient to offset a marked decline in shoot growth with increasing proportion of C3 plants in mixed cultures. The unexpected stimulation of growth of C4 plants by elevated CO2 was correlated with more negative delta- C-13 values of C4 root biomass, suggesting a partial failure of the CO2 concentrating mechanism of C4 photosynthesis in Echinochloa under low-N. These experiments show that for these species nitrogen was more importaA^3022^Seedlings of nine tropical species varying in growth and carbon metabolism were exposed to twice the current atmospheric level of CO2 for a 3 month period on Barro Colorado Island, Panama. A doubling of the CO2 concentration resulted in increases in photosynthesis and greater water use efficiency (WUE) for all species possessing C3 metabolism, when compared to the ambient condition. No desensitization of photosynthesis to increased CO2 was observed during the 3 month period. Significant increases in total plant dry weight were also noted for 4 out of the 5 C3 species tested and in one CAM species, Aechmea magdalenae at high CO2. In contrast, no significant increases in either photosynthesis or total plant dry weight were noted for the C4 grass, Paspallum conjugatum. Increases in the apparent quantum efficiency (AQE) for all C3 species suggest that elevated CO2 may increase photosynthetic rate relative to ambient CO2 over a wide range of light conditions. The response of CO2 assimilation to internal C(i) suggested a reduction in either the RuBP and/or Pi regeneration limitation with long term exposure to elevated CO2. This experiment suggests that: (1) a global rise in CO2 may have significant effects on photosynthesis and productivity in a wide variety of tropical species, and (2) increases in productivity and photosynthesis may be related to physiological adaptation(s) to increased CO2.83^6^Bhattacharya,NC^Hileman,DR^Ghosh,PP^Musser,RL^Bhattacharya,S^Biswas,PK^1990^1^Interaction of enriched CO2 and water-stress on the physiology of and biomass production in sweet-potato grown in open-top chambers^9^13^9^933-940^^^^^Dec^^^^^3025243^264^344^398^434^530^ant increases in either photosynthesis or total plant dry weight were noted for the C4 grass, Paspallum conjugatum. Increases in the apparent quantum efficiency (AQE) for all C3 species suggest that elevated CO2 may increase photosynthetic rate relative to ambient CO2 over a wide range of light conditions. The response of CO2 assimilation to internal C(A^3024^The objective of this study was to investigate the effects of water stress in sweet potato (Ipomoea batatas L. [Lam] 'Georgia Jet') on biomass production and plant-water relationships in an enriched CO2 atmosphere. Plants were grown in pots containing sandy loam soil (Typic Paleudult) at two concentrations of elevated CO2 and two water regimes in open-top field chambers. During the first 12 d of water stress, leaf xylem potentials were higher in plants grown in a CO2 concentration of 438 and 666-mu-mol mol-1 than in plants grown at 364-mu-mol mol-1. The 364-mu-mol mol-1 CO2 grown plants had to be rewatered 2d earlier than the high CO2-grown plants in response to water stress. For plants grown under water stress, the yield of storage roots and root:shoot ratio were greater at high CO2 than at 364-mu-mol mol-1; the increase, however, was not linear with increasing CO2 concentrations. In well-watered plants, biomass production and storage root yield increased at elevated CO2, and these were greater as compared to water-stressed plants grown at the same CO2 concentration.84^2^Imai,K^Okamotosato,M^1991^1^Effects of temperature on CO2 dependence of gas exchanges in C3 and C4 crop plants^160^60^1^139-145^^^^^Mar^^^^^3027 Plants were grown in pots containing sandy loam soil (Typic Paleudult) at two concentrations of elevated CO2 and two water regimes in open-top field chambers. During the first 12 d of water stress, leaf xylem potentials were higher in plants grown in a CO2 concentration of 438 and 666-mu-mol mol-1 than in plants grown at 364-mu-mol mol-1. The 364-mu-mol mol-1 CO2 grown plants had to be rewatered 2d earlier than the high CO2-grown plants in response to water stress. For plants grown under water stress, the yield of storage roots and root:shoot ratio were greater at high CO2 than at 364-mu-mol mol-1; the increase, however, was not linear with increasing CO2 concentrations. In well-watered plants, biomass production and storage root yield increased at elevated CO2, and these were greater as coA^3026^The effects of elevated CO2 in the atmosphere and the accompanied temperature rise predicted for the future on gas exchanges of two summer C3 (rice, soybean) and two C4 (Japanese millet, finger millet) crop plants were examined. Plants were grown in artificially illuminated growth cabinets under 350 and 500-mu-mol mol-1 ambient CO2 (C(a)) and were measured for rates of CO2 exchange (CER) and transpiration (E) of leaves at 23, 28 and 33-degrees-C in terms of C(a) (0-500-mu-mol mol-1). The responses of CER to C(a) were slightly lower in plants grown in high C(a) than those in normal C(a) and were largely influenced by temperature. The promotive effect of elevating C(a) on CER was larger at higher temperatures, especially in C4 crop plants. With the rise of C(a), the E in C4 crop plants decreased more than in C3 crop plants and it was correlated with the decrease in stomatal conductance to CO2 transfer. The water use efficiency (WUE) of leaves increased with the rise in C(a) but the effect of temperature on WUE was unclear. It is concluded that, whthin limits, under high C(a), C4 crop plants expand their photosynthetic capacity in an environment of high temperature.85^3^Israel,DW^Rufty,TW^Cure,JD^1990^1^Nitrogen and phosphorus nutritional interactions in a CO2 enriched environment^166^13^11^1419-1433^^^^^^^^^^3029374^398^417^433^542^543^544^92^ were measured for rates of CO2 exchange (CER) and transpiration (E) of leaves at 23, 28 and 33-degrees-C in terms of C(a) (0-500-mu-mol mol-1). The responses of CER to C(a) were slightly lower in plants grown in high C(a) than those in normal C(a) and were largely influenced by temperature. The promotive effect of elevating C(a) on CER was larger at higher temperatures, especially in C4 crop plants. With the rise of C(a), the E in C4 crop plants decreased more than in C3 crop plants and it was correlated with the decrease in stomatal conductance to CO2 transfer. The water use efficiency (WUE) of leaves increased with the rise in C(a) but the effect of temperatureA^3028^Nonnodulated soybean plants (Glycine max. [L.] Merr. 'Lee') were supplied with nutrient solutions containing growth limiting concentrations of N or P to examine effects on N- and P-uptake efficiencies (mg nutrient accumulated/gdw root) and utilization efficiencies in dry matter production (gdw2/mg nutrient). Nutritional treatments were imposed in aerial environments containing either 350 or 700-mu-L/L atmospheric CO2 to determine whether the nutrient interactions were modified when growth rates were altered. Nutrient-stress treatments decreased growth and N- and P-uptake and utilization efficiencies at 27 days after transplanting (DAT) and seed yield at maturity (98 DAT). Atmospheric CO2 enrichment increased growth and N- and P-utilization efficiencies at 27 DAT and seed yield in all nutritional treatments and did not affect N- and P-uptake efficiencies at 27 DAT. Parameter responses to nutrient stress at 27 DAT were not altered by atmospheric CO2 enrichment and vice versa. Nutrient-stress treatments lowered the relative seed yield response to atmospheric CO2 enrichment. Decreased total-N uptake by P- stressed plants was associated with both decreased root growth and N-uptake efficiency of the roots. Nitrogen-utilization efficiency was also decreased by P-stress. This response was associated with decreased plant growth as total-N uptake and plant growth were decreased to the same extent by P stress resulting in unaltered tissue N concentrations. In contrast, decreased total P-uptake by N-stressed plants was associated with a restriction in root growth as P-uptake efficiency of the roots was unaltered. This response was coupled with an increased root-to-shoot dry weight ratio; thus shoot and wholeplant growth were decreased to a much greater extent than total-P uptake which resulted in elevated P concentrations in the tissue. Therefore, P-utilization efficiency was markedly reduced by N stress.ent stress at 27 DAT were not altered by atmospheric CO2 enrichment and vice versa. Nutrient-stress treatments 86^4^Maevskaya,SN^Andreeva,TF^Voevudskaya,SY^Cherkanova,NN^1990^1^Effect of elevated CO2 concentration on photosynthesis and nitrogen-metabolism of mustard plants^168^37^5^687-692^^^^^Sep-Oct^^^^^3031341^409^92^utilization efficiency was also decreased by P-stress. This response was associated with decreased plant growth as total-N uptake and plant growth were decreased to the same extent by P stress resulting in unaltered tissue N concentrations. In contrast, decreased total P-uptake by N-stressed plants was associated with a restriction in root growth as P-uptake efficiency of the roots was unaltered. This response was coupled with an increased root-to-shoot dry weight ratio; thus shoot and wholeplant growth were decreased to a much greater extent than total-P uptake which resulted in elevated P concentrations in the tissue. Therefore, P-utilization efficiency was markedly reduced by N stress.ent stress at 27 DAT were not altered by atmospheric CO2 enrichment and vice versa. Nutrient-stress treatments A^3030^We investigated the effect of prolonged (8- to 10-day) influence of elevated atmospheric CO2 content (0.14%) on the photosynthetic rate and nitrogen metabolism in mustard plants (Brassica juncea L.). The photosynthetic rate and intensity of nitrogen metabolism in leaves of mustard plants in the vegetative phase of growth are higher under conditions of elevated atmospheric CO2 concentration than in leaves of plants that developed under conditions of normal CO2 content in the atmosphere. Intensification of nitrogen metabolism occurred mainly due to increase of NR activity. Activity of GS and GO increased to a lesser extent. Significant changes were detected in the rates of synthesis of separate amino acids. Thus, formation of alanine and aspartic acid increased by 84 and 40%, respectively, but the rates of glycine and serine synthesis declined. The excess of amino acids (alanine and aspartic acid) is evacuated from the metabolic pool into vacuoles, with the result that a normal metabolic pool of amino acids is preserved. A state of homeostasis is preserved, protein and chlorophyll synthesis is not disturbed, and growth and biomass accumulation intensify in plants under conditions of elevated CO2 concentration.87^5^Mooney,HA^Drake,BG^Luxmoore,RJ^Oechel,WC^Pitelka,LF^1991^1^Predicting ecosystem responses to elevated CO2 concentrations^14^41^2^96-104^^^^^Feb137^343^377^378^426^511^512^513^545^546^88^2^Nobel,PS^Decortazar,VG^1991^1^Growth and predicted productivity of Opuntia ficus-indica for current and elevated carbon-dioxide^48^83^1^224-230^^^^^Jan-Feb^^^^^3034174^374^412^547^548^549^S and GO increased to a lesser extent. Significant changes were detected in the rates of synthesis of separate amino acids. Thus, formation of alanine and aspartic acid increased by 84 and 40%, respectively, but the rates of glycine and serine synthesis declined. The excess of amino acids (alanine and aspartic acid) is evacuated from the metabolic pool into vacuoles, with the result that a normal metabolic pool of amino aA^3033^Opuntia ficus-indica (L.) Mill., a prickly pear cactus cultivated worldwide for its fruits and stem segments, can have an annual dry weight productivity exceeding that of many crops. Using a recently introduced environmental productivity index (EPI), the influences of water status, temperature, and photosynthetically active radiation (PAR) on its productivity can be predicted. This investigation calculated the water index the temperature index, and the PAR index, whose product equals EPI, for 169 sites distributed approximately uniformly across the contiguous USA for present climatic conditions as well as for those associated with an elevated CO2 concentration of 650-mu-L L-1. The effect of elevated CO2 on growth of O. ficus-indica was directly measured, and low temperature limitations on productivity were considered. The dry weight gain of O. ficus-indica during 6 mo in an environmental growth chamber was 23% greater at 650 compared with 350-mu-L L-1 CO2 and increased as the duration of the wet period increased, in agreement with predictions of the water index (the fraction of maximal net CO2 uptake during a 24-h period for the prevailing plant water status). For closely spaced plants that lead to a high productivity per unit ground area, EPI averaged about 0.10, except in desert regions where the water index lowered EPI, in the far North or South and at high elevations where the temperature index lowered EPI, and in the Northeast and Northwest where the PAR index lowered EPI. The predicted annual dry weight productivity for O. ficus-indica was 12.8 Mg ha-1 yr-1 under current conditions, and 16.3 Mg ha-1 yr-1 under those associated with 650-mu-L L-1 CO2. Both productivities are relatively high compared with other agronomic plants. The percentage of sites where temperatures fall below - 15-degrees- C at least once during the 10 years simulated, which would be lethal to most prickly pear cacti, was reduced from 49 to 18% by the general warming expected to accompany an approximate doubling of the atmospheric CO2 concentration.89^4^Prior,SA^Rogers,HH^Sionit,N^Patterson,RP^1991^1^Effects of elevated atmospheric CO2 on water relations of soya bean^169^35^1^13-25^^^^^Mar^^^^^3036243^264^312^374^386^409^434^530^92^ductivity per unit ground area, EPI averaged about 0.10, except in desert regions where the water index lowered EPI, in the far North or South and at high elevations where the temperature index lowered EPI, and in the Northeast and Northwest where the PAR index lowered EPI. The predicted annual dry weight productivity for O. ficus-indica was 12.8 Mg ha-1 yr-1 under current conditions, and 16.3 Mg ha-1 yr-1 under those associated with 650-mu-L L-1 CO2. Both productivities are relatively high compared with other agronomic plants. The percentage of sites where temperatures fall below - 15-degrees- C at least once during the 10 years simulated, which would be lethal to most prickly pear cacti, was reduced from 49 to 18% by the general warming expected to accompany an approximate doubling of the atmospherA^3035^Soya bean (Glycine max (L.) Merr. 'Bragg') plants were grown in large containers in open-top field chambers under five atmospheric CO2 concentrations (349-946-mu-l-l-1) and two water regimes. Rate of soil water depletion for the high CO2 treatments started to decrease under well-watered conditions during anthesis and by early pod formation under water-stressed conditions. During reproductive growth, normal and stressed plants at 349-mu-l-l-1 (ambient level) received irrigation water 29 and 12 times, respectively, compared with 21 and 9 times, respectively, at 946-mu-l-l-1 CO2. At both anthesis and pod fill, plants grown under CO2 enrichment exhibited greater leaf area. Nevertheless, water use per plant either remained constant (stressed plants at anthesis) or else declined (well- watered plants at pod fill; both moisture levels during pod fill) in response to CO2 enrichment. At pod fill, leaves of CO2-enriched plants generally displayed a higher stomatal resistance, except near the end of the sampling period when a sudden increase in resistance was observed under low CO2 owing to low soil water availability. Midday xylem potential for well-watered plants was greater than values for stressed plants and was unaffected by CO2 treatment. Under low moisture conditions, elevated CO2 had no effect on xylem potential at anthesis; however, during pod fill potential increased significantly with increasing CO2 concentration, as elevated CO2 decreased water use rates, lowering soil water stress. Alleviation of water stress during critical reproductive phases was strongly suggested.90^7^Rozema,J^Dorel,F^Janissen,R^Lenssen,G^Broekman,R^Arp,W^Drake,BG^1991^1^Effect of elevated atmospheric CO2 on growth, photosynthesis and water relations of salt-marsh grass species^159^39^1-2^45-55^^^^^Feb^^^^^3038130^230^312^376^378^494^57^h moisture levels during pod fill) in response to CO2 enrichment. At pod fill, leaves of CO2-enriched plants generally displayed a higher stomatal resistance, except near the end of the samplingA^3037^The C3 grass species Scirpus maritimus L. and Puccinellia maritima (Huds.) Parl., and the C4 grass species Spartina anglica C.E. Hubbard and Spartina patens (Ait.) Muhl. were grown at ambient (340 p.p.m. CO2) and elevated (580 p.p.m. CO2) atmospheric CO2 concentration, at low (10 mM NaCl) and high salinity (250 mM NaCl) under aerated and anaerobic conditions in the culture solution. The relative growth rate of both the C3 grass species was enhanced with atmospheric CO2 enrichment, no such increase was found in the C4 grass species. High salinity reduced growth of the C3 species tested, but this relative growth reduction was not prevented by elevated CO2 concentration. The growth increase at elevated CO2 of Scirpus maritimus and Puccinellia maritima is greater under aerated than under anaerobic solution conditions. Water-use efficiency of all species was increased by elevated CO2. In the case of Scirpus (C3), this increase was caused by increased net photosynthesis, for Spartina patens (C4) photosynthesis was not increased, but transpiration was reduced. The water potential of the shoot was less negative under conditions of CO2 enrichment, in particular at increased salinity (250 mM NaCl).91^1^Sage,RF^1990^1^A model describing the regulation of ribulose-1,5-bisphosphate carboxylase, electron-transport, and triose phosphate use in response to light-intensity and CO2 in C3 plants^8^94^4^1728-1734^^^^^Dec^^^^^3040130^243^355^372^384^550^551^552^553^554^ith atmospheric CO2 enrichment, no such increase was found in the C4 grass species. High salinity reduced growth of the C3 species tested, but this relative growth reduction was not prevented by elevated CO2 concentration. The growth increase at elevated CO2 of Scirpus maritimus and Puccinellia maritima is greater under aerated than under anaerobic solution conditions. Water-use efficiency of all species was increased by elevated CO2. In the case of Scirpus (C3), this increase was caused by increased net photosynthesis, for Spartina patens (C4) photosyntheA^3039^A model of the regulation of the activity of ribulose-1,5-bis- phosphate carboxylase, electron transport, and the rate of orthophosphate regeneration by starch and sucrose synthesis in response to changes in light intensity and partial pressures of CO2 and O2 is presented. The key assumption behind the model is that nonlimiting processes of photosynthesis are regulated to balance the capacity of limiting processes. Thus, at CO2 partial pressures below ambient, when a limitation on photosynthesis by the capacity of rubisco is postulated, the activities of electron transport and phosphate regeneration are down-regulated in order that the rate of RuBP regeneration matches the rate of RuBP consumption by rubisco. Similarly, at subsaturating light intensity or elevated CO2, when electron transport or Pi regeneration may limit photosynthesis, the activity of rubisco is downregulated to balance the limitation in the rate of RuBP regeneration. Comparisons with published data demonstrate a general consistency between modelled predictions and measured results.92^3^Sage,RF^Sharkey,TD^Seemann,JR^1990^1^Regulation of ribulose-1,5-bisphosphate carboxylase activity in response to light-intensity and CO2 in the C3 annuals Chenopodium album L and Phaseolus vulgaris L^8^94^4^1735-1742^^^^^Dec^^^^^3042243^355^383^384^551^552^553^555^556^557^ting processes of photosynthesis are regulated to balance the capacity of limiting processes. Thus, at CO2 partial pressures below ambient, when a limitation on photosynthesis by the capacity of rubisco is postulated, the activities of electron transport and phosphate regeneration are down-regulated in order that the rate of RuBP regeneration matches the rate of RuBP consumption by rubisco. Similarly, at subsaturating light intensity or elevated CO2, when electron transport or Pi regeneration may limit photosynthesis, the activity of rubisco is downregulated to balance the limitation in the rate of RuBP regeneration. Comparisons with published data demonstrate a general consistency A^3041^The light and CO2 response of (a) photosynthesis, (b) the activation state and total catalytic efficiency (K(cata)) of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) the pool sizes of ribulose 1,5-bisphosphate, (RuBP), ATP, and ADP were studied in the C3 annuals Chenopodium album and Phaseolus vulgaris at 25-degrees-C. The initial slope of the photosynthetic CO2 response curve was dependent on light intensity at reduced light levels only (less than 450 micromoles per square meter per second in C. album and below 200 micromoles per square meter per second in P. vulgaris). Modeled simulations indicated that the initial slope of the CO2 response of photosynthesis exhibited light dependency when the rate of RuBP regeneration limited photosynthesis, but not when rubisco capacity limited photosynthesis. Measured observations closely matched modeled simulations. The activation state of rubisco was measured at three light intensities in C. album (1750, 550, and 150 micromoles per square meter per second) and at intercellular CO2 partial pressures (C(i)) between the CO2 compensation point and 500 microbars. Above a C(i) of 120 microbars, the activation state of rubisco was light dependent. At light intensities of 550 and 1750 micromoles per square meter per second, it was also dependent on C(i), decreasing as the C(i) was elevated above 120 microbars at 550 micromoles per square meter per second and above 300 microbars at 1750 micromoles per square meter per second. The pool size of RuBP was independent of C(i) only under conditions when the activation state of rubisco was dependent on C(i). Otherwise, RuBP pool sizes increases as C(i) was reduced. ATP pools in C. album tended to increase as C(i) was reduced. In P. vulgaris, decreasing C(i) at a subsaturating light intensity of 190 micromoles per square meter per second increased the activation state of rubisco but had little effect on the K(cat). These results support modelled simulations of the rubisco response to light and CO2, where rubisco is assumed to be down-regulated when photosynthesis is limited by the rate of RuBP regeneration.93^2^Sasek,TW^Strain,BR^1991^1^Effects of CO2 enrichment on the growth and morphology of a native and an introduced honeysuckle vine^5^78^1^69-75^^^^^Jan^^^^^3044227^341^344^345^558^was also dependent on C(i), decreasing as the C(i) was elevated above 120 microbars at 550 micromoles per square meter per second and above 300 microbars at 1750 micromoles per square meter per second. The pool size of RuBP was independent of C(i) only under conditions when the activation state of rubisco was dependent on C(i). Otherwise, RuBP pool sizes increases as C(i) was reduced. ATP pools in C. album tended to increase as C(i) was reduced. In P. vulgaris, decreasing C(i) at a subsaturating light intensity of 190 micromoles per square meter per second increased the activation state of rubisco but had little effect on the K(cat). These results support modelled simulations of the rubisco response to light and CO2, where rubisco is assumA^3043^Japanese honeysuckle (Lonicera japonica Thunb.), introduced to the United States, and the native coral honeysuckle (Lonicera sempervirens L.) were compared to determine how intrinsic differences in their growth characteristics would affect their response to atmospheric carbon dioxide enrichment. Plants of both species grown from cuttings were harvested after 54 days of growth in controlled environment growth chambers at 350, 675, or 1,000-mu-l/liter CO2. The biomass of Japanese honeysuckle was increased 135% at 675-mu-l/liter CO2 and 76% at 1,000-mu-l/liter CO2 after 54 days. Morphologically, the main effect of CO2 enrichment was to triple the number of branches and to increase total branch length six times. Enhanced and accelerated branching also increased total leaf area 50% at elevated CO2 concentrations. In coral honeysuckle, total biomass was only 40% greater in the elevated CO2 treatments. Branching was quadrupled but had not proceeded long enough to affect total leaf area. Main stem height was increased 36% at 1,000-mu-l/liter CO2. The much less significant height response of other woody erect growth forms suggests that vines may increase in importance during competition if atmospheric CO2 concentrations increase as predicted. The impact of Japanese honeysuckle in the United States may become more serious.94^2^Prince,TA^Cunningham,MS^1991^1^Forcing characteristics of easter lily bulbs exposed to elevated-ethylene and elevated-carbon dioxide and low-oxygen atmospheres^154^116^1^63-67^^^^^Jan^^^^^3046% at 675-mu-l/liter CO2 and 76% at 1,000-mu-l/liter CO2 after 54 days. Morphologically, the main effect of CO2 enrichment was to triple the number of branches and to increase total branch length six times. Enhanced and accelerated branching also increased total leaf area 50% at elevated CO2 concentrations. In coral honeysuckle, total biomass was only 40% greater in the elevated CO2 treatments. Branching was quadrupled but had not proceeded long enough to affect total leaf area. Main stem height was A^3045^Exposure of bulbs of Easter Lily (Lilium longiflorum Thunb.) to a maximum of 2-mu-l ethylene/liter during vernalization delayed flowering by 5 to 7 days and decreased the number of flower buds. Ethylene exposure for 5 days at 21C after vernalization accelerated shoot emergence and flowering by up to 3 days. No floral or plant abnormalities were observed after bulb exposure to ethylene. Exposure to atmospheres with 0%, 0.5%, or 1% O2 at 21C for up to 2 weeks before or 10 days after vernalization did not significantly impair subsequent bulb forcing. Storage in 1% O2 at 21C for 1 week before vernalization resulted in nearly one additional secondary bud initiated per plant. Exposure to up to 15% CO2 at 21C for up to 2 weeks before or 10 days after vernalization did not significantly impair subsequent forcing.95^3^Colelli,G^Mitchell,FG^Kader,AA^1991^1^Extension of postharvest life of mission figs by CO2-enriched atmospheres^170^26^9^1193-1195^^^^^Sep^^^^^3048ffect total leaf area. Main stem height was A^3047^Good quality of fresh 'Mission' figs (Ficus carica L.) was maintained for up to 4 weeks when kept at 0, 2.2, or 5C in atmospheres enriched with 15% or 20% CO2. The visible benefits of exposure to high CO2 levels were reduction of decay incidence and maintenance of bright external appearance. Ethylene production was lower, and fruit softening (as measured with a deformation tester) was slower in the high-CO2-stored figs than in those kept in air. Ethanol content of the CO2-treated fruit increased slightly during the first 3 weeks and moderately during the 4th week, while acetaldehyde concentration increased during the first week, then decreased. The results may be applicable to the transport and storage of fresh 'Mission' figs, as high CO2 extended their postharvest life, especially near 0C.uent forcing.95^3^Colelli,G^Mitchell,FG^Kader,AA^1991^1^Extension of postharvest life of mission figs by CO2-enriched atmospheres^170^26^9^1193-1195^^^^^Sep^^^^^3048ffect total leaf area. Main stem height was 96^5^Cournac,L^Dimon,B^Carrier,P^Lohou,A^Chagvardieff,P^1991^1^Growth and photosynthetic characteristics of Solanum tuberosum plantlets cultivated invitro in different conditions of aeration, sucrose supply, and CO2 enrichment^8^97^1^112-117^^^^^Sep^^^^^3050188^310^312^348^529^559^560^561^562^563^Ethylene production was lower, and fruit softening (as measured with a deformation tester) was slower in the high-CO2-stored figs than in those kept in air. Ethanol content of the CO2-treated fruit increased slightly during the first 3 weeks and moderately during the 4th week, while acetaldehyde concentration increased during the first week, then decreased. The results may be applicable to the transport and storage of fresh 'Mission' figs, as high CO2 extended thei