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 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 A^3049^Growth characteristics, oxygen exchange, and carbohydrate and chlorophyll contents were determined 30 days after subculturing of single node-derived plantlets of Solanum tuberosum cv Haig cultivated in vitro. Cultivation conditions were: (a) photomixotrophy in closed vessel, (b) photomixotrophy in closed vessel on medium supplemented with silver thiosulfate, (c) photomixotrophy in aerated vessel, (d) photoautotrophy in air, (e) photoautotrophy in CO2-enriched air. In photomixotrophic conditions, aeration of the vessel enhanced sucrose utilization and had a positive effect on plantlet growth. In photoautotrophic conditions, growth of the plantlets was slow in air and was strongly enhanced by CO2 enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouse plant leaves. In high light, however, plantlets grown photoautotrophically in a CO2-enriched atmosphere had higher oxygen exchange rates. We concluded from these results that potato plantlets in vitro in conditions (c), (d), and (e) developed C3-plant photosynthetic characteristics, which were in photoautotrophically grown plantlets comparable to those of field-grown plants.97^2^Geethakumari,VL^Shivashankar,K^1991^1^Studies on organic amendment and CO2 enrichment in ragi soybean intercropping systems^171^36^2^202-206^^^^^Jun^^^^^3052ose utilization and had a positive effect on plantlet growth. In photoautotrophic conditions, growth of the plantlets was slow in air and was strongly enhanced by CO2 enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouseA^3051^Organic amendment comprising of ragi husk and FYM mixed in 1:1 ratio by weight promoted organic carbon content and available P status of the soil. A level of 4 t/ha of organic amendment promoted the uptake of N significantly by both ragi and soybean. Availability of P and K were also favourably influenced. Uptake of nutrients by soybean was promoted by CO2 enrichment. Available P status was higher in intercropped ragi and soybean as compared to pure crops but nutrient uptake was higher by pure crops.98^3^Hartz,TK^Baameur,A^Holt,DB^1991^1^Carbon-dioxide enrichment of high-value crops under tunnel culture^154^116^6^970-973^^^^^Nov^^^^^3054174^374^564^565^92^ir and was strongly enhanced by CO2 enrichment of the atmosphere. Starch to sucrose ratios were higher in plants grown photoautotrophically than in plants grown with sucrose in the medium. Oxygen exchange characteristics on a chlorophyll basis were similar between the plantlets when measured under moderate light, and resembled those of greenhouseA^3053^The feasibility of field-scale CO2 enrichment of vegetable crops grown under tunnel culture was studied with cucumber (Cucumis sativus L. cv. Dasher II, summer squash (Cucurbita pepo L. cv. Gold Bar), and tomato (Lycopersicon esculentum Mill. cv. Bingo) grown under polyethylene tunnels. The drip irrigation system was used to uniformly deliver a CO2-enriched air stream independent of irrigation. Carbon dioxide was maintained between 700 and 1000-mu-l.liter-1 during daylight hours. Enrichment began immediately after crop establishment and continued for almost-equal-to 4 weeks. At the end of the treatment phase, enrichment had significantly increased plant dry weight in the 2 years of tests. This growth advantage continued through harvest, with enriched cucumber, squash, and tomato plots yielding 30%, 20%, and 32% more fruit, respectively, in 1989. In 1990, cucumber and squash yields were increased 20%, and 16%, respectively. As performed, the expense of CO2 enrichment represented less than a 10% increase in total preharvest costs. A similar test was conducted on fall-planted strawberries (Fragaria X ananassa Duch. cvs. Irvine and Chandler). Carbon dioxide enrichment under tunnel culture modestly increased 'Irvine' yields but did not affect 'Chandler'.99^3^Hilbert,DW^Larigauderie,A^Reynolds,JF^1991^1^The influence of carbon-dioxide and daily photon-flux density on optimal leaf nitrogen concentration and root - shoot ratio^52^68^4^365-376^^^^^Oct188^256^348^349^361^423^431^566^567^92^100^2^Hollander,B^Krug,H^1991^1^Effects of high CO2 concentrations on vegetable species .1. Symptoms, ranges of injuries, and reactions of species^172^56^5^193-205^^^^^Sep-Oct^^^^^3057230^312^360^370^376^568^. This growth advantage continued through harvest, with enriched cucumber, squash, and tomato plots yielding 30%, 20%, and 32% more fruit, respectively, in 1989. In 1990, cucumber and squash yields were increased 20%, and 16%, respectively. As performed, the expense of CO2 enrichment represented less than a 10% increasA^3056^To test the reactions of various vegetable species to high CO2-concentrations, the plants were treated with 1-3% technical CO2 day and night for 10-42 days in growth chambers (table 1). The development of CO2 injury symptoms as well as growth rates were noted and measured. With exception of spinach and sweet pepper, which showed no symptoms in the range tested, CO2 injuries occurred in the form of morphological alterations (epinastic and hyponastic rolling of the leaves, crisping, reduction and thickening of the leaf lamina), chlorosis (marginal or in areas between the veins), necrosis, wilting, drying up and browning ot the veins (kohlrabi). The symptoms mentioned varied between the species and between the cultivars. The injuries occurred at young leaves only (beans), at older leaves (kohlrabi) or at all leaves (fig. 1-5, table 6). Moreover, high CO2-concentrations caused a remarkable reduction of growth (fig. 6). Ensuring favourable growth conditions the cold-season species tolerated concentrations of 1% CO2 for 4-6 weeks showing only week (radish var. niger, kohlrabi, corn salad) or no significant growth reductions (radish, var. sativus, lettuce). Light injuries and morphological alterations were identifiable after 2-3 weeks. Higher concentrations caused stronger growth reductions, injuries appeared after 1 week using 2% CO2 and after 2-3 days using 3% CO2. The warm-season species tested reacted more sensitive. Cucumbers tolerated 1% CO2 for 2-3 weeks, using 2% CO2 wilting and driving injuries occurred already after 1 day table 2). In case of disturbances of the water status of the plants by transplanting, top dressing or sharp decrease of air humidity cucumber wilted with 1% CO2 already after a few days. Equal reactions were observed with radish, var. sativus. With tomatoes strong injuries of the leaves causing leaf death were observed after 7 days with 1% CO2 and after 5 days with 2% CO2. Bush beans reacted by a distinct reduction of leaf area growth and by chlorotic discolorations.concentrations 101^1^Idso,SB^1991^1^A general relationship between CO2-induced increases in net photosynthesis and concomitant reductions in stomatal conductance^173^31^4^381-383^^^^^Oct^^^^^3059456^A^3058^Simultaneous measurements of net photosynthesis and stomatal conductance of leaves of sour orange trees growing in normal and CO2-enriched air, together with similar data for cotton, cotton, soybeans and water hyacinth, suggest that a plant's photosynthetic response to atmospheric CO2 enrichment is inversely proportional to its degree of CO2-induced stomatal closure.102^2^Marek,LF^Spalding,MH^1991^1^Changes in photorespiratory enzyme-activity in response to limiting CO2 in Chlamydomonas reinhardtii^8^97^1^420-425^^^^^Sep^^^^^3061243^529^569^570^571^572^573^574^ var. sativus. With tomatoes strong injuries of the leaves causing leaf death were observed after 7 days with 1% CO2 and after 5 days with 2% CO2. Bush beans reacted by a distinct reduction of leaf area growth and by chlorotic discolorations.concentrations A^3060^The activity of two photorespiratory enzymes, phosphoglycolate phosphatase (PGPase) and glycolate dehydrogenase (glycolate DH), changes when CO2-enriched wild-type (WT) Chlamydomonas reinhardtii cells are transferred to air levels of CO2. Adaptation to air levels of CO2 by Chlamydomonas involves induction of a CO2-concentrating mechanism (CCM) which increases the internal inorganic carbon concentration and suppresses oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase. PGPase in cell extracts shows a transient increase in activity that reaches a maximum 3 to 5 hours after transfer and then declines to the original level within 48 hours. The decline in PGPase activity begins at about the time that physiological evidence indicates the CCM is approaching maximal activity. Glycolate DH activity in 24 hour air-adapted WT cells is double that seen in CO2-enriched cells. Unlike WT, the high-CO2-requiring mutant, cia-5, does not respond to limiting CO2 conditions: it does not induce any known aspects of the CCM and it does not show changes in PGPase or glycolate DH activities. Other known mutants of the CCM show patterns of PGPase and glycolate DH activity after transfer to limiting CO2 which are different from WT and cia-5 but which are consistent with changes in activity being initiated by the same factor that induces the CCM, although secondary regulation must also be involved.103^3^Wheeler,RM^Tibbitts,TW^Fitzpatrick,AH^1991^1^Carbon-dioxide effects on potato growth under different photoperiods and irradiance^164^31^5^1209-1213^^^^^Sep-Oct^^^^^3063130^188^230^243^344^349^575^576^577^578^d then declines to the original level within 48 hours. The decline in PGPase activity begins at about the time that physiological evidence indicates the CCM is approaching maximal activity. Glycolate DH activity in 24 hour air-adapted WT cells is double that seen in CO2-enriched cells. Unlike WT, the high-CO2-requiring mutant, cia-5, does not respond to limiting CO2 conditions: it does not induce any knowA^3062^Carbon dioxide concentration can exert a strong influence on plant growth, but this influence can vary depending on irradiance. To study this, potato plants (Solanum tuberosum L.) cultivars 'Norland'. 'Russet Burbank', and 'Denali' were grown in controlled-environment rooms at different levels of CO2 and irradiance. Carbon dioxide levels were maintained either at 350 or 100-mu-mol mol-1 and applied in combination with 12- or 24-h photoperiods at 400 or 800-mu-mol m-2 s-1 photosynthetic photon flux. Air temperatures and relative humidity were held constant at 16-degrees-C and 70%, respectively, and plants were harvested 90 d after planting. When averaged across all cultivars, CO2 enrichment increased tuber yield and total plant dry weight by 39 and 34%, respectively, under a 12-h photoperiod at 400-mu-mol m-2 s-1; 27 and 19% under 12 h at 800-mu-mol m-2 s-1; 9 and 9% under 24 h at 400-mu-mol m-2 s-1. It decreased dry weights by 9 and 9% under 24 h at 800-mu-mol m-2 s-1. Tuber yield of Denali showed the greatest increase (21%) in response to increased CO2 across all irradiance treatments, while tuber yields of Russet Burbank and Norland were increased 18 and 9%, respectively. The results show a pattern of greater plant growth from CO2 enrichment under lower PPF and a short photoperiod.104^4^Allen,LH^Bisbal,EC^Boote,KJ^Jones,PH^1991^1^Soybean dry-matter allocation under subambient and superambient levels of carbon-dioxide^48^83^5^875-883^^^^^Sep-Oct^^^^^3065230^243^379^434^456^508^579^580^581^n flux. Air temperatures and relative humidity were held constant at 16-degrees-C and 70%, respectively, and plants were harvested 90 d after planting. When averaged across all cultivars, CO2 enrichment increased tuber yield and total plant dry weight by 39 and 34%, respectively, under a 12-h photoperiod at 400-mu-mol m-2 s-1; 27 and 19% under 12 h at 800-mu-mol m-2 s-1; 9 and 9% under 24 h at 400-mu-mol m-2 s-1. It decreased dry weights by 9 and 9% under 24 h at 800-mu-mol m-2 s-1. Tuber yield of Denali showed theA^3064^Rising atmospheric carbon dioxide concentration [CO2] is expected to cause increases in crop growth and yield. The objective of this study was to investigate effects of subambient, as well as superambient, [CO2] on soybean [Glycine max (L.) Merr.] dry matter production and allocation for two reasons: to assess response of plants to prehistoric as well as future expected CO2 levels and to increase confidence in [CO2] response curves by imposing a wide range of [CO2] treatments. Soybean was grown in outdoor, sunlit, controlled- environment chambers at CO2 levels of 160, 220, 280, 330, 660, and 990-mu-mol (CO2) mol-1 (air). Total dry matter growth rates during the linear phase of vegetative growth were 5.0, 8.4, 10.9, 12.5, 18.2, and 20.7 g m-2 d-1 for the above respective [CO2]. Samples taken from 24 to 94 d after planting showed that the percentage of total plant mass in leaf trifoliolates decreased with increasing [CO2] whereas the percentage in structural components (petioles and stems) increased. At final harvest the respective [CO2] treatments resulted in 38, 53, 62, 100, 120, and 92% seed yield with respect to the 330-mu-mol mol-1 treatment. Total dry weight responses were similar. Late season spider mite damage of the 990 and 280-mu-mol mol-1 treatments reduced yields. These data confirm not only that rising CO2 should increase plant growth, but also that plant growth was probably seriously limited by atmospheric [CO2] in preindustrial revolution times back to the previous global glaciation.105^1^Anderson,JM^1991^1^The effects of climate change on decomposition processes in grassland and coniferous forests^56^1^3^326-347^^^^^Aug^^^^^3067178^377^582^583^584^585^586^587^588^589^ative growth were 5.0, 8.4, 10.9, 12.5, 18.2, and 20.7 g m-2 d-1 for the above respective [CO2]. Samples taken from 24 to 94 d after planting showed that the percentage of total plant mass in leaf trifoliolates decreased with increasing [CO2] whereas the percentage in structural components (petioles and stems) increased. AtA^3066^Current models of climate change predict a reduction of area covered by northern coniferous forests and tundra, and an increase in grasslands. These scenarios also indicate a northerly shift in agricultural regions, bringing virgin soils under cultivation. The direct effects of man on tundra,boreal forest, and temperate grassland ecosystems are likely to result in less carbon mobilization from soils and vegetation than from tropical forests. However, as a consequence of climate change, carbon mineralization rates from arctic and sub-arctic soils could be very rapid under warmer and drier conditions because of low stabilization of soil organic matter (SOM) and enhanced microbial responses to small changes in soil moisture and temperature. Predicting the response of these systems to climate change is complicated where the edaphic environment regulating SOM dynamics is not a direct function of macroclimatic conditions. Grasslands contain a greater proportion of highly stabilized SOM than coniferous forests, distributed over greater depth in the soil profile, which is less susceptible to changes in mineralization rates. It is concluded that short-term responses of soil processes to climate change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2. The primary recommendation for future research is for integrated studies on plant and soil processes.ilized SOM than coniferous fores106^1^Andersson,NE^1991^1^The influence of constant and diurnally changing CO2 concentrations on plant-growth and development^174^66^5^569-574^^^^^Sep^^^^^3069341^418^434^492^529^590^591^change are more predictable in well-drained grassland and forest soils than in waterlogged soils of the tundra and boreal region. Over longer periods of time, however, plant species and soil types will alter in response to new temperature and moisture regimes above- and belowground interacting with the effects of carbon enrichment and changes in nutrient availability. The dynamics of these plant-soil interactions and the future status of soils in different life zones as sources or sinks of carbon is poorly understood. More data are also needed on the distribution of waterlogged forest soils in the boreal zone and responses to warming, which include the production of methane as well as CO2. The primary recommendation for future research is for integrated studies on plant and soil processes.ilized SOM than coniferous foresA^3068^Plants of Ficus benjamina and miniature rose (Rosa hybrida cv. Red Minimo) were grown under four CO2 treatments. Two had constant CO2 levels (600 and 900 ppm) and the other two had diurnal changes in CO2 levels, one increasing from 600 to 1500 ppm and one decreasing from 1500 to 600 ppm, each in four steps of 300 ppm during the day-time. In all treatments 900 ppm CO2 was maintained during the night when supplementary light was used, except in the treatment with constant 600 ppm where 600 ppm was also continued throughout the night. Plant growth was monitored under both decreasing and increasing natural daylength and irradiance. The tallest plants and greatest increment in height for Ficus occurred with plants grown under constant CO2 concentration at 600 ppm and also with increasing CO2 concentration. In both experiments the dry weight per pot was lowest when plants were grown under a constant CO2 concentration at 900 ppm. In both experiments with miniature roses the number of flower buds was significantly increased under diurnally changing CO2 concentration or when the CO2 level was constant at 600 ppm compared with a constant 900 ppm. Time to flowering was decreased by constant CO2 at 900 ppm as compared with the other treatments.107^5^Beerling,DJ^Chaloner,WG^Huntley,B^Pearson,A^Tooley,MJ^1991^1^Tracking stomatal densities through a glacial cycle - their significance for predicting the response of plants to changing atmospheric CO2 concentrations^175^1^5^136-142^^^^^Sep^^^^^3071376^592^593^as also continued throughout the night. Plant growth was monitored under both decreasing and increasing natural daylength and irradiance. The tallest plants and greatest increment in height for Ficus occurred with plants grown under constant CO2 concentration at 600 ppm and also with increasing CO2 concentration. In both experiments the dry weight per pot was lowest when plants were grown under a constant CO2 concentration at 900 ppm. In both experiments with miniature roses the number of flower buds was significA^3070^Continued increases in the global atmospheric CO2 concentration have been predicted from current and projected rates of fossil fuel burning. Understanding the response of stomatal density as an important ecophysiological parameter controlling the productivity of vegetation is essential if the role of plants in the global carbon budget are to be predicted. Experimental exposure of plants to elevated CO2 regimes in controlled environment chambers can only indicate immediate, phenotypic, short-term responses. The investigation of fossil leaves of extant species growing under the different atmospheric conditions of the last glacial and deglacial transition, when evidence from an Antarctic ice core (Barnola et al., 1987) indicates CO2 levels markedly different from pre-industrial levels, provides one means for eliciting long-term plant responses to changing CO2 regimes. We have prepared cuticles from Quaternary leaf fossils, from which stomatal density and index can be calculated. Our preliminary results give promise of extending the record of stomatal density response back at least 10,000 years.108^4^Couteaux,MM^Mousseau,M^Celerier,ML^Bottner,P^1991^1^Increased atmospheric CO2 and litter quality - decomposition of sweet chestnut leaf litter with animal food webs of different complexities^15^61^1^54-64^^^^^May^^^^^3073427^57^594^595^596^597^598^599^600^601^d. Experimental exposure of plants to elevated CO2 regimes in controlled environment chambers can only indicate immediate, phenotypic, short-term responses. The investigation of fossil leaves of extant species growing under the different atmospheric conditions of the last glacial and deglacial transition, when evidence from an Antarctic ice core (Barnola et al., 1987) indicates CO2 levels markedly different from pre-industrial levels, provides one means for eliciting long-term plant responses to changing CO2 regimes. We have prepared cuticles from Quaternary leaf fossils, from which stomatal density and index can be calculated. Our preliminary results gA^3072^Two-year-old chestnut trees were grown for two yr under ambient (350 ppm) and enriched (700 ppm) CO2 concentrations, in two naturally lit growth chambers. The doubling of CO2 resulted in a dilution of the nitrogen concentration in the leaf litter, with C:N ratios of 40 and 75 for the ambient and enriched CO2 concentrations, respectively. The litter was sterilized and inoculated with microflora and animal groups of increasing complexity (microflora + Protozoa; + nematodes; + Collembola; + Isopoda) and incubated over 24 wk. Every two wk, the CO2 release was measured and the litter was leached with demineralized H2O. The following analyses were performed on the leachates: pH, total nitrogen, dissolved and particulate carbon, inorganic nitrogen (NH4+ and NO3-), phosphate, and biological counts (Protozoa, nematodes and Rotifera). The initial decomposition stages (the first 12 wk) were dominated by the litter quality factor: CO2 release and nitrogen losses in leachates were higher and carbon losses lower in water leaching from the litter with low C:N ratio. Towards the late stages, when carbon mineralization decreased in the control litter, the animal effect emerged in litter with a high C:N ratio. Two groups appeared: (1) In the microflora + Protozoa units, carbon mineralization was reduced by 60% compared with the control litter. (2) In the diversified food web combinations, it became progressively higher with increasing complexity of the animal community and was enhanced by 30% compared with the control litter. This unexpected fundamental difference was explained by a change in the composition and activity of the microflora. Litter bleaching, respiration, C and N leaching and acidification rose with increasing animal complexity of the systems. Biological and chemical reasons explaining the invasion by white-rot fungi and its activity only in the material with a high C:N ratio are discussed. During the 24 wk. nitrogen and phosphorus mineralization was very low, indicating a high incorporation of the nutrient in the soil biomass.109^2^Eamus,D^Murray,M^1991^1^Photosynthetic and stomatal conductance responses of norway spruce and beech to ozone, acid mist and frost - a conceptual-model^35^72^1^23-44^^^^^^^^^^3075299^361^602^603^604^605^606^607^608^92^ units, carbon mineralization was reduced by 60% compared with the control litter. (2) In the diversified food web combinations, it became progressively higher with increasing complexity of the animal community and was enhanced by 30% compared with the control litter. This unexpected fundamental difference was explained by a change in the composition and activity of the microflora. Litter bleaching, respiration, C and N leaching and acidification rose with increasing animal complexity of the systems. Biological and chemical reasons explaining the invasion by white-rot fungi and its activity only in the material with a high C:N ratio are discussed. During the 24 wk. nitrogen and phosphorus mineralization was very low, indicating a high incorporation of the nutrientA^3074^Two-year-old beech and Norway spruce seedlings were exposed to a combination of ozone and acid mist treatments in open-top chambers in Scotland during the months of July through to September 1988. Replicate pairs of chambers received charcoal- filtered air (control), ozone-enriched air (140 nl ozone litre- 1) or 140 nl ozone litre-1 plus a synthetic acid mist (pH 2.5) composed of ammonium nitrate and sulphuric acid. Field measurements of assimilation and stomatal conductance were made during August. In addition, measurements of assimilation and conductance were made during September in the laboratory. Light response curves of assimilation and conductance were determined using a GENSTAT non-rectangular hyperbolic model. During February 1988/9 the Norway spruce were subject to a four day warming period at 12-degrees-C and the light response of assimilation determined. The same plants were then subject to a 3-h night-time frost of -10-degrees-C. The following day the time-course of the recovery of assimilation was determined. It was found that ozone fumigation did not influence the light response of assimilation of beech trees in the field, although stomatal conductance was reduced in the ozone-fumigated trees. The rate of light-saturated assimilation of Norway spruce was increased by ozone fumigation when measured in the field. Measurements of assimilation of Norway spruce made during the winter showed that prior to rewarming there was no difference in the rate of light-saturated assimilation for control and ozone-fumigated trees. However, the ozone plus acid mist- treated trees exhibited a significantly higher rate. The 4-day period of warming to 12-degrees-C increased the rate of light-saturated assimilation in all treatments but only the ozone plus acid mist-treated trees showed a significant increase. Following a 3-h frost to -10-degrees-C the control trees exhibited a reduction in the rate of light-saturated assimilation (A(max)) to 80% of the pre-frost value. In comparison, following the frost, the ozone-fumigated trees showed an A(max) of 74% of the pre-frost value. The ozone plus acid mist-treated trees showed an A(max) of 64% of the pre- frost trees. The time taken for A(max) to attain 50% of the pre-frost value increased from 30 min (control) to 85 min for ozone-fumigated trees to 190 min (ozone plus acid mist). These results are discussed in relation to the impact of mild, short- term frosts, which are known to occur with greater frequency than extreme, more catastrophic frost events. A simple conceptual framework is proposed to explain the variable results obtained in the literature with respect to the impact of ozone upon tree physiology.110^4^Hunt,R^Hand,DW^Hannah,MA^Neal,AM^1991^1^Response to CO2 enrichment in 27 herbaceous species^43^5^3^410-421^^^^^^^^^^3077showed a significant increase. Following a 3-h frost to -10-degrees-C the control trees exhibited a reduction in the rate of light-saturated assimilation (A(max)) to 80% of the pre-frost value. In comparison, following the frost, the oA^3076^CO2-enrichment experiments were performed on 25 British native species of widely differing ecology. Two crops, one C3 (sunflower) and one C4 (maize), were also included. The background regime involved full-light, glasshouse conditions, non-limiting supplies of water and mineral nutrients and a daytime mean temperature of 18-degrees-C. Four CO2 treatments were maintained at nominal concentrations of 350, 500, 650 or 800 v.p.m. over a 56-day period. Hyperbolic functions were fitted to yield vs CO2 concentration. The functions were then used to generate predictions of Q540/350 (the quotient of present yield under the CO2 regime predicted for the year 2050) and Q700/350 (the quotient of present yield predicted for a doubling of ambient CO2 concentration). Values of Q540/350 for whole-plant dry weight ranged from below 1.01 to 1.49, the upper values being at least similar in magnitude to those already observed in C3 crops. The mean value of whole-plant Q700/350 for 11 species of near-competitive strategy was 1.43. Four species of stress-tolerant or ruderal strategy had a mean Q700/350 of only 1.05. High CO2 responsiveness was common only within the competitive strategy and its close relations. The fitted Q540/350 for species of the pure strategy was 1.38. In the centre of the strategic range the fitted value was 1.12, and at the far extreme, the value for species of ruderal or stress-tolerant strategy was only 1.03.111^2^Idso,SB^Kimball,BA^1991^1^Effects of 2 and a half years of atmospheric CO2 enrichment on the root density distribution of 3-year-old sour orange trees^107^55^3-4^345-349^^^^^Jun^^^^^3079ield under the CO2 regime predicted for the year 2050) and Q700/350 (the quotient of present yield predicted for a doubling of ambient CO2 concentration). Values of Q540/350 for whole-plant dry weight ranged from below 1.01 to 1.49, the upper values being at least similar in magnitude to those already observed in C3 crops. The mean value of whole-plant Q700/350 for 11 species of near-competitive strategy wA^3078^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 which have been continuously supplied with a CO2 enriched atmosphere consisting of an extra 300 cm3 CO2 m-3 of air. Extensive soil coring of the trees' root zones conducted in July 1990 indicated that two and a half years of growth under these conditions produced a fine root biomass enhancement of 175% in the CO2 enriched trees. This growth enhancement is of the same order of magnitude as our previously reported results for net photosynthesis and trunk and branch volumes for these trees.112^4^Laforge,F^Lussier,C^Desjardins,Y^Gosselin,A^1991^1^Effect of light-intensity and CO2 enrichment during invitro rooting on subsequent growth of plantlets of strawberry, raspberry and asparagus in acclimatization^165^47^3-4^259-269^^^^^Jul^^^^^3081361^407^609^610^1 species of near-competitive strategy wA^3080^Growth of plantlets of asparagus (Asparagus officinalis L.), raspberry (Rubus idaeus L.) and strawberry (Fragaria X ananassa Duch.), treated during the in vitro rooting stage under three photosynthetic photon flux densities (PPFD) (80, 125 and 250- mu-mol s-1 m-2) (17.5, 26.9 and 53.8 W m-2 (PAR), respectively) and three CO2 enrichment levels (CDE) (330, 1650 and 3000-mu- mol mol-1), was monitored during the acclimatization stage. For the three species, generic differences were observed in the plant response to treatments. A significant residual growth enhancement was caused by CDE. High PPFD in vitro increased the dry weight of strawberry and fresh weight of asparagus in acclimatization. Raspberry leaf dry weight was increased by 262% in acclimatization after in vitro treatment with high CDE. This enhanced the performance of micropropagated plantlets in acclimatization and reduced by 2 weeks the acclimatization period with raspberry. Our results suggest that in vitro leaves may be a source of nutritional reserves for leaves initiated ex vitro, but do not exclude a morphogenetic effect of CO2 during the in vitro rooting stage.113^5^Novero,R^Smith,DH^Moore,FD^Shanahan,JF^Dandria,R^1991^1^Field-grown tomato response to carbonated water application^48^83^5^911-916^^^^^Sep-Oct^^^^^3083344^362^442^R), respectively) and three CO2 enrichment levels (CDE) (330, 1650 and 3000-mu- mol mol-1), was monitored during the acclimatization stage. For the three species, generic differences were observed in the plant response to treatments. A significant residual growth enhancement was caused by CDE. High PPFD in vitro increased the dry weight of strawberry and fresh weight of asparagus in acclimatization. Raspberry leaf dry weight was increased by 262% in acclimatization after in vitro treatment with high CDE. This enhanced the performance of micropropagated plantlets in acclimatization and reduced by 2 weeks the acclimatization period with raspberry. Our results suggest that in vitro leaves may be a source of nutritiA^3082^Direct release of CO2 gas to achieve a cost-effective method of atmospheric CO2 enrichment has not been proven feasible under field conditions. We hypothesized that greater efficiency of application would occur by applying CO2 via carbonated water and that application would also result in beneficial modifications of the soil environment. Our objectives were to evaluate crop, soil, and atmospheric CO2 responses to application of carbonated water under pressure through a drip irrigation system. Studies were conducted under mulched and unmulched conditions in 1988 using tomato (Lycopersicon esculentum Mill.). In 1989, carbonated water was applied at approximately 2-, 4-, and 6-d intervals to determine the effect of irrigation frequency. In 1988, a positive yield response of 9% was obtained in the presence of mulch. No response was observed in open beds. Fruit yields were increased at all three irrigation frequencies in 1989, with increases in fresh-market and total fruit yields averaging 16.4 and 15.9%, respectively. Atmospheric enrichment was observed during carbonated water application, but residual enrichment between irrigations was difficult to detect. Significant increase in soil-air CO2 from carbonated water application was noted throughout the intervals between successive irrigation events. Carbonated water application also decreased soil pH for periods of up to 5 d after irrigation and increased apparent uptake of P, K, Ca, Mg, Zn, Fe, Mn, Cu, and B. Based on the limited duration of enrichment relative to the entire growing season for any of the carbonated water treatments, the yield responses observed could not be attributed solely to atmospheric enrichment. Thus, we conclude that yield increases resulted from the combined effects of limited atmospheric CO2 enrichment and soil environment modifications leading to improved nutrient uptake.n beds. Fruit yields were increased at all three irrigation frequencies in 1989, with increases in fresh-market and total fruit yields averaging 16.4 and 15.9%, 114^5^Agren,GI^McMurtrie,RE^Parton,WJ^Pastor,J^Shugart,HH^1991^1^State-of-the-art of models of production decomposition linkages in conifer and grassland ecosystems^56^1^2^118-138^^^^^May^^^^^3085230^312^456^474^611^612^613^614^615^616^hroughout the intervals between successive irrigation events. Carbonated water application also decreased soil pH for periods of up to 5 d after irrigation and increased apparent uptake of P, K, Ca, Mg, Zn, Fe, Mn, Cu, and B. Based on the limited duration of enrichment relative to the entire growing season for any of the carbonated water treatments, the yield responses observed could not be attributed solely to atmospheric enrichment. Thus, we conclude that yield increases resulted from the combined effects of limited atmospheric CO2 enrichment and soil environment modifications leading to improved nutrient uptake.n beds. Fruit yields were increased at all three irrigation frequencies in 1989, with increases in fresh-market and total fruit yields averaging 16.4 and 15.9%, A^3084^We review the state-of-the-art of models of forests and grasslands that could be used to predict the impact of a future climate change arising from increased atmospheric carbon dioxide concentration. Four levels of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in great detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationships between the plants and the soil system, but at the expense of requiring more ad hoc formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. However, our conclusion is that, in spite of the gaps in knowledge, there are several models based on dominant processes that are well enough understood for the predictions of those models to be taken seriously.115^1^Amthor,JS^1991^1^Respiration in a future, higher-CO2 world^9^14^1^13-20^^^^^Jan^^^^^3087130^243^312^349^384^385^389^417^617^92^els of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in great detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationships between the plants and the soil system, but at the expense of requiring more ad hoc formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. However, our conclusion is that, in spite of the gaps in knowledge, there are several models based on dominant processes that are welA^3086^Apart from its impact on global warming, the annually increasing atmospheric [CO2] is of interest to plant scientists primarily because of its direct influence on photosynthesis and photorespiration in C3 species. But in addition, 'dark' respiration, another major component of the carbon budget of higher plants, may be affected by a change in [CO2] independent of an increase in temperature. Literature pertaining to an impact of [CO2] on respiration rate is reviewed. With an increase in [CO2], respiration rate is increased in some cases, but decreased in others. The effects of [CO2] on respiration rate may be direct or indirect. Mechanisms responsible for various observations are proposed. These proposed mechanisms relate to changes in: (1) levels of nonstructural carbohydrates, (2) growth rate and structural phytomass accumulation, (3) composition of phytomass, (4) direct chemical interactions between CO2 and respiratory enzymes, (5) direct chemical interactions between CO2 and other cellular components, (6) dark CO2 fixation rate, and (7) ethylene biosynthesis rate. Because a range of (possibly interactive) effects exist, and present knowledge is limited, the impact of future [CO2] on respiration rate cannot be predicted. Theoretical considerations and types of experiments that can lead to an increase in the understanding of this issue are outlined.116^1^Brown,KR^1991^1^Carbon-dioxide enrichment accelerates the decline in nutrient status and relative growth-rate of Populus tremuloides Michx seedlings^13^8^2^161-173^^^^^Mar^^^^^3089es, but decreased in others. The effects of [CO2] on respiration rate may be direct or indirect. Mechanisms responsible for various observations are proposed. These proposed mechanisms relate to changes in: (1) levels of nonstructural carbohydrates, (2) growth rate and structural phytomass accumulation, (3) composition of phytomass, (4) direct chemical interactions between CO2 and respiratory enzymes, (5) direct chemical interactions between CO2 and other cellular componenA^3088^Changes in growth dynamics and mineral nutrient concentrations were measured in Populus tremuloides Michx., trembling aspen, grown for 100 days following germination in atmospheres containing 350 or 750-mu-l l-1 CO2. Seedlings were fertilized with nitrogen (N) at concentrations of 15.5 mM (high-N), 1.55 mM (medium-N), or 0.155 mM (low-N). Initially, relative growth rates were enhanced by CO2 enrichment in each N regime, but the effects did not persist. In plants grown in high-N or medium-N, foliar concentrations of Ca and Mg decreased in response to CO2 enrichment. During the 100-day study, whole-plant concentrations of N and P decreased in all treatments. The decreases in mineral nutrient concentrations over time were accelerated in CO2-enriched plants and accompanied the disappearance of the CO2-induced growth enhancement. It is concluded that the depression of relative growth rates often associated with long-term CO2 enrichment of plants may result from decreases in plant nutrient status.componen117^3^Caporn,SJM^Mansfield,TA^Hand,DW^1991^1^Low temperature-enhanced inhibition of photosynthesis by oxides of nitrogen in lettuce (Lactuca sativa L)^84^118^2^309-313^^^^^Jun^^^^^3091349^417^461^463^464^618^92^l l-1 CO2. Seedlings were fertilized with nitrogen (N) at concentrations of 15.5 mM (high-N), 1.55 mM (medium-N), or 0.155 mM (low-N). Initially, relative growth rates were enhanced by CO2 enrichment in each N regime, but the effects did not persist. In plants grown in high-N or medium-N, foliar concentrations of Ca and Mg decreased in response to CO2 enrichment. During the 100-day study, whole-plant concentrations of N and P decreased in all treatments. The decreases in mineral nutrient concentrations over time were accelerated in CO2-enriched plants and accompanied the disappearance of the CO2-induced growth enhancement. It is concluded that the depression of relative growth rates often associated with long-term CO2 enrichment of plants may result from decreases in plant nutrient status.componenA^3090^The response of photosynthetic gas exchange to oxides of nitrogen (NO(x)) was studied in leaves of lettuce (Lactuca sativa L.) at different temperatures. Exposure to high concentrations (e.g. 1.3-mu-mol NO(x) mol-1), similar to those often found in commercial glasshouses, caused a rapid inhibition of the net assimilation of CO2. This appeared to be by a direct effect on photosynthesis rather than by a change in the stomatal conductance. In ambient CO2 (345-mu-mol mol-1), the percentage inhibition at 10 and 5-degrees-C was approximately 3 x and 5 x, respectively, that measured at 20- degrees-C. This effect of temperature also occurred when measured in CO2 enriched air (1050-mu-mol mol-1), which would normally accompany NO(x) in a glasshouse. The extent of photosynthetic inhibition caused by NO(x) was, however, always less in high than in low CO2. The results suggest that when burning fuel to raise the CO2 concentration and heat the glasshouse air, growers should avoid generating high concentrations of NO(x) in conditions of low temperature.118^3^Elkohen,A^Pontailler,JY^Mousseau,M^1991^1^Effect of doubling of atmospheric CO2 concentration on dark respiration in aerial parts of young chestnut trees (Castanea sativa mill)^176^312^9^477-481^^^^^25 Apr^^^^^3093312^376^385^ses, caused a rapid inhibition of the net assimilation of CO2. This appeared to be by a direct effect on photosynthesis rather than by a change in the stomatal conductance. In ambient CO2 (345-mu-mol mol-1), the percentage inhibition at 10 and 5-degrees-C was approximately 3 x and 5 x, respectively, that measured at 20- degrees-C. This effect of temperature also occurred when measured in CO2 enriched air (1050-mu-mol mol-1), which would normally accompany NO(x) in a glasshouse. The extent of photosynthetic inhibition caused by NO(x) was, however, always less in high than in low CO2. The results suggest that when burning fuel to raise the CO2 concentration and heat the glasshouse air, growers should avoid generating high concentrations of A^3092^Two-year-old sweet chestnut seedlings were grown in constantly ventilated tunnels at ambient (350 vpm) or double (700 vpm) CO2 concentration during a full growing season. End-of-night dark respiration of aerial parts was measured in each CO2 concentration throughout the growing season. Dark respiration rate of enriched plants showed a net decrease as compared to control plants during the first half of the growing season. This difference decreased with time and became negligible in the fall. Atmospheric CO2 concentration acted instantaneously on the respiration rate: when doubled, it decreased control plant respiration and when decreased, it enhanced CO2 enriched plant respiration. The explanation of these findings remains hypothetical. It is concluded that the rise in carbon dioxide level of the atmosphere will affect the carbon balance of young trees not only through an increase in net photosynthesis during the day, but also at night by reducing respiratory losses.generating high concentrations of 119^3^Idso,SB^Kimball,BA^Allen,SG^1991^1^CO2 enrichment of sour orange trees - 2.5 years into a long- term experiment^9^14^3^351-353^^^^^Apr^^^^^3095312^a full growing season. End-of-night dark respiration of aerial parts was measured in each CO2 concentration throughout the growing season. Dark respiration rate of enriched plants showed a net decrease as compared to control plants during the first half of the growing season. This difference decreased with time and became negligible in the fall. Atmospheric CO2 concentration acted instantaneously on the respiration rate: when doubled, it decreased control plant respiration and when decreased, it enhanced CO2 enriched plant respiration. The explanation of these findings remains hypothetical. It is concluded that the rise in carbon dioxide level of the atmosphere will affect the carbon balance of young trees not only through an increase in net photosynthesis during the day, but also at night by reducing respiratory losses.generating high concentrations of A^3094^Eight sour orange trees have been grown from seedling stage in the field at Phoenix, Arizona, U.S.A., in four identically-vented, open-top, clear-plastic-wall chambers for close to 2.5 years. Half of the chambers have been maintained at ambient atmospheric CO2 concentrations over this period, while half of them have been maintained at 300 ppm (300-mu-mol CO2 per mol air) above ambient. Initially, the trees in each treatment were essentially identical; but in less than 2 years, the trunks of the CO2-enriched trees had become twice as large as their ambient-treatment counterparts. After 2 full years of growth, the enriched trees had 79% more leaves, 56% more primary branches with 172% more volume, 70% more secondary branches with 190% more volume, and 240% more tertiary branches with 855% more volume. In addition, the CO2-enriched trees also had fourth-, fifth- and sixth-order branches, while the ambient- treatment trees had no branches above third order. Total trunk plus branch volume of the CO2-enriched trees was 2.79 times that of the ambient-treatment trees after 2 full years of growth.120^3^Jiao,J^Tsujita,MJ^Grodzinski,B^1991^1^Influence of temperature on net CO2 exchange in roses^146^71^1^235-243^^^^^Jan^^^^^3097243^302^385^417^427^543^ent atmospheric CO2 concentrations over this period, while half of them have been maintained at 300 ppm (300-mu-mol CO2 per mol air) above ambient. Initially, the trees in each treatment were essentially identical; but in less than 2 years, the trunks of the CO2-enriched trees had become twice as large as their ambient-treatment counterparts. After 2 full years of growth, the enriched trees had 79% more leaves, 56% more primary branches with 172% more volume, 70% more secondary branches with 190% more volume, and 240% more tertiary branches with 855% more volume. In addition, the CO2-enriched trees also had fourth-, fifth- and sixth-order branches, while the ambient- treatment trees had no branches above third order. Total trunk plus branch volume of the CO2-enrichA^3096^The effect of temperature on net CO2 exchange of source and sink tissues of the flowering shoots and of whole plants was examined using single-stemmed Samantha roses. At all stages of shoot development, the optimal temperature range for whole-plant carbon (C) gain at saturating irradiance and ambient CO2 level was between 20-degrees and 25-degrees-C, narrower than the temperature range for optimal leaf net photosynthesis. Dark respiration increased more dramatically than photosynthesis with temperatures between 15 and 35-degrees-C. At 25-degrees-C, C loss due to respiration from the flower bud at colour bud stage accounted for 45% of the C loss of the flowering shoot. At low irradiance levels (e.g. 200-mu-mol m-2 s-1) whole-plant net photosynthesis was greater at 16-degrees than at 22-degrees-C because of a greater reduction in respiration. Lowering the night temperature from 27 to 17- degrees-C also increased daily C gain due to a reduction in the C lost at night. Whole-plant net photosynthesis of plants grown and measured at enriched (1000 +/- 100-mu-L L-1) CO2 was greater than that of plants grown and measured at ambient (350 +/- 50-mu-L L-1) level at temperatures between 15-degrees and 35-degrees-C. Furthermore, the optimal temperatures for whole- plant net photosynthesis in CO2 enrichment was higher than at ambient CO2 level.121^4^Kozai,T^Iwabuchi,K^Watanabe,K^Watanabe,I^1991^1^Photoautotrophic and photomixotrophic growth of strawberry plantlets invitro and changes in nutrient composition of the medium^177^25^2^107-115^^^^^May^^^^^3099376^619^C loss due to respiration from the flower bud at colour bud stage accounted for 45% of the C loss of the flowering shoot. At low irradiance levels (e.g. 200-mu-mol m-2 s-1) whole-plant net photosynthesis was greater at 16-degrees than at 22-degrees-C because of a greater reduction in respiration. Lowering the night temperature from 27 to 17- degrees-C also increased daily C gain due to a reduction in the C lost at night. Whole-plant net photosynthesis of plA^3098^Explants excised from strawberry (Fragaria x ananassa Duch.) plantlets were cultured in vitro for 21 days on half-strength MS (Murashige & Skoog 1962) basal liquid medium with 20 g l-1 sucrose and without sugar in the vessels capped with gas permeable microporous polypropylene film. The experiments were conducted under CO2 nonenriched (350-450-mu-mol mol-1 in the culture room) and CO2 enriched (2,000-mu-mol mol-1 during the photoperiod in the culture room) conditions with a PPF (photosynthetic photon flux) of 200-mu-mol m-2 s-1. The CO2 concentration in the vessels decreased to approximately 200-mu- mol mol-1 during the photoperiod on day 21 under CO2 nonenriched conditions. The fresh and dry weight, net photosynthetic rate (NPR) per plantlet, NPR per g leaf fresh weight, NPR per g leaf dry weight, the number of unfolded leaves, and ion uptake of PO4(3-), NO3-, Ca2+, Mg2+ and K+ on day 21 were the greatest under photoautotrophic (no sugar in the medium) and CO2 enriched conditions. The residual percent of PO4(3-) was 3% on day 21 under photoautotrophic and CO2 enriched conditions.122^2^Paffen,BGP^Roelofs,JGM^1991^1^Impact of carbon-dioxide and ammonium on the growth of submerged Sphagnum cuspidatum^159^40^1^61-71^^^^^Apr^^^^^3101620^621^622^623^624^A^3100^In a culture experiment, the influence of carbon dioxide and ammonium on the growth of Sphagnum cuspidatum Hoffin. was studied. During a 12-week period, S. cuspidatum was grown in a solution with various concentrations of carbon dioxide and ammonium. The culture experiment clearly demonstrated that the biomass and the length of S. cuspidatum only increased strongly when the carbon dioxide concentration of the water was high. Further it is shown that ammonium enrichment without CO2 enrichment does not lead to an increase in biomass of S. cuspidatum.123^3^Baker,JT^Allen,LH^Boote,KJ^1990^1^Growth and yield responses of rice to carbon-dioxide concentration^178^115^^313-320^^^^^Dec^^^^^3103130^230^344^376^400^409^436^625^626^627^. The residual percenA^3102^Rice plants (Oryza sativa L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 mu-mol CO2/mol air) CO2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO2 concentration, the greatest increase occurring between the 160 and 500 mu-mol CO2/mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasing CO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO2 treatments. Doubling the CO2 concentration from 330 to 660 mu-mol CO2/mol air resulted in a 32% increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO2 concentration of the earth's atmosphere continues to rise.124^3^Fajer,ED^Bowers,MD^Bazzaz,FA^1991^1^The effects of enriched CO2 atmospheres on the buckeye butterfly, Junonia coenia^11^72^2^751-754^^^^^Apr227^489^490^628^125^1^Jansen,DM^1990^1^Potential rice yields in future weather conditions in different parts of asia^179^38^4^661-680^^^^^Dec^^^^^3106130^243^349^57^629^92^; although the ratio decreased during the growing season, net assimilation rate increased with increasing CO2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences A^3105^Future climate change is expected to vary between regions, with possible different effects on crop growth. Various sites in Asia were selected to represent major rice growing environments. Historic weather data of these sites were adapted to possible changes in temperature and in CO2 level, to mimic climate change. Potential rice yields at present, and for the years 2020 and 2100 were calculated with a crop growth simulation model. Simulated yields rose in low and middle temperature change scenarios, but decreased in the high temperature scenario. Effects were stronger in the year 2100, when also regional differences became clear: more than elsewhere, yields were affected by high temperatures between 10 and 35-degrees-N. Water use efficiency decreased in the high temperature scenario irrespective of CO2 scenario, and increased otherwise.126^3^Jiao,J^Tsujita,MJ^Grodzinski,B^1991^1^Influence of radiation and CO2 enrichment on whole plant net CO2 exchange in roses^146^71^1^245-252^^^^^Jan^^^^^3108ces 174^243^312^92^imate change is expected to vary between regions, with possible different effects on crop growth. Various sites in Asia were selected to represent major rice growing environments. Historic weather data of these sites were adapted to possible changes in temperature and in CO2 level, to mimic climate change. Potential rice yields at present, and for the years 2020 and 2100 were calculated with a crop growth simulation model. Simulated yields rose in low and middle temperature change scenarios, but decreased in the high temperature scenario. Effects were stronger in the year 2100, when also regional differences became clear: more than elsewhere, yields were affected by high temperatures between 10 and 35-degrees-N. Water use efficiency decreased in the high temperature scenario irrespective of CO2 scenario, and increased otherwise.126^3^Jiao,J^Tsujita,MJ^Grodzinski,B^1991^1^Influence of radiation and CO2 enrichment on whole plant net CO2 exchange in roses^146^71^1^245-252^^^^^Jan^^^^^3108ces A^3107^At three stages of flowering shoot development, varying the irradiance and CO2 levels had a similar effect on the whole- plant net CO2 exchange rate (NCER) of Samantha rose plants. At 22-degrees-C, the NCER was saturated at 1000-mu-mol m-2 s-1 photosynthetically active radiation (PAR). The duration of the light period was also important in determining daily carbon (C) gain. When roses were exposed to a constant daily radiant energy dose of 17.6-mu-mol m-2 provided either as a 12-h irradiation interval at 410-mu-mol m-2 s-1 PAR or 24 h of irradiation at 204-mu-mol m-2 s-1 PAR, the plants exposed to 24 h of continuous irradiation at the lower photon flux density retained 80% more C. Under saturating irradiance, the net photosynthetic rate at an enriched (1000-mu-L L-1) CO2 level was almost double that at ambient (350-mu-L L-1) CO2. However, plants grown at ambient and enriched CO2 levels had similar whole-plant NCERs when compared at the same assay CO2 level. Under CO2 enrichment the flower stem was longer and thicker but the flower bud size at harvest was not significantly different to that of roses grown at the ambient CO2 level.127^5^Kurooka,H^Fukunaga,S^Yuda,E^Nakagawa,S^Horiuchi,S^1990^1^Effect of carbon-dioxide enrichment on vine growth and berry quality of kyoho grapes^180^59^3^463-470^^^^^Dec^^^^^3110349^374^434^442^630^631^rtant in determining daily carbon (C) gain. When roses were exposed to a constant daily radiant energy dose of 17.6-mu-mol m-2 provided either as a 12-h irradiation interval at 410-mu-mol m-2 s-1 PAR or 24 h of irradiation at 204-mu-mol m-2 s-1 PAR, the plants exposed to 24 h of continuous irradiation at the lower photon flux density retained 80% more C. Under saturating irradiance, the net photosynthetic rate at an enriched (1000-mu-L L-1) CO2 level was almost double that at ambient (350-mu-L L-1) CO2. However, plants grown at ambient and enriched CO2 levels had similar whole-plant NCERs when compared at the same assay CO2 level. Under CO2 enrichment the flower stem was lonA^3109^Although ambient temperature is kept adequate, grape cultivation under covered facilities during winter months in Japan gives rise to low yields of poor quality berries because of low light intensities. This investigation was conducted in leaf chamber, using Vitis labruscana Bailey cv. Kyoho, to determine the influence of leaf age, light intensity, and CO2 concentrations on photosynthesis. The effects of CO2 enrichment on vine growth and fruit quality were also investigated in growth chambers. 1. The rate of photosynthesis per unit leaf area (Pn) between May 28 and September 19 rapidly increased with leaf growth, reaching a maximum of 18.9 mg CO2/dm2/hr, 37 days after the unfolding of a leaf. Pn then gradually decreased with leaf age. In young leaves, higher CO2 concentrations and stronger light intensities resulted in a significant increase in Pn. Older leaves exhibited a similar enhancement of Pn upon exposure to high light intensity. Pn was saturated at 828 ppm CO2. 2. Administration of 1,000 to 1,100 ppm CO2 to vines for an 8 hr/day at a late stage of berry development until harvest had no effect on berry size but resulted in an increase in sugar and anthocyanin contents but a decrease in organic acid content. Dry weight of newly developed roots doubled as a result of CO2 enrichment. 3. Application of CO2 under a long-day photoperiod at an early stage of berry development to a week before veraison markedly promoted shoot elongation. Furthermore, CO2 enrichment gave a 36% increase in both berry and cluster weights and also a higher sugar-acid ratio at harvest.128^2^Lindhout,P^Pet,G^1990^1^Effects of CO2 enrichment on young plant-growth of 96 genotypes of tomato (Lycopersicon esculentum)^181^51^2^191-196^^^^^Dec^^^^^3112h leaf age. In young leaves, higher CO2 concentrations and stronger light intensities resulted in a significant increase in Pn. Older leaves exhibited a similar enhancement of Pn upon exposure to high light intensity. Pn was saturated at 828 ppm CO2. 2. Administration of 1,000 to 1,A^3111^The early growth of 96 genotypes of tomato was studied at 320 ppm CO2 and at 750 ppm CO2 in separate climate rooms. Plants were harvested at 40 and 55 days after sowing. Fresh and dry weights were determined. Large differences between genotypes were found for average plant fresh and dry weights and for relative growth rates. The average overall growth enhancement by CO2 enrichment was 2.3. Two genotypes showed significant genotype x CO2 interaction. The consequences of these results for tomato breeding are discussed.129^4^Rowlandbamford,AJ^Allen,LH^Baker,JT^Boote,KJ^1990^1^Carbon-dioxide effects on carbohydrate status and partitioning in rice^78^41^233^1601-1608^^^^^Dec^^^^^3114174^243^376^417^434^57^632^92^c^^^^^3112h leaf age. In young leaves, higher CO2 concentrations and stronger light intensities resulted in a significant increase in Pn. Older leaves exhibited a similar enhancement of Pn upon exposure to high light intensity. Pn was saturated at 828 ppm CO2. 2. Administration of 1,000 to 1,A^3113^The atmospheric carbon dioxide (CO2) concentration has been rising and is predicted to reach double the present concentration sometime during the next century. The objective of this investigation was to determine the long-term effects of different CO2 concentrations on carbohydrate status and partitioning in rice (Oryza sativa L. cv. IR-30). Rice plants were grown season-long in outdoor, naturally sunlit, environmentally controlled growth chambers with CO2 concentrations of 160, 250, 330, 500, 660, and 900 mu-mol CO2 mol-1 air. In leaf blades, the priority between the partitioning of carbon into storage carbohydrates or into export changed with development stage and CO2 concentration. During vegetative growth, leaf sucrose and starch concentrations increased with increasing CO2 concentration but tended to level off above 500 mu-mol mol-1 CO2. Similarly, photosynthesis also increased with CO2 concentrations up to 500 mu-mol mol-1 and then reached a plateau at higher concentrations. The ratio of starch to sucrose concentration was positively correlated with the CO2 concentration. At maturity, increasing CO2 concentration resulted in an increase in total non-structural carbohydrate (TNC) concentration in leaf blades, leaf sheaths and culms. Carbohydrates that were stored in vegetative plant parts before heading made a smaller contribution to grain dry weight at CO2 concentrations below 330 mu-mol mol-1 than for treatments at concentrations above ambient. Increasing CO2 concentration had no effect on the carbohydrate concentration in the grain at maturity.130^1^Wittwer,SH^1990^1^Implications of the greenhouse-effect on crop productivity^170^25^12^1560-1567^^^^^Dec209^312^409^416^434^456^559^633^634^92^131^1^Peterson,RB^1991^1^Effects of O2 and CO2 concentrations on quantum yields of photosystem-I and photosystem-II in tobacco leaf tissue^8^97^4^1388-1394^^^^^Dec^^^^^3117243^348^493^529^635^636^637^638^639^640^ to 500 mu-mol mol-1 and then reached a plateau at higher concentrations. The ratio of starch A^3116^The interactive effects of irradiance and O2 and CO2 levels on the quantum yields of photosystems I and II have been studied under steady-state conditions at 25-degrees-C in leaf tissue of tobacco (Nicotiana tabacum). Assessment of radiant energy utilization in photosystem II was based on changes in chlorophyll fluorescence yield excited by a weak measuring beam of modulated red light. Independent estimates of photosystem I quantum yield were based on the light-dark in vivo absorbance change at 830 nanometers, the absorption band of P700+. Normal (i.e. 20.5%, v/v) levels of O2 generally enhanced photosystem II quantum yield relative to that measured under 1.6% O2 as the irradiance approached saturation. Photorespiration is suspected to mediate such positive effects of O2 through increases in the availability of CO2 and recycling of orthophosphate. Conversely, at low intercellular CO2 concentrations, 41.2% O2 was associated with lower photosystem II quantum yield compared with that observed at 20.5% O2. Inhibitory effects of 41.2% O2 may occur in response to negative feedback on photosystem II arising from a build-up in the thylakoid proton gradient during electron transport to O2. Covariation between quantum yields of photosystems I and II was not affected by concentrations of either O2 or CO2. The dependence of quantum yield of electron transport to CO2 measured by gas exchange upon photosystem II quantum yield as determined by fluorescence was unaffected by CO2 concentration.132^2^Plaut,Z^Federman,E^1991^1^Acclimation of CO2 assimilation in cotton leaves to water- stress and salinity^8^97^2^515-522^^^^^Oct^^^^^3119417^552^637^641^642^643^644^645^646^92^1.6% O2 as the irradiance approached saturation. Photorespiration is suspected to mediate such positive effects of O2 through increases in the availability of CO2 and recycling of orthophosphate. Conversely, at low intercellular CO2 concentrations, 41.2% O2 was associated with lower photosystem II quantum yield compared with that observed at 20.5% O2A^3118^Cotton (Gossypium hirsutum L. cv Acala SJ2) plants were exposed to three levels of osmotic or matric potentials. The first was obtained by salt and the latter by withholding irrigation water. Plants were acclimated to the two stress types by reducing the rate of stress development by a factor of 4 to 7. CO2 assimilation was then determined on acclimated and nonacclimated plants. The decrease of CO2 assimilation in salinity-exposed plants was significantly less in acclimated as compared with nonacclimated plants. Such a difference was not found under water stress at ambient CO2 partial pressure. The slopes of net CO2 assimilation versus intercellular CO2 partial pressure, for the initial linear portion of this relationship, were increased in plants acclimated to salinity of -0.3 and -0.6 megapascal but not in nonacclimated plants. In plants acclimated to water stress, this change in slopes was not significant. Leaf osmotic potential was reduced much more in acclimated than in nonacclimated plants, resulting in turgor maintenance even at -0.9 megapascal. In nonacclimated plants, turgor pressure reached zero at approximately -0.5 megapascal. The accumulation of Cl- and Na+ in the salinity-acclimated plants fully accounted for the decrease in leaf osmotic potential. The rise in concentration of organic solutes comprised only 5% of the total increase in solutes in salinity- acclimated and 10 to 20% in water-stress-acclimated plants. This acclimation was interpreted in light of the higher protein content per unit leaf area and the enhanced ribulose bisphosphate carboxylase activity. At saturating CO2 Partial pressure, the declined inhibition in CO2 assimilation of stress-acclimated plants was found for both salinity and water stress.133^1^Stitt,M^1991^1^Rising CO2 levels and their potential significance for carbon flow in photosynthetic cells^9^14^8^741-762^^^^^Oct^^^^^3121343^355^363^550^575^647^648^649^650^651^. Leaf osmotic potential was reduced much more in acclimated than in nonacclimated plants, resuA^3120^In the first part of this review, I discuss how we can predict the direct short-term effect of enhanced CO2 on photosynthetic rate in C3 terrestrial plants. To do this, I consider: (1) to what extent enhanced CO2 Will stimulate or relieve demand on partial processes like carboxylation, light harvesting and electron transport, the Calvin cycle, and end-product synthesis; and (2) the extent to which these various processes actually control the rate of photosynthesis. I conclude that control is usually shared between Rubisco (which responds sensitively to CO2) and other components (which respond less sensitively), and that photosynthesis will be stimulated by 25- 75% when the CO2 concentration is doubled from 35 to 70 Pa. This is in good agreement with the published responses. In the next part of the review, I discuss the evidence that most plants undergo a gradual inhibition of photosynthesis during acclimation to enhanced CO2. I argue that this is related to an inadequate demand for carbohydrate in the remainder of the plant. Differences in the long-term response to CO2 may be explained by differences in the sink-source status of plants. depending upon the species, the developmental stage, and the developmental conditions. In the third part of the review, I consider the biochemical mechanisms which are involved in 'sink' regulation of photosynthesis. Accumulating carbohydrate could lead to a direct inhibition of photosynthesis, involving mechanical damage by large starch grains or Pi-limitation due to inhibition of sucrose synthesis. I argue that Pi is important in the short-term regulation of partitioning to sucrose and starch, but that its contribution to 'sink' regulation has not yet been conclusively demonstrated. Indirect or 'adaptive' regulation of photosynthesis is probably more important, involving decreases in amounts of key photosynthetic enzymes, including Rubisco. This decreases the rate of photosynthesis, and potentially would allow resources (e.g. amino acids) to be remobilized from the leaves and reinvested in sink growth to readjust the sink-source balance. In the final part of the review, I argue that similar changes of Rubisco and, possibly, other proteins are probably also involved during acclimation to high CO2.134^2^Singh,T^Wheaton,EE^1991^1^Boreal forest sensitivity to global warming - implications for forest management in western interior canada^66^67^4^342-348^^^^^Aug^^^^^3123A^3122^Unmitigated global warming due to the enhanced greenhouse effect could have significant impacts on the boreal forest in interior western Canada. Increases in annual temperature of 3 to 7-degrees-C are projected for Alberta under a 2 x CO2 scenario by 2030-2050 A.D. Such an unprecedented rate of change has many short- and long-term implications for forest management and for industries. As the boreal forest is highly sensitive to climatic changes, foresters need to develop a set of safe strategies to minimize the negative impacts and maximize the benefits of these changes.o be remobilized from the leav135^3^Delatorre,A^Delgado,B^Lara,C^1991^1^Nitrate-dependent O2 evolution in intact leaves^8^96^3^898-901^^^^^Jul^^^^^3125637^639^652^653^654^655^A^3124^Evolution Of O2 by illuminated intact detached leaves from barley (Hordeum vulgare L. cv Athos) and pea (Pisum sativum L. cv Lincoln) in a CO2-saturating atmosphere was enhanced when KNO3 (1-2.5 millimolar) had been previously supplied through the transpiration stream. The extra O2 evolution observed after feeding KNO3 increased with the light intensity, being maximal at near saturating photon flux densities and resulting in no changes in the initial slope of the O2 versus light-intensity curve. No stimulation Of O2 evolution was otherwise observed after feeding KCl or NH4Cl. The data indicate that nitrate assimilation uses photosynthetically generated reductant and stimulates the rate of noncyclic electron flow by acting as a second electron-accepting assimilatory process in addition to CO2 fixation.efits of these changes.o be remobilized from the leav136^3^Jenkinson,DS^Adams,DE^Wild,A^1991^1^Model estimates of CO2 emissions from soil in response to global warming^36^351^6324^304-306^^^^^23 May^^^^^3127264^354^56^656^657^658^nated intact detached leaves from barley (Hordeum vulgare L. cv Athos) and pea (Pisum sativum L. cv Lincoln) in a CO2-saturating atmosphere was enhanced when KNO3 (1-2.5 millimolar) had been previously supplied through the transpiration stream. The extra O2 evolution observed after feeding KNO3 increased with the light intensity, being maximal at near saturating photon flux densities and resulting in no changes in the initial slope of the O2 versus light-intensity curve. No stimulation Of O2 evolution was otherwise observed after feeding KCl or NH4Cl. The data indicate that nitrate assimilation uses photosynthetically generated reductant and stimulates the rate of noncyclic electron flow by acting as a second electron-accepting assimilatory process in addition to CO2 fixation.efits of these changes.o be remobilized from the leavA^3126^ONE effect of global warming will be to accelerate the decomposition of soil organic matter, thereby releasing CO2 to the atmosphere, which will further enhance the warming trend 1- 7. Such a feedback mechanism could be quantitatively important, because CO2 is thought to be responsible for approximately 55% of the increase in radiative forcing arising from anthropogenic emissions of gases to the atmosphere 8, and there is about twice as much carbon in the top metre of soil as in the atmosphere 9. Here we use the Rothamsted model for the turnover of organic matter in soil 3 to calculate the amount of CO2 that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant. If world temperatures rise by 0.03-degrees-C yr-1 (the increase considered as most likely by the Intergovernmental Panel on Climate Change 8), we estimate that the additional release of CO2 from soil organic matter over the next 60 years will be 61 x 10(15) gC. This is approximately 19% of the CO2 that will be released by combustion of fossil fuel during the next 60 years if present use of fuel continues unabated.137^2^Bassman,JH^Zwier,JC^1991^1^Gas-exchange characteristics of Populus trichocarpa, Populus deltoides and Populus trichocarpa X Populus deltoides clones^13^8^2^145-159^^^^^Mar^^^^^3129nic emissions of gases to the atmosphere 8, and there is about twice as much carbon in the top metre of soil as in the atmosphere 9. Here we use the Rothamsted model for the turnover of organic matter in soil 3 to calculate the amount of CO2 that would be released from the world stock of soil organic matter if temperatures increase as predicted, the annual return of plant debris to the soil being held constant. If world temperatures rise by 0.03-degrees-C yr-1 (the increase considered as most likely by the Intergovernmental Panel on Climate Change 8), we estimate that the additional release of CO2 from soil organic matter over the next 60 A^3128^Responses of net photosynthesis, dark respiration, photorespiration, transpiration, and stomatal conductance to irradiance, temperature, leaf-to-air vapor density difference (VDD), and plant water stress were examined in two Populus trichocarpa clones (one from a moist, coastal climate in western Washington and one from a dry, continental climate in eastern Washington), one P. deltoides clone, and two P. trichocarpa x P. deltoides clones. Light saturation of photosynthesis in greenhouse-grown trees occurred at about 800- mu-mol m-2 s-1 for P. deltoides, P. trichocarpa x P. deltoides, and the eastern Washington ecotype of P. trichocarpa, but at about 600-mu-mol m-2 s-1 for the western Washington ecotype of P. trichocarpa. Average net photosynthesis (at saturating irradiance and the optimum temperature of 25-degrees-C) was 20.7, 18.8, 18.2 and 13.4-mu-mol CO2 m-2 s-1 for P. deltoides, P. trichocarpa x P. deltoides, and the eastern and western Washington clones of P. trichocarpa, respectively. In all clones, net photosynthesis decreased about 14% as VDD increased from 3 to 18 g H2O m-3. Stomatal conductance decreased sharply with decreasing xylem pressure potential (XPP) in all clones except the western Washington clone of P. trichocarpa. Stomata in this clone were insensitive to changes in XPP and did not control water loss. Complete stomatal closure (stomatal conductance < 0.05 cm s-1) occurred at about -2.0 MPa in the eastern Washington clone of P. trichocarpa and around -1.25 MPa in the P. deltoides and P. trichocarpa x P. deltoides clones. Transpiration rates were highest in the P. trichocarpa x P. deltoides clone and lowest in the western Washington clone of P. trichocarpa. The P. deltoides clone and eastern Washington clone of P. trichocarpa had the highest water use efficiency (WUE) and the western Washington clone of P. trichocarpa had the lowest WUE. The hybrids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa reflected adaptation to their native environment; (2) crossing the western Washington clone of P. trichocarpa with the more drought resistant P. deltoides clone produced plants better adapted to the interior Pacific Northwest climate, although the stomatal response to soil water deficits in the hybrid was conservative compared with that of the eastern Washington clone of P. trichocarpa; and (3) introducing eastern Washington clones of black cottonwood into breeding programs is likely to yield lines with favorable growth characteristics combined with enhanced WUE and adaptation to soil water deficits.138^2^Singh,B^Stewart,RB^1991^1^Potential impacts of a CO2-induced climate change using the GISS scenario on agriculture in quebec, canada^169^35^4^327-347^^^^^May^^^^^3131174^312^409^411^434^633^659^660^661^662^ashington clone of P. trichocarpa had the lowest WUE. The hybrids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa refA^3130^This study examines the potential impacts of a climate change resulting from an effective doubling of atmospheric CO2 on the potential and anticipated yields of a variety of agricultural crops including corn, soya, potatoes, wheat, phaseolus beans, sorghum, barley, oats, rapeseed and sunflowers and two horticultural crops namely apples and grapes, for southern Quebec. The GISS climate change scenario is used. Our results show that yields would increase for some crops such as corn, soybeans, potatoes, phaseolus beans and sorghum and would decrease for the cereal and oilseed crops, namely wheat, barley, oats, sunflowers and rapeseed. Production opportunities for apples and grapes are enhanced. Also it would seem that the more northerly regions of Abitibi- Temiscamingue and Lac St-Jean would benefit most, in terms of agriculture, from a CO2-induced climate change.ids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa ref139^1^Graumlich,LJ^1991^1^Sub-alpine tree growth, climate, and increasing CO2 - an assessment of recent growth trends^11^72^1^1-11^^^^^Feb^^^^^3133182^374^377^425^663^664^iety of agricultural crops including corn, soya, potatoes, wheat, phaseolus beans, sorghum, barley, oats, rapeseed and sunflowers and two horticultural crops namely apples and grapes, for southern Quebec. The GISS climate change scenario is used. Our results show that yields would increase for some crops such as corn, soybeans, potatoes, phaseolus beans and sorghum and would decrease for the cereal and oilseed crops, namely wheat, barley, oats, sunflowers and rapeseed. Production opportunities for apples and grapes are enhanced. Also it would seem that the more northerly regions of Abitibi- Temiscamingue and Lac St-Jean would benefit most, in terms of agriculture, from a CO2-induced climate change.ids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa refA^3132^LaMarche et al. (1984) hypothesized that recent trends of increasing ring widths in subalpine conifers may be due to the fertilizing effects of increased atmospheric CO2. Five tree- ring series from foxtail pine (Pinus balfouriana), lodgepole pine (P. murrayana), and western juniper (Juniperus occidentalis) collected in the Sierra Nevada, California, were analyzed to determine if the temporal and spatial patterns of recent growth were consistent with the hypothesized CO2-induced growth enhancement. Specifically, I address the following questions: (1) Can growth trends be explained solely in terms of climatic variation? (2) Are recent growth trends unusual with respect to long-term growth records? For three of the five sites, 20th-century growth variation can be adequately modeled as a function of climatic variation. For the remaining two sites, trends in the residuals from the growth/climate models indicate systematic underestimation of growth during the past decade that could be interpreted as either CO2 fertilization or as a response to extreme climatic events during the mid 1970s. At all five sites, current growth levels have been equalled or exceeded during some preindustrial periods. Taken together, these results do not indicate that CO2-induced growth enhancement is occurring among subalpine conifers in the Sierra Nevada. While the results presented here offer no support for the hypothesized CO2 fertilization effect, they do provide insights into the response of subalpine conifers to climatic variation. Response surfaces demonstrate that precipitation during previous winter and temperature during the current summer interact in controlling growth and that the response can be nonlinear. Although maximum growth rates occur under conditions of high winter precipitation and warm summers for all three species, substantial species-to-species variation occurs in the response to these two variables.els indicate systematic underestimation of growth during the past decade that could be interpreted as either140^1^Mitchell,JFB^1990^1^Greenhouse warming - is the midholocene a good analog^126^3^11^1177-1192^^^^^Nov^^^^^3135h levels have been equalled or exceeded during some preindustrial periods. Taken together, these results do not indicate that CO2-induced growth enhancement is occurring among subalpine conifers in the Sierra Nevada. While the results presented here offer no support for the hypothesized CO2 fertilization effect, they do provide insights into the response of subalpine conifers to climatic variation. Response surfaces demonstrate that precipitation during previous winter and temperature during the current summer interact in controlling growth and that the response can be nonlinear. Although maximum growth rates occur under conditions of high winter precipitation and warm summers for all three species, substantial species-to-species variation occurs in the response to these two variables.els indicate systematic underestimation of growth during the past decade that could be interpreted as eitherA^3134^The mid-Holocene period (from approximately 9000 to 6000 years before present) is often suggested as an analogue for enhanced greenhouse warming. The changes in net radiative forcing at the top of atmosphere are very different; increases in greenhouse gases producing a small annual mean warming of little seasonal or latitudinal variation, whereas during the Holocene the annual mean did not change but there were large seasonal and latitudinal variations. Two climate model experiments, one in which CO2 amounts are doubled and the other in which the value of the earth's orbital parameters are altered to those appropriate to 9000 years before present (BP), are compared. Any similarity in the simulated response is found to be limited to the northern continents and, even there, the mechanisms producing the changes differ between the two experiments. Assuming that the gross behavior of the model is realistic, the Holocene is not a good analogue for a "greenhouse" warming. Furthermore, as the mechanisms operating in the two experiments are different, a model which produces a realistic simulation for the mid-Holocene and present climate need not necessarily produce a reliable simulation of greenhouse warming. However, a comparison of simulated climates for the mid-Holocene and that reconstructed from paleoclimatic data may help to constrain the existing range of subgridscale parametrizations used in climate models.141^6^Stitt,M^Quick,WP^Schurr,U^Schulze,ED^Rodermel,SR^Bogorad,L^1991^1^Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with antisense rbcs .2. Flux- control coefficients for photosynthesis in varying light, CO2, and air humidity^6^183^4^555-566^^^^^^^^^^3137244^348^424^57^640^665^666^o the northern continents and, even there, the mechanisms producing the changes differ between the two experiments. Assuming that the gross behavior of the model is realistic, the Holocene is not a good analogue for a "greenhouse" warming. Furthermore, as the mechanisms operaA^3136^Transgenic tobacco (Nicotiana tabacum L.) plants transformed with 'antisense' rbcS to produce a series of plants with a progressive decrease in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been used to investigate the contribution of Rubsico to the control of photosynthesis at different irradiance, CO2 concentrations and vapour-pressure deficits. Assimilation rates, transpiration, the internal CO2 concentration and chlorophyll fluorescence were measured in each plant. (i) The flux-control coefficient of Rubisco was estimated from the slope of the plot of Rubisco content versus assimilation rate. The flux-control coefficient had a value of 0.8 or more in high irradiance, (1050 mumol m-2 s-1), low-vapour pressure deficit (4 mbar) and ambient CO2 (350-mu-bar). Control was marginal in enhanced CO2 (450-mu-bar) or low light (310 mumol m-2 s-1) and was also decreased at high vapour- pressure deficit (17 mbar). No control was exerted in 5% CO2. (ii) The flux-control coefficients of Rubisco were compared with the fractional demand placed on the calculated available Rubisco capacity. Only a marginal control on photosynthetic flux is exerted by Rubisco until over 50% of the available capacity is being used. Control increases as utilisation rises to 80%, and approaches unity (i.e. strict limitation) when more than 80% of the available capacity is being used. (iii) In low light, plants with reduced Rubisco have very high energy-dependent quenching of chlorophyll fluorescence (qE) and a decreased apparent quantum yield. It is argued that Rubisco still exerts marginal control in these conditions because decreased Rubisco leads to increased thylakoid energisation and high-energy dependent dissipation of light energy, and lower light-harvesting efficiency. (iv) The flux-control coefficient of stomata for photosynthesis was calculated from the flux- control coefficient of Rubisco and the internal CO2 concentration, by applying the connectivity theorem. Control by the stomata varies between zero and about 0.25. It is increased by increased irradiance, decreased CO2 or decreased vapour-pressure deficit. (v) Photosynthetic oscillations in saturating irradiance and CO2 are suppressed in decreased- activity transformants before the steady-state rate of photosynthesis is affected. This provides direct evidence that these oscillations reveal the presence of "excess" Rubisco. (vi) Comparison of the flux-control coefficients of Rubisco with mechanistic models of photosynthesis provides direct support for the reliability of these models in conditions where Rubisco has a flux-control coefficient approach unity (i.e. "limits" photosynthesis), but also indicates that these models are less useful in conditions where control is shared between Rubisco and other components of the photosynthetic apparatus.142^1^Austin,MP^1992^1^Modeling the environmental niche of plants - implications for plant community response to elevated CO2 levels^182^40^4-5^615-630^^^^^^^^^^3139264^51^667^668^669^670^671^672^673^92^nA^3138^No simple natural gradients in CO2 concentration exist for testing predictions about changes in plant communities in response to elevated CO2. However indirect effects of CO2 via temperature increases can be tested by reference to natural analogues. Physiologists, vegetation modellers of climate change and community ecologists assume very different temperature responses for plants. Physiologists often assume a skewed non-monotonic curve with a tail towards low temperatures, forest modellers using FORET type models, a symmetric curve, and community ecologists a skewed response with a tail towards high temperatures. These assumptions are reviewed in relation to niche theory, and recent propositions concerning the continuum concept. Confusion exists between the different approaches over the shape of response curves to temperature. Distinctions need to be made between responses due to growth (physiological response), potential fitness (fundamental niche) and observed performance (realised niche). These types of response should be quantified and related to each other if process-models are to be tested for predictive success by reference to naturally occurring communities and temperature gradients. An example of a statistical method for quantifying the realised environmental niche respone of a species to temperature is provided. It is based on generalised linear modelling (GLM) of presence/absence data on Eucalyptus fastigata for 8377 sites in southern New South Wales, Australia. Seven environmental variables or factors are considered: mean annual temperature, mean annual rainfall, mean monthly solar radiation, topographic position, rainfall seasonality, lithology, and soil nutrient status. The temperature response is modelled with a beta-function, log y = a + alpha log (t - a) + delta log (b - t), where t is temperature and letters are parameters. The probability of occurrence is shown to be a skewed function of mean annual temperature. Any process-models of climate change for vegetation incorporating temperature changes due to elevated CO2 must be capable of generating such realised environmental niche responses for species.143^1^Badger,M^1992^1^Manipulating agricultural plants for a future high CO2 environment^182^40^4-5^421-429^^^^^^^^^^3141130^243^245^312^360^374^674^675^92^ respone of a species to temperature is provided. It is based on generalised linear modelling (GLM) of presence/absence data on Eucalyptus fastigata for 8377 sites in southern New South Wales, Australia. Seven environmental variables or factors are considered: mean annual temperature, mean annual rainfall, mean monthly solar radiation, topographic position, rainfall seasonality, lithology, and soil nutrient status. The temperature response is modelled with a beta-function, log y = a + alpha log (t - a) + delta log (b - t), where t is temperature and letters are parameters. The probability of occurrence is shown to be a skewed function of mean annual temperature. Any process-models of climate change for vegetation incorporating temperaA^3140^This paper discusses the potential ways in which C3 plant performance may benefit from a future high-CO2 environment. These include increases in the efficiencies for light, nitrogen and water utilisation, particularly at elevated temperatures, resulting from the improvement which will occur in the performance of the primary carboxylating enzyme, Rubisco. However, while growth experiments at elevated CO2 indicate that C3 plants show stimulation of dry matter accumulation, the potential gains are greatly ameliorated by a redistribution of plant resources. This primarily occurs via a reduction in the leaf area ratio which offsets increases in the net assimilation rate. In addition, there may be an overcommitment of nitrogen in key photosynthetic components such as Rubisco and the thylakoid electron transport system. It is concluded that plants may not be genetically adapted to optimise their growth and performance at elevated CO2 and that consideration should be given to exploring avenues for manipulating plants for more optimal responses. Targets for improvement of growth at elevated CO2 include (1) altering source-sink relations; (2) improving the redistribution of nitrogen between the photosynthetic machinery and the rest of the plant; and (3) changing the response of stomata to CO2 and humidity to increase water-use efficiency even further than is currently predicted.144^2^Ball,MC^Munns,R^1992^1^Plant-responses to salinity under elevated atmospheric concentrations of CO2^182^40^4-5^515-525^^^^^^^^^^3143243^312^384^514^642^666^676^677^678^92^resources. This primarily occurs via a reduction in the leaf area ratio which offsets increases in the net assimilation rate. In addition, there may be an overcommitment of nitrogen in key photosynthetic components such as Rubisco and the thylakoid electron transport system. It is concluded that plants may not be genetically adapted to optimise their growth and performance at elevated CO2 and that consideration should be given to exploring avenues for manipulatinA^3142^This review explores effects of elevated CO2 concentrations on growth in relation to water use and salt balance of halophytic and non-halophytic species. Under saline conditions, the uptake and distribution of sodium and chloride must be regulated to protect sensitive metabolic sites from salt toxicity. Salt-tolerant species exclude most of the salt from the transpiration stream, but the salt flux from a highly saline soil is still considerable. To maintain internal ion concentrations within physiologically acceptable levels, the salt influx to leaves must match the capacities of leaves for salt storage and/or salt export by either retranslocation or secretion from glands. Hence the balance between carbon gain and the expenditure of water in association with salt uptake is critical to leaf longevity under saline conditions. Indeed, one of the striking features of halophytic vegetation, such as mangroves, is the maintenance of high water use efficiencies coupled with relatively low rates of water loss and growth. These low evaporation rates are further reduced under elevated CO2 conditions. This, with increased growth, leads to even higher water use efficiency. Leaves of plants grown under elevated CO2 conditions might be expected to contain lower salt concentrations than those grown under ambient CO2 if salt uptake is coupled with water uptake. However, salt concentrations in shoot tissues are similar in plants grown under ambient and elevated CO2 conditions despite major differences in water use efficiency. This phenomenon occurs in C3 halophytes and in both C3 and C4 non-halophytes. These results imply shoot/root communication in regulation of the salt balance to adjust to environmental factors affecting the availability of water and ions at the roots (salinity) and those affecting carbon gain in relation to water loss at the leaves (atmospheric concentrations of water vapour and carbon dioxide).groves, is the maintenance of high water use efficiencies coupled with relatively low rates of water loss 145^2^Bazzaz,FA^McConnaughay,KDM^1992^1^Plant interactions in elevated CO2 environments^182^40^4-5^547-563^^^^^^^^^^3145189^23^377^378^419^484^505^679^680^681^. Leaves of plants grown under elevated CO2 conditions might be expected to contain lower salt concentrations than those grown under ambient CO2 if salt uptake is coupled with water uptake. However, salt concentrations in shoot tissues are similar in plants grown under ambient and elevated CO2 conditions despite major differences in water use efficiency. This phenomenon occurs in C3 halophytes and in both C3 and C4 non-halophytes. These results imply shoot/root communication in regulation of the salt balance to adjust to environmental factors affecting the availability of water and ions at the roots (salinity) and those affecting carbon gain in relation to water loss at the leaves (atmospheric concentrations of water vapour and carbon dioxide).groves, is the maintenance of high water use efficiencies coupled with relatively low rates of water loss A^3144^Increasing atmospheric carbon dioxide concentrations present a novel resource condition for plant communities. In order to understand and predict how plant community structure and function may be altered in a high CO2 world, we need to understand how interactions among neighbouring plants within a community will alter the growth and reproduction of component species. Because CO2 is readily diffusible, plants have little influence on the CO2 acquisition of their neighbours, except within particularly dense canopies. Thus, plants seldom compete directly for CO2. Rather, CO2 availability is likely to alter plant-plant interactions indirectly through its effects on plant growth and competition for other resources. As a consequence, competitive outcome under elevated CO2 atmospheres within even simple systems is not easy to predict. For example, under some conditions, C4 species in competitive assemblages have improved competitive ability relative to C3 competitors as a result of CO2 enrichment, contrary to expectations based on their photosynthetic pathways. It is now clear that individually grown plants can differ substantially from those within mono- or multispecific stands in response to CO2 enrichment. At present, our understanding of how stands of interacting plants modify the availability of CO2 and other resources is incomplete. We urgently need information about how elevated CO2 atmospheres influence stand formation and population dynamics, specifically with regard to the identities, numbers, sizes and reproductive fitnesses of individuals within single and multiple species stands, if we are to make multi-generational predictions concerning the fate of populations and communities in an elevated CO2 world.146^1^Conroy,JP^1992^1^Influence of elevated atmospheric CO2 concentrations on plant nutrition^182^40^4-5^445-456^^^^^^^^^^3147243^245^312^376^386^409^508^682^683^92^s in competitive assemblages have improved competitive ability relative to C3 competitors as a result of CO2 enrichment, contrary tA^3146^The rising levels of atmospheric CO2 are likely to increase biomass production of C3 species in both natural and managed ecosystems because photosynthetic rates will be higher. The greatest absolute increase in productivity will occur when nitrogen and phosphorus availability in the soil is high. Low nitrogen does not preclude a growth response to high CO2, whereas some C3 species fail to respond to high CO2 when phosphorus is low, possibly because insufficient phosphorus is available to maintain maximum photosynthetic activity at high CO2. C3 plants response to high CO2 because the flux of carbon through the photoreductive cycle is increased and photorespiration is suppressed. This change in metabolism appears to alter the foliar nutrient concentration required to promote maximum productivity (critical concentration). Higher phosphorus concentrations are needed at elevated CO2, whereas the nitrogen requirement is reduced by CO2 enrichment. Since critical concentrations are used to evaluate nutrient status of crop and forest species and to manage fertiliser programs, they will need reassessing as the atmospheric CO2 concentration rises. Another consequence of the altered nutrient requirement at high CO2 is that the nitrogen concentrations of foliage, roots and grain are consistently lower in plants grown at elevated CO2, irrespective of availability of nitrogen in the soil. In natural ecosystems, the lower nitrogen to carbon ratio of the litter may alter rates of nutrient cycling. For farmers, the rising CO2 concentrations could cause reductions in grain nitrogen, and therefore protein content. This could have important implications for baking quality of hard wheats as well as affecting the nutrient value of grain such as rice.147^1^Drake,BG^1992^1^A field-study of the effects of elevated CO2 on ecosystem processes in a Chesapeake Bay wetland^182^40^4-5^579-595^^^^^^^^^^3149341^343^344^378^379^684^685^686^687^688^reduced by CO2 enrichment. Since critical concentrations are used to evaluate nutrient sA^3148^Open top chambers are being used in a long-term project to determine the effects of elevated CO2 on ecosystem processes on a Chesapeake Bay wetland. Three communities are studied: mono-specific stands of the C3 sedge, Scirpus olneyi, and the C4 grass, Spartina patens, and a mixed community of these two species and the C4 grass, Distichlis spicata. Treatment began in the spring of 1987 and will continue through the 1994 growing season. During the first 4 years of exposure, elevated CO2 had the following effects on mono-specific stands of the C3 sedge, Scirpus olneyi: increased quantum yield and photosynthetic capacity, reduced dark respiration, increased numbers of shoots, roots and rhizomes, reduced nitrogen concentration of all tissues, increased nitrogen fixation and increased ecosystem carbon accumulation. In a mixed community of the sedge and C4 grass species, Spartina patens and Distichlis spicata, biomass of the C3 component increased over 100% and this was accompanied by decreased biomass in the C4 component of the community. Elevated CO2 reduced water loss, increased water potential and delayed senescence in all three species. Many factors contributed to CO2 stimulated carbon accumulation in the plant community dominated by the C3 sedge, Scirpus olneyi, including: sustained high photosynthetic capacity, decreased respiration, delayed senescence, and allocation of the additional carbon to roots and rhizomes. The complex interaction of these diverse responses suggests that the rising atmospheric CO2 may have a significant impact on ecosystem processes.148^4^Field,CB^Chapin,FS^Matson,PA^Mooney,HA^1992^1^Responses of terrestrial ecosystems to the changing atmosphere - a resource-based approach^27^23^^201-235^35^399^497^689^690^691^692^693^694^695^149^1^Gifford,RM^1992^1^Implications of the globally increasing atmospheric CO2 concentration and temperature for the Australian terrestrial carbon budget - integration using a simple-model^182^40^4-5^527-543^^^^^^^^^^3152nied by decreased biomass in th189^243^360^362^372^407^416^429^57^92^ed CO2 reduced water loss, increased water potential and delayed senescence in all three species. Many factors contributed to CO2 stimulated carbon accumulation in the plant community dominated by the C3 sedge, Scirpus olneyi, including: sustained high photosynthetic capacity, decreased respiration, delayed senescence, and allocation of the additional carbon to roots and rhizomes. The complex interaction of these diverse responses suggests that the rising atmospheric CO2 may have a significant impact on ecosystem processes.148^4^Field,CB^Chapin,FS^Matson,PA^Mooney,HA^1992^1^Responses of terrestrial ecosystems to the changing atmosphere - a resource-based approach^27^23^^201-235^35^399^497^689^690^691^692^693^694^695^149^1^Gifford,RM^1992^1^Implications of the globally increasing atmospheric CO2 concentration and temperature for the Australian terrestrial carbon budget - integration using a simple-model^182^40^4-5^527-543^^^^^^^^^^3152nied by decreased biomass in thA^3151^A simple continentally aggregated model of the Australian terrestrial carbon budget (CQUESTA) integrates information on CO2 and temperature effects and is applied to evaluating whether vegetation is absorbing anthropogenic CO2. Information from the literature is used to parameterise CQUESTA. A standard set of parameters is adopted for exploratory purposes. Historical information is used to describe the average CO2 concentration and temperature over the southern hemisphere from 1750 AD to the present. From the present to 2050 AD the 'business-as-usual' scenario described by the Intergovernmental Panel on Climate Change (IPCC) is applied. The standard parameterisation of the model suggests that the changing CO2 concentration and temperature regime since 1750 AD has been causing continuous net sequestration of carbon into Australian live vegetation and soils. The present modelled rate of net sequestration is of a similar magnitude to CO2 emissions from continental fossil fuel burning and land clearing combined. The rate of sequestration is predicted to continue to increase until 2050 AD and beyond if atmospheric CO2 concentration and temperature continue to increase. However, there remains considerable experimental uncertainty about the correct parameterisation of the model. The findings have implications for policies on greenhouse effect gas emissions.150^4^Hatton,TJ^Walker,J^Dawes,WR^Dunin,FX^1992^1^Simulations of hydroecological responses to elevated CO2 at the catchment scale^182^40^4-5^679-696^^^^^^^^^^3154137^243^639^643^674^696^697^698^699^700^l' scenario described by the Intergovernmental Panel on Climate Change (IPCC) is applied. The standard parameterisation of the model suggests that the changing CO2 concentration and temperature regime since 1750 AD has been causing continuous net sequestration of carbon into Australian live vegetation and soils. The present modelled rate of net sequestration is of a similar magnitude to CO2 emissions from continental fossil fuel burning and land clearing coA^3153^A spatially explicit hydroecological landscape model of water, carbon and energy balances (Topog-IRM) is described. The landscape is envisaged as a catchment forested with a single stratum comprising Eucalyptus maculata trees. The model was used to simulate the direct effects of a 2X elevation in atmospheric carbon dioxide at two levels of nitrogen on catchment water yield, soil moisture status and tree growth, Experimental results used to parameterise the model are detailed. Key features of the model are (1) an ability to scale hydrological processes at the catchment scale in three dimensions, and (2) a means to integrate multiple factors/stresses on plant growth. The effects of CO2 on catchment hydrology (water yield or soil moisture content) and forest growth (expressed as leaf area index, LAI) were modelled for a 2-year period, and contrasted with the effects of added nitrogen. Results were expressed as totals for the catchment or spatially distributed across the catchment. For the total catchment, water yield increased in the order: high CO2 with low N, high CO2 with high N, ambient CO2 with low N, ambient CO2 with high N. LAI increased from 3.3 to 5.7 in the order: ambient CO2 with low N, ambient CO2 with high N, high CO2 with low N, high CO2 with high N. These results agree with previous data. New findings are: (1) with elevated CO2 a new equilibrium in transpiration is established in which leaf area increases offset decreases in stomatal conductance; (2) the addition of nitrogen increases transpiration without any indication of a new equilibrium being reached during the simulated period; (3) the spatial distribution of soil moisture changes, presenting a new resource base for spatial changes to species composition and growth rates. The major hydroecological responses to elevated CO2 are seen as increased maximum upper canopy leaf area, increased litter inputs, especially at times of drought (hence changed fire regimes), changes in the composition of the understorey (hence litter composition, soil microfauna, and the spatial expression of biological diversity) and a slight increase in water yield.151^2^Landsberg,J^Smith,MS^1992^1^A functional scheme for predicting the outbreak potential of herbivorous insects under global atmospheric change^182^40^4-5^565-577^^^^^^^^^^3156312^701^702^703^704^705^92^ndings are: (1) with elevated CO2 a new equilibrium in transpiration is established in which leaf area increases offset decreases in stomatal conductance; (2) the addition of nitrogen increases transpiration without any indication of a new equilibrium being reached during the simulated period; (3) the spatial distribution of soil moisture changes, presenting a new resource base for spatial changes to species composition and growth rates. The major hydroecological responses to elevated CO2 are seen as increased maximum upper canopy leaf area, increased litter inputs, especially at times of drought (hence changed fire regimes), changes in the composition of the understorey (hence litter composition, soilA^3155^There are many possible ways in which changes in the global atmosphere could influence the outbreak potential of herbivorous insects; we clarify these by developing a scheme for analysing insect populations in terms of functional attributes that are both important in population regulation and responsive to global change. This analysis shows that elevated CO2 is not likely to have a major influence on probability of insect outbreak, except possibly in systems in which nitrogen-based defensive compounds are produced by plants in response to herbivory. Systems that will have high potential to outbreak, if climatic conditions become more favourable for plant growth and responses are not constrained by other resources, include those in which both herbivorous insects and host plants have highly flexible growth patterns and activity cues. Global changes that increase environmental stress on host plants are most likely to favour sap-feeding insects. Critical enemy (predator or parasitoid) control of the dormant phase of herbivorous insects may be very important in preventing or allowing outbreaks, but is often poorly understood.152^5^Leishman,MR^Hughes,L^French,K^Armstrong,D^Westoby,M^1992^1^Seed and seedling biology in relation to modeling vegetation dynamics under global climate change^182^40^4-5^599-613^^^^^^^^^^3158174^393^607^706^707^708^709^710^711^92^ted CO2 is not likely to have a major influence on probability of insect outbreak, except possibly in systems in which nitrogen-based defensive compounds are produced by plants in response to herbivory. Systems that will have high potential to outbreak, if climatic conditions become more favourable for plant growth and responses are not constrained by other resources, include those in which both herbivorous insects and host plants have highly flexible growth patterns and activity cues. Global changes that increase environmental stress on host plants are most likely to favour sap-feeding insects. Critical enemy (predator or parasitoid) control of the dormaA^3157^The distribution of many plant species will change with global climate change, depending on their ability to disperse into, and establish in, new communities. Past migrations of species under climate change have been an order of magnitude slower than the rate of predicted climate change for the next century. The limited evidence available suggests that chance long distance dispersal events will be critically important in determining migration rates. We examine the JABOWA-derived gap replacement models and vital attributes/FATE models and ask: what do we need to know about dispersal and establishment to make improved projections of vegetation dynamics under climate change using these models? The minimal modifications of these models required to incorporate directional migration of species are described. To predict establishment success of species, we suggest that a more fundamental understanding is needed of how establishment ability under different conditions relates to seed and seedling attributes and how this may be affected by elevated CO2. Finally, we examine whether plant functional types based on vegetative attributes (used to model the response of adult plants) are correlated with functional types based on seed and seedling attributes. Available evidence suggests that the two sets of attributes are not strongly correlated; consequently, models of vegetation dynamics will need to incorporate seed biology explicitly.153^1^Masle,J^1992^1^Will plant performance on soils prone to drought or with high mechanical impedance to root penetration be improved under elevated atmospheric CO2 concentration?^182^40^4-5^491-500^^^^^^^^^^3160256^312^348^383^546^550^551^641^712^92^ using these models? The minimal modifications of these models required to incorporate directional migration of species are described. To predict establishment success of species, we suggest that a more fundamental understanding is needed of how establishment ability under different conditions relates to seed and seedling attributes anA^3159^Plants growing on dry soils or on soils with high mechanical resistance to root penetration grow more slowly and exhibit lower stomatal conductance than those growing on moist and loose soils. In most situations in nature where edaphic stresses develop rather slowly (compared to stresses imposed in most pot experiments conducted under controlled conditions), photosynthesis is mainly reduced via stomatal effects rather than via changes in mesophyll capacity for photosynthesis. Elevated CO2 will induce an increase in the internal partial pressure of CO2, despite stomatal conductance being lowered even further. Photosynthesis will therefore be improved, and leaf turgor will be increased. It is widely thought that growth on dry or hard soils is not carbon limited because levels of soluble carbohydrates in the leaves and root cells are increased. It is shown in this paper that growth on soil with high mechanical resistance does respond to elevated CO2. However, this response is smaller than expected from the increase of carbon assimilation rate because: (a) carbon partitioning is altered so that supplementary carbohydrates are preferentially allocated to the roots; (b) leaf growth sensitivity to internal availability of sugars is lower than in plants growing on loose soils. These alterations of 'sink activity' and carbon partitioning are mediated by unknown signalling factor(s) induced in the roots. It is not known whether the root factors acting in droughted plants are of the same nature. In both droughted and impeded plants the interacting effects of these factors and of ambient CO2 levels are likely to result in improved transpiration efficiency. More experiments are needed in this area, however, especially to ascertain the relative contribution of changes in growth patterns versus changes in the patterns of water use. In conclusion, the importance of identifying the nature of the sink limitations induced by root signals is emphasised. It is a fundamental area of research to be developed not only for assessing growth responses to rising CO2 under edaphic stress, but likely also for reconciling conflicting responses of field- grown and pot-grown plants.154^4^McMurtrie,RE^Comins,HN^Kirschbaum,MUF^Wang,YP^1992^1^Modifying existing forest growth-models to take account of effects of elevated CO2^182^40^4-5^657-677^^^^^^^^^^3162130^243^494^58^713^714^715^716^717^718^ing factor(s) induced in the roots. It is not known whether the root factors acting in droughted plants are of the same nature. In both droughted and impeded plants the interacting effects of these factors and of ambient CO2 levels are likely to result in improved transpiration efficiency. More experiments are needed in this area, however, especially to ascertain the relative contribution of changes in growth patterns versus changes in the patterns of water use. In conclusion, the importance of identifying the nature of the sink limitations induced by root signals is emphasised. It is a fundamental area of research to be developed not only for assesA^3161^Most published process models of the growth of forest stands are concerned predominantly with either tree physiology or nutrient cycling, concentrating respectively on photosynthetic carbon gain and allocation, or on decomposition and nutrient uptake processes. Mechanistic formulations of direct CO2 effects on photosynthesis have been incorporated in some physiology-based models, whereas modifications incorporating direct CO2 effects in nutrient-driven models have usually been more empirical. Physiology-based models predict considerable CO2-fertiliser effects, while nutrient driven models tend to be less sensitive to elevated ambient CO2 concentration (C(a)). This paper describes how effects of elevated C(a) can be incorporated in these various types of forest growth models. The magnitude of the simulated response to elevated C(a) varies markedly depending on a particular model's spatial and temporal resolution and on which processes are incorporated. Two physiology-based models of forest canopy processes (MAESTRO and BIOMASS) and a plant-soil model (G'DAY) are considered here. MAESTRO and BIOMASS incorporate mechanistic descriptions of the biochemical basis of photosynthesis by C3 plants, while G'DAY contains a simplified formulation but includes soil processes. All three models are used to simulate the response to an instantaneous doubling of C(a). Simulations of MAESTRO and BIOMASS show that on a clear day total canopy photsynthesis is temperature-dependent with increases of approximately 10, 45 and 70% at 10. 25 and 40-degrees-C respectively. A simulation for a stand of Pinus radiata growing with abundant water and nutrients and mean annual day-time temperature of 14.8-degrees-C shows an increase of 25% in annual canopy photosynthesis. On nutrient-limited sites plant responses to elevated C(a) are constrained by feedbacks associated with rates of decomposition and nutrient cycling. According to the G'DAY model, which incorporates these feedbacks, an instantaneous doubling of C(a) leads to a 27% initial productivity increase lasting less than a decade and a more modest increase of 8% sustained in the long term.155^1^Nederhoff,EM^1992^1^Effects of CO2 on greenhouse grown eggplant (solanum-melongena L) .1. Leaf conductance^174^67^6^795-803^^^^^Nov^^^^^3164348^374^376^383^546^719^720^sed to simulate the response to an instantaneous doubling of C(a). Simulations of MAESTRO and BIOMASS show that on a clear day total canopy photsynthesis is temperature-dependent with increases of approximately 10, 45 and 70% at 10. 25 and 40-degrees-C respectively. A simulation for a stand of Pinus radiata growing with abundant water and nutrients and mean annual day-time temperature of 14.8-degrees-C shows an increase of 25% in annual canopy photosynthesis. On nutrient-limited sites plant responses to elevated C(a) are constrained by feedbacks associated with rates of decomposition and nutrient cycling. According to the G'DAY model, which incorporates these feedbacks, an instantaneous doubling of C(a) leads to a 27% initiA^3163^Leaf conductance of eggplant (Solanum melongena L., cv. Cosmos) was measured comparatively in two glasshouse compartments, with continuously low or high CO2 (on average 415 or 685 mumol mol-1, respectively). Measurements were carried out on eight days between February and June 1991 in an early planted crop. A regression equation was fitted to the data to account for the effects of PAR, air humidity and CO2 on leaf conductance. Calculations with this equation demonstrated that leaf conductance was reduced by 10.2% per 100 mumol mol-1 increase in CO2, which is a three to four times stronger response than in other fruit vegetable crops. When, on some occasional days, CO2 was kept equal in the two compartments, leaf conductance was not different, indicating that stomatal behaviour had not adapted to long lasting CO2 conditions. The rate of crop transpiration, as estimated with the Penman-Monteith combination equation, was reduced by elevated CO2 by only a few percent on average and by about 15% in a period of some weeks in spring.156^5^Nie,D^Kirkham,MB^Ballou,LK^Lawlor,DJ^Kanemasu,ET^1992^1^Changes in prairie vegetation under elevated carbon-dioxide levels and 2 soil-moisture regimes^42^3^5^673-678^^^^^Dec^^^^^3166surements were carried out on eight days between February and June 1991 in an early planted crop. A regression equation was fitted to the data to account for the effects of PAR, air humidity and CO2 on leaf conductance. Calculations with this equation demonstrated that leaf conductance was reduced by 10.2% per 100 mumol mol-1 increase in CO2, which is a three to four times stronger response than in other fruit vegetable crops. When, on some occasional days, CO2 was kept equal in the two compartments, leaf conductance was not different, indicating that stomatal behaviour had not adapted to long lasting CO2 conditions. The rate of crop transpiration, as estimated with the Penman-Monteith combination equation, was reduced by elevated CO2 by only a few percent on average and by about 15% in a perioA^3165^It is important to know how increasing levels of atmospheric CO2 will affect native vegetation. The objective of this study was to determine the effect of elevated CO2 concentrations on species composition in a tallgrass prairie kept at a high water level (730 mm of water in a 2000 mm soil profile) and a low water level (660 mm of water in 2000 mm). 16 cylindrical plastic chambers were placed on the prairie to maintain two levels of CO2 (ambient or twice ambient) during two growing seasons in 1989 and 1990. Frequency of species was determined on 25 July 1989 and on 5 and 10 October 1990. At the beginning of the study, Poa pratensis (Kentucky bluegrass), the dominant C3 species, had the highest frequency of 43.3%, but decreased with time. However, at the end of the experiment and under the high soil-water level, there were more P. pratensis plants in the elevated CO2 treatment (frequency: 13.5%) than in the ambient CO2 treatment (1.0%). Under the low soil water regime, the reverse occurred (frequencies: 3.6 % and 11.0 % for high and low CO2, respectively). The frequency of major C4 plants, Andropogon gerardii (big bluestem), A. scoparius (little bluestem) and Sorghastrum nutans (Indian grass) was not affected by CO2. However, water did affect their frequency. Under low water, the frequency of A. gerardii decreased between 1989 and 1990. Under both soil moisture levels, the frequencies of S. nutans and A. scoparius increased. At the end of the study, Indian grass grown with high water had the highest frequency of all species on the prairie (frequency at the end of the study in October, 1990, of 44.4% and 47.4% for the high and low CO2 levels, respectively). Unlike Indian grass, little bluestem grew better under low water conditions than under high water conditions. These results suggest that, if the climate becomes drier, A. scoparius will flourish more than S. nutans or A. gerardii, and P. pratensis may die out. Elevated CO2 might not increase survival of C3 Plants under dry conditions, if temperatures are too high for them.157^4^Poorter,H^Gifford,RM^Kriedemann,PE^Wong,SC^1992^1^A quantitative-analysis of dark respiration and carbon content as factors in the growth-response of plants to elevated CO2^182^40^4-5^501-513^^^^^^^^^^3168130^243^346^376^434^506^529^57^721^722^ater, the frequency of A. gerardii decreased between 1989 and 1990. Under both soil moisture levels, the frequencies of S. nutans and A. scoparius increased. At the end of the study, Indian grass grown with high water had the highest frequency of all species on the prairie (frequency at the end of the study in October, 1990, of 44.4% and 47.4% for the high and low CO2 levels, respectively). Unlike Indian grass, little bluestem grew better under low water conditions than under high water conditions. These results suggest that, if the climate becomes drier, A. scoparius will flourish more than S. nutans or A. gerardii, and P. pratensis may die out. Elevated CO2 might not increase survival of C3 Plants under dry conditions, if temperatures arA^3167^An analysis of elevated CO2 effects (2-4 times ambient) on dark respiration rate and carbon content was undertaken for a wide range of plant species, using both published reports and new data. On average, leaf respiration per unit leaf area was slightly higher for plants grown at high CO2 (16%), whereas a small decrease was found when respiration was expressed on a leaf weight basis (14%). For the few data on root respiration, no significant change due to high CO2 could be detected. Carbon content of leaves and stem showed a small increase (1.2 and 1.7% respectively), whereas C-content of roots was not significantly affected. In both data sets direction of responses was variable. A sensitivity analysis of carbon budgets under elevated CO2 identified changes in respiration rate, and to a lesser extent carbon content, as important factors affecting the growth response to elevated CO2 in quite a number of cases. Any comprehensive analysis of growth responses to increased CO2 should therefore include measurements of these two variables.158^1^Rawson,HM^1992^1^Plant-responses to temperature under conditions of elevated CO2^182^40^4-5^473-490^^^^^^^^^^3170341^344^402^435^508^542^558^723^724^725^ata. On average, leaf respiration per unit leaf area was slightly higher for plants grown at high CO2 (16%), whereas a small decrease was found when respiration was expressed on a leaf weight basis (14%). For the few data on root respiration, no significant change due to high CO2 could be detected. Carbon content of leaves and stem showed a small increase (1.2 and 1.7% respectively), whereas C-content of roots was not significantly affected. In both data sets direction of responses was variable. A sensitivity analysis of carbon budgets under elevated CO2 identified changes in respiration rate, and to a lesser extent carbon content, as important factors affecting the growth response to elevated CO2 in quite a number of cases. Any comprehensive analysis of growth responses to increased CO2 should therefore include measA^3169^A literature survey of the interactive effects of CO2 enrichment and temperature on plant development and growth, indicated that the responses cannot be interpreted within a simple framework. For example, although plant development is generally accelerated by increased temperature, CO2 enrichment can accelerate it even further in some instances, or CO2 enrichment may have neutral or even retarding effects in other cases. Where the temperature and CO2 effects are additive, it is argued that CO2 is operating in the same way as radiation to reduce a carbon limitation. If this were true, CO2 enrichment would be most likely to accelerate development in tropical regions during the low-radiation monsoon season. Similarly, while it would be expected that CO2-enrichment would have increasingly enhancing effects with increasing temperature on phytomass growth, this is not invariably the case. In extreme examples which followed the expected trend, plants grown in twice-normal CO2-enriched atmospheres performed progressively better than those grown at current levels of CO2 by 8.7% for every 1-degrees-C rise in temperature. However, the difference between the two CO2 treatments more commonly increased by only around 2% for every 1-degrees-C rise in temperature. Of examples examined, both sunflower and nodulated cowpea showed the reverse response to temperature, while non-nodulated cowpea, supplied with luxuriant levels of nutrition, showed no interaction with temperature but a strong interaction between CO2 and radiation. Other aspects of the environment such as nutrition and radiation strongly modify the responses to temperature. It is also clear that plant factors such as stage of development can alter the response to CO2. Long-term studies with several species are required which will take into account many environmental variables within a realistic envelope. One methodology for doing this is presented. There was no evidence among species that responses to CO2 arise through any consistent change in morphology such as via increased branching or increased leaf number. Plant plasticity is such that responses can be expressed in a variety of ways determined by other environmental variables.159^2^Rochefort,L^Bazzaz,FA^1992^1^Growth-response to elevated CO2 in seedlings of 4 cooccurring birch species^155^22^11^1583-1587^^^^^Nov^^^^^3172342^345^376^547^57^669^705^, while non-nodulated cowpea, supplied with luxuriant levels of nutrition, showed no interaction with temperature but a strong interaction between CO2 and radiation. Other aspects of the environment such as nutrition and radiation strongly modify the responses to temperature. It is also clear that plant factors such as stage of development can alter the response to CO2. Long-term studies with several species are required which will take into account many environmental variables within a realistic envelope. One methodology for doing this is presented. There was no evidence among species that responses to CO2 arise through any consistent change in morphology such A^3171^Seedlings of four birch species were examined to evaluate the presence and extent of phylogenetic constraints on the response of species to global CO2 change. The species differ in their habitat preferences and their successional status. Seedlings were grown for 3 months at near ambient (380 muL L-1) and double (690 muL L-1) CO2 concentrations in glasshouses. We found the following: (i) yellow birch (Betula alleghaniensis Britton) was the only species whose survival differed among CO2 treatments. Survival was slightly increased by elevated CO2. (ii) All growth parameters considered in all four species were significantly stimulated by enriched CO2 Conditions, but the magnitude of response was different among species. The most shade-intolerant, fast-growing species (grey birch; Betula populifolia Marsh.) took greater advantage of the elevated CO2 resource than the more shade-tolerant, later successional species (e.g., yellow birch). (iii) Patterns of allocation, shoot architecture, and leaf nitrogen content were affected differently by CO2 concentrations for the different species. (iv) The presence and identity of a neighbor did not influence the magnitude or pattern of response to CO2 in birches of a given community. Our results suggest that congeneric species might be more similar in their response to global CO2 in comparison to unrelated species of the same ecosystem that had been studied by others, despite the fact that these closely related birch species differ in their habitat preferences and successional status.160^3^Wong,SC^Kriedemann,PE^Farquhar,GD^1992^1^CO2 X nitrogen interaction on seedling growth of 4 species of eucalypt^182^40^4-5^457-472^^^^^^^^^^3174243^312^376^417^698^726^727^different among species. The most shade-intolerant, fast-growing species (grey birch; Betula populifolia Marsh.) took greater advantage of the elevated CO2 resource than the more shade-tolerant, later successional species (e.g., yellow birch). (iii) Patterns of allocation, shoot architecture, and leaf nitrogen coA^3173^Four eucalypt species were selected to represent two ecologically disparate groups which would be expected to contrast in seedling vigour and in the nature of growth responses to CO2 X nitrogen supply. Eucalyptus camaldulensis and E. cypellocarpa were taken as examples of fast-growing species with a wide distribution, that develop into large trees. By contrast, E. pauciflora and E. pulverulenta become smaller trees, and show a more limited distribution. Seedlings were established in pots (5 L) of a loamy soil and supplied with nutrient solution containing either 1.2 or 6.0 mM NO3- in both ambient (33 Pa) and CO2-enriched (66 Pa) greenhouses. Analysis of growth response to treatments (2 X 2 factorial) was based on destructive harvest of plants sampled on four occasions over 84 days for E. camaldulensis and E. cypellocarpa, and 100 days for E. pulverulenta and E. pauciflora. A positive CO2 X N interaction on plant dry mass and leaf area was expressed in all species throughout the study period. In E. camaldulensis and E. cypellocarpa, plant mass was doubled by high N at 33 Pa CO2, compared with a three to four- fold increase at 66 Pa to reach 34 g by final harvest. In E. pulverulenta and E. pauciflora, slower growth resulted in about 50% less mass at a given age, but relative increases due to CO2 and N were of a similar order. A distinction can be made between N and CO2 effects on growth processes as follows. When trees were grown on low N, elevated CO2 increased nitrogen-use efficiency (NUE) at both leaf and whole plant levels. On high N, leaf NUE was increased in E. camaldulensis and E. cypellocarpa, but decreased in E. pulverulenta and E. pauciflora. Whole plant NUE showed no consistent response to elevated CO2 when plants were supplied high N. Net assimilation rate (NAR) was increased by elevated CO2 in all species on either N treatment. Moreover, high N increased NAR under either CO2 treatment in all species. There was a positive N X CO2 interaction on NAR in E. camaldulensis and E. cypellocarpa, but not in E. pulverulenta and E. pauciflora. Growth indices for E. camaldulensis and E. cypellocarpa species, and especially E. camaldulensis, generally exceeded those for E. pulverulenta and E. pauciflora in terms of NAR, leaf NUE, N-enhancement of CO2 effects on leaf area and biomass, and non-structural carbohydrate content of foliage.161^2^Wullschleger,SD^Norby,RJ^1992^1^Respiratory cost of leaf growth and maintenance in white oak saplings exposed to atmospheric co2 enrichment^155^22^11^1717-1721^^^^^Nov^^^^^3176705^nt levels. On high N, leaf NUE was increased in E. camaldulensis and E. cypellocarpa, but decreased in E. pulverulenta and E. pauciflora. Whole plant NUE showed no consistent response to elevated CO2 when plants were supplied high N. Net assimilation rate (NAR) was increased by elevated CO2 in all species on either N treatment. Moreover, high N increased NAR under either CO2 treatment in all species. There was a positive N X CO2 interaction on NAR in E. camaldulensis and E. cypellocarpa, but nA^3175^Atmospheric CO2 enrichment reportedly reduces respiration of mature leaves in a number of woody and herbaceous perennials. It has vet to be determined, however, whether these reductions reflect changes in maintenance respiration alone or whether CO2 might affect growth respiration as well. This possibility was examined in white oak (Quercus alba L.) seedlings that had been planted directly into the ground within open-top chambers and exposed to ambient, ambient + 150 muL.L-1, and ambient + 300 muL.L-1 CO2 concentrations over a 3-year period. In the spring of 1992, respiration rates were measured repeatedly during leaf expansion, and the growth and maintenance coefficients were determined using a two-component model. Specific respiration rates (mg CO2.g-1.h-1) were consistently lower for leaves of CO2 enriched saplings than for leaves of ambient-grown saplings. Partitioning these reductions in leaf respiration to either the growth or maintenance coefficients indicated a strong effect of CO2 on both components. The growth coefficient for leaves exposed to the ambient CO2 treatment was 964 Mg CO2.g-1 compared with 849 and 664 mg CO2.g-1 for leaves from the two elevated CO2 concentrations, respectively. The maintenance coefficient was similarly reduced from a control rate of 114 mg CO2.g-1 d-1 to below 65 mg CO2.g-1.d-1 for leaves exposed to CO2 enrichment. Our results quantitatively describe the magnitude by which growth and maintenance respiration are affected by CO2 enrichment and as such should provide useful information for the future modeling of this phenomenon.162^5^Abdullaev,AA^Dzhumaev,BB^Abdurakhmanova,ZN^Kaler,VL^Magmedov,IM^1992^1^Integral effect of environmental-factors on photosynthetic metabolism of carbon in cotton leaves^168^39^2^140-144^^^^^Mar-Apr^^^^^3178422^y lower for leaves of CO2 enriched saplings than for leaves of ambient-grown saplings. Partitioning these reductions in leaf respiration to either the growth or maintenance coefficients indicated a strong effect of CO2 on both comA^3177^We used the method of mathematical experiment planning (a 2(3) scheme) to study the influence of environmental factors separately or in combination on the photosynthetic rate and distribution of C-14 among products of photosynthetic carbon metabolism in the cotton (Gossypium hirsutum L.) leaf Increase of light intensity during cultivation accelerated photosynthesis and stimulated incorporation of C-14 into phosphoglyceric acid (PGA), sugar diphosphate (SDP), fructose monophosphate (FMP), and malate, but suppressed incorporation of C-14 into sucrose, glucose monophosphate (GMP), and glycerate. Temperature increase by itself and in any combination with other factors at the upper level suppressed photosynthesis. Elevated temperature increased accumulation of the label in PGA, sucrose, and malate, but lowered it in GMP, alanine, glycine, and serine. Growing plants at enhanced CO2 concentration led to acceleration of photosynthesis and increase of the share of C-14 in SDP, GMP, and malate, but decrease of it in sucrose, alanine, glycine, and serine. Very perceptible effects of interaction are discernible in different combinations of factors. All three factors at the upper level appreciably induced activity of phosphoenolpyruvate carboxylase (PEPCase) in cotton leaves.163^4^Allen,LH^Drake,BG^Rogers,HH^Shinn,JH^1992^1^Field techniques for exposure of plants and ecosystems to elevated co-2 and other trace gases^183^11^2-3^85-119^364^378^379^456^688^728^729^730^731^732^164^1^Bunce,JA^1992^1^Light, temperature and nutrients as factors in photosynthetic adjustment to an elevated concentration of carbon-dioxide^37^86^1^173-179^^^^^Sep^^^^^3181174^343^348^374^376^417^442^529^92^he upper level suppressed photosynthesis. Elevated temperature increased accumulation of the label in PGA, sucrose, and malate, but lowered it in GMP, alanine, glycine, and serine. Growing plants at enhanced CO2 concentration led to acceleration of photosynthesis and increase of the share of C-14 in SDP, GMP, and malate, but decrease of A^3180^The short-term stimulation of the net rate of carbon dioxide exchange of leaves by elevated concentrations of CO2 usually observed in C3 plants sometimes does not persist. Experiments were conducted to test whether the patterns of response to the environment during growth were consistent with the hypotheses that photosynthetic adjustment to elevated CO2 concentration is due to (1) feedback inhibition or (2) nutrient stress. Soybean [Glycine max (L.) Merr. cv. Williams] and sugar beet (Beta vulgaris L. cv. Mono Hye-4) were grown from seed at 350 and 700 mul l-1 CO2, at 20 and 25-degrees-C, at a photon flux density of 0.5 and 1.0 mmol m-2 s-1 and with three nutrient regimes until the third trifoliolate leaf of soybean or the sixth leaf of sugar beet had finished expanding. Net rates Of CO2 exchange of the most recently expanded leaves were then measured at both 350 and 700 mul l-1 CO2. Plants grown at the elevated CO2 concentration had net rates of leaf CO2 exchange which were reduced by 33% in sugar beet and 23% in soybean when measured at 350 mul l-1 CO2 and when averaged over all treatments. Negative photosynthetic adjustment to elevated CO2 concentration was not greater at 20 than at 25-degrees-C, was not greater at a photon flux density of 1.0 than at 0.5 mmol M- 2 s-1 and was not greater with limiting nutrients. Furthermore, in soybean, negative photosynthetic adjustment could be induced by a single night at elevated CO2 concentration, with net rates of CO2 exchange the next day equal to those of leaves of plants grown from seed at the elevated concentration Of CO2. These patterns do not support either the feedback-inhibition or the nutrient-stress hypothesis of photosynthetic adjustment to elevated concentrations of CO2.165^2^Curtis,PS^Teeri,JA^1992^1^Seasonal responses of leaf gas-exchange to elevated carbon- dioxide in populus-grandidentata^155^22^9^1320-1325^^^^^Sep^^^^^3183131^342^343^345^348^360^426^456^512^673^tration had net rates of leaf CO2 exchange which were reduced by 33% in sugar beA^3182^Rising atmospheric carbon dioxide concentrations may have important consequences for forest ecosystems. We studied above- and below-ground growth and leaf gas exchange responses of Populus grandidentata Michx. to elevated CO2 under natural forest conditions over the course of a growing season. Recently emerged P. grandidentata seedlings were grown in native, nutrient-poor soils at ambient and twice ambient (707 mubar (1 bar = 100 kPa)) CO2 partial pressure for 70 days in open-top chambers in northern lower Michigan. Total leaf area and shoot and root dry weight all increased in high CO2 grown plants. Photosynthetic light and CO2 response characteristics were measured 28, 45, and 68 days after exposure to elevated CO2. In ambient grown plants, light saturated assimilation rates increased from day 28 to day 45 and then declined at day 68 (15 September). This late-season decline, typical of senescing Populus leaves, was due both to a decrease in the initial slope of the net CO2 assimilation versus intercellular CO2 Partial pressure relationship and to decreased CO2 saturated assimilation rates. Specific leaf nitrogen (mg N . (cm2 leaf area)-1) did not change during this period, although leaf carbon content and leaf weight (mg . cm-2) both increased. In ambient grown plants stomatal conductance also declined at day 68. In contrast, plants grown at elevated CO2 showed no late- season decline in photosynthetic capacity or changes in leaf weight, suggesting a delay in senescence with long-term exposure to high CO2. High CO2 grown plants also maintained photosynthetic sensitivity to increasing C(i) throughout the exposure period, while ambient CO2 grown plants were insensitive to C(i) above 400 mubar on day 68. These results indicate the potential for direct CO2 fertilization of P. grandidentata in the field and provide evidence for a new mechanism by which elevated atmospheric CO2 could influence seasonal carbon gain.es, was due both to a decrease in the initial slope of the net CO2 assimilation versus interc166^1^Hendrey,GR^1992^1^Global greenhouse studies - need for a new approach to ecosystem manipulation^183^11^2-3^61-74^130^189^243^264^312^374^376^660^733^92^167^6^Hileman,DR^Bhattacharya,NC^Ghosh,PP^Biswas,PK^Lewin,KF^Hendrey,GR^1992^1^Responses of photosynthesis and stomatal conductance to elevated carbon-dioxide in field-grown cotton^183^11^2-3^227-231^349^408^417^734^735^736^91^168^2^Leadley,PW^Reynolds,JF^1992^1^Long-term response of an arctic sedge to climate change - a simulation study^56^2^4^323-340^^^^^Nov^^^^^3187130^243^30^312^417^691^737^738^739^92^nsitivity to increasing C(i) throughout the exposure period, while ambient CO2 grown plants were insensitive to C(i) above 400 mubar on day 68. These results indicate the potential for direct CO2 fertilization of P. grandidentata in the field and provide evidence for a new mechanism by which elevated atmospheric CO2 could influence seasonal carbon gain.es, was due both to a decrease in the initial slope of the net CO2 assimilation versus intercA^3186^It appears that polar regions of the Ear-th will bear the brunt of global temperature increases. Because of the ecological importance of the sedge Eriophorum vaginatum in the arctic and the large amount ot data available on its growth and physiology, we chose this species as a test case to model the potential long-term response of arctic plants to global climate change. Our simulation model utilizes a mechanistic framework and includes the effects of light, temperature, season length, nitrogen availability, and CO2 concentration on E. vaginatum growth dynamics. The model was parameterized based on a series of published studies of the growth responses of E. vaginatum to nutrients and validated using (1) field studies on the growth responses of E. vaginatum to temperature and shading, and (2) the effects of elevated CO2 and temperature on E. vaginatum photosynthesis. The effect of a 50-yr period of climate change on peak biomass (overwintering biomass plus seasonal production) in E. vaginatum was explored. We use climate change here to refer to linear increases over a 50-yr period in temperature (from 8-degrees to 13-degrees-C), season length (from 100 to 120 d), and atmospheric CO2 (from 340 to 680 muL/L). Similarly, a wide range of nitrogen availabilities (from 9 to 18 g.m 2.vr-1) was also examined because of its importance in productivity. The model predicts that a simultaneous increase in the direct effects of temperature, season length, and CO2, with no change in nitrogen availability, will result in a slight decrease in peak biomass. A simulated long-term doubling of nitrogen availability results in an almost-equal-to 70% increase in peak biomass, whereas with concurrent changes in climate and nitrogen availability, the model predicts a slight decline in peak biomass compared to increases in nitrogen alone. In essence, the model predicts that climate change will have substantial effects on E. vaginatum only indirectly through changes in nitrogen availability. Simulated peak biomass responds linearly up to a doubling of current nitrogen availabilities. Therefore, at low- to-moderate increases in nitrogen availability, the predicted response of E. vaginatum to climate change is linearly (and almost exclusively) dependent on our ability to predict the effects of climate change on nitrogen cycling. At nitrogen availabilities > 2 x current availabilities, the relationship flattens out very rapidly because the plant becomes limited by carbon uptake. Thus, if nitrogen availabilities more than double in the future, E. vaginatum may shift from being a nutrient-limited to a carbon-limited system and, consequently, increased season length and elevated CO2 concentrations may play an important role in controlling E. vaginatum productivity.169^5^Nie,D^He,H^Mo,G^Kirkham,MB^Kanemasu,ET^1992^1^Canopy photosynthesis and evapotranspiration of rangeland plants under doubled carbon-dioxide in closed-top chambers^107^61^3-4^205-217^^^^^Oct^^^^^3189508^740^n nitrogen availability. Simulated peak biomass responds linearly A^3188^It is important to know how the increasing atmospheric concentration of carbon dioxide (CO2) will affect growth of agricultural plants. The objective of this study was to determine the effect of elevated CO2 on canopy photosynthetic rate of prairie (rangeland) plants growing under natural field conditions. The dominant plants were warm-season grasses with the C4 type of photosynthesis. Sixteen closed-top, cylindrical, plastic chambers (1.5 m in diameter; 1.8 m tall) were placed on the prairie to maintain two levels of CO2 (ambient and twice ambient) over a full growing season in 1990. The soil (silty clay loam) was kept at a high water (field capacity) or a low water level (no water added). Carbon dioxide concentration, air temperature, net radiation, canopy photosynthetic rate, and canopy evapotranspiration rate were measured in the 16 chambers on 49 sunny days during the season. The target value for high- CO2 chambers was 720 cm3 CO2 m-3; the measured mean concentrations varied from 710.8 to 720.1 cm3 CO2 m-3. For chambers with ambient CO2, the chamber-to-chamber variation was minor, with mean values ranging from 350.8 to 356.0 cm3 CO2 m- 3. Daytime air temperatures at 100 cm aboveground in the chambered plots averaged 2.7-degrees-C warmer than outside. Early in the season, net radiation was usually similar among chambers with the different CO2 and water treatments, but late in the season, differences occurred among chambers, possibly because of the amount of tall grasses that shaded the radiometers. Under the high-water treatment, canopy photosynthesis of plants grown with doubled and ambient CO2 averaged 41.8 mumol m-2 s-1 and 44.5 mumol m-2 s-1, respectively. These results are consistent with previous findings, which showed that the photosynthetic rate of C4 plants on rangeland was not augmented when the CO2 concentration was increased. Under the low-water treatment, photosynthesis of plants grown with doubled CO2 was slightly more (36.9 mumol m-2 s-1) than that of plants grown with ambient CO2 (31.7 mumol m-2 s-1). This observation is in agreement with other results, which have shown that high CO2 alleviates water-stress effects on plants. Elevated CO2 reduced canopy evapotranspiration rate by 18 and 8%, under the high- and low-water levels, respectively. The results suggested that, as the CO2 concentration in the atmosphere increases, water lost from rangelands will be reduced.170^4^Pennanen,A^Kemppi,V^Lawlor,D^Pehu,E^1992^1^The effect of elevated co2 on photosynthesis and chloroplast thylakoid structure of crop plants^91^34^1^243^^^^^Oct171^2^Pettersson,R^McDonald,AJS^1992^1^Effects of elevated carbon-dioxide concentration on photosynthesis and growth of small birch plants (betula-pendula roth) at optimal nutrition^9^15^8^911-919^^^^^Oct^^^^^3192348^361^376^399^434^664^692^741^742^743^nted when the CO2 concentration was increased. Under the low-water treatment, photosynthesis of plants grown with doubled CO2 was slightly more (36.9 mumol m-2 s-1) than that of plants grown with ambient CO2 (31.A^3191^Small birch plants (Betula Pendula Roth.) were grown from seed for periods of up to 70 d in a climate chamber at optimal nutrition and at present (350 mumol mol-1)or elevated (700 mumol mol-1) concentrations of atmospheric CO2. Nutrients were sprayed over the roots in Ingestad-type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO2, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO2 had higher starch concentrations (dry weight basis) than leaves grown at present levels Of CO2. Biomass allocation showed no change with CO2, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO2. No large difference in the response of carbon assimilation to intercellular CO2 concentration (A/C(i) curves) were found between CO2 treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO2 than in plants grown at present CO2. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO2. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum growth, small birch plants may potentially increase in size more rapidly at elevated CO2.172^3^Polley,HW^Johnson,HB^Mayeux,HS^1992^1^Growth and gas-exchange of oats (avena-sativa) and wild mustard (brassica-kaber) at subambient co2 concentrations^104^153^3^453-461^^^^^Sep^^^^^3194344^348^372^374^399^430^442^685^744^745^ion to intercellular CO2 concentration (A/C(i) curves) were found between CO2 treatments. When measured at the growth envirA^3193^A repeated sequence of monocultures and mixtures of oats (A vena sativa L.) and wild mustard (Brassica kaber (DC.) Wheeler) was grown along a daytime gradient of CO2 concentrations ([CO2]) from near 330 to a minimum of 150 mumol mol-1. The objectives were to determine effects of subambient [CO2] on leaf gas exchange, biomass production, and competitive interactions of these C3 species. A decrease in stomatal conductance did not prevent a nearly linear increase in leaf internal [CO2] and net assimilation of oat leaves as [CO2] increased. Net assimilation of oats and wild mustard increased from 5.0 and 2.5 mumol m-2 s-1 at 150 mumol mol-1, respectively, to 16.1 and 15.9 mumol m-2 s-1 at 330 mumol mol-1 CO2, respectively, when measured at 1,200-1,500 mumol m-2 s-1 incident light. Aboveground biomass per plant of wild mustard and oats increased 106% and 198%, respectively, and leaf area rose more than two- and threefold, respectively, from 154 to 331 mumol mol-1 CO2. The CO2-induced increase in aboveground biomass of plants of each species did not vary among monocultures and mixtures. Responses of oats and wild mustard to higher subambient [CO2] were large relative to reported responses of C3 species to comparable increases above the current atmospheric [CO2]. This suggests that past changes in atmospheric [CO2], including the 27% rise since the beginning of the nineteenth century, may have profoundly altered the productivity of C3 plants.173^3^Radoglou,KM^Aphalo,P^Jarvis,PG^1992^1^Response of photosynthesis, stomatal conductance and water-use efficiency to elevated co2 and nutrient supply in acclimated seedlings of phaseolus-vulgaris L^52^70^3^257-264^^^^^Sep131^224^348^355^376^377^441^739^746^92^174^2^Radoglou,KM^Jarvis,PG^1992^1^The effects of co2 enrichment and nutrient supply on growth- morphology and anatomy of phaseolus-vulgaris L seedlings^52^70^3^245-256^^^^^Sep229^243^348^377^417^526^664^746^747^748^reefold, respectively, from 154 to 331 mumol mol-1 CO2. The CO2-induced increase in abovegroun175^6^Reynolds,JF^Chen,JL^Harley,PC^Hilbert,DW^Dougherty,RL^Tenhunen,JD^1992^1^Modeling the effects of elevated co2 on plants - extrapolating leaf response to a canopy^107^61^1-2^69-94^^^^^Sep^^^^^3198227^243^245^312^376^423^508^57^672^92^ atmospheric [CO2]. This suggests that past changes in atmospheric [CO2], including the 27% rise since the beginning of the nineteenth century, may have profoundly altered the productivity of C3 plants.173^3^Radoglou,KM^Aphalo,P^Jarvis,PG^1992^1^Response of photosynthesis, stomatal conductance and water-use efficiency to elevated co2 and nutrient supply in acclimated seedlings of phaseolus-vulgaris L^52^70^3^257-264^^^^^Sep131^224^348^355^376^377^441^739^746^92^174^2^Radoglou,KM^Jarvis,PG^1992^1^The effects of co2 enrichment and nutrient supply on growth- morphology and anatomy of phaseolus-vulgaris L seedlings^52^70^3^245-256^^^^^Sep229^243^348^377^417^526^664^746^747^748^reefold, respectively, from 154 to 331 mumol mol-1 CO2. The CO2-induced increase in abovegrounA^3197^The response of canopies to short-duration exposure to elevated CO2 was examined by using a detailed submodel of single-leaf ps exchange combined with a model of canopy structure and light penetration. The leaf model included a mechanistic ps exchange model and leaf energy balance equations, and the canopy model included a detailed description of spatial variability in environmental conditions within the canopy. The structure of the canopy model was designed to facilitate implementation of different leaf aggregation schemes. To compare six aggregation methods of increasing simplicity, daily carbon gain, and water use were simulated for Quercus coccifera under current ambient and future doubled CO2. Analyses of simulated canopy responses confirmed the importance of including (1) leaf energy balance and (2) distinguishing between sunlit and shaded leaves. A multi-layer canopy model with Gaussian integration for sunlit leaves and a single leaf class for shaded leaves in each layer gave excellent results. A multi-layer model with one shaded and one sunlit leaf class gave a reasonable approximation, and the single-layer model with one sunlit and one shaded leaf class resulted in errors of up to 15%. Vertical gradients in leaf nitrogen content and leaf and stem area index had greater effects on canopy assimilation and transpiration than did gradients of stem or leaf inclination or leaf width. However, predictions of the relative response of CO2 assimilation and transpiration to doubled CO2 are rather robust and were not greatly affected by simplifications of the canopy model.176^3^Ryle,GJA^Powell,CE^Davidson,IA^1992^1^Growth of white clover, dependent on n2 fixation, in elevated co2 and temperature^52^70^3^221-228^^^^^Sep230^243^310^312^376^57^632^177^4^Ryle,GJA^Woledge,J^Tewson,V^Powell,CE^1992^1^Influence of elevated co2 and temperature on the photosynthesis and respiration of white clover dependent on n2 fixation^52^70^3^213-220^^^^^Sep230^348^376^377^384^57^749^750^ each layer gave excellent results.178^4^Shipley,B^Lechowicz,M^Dumont,S^Hendershot,WH^1992^1^Interacting effects of nutrients, ph-al and elevated co2 on the growth of red spruce (picea-rubens sarg) seedlings^94^64^3-4^585-600^^^^^Sep^^^^^3202227^312^374^447^483^664^751^752^753^754^f and stem area index had greater effects on canopy assimilation and transpiration than did gradients of stem or leaf inclination or leaf width. However, predictions of the relative response of CO2 assimilation and transpiration to doubled CO2 are rather robust and were not greatly affected by simplifications of the canopy model.176^3^Ryle,GJA^Powell,CE^Davidson,IA^1992^1^Growth of white clover, dependent on n2 fixation, in elevated co2 and temperature^52^70^3^221-228^^^^^Sep230^243^310^312^376^57^632^177^4^Ryle,GJA^Woledge,J^Tewson,V^Powell,CE^1992^1^Influence of elevated co2 and temperature on the photosynthesis and respiration of white clover dependent on n2 fixation^52^70^3^213-220^^^^^Sep230^348^376^377^384^57^749^750^ each layer gave excellent results.A^3201^A 4 mo growth chamber experiment was conducted to evaluate the presence and importance of interactions between nutrient supply, atmospheric CO2 concentration, and four different combinations of pH - Al concentration on the growth, vitality, and tissue element concentrations of 1-yr-old red spruce seedlings. Solution chemistry was chosen to simulate soil conditions at a red spruce dic-back site at Roundtop Mountain (Quebec) that has high acid loadings. CO2 levels were chosen to simulate ambient levels and those expected in the next century. All three experimental factors affected growth and all factors except CO2 affected the visual symptoms of die-back. There was an important interaction between nutrient levels and the different pH - Al combinations, indicating that the response of red spruce to various pH and Al concentrations changes with soil fertility. The positive growth response to enriched CO2 was not sufficient to offset the negative effects of the acid rain induced stresses. A principal component analysis showed that multivariate functions of foliar element concentrations could clearly distinguish plants from different experimental regimes.179^3^Vanoosten,JJ^Afif,D^Dizengremel,P^1992^1^Long-term effects of a co-2 enriched atmosphere on enzymes of the primary carbon metabolism of spruce trees^184^30^5^541-547^^^^^Sep-Oct^^^^^3204360^362^367^372^426^448^755^756^757^92^uce dic-back site at Roundtop Mountain (Quebec) that has high acid loadings. CO2 levels were chosen to simulate ambient levels and those expected in the next century. All three experimental factors affected growth and all factors except CO2 affected the visual symptoms of die-back. There was an important interaction between nutrient levels and the different pH - Al combinations, indicating that the response of red spruce to various pH and Al concentrations changes with soil fertility. The positive growth response to enriched CO2 was not sufficient to offset the negative effects of the acid rain induced stresses. A principal compoA^3203^The long-term effects of an enriched CO2 atmosphere on the primary carbon metabolism of 4-year-old spruce trees (Picea abies L. Karst) were examined. Eight key enzymes were studied in 1-year-old needles of trees submitted for two years in open- top chambers to three CO2 levels (350, 480 and 570 ppm V). The specific activity and quantity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, EC 4.1.1.39), and the specific activities of photorespiratory enzymes, glycolate oxidase (EC 1.1.3.15) and hydroxypyruvate reductase (HPR, EC 1.1.1.29) showed a significant decrease in the CO2-enriched atmospheres. By contrast, a net increase was found for the specific activities of the mitochondrial enzymes, NAD-malic enzyme (NAD- ME, EC 1.1.1.39) and especially fumarase (EC 4.2.1.2). The specific activity of phosphofructophosphotransferase (PFP, EC 2.7.1.90), a glycolytic enzyme, did not change while a slight decrease of the activity of glucose 6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), a pentose phosphate pathway enzyme, was observed. The carboxylating enzyme, phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) showed a marked decrease in activity. These results clearly demonstrate both increases in enzyme activities linked to the respiratory process and decreases in activities of CO2-fixing enzymes as a result of long-term exposure to less than twice the ambient level of CO2.180^3^Wise,RR^Ortizlopez,A^Ort,DR^1992^1^Spatial-distribution of photosynthesis during drought in field- grown and acclimated and nonacclimated growth chamber-grown cotton^8^100^1^26-32^^^^^Sep^^^^^3206383^384^386^441^758^759^760^761^762^763^rast, a net increase was found for the specific activities of the mitochondrial enzymes, NAD-malic enzyme (NAD- ME, EC 1.1.1.39) and especially fumarase (EC 4.2.1.2). The specific activity of phosphofructophosphotransferase (PFP, EC 2.7.1.90), a glycolytic enzyme, did not change while a slight decrease of the activity of glucose 6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), a pentose phospA^3205^Inhomogeneous photosynthetic activity has been reported to occur in drought-stressed leaves. In addition, it has been suggested that these water stress-induced nonuniformities in photosynthesis are caused by "patchy" stomatal closure and that the phenomenon may have created the illusion of a nonstomatal component to the inhibition of photosynthesis. Because these earlier studies were performed with nonacclimated growth chamber-grown plants, we sought to determine whether such "patches" existed in drought-treated, field-grown plants or in chamber-grown plants that had been acclimated to low leaf water potentials (psi(leaf)). Cotton (Gossypium hirsutum L.) was grown in the field and subjected to drought by withholding irrigation and rain from 24 d after planting. The distribution of photosynthesis, which may reflect the stomatal aperture distribution in a heterobaric species such as cotton, was assayed by autoradiography after briefly exposing attached leaves of field-grown plants to (CO2)-C-14. A homogeneous distribution of radioactive photosynthate was evident even at the lowest psi(leaf) of -1.34 MPa. "Patchiness" could, however, be induced by uprooting the plant and allowing the shoot to air dry for 6 to 8 min. In parallel studies, growth chamber-grown plants were acclimated to drought by withholding irrigation for three 5-d drought cycles interspersed with irrigation. This drought acclimation lowered the psi(leaf) value at which control rates of photosynthesis could be sustained by approximately 0.7 MPa and was accompanied by a similar decline in the psi(leaf) at which patchiness first appeared. Photosynthetic inhomogeneities in chamber-grown plants that were visible during moderate water stress and ambient levels of CO2 could be largely removed with elevated CO2 levels (3000 muL L-1), suggesting that they were stomatal in nature. However, advanced dehydration (less than approximately 2.0 MPa) resulted in "patches" that could not be so removed and were probably caused by nonstomatal factors. The demonstration that patches do not exist in drought-treated, field-grown cotton and that the presence of patches in chamber-grown plants can be altered by treatments that cause an acclimation of photosynthesis leads us to conclude that spatial heterogeneities in photosynthesis probably do not occur frequently under natural drought conditions.181^1^Woodward,FI^1992^1^Predicting plant-responses to global environmental-change^84^122^2^239-251^^^^^Oct^^^^^3208243^372^377^378^512^764^765^766^767^768^oximately 0.7 MPa and was accompanied by a similar decline in the psi(leaf) at which patchiness first appeared. Photosynthetic inhomogeneities in chamber-grown plants that were visible during moderate water stress and ambient levels of CO2 could be largely removed with elevated CO2 levels (3000 muL L-1), suggesting that they were stomatal in nature. However, advanced dehydration (less than approximately 2.0 MPa) resulted in "patches" that could not be so removed and were probably caused by nonstomatal factors. The demonA^3207^Predicting the future responses of plants and ecosystems to further changes in the CO2 concentration of the atmosphere and to the possibility of global warming are important current concerns. Predictions have been most frequently attempted using short-term, single-factor experiments in controlled environments. However, these experiments have failed to indicate the outcome of field experiments at larger spatial and temporal scales. Some of this failure is due to ignorance of environmental conditions and interactions while some is due to the use of inappropriate short-cuts, such as the addition of fertilizers for simulating enhanced mineralization, and some is due to ignorance of the processes involved in scaling-up from individual plants to populations. Long-term observations on plants in ecosystems nevertheless indicate that community-scale experiments may provide a useful but imperfect capacity to predict ecosystem responses. Although difficult to implement in practice, it is concluded that catchment-scale experiments offer the best opportunity to predict plant, community and ecosystem responses to environmental change.182^2^Barnes,JD^Pfirrmann,T^1992^1^The influence of co2 and o-3, singly and in combination, on gas-exchange, growth and nutrient status of radish (raphanus- sativus L)^84^121^3^403-412^^^^^Jul^^^^^3210243^312^376^409^417^431^446^602^769^770^te the outcome of field experiments at larger spatial and temporal scales. Some of this failure is due to ignorance of environmental conditions and interactions while some is due to the use of inappropriate short-cuts, such as the addition of fertilizers for simulating enhanced mineralization, and some is due to ignorance of the processes involved in scaling-up from individual plants to populations. Long-term observations on plants in ecosystems nevertheless indicate that community-scale experiments may provide a useful but imperfect capacity to predict ecosystem responses. Although difficult to implement in practice, it is concluded that catchmentA^3209^Five days after emergence radish (Raphanus sativus L. cv. Cherry Belle) plants were transferred to a phytotron at the GSF Munchen, where they were exposed in four large controlled climate chambers to two at atmospheric concentrations of CO2 ('ambient', daily means of almost-equal-to 385-mu-mol mol-1; elevated, daily means of almost-equal-to 765-mu-mol mol-1) and two O3 regimes ('non-polluted' air, 24 h mean of 20 nmol mol-1; polluted air, 24 h mean of 73 nmol mol-1) Leaf gas-exchange measurements were made at intervals, and visible O3 damage, effects on growth, dry matter partitioning and mineral composition were assessed at a final whole-plant harvest after 27 d. In 'non-polluted air' CO2 enrichment resulted in a progressive stimulation in A(sat), whilst there was a decline in g(s) which decreased E (i.e. improved WUE(i)). The extra carbon fixed in elevated CO2 stimulated growth of the root (+ hypocotyl) by 43 %, but there was no significant effect on shoot growth or leaf area. Moreover, a decline in SLA and LAR in CO2-enriched plants suggested that less dry matter was invested in leaf area expansion. Tissue concentrations of N, S, P, Mg and Ca were lower (particularly in the root + hypocotyl) in elevated CO2, indicating that total uptake of these nutrients was not affected by CO2, and there was an increase in the C:N ratio in root (+ hypocotyl) tissue. In contrast, O3 depressed A(sat), (almost-equal-to 26 %) and induced slight stomatal closure, with the result that WUE(i) declined. All plants exposed to 'polluted' air developed typical visible symptoms of O3 injury, and effects on carbon assimilation were reflected in reduced growth, with shoot growth maintained at the expense of the root. In addition, O3 increased the P and K concentration in shoot and root (+hypocotyl) tissue, indicating enhanced uptake of these nutrients from the growth medium. However, there was no affect of O3 on tissue concentrations of N, S, Mg and Ca. Interactions between the gases were complex, and often subtle. In general, elevated CO2 counteracted (at least in part) the detrimental effects of phytotoxic concentrations of O3, whilst conversely, O3 reduced the impact of elevated CO2. Moreover, there were indications that cumulative changes in source:sink relations in O3-exposed plants may limit plant response to CO2-enrichment to an even greater extent in the long-term. The future ecological significance of interactions between CO2 and O3 are discussed.183^2^Chaves,MM^Pereira,JS^1992^1^Water-stress, co2 and climate change^78^43^253^1131-1139^^^^^Aug^^^^^3212164^343^355^372^377^426^550^647^745^771^ects on carbon assimilation were reflected in reduced growth, with shoot growth maintained at the expense of the root. In addition, O3 increased the P and K concentration in shoot and root (+hypocotyl) tissue, indicating enhanced uptake of these nutrients from the growth medium. However, there was no affect of O3 on tissue concentrations of N, S, Mg and Ca. Interactions between the gases were complex, and often subtle. In general, elA^3211^Climatic change may bring about increased aridity to large areas of Europe. Higher temperatures, larger water deficits and high light stress are likely to occur in conjunction with elevated atmospheric CO2. This raises the question whether a high CO2 concentration in the atmosphere can compensate for the decrease in carbon gain in water-stressed plants. The processes which determine dry matter production and the ways they are affected by soil water deficits are discussed. It is now well established that in most species and under most circumstances stomata are the main limiting factor to carbon uptake under water deficit, the photosynthetic machinery being highly resistant to dehydration. However, when other stresses are superimposed, a decline in photosynthetic capacity may be observed. In the short term, under drought conditions, the increase in CO2 in the atmosphere may diminish the importance of stomatal limitation for carbon assimilation, inhibit photorespiration, stimulate carbon partitioning to soluble sugars and increase water-use efficiency. Some recent evidence seems to indicate that under conditions of high irradiance, plants growing at elevated CO2 may develop protection towards photoinhibition, which might otherwise result in significant losses in plant production under stress conditions. In the longer term though, a negative acclimation of photosynthesis appears to occur in many species, an explanation for which still needs to be clearly identified. Similarly, the effects of extended exposure to elevated CO2 under arid conditions are not known. Plant production is more closely related to the integral of photosynthesis over time and total foliage area than to the instantaneous rates of the photosynthetic process. Water deficits result in a decrease in foliage area biomass and, therefore, in productivity. On the other hand, the increase in air temperature may result in more respiratory losses. However, experimental as well as simulatory evidence suggests that doubling CO2 concentration in the air may improve carbon assimilation and compensate partially for the negative effects of water stress even if we assume a down-regulation of the photosynthetic process as a result of acclimation to elevated CO2.184^3^Conroy,JP^Milham,PJ^Barlow,EWR^1992^1^Effect of nitrogen and phosphorus availability on the growth- response of eucalyptus-grandis to high co2^9^15^7^843-847^^^^^Sep^^^^^3214244^312^361^376^386^409^417^438^682^h still needs to be clearly identified. Similarly, the effects of extended exposure to elevated CO2 under arid conditions are not known. Plant production is more closely related to the integral of photosynthesis over time and total foliage area than to the instantaneous rates of the photosynthetic process. Water deficits result in a decrease in foliage area biomass and, therefore, in productivity. On the other hand, the increase in air temperature may result in more respiratory losses. However, experimental as well as simulatory evidence suggests that doubling CO2 concentration in the A^3213^The response of Eucalyptus grandis seedlings to elevated atmospheric CO2 concentrations was examined by growing seedlings at either 340 or 660-mu-mol CO2 mol-1 for 6 weeks. Graded increments of phosphorus and nitrogen fertilizers were added to a soil deficient in these nutrients to establish if the growth response to increasing nutrient availability was affected by CO2 concentration. At 660-mu-mol CO2 mol-1, seedling dry weight was up to five times greater than at 340- mu-mol CO2 mol-1. The absolute response was largest when both nitrogen and phosphorus availability was high but the relative increase in dry weight was greatest at low phosphorus availability. At 340-mu-mol CO2 mol-1 and high nitrogen availability, growth was stimulated by addition of phosphorus up to 76 mg kg-1 soil. Further additions of phosphorus had little effect. However, at 660-mu-mol CO2 mol-1, growth only began to plateau at a phosphorus addition rate of 920 mg kg-1 soil. At 340-mu-mol CO2 mol-1 and high phosphorus availability, increasing nitrogen from 40 to 160 mg kg-1 soil had little effect on plant growth. At high CO2, growth reached a maximum at between 80 and 160 mg nitrogen kg-1 soil. Total uptake of phosphorus was greater at high CO2 concentration at all fertilizer addition rates, but nitrogen uptake was either lower or unchanged at high CO2 concentration except at the highest nitrogen fertilizer rate. The shoot to root ratio was increased by CO2 enrichment, primarily because the specific leaf weight was greater. The nitrogen and phosphorus concentration in the foliage was lower at elevated CO2 concentration partly because of the higher specific leaf weight. These results indicate that critical foliar concentrations currently used to define nutritional status and fertilizer management may need to be reassessed as the atmospheric CO2 concentration rises. However, at 660-mu-mol CO2 mol-1, growth only began to plateau at a phosphorus addition rate of 920 mg kg-1 soil. At 340-mu-mol CO2 mol-1 and high phosphorus availability,185^3^Fajer,ED^Bowers,MD^Bazzaz,FA^1992^1^The effect of nutrients and enriched co2 environments on production of carbon-based allelochemicals in plantago - a test of the carbon nutrient balance hypothesis^16^140^4^707-723^^^^^Oct^^^^^3216485^486^487^764^772^773^774^775^776^777^ptake was either lower or unchanged at high CO2 concentration except at the highest nitrogen fertilizer rate. The shoot to root ratio was increased by CO2 enrichment, primarily because the specific leaf weight was greater. The nitrogen and phosphorus concentration in the foliage was lower at elevated CO2 concentration partly because of the higher specific leaf weight. These results indicate that critical foliar concentrations currently used to define nutritional status and fertilizer management may need to be reassessed as the atmospheric CO2 concentration rises. However, at 660-mu-mol CO2 mol-1, growth only began to plateau at a phosphorus addition rate of 920 mg kg-1 soil. At 340-mu-mol CO2 mol-1 and high phosphorus availability,A^3215^In a test of the carbon/nutrient (C/N) balance hypothesis, we grew the perennial herb Plantago lanceolata in different CO2 and nutrient environments and then (1) measured the total allocation to shoots, roots, and reproductive parts and (2) quantified aucubin, catalpol, and verbascoside contents of replicate plants of six genotypes. Plants grown under low- nutrient conditions do have higher concentrations of carbon- based allelochemicals than plants grown under high-nutrient conditions. However, in contrast to the C/N balance hypothesis, plants grown in elevated (700-mu-L.L-1) CO2 conditions had similar, or lower, concentrations of carbon-based allelochemicals than plants grown in ambient (350-mu-L.L-1) CO2 conditions. We suggest that augmented substrate concentrations (i.e., excess carbohydrates) are a necessary but insufficient trigger for increased secondary metabolism; instead, hormonal and/or direct physical cues (such as light) may be essential to synthesize or activate the appropriate enzyme systems. Moreover, although plant genotype significantly affected plant growth, reproduction, and chemistry, we never observed significant genotype-by-CO2 interactions for these factors, which suggests that changing CO2 environments may not improve the fitness of certain genotypes over others.186^2^Korner,C^Arnone,JA^1992^1^Responses to elevated carbon-dioxide in artificial tropical ecosystems^32^257^5077^1672-1675^^^^^18 Sep^^^^^3218130^189^343^361^376^442^504^685^778^92^utrient conditions. However, in contrast to the C/N balance hypothesis, plants grown in elevated (700-mu-L.L-1) CO2 conditions had similar, or lower, concentrations of carbon-based allelochemicals than plants grown in ambient (350-mu-L.L-1) CO2 conditions. We suggest that augmented substrate concentrations (i.e., excess carbohydrates) are a necessary but insufficient trigger for increased secondary metabolism; instead, hormonal and/or direct physical cues (such as light) may be essential to synthesize or activate the appropriate enzyme syA^3217^Carbon, nutrient, and water balance as well as key plant and soil processes were simultaneously monitored for humid tropical plant communities treated with CO2-enriched atmospheres. Despite vigorous growth, no significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO2 treatments. Major responses under elevated CO2 included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO2 evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.hesize or activate the appropriate enzyme sy187^4^Lim,LY^Hew,YC^Wong,SC^Hew,CS^1992^1^Effects of light-intensity, sugar and co-2 concentrations on growth and mineral uptake of dendrobium plantlets^174^67^5^601-611^^^^^Sep^^^^^3220243^312^372^749^779^780^781^ significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO2 treatments. Major responses under elevated CO2 included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO2 evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.hesize or activate the appropriate enzyme syA^3219^The effects of light intensity, sugar and CO2 concentrations on nitrate and ammonium uptake, growth and photosynthetic activity of dendrobium plantlets grown on agar medium were studied. There was a preferential uptake of ammonium over nitrate. Uptake of nitrate was relatively low and increased with increase in light intensity or when the culture medium was supplemented with sugar. Ammonium uptake was also affected by light. However, the rates of ammonium and nitrate uptake were sluggish. The fresh weight of plantlets increased with the presence of sugar in the media but the relative growth rate decreased. CO2 enrichment did not increase ion uptake or growth. The nutrition of plantlets in culture was mainly heterotrophic, as indicated by the changes in titratable acidity, delta-C-13 values and (CO2)-C-14 fixation.188^7^Mo,G^Nie,D^Kirkham,MB^He,H^Ballou,LK^Caldwell,FW^Kanemasu,ET^1992^1^Root and shoot weight in a tallgrass prairie under elevated carbon-dioxide^173^32^3^193-201^^^^^Jul^^^^^3222yme sy174^245^374^376^407^434^508^778^92^y, sugar and CO2 concentrations on nitrate and ammonium uptake, growth and photosynthetic activity of dendrobium plantlets grown on agar medium were studied. There was a preferential uptake of ammonium over nitrate. Uptake of nitrate was relatively low and increased with increase in light intensity or when the culture medium was supplemented with sugar. Ammonium uptake was also affected by light. However, the rates of ammonium and nitrate uptake were sluggish. The fresh weight of plantlets increased with the presence of sugar in the media but the relative growth rate decreased. CO2 enrichment did not increase ion uptake or growth. The nutrition of plantlets in culture was mainly heterotrophic, as indicated by the changes in titratable acidity, delta-C-13 values and (CO2)-C-14 fixation.188^7^Mo,G^Nie,D^Kirkham,MB^He,H^Ballou,LK^Caldwell,FW^Kanemasu,ET^1992^1^Root and shoot weight in a tallgrass prairie under elevated carbon-dioxide^173^32^3^193-201^^^^^Jul^^^^^3222yme syA^3221^The atmospheric concentration of carbon dioxide (CO2) is increasing and knowing how this will affect native vegetation is important. The objective of this study was to determine the effect of elevated CO2 on root growth in a tallgrass prairie kept at a high water level (73 cm of water in a 200 cm soil profile) and a low water level (66 cm of water in 200 cm). Sixteen cylindrical plastic chambers were placed on the prairie to maintain two levels of CO2 (ambient or twice ambient). At the end of two seasons' exposure to the different treatments, dry weight and length of roots in the 0-40 cm depth were determined. Shoot growth also was measured to determine shoot: root ratios. The CO2 and water treatments had no significant effect on root dry weight in the 0-40 cm depth. In the 0-10 cm depth, doubled CO2 reduced dry weight and length of roots of plants grown under the high water level by 47 and 31 %, respectively. Warm-season, C4 grasses had the highest shoot dry weight, which was greatest under the high water, ambient CO2 treatment. The shoot: root ratio did not change with treatment.189^2^Mousseau,M^Saugier,B^1992^1^The direct effect of increased co2 on gas-exchange and growth of forest tree species^78^43^253^1121-1130^^^^^Aug^^^^^3224361^374^376^377^385^389^417^545^595^749^cm of water in a 200 cm soil profile) and a low water level (66 cm of water in 200 cm). Sixteen cylindrical plastic chambers were placed on the prairie to maintain two levels of CO2 (ambient or twice ambient). At the end of two seasons' exposure to the different treatments, dry weight and length of roots in the 0-40 cm depth were determined. Shoot growth also was measured to determine shoot: root ratios. The CO2 and water treatments had no significant effect on root dry weight in the 0-40 cm depth. In the 0-10 cm depth, doubled CO2 reduced dry weight and length of roots of plants grown under the high water level by 47 and 31 %, respectively. Warm-season, C4 grasses had the highest shoot dry weight, which was greatest under the high A^3223^CO2 enrichment of the atmosphere is now well documented and its effect on the growth of world forests is being questioned by the scientific community. The direct effects of increased CO2 on tree species are reviewed: the different experimental approaches are described, as well as the principal results already obtained. Short-term experiments have shown an increased photosynthetic rate, as predicted by leaf models. In longer experiments this increase is reduced after a few weeks or months by mechanisms that remain to be found. Elevated CO2 seems to decrease the dark respiration rate, but the results are still controversial. Biomass partitioning in elevated CO2 is clearly related to the mineral supply of the trees: An increase in root investment in elevated CO2 is related to a poor mineral status. The mineral content of trees grown in elevated CO2 is generally lowered compared to controls. No general rule has yet been found for the effect of increased CO2 on leaf area development. The paper emphasizes large areas of ignorance: the reasons for the different responses of different species, which may be related to their developmental strategies, are largely ignored. Much experimental effort is needed to parameterize all the physiological processes which are susceptible to change with an increase in atmospheric CO2, leading to a change in forest tree growth.190^3^Nijs,I^Impens,I^Vanhecke,P^1992^1^Diurnal changes in the response of canopy photosynthetic rate to elevated co2 in a coupled temperature-light environment^91^32^2^121-130^^^^^May^^^^^3226402^417^430^434^92^dark respiration rate, but the results are still controversial. Biomass partitioning in elevated CO2 is clearly related to the mineral supply of the trees: An increase in root investment in elevated CO2 is related to a poor mineral status. The mineral content of trees grown in elevated CO2 is generally lowered compared to controls. No general rule has yet been found for the effect of increased CO2 on leaf area development. The paper emphasizes lA^3225^The relative increase with elevated CO2 of canopy CO2 uptake rate (A), derived from continuous measurements during the day, was examined in full-cover vegetative Lolium perenne canopies after 17 days of regrowth. The stands were grown at ambient (358 +/- 50-mu-mol mol-1) and increased (626 +/- 50-mu-mol mol- 1) CO2 concentration in sunlit growth chambers. Over the entire range of temperature and light conditions (which were strongly coupled and increased simultaneously), A was on average twice as large in high compared to ambient CO2. This response (called M = A in high CO2/A in ambient CO2) could not be explained by changes in canopy conductance for CO2 diffusion (GC). In spite of interaction and strong coupling between temperature and light intensity, there was evidence that temperature rather than light determined M. Further, high CO2 treatment was found to alleviate the afternoon depression in A observed in ambient CO2. A temperature optimum shift or/and a larger carbohydrate sink capacity through altered root/shoot ratio are proposed in explanation.191^4^Rogers,HH^Peterson,CM^McCrimmon,JN^Cure,JD^1992^1^Response of plant-roots to elevated atmospheric carbon-dioxide^9^15^6^749-752^^^^^Aug^^^^^322892^A^3227^Plant root response to atmospheric CO2 enrichment can be great. Results from this controlled environment investigation demonstrate substantial effects on root system architecture, micromorphology and physiology. The most pronounced effects were an increase in root length (110%) and root dry weight (143%). Root diameter, stele diameter, cortex width, root/shoot and root weight ratios all increased; root numbers did not increase. The long-term implications for belowground processes could be enormous.192^2^Ryle,GJA^Stanley,J^1992^1^Effect of elevated co2 on stomatal size and distribution in perennial ryegrass^52^69^6^563-565^^^^^Jun376^92^193^1^Schwartz,MW^1992^1^Potential effects of global climate change on the biodiversity of plants^66^68^4^462-471^^^^^Aug^^^^^3231ate sink capacity throughA^3230^Climatologists have observed a consistent increase in atmospheric CO2 over the past 30 years. It is predicted that CO2 levels could double the pre-industrial level of 280 ppm by the year 2100, perphaps much earlier. Climate models of doubled atmospheric CO2 predict that mean temperatures will increase between 1.5 and 4.5-degrees-C globally; these temperature changes will be greater at high latitudes. Mid-continental regions will experience lower rainfall. Predictions of species northward range shifts in response to climate change vary from 100 km to over 500 km. Historical evidence of species range movements following the Pleistocene indicate that tree species typically migrated at rates of 10 km to 40 km per century. A simulation model that predicts the migration response of trees through modem fragmented landscapes predicts migration rates much lower than Pleistocene observations. Thus migration response is likely to lag far behind rates of climatic change, potentially threatening narrowly distributed species whose predicted future ranges do not overlap with their current range. Insect pests and microbial pathogens should respond to climatic warming faster than long-lived trees. Predicted increased drought frequency may increase plant stress and thereby increase the frequency of insect outbreaks and disease. Predictions of species responses are complicated by direct effects of increased CO2, such as increased water-use. efficiency. However, response to elevated CO2 vanes among species. Thus, shifts in composition within plant communities are also likely, but are, as yet, unpredictable.194^3^Wullschleger,SD^Norby,RJ^Gunderson,CA^1992^1^Growth and maintenance respiration in leaves of liriodendron- tulipifera L exposed to long-term carbon-dioxide enrichment in the field^84^121^4^515-523^^^^^Aug^^^^^3233245^314^344^372^374^417^57^634^782^ates much lower than Pleistocene observations. Thus migration response is likely to lag far behind rates of climatic change, potentially threatening narrowly distributA^3232^Specific respiration rate (SRR) was mathematically partitioned into its growth and maintenance components for leaves of yellow-poplar (Liriodendron tulipifera L.) after 3 vr of CO2 enrichment in open-top field chambers. Despite the absence of a CO2 effect on individual leaf expansion or specific growth rate (SGR), increasing the CO2 concentration to ambient + 150 or + 300 cm3 m-3 decreased SRR by 28 to 45 % compared with ambient- grown controls. These lower leaf respiration rates were correlated with reduced leaf nitrogen concentrations. As described by the two-component model of growth and maintenance respiration, SRR was a linear function of SGR. Ambient-grown leaves had a growth respiration coefficient of 704 mg CO2 g-1 dry mass compared with 572 and 570 mg CO2 g-1 for leaves grown at the two higher CO2 concentrations. Leaves from the elevated CO2 treatments had an average maintenance respiration coefficient of 88 mg CO2 g-1 dry mass d-1 compared with 135 mg CO2 g-1 d-1 for leaves from the ambient treatment. Incorporating these growth and maintenance coefficients into a leaf growth simulation model indicated that total respiration would be reduced by 21 to 26 % for a leaf exposed to + 150 or + 300 cm3 m-3 CO2 throughout its 50-d lifespan compared with one grown at ambient CO2 conditions. Reductions in total respiration were dominated by a lower rate of maintenance respiration, while the contribution of a lower specific rate of growth respiration was largely offset by a greater dry mass for leaves grown at elevated CO2 concentrations. Although reductions in the respiratory loss of carbon could be beneficial, respiration is unlikely to decrease without a concomitant decrease in other metabolic processes. Whether these reductions are beneficial or detrimental to the long-term growth of plants exposed to elevated CO2 remains unresolved.195^4^Ackerly,DD^Coleman,JS^Morse,SR^Bazzaz,FA^1992^1^Co2 and temperature effects on leaf-area production in 2 annual plant-species^11^73^4^1260-1269^^^^^Aug^^^^^3235nt 188^243^245^341^348^372^374^735^783^92^d maintenance coefficients into a leaf growth simulation model indicated that total respiration would be reduced by 21 to 26 % for a leaf exposed to + 150 or + 300 cm3 m-3 CO2 throughout its 50-d lifespan compared with one grown at ambient CO2 conditions. Reductions in total respiration were dominated by a lower rate of maintenance respiration, while the contribution of a lower specific rate of growth respiration was largely offset by a greater dry mass for leaves grown at elevated CO2 concentrations. Although reductions in the respiratory loss of carbon could be beneficial, respiration is unlikely to decrease without a concomitant decrease in other metabolic processes. Whether these reductions are beneficial or detrimental to the long-term growth of plants exposed to elevated CO2 remains unresolved.195^4^Ackerly,DD^Coleman,JS^Morse,SR^Bazzaz,FA^1992^1^Co2 and temperature effects on leaf-area production in 2 annual plant-species^11^73^4^1260-1269^^^^^Aug^^^^^3235nt A^3234^We studied leaf area production in two annual plant species, Abutilon theophrasti and Amaranthus retroflexus, under three day/night temperature regimes (18-degrees/14-degrees, 28- degrees/22-degrees, and 38-degrees/31-degrees-C) and two concentrations of carbon dioxide (400 and 700-mu-L/L). The production of whole-plant leaf area during the first 30 d of growth was analyzed in terms of the leaf initiation rate, leaf expansion, individual leaf area, and, in Amaranthus, production of branch leaves. Temperature and CO2 influenced leaf area production through effects on the rate of development, determined by the production of nodes on the main stem (the plastochron index), and through shifts in the relationship between whole-plant leaf area and the number of main stem nodes. In Abutilon, leaf initiation rate was highest at 38- degrees, but area of individual leaves was greatest at 28- degrees. Total leaf area was greatly reduced at 18-degrees due to slow leaf initiation rates. Elevated CO2 concentration increased leaf initiation rate at 28-degrees, resulting in an increase in whole-plant leaf area. In Amaranthus, leaf initiation rate increased with temperature, and was increased by elevated CO2 at 28-degrees. Individual leaf area was greatest at 28-degrees, and was increased by elevated CO2 at 28-degrees but decreased at 38-degrees. Branch leaf area displayed a similar response to CO2, but was greater at 38- degrees. Overall, whole-plant leaf area was slightly increased at 38-degrees relative to 28-degrees, and elevated CO2 levels resulted in increased leaf area at 28-degrees but decreased leaf area at 38-degrees. The effects on leaf area closely parallel rates of biomass accumulation in the same experiment, suggesting that responses of developmental processes to elevated CO2 and interacting factors may play an important role in mediating effects on plant growth.196^3^Baker,JT^Allen,LH^Boote,KJ^1992^1^Temperature effects on rice at elevated co2 concentration^78^43^252^959-964^^^^^Jul^^^^^3237ncentration i243^374^376^409^430^434^629^674^784^92^ees, resulting in an increase in whole-plant leaf area. In Amaranthus, leaf initiation rate increased with temperature, and was increased by elevated CO2 at 28-degrees. Individual leaf area was greatest at 28-degrees, and was increased by elevated CO2 at 28-degrees but decreased at 38-degrees. Branch leaf area displayed a similar response to CO2, but was greater at 38- degrees. Overall, whole-plant leaf area was slightly increased at 38-degrees relative to 28-degrees, and elevated CO2 levels resulted in increased leaf area at 28-degrees but decreased leaf area at 38-degrees. The effects on leaf area closely parallel rates of biomass accumulation in the same experiment, suggesting that responses of developmental processes to elevated CO2 and interacting factors may play an important role in mediating effects on plant growth.196^3^Baker,JT^Allen,LH^Boote,KJ^1992^1^Temperature effects on rice at elevated co2 concentration^78^43^252^959-964^^^^^Jul^^^^^3237ncentration iA^3236^The continuing increase in atmospheric carbon dioxide concentration ([CO2]) and projections of possible future increases in global air temperatures have stimulated interest in the effects of these climate variables on agriculturally important food crops. This study was conducted to determine the effects of [CO2] and temperature on rice (Oryza sativa L., cv. IR-30). Rice plants were grown season-long in outdoor, naturally sunlit, controlled-environment, plant growth chambers in temperature regimes ranging from 25/18/21-degrees-C to 37/30/34-degrees-C (daytime dry bulb air temperature/night-time dry bulb air temperature/paddy water temperature) and [CO2] of 660-mu-mol CO2 mol-1 air. An ambient chamber was maintained at a [CO2] of 330-mu-mol mol-1 and temperature regime of 28/21/25- degrees-C. Carbon dioxide enrichment at 28/21/25-degrees-C increased both biomass accumulation and tillering and increased grain yield by 60%. In the 660-mu-mol mol-1 [CO2] treatment, grain yield decreased from 10.4 to 1.0 Mg ha-1 with increasing temperature from 28/21/25-degrees-C to the 37/30/34-degrees-C temperature treatment. Across this temperature range, the number of panicles plant-1 nearly doubled while the number of seeds panicle-1 declined sharply. These results indicate that while future increases in atmospheric [CO2] are likely to be beneficial to rice growth and yield, potentially large negative effects on rice yield are possible if air temperatures also rise.197^2^Berntson,GM^Woodward,FI^1992^1^The root-system architecture and development of senecio- vulgaris in elevated co2 and drought^43^6^3^324-333^^^^^^^^^^3239r temperature/paddy water temperature) and [CO2] of 660-mu-mol CO2 mol-1 air. An ambient chamber was maintained at a [CO2] of 330-mu-mol mol-1 and temperature regime of 28/21/25- degrees-C. Carbon dioxide enrichment at 28/21/25-degrees-C increased both biomass accumulation and tillering and increased grain yield by 60%. In the 660-mu-mol mol-1 [CO2] treatment, grain yield decreased from 10.4 to 1.0 MgA^3238^1. The impact of elevated CO2 and drought on the architecture and development of root systems of Senecio vulgaris was examined and implications for water and nutrient uptake discussed. Plants were grown in miniature rhizotrons to non- destructively monitor the development of roots in situ at both an elevated (700-mu-mol mol-1) and ambient (350-mu-mol mol-1) atmospheric CO2 concentration and a high or a low supply of water. 2. CO2 and water had a significant impact on the way that S. vulgaris root systems filled the soil matrix. Elevated CO2 resulted in more branched, longer root systems that foraged through larger volumes of soil. Under elevated CO2 and a low water supply, root systems had branching and foraging patterns and root length similar to those grown under ambient CO2 with a high water supply. 3. Overall, water had a more pronounced impact on the growth rate of S. vulgaris roots than did CO2. The density of rooting remained unchanged across all treatments. Thus, under elevated CO2 the intensity of foraging S. vulgaris root systems might be unchanged while the extent of foraging by these root systems, as indicated by the horizontal spread of roots, may be increased.198^1^Bunce,JA^1992^1^Stomatal conductance, photosynthesis and respiration of temperate deciduous tree seedlings grown outdoors at an elevated concentration of carbon-dioxide^9^15^5^541-549^^^^^Jun^^^^^3241374^664^741^nd a high or a low supply of water. 2. CO2 and water had a significant impact on the way that S. vulgaris root systems filled the soil matrix. Elevated CO2 resulted in more branched, longer root systems that foraged through larger volumes of soil. Under elevated CO2 and a low water supply, root systems had branching and foraging patterns and root length similar to those grown under ambient CO2 with a high water supply. 3. Overall, water had a more pronounced impact on the growth rate of S. vulgaris roots than did CO2. The density of rooting remained unchanged across all treatments. Thus, under elevated CO2 the intensiA^3240^Seedlings of temperate deciduous tree species were grown outdoors at ambient and at an elevated concentration of carbon dioxide to examine how aspects of their gas exchange would be altered by growth at elevated carbon dioxide concentration. Leaf conductances to water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole- plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm3 m-3 carbon dioxide did not differ from that of plants grown and measured at 350 cm3 m-3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33- degrees-C. Photosynthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of mass when grown and measured at elevated carbon dioxide concentration.199^2^Coleman,JS^Bazzaz,FA^1992^1^Effects of co2 and temperature on growth and resource use of cooccurring C3 and C4 annuals^11^73^4^1244-1259^^^^^Aug^^^^^3243344^35^372^376^423^494^509^714^765^785^o water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole- plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm3 m-3 carbon dioxide did not differ from that of plants grown and measured at 350 cm3 m-3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33- degrees-C. Photosynthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of massA^3242^We examined how CO2 concentrations and temperature interacted to affect growth, resource acquisition, and resource allocation of two annual plants that were supplied with a single pulse of nutrients. Physiological and growth measurements were made on individuals of Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) grown in environments with atmospheric CO2 levels of 400 or 700-muL/L and with light/dark temperatures of 28-degrees/22-degrees or 38-degrees/31-degrees-C. Elevated CO2 and temperature treatments had significant independent and interactive effects on plant growth, resource allocation, and resource acquisition (i.e., photosynthesis and nitrogen uptake), and the strength and direction of these effects were often dependent on plant species. For example, final biomass of Amaranthus was enhanced by elevated CO2 at 28-degrees but was depressed at 38-degrees. For Abutilon, elevated CO2 increased initial plant relative growth rates at 28-degrees but not at 38-degrees, and had no significant effects on final biomass at either temperature. These results are interpreted in light of the interactive effects of CO2 and temperature on the rates of net leaf area production and loss, and on net whole- plant nitrogen retention. At 28-degrees-C, elevated CO2 stimulated the initial production of leaf area in both species, which led to an initial stimulation of biomass accumulation at the higher CO2 level. However, in elevated CO2 at 28-degrees, the rate of net leaf area loss for Abutilon increased while that of Amaranthus decreased. Furthermore, high CO2 apparently enhanced the ability of Amaranthus to retain nitrogen at this temperature, which may have helped to enhance photosynthesis, whereas nitrogen retention was unaffected in Abutilon. Thus, at 28-degrees, final biomass of Abutilon was not stimulated in a high CO2 environment whereas the final biomass of Amaranthus was. At 38-degrees, Abutilon had slightly reduced peak leaf areas under elevated CO2 in comparison to ambient CO2 grown plants, but increased rates of photosynthesis per unit leaf area early in the experiment apparently compensated for reduced leaf area. For Amaranthus at 38-degrees, peak leaf area production was not affected by CO2 treatment, but the rate of net leaf area loss hastened under elevated CO2 conditions and was accompanied by substantial reductions of whole-plant nitrogen content and leaf photosynthesis. This may have led to the reduced biomass accumulation of high CO2 grown plants that we observed during the last 30 d of growth. Plants of both species grown in elevated CO2 exhibited reduced tissue-specific rates of nitrogen absorption, increased plant photosynthetic rate per unit of conductance, and increased initial allocation of biomass to roots, irrespective of temperature. Plants of both species grown under an elevated temperature regime had substantially decreased reproductive allocation, increased allocation to stem biomass, and increased plant water flux at both CO2 treatments. The age of plants also affected our interpretations of plant responses to CO2 and temperature treatments. For example, significant effects of CO2 treatment on the growth of Abutilon were evident early, prior to the initiation of flowering, when nitrogen availability would have been highest and pot space would not have been limited. Nevertheless, the opposite was true for Amaranthus, in which significant effects of CO2 treatment on plant growth were not detectable until the final 30 d of the experiment. Elevated CO2 interacted with temperature to affect plant productivity in different ways than would have been predicted from plant responses to elevated CO2 alone. Furthermore, a majority of the interactive effects of CO2 concentration and temperature on plant growth could be interpreted in light of their effects on the rates of net leaf area production and loss, nitrogen retention, and, to a lesser degree, photosynthesis and resource partitioning.200^1^Drake,BG^1992^1^The impact of rising co2 on ecosystem production^94^64^1-2^25-44^^^^^Aug^^^^^3245ret189^256^341^343^379^383^384^426^449^733^erature treatments. For example, significant effects of CO2 treatment on the growth of Abutilon were evident early, prior to the initiation of flowering, when nitrogen availability would have been highest and pot space would not have been limited. Nevertheless, the opposite was true for Amaranthus, in which significant effects of CO2 treatment on plant growth were not detectable until the final 30 d of the experiment. Elevated CO2 interacted with temperature to affect plant productivity in different ways than would have been predicted from plant responses to elevated CO2 alone. Furthermore, a majority of the interactive effects of CO2 concentration and temperature on plant growth could be interpreted in light of their effects on the rates of net leaf area production and loss, nitrogen retention, and, to a lesser degree, photosynthesis and resource partitioning.200^1^Drake,BG^1992^1^The impact of rising co2 on ecosystem production^94^64^1-2^25-44^^^^^Aug^^^^^3245retA^3244^A fundamental property of green plants is that the rate of photosynthesis is dependent in the ambient CO2 concentration. There is overwhelming experimental evidence that this effect increases plant production in most C3 Plants: hundreds of experiments with many species show that plant growth increases an average 30% to 40% for a doubling of the present normal ambient CO2 concentration (Kimball, 1986). External environmental factors, such as temperature and the availability of nutrients, modify this response. The greatest stimulation of photosynthesis and growth can be expected to occur at high temperatures and much smaller responses at low temperature. Factors which restrict growth, such as low nutrients, will reduce but usually do not eliminate the stimulation of production with increasing CO2 even when nitrogen is severly limiting. There are also reports of direct effects of ambient CO2 concentration on dark respiration which show that there is an immediate reduction in the rate of CO2 efflux or O2 consumption when the CO2 around plant tissues is increased. There have been very few long-term field studies of the effects of increased CO2 on whole plants and ecosystem processes but the data from these studies are consistent in showing an increase in plant production with an increase in CO2 concentration of the ambient air.201^3^Miao,SL^Wayne,PM^Bazzaz,FA^1992^1^Elevated co-2 differentially alters the responses of cooccurring birch and maple seedlings to a moisture gradient^2^90^2^300-304^^^^^May^^^^^3247312^342^345^349^512^546^tion of photosynthesis and growth can be expected to occur at high temperatures and much smaller responses at low temperature. Factors which restrict growth, such as low nutrients, will reduce but usually do not eliminate the stimulation of production with increasing CO2 even when nitrogen is severly limiting. There are also reports of direct effects of ambient CO2 concentration on dark respiration which show that there is an immediate reduction in the rate of CO2 efflux or O2 A^3246^To determine the effects of elevated CO2 and soil moisture status on growth and niche characteristics of birch and maple seedlings, gray birch (Betula populifolia) and red maple (Acer rubrum) were experimentally raised along a soil moisture gradient ranging from extreme drought to flooded conditions at both ambient and elevated atmospheric CO2 levels. The magnitude of growth enhancement due to CO2 was largely contingent on soil moisture conditions, but differently so for maple than for birch seedlings. Red maple showed greatest CO2 enhancements under moderately moist soil conditions, whereas gray birch showed greatest enhancements under moderately dry soil conditions. Additionally, CO2 had a relatively greater ameliorating effect in flooded conditions for red maple than for gray birch, whereas the reverse pattern was true for these species under extreme drought conditions. For both species, elevated CO2 resulted in a reduction in niche breadths on the moisture gradient; 5% for gray birch and 23% for red maple. Species niche overlap (proportional overall) was also lower at elevated CO2 (0.98 to: 0.88:11%). This study highlights the utility of of experiments crossing CO2 levels with gradients of other resources as effective tools for elucidating the potential consequences of elevated CO2 on species distributions and potential interactions in natural communities.202^3^Morin,F^Andre,M^Betsche,T^1992^1^Growth-kinetics, carbohydrate, and leaf phosphate content of clover (trifolium-subterraneum L) after transfer to a high co2 atmosphere or to high light and ambient air^8^99^1^89-95^^^^^May^^^^^3249243^348^360^362^376^543^637^786^787^788^under moderately dry soil conditions. Additionally, CO2 had a relatively greater ameliorating effect in flooded conditions for red maple than for gray birch, whereas the reverse pattern was true for these species under extreme drought conditions. For both species, elevated CO2 resulted in a reduction in niche breadths on the moisture gradient; 5% for gray birch and 23% for rA^3248^Intact air-grown (photosynthetic photon flux density, 400 microeinsteins per square meter per second) clover plants (Trifolium subterraneum L.) were transferred to high CO2 (4000 microliters CO2 per liter; photosynthetic photon flux density, 400 microeinsteins per square meter per second) or to high light (340 microliters CO2 per liter; photosynthetic photon flux density, 800 microeinsteins per square meter per second) to similarly stimulate photosynthetic net CO2 uptake. The daily increment of net CO2 uptake declined transiently in high CO2, but not in high light, below the values in air/standard light. After about 3 days in high CO2, the daily increment of net CO2 uptake increased but did not reach the high light values. Nightly CO2 release increased immediately in high light, whereas there was a 3-day lag phase in high CO2. During this time, starch accumulated to a high level, and leaf deterioration was observed only in high CO2. After 12 days, starch was two- to threefold higher in high CO2 than in high light, whereas sucrose was similar. Leaf carbohydrates were determined during the first and fourth day in high CO2. Starch increased rapidly throughout the day. Early in the day, sucrose was low and similar in high CO2 and ambient air (same light). Later, sucrose increased considerably in high CO2. The findings that (a) much more photosynthetic carbon was partitioned into the leaf starch pool in high CO2 than in high light, although net CO2 uptake was similar, and that (b) rapid starch formation occurred in high CO2 even when leaf sucrose was only slightly elevated suggest that low sink capacity was not the main constraint in high CO2. It is proposed that carbon partitioning between starch (chloroplast) and sucrose (cytosol) was perturbed by high CO2 because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants to high CO2 but changed little in high light/ambient air. During this time, the ratio of orthophosphate to soluble esterified phosphate decreased considerably in high CO2 and increased slightly in high light/ambient air. It appears that phosphate uptake and growth were similarly stimulated by high light, whereas the coordination was weak in high CO2.203^4^Noble,R^Jensen,KF^Ruff,BS^Loats,K^1992^1^Response of acer-saccharum seedlings to elevated carbon-dioxide and ozone^185^92^3^60-62^^^^^Jun^^^^^3251174^673^92^ high CO2 even when leaf sucrose was only slightly elevated suggest that low sink capacity was not the main constraint in high CO2. It is proposed that carbon partitioning between starch (chloroplast) and sucrose (cytosol) was perturbed by high CO2 because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants A^3250^Newly germinated seedlings of Acer saccharum were grown in atmospheres of elevated carbon dioxide (CO2) or ozone (O3) for 85 days. Net photosynthesis measured on initial leaves and recently formed leaves tended (though not always statistically significant) to increase with an increase in CO2. Biomass measured at the end of the study also increased with and increase in CO2. Ozone at 0.15 ppm did not have a significant impact on either net photosynthesis or growth; however, with O3-treatment, biomass increased at elevated CO2 levels.204^5^Norby,RJ^Gunderson,CA^Wullschleger,SD^Oneill,EG^McCracken,MK^1992^1^Productivity and compensatory responses of yellow-poplar trees in elevated co2^36^357^6376^322-324^^^^^28 May^^^^^3253) was perturbed by high CO2 because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants A^3252^INCREASED forest growth in response to globally rising CO2 concentrations could provide an additional sink for the excess carbon added to the atmosphere from fossil fuels 1,2. The response of trees to increased CO2, however, can be expected to be modified by the interactions of other environmental resources and stresses, higher-order ecological interactions and internal feedbacks inherent in the growth of large, perennial organisms 3,4. To test whether short-term stimulation of tree growth by elevated CO2 can be sustained without inputs from other environmental resources, we grew yellow-poplar (Liriodendron tulipifera L.) saplings for most of three growing seasons with continuous exposure to ambient or elevated concentrations of atmospheric CO2. Despite a sustained increase in leaf-level photosynthesis and lower rates of foliar respiration in CO2-enriched trees, whole-plant carbon storage did not increase. The absence of a significant growth response is explained by changes in carbon allocation patterns, specifically a relative decrease in leaf production and an increase in fine root production. Although these compensatory responses reduced the potential increase in carbon storage in increased CO2 concentrations, they also favour the efficient use of resources over the longer term.205^4^Post,WM^Pastor,J^King,AW^Emanuel,WR^1992^1^Aspects of the interaction between vegetation and soil under global change^94^64^1-2^345-363^^^^^Aug^^^^^3255174^19^377^611^664^668^715^789^790^791^of tree growth by elevated CO2 can be sustained without inputs from other environmental resources, we grew yellow-poplar (Liriodendron tulipifera L.) saplings for most of three growing seasons with continuous exposure to ambient or elevated concentrations of atmospheric CO2. Despite a sustained increase in leaf-level photosynthesis and lower rates of foliar respiration in CO2-enriched trees, whole-plant carbon storage did not increase. The absence of a significant growth response is explained by changes in carbon allocation patterA^3254^Responses of terrestrial ecosystems to a world undergoing a change in atmospheric CO2 concentration presents a formidable challenge to terrestrial ecosystem scientists. Strong relationships among climate, atmosphere, soils and biota at many different temporal and spatial scales make the understanding and prediction of changes in net ecosystem production (NEP) at a global scale difficult. Global C cycle models have implicitly attempted to account for some of this complexity by adapting lower pool sizes and smaller flux rates representing large regions and long temporal averages than values appropriate for a small area. However, it is becoming increasingly evident that terrestrial ecosystems may be experiencing a strong transient forcing as a result of increasing levels of atmospheric CO2 that will require a finer temporal and spatial representation of terrestrial systems than the parameters for current global C cycle models allow. To adequately represent terrestrial systems. in the global C cycle it is necessary to explicitly model the response of terrestrial systems to primary environmental factors. While considerable progress has been. made experimentally and conceptually in aspects of photosynthetic responses, and gross and net primary production, the application of this understanding to NEP at individual sites is not well developed. This is an essential step in determining effects of plant physiological responses on the global C cycle. We use a forest stand succession model to explore the effects of several possible plant responses to elevated atmospheric CO2 concentration. These simulations show that ecosystem C storage can be increased by increases in individual tree growth rate, reduced transpiration, of increases in fine root production commensurate with experimental observations.206^2^Ryle,GJA^Powell,CE^1992^1^The influence of elevated co2 and temperature on biomass production of continuously defoliated white clover^9^15^5^593-599^^^^^Jun^^^^^3257243^312^376^434^792^92^he global C cycle it isA^3256^Clonal plants of white clover (Trifolium repens L.), grown singly in pots of Perlite and solely dependent for nitrogen on root nodule N2 fixation, were maintained in controlled environments which provided four environments: 18/13-degrees-C day/night temperature at 340 and 680-mu-mol mol-1 CO2 and 20.5/15.5-degrees-C day/night temperature at 340 and 680-mu-mol mol-1 CO2. The daylength was 12h and the photon flux density 500+/-25-mu-mol m-2 s-1 (PFD). All plants were defoliated for about 80d, nominally every alternate day, to leave the youngest expanded leaf intact on 50% of stolons, plus expanding leaves (simulated grazing). Elevated CO2 increased the yield of biomass removed at defoliation by a constant 45% during the second 40d of the experiment and by a varying amount in the first half of the experiment. Elevated temperature had little effect on biomass yield. Nitrogen, as a proportion of the harvested biomass, was only fractionally affected by elevated CO2 or temperature. In contrast, N2 fixation increased in concert with the promoting effect of elevated CO2 on biomass production. The increased yield of biomass harvested in 680 mu- mol mol-1 CO2 was primarily due to the early development and continued maintenance of more stolons. However, the stolons of plants grown in elevated CO2 also developed leaves which were heavier and slightly larger in area than their counterparts in ambient CO2. The conclusion is that, when white clover plants are maintained at constant mass by simulated grazing, they continue to respond to elevated CO2 in terms of a sustained increase in biomass production.207^3^Ryle,GJA^Powell,CE^Tewson,V^1992^1^Effect of elevated co2 on the photosynthesis, respiration and growth of perennial ryegrass^78^43^251^811-818^^^^^Jun^^^^^3259188^374^376^417^430^57^793^first half of the experiment. Elevated temperature had little effect on biomass yield. Nitrogen, as a proportion of the harvested biomass, was only fractionally affected by elevated CO2 or temperature. In contrast, N2 fixation iA^3258^Single, seed-grown plants of ryegrass (Lolium perenne L. cv. Melle) were grown for 49 d from the early seedling stage in growth cabinets at a day/night temperature of 20/15-degrees-C, with a 12 h photoperiod, and a CO2 concentration of either 340 or 680-mu-l l-1 CO2. Following complete acclimation to the environmental regimes, leaf and whole plant CO2 effluxes and influxes were measured using infra-red gas analysis techniques. Elevated CO2 increased rates of photosynthesis of young, fully expanded leaves by 35-46% and of whole plants by more than 50%. For both leaves and whole plants acclimation to 680-mu-l l-1 CO2 reduced rates of photosynthesis in both CO2 regimes, compared with plants acclimated to 340-mu-l l-1. There was no significant effect of CO2 regime on respiration rates of either leaves or whole plants, although leaves developed in elevated CO2 exhibited generally lower rates than those developed in 340-mu-l l-1 CO2. Initially the seedling plants in elevated CO2 grew faster than their counterparts in 340-mu-l l-1 CO2, but this effect quickly petered out and final plant weights differed by only c. 10%. Since the total area of expanded and unexpanded laminae was unaffected by CO2 regime, specific leaf area was persistently 13-40% lower in elevated CO2 while, similarly, root/shoot ratio was also reduced throughout the experiment. Elevated CO2 reduced tissue nitrogen contents of expanded leaves, but had no effect on the nitrogen contents of unexpanded leaves, sheaths or roots. The lack of a pronounced effect of elevated CO2 on plant growth was primarily due to the fact that CO2 concentration did not influence tiller (branch) numbers. In the absence of an effect on tiller numbers, any possible weight increment was restricted to the c. 2.5 leaves of each tiller. The reason for the lack of an effect on tillering is not known.s developed in elevated CO2 exhibited generally lower rates than those developed in 340-mu-l l-1 CO2. Initially the seedling plants in elevated CO2 grew faster than their count208^3^Smith,TM^Leemans,R^Shugart,HH^1992^1^Sensitivity of terrestrial carbon storage to co2-induced climate change - comparison of 4 scenarios based on general- circulation models^50^21^4^367-384^^^^^Aug^^^^^3261174^634^ persistently 13-40% lower in elevated CO2 while, similarly, root/shoot ratio was also reduced throughout the experiment. Elevated CO2 reduced tissue nitrogen contents of expanded leaves, but had no effect on the nitrogen contents of unexpanded leaves, sheaths or roots. The lack of a pronounced effect of elevated CO2 on plant growth was primarily due to the fact that CO2 concentration did not influence tiller (branch) numbers. In the absence of an effect on tiller numbers, any possible weight increment was restricted to the c. 2.5 leaves of each tiller. The reason for the lack of an effect on tillering is not known.s developed in elevated CO2 exhibited generally lower rates than those developed in 340-mu-l l-1 CO2. Initially the seedling plants in elevated CO2 grew faster than their countA^3260^The potential impacts of CO2-induced climate change on terrestrial carbon storage was estimated using the Holdridge Life-Zone Classification and four climate change scenarios derived from general circulation models. Carbon values were assigned to life-zones and their associated soils from published studies. All four scenarios suggest an increase in area occupied by forests although details of predicted patterns vary among the scenarios. There is a poleward shift of the forested zones, with an increase in the areal extent of tropical forests and a shift of the boreal forest zone into the region currently occupied by tundra. Terrestrial carbon storage increased from 0.4% (8.5 Gt) to 9.5% (180.5 Gt) above estimates for present conditions. These changes represent a potential reduction of 4 to 85 ppm on elevated atmospheric CO2 levels.209^2^Strain,BR^Thomas,RB^1992^1^Field-measurements of co2 enhancement and climate change in natural vegetation^94^64^1-2^45-60^^^^^Aug^^^^^3263rew faster than their count189^229^342^345^372^377^378^546^794^795^ed climate change on terrestrial carbon storage was estimated using the Holdridge Life-Zone Classification and four climate change scenarios derived from general circulation models. Carbon values were assigned to life-zones and their associated soils from published studies. All four scenarios suggest an increase in area occupied by forests although details of predicted patterns vary among the scenarios. There is a poleward shift of the forested zones, with an increase in the areal extent of tropical forests and a shift of the boreal forest zone into the region currently occupied by tundra. Terrestrial carbon storage increased from 0.4% (8.5 Gt) to 9.5% (180.5 Gt) above estimates for present conditions. These changes represent a potential reduction of 4 to 85 ppm on elevated atmospheric CO2 levels.209^2^Strain,BR^Thomas,RB^1992^1^Field-measurements of co2 enhancement and climate change in natural vegetation^94^64^1-2^45-60^^^^^Aug^^^^^3263rew faster than their countA^3262^It is generally assumed that healthy, natural ecosystems have the potential to sequester carbon under favorable environmental conditions. There is also evidence that CO2 acts as a plant fertilizer. It is of interest to know if these assumptions are valid and how natural systems might respond under future scenarios of CO2 increase and possible climate changes. Few measurements of the effects of CO2 and global climate change have been made on "natural" ecosystems under realistic field conditions. Most measurements have been conducted in the synthetic environments of totally controlled greenhouses and growth chambers. Several lines of evidence indicate that controlled environment studies using plants growing in pots induce experimental artifacts that reduce confidence in the use of results for prediction of future global responses. Open top chambers are being used in several autecological field studies in an attempt to obtain more realistic field environments. A few field microcosm studies have been completed and a system for the free air release of CO2 has been applied in cotton fields. Unfortunately, the requirement of large amounts of CO2 and financial restrictions have precluded the initiation of larger scale field studies in natural vegetation. This paper lists and summarizes the best field studies available but draws heavily on studies from artificial environments and conditions in an attempt to summarize knowledge of global environmental change on forests and other non-agricultural ecosystems. Finally the paper concludes that there is a need for the development and application of equipment for field measurements in several representative natural ecosystems and makes specific recommendation of the creation of a tropical research center.210^2^Welker,JM^Briske,DD^1992^1^Clonal biology of the temperate, caespitose, graminoid schizachyrium-scoparium - a synthesis with reference to climate change^15^63^3^357-365^^^^^Apr^^^^^3265243^372^374^386^547^704^796^797^91^92^ield microcosm studies have been compA^3264^Caespitose graminoids are characterized by the compact spatial arrangement of ramets within clones and the absence of rhizomes or stolons. Resource allocation is principally acropetal with established ramets supporting juvenile ramets during early development. However, after juvenile ramet maturation a responsive resource transfer system is maintained by a low level of continuous resource allocation between parental and juvenile ramets. Isotopic and severing experiments demonstrated that physiological integration in the caespitose graminoid Schizachyrium scoparium is restricted to individual ramet sequences consisting of three connected ramet generations as opposed to all ramets within the clone. This number of ramet generations comprising the physiological individual is determined by demographic variables influencing the recruitment and longevity of individual ramets. Restricted resource allocation among ramet sequences within clones is primarily caused by the disintegration of vascular connections among ramet sequences following death of the seminal ramet. The survival value conferred by a clonal architecture composed of an assemblage of autonomous physiological individuals growing within close proximity requires further evaluation but may center on intra-plant competitive interactions. The response of this large sub-group of clonal plants to climate change will significantly impact community structure and function because of their diversity and dominance in numerous biomes. The impact of climate change on the caespitose graminoid growth form is difficult to anticipate because: 1) caespitose graminoids consist of both C3 and C4 species which will complicate the response of the growth form, 2) our understanding about the clonal biology and population ecology of this growth form is still evolving and 3) the modular construction of this growth form may result in variable responses at the ramet, clone and population levels of organization.s primarily caused by the disintegration of vascular connections a211^2^Ziska,LH^Teramura,AH^1992^1^Co2 enhancement of growth and photosynthesis in rice (oryza- sativa) - modification by increased ultraviolet-b radiation^8^99^2^473-481^^^^^Jun^^^^^3267245^310^312^343^348^372^417^441^urther evaluation but may center on intra-plant competitive interactions. The response of this large sub-group of clonal plants to climate change will significantly impact community structure and function because of their diversity and dominance in numerous biomes. The impact of climate change on the caespitose graminoid growth form is difficult to anticipate because: 1) caespitose graminoids consist of both C3 and C4 species which will complicate the response of the growth form, 2) our understanding about the clonal biology and population ecology of this growth form is still evolving and 3) the modular construction of this growth form may result in variable responses at the ramet, clone and population levels of organization.s primarily caused by the disintegration of vascular connections aA^3266^Two cultivars of rice (Oryza sativa L.) IR-36 and Fujiyama-5 were grown at ambient (360 microbars) and elevated CO2 (660 microbars) from germination through reproduction in unshaded greenhouses at the Duke University Phytotron. Growth at elevated CO2 resulted in significant decreases in nighttime respiration and increases in photosynthesis, total biomass, and yield for both curtivars. However, in plants exposed to simultaneous increases in CO2 and ultraviolet-B (UV-B) radiation, CO2 enhancement effects on respiration, photosynthesis, and biomass were eliminated in IR-36 and significantly reduced in Fujiyama-5. UV-B radiation simulated a 25% depletion in stratospheric ozone at Durham, North Carolina. Analysis of the response of CO2 uptake to internal CO2 concentration at light saturation suggested that, for IR-36, the predominant limitation to photosynthesis with increased UV- B radiation was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosynthetic decrease appeared to be related to a decline in apparent carboxylation efficiency. Changes in the RuBP regeneration limitation in IR-36 were consistent with damage to the photochemical efficiency of photosystem II as estimated from the ratio of variable to maximum chlorophyll fluorescence. Little change in RuBP regeneration and photochemistry was evident in cultivar Fujiyama-5, however. The degree of sensitivity of photochemical reactions with increased UV-B radiation appeared to be related to leaf production of UV-B- absorbing compounds. Fujiyama-5 had a higher concentration of these compounds than IR-36 in all environments, and the production of these compounds in Fujiyama-5 was stimulated by UV-B fluence. Results from this study suggest that in rice alterations in growth or photosynthesis as a result of enhanced CO2 may be eliminated or reduced if UV-B radiation continues to increase.ion was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosyntheti212^3^Ashenden,TW^Baxter,R^Rafarel,CR^1992^1^An inexpensive system for exposing plants in the field to elevated concentrations of co2^9^15^3^365-372^^^^^Apr^^^^^3269580^798^A^3268^An inexpensive, potentially mobile field exposure system is described which may be easily constructed by a small workshop. It may be operated as an open-top with a frustrum or covered with a polycarbonate 'lid'. The system is cost-effective for CO2 exposure work because the small size allows provision of CO2-enriched atmospheres over prolonged periods at relatively low cost. A preliminary assessment of the chambers has been made and concentrations can be maintained at +/- 6% for a target atmosphere of 680 cm3 m-3 CO2 under normal operating conditions. Other chamber environmental conditions are reported..synthesis as a result of enhanced CO2 may be eliminated or reduced if UV-B radiation continues to increase.ion was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosyntheti213^3^Chu,CC^Coleman,JS^Mooney,HA^1992^1^Controls of biomass partitioning between roots and shoots - atmospheric co2 enrichment and the acquisition and allocation of carbon and nitrogen in wild radish^2^89^4^580-587^^^^^Apr^^^^^3271230^314^362^372^374^433^540^618^799^800^nstructed by a small workshop. It may be operated as an open-top with a frustrum or covered with a polycarbonate 'lid'. The system is cost-effective for CO2 exposure work because the small size allows provision of CO2-enriched atmospheres over prolonged periods at relatively low cost. A preliminary assessment of the chambers has been made and concentrations can be maintained at +/- 6% for a target atmosphere of 680 cm3 m-3 CO2 under normal operating conditions. Other chamber environmental conditions are reported..synthesis as a result of enhanced CO2 may be eliminated or reduced if UV-B radiation continues to increase.ion was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosynthetiA^3270^The effects of CO2 enrichment on plant growth, carbon and nitrogen acquisition and resource allocation were investigated in order to examine several hypotheses about the mechanisms that govern dry matter partitioning between shoots and roots. Wild radish plants (Raphanus sativus x raphanistrum) were grown for 25 d under three different atmospheric CO2 concentrations (200 ppm, 330 ppm and 600 ppm) with a stable hydroponic 150-mu- mol l-1 nitrate supply. Radish biomass accumulation, photosynthetic rate, water use efficiency, nitrogen per unit leaf area, and starch and soluble sugar levels in leaves increased with increasing atmospheric CO2 concentration, whereas specific leaf area and nitrogen concentration of leaves significantly decreased. Despite substantial changes in radish growth, resource acquisition and resource partitioning, the rate at which leaves accumulated starch over the course of the light period and the partitioning of biomass between roots and shoots were not affected by CO2 treatment. This phenomenon was consistent with the hypothesis that root/shoot partitioning is related to the daily rate of starch accumulation by leaves during the photoperiod, but is inconsistent with hypotheses suggesting that root/shoot partitioning is controlled by some aspect of plant C/N balance.214^2^Dube,SL^Vidaver,W^1992^1^Photosynthetic competence of plantlets grown-invitro - an automated-system for measurement of photosynthesis invitro^37^84^3^409-416^^^^^Mar^^^^^3273348^349^407^530^561^801^802^ic rate, water use efficiency, nitrogen per unit leaf area, and starch and soluble sugar levels in leaves increased with increasing atmospheric CO2 concentration, whereas specific leaf area and nitrogen concentration of leaves significantly decreased. Despite substantial changes in radish growth, resource acquisition and resource partitioning, the rate at which leaves accumulated starch over the course of the light period and the partitioning of biomass between roots and shoots were not affected by CO2 treatment.A^3272^An aseptic gas exchange and hydroponic system (AGEHS) has been developed in an attempt for characterization of physiological requirements for photoautotrophic growth in vitro and alleviation of the needs for ex vitro acclimatization. The AGEHS monitors and controls several parameters relevant to plant growth. Shootlets of Chrysanthemum, x morifolium Ramat. cv. Envy were treated with flow of air or CO2-enriched air under controlled relative humidity, elevated photosynthetic photon flux density (PPFD) and hydroponic irrigation. After 15 days of treatment, plantlets gained more than 3 times as much dry weight as those from a conventional culture tube treatment. This study shows that it is possible to favour photoautotrophic growth when elevated PPFD, enhanced air-exchange and hydroponic medium flow are provided concurrently. This enhancement is achievable through careful increments of light quanta, balanced with increments of humidified air flow and/or CO2 content in air which seem to be necessary to avoid potential photoinhibition and premature water exhaustion from gelled media.215^3^Elkohen,A^Rouhier,H^Mousseau,M^1992^1^Changes in dry-weight and nitrogen partitioning induced by elevated co2 depend on soil nutrient availability in sweet chestnut (castanea-sativa mill)^186^49^2^83-90^^^^^^^^^^3275312^361^376^417^419^664^803^92^santhemum, x morifolium Ramat. cv. Envy were treated with flow of air or CO2-enriched air under controlled relative humidity, elevated photosynthetic photon flux density (PPFD) and hydroponic irrigation. After 15 days of treatment, plantlets gained more than 3 times as much dry weight as those from a conventional culture tube treatment. This study shows that it is possible to favour photoautotrophic growth when elevated PPFD, enhanced air-exchange and hydroponic medium flow are provided concurrently. This enhancement is achievable through careful increments of light quanta, balanced with increments of humidified air flow and/or CO2 content in air which seem to be necessary to avoA^3274^The effect of 2 levels of atmospheric carbon dioxide (ambient, ie 350 ppm, and double, ie 700 ppm) and 2 contrasting levels of mineral nutrition on dry weight, nitrogen accumulation and partitioning were examined in 2-year-old chestnut seedlings (Castanea sativa Mill), grown in pots outdoors throughout the vegetative season. Fertilization had a pronounced effect on dry weight accumulation, tree height, leaf area, and plant nitrogen content. Carbon dioxide enrichment significantly increased total biomass by about 20%, both on fertilized and on unfertilized forest soil. However, the partitioning of biomass was very different: on the unfertilized soil, only the root biomass was increased, leading to an increase in the root: shoot ratio. Contrastingly, on fertilized soil only stem biomass and diameter but not height were increased. Carbon dioxide enrichment significantly reduced the nitrogen concentration in all organs, irrespective of the nutrient availability. However, the biomass increase made up for this reduction in such a way that the total nitrogen pool per tree remained unchanged.216^4^Harley,PC^Thomas,RB^Reynolds,JF^Strain,BR^1992^1^Modeling photosynthesis of cotton grown in elevated co2^9^15^3^271-282^^^^^Apr^^^^^3277130^312^348^356^376^384^562^665^666^675^ill), grown in pots outdoors throughout the vegetative season. Fertilization had a pronounced effect on dry weight accumulation, tree height, leaf area, and plant nitrogen content. Carbon dioxide enrichment significantly increased total biomass by about 20%, both on fertilized and on unfertilized forest soil. However, the partitioning of biomass was very different: on the unfertilized soil, only the root biomass was increased, leading to an increase in the root: shoot ratio. Contrastingly, on fertilized soil only stem biomass and diameter but not height were increased. Carbon dioxide enrichment significantly reduced the nitrogen concentration in all organs, irrespective of the nutrient availability. However, the biomass increase made up for tA^3276^Cotton plants were grown in CO2-controlled growth chambers in atmospheres of either 35 or 65 Pa CO2. A widely accepted model of C3 leaf photosynthesis was parameterized for leaves from both CO2 treatments using non-linear least squares regression techniques, but in order to achieve reasonable fits, it was necessary to include a phosphate limitation resulting from inadequate triose phosphate utilization. Despite the accumulation of large amounts of starch (> 50 g m-2) in the high CO2 plants, the photosynthetic characteristics of leaves in both treatments were similar, although the maximum rate of Rubisco activity (Vc(max)), estimated from A versus C(i) response curves measured at 29-degrees-C, was almost-equal-to 10% lower in leaves from plants grown in high CO2. The relationship between key model parameters and total leaf N was linear, the only difference between CO2 treatments being a slight reduction in the slope of the line relating Vc(max) to leaf N in plants grown at high CO2, Stomatal conductance of leaves of plants grown and measured at 65 Pa CO2 was approximately 32% lower than that of plants grown and measured at 35 Pa. Because photosynthetic capacity of leaves grown in high CO2 was only slightly less than that of leaves grown in 35Pa CO2, net photosynthesis measured at the growth CO2, light and temperature conditions was approximately 25% greater in leaves of plants grown in high CO2, despite the reduction in leaf conductance. Greater assimilation rate was one factor allowing plants grown in high CO2 to incorporate 30% more biomass during the first 36 d of growth.217^2^Idso,SB^Kimball,BA^1992^1^Seasonal fine-root biomass development of sour orange trees grown in atmospheres of ambient and elevated co2 concentration^9^15^3^337-341^^^^^Apr^^^^^3279376^392^454^lationship between key model parameters and total leaf N was linear, the only difference between CO2 treatments being a slight reduction in the slope of the line relating Vc(max) to leaf N in plants grown at high CO2, Stomatal conductancA^3278^Sour orange trees have been grown from the seedling stage out- of-doors at Phoenix, Arizona, USA, in open-top enclosures with clear plastic walls for 3.5 years. For the last 3 years of this period, half of the trees have been continuously exposed to air enriched with CO2 to 300-mu-mol mol-1 above the ambient concentration. At 2-month intervals over the last 12 months, we have determined the fine-root biomass in the top 0.4 m of the soil profile beneath the trees. Results from both treatments define a single relationship between fine-root biomass and trunk cross-sectional area. The data also show the CO2-enriched trees to have approximately 2.3 times more fine-root biomass in this soil layer than the trees grown in ambient air.218^2^Luo,YH^Strain,BR^1992^1^Leaf water status in velvetleaf under long-term interactions of water-stress, atmospheric humidity, and carbon-dioxide^4^139^5^600-604^^^^^Mar^^^^^3281349^374^407^417^514^529^ting Vc(max) to leaf N in plants grown at high CO2, Stomatal conductancA^3280^Well watered and water-stressed Abutilon theophrastic, were grown with relative humidity of 45% or 85% at 30-degrees-C and CO2 concentrations of 350 or 650-mu-mol mol-1. Elevated leaf water potentials of the water-stressed plants grown in both high and low humidities were caused by CO2 enrichment. Elevated water content (kg m-2 leaf area) caused by CO2 enrichment, higher water content at a given water potential, and notably lower rate in desiccation from detached leaves all occurred only in the plants grown in low humidity. These results may be related to enhanced dehydration resistance of the plants that experienced long-term low humidity.219^3^Simola,LK^Lemmetyinen,J^Santanen,A^1992^1^Lignin release and photomixotrophism in suspension-cultures of picea-abies^37^84^3^374-379^^^^^Mar^^^^^3283710^804^805^806^807^808^809^810^811^92^atmospheric humidity, and carbon-dioxide^4^139^5^600-604^^^^^Mar^^^^^3281349^374^407^417^514^529^ting Vc(max) to leaf N in plants grown at high CO2, Stomatal conductancA^3282^The effect of different concentrations of sucrose (0-4%) and of two growth regulators (0-50-mu-M 2,4-D and 0-25-mu-M kinetin) was tested on growth and chlorophyll content of suspension cultures of Picea abies (L.) Karst. originating from chlorophyllous embryo callus in an elevated CO2 (2%) atmosphere. A continuous chlorophyllous suspension culture was achieved on a medium containing 2% sucrose and a low level of organic nitrogen (0.25 mM arginine and 0.5 mM glutamine) supplemented with 2,4-D (0.5-mu-M) and kinetin (2.5-mu-M). The same medium with 4% sucrose gave the best growth response, but a negative correlation between chlorophyll level and growth was observed. The chlorophyllous cultures grew slowly in a medium with low (0.5%) sucrose or without any carbohydrate source, suggesting photomixotrophism. A high concentration of kinetin inhibited both growth and chlorophyll synthesis. Release of lignin into the nutrient medium was observed in several experiments, especially in slow-growing cultures supplemented with sucrose. Only a few successive passages of suspensions that produced lignin could be cultured before cell death. The cultures releasing lignin may be unique for studies on synthesis and biodegradation of this very complex compound.220^1^Svedang,MU^1992^1^Carbon-dioxide as a factor regulating the growth dynamics of juncus-bulbosus^159^42^3^231-240^^^^^Apr^^^^^3285243^417^621^622^623^624^812^A^3284^The unusual growth pattern exhibited by Juncus bulbosus L. in a slightly acidic Swedish brown-water lake is due to a CO2 deficit. Decrease in growth rate during the summer can be avoided through CO2 addition in July when CO2 availability is low and epiphytes are thriving. Growth of J. bulbosus in the laboratory is stimulated by CO2 addition up to a concentration somewhat higher than in air (500 ppm). while higher CO2 pressure restrains growth. Root growth reflects the leaf biomass development, but is favoured by elevated CO2 levels even more than the leaves.specially in slow-growing cultures supp221^3^Winder,TL^Anderson,JC^Spalding,MH^1992^1^Translational regulation of the large and small subunits of ribulose bisphosphate carboxylase oxygenase during induction of the co2-concentrating mechanism in chlamydomonas-reinhardtii^8^98^4^1409-1414^^^^^Apr^^^^^3287502^543^571^813^814^815^816^817^egulating the growth dynamics of juncus-bulbosus^159^42^3^231-240^^^^^Apr^^^^^3285243^417^621^622^623^624^812^A^3284^The unusual growth pattern exhibited by Juncus bulbosus L. in a slightly acidic Swedish brown-water lake is due to a CO2 deficit. Decrease in growth rate during the summer can be avoided through CO2 addition in July when CO2 availability is low and epiphytes are thriving. Growth of J. bulbosus in the laboratory is stimulated by CO2 addition up to a concentration somewhat higher than in air (500 ppm). while higher CO2 pressure restrains growth. Root growth reflects the leaf biomass development, but is favoured by elevated CO2 levels even more than the leaves.specially in slow-growing cultures suppA^3286^In conditions of limiting external inorganic carbon, the unicellular alga Chlamydomonas reinhardtii induces a mechanism to actively transport and accumulate inorganic carbon within the cell. A high internal inorganic carbon concentration enables the cell to photosynthesize efficiently with little oxygen inhibition, even in conditions of limiting external inorganic carbon. A correlation between limiting inorganic carbon-induced induction of the CO2-concentrating mechanism and decreased synthesis of the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase has been observed. Cells that had been transferred from elevated CO2 to limiting CO2 exhibit transient declines of label incorporation into both subunit polypeptides. We have found that this decrease in synthesis of large and small subunits results from specific and coordinated down-regulation of translation of both subunits possibly resulting, at least in part, from modification of large and small subunit transcripts.ures supp222^2^Ziska,LH^Teramura,AH^1992^1^Intraspecific variation in the response of rice (oryza-sativa) to increased co2 - photosynthetic, biomass and reproductive characteristics^37^84^2^269-276^^^^^Feb^^^^^3289312^348^360^363^372^409^441^528^639^665^ables the cell to photosynthesize efficiently with little oxygen inhibition, even in conditions of limiting external inorganic carbon. A correlation between limiting inorganic carbon-induced induction of the CO2-concentrating mechanism and decreased synthesis of the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase has been observed. Cells that had been transferred from elevated CO2 to limiting CO2 exhibit transient declines of label incorporation into both subunit polypeptides. We have found that this decrease in synthesis of large and small subunits results from specific and coordinated down-regulation of translation of both subunits possibly resulting, at least in part, from modification of large and small subunit transcripts.ures suppA^3288^Two rice (Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360-mu-l l-1) and ambient plus 300-mu-l l-1 CO2 from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO2 resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO2 environment. The photosynthetic response at 5% CO2 and the response of CO2 assimilation (A) to internal CO2 (C(i)) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO2 were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO2 environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO2 environment.223^2^Arp,WJ^Drake,BG^1991^1^Increased photosynthetic capacity of scirpus-olneyi after 4 years of exposure to elevated co2^9^14^9^1003-1006^^^^^Dec^^^^^3291245^264^312^344^348^378^417^818^cement was still evident after 3 months of exposure to a high CO2 environment. The photosynthetic response at 5% CO2 and the response of CO2 assimilation (A) to internal CO2 (C(i)) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO2 were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO2 environment with a significant increase in harvest index for IR-36 but notA^3290^While a short-term exposure to elevated atmospheric CO2 induces a large increase in photosynthesis in many plants, long-term growth in elevated CO2 often results in a smaller increase due to reduced photosynthetic capacity. In this study, it was shown that, for a wild C3 species growing in its natural environment and exposed to elevated CO2 for four growing seasons, the photosynthetic capacity has actually increased by 31%. An increase in photosynthetic capacity has been observed in other species growing in the field, which suggests that photosynthesis of certain field grown plants will continue to respond to elevated levels of atmospheric CO2.224^3^Cure,JD^Rufty,TW^Israel,DW^1991^1^Assimilate relations in source and sink leaves during acclimation to a co2-enriched atmosphere^37^83^4^687-695^^^^^Dec^^^^^3293243^349^398^417^542^546^57^819^820^92^oductive characteristics were also observed between cultivars at an elevated CO2 environment with a significant increase in harvest index for IR-36 but notA^3292^Evidence from previous studies suggested that adjustments in assimilate formation and partitioning in leaves might occur over time when plants are exposed to enriched atmospheric CO2. We examined assimilate relations of source (primary unifoliolate) and developing sink (second mainstem trifoliolate) leaves of soybean [Glycine max (L.) Merr. cv. Lee] plants for 12 days after transfer from a control (350-mu-l l-1) to a high (700-mu-l l-1) CO2 environment. Similar responses were evident in the two leaf types. Net CO2 exchange rate (CER) immediately increased and remained elevated in high CO2. Initially, the additional assimilate at high CO2 levels in the light and was utilized in the subsequent dark period. After approximately 7 days, assimilate export in the light began to increase and by 12 days reached rates 3 to 5 times that of the control. In the developing sink leaf, high rates of export in the light occurred as the leaf approached full expansion. The results indicate that a specific acclimation process occurs in source leaves which increases the capacity for assimilate export in the light phase of the diurnal cycle as plants adjust to enriched CO2 and a more rapid growth rate.225^6^Gao,K^Aruga,Y^Asada,K^Ishihara,T^Akano,T^Kiyohara,M^1991^1^Enhanced growth of the red alga porphyra-yezoensis ueda in high co2 concentrations^187^3^4^355-362^^^^^Dec^^^^^3295243^416^417^543^639^821^822^823^824^825^ (350-mu-l l-1) to a high (700-mu-l l-1) CO2 environment. Similar responses were evident in the two leaf types. Net CO2 exchange rate (CER) immediately increased and remained elevated in high CO2. Initially, the additional assimilate at high CO2 levels in the light and was utilized in the subsequent dark period. After approximately 7 days, assimilate export in the light began to increase and by 12 days reached rates 3 to 5 times that of the control. In the developing sink leaf, high rates of export in the light occurred as the leaf approached full expansion. The results indicate that a specific acclimation prA^3294^Leafy thalli of the red alga Porphyra yezoensis Ueda, initiated from conchospores released from free-living conchocelis, were cultured using aeration with high CO2. It was found that the higher the CO2 concentration, the faster the growth of the thalli. Aeration with elevated CO2 lowered pH in dark, but raised pH remarkably in light with the thalli, because the photosynthetic conversion of HCO3- to OH- and CO2 proceeded much faster than the dissociation of hydrated CO2 releasing H+. Photosynthesis of the alga was found to be enhanced in the seawater of elevated dissolved inorganic carbon (DIC, CO2 + HC O3- + CO3-). It is concluded that the increased pH in the light resulted in the increase of DIC in the culture media, thus enhancing photosynthesis and growth. The relevance of the results to removal of atmospheric CO2 by marine algae is discussed.226^3^Gimenez,C^Mitchell,VJ^Lawlor,DW^1992^1^Regulation of photosynthetic rate of 2 sunflower hybrids under water-stress^8^98^2^516-524^^^^^Feb^^^^^3297 pr245^348^356^417^441^553^826^827^828^829^yra yezoensis Ueda, initiated from conchospores released from free-living conchocelis, were cultured using aeration with high CO2. It was found that the higher the CO2 concentration, the faster the growth of the thalli. Aeration with elevated CO2 lowered pH in dark, but raised pH remarkably in light with the thalli, because the photosynthetic conversion of HCO3- to OH- and CO2 proceeded much faster than the dissociation of hydrated CO2 releasing H+. Photosynthesis of the alga was found to be enhanced in the seawater of elevated dissolved inorganic carbon (DIC, CO2 + HC O3- + CO3-). It is concluded that the increased pH in the light resulted in the increase of DIC in the culture media, thus enhancing photosynthesis and growth. The relevance of the results to removal of atmospheric CO2 by marine algae is discussed.226^3^Gimenez,C^Mitchell,VJ^Lawlor,DW^1992^1^Regulation of photosynthetic rate of 2 sunflower hybrids under water-stress^8^98^2^516-524^^^^^Feb^^^^^3297 prA^3296^The effect of short-term water stress on photosynthesis of two sunflower hybrids (Helianthus annuus L. cv Sungro-380 and cv SH-3622), differing in productivity under field conditions, was measured. The rate of CO2 assimilation of young, mature leaves of SH-3622 under well-watered conditions was approximately 30% greater than that of Sungro-380 in bright light and elevated CO2; the carboxylation efficiency was also larger. Growth at large photon flux increased assimilation rates of both hybrids. The changes in leaf composition, including cell numbers and sizes, chlorophyll content, and amounts of total soluble and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein, and in Rubisco activity and amount of ribulose-1,5- bisphosphate (RuBP) were determined to assess the factors regulating the differences in assimilation of the hybrids at high and low water potentials. The amounts of chlorophyll, soluble protein, Rubisco protein and the initial activity of Rubisco and its activation state did not differ significantly between hybrids. However, unstressed leaves of SH-3622 had more, smaller cells per unit area and 60% more RuBP per unit leaf area than that of Sungro-380. Water stress developing over 4 days decreased the assimilation of both hybrids similarly. Changes in the amounts of chlorophyll, soluble and Rubisco protein, and Rubisco activity and activation state were small and were not sufficient to explain the decrease in photosynthesis; neither was decreased stomatal conductance (or stomatal "patchiness"). Reduction of photosynthesis per unit leaf area from 25 to 5 micromoles CO2 per square meter per second in both hybrids was caused by a decrease in the amount of RuBP from approximately 130 to 40 micromoles per square meter in SH-3622 and from 80 to 40 micromoles per square meter in Sungro. Differences between hybrids and their response to water stress is discussed in relation to control of RuBP regeneration.Rubisco protein and the initial activity of Rubisco and its activation state did 227^3^Kelly,DW^Hicklenton,PR^Reekie,EG^1991^1^Photosynthetic response of geranium to elevated co2 as affected by leaf age and time of co2 exposure^188^69^11^2482-2488^^^^^Nov^^^^^3299312^343^348^355^360^376^380^417^529^632^ the assimilation of both hybrids similarly. Changes in the amounts of chlorophyll, soluble and Rubisco protein, and Rubisco activity and activation state were small and were not sufficient to explain the decrease in photosynthesis; neither was decreased stomatal conductance (or stomatal "patchiness"). Reduction of photosynthesis per unit leaf area from 25 to 5 micromoles CO2 per square meter per second in both hybrids was caused by a decrease in the amount of RuBP from approximately 130 to 40 micromoles per square meter in SH-3622 and from 80 to 40 micromoles per square meter in Sungro. Differences between hybrids and their response to water stress is discussed in relation to control of RuBP regeneration.Rubisco protein and the initial activity of Rubisco and its activation state did A^3298^Geranium plants were grown from seed in chambers maintained at 350 or 1000-mu-L.L-1 CO2. Photopsynthesis as affected by leaf age and by leaf position was determined. Elevated CO2 enhanced photosynthesis to the greatest extent in middle-aged leaves; very young leaves exhibited little enhancement, and net photosynthesis in the oldest leaves was depressed by elevated CO2. Temporary increases in net photosynthesis (relative to leaves developed at high CO2) resulted when young leaves grown at 350-mu-L.L-1 CO2 were switched to 1000-mu-L.L-1 CO2. Leaves switched later in development exhibited permanent enhancement. Middle-aged leaves exhibited a temporary depression followed by permanent enhancement. Leaves developed at high CO2 and switched to low CO2 did not exhibit any photosynthetic depression relative to plants grown continuously at low CO2. Similarly, leaves developed at low CO2 switched to high CO2 for various lengths of time, and returned to low CO2 showed no photosynthetic depression. Leaves developed at low CO2 and switched to high CO2 exhibited increases in specific leaf weight and leaf thickness. The increase in leaf thickness was proportional to length of time spent at high CO2. High CO2 depressed the rate at which stomata developed but did not affect final stomatal density. Results suggest that photosynthesis at low CO2 was limited by CO2 regardless of developmental environment, whereas photosynthesis at high CO2 was limited by the developmental characteristics of the leaf. Further, both biochemical and structural modifications appear to be involved in this response. Because of the very different responses of young versus old leaves, future studies should be careful to consider leaf age in assessing response to elevated CO2.228^6^Oechel,WC^Riechers,G^Lawrence,WT^Prudhomme,TJ^Grulke,N^Hastings,SJ^1992^1^Co2lt an automated, null-balance system for studying the effects of elevated co2 and global climate change on unmanaged ecosystems^43^6^1^86-100^^^^^^^^^^3301synthetic depression. Leaves developA^3300^An automated, CO2-controlled, long-term greenhouse system ('CO2LT') has been developed to provide replicated in situ ecosystem-level manipulation of atmospheric CO2 concentration and temperature for intact plots of tussock tundra, and to measure the instantaneous ecosystem-level CO2 exchange rates within each of the plots under the treatments imposed. This is a computer-controlled, closed, null-balance greenhouse system consisting of 12 chambers with individual control of CO2 concentration and temperature. Carbon dioxide can be maintained in each chamber at concentrations from well below ambient (150-200-mu-l l-1) to more than 900-mu-l l-1. Air temperature can be fixed, set to track ambient, or can track ambient temperature with a specified offset allowing studies of the interaction of CO2 and temperature. Despite the complications involved in tracking a naturally fluctuating environment, the CO2LT system performs very well. Temperatures in individual chambers average within 1-degrees-C of ambient or target temperatures over a 24-h period and carbon dioxide concentration control rivals that of laboratory-based, control- environment systems. Photon flux density within the chambers is within 93% of ambient values. Comparison to unenclosed tundra indicates minimal chamber effects on depth of thaw, air, leaf, or soil temperatures, or net ecosystem CO2 flux. Chamber effects are generally small, and the experimental design allows separation and interpretation of treatment effects despite any unavoidable chamber effects. Both diurnal and seasonal patterns of net ecosystem CO2 flux can be accurately tracked with this system. Field measurements indicate net ecosystem CO2 loss under current environmental conditions, a possible response to recent climate change. Field measurements also indicate initial enhancement of net ecosystem CO2 uptake with elevated atmospheric CO2. Photosynthetic adjustment to elevated CO2 lowers ecosystem response to that of ambient chambers by mid-season. Also indicated is the possibility of delayed senescence of photosynthetic capacity at elevated CO2.229^2^Reekie,EG^Bazzaz,FA^1991^1^Phenology and growth in 4 annual species grown in ambient and elevated co2^188^69^11^2475-2481^^^^^Nov^^^^^3303312^415^568^830^831^nclosed tundra indicates minimal chamber effects on depth of thaw, air, leaf, or soil temperatures, or net ecosystem CO2 flux. Chamber effects are generally small, and the experimental design allows separation and interpretation of treatment effects despite any unavoidable chamber effects. Both diurnal and seasonal patterns of net ecosystem CO2 flux can be accurately tracked with this system. Field measurements indicate net ecosystem CO2 loss under current environmental conditions, a possible response to recent climate change. Field measurements also indicate initial enhancement of net ecosystem CO2 uptake with elevated atmospheric CO2. Photosynthetic adjustment to elevated CO2 lowers ecosystem response to that of ambient chambers by mid-season. Also indicated is the possibility A^3302^The objectives of this study were (i) to test the hypothesis that changes in phenology with CO2 are a function of the effect of CO2 upon growth and (ii) to determine if CO2-induced changes in phenology can influence competitive outcome. We examined the effect of 350, 525, and 700-mu-L.L-1 CO2 on Guara brachycarpa, Gailardia pulchella, Oenothera laciniata, and Lupinus texensis. Plants were grown as individuals in 150-, 500-, or 1000-mL pots and in competition in 1000-mL pots. Growth and development were monitored at twice-weekly intervals, by recording the number of leaves and noting the presence or absence of stem elongation, branching, flower buds, and open flowers. Elevated CO2 affected both growth and phenology, but the direction and magnitude of effects varied with species and soil volume. Elevated CO2 did not appear to affect development through its effect on growth. Those treatments in which there were significant effects of CO2 on growth were generally different from those treatments in which CO2 affected phenology. Rather than affecting phenology by changing plant size, CO2 appeared to affect phenology by modifying the size at which plants switched from one stage to the next. The level of CO2 changed competitive outcome; the importance of Lupinus increased whereas that of Oenothera decreased with increased CO2. These changes were more closely related to the effect of CO2 on growth than its effect on phenology.230^2^Shainsky,LJ^Radosevich,SR^1992^1^Mechanisms of competition between douglas-fir and red alder seedlings^11^73^1^30-45^^^^^Feb^^^^^3305372^417^58^832^833^834^835^836^91^92^ence or absence of stem elongation, branching, flower buds, and open flowers. Elevated CO2 affected both growth and phenology, but the direction and magnitude of effects varied with species and soil volume. Elevated CO2 did not appear to affect development through its effect on growth. Those treatments in which there were significant effects of CO2 on growth were generally different from those treatments in which CA^3304^Mechanisms of interactions between Douglas-fir (Pseudotsuga menziesii) and red alder (Alnus rubra) seedlings were assessed in experimentally manipulated stands. The density of each species was varied systematically, creating a matrix of competitive regimes that consisted of five monoculture densities and 25 mixtures of all possible pairwise combinations of the monoculture densities. Response surfaces for growth rates, leaf area, photon flux density, soil moisture content and depletion, and plant water potential were generated within the matrix. Regression coefficients quantified the effects of species densities on response variables, and correlation analysis yielded insight into interrelationships between variables. Tree performance, leaf area per square metre of ground surface area, resources, and physiological variables were all quantitatively altered by alder density, Douglas-fir density, and the interaction between species densities. Alder was the dominant competitor and overtopped the Douglas-fir. Competition for light was mediated by density effects on the leaf area of each species per square metre of ground surface area. Increasing alder leaf area reduced the light reaching the understory Douglas-fir. In contrast, increasing Douglas-fir leaf areas increased the light penetrating through to the understory conifers, due to Douglas-fir's suppression of alder leaf area per square metre. Soil moisture limitations were also created by increasing the density of both species and resulted in increasingly negative leaf water potentials for both species. Growth rates concurrently declined as plant water stress increased. Response variables were assembled into a conceptual modeling proposing how species density regulated growth through the interactions between resource limitations and impairment of physiological function.231^1^Allen,LH^1992^1^Free-air co-2 enrichment field experiments - an historical overview^183^11^2-3^121-134^174^312^417^442^461^466^467^685^720^837^petitor and overtopped the Douglas-fir232^4^Chabot,S^Belrhlid,R^Chenevert,R^Piche,Y^1992^1^Hyphal growth promotion invitro of the va mycorrhizal fungus, gigaspora-margarita becker and hall, by the activity of structurally specific flavonoid compounds under co2-enriched conditions^84^122^3^461-467^^^^^Nov^^^^^3308838^839^840^841^842^843^844^845^846^847^onifers, due to Douglas-fir's suppression of alder leaf area per square metre. Soil moisture limitations were also created by increasing the density of both species and resulted in increasingly negative leaf water potentials for both species. Growth rates concurrently declined as plant water stress increased. Response variables were assembled into a conceptual modeling proposing how species density regulated growth through the interactions between resource limitations and impairment of physiological function.231^1^Allen,LH^1992^1^Free-air co-2 enrichment field experiments - an historical overview^183^11^2-3^121-134^174^312^417^442^461^466^467^685^720^837^petitor and overtopped the Douglas-firA^3307^Plant phenolic compounds are known to be inducers of virulence genes in plant-pathogen interactions such as those involving Agrobacterium, and flavonoids are known to be inducers or inhibitors of Nod genes in Rhizobium-legume symbiosis. More recent studies suggest that some of these compounds act as molecular signals in the development of vesicular-arbuscular mycorrhizas (VAM). The present study has shown that hyphal growth of the VAM fungus, Gigaspora margarita Becker & Hall, is affected by both stimulatory and inhibitory flavonoids, when applied at 10 muM together with an optimal carbon dioxide enrichment. Stimulatory compounds were all flavonols (kaempferol, quercetin and morin) and possessed at least one hydroxyl group on the B ring. Conversely, two isoflavones (biochanin A, and genistein), a single flavanone (hesperetin) and two compounds without any hydroxyl group on the B ring, galangin (flavonol) and chrysin (flavone), were all inhibitors of hyphal growth.titor and overtopped the Douglas-fir233^4^Kano,A^Fukazawa,Y^Aono,M^Ohkawa,K^1992^1^Effect of age of cuttings, propagation media, and cutting methods on rooting of stephanotis-floribunda brongn^180^61^3^619-624^^^^^Dec^^^^^3310A^3309^The effects of cutting methods, cutting media, and age of cutting on rooting capacity of Stephanotis floribunda Brongn. were investigated to improve propagation efficiency. The effects of CO2 enrichment and a new acclimatization technique for cutting were also tested. 1. Cuttings made from older shoots showed a higher rooting percentage than those made from younger ones. 2. Rockwool mats were found to be useful as a cutting medium for S. floribunda. 3. Cuttings with differentiated leaf buds showed higher rooting percentage than those without buds. 4. Rooting was stimulated by placing cuttings in a closed frame, especially when CO2 concentration was high. 5. An acclimatization technique using a computer controlled fan was developed to decrease water stress during the acclimatization period.topped the Douglas-fir234^3^Rogers,HH^Prior,SA^Oneill,EG^1992^1^Cotton root and rhizosphere responses to free-air co-2 enrichment^183^11^2-3^251-263^174^312^407^409^434^848^849^92^235^1^Titus,JE^1992^1^Submersed macrophyte growth at low ph .2. Co2 X sediment interactions^2^92^3^391-398^^^^^Dec^^^^^3313344^374^376^416^57^850^851^852^853^854^investigated to improve propagation efficiency. The effects of CO2 enrichment and a new acclimatization technique for cutting were also tested. 1. Cuttings made from older shoots showed a higher rooting percentage than those made from younger ones. 2. Rockwool mats were found to be useful as a cutting medium for S. floribunda. 3. Cuttings with differentiated leaf buds showed higher rooting percentage than those without buds. 4. Rooting was stimulated by placing cuttings in a closed frame, especially when CO2 concentration was high. 5. An acclimatization technique using a computer controlled fan was developed to decrease water stress during the acclimatization period.topped the Douglas-firA^3312^The submersed macrophyte Vallisneria americana was grown for seven weeks in a greenhouse to test for differences in the ability of three different sediments to support growth stimulation in response to CO2 enrichment at low pH. Plants accumulated 21- to 24-fold greater biomass at 10 x ambient CO2 concentrations than at ambient CO2 on all sediments. At both CO2 levels, plants grown on sediment from an acidified lake accumulated ca. 81%, and those grown on oligotrophic lake sediment ca. 47% as much biomass as plants grown on alkaline lake sediment. Despite striking CO2 and sediment effects on biomass accumulation, there was no significant interaction (using log-transformed data) between CO2 and sediment effects, indicating that all sediments allowed similar proportionate growth responses to CO2 enrichment. Plants grown on the less fertile sediments showed greater relative allocation to horizontal versus vertical growth by producing more rosette- bearing stolons in relation to plant height (leaf length) than plants grown on relatively fertile, alkaline lake sediment. Tissue analysis suggested that sediment effects on Vallisneria growth could be attributed neither to mineral nutrient (nitrogen and phosphorus) limitation nor to aluminum toxicity in these low pH treatments. In any case, CO2 availability can be an important regulator of submersed macrophyte growth at low pH on a variety of sediment types, including those from oligotrophic and acidic lakes.236^4^Tripp,KE^Kroen,WK^Peet,MM^Willits,DH^1992^1^Fewer whiteflies found on co2-enriched greenhouse tomatoes with high C-n ratios^170^27^10^1079-1080^^^^^Oct^^^^^3315373^417^489^490^628^855^ interaction (using log-transformed data) between CO2 and sediment effects, indicating that all sediments allowed similar proportionate growth responses to CO2 enrichment. Plants grown on the less fertile sediments showed greater relative allocation to horizontal versus vertical growth by producing more rosette- bearing stolons in relation to plant height (leaf length) A^3314^Eight tomato (Lycopersicon esculentum) cultivars were grown for 16 weeks in greenhouses enriched for an average of 8.1 hours daily to 1000 mul CO2/liter of air or in greenhouses maintained at ambient CO2. Carbon dioxide enrichment significantly decreased the mean number of greenhouse whiteflies [Trialeurodes vaporariorum (Westward), Homoptera: Aleyrodidae] as measured by counts from commercial yellow sticky traps. The number of whiteflies present was negatively correlated with both seasonal foliar C:N ratio and percent C but positively correlated with percent N in the foliage. Thus, CO2 enrichment apparently alters plant composition in such a way as to reduce significantly the population growth of greenhouse whiteflies.237^3^Baker,JT^Allen,LH^Boote,KJ^1992^1^Response of rice to carbon-dioxide and temperature^107^60^3-4^153-166^^^^^31 Aug^^^^^3317230^243^349^402^409^434^629^674^784^792^ontal versus vertical growth by producing more rosette- bearing stolons in relation to plant height (leaf length) A^3316^The current increase in atmospheric carbon dioxide concentration ([CO2]) along with predictions of possible future increases in global air temperatures have stimulated interest in the effects of [CO2] and temperature on the growth and yield of food crops. This study was conducted to determine the effects and possible interactions of [CO2] and temperature on the growth and yield of rice (Oryza sativa L., cultivar IR-30). Rice plants were grown for a season in outdoor, naturally sunlit, controlled-environment, and plant growth chambers. Temperature treatments of 28/21/25, 34/27/31, and 40/33/37- degrees-C (daytime dry bulb air temperature/night-time dry bulb air temperature/paddy water temperature) were maintained in [CO2] treatments of 330 and 660-mu-mol CO2 mol-1 air. In the 40/33/37-degrees-C temperature treatment, plants in the 330-mu- mol mol-1 [CO2] treatment died during stem extension while the [CO2] enriched plants survived but produced sterile panicles. Plants in the 34/27/31-degrees-C temperature treatments accumulated biomass and leaf area at a faster rate early in the growing season than plants in the 28/21/25-degrees-C temperature treatments. Tillering increased with increasing temperature treatment. Grain yield increases owing to [CO2] enrichment were small and non-significant. This lack of [CO2] response on grain yield was attributed to the generally lower levels of solar irradiance encountered during the late fall and winter when this experiment was conducted. Grain yields were affected much more strongly by temperature than [CO2] treatment. Grain yields declined by an average of approximately 7-8% per 1-degrees-C rise in temperature from the 28/21/25 to 34/27/31-degrees-C temperature treatment. The reduced grain yields with increasing temperature treatment suggests potential detrimental effects on rice production in some areas if air temperatures increase, especially under conditions of low solar irradiance.survived but produced sterile panicles. Plants in the 34/27/31-degrees-C temperat238^3^Diiorio,AA^Cheetham,RD^Weathers,PJ^1992^1^Carbon-dioxide improves the growth of hairy roots cultured on solid medium and in nutrient mists^189^37^4^463-467^^^^^Jul^^^^^3319856^reasing temperature treatment. Grain yield increases owing to [CO2] enrichment were small and non-significant. This lack of [CO2] response on grain yield was attributed to the generally lower levels of solar irradiance encountered during the late fall and winter when this experiment was conducted. Grain yields were affected much more strongly by temperature than [CO2] treatment. Grain yields declined by an average of approximately 7-8% per 1-degrees-C rise in temperature from the 28/21/25 to 34/27/31-degrees-C temperature treatment. The reduced grain yields with increasing temperature treatment suggests potential detrimental effects on rice production in some areas if air temperatures increase, especially under conditions of low solar irradiance.survived but produced sterile panicles. Plants in the 34/27/31-degrees-C temperatA^3318^The effect of varying CO2 concentrations on the growth of beet and safflower hairy roots was measured for tissues cultured in nutrient mists and on solid media in chambers fed mixtures of humidified air supplemented with different CO2 concentrations. Hairy root tissue grown on solid media in air enriched with CO2 showed increased growth, as measured by dry weight increases vs air-fed controls. Growth increased with CO2 enrichment as much as 2.5 times more than the air-fed control for safflower at 1.0 % CO2 and 1.4 times more than the air-fed control for beets at 1.5 % CO2 over a 12-day period. Beet hairy root tissue was also cultured aeroponically in nutrient mists. Beet hairy root cultured in nutrients mists enriched with 1.0 % CO2 showed a 15 % increase in biomass over a 7-day period vs tissue cultured in nutrient mists (with ambient air) or in shake flasks. The stimulation of root growth via CO2 enrichment reduced the time required for biomass accumulation.lants in the 34/27/31-degrees-C temperat239^1^Idso,SB^1992^1^Shrubland expansion in the american southwest^50^22^1^85-86^^^^^Sep174^312^376^857^240^2^Idso,SB^Kimball,BA^1992^1^Aboveground inventory of sour orange trees exposed to different atmospheric co2 concentrations for 3 full years^107^60^1-2^145-151^^^^^15 Aug^^^^^3322376^ia in air enriched with CO2 showed increased growth, as measured by dry weight increases vs air-fed controls. Growth increased with CO2 enrichment as much as 2.5 times more than the air-fed control for safflower at 1.0 % CO2 and 1.4 times more than the air-fed control for beets at 1.5 % CO2 over a 12-day period. Beet hairy root tissue was also cultured aeroponically in nutrient mists. Beet hairy root cultured in nutrients mists enriched with 1.0 % CO2 showed a 15 % increase in biomass over a 7-day period vs tissue cultured in nutrient mists (with ambient air) or in shake flasks. The stimulation of root growth via CO2 enrichment reduced the time required for biomass accumulation.lants in the 34/27/31-degrees-C temperatA^3321^Sour orange trees have been grown from the seedling stage out- of-doors at Pheonix, Arizona in clear-plastic-wall, open-top enclosures for 3.5 years. For the last 3 years of this period, half of the trees have been continuously exposed to air enriched with an extra 300 cm3 of CO2 m-3 of air. Inventories of all aboveground plant parts conducted at the conclusions of the second and third years of the study reveal that the total number of branches per tree, the total number of leaves per tree, and the total trunk plus branch volume per tree can all be adequately inferred from measurements of trunk cross- sectional area. They also reveal a sustained beneficial impact of atmospheric CO2 enrichment. After 3 full years of differential CO2 exposure, the CO2-enriched trees had nearly 100% more branches, 75% more leaves, approximately 160% more trunk and branch volume, and 190% more trunk, branch and fruit rind volume than the ambient-treatment trees.ass accumulation.lants in the 34/27/31-degrees-C temperat241^2^Mortensen,LM^Moe,R^1992^1^Effects of co2 enrichment and different day night temperature combinations on growth and flowering of rosa L and kalanchoe- blossfeldiana V poelln^165^51^1-2^145-153^^^^^Jul^^^^^3324 been continuously exposed to air enriched with an extra 300 cm3 of CO2 m-3 of air. Inventories of all aboveground plant parts conducted at the conclusions of the second and third years of the study reveal that the total number of branches per tree, the total number of leaves per tree, and the total trunk plus branch volume per tree can all be adequately inferred from measurements of trunk cross- sectional area. They also reveal a sustained beneficial impact of atmospheric CO2 enrichment. After 3 full years of differential CO2 exposure, the CO2-enriched trees had nearly 100% more branches, 75% more leaves, approximately 160% more trunk and branch volume, and 190% more trunk, branch and fruit rind volume than the ambient-treatment trees.ass accumulation.lants in the 34/27/31-degrees-C temperatA^3323^The effects of increasing the CO2 concentration from 350 to 700-mu-l l-1 on growth and flowering of Rosa L. and Kalanchoe blossfeldiana at four different day/night temperature combinations (20/20-degrees-C, 23/14-degrees-C and 17/26- degrees-C day/night, and 20/20-degrees-C with 2 h at 14- degrees-C in the morning) were studied in 16 growth chambers. An increase in the CO2 concentration resulted in enhanced total dry weight, stem: leaf fresh weight ratio, flower fresh weight, length and diameter of the rose shoot, while the number of days until flowering was not affected. With the 17/26-degrees-C treatment, rose shoots were 3-4 cm shorter, and with the 23/14- degrees-C treatment flowering occurred about 2 days earlier than with the other temperature treatments. The results were the same for Rosa cultivars 'Frisco' and 'Kiss'. No significant interactions between CO2 and temperature were found. Plant dry weight and fresh weight of flowers in Kalanchoe were generally enhanced by CO2 enrichment. The effects of CO2 on dry weight, plant height and flower stem length were greater with the 23/14-degrees-C treatment compared with the effects of the other temperature treatments. A constant temperature (20/20- degrees-C) and the 23/14-degrees-C treatments gave the shortest and tallest plants, respectively.242^1^Sinclair,TR^1992^1^Mineral-nutrition and plant-growth response to climate change^78^43^253^1141-1146^^^^^Aug^^^^^3326179^341^349^542^858^859^h weight ratio, flower fresh weight, length and diameter of the rose shoot, while the number of days until flowering was not affected. With the 17/26-degrees-C treatment, rose shoots were 3-4 cm shorter, and with the 23/14- degrees-C treatment flowering occurred about 2 days earlier than with the other temperature treatments. The results were the same for Rosa cultivars 'Frisco' and 'Kiss'. No significant interactions between CO2 and temperature were found. Plant dry weight and fresh weight of flowers in Kalanchoe were generally enhanced by CO2 enrichment. The effecA^3325^The limiting factor concept has often been used to describe plant growth responses to altered availability of resources. However, even preliminary experiments, where atmospheric CO2 concentrations and solution mineral concentrations were varied, demonstrated that a more complex concept was required to interpret the potential effects of climate change and mineral availability on plant growth. It is proposed that these resources for plant growth may be better viewed as simultaneously limiting. Further, in considering the limitation in plant growth to mineral nutrition it is important to consider both the solution concentration and the total amount of the individual minerals available to the plant. Sustaining a positive response to increased CO2 concentration, for example, requires an increase in plant uptake of the total amount of minerals. Consequently, it is very difficult to predict the plant growth response to climate change because of the large uncertainty about mineral availability. On the one hand, increased CO2 concentrations should stimulate nitrogen fixation by both free-living organisms and symbiotic systems, and improve soil properties for mineral availability as a result of increased organic matter deposition in the soil. On the other hand, increased temperature and altered rainfall patterns may result in increased losses of soil minerals. Even the direction in the net change in available soil minerals is unclear. Realistic evaluations of the effects of climate change on plant growth will be challenged to contend with the large uncertainty and complexities in understanding mineral availability and plant mineral nutrition.243^2^Sritharan,R^Lenz,F^1992^1^Effects of carbon-dioxide enrichment and nitrogen supply on kohlrabi (brassica-oleracea var gongylodes L) .1. Water-use, gas-exchange, and carbohydrate partitioning^172^57^3^138-145^^^^^May-Jun^^^^^3328174^243^348^386^442^465^674^739^growth response to climate change because of the large uncertainty about mineral availability. On the one hanA^3327^Six weeks old kohlrabi plants (Brassica oleracea var, gongylodes [L.] cv. Express Forcer) were grown in growth chambers for three weeks at two levels of CO2 concentration (300-mu-l CO2 l-1-low or 900-mu-l CO2 l-1-high) and three levels of N-nutritional regimes (0.1, 1.0 or 6.0 mM nitrate supply). Carbon dioxide enrichment significantly increased total water uptake of plants at all N supply levels. Water use efficiency, photosynthesis and stomatal conductance were increased by high CO2 only at 1.0 and 6.0 mM supply and reduced at the lowest N level. Photosynthetic efficiency (mu-Mol CO2 fixed m-2 s-1 per mu-l intercellular CO2 l-1) was reduced by both low N supply and CO2 enrichment. Intercellular CO2 concentration was not affected by N deficiency at both CO2 levels. Low NO3 had a lesser effect on photosynthesis than on leaf area growth; photosynthetic rates of mature leaves at both CO2 levels were lowered by about 30 % as compared to the respective controls, after seven weeks of reduction in NO3 supply. In leaves lowest NO3 treatment increased starch and sucrose and in roots starch glucose, fructose, and sucrose and in tuber starch concentrations. Photosynthetic reduction at low N supply showed a significant correlation with leaf starch concentration at both CO2 levels indicating that the inhibition is a result of feed back inhibition. Carbohydrate partitioning within the plant organs were predominantly governed by N supply levels than CO2 treatments.244^6^Beerling,DJ^Chaloner,WG^Huntley,B^Pearson,JA^Tooley,MJ^Woodward,FI^1992^1^Variations in the stomatal density of salix-herbacea L under the changing atmospheric co2 concentrations of late-glacial and postglacial time^190^336^1277^215-224^^^^^29 May^^^^^3330130^227^243^312^374^376^399^526^860^92^at both CO2 levels. Low NO3 had a lesser effect on photosynthesis than on leaf area growth; photosynthetic rates of mature leaves at both CO2 levels were lowered by about 30 % as compared to the respective controls, after seven weeks of reduction in NO3 supplA^3329^The rapidly rising CO2 concentration of the past 200 years has been shown to be accompanied by a fall in stomatal density in the leaves of temperate trees. The present study attempts to investigate the relationship of atmospheric CO2 change and stomatal density in the arctic-alpine shrub, Salix herbacea, over the longer time span of 11 500 years offered by fossil leaves from post-glacial deposits. Comparisons of fossil material from Scotland and Norway are made with leaves from living populations growing in Austria, Greenland and Scotland. The Austrian material, from an altitudinal gradient between 2000 and 2670 m above sea level, gives added comparison of contemporary differences of CO2 partial pressure with altitude. The results of our investigation indicate, rather surprisingly, that the rising CO2 concentration of the past 11 500 years has been accompanied by an increase in the stomatal density of S. herbacea in contrast to the shorter-term observations on the herbarium material of temperate trees. The most likely explanation appears to centre on the temperatures and water availability of the early post-glacial environment overriding the effect of the lower CO2 regime. However, the scale of the time interval involved may also be significant. Natural selection over the 11 500 year period concerned may have favoured a different response to what is, in effect, an acclimatory response observed in trees within the period of rapid CO2 rise of the past 200 years.245^2^Grimm,AG^Fuhrer,J^1992^1^The response of spring wheat (triticum-aestivum L) to ozone at higher elevations .1. Measurement of ozone and carbon-dioxide fluxes in open-top field chambers^84^121^2^201-210^^^^^Jun^^^^^3332243^384^397^602^674^678^861^862^863^864^ The results of our investigation indicate, rather surprisingly, that the rising CO2 concentration of the past 11 500 years has been accompanied by an increase in the stomatal density of S. herbacea in contrast to the shorter-term observations on the herbarium material of temperate treesA^3331^The flux of O3 was determined in open-top chambers (OTC) used to investigate its effect on spring wheat (Triticum aestivum L., cv. Albis) in 1989 and 1990. The experimental site was located at 900 m above sea level at Zimmerwald, near Bern (Switzerland). The aims were to evaluate the use of OTCs for O3 flux measurements under field conditions, to assess the role of stomata in controlling the O3 fluxes, and to establish a quantitative relationship between radiation-weighted O3 concentrations and O3 flux. Measurements were carried out from full expansion of flag leaves until the onset of senescence. Ozone flux was determined by mass balance using the concentrations of O3 measured at the inlet and outlet of the OTC. The CO2 exchange rate was corrected for soil-borne CO2 and used as a reference. Measurements of temperature, photosynthetically active radiation (PAR), saturated water vapour pressure deficit (SVPD), and boundary layer conductance were used to describe the microclimate inside OTCs. In the warmer microclimate in 1989, the plant canopy was characterized by a smaller leaf area index (LAI) than in 1990, while the fluxes of O3 and CO2 during daytime were generally larger in 1989. The diurnal patterns of fluxes of O3 and CO2 in OTCs supplied with unfiltered air were similar. It is estimated that O3 absorption via the stomata contributed 50-70 % of its total flux. Identical relationships between leaf conductance for O3 measured by porometry and leaf conductance calculated from O3 flux were found in both years, but measured leaf conductance during daytime was generally smaller in 1990 than in 1989. The results indicate that stomatal conductance largely controlled O3 flux, and that the canopy structure has an influence on the overall conductance of the canopy. Different linear functions were obtained for the relationship between radiation-weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal-filtered air, unfiltered air or unfiltered air enriched with O3 (two levels). These relationships form the basis for the calculation of mean O3 fluxes which can be used as an exposure index in the exposure-response analysis.246^1^Grodzinski,B^1992^1^Plant nutrition and growth-regulation by co2 enrichment^14^42^7^517-525^^^^^Jul-Aug243^344^360^383^502^528^529^560^745^865^247^2^Idso,SB^Kimball,BA^1992^1^Effects of atmospheric co2 enrichment on photosynthesis, respiration, and growth of sour orange trees^8^99^1^341-343^^^^^May^^^^^3335312^434^lculated from O3 flux were found in both years, but measured leaf conductance during daytime was generally smaller in 1990 than in 1989. The results indicate that stomatal conductance largely controlled O3 flux, and that the canopy structure has an influence on the overall conductance of the canopy. Different linear functions were obtained for the relationship between radiation-weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal-filtered air, unfiltered air or unfiltered air enriched with O3 (two levels). A^3334^Numerous net photosynthetic and dark respiratory measurements were made over a period of 4 years on leaves of 24 sour orange (Citrus aurantium) trees; 8 of them growing in ambient air at a mean CO2 concentration of 400 microliters per liter, and 16 growing in air enriched with CO2 to concentrations approaching 1000 microliters per liter. Over this CO2 concentration range, net photosynthesis increased linearly with CO2 by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent above-ground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO2 concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.etween radiation-weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal-filtered air, unfiltered air or unfiltered air enriched with O3 (two levels). 248^4^Kozai,T^Kushihashi,S^Kubota,C^Fujiwara,K^1992^1^Effect of the difference between photoperiod and dark period temperatures, and photosynthetic photon flux-density on the shoot length and growth of potato plantlets invitro^180^61^1^93-98^^^^^Jun^^^^^3337ing in air enriched with CO2 to concentrations approaching 1000 microliters per liter. Over this CO2 concentration range, net photosynthesis increased linearly with CO2 by more than 200%, whereas dark respiration decreased linearly to only 20% of its initial value. These results, together with those of a comprehensive fine-root biomass determination and two independent above-ground trunk and branch volume inventories, suggest that a doubling of the air's current mean CO2 concentration of 360 microliters per liter would enhance the growth of the trees by a factor of 3.8.etween radiation-weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal-filtered air, unfiltered air or unfiltered air enriched with O3 (two levels). A^3336^Potato plantlets (Solanum tuberosum L. cv. Benimaru) under CO2 enriched and photoautotrophic culture conditions were subjected to three different photo-/dark period temperature combinations (25-degrees/15-degrees-C, 200/20-degrees-C and 15-degrees/25- degrees-C) and two levels of photosynthetic photon flux densities (74 and 147-mu-mol.m-2.sec-1). The shoot length of the plantlets under the same photosytnthetic photon flux density (PPF) was reduced with decreasing the difference between photoperiod and dark period temperatures (it is named DIF, photoperiod temperature minus dark period temperature). No marked differences in the fresh and dry weights per plantlet were observed among the three DIF treatments in each PPF treatment. The higher PPF led to a decrease in the shoot length, an increase in the fresh weight, dry weight and leaf area per plantlet in each DIF treatment. It is suggested that shoot length of plantlets in vitro under CO2 enriched and photoautotrophic culture conditions can be controlled without reducing the weight increments and leaf area per plantlet by regulating the difference between photoperiod and dark period temperatures.249^3^Nederhoff,EM^Dekoning,ANM^Rijsdijk,AA^1992^1^Leaf deformation and fruit production of glasshouse grown tomato (lycopersicon-esculentum mill) as affected by co-2 plant-density and pruning^174^67^3^411-420^^^^^May^^^^^3339281^349^436^ under the same photosytnthetic photon flux density (PPF) was reduced with decreasing the difference between photoperiod and dark period temperatures (it is named DIF, photoperiod temperature minus dark period temperature). No marked differences in the fresh and dry weights per plantlet were observed among the three DIF treatments in each PPF treatment. The higher PPF led to a decrease in the shoot length, an increase in the fresh weight, dry weight and leaf area per plantlet in each DIF treatment. It is suggested that shoot length of plantlets in vitro under CO2 enriched and photoautotrophic culture conditions can be controllA^3338^During summer, glasshouse grown tomato plants (Lycopersicon esculentum Mill.) often demonstrate leaf deformation, reduced leaf area (short leaves) and low Specific Leaf Area (SLA), sometimes accompanied by higher dry matter content of leaves and stems and higher leaf starch content. This so-called "Short Leaves Syndrome" (SLS), which decreases the production capacity, was investigated with emphasis on the effects of CO2 concentration. As a working hypothesis it was postulated that SLS is indirectly caused by an oversupply of assimilates relative to the sink capacity. An experiment was conducted between 10 May and 31 July 1990 in 12 glasshouse compartments. The sink/source ratio was varied by maintaining two levels of CO2, multifactorially combined with two plant densities and three pruning treatments. CO2 enrichment and wider planting enhanced SLS and decreased leaf area and SLA of upper leaves. Leaf pruning and fruit pruning, however, did not give clear effects on vegetative characteristics, although the impact on the sink/source ratio was of the same order of magnitude. As a mechanism for these effects, we suggest that SLS is caused by calcium deficiency in the apex, a condition more severe when much phloem sap (with low calcium content) is available, i.e. when the sink/source ratio is lower. Stronger effects of CO2 and plant density than of pruning on the incidence of SLS, may be due to local effects of sink/source relationships or to involvement of other processes, like transpiration. In crops with little SLS-symptoms, CO2 enrichment increased the weight of fruits grown during the treatment period by 31%, whereas in crops with severe SLS, CO2 enrichment aggravated SLS and had no significant effect on fruit production. CO2 enrichment in summer is beneficial if SLS is prevented, which can be achieved by maintaining a higher plant density or, in an early crop, an extra shoot on the plants in spring and summer.nd fruit pruning, however, did not give clear effects on vegetative characteristics, although250^2^Rastetter,EB^Shaver,GR^1992^1^A model of multiple-element limitation for acclimating vegetation^11^73^4^1157-1174^^^^^Aug^^^^^3341130^243^349^417^540^587^672^866^867^92^dition more severe when much phloem sap (with low calcium content) is available, i.e. when the sink/source ratio is lower. Stronger effects of CO2 and plant density than of pruning on the incidence of SLS, may be due to local effects of sink/source relationships or to involvement of other processes, like transpiration. In crops with little SLS-symptoms, CO2 enrichment increased the weight of fruits grown during the treatment period by 31%, whereas in crops with severe SLS, CO2 enrichment aggravated SLS and had no significant effect on fruit production. CO2 enrichment in summer is beneficial if SLS is prevented, which can be achieved by maintaining a higher plant density or, in an early crop, an extra shoot on the plants in spring and summer.nd fruit pruning, however, did not give clear effects on vegetative characteristics, althoughA^3340^In this paper we present a simple model of multiple-element limitation of plant production and biomass accumulation. The primary aim of this model is to develop a theoretical framework for examining multiple-element limitation vs. single-element limitation and for examining the relationship between short- term and long-term responses to changes in element availability. In the model we assume that there is an "optimal" ratio of mineral elements in vegetation biomass, and that the vegetation continually adjusts its relative element uptake capacities to compensate for shifts away from this optimum. We examine the responses of this model to changes in element availability in the plant environment, where "availability" is defined either as fixed concentrations of non-depletable elements or as fixed replenishment rates of depletable elements. The model results suggest that the nature of the controls on element availability has a major impact on whether single- or multiple-element limitation prevails, even when plants can acclimate so as to maintain an "optimal" nutritional balance. Single-element limitation occurs when the replenishment rate of an essential element to the available pool is limited and sustainable plant uptake of that element equals the replenishment rate. Furthermore, when single- element limitation prevails, there is little or no correlation between short-term responses to a change in element availability and long-term, equilibrium responses. In general, previous experimental studies and models of plant growth in response to changes in relative availability of multiple, essential elements have either not specified how those resources are controlled, or have examined only one type of control. Our results help to explain the diversity of results of past studies of multiple-element limitation, suggest some improvements in experimental design for future studies, and have important implications for the extrapolation of the results of controlled experiments to field situations.on prevails, even w251^3^Watanabe,Y^Ohmura,N^Saiki,H^1992^1^Isolation and determination of cultural-characteristics of microalgae which functions under co2 enriched atmosphere^191^33^5-8^545-552^^^^^May-Aug^^^^^3343A^3342^A fresh-water microalgae, which functions under CO2 enriched atmosphere conditions, was isolated and its cultural characteristics were investigated. The HA-1 strain, identified as genus Chlorella, was newly isolated from a paddy field by an enrichment culture using reproduced stack gases from a thermal power plant with a concentration of CO2 and O2 of 15 % and 2 % respectively. It showed maximum growth at 10 % CO2 enriched air flowing condition, and showed a good growth rate in a broad range of physically controllable conditions, including CO2 enriched air flow rate, temperature and pH value. The results indicated the feasibility of the HA-1 strain for mass cultivation using stack gases.252^1^Goudriaan,J^1992^1^Where goes the carbon-dioxide - the role of vegetation^192^23^243^597^^^^^May prevails, even w349^449^547^868^869^253^4^Doi,M^Oda,H^Ogasawara,N^Asahira,T^1992^1^Effects of co2 enrichment on the growth and development of invitro cultured plantlets^180^60^4^963-970^^^^^Mar^^^^^3346^^^3343A^3342^A fresh-water microalgae, which functions under CO2 enriched atmosphere conditions, was isolated and its cultural characteristics were investigated. The HA-1 strain, identified as genus Chlorella, was newly isolated from a paddy field by an enrichment culture using reproduced stack gases from a thermal power plant with a concentration of CO2 and O2 of 15 % and 2 % respectively. It showed maximum growth at 10 % CO2 enriched air flowing condition, and showed a good growth rate in a broad range of physically controllable conditions, including CO2 enriched air flow rate, temperature and pH value. The results indicated the feasibility of the HA-1 strain for mass cultivation using stack gases.252^1^Goudriaan,J^1992^1^Where goes the carbon-dioxide - the role of vegetation^192^23^243^597^^^^^May prevails, even wA^3345^Plantlets of Caladium bicolor (C3 plant), Saccharum officinarum (C4 plant), and Phalaenopsis hybrid (CAM plant) at the preparation stage for acclimatization (the final stage of in vitro culture) were cultured on the medium containing 2% sucrose. The culture vessels were kept under continuous, 16 hr, or 8 hr lighting conditions; half of the vessels were ventilated continuously with 0.8 +/- 0.4% CO2 enriched atmosphere; while the remainder was exposed to ambient atmosphere. The growth of plantlets was promoted with an increase in daylength under both ambient and CO2 enriched atmospheres. When the plantlets were supplied with adequate CO2, dry matter production increased under all daylength treatments except Caladium cultured under continuous lighting. This promotive effect of CO2 enrichment was especially noticeable in root growth. In Caladium and Phalaenopsis, the leaf chlorophyll content of plantlets cultured under CO2 enriched atmosphere was less than that of leaves from plantlets grown in ambient atmosphere. Although the chlorophyll was less concentrated in leaves of plantlets growing under the CO2 enriched treatment, the rate of CO2 uptake of these plantlets measured at the midpoint of the light period was higher than that of leaves exposed to ambient atmosphere. Increasing the O2 concentration in culture vessels to 37% also promoted the growth of Caladium and Dendrobium phalaenopsis (CAM plant) under CO2 enriched condition. Because of the development of photoautotrophy, the Caladium plantlets exposed to enriched CO2 atmosphere and cultured on sugar-free medium using ceramic wool plug system responded with vigorous growth when transplanted into pots.254^4^Easterling,WE^Rosenberg,NJ^Lemon,KM^McKenney,MS^1992^1^Simulations of crop responses to climate change - effects with present technology and currently available adjustments (the smart farmer scenario)^107^59^1-2^75-102^^^^^15 Apr^^^^^3348848^ets cultured under CO2 enriched atmosphere was less than that of leaves from plantlets grown in ambient atA^3347^If climate changes, farmers will have to adapt to a new set of climate constraints. In this paper we examine the efficacy of strategies for dealing with climate change that are currently available to farmers and that are inexpensive to use; we refer to this group of strategies as 'adjustments'. Adjustment schemes of various kinds were identified for us by agricultural experts in the Missouri-Iowa-Nebraska-Kansas (MINK) states. These can involve changes in land use, changes in variety and crop selection, changes in planting and harvesting practices, and changes in fertility and pest management. Using the erosion productivity impact calculator (EPIC) model on a small set of representative farms, we tested adjustments of these kinds. The simulations show that earlier planting, longer- season cultivars and the use of furrow diking for moisture conservation would offset some of the yield losses induced by climate change in warm-season crops. Longer-season varieties of wheat (a cool-season crop) and shorter-season varieties of the perennials wheatgrass and alfalfa were also effective. The adjustments to climate change diminished yield losses in all crops but irrigated wheat. Despite the positive effects of adjustments, however, yields of all dryland warm-season crops remained lower than control levels. The adjustments also increased demand for irrigation water. Carbon dioxide enrichment had the same incremental effect on crop yields with or without adjustments (see the fourth paper in this issue), except in the case of alfalfa and sorghum, where a CO2- adjustment interaction was found. We conclude that currently available techniques would partially offset the yield reductions caused by a 1930s-like climate, but that in most crops the yield reductions would still be substantial.255^3^Grobbelaar,N^Chou,WM^Huang,TC^1992^1^Effect of co2, o2, dcmu, fccp, and dl-glyceraldehyde on the nitrogenase activity of synechococcus rf-1^193^33^2^167-174^^^^^Apr^^^^^3350188^243^870^871^872^t (a cool-season crop) and shorterA^3349^Elevated atmospheric CO2 concentrations drastically inhibit nitrogenase activity of the unicellular Synechococcus RF-1 but stimulate photosynthetic CO2 assimilation. The inhibitory effect on nitrogenase activity is stronger in the light than in the dark. During three hours, 1% CO2 in air can reduce nitrogenase activity in the light by about 50% compared to that in unenriched air. The inhibitory effect of elevated CO2 concentrations on nitrogenase activity persists for many hours after the organism has been returned to air not enriched with CO2. The nitrogenase activity of heterocystous cyanobacteria, generally, does not appear to be affected by 5% CO2 in the air. DCMU strongly enhanced nitrogenase activity and inhibited the assimilation of CO2 by Synechococcus RF-1 in the light, and elevated atmospheric O2 concentrations reduced the nitrogenase activity, especially in the dark. DL-glyceraldehyde at a concentration of 19.4 mM strongly inhibited nitrogenase activity, dark respiration, and photosynthesis. FCCP had no effect on dark respiration but depressed nitrogenase activity and photosynthesis of Synechococcus RF-1. The inhibitory effect of FCCP on nitrogenase activity was stronger in the dark than in the light.256^2^Hollander,B^Krug,H^1992^1^Effects of high co2-concentrations on vegetable species .2. Growth, co2-gas-exchange and stomata resistance^172^57^1^32-43^^^^^Jan-Feb^^^^^3352230^348^349^374^389^430^575^630^674^873^trations on nitrogenase activity persists for many hours after the organism has been returned to air not enriched with CO2. The nitrogenase activity of heterocystous cyanobacteria, generally, does not appear to be affected by 5% CO2 in the air. DCMU strongly enhanced nitrogenase activity and inhibited the assimilation of CO2 by Synechococcus RF-1 in the light, and elevated atmospheric O2 concentrations reduced the nitrogenase activity, especially in the dark. DL-glyceraldehyde at a concentration of 19.4 mM strongly inhibited nitrogenase activity, dark respiration, and photosynthesisA^3351^In the climatic conditions tested the growth of young cucumber plants (3-7 leaf stage) was slightly promoted as well by day as by continuous enrichment with 5000-mu-l/l CO2 compared to the control (400-mu-l/l CO2). A definite effect of enrichment during the night was not evident. The analysis of the growth components and gas exchange measurements revealed, that CO2 enrichment during the day as well as during day and night increased net assimilation rate and dark respiration distinctly. Enrichment during the night showed no effect on net assimilation rate and increased dark respiration only slightly. The specific leaf area was strongly reduced by the high CO2 concentration, but leaf weight ratio was rarely changed. By these morphogenetic effects growth promotion by an increased net assimilation rate was diminished. Continuous CO2 enrichment to cucumber plants with CO2 concentrations greater- than-or-equal-to 1000-mu-l/l decreased stomata resistance. This effect increased with higher CO2 concentrations and longer treatments. The stomata remained open even at night and at low air humidity. Also with CO2 enrichment up to 5000-mu-l/l during the day or during the night only the stomata remained wider open than in the control plants. The reaction of stomata to high CO2-concentrations is reversible. The regeneration proceeds all the faster as lower the proceeding concentration and shorter the exposition. The actions of high CO2- concentrations on stomata movement of cucumbers were confirmed with other species.257^1^Smith,RB^1992^1^Controlled-atmosphere storage of redcoat strawberry fruit^154^117^2^260-264^^^^^Mar^^^^^3354874^875^was strongly reduced by the high CO2 concentration, but leaf weight ratio was rarely changed. By these morphogenetic effects growth promotion by an increased net assimilation rate was diminished. Continuous CO2 enrichment to cucumber plants with CO2 concentrations greater- than-or-equal-to 1000-mu-l/l decreased stomata resistance. This effect increased with higher CO2 concentrations A^3353^Strawberries (Fragaria x ananassa Duch.) cv. Redcoat were stored at several temperatures and for various intervals in controlled atmospheres (CA) containing 0% to 18% CO2 and 15% to 21% O2. Bioyield point forces recorded on the CA-stored fresh fruit indicated that the addition of CO2 to the storage environment enhanced fruit firmness. Fruit kept under 15% CO2 for 18 hours was 48% firmer than untreated samples were initially. Response to increasing CO2 concentrations was linear. There was no response to changing O2 concentrations. Maximum enhancement of firmness was achieved at a fruit temperature of 0C; there was essentially no enhancement at 21C. In some instances, there was a moderate firmness enhancement as time in storage increased. Carbon dioxide acted to reduce the quantity of fruit lost due to rot. Fruit that was soft and bruised after harvest became drier and firmer in a CO2-enriched environment.o 1000-mu-l/l decreased stomata resistance. This effect increased with higher CO2 concentrations 258^2^Vanhinsberg,N^Horton,RF^1992^1^Ethylene metabolism in pulvini of phaseolus-vulgaris L^194^188^1^51-55^^^^^Feb^^^^^3356348^856^876^877^878^879^A^3355^The ability of leaf blade, pulvinar and petiolar tissue from primary leaves of Phaseolus vulgaris to release ethylene when incubated in a 1 mM solution of the ethylene-biosynthesis precursor, 1-aminocyclopropane-1-carboxylic acid, was determined over a 6h period. Ethylene release was measured under CO2-enriched and CO2-depleted conditions in the light and dark. In contrast to blade and petiolar tissue, the pulvini released more ethylene in the light than in the dark when held in sealed flanks. The amount of the gas released is largely independent of external levels of carbon dioxide.259^3^Wilson,JW^Hand,DW^Hannah,MA^1992^1^Light interception and photosynthetic efficiency in some glasshouse crops^78^43^248^363-373^^^^^Mar^^^^^3358273^374^376^880^881^882^883^92^0-mu-l/l decreased stomata resistance. This effect increased with higher CO2 concentrations A^3357^Productivity of glasshouse crops is strongly limited by light receipt, and efficient interception and use of light in photosynthesis is correspondingly important. Mature row crop canopies of cucumber and tomato intercepted about 76% of the light incident on their upper surfaces; about 18% was lost through gaps between the rows. Light transmitted through the entire depth of the canopy was reflected back by white plastic on the ground, so that the lower surface of the canopy received approximately 13% of the light incident on the upper surface. The light flux incident on the sides of these canopies (c. 2 m tall and 6 m x 16 m in area) amounted to some 20-30% of that incident on the upper surface. About 32% of daylight falling on the glasshouse (c. 9 m x 18 m in area) was intercepted by the glasshouse structure and glazing; of the 68% entering the house, some fell on headlands occupying 35% of the glasshouse area. The loss of light to headlands, and the gain from canopy side-lighting, would be relatively smaller for larger glasshouses. At near-ambient CO2 concentrations, net photosynthetic rates of the cucumber canopy were comparable to those of closed canopies of other glasshouse and field crops which have maximum light conversion efficiencies of 5-8-mu-g CO2 J-1 at 50-200 W m-2 incident light flux density. Efficiency decreases only slightly with stronger light. Glasshouse crops with CO2 enrichment to 1200 vpm achieve conversion efficiencies of 7-10-mu-g CO2 J-1. Efficiencies of utilization of intercepted light, on an energy basis, reach 6-10% in various field and glasshouse crops with near-ambient CO2, and reached an exceptional 11% for the cucumber canopy. Glasshouse crops with CO2 enrichment achieve maximum efficiency of light energy utilization between 12% and 13%.260^2^Chalabi,Z^Fernandez,JE^1992^1^Spatiotemporal responses of a glasshouse to gaseous enrichment^195^51^2^139-151^^^^^Feb434^884^885^house area. The loss of light to headlands, and the gain from canopy side-lighting, would be relatively261^1^Mortensen,LM^1992^1^Effects of ozone concentration on growth of tomato at various light, air humidity and carbon-dioxide levels^165^49^1-2^17-24^^^^^Jan^^^^^3361348^434^607^674^884^d crops which have maximum light conversion efficiencies of 5-8-mu-g CO2 J-1 at 50-200 W m-2 incident light flux density. Efficiency decreases only slightly with stronger light. Glasshouse crops with CO2 enrichment to 1200 vpm achieve conversion efficiencies of 7-10-mu-g CO2 J-1. Efficiencies of utilization of intercepted light, on an energy basis, reach 6-10% in various field and glasshouse crops with near-ambient CO2, and reached an exceptional 11% for the cucumber canopy. Glasshouse crops with CO2 enrichment achieve maximum efficiency of light energy utilization between 12% and 13%.260^2^Chalabi,Z^Fernandez,JE^1992^1^Spatiotemporal responses of a glasshouse to gaseous enrichment^195^51^2^139-151^^^^^Feb434^884^885^house area. The loss of light to headlands, and the gain from canopy side-lighting, would be relativelyA^3360^The effect of ozone (O3) Concentration on the growth of Lycopersicon esculentum was studied at different photosynthetic photon flux densities (PPFD), relative air humidities (RH) and carbon dioxide (CO2) concentrations. Increasing the O3 concentration from < 10 to 85 nl l-1 for 6 h per day reduced the shoot dry weight 35% at 70% RH and 62% at 90% RH. Increasing the PPFD from 100 to 350-mu-mol m-2 s-1 significantly reduced the effect of O3 in one of two experiments. The most pronounced interaction between RH, PPFD and O3 was found on plant height. High O3 levels generally decreased plant height at low PPFD and had no, or a stimulating, effect at high PPFD. Raising the RH from 70 to 90% significantly increased the negative effect of O3 on height. Increasing the O3 concentration from < 10 to 65 nl l-1 significantly decreased plant height at low CO2 concentration (300-340-mu-l l-1), but small effects were found at high CO2 concentration (700-800-mu-l l-1).n from canopy side-lighting, would be relatively262^3^Suzuki,T^Ohtaguchi,K^Koide,K^1991^1^Effects of gas-flow rate of co2-enriched air, high co2 concentration, and anaerobic atmosphere on the growth of blue- green-alga anacystis-nidulans^196^24^6^797-798^^^^^Dec263^3^Wullschleger,SD^Norby,RJ^Hendrix,DL^1992^1^Carbon exchange-rates, chlorophyll content, and carbohydrate status of 2 forest tree species exposed to carbon-dioxide enrichment^13^10^1^21-31^^^^^Jan^^^^^3364duced the effect of O3 in one of two experiments. The most pronounced interaction between RH, PPFD and O3 was found on plant height. High O3 levels generally decreased plant height at low PPFD and had no, or a stimulating, effect at high PPFD. Raising the RH from 70 to 90% significantly increased the negative effect of O3 on height. Increasing the O3 concentration from < 10 to 65 nl l-1 significantly decreased plant height at low CO2 concentration (300-340-mu-l l-1), but small effects were found at high CO2 concentration (700-800-mu-l l-1).n from canopy side-lighting, would be relativelyA^3363^Seedlings of yellow-poplar (Liriodendron tulipifera L.) and white oak (Quercus alba L.) were exposed continuously to one of three CO2 concentrations in open-top chambers under field conditions and evaluated after 24 weeks with respect to carbon exchange rates (CER), chlorophyll (Chl) content, and diurnal carbohydrate status. Increasing the CO2 concentration from ambient to +150 or +300-mu-l l-1 stimulated CER of yellow- poplar and white oak seedlings by 60 and over 35%, respectively, compared to ambient-grown seedlings. The increases in CER were not associated with a significant change in stomatal conductance and occurred despite a reduction in the amounts of Chl and accessory pigments in the leaves of plants grown in CO2-enriched air. Total Chl contents of yellow-poplar and white oak seedlings grown at +300-mu-l l-1 were reduced by 27 and over 55%, respectively, compared with ambient-grown seedlings. Yellow-poplar and white oak seedlings grown at +300-mu-l l-1 contained 72 and 67% more morning starch, respectively, than did ambient-grown plants. In contrast, yellow-poplar and white oak seedlings grown at +300-mu-l l-1 contained 17 and 27% less evening sucrose, respectively, than did plants grown at ambient CO2 concentration. Diurnal starch accumulation and the subsequent depletion of sucrose contributed to a pronounced increase in the starch/sucrose ratio of plants grown in CO2-enriched air. All seedlings exhibited a substantial reduction in dark respiration as CO2 concentration increased, but the significance of this increase to the carbohydrate status and carbon economy of plants grown in CO2-enriched air remains unclear.264^6^Briones,GL^Varoquaux,P^Chambroy,Y^Bouquant,J^Bureau,G^Pascat,B^1992^1^Storage of common mushroom under controlled atmospheres^197^27^5^493-505^^^^^Oct^^^^^3366886^ngs grown at +300-mu-l l-1 were reduced by 27 and over 55%, respectively, compared with ambient-grown seedlings. Yellow-poplar and white oak seedlings grown at +300-mu-l l-1 contained 72 and 67% more morning starchA^3365^The effect of controlled atmosphere (CA) on the shelf-life of the common mushroom (Agaricus bisporus) was assessed using six parameters correlated with its commerical qualities. Low CO2 concentrations (up to 2.5%) reduced brown discolouration compared to the control in air. Higher CO2 concentrations enhanced both internal and external browning. Low O2 concentrations reduced growth of micro-organisms, including pseudomonads. Respiration rate, when the mushrooms are placed again in normal air, is proportional to CO2 concentration during storage suggesting that CO2 exhibits a phytotoxic effect on mushrooms. A lower mannitol content was noted in mushrooms stored under CA than those stored in air (control). Mushrooms stored in a 5% CO2 atmosphere for 7 days did not break their veil but their texture was very soft and spongy. Texture losses decreased when CO2 concentrations increased.ient-grown seedlings. Yellow-poplar and white oak seedlings grown at +300-mu-l l-1 contained 72 and 67% more morning starch265^5^Gordon,HB^Whetton,PH^Pittock,AB^Fowler,AM^Haylock,MR^1992^1^Simulated changes in daily rainfall intensity due to the enhanced greenhouse-effect - implications for extreme rainfall events^198^8^2^83-102^^^^^Dec^^^^^3368130^174^659^887^888^889^compared to the control in air. Higher CO2 concentrations enhanced both internal and external browning. Low O2 concentrations reduced growth of micro-organisms, including pseudomonads. Respiration rate, when the mushrooms are placed again in normal air, is proportional to CO2 concentration during storage suggesting that CO2 exhibits a phytotoxic effect on mushrooms. A lower mannitol content was noted in mushrooms stored under CA than those stored in air (control). Mushrooms stored in a 5% CO2 atmosphere for 7 days did not break their veil but their texture was very soft and spongy. Texture losses decreased when CO2 concentrations increased.ient-grown seedlings. Yellow-poplar and white oak seedlings grown at +300-mu-l l-1 contained 72 and 67% more morning starchA^3367^In this study we present rainfall results from equilibrium 1 x - and 2 x CO2 experiments with the CSIRO 4-level general circulation model. The 1 X CO2 results are discussed in relation to observed climate. Discussion of the 2 x CO2 results focuses upon changes in convective and non-convective rainfall as simulated in the model, and the consequences these changes have for simulated daily rainfall intensity and the frequency of heavy rainfall events. In doing this analysis, we recognize the significant shortcomings of GCM simulations of precipitation processes. However, because of the potential significance of any changes in heavy rainfall events as a result of the enhanced greenhouse effect, we believe a first examination of relevant GCM rainfall results is warranted. Generally, the model results show a marked increase in rainfall originating from penetrative convection and, in the mid- latitudes, a decline in large-scale (non-convective) rainfall. It is argued that these changes in rainfall type are a consequence of the increased moisture holding capacity of the warmer atmosphere simulated for 2 x CO2 conditions. Related to changes in rainfall type, rainfall intensity (rain per rain day) increases in the model for most regions of the globe. Increases extend even to regions where total rainfall decreases. Indeed, the greater intensity of daily rainfall is a much clearer response of the model to increased greenhouse gases than the changes in total rainfall. We also find a decrease in the number of rainy days in the middle latitudes of both the Northern and Southern Hemispheres. To further elucidate these results daily rainfall frequency distributions are examined globally and for four selected regions of interest. In all regions the frequency of high rainfall events increases, and the return period of such events decreases markedly. If realistic, the findings have potentially serious practical implications in terms of an increased frequency and severity of floods in most regions. However, we discuss various important sources of uncertainty in the results presented, and indicate the need for rainfall intensity results to be examined in enhanced greenhouse experiments with other GCMs.266^2^Polglase,PJ^Wang,YP^1992^1^Potential co2-enhanced carbon storage by the terrestrial biosphere^182^40^4-5^641-656^^^^^^^^^^3370362^373^399^407^58^672^890^891^892^92^all is a much clearer response of the model to increased greenhouse gases than the changes in total rainfall. We also find a decrease in the number of rainy days in the middle latitudes of both the Northern and Southern Hemispheres. To further elucidate these results daily rainfall frequency distributions are examined globally and for four selected regions of interest. In all regions the frequency of high rainfall events increases, and the return period of such events decreases markedly. If realistic, the findings have potentially serious practical implications in terms of an increased frequency and severity of floods in most regions. However, we discuss variouA^3369^Geochemical models that deduce latitudinal source/sink relationships of atmospheric CO2 suggest that, in tropical regions, there is almost zero net exchange of CO2 between the atmosphere and the terrestrial biosphere. The implication is that CO2-enhanced carbon storage (CO2-ECS) by tropical biomes is negating the output of CO2 from deforestation. We describe here a 10-biome model for CO2-ECS, in which carbon accumulation in living vegetation is coupled to the Rothamsted soil carbon model. A biotic growth factor (beta) was used to describe the relationship between literature estimates of net primary production (NPP) and atmospheric CO2 concentration. Using beta = 0.3 as a reference state, CO2-ECS by the global biosphere in 1990 was 1.1 Gt. When more appropriate values of beta were used (derived from a theoretical response of vegetation to increasing temperature and CO2), CO2-ECS was 1.3 Gt, of which tropical biomes accounted for 0.7 Gt. There are many uncertainties in this (and other) models; total CO2-ECS is particularly sensitive to changes in NPP. Unless published surveys have underestimated tropical NPP by a factor of about 2, then it is unlikely that CO2-ECS could have negated the 1.5- 3.0 Gt of carbon that are estimated to have been emitted by tropical deforestation in 1990.267^2^Taylor,JA^Lloyd,J^1992^1^Sources and sinks of atmospheric co2^182^40^4-5^407-418^^^^^^^^^^3372312^428^893^894^n which carbon accumulation in living vegetation is coupled to the Rothamsted soil carbon model. A biotic growth factor (beta) was used to describe the relationship between literature estimates of net primary production (NPP) and atmospheric CO2 concentration. Using beta = 0.3 as a reference state, CO2-ECS by the global biosphere in 1990 was 1.1 Gt. When more appropriate values of beta were used (derived from a theoretical response of vegetation to increasing temperature and CO2), CO2-ECS was 1.3 Gt, of which tropical biomes accounted for 0.7 Gt. There are many uncertainties in this (and other) models; total CO2A^3371^The biosphere plays an important role in determining the sources, sinks, levels and rates of change of atmospheric CO2 concentrations. Significant uncertainties remain in estimates of the fluxes of CO2 from biomass burning and deforestation, and uptake and storage of CO2 by the biosphere arising from increased atmospheric CO2 concentrations. Calculation of probable rates of carbon sequestration for the major ecosystem complexes and global 3-D tracer transport model runs indicate the possibility that a significant net CO2 uptake (> 1 Pg C yr- 1), a CO2 'fertilisation effect', may be occurring in tropical rainforests, effectively accounting for much of the 'missing sink'. This sink may currently balance much of the CO2 added to the atmosphere from deforestation and biomass burning. Interestingly, CO2 released from biomass burning may itself be playing an important role in enhanced carbon storage by tropical rainforests. This has important implications for predicting future CO2 concentrations. If tropical rainforest destruction continues then much of the CO2 stored as a result of the CO2 'fertilisation effect' will be rereleased to the atmosphere and much of the 'missing sink' will disappear. These effects have not been considered in the IPCC (Intergovernmental Panel on Climate Change) projections of future atmospheric CO2 concentrations. Predictions which take account of the combined effects of deforestation, the return of carbon previously stored through the CO2 'fertilisation effect' and the loss of a large proportion of the 'missing sink' as a result of deforestation, would result in much higher predicted concentrations and rates of increase of atmospheric CO2 and, as a consequence, accelerated rates of climate change.268^1^Martin,P^1992^1^Exe: a climatically sensitive model to study climate change and co2 enhancement effects on forests^182^40^4-5^717-735^^^^^^^^^^3374895^896^ carbon storage by tropical rainforests. This has important implications for predicting future CO2 concentrations. If tropicaA^3373^Vegetation plays a significant role in determining the local and regional hydrology of ice-free continental surfaces and the dynamics of the atmosphere above it. Vegetation also influences the global climate directly by affecting atmospheric chemistry. In particular, it partially controls the carbon cycle. In turn, vegetation is influenced by climate and changes in the ambient concentration of CO2. This may have important consequences for agriculture and natural resource exploitation. A formal recognition of atmosphere/biosphere interrelationships is crucial but insufficient. Systematic investigations of the interactions between climate, plant physiology and ecology are badly needed. In this spirit, this paper presents the results of numerical simulations performed with the Energy, water and momentum exchange, and Ecological dynamics (EXE) model at a local scale over periods of 400-800 (simulation) years. EXE constitutes a first attempt to couple a physiologically based water budget and an explicit treatment of ecological dynamics. In principle, EXE could be forced by the output of an atmospheric general circulation model (GCM). Within this context, the paper demonstrates through the examples it analyses that both potential stomatal response to CO2 and the possible range of changes in atmospheric relative humidity are likely major factors in determining the ecosystem response to greenhouse warming. Consequently, they should be considered in future studies of this kind. The paper also provides explanations regarding the movement of ecotones, defined as the transition zones between different vegetation assemblages. Taking the North American forest/prairie boundary as a case study, the analysis of the results shows how, in a greenhouse warmed world, St Paul, MN, might look like North Platte, NE. Finally, building on the previous example by using two different models, this study illustrates that results can be strongly model dependent and encourages extreme caution in their interpretation.nd an explicit tr269^4^Retamales,J^Cooper,T^Streif,J^Kania,JC^1992^1^Preventing cold-storage disorders in nectarines^174^67^5^619-626^^^^^Sep^^^^^3376607^897^898^ext, the paper demonstrates through the examples it analyses that both potential stomatal response to CO2 and the possible range of changes in atmospheric relative humidity are likely major factors in determining the ecosystem response to greenhouse warming. Consequently, they should be considered in future studies of this kind. The paper also provides explanations regarding the movement of ecotones, defined as the transition zones between different vegetation assemblages. Taking the North American forest/prairie boundary as a case study, the analysis of the results shows how, in a greenhouse warmed world, St Paul, MN, might look like North Platte, NE. Finally, building on the previous example by using two different models, this study illustrates that results can be strongly model dependent and encourages extreme caution in their interpretation.nd an explicit trA^3375^A storage experiment was aimed at preventing low temperature storage disorders in nectarine fruits, of cvs July Red and Autumn Grand. Fruit was either cooled immediately after harvest or kept at 20-degrees-C for 48 h, before transfer to controlled atmosphere (CA) conditions at 0-degrees-C. Combinations of 0, 10, 15 and 20% CO2 with 8 and 16% O2 were assayed. The fruit was evaluated following cold storage, 31 days after harvest, and after four and eight days under 'shelf conditions'(ripening at 15-18-degrees-C). Warming of the fruit at 20-degrees-C before cold storage prevented woolliness in the absence of elevated CO2 levels but did not affect internal browning and increased reddish discoloration; further, it enhanced water loss and ripening, increasing fruit softening markedly. Conversely, high CO2 delayed fruit ripening in CA storage, keeping the fruit firmer, and preventing the development of woolliness, internal browning and reddish discoloration during ripening, the best results being mostly obtained with 20% CO2. O2 levels assayed did not show clear effects, but decreased O2 concentration in absence of high CO2 showed some benefit in 'July Red'. No deleterious effect of CO2 concentrations even as high as 20% could be detected. Thus, even though high CO2 in CA conditions showed promise for controlling disorders and preventing over-ripening, further work is needed on other cultivars, and lower O2 concentrations should be investigated before making a general recommendation.270^3^Whiting,DC^Vandenheuvel,J^Foster,SP^1992^1^Potential of low oxygen moderate carbon-dioxide atmospheres for postharvest disinfestation of new-zealand apples^199^20^2^217-222^^^^^^^^^^3378increased reddish discoloration; further, it enhanced water loss and ripening, increasing fruit softening markedly. Conversely, high CO2 delayed fruit ripening in CA storage, keeping the fruit firmer, and preventing the development of woolliness, internal browning and reddish discoloration during ripening, the best results being mostly obtaA^3377^Work on the mortality responses of four lepidopteran pests of apples in New Zealand-Epiphyas postvittana (Walker), Cydia pomonella (L.), Planotortrix octo Dugdale, and Ctenopseustis obliquana (Walker)-to low O2/moderate CO2 atmospheres is reviewed and additional data are presented. For both E. postvittana and C pomonella, reducing the O2 concentration and elevating the treatment temperature enhanced controlled atmosphere (CA) efficacy more than did increasing the CO2 concentration. Thus at 20-degrees-C, a 0.4% O2/5.0% CO2 CA gave the most rapid kill of the mixtures tested. The order of lifestage tolerance to this CA was similar for E. postvittana, C. pomonella, P. octo, and C. obliquana i.e., fifth instar > third instar > 3-day eggs > first instar. The four species exhibited a trend of tolerance of C pomonella > E. postvittana = P. octo = C obliquana. An increase in the temperature to 30- degrees-C decreased the time for high mortality for all four species. However, this decrease was much greater for P. octo and C obliquana than for C pomonella and E. postvittana. The potential of these CA treatments for disinfestation of New Zealand apples for the Japanese and United States markets is discussed.271^4^Bachelet,D^Brown,D^Bohm,M^Russell,P^1992^1^Climate change in thailand and its potential impact on rice yield^50^21^4^347-366^^^^^Aug^^^^^3380740^ration and elevating the treatment temperature enhanced controlled atmosphere (CA) efficacy more than did increasing the CO2 concentration. Thus at 20-degrees-C, a 0.4% O2/5.0% CO2 CA gave the most rapid kill of the mixtures tested. The order of lifestage tolerance to this CA was similar for E. postvittana, C. pomonella, P. octo, and C. obliquana i.e., fifth instar > third instar > 3-day eggs > first instar. The four species exhibited a trend of tolerance of C pomonella > E. postvittana = P. octo = C obliquana. An increase in the temperature to 30- degrees-C decreased the time for high mortality for all four species. However, this decrease was much greater for A^3379^In Thailand, the world's largest rice exporter, rice constitutes a major export on which the economy of the whole country depends. Climate change could affect rice growth and development and thus jeopardize Thailand's wealth. Current climatic conditions in Thailand are compared to predictions from four general circulation models (GCMs). Temperature predictions correlate well with the observed values. Predictions of monthly rainfall correlate poorly. Virtually all models agree that significant increases in temperature (from 1 to 7-degrees-C) will occur in the region including Thailand following a doubling in atmospheric carbon dioxide (CO2) concentration. The regional seasonality and extent of the rise in temperature varies with each model. Predictions of changes in rainfall vary widely between models. Global warming should in principle allow a northward expansion of rice-growing areas and a lengthening of the growing season now constrained by low temperatures. The expected increase in water-use efficiency due to enhanced CO2 might decrease the water deficit vulnerability of dryland rice areas and could make it possible to slightly expand them.272^2^Downing,JP^Cataldo,DA^1992^1^Natural sinks of co2 - technical synthesis from the palmas-del- mar workshop^94^64^1-2^439-453^^^^^Aug^^^^^3382314^889^om four general circulation models (GCMs). Temperature predictions correlate well with the observed values. Predictions of monthly rainfall correlate poorly. Virtually all models agree that significant increases in temperature (from 1 to 7-degrees-C) will occur in the region including Thailand following a doubling in atmospheric carbon dioxide (CO2) concentration. The regional seasonality and extent of the rise in temperature varies with each model. Predictions of changes in rainfall vary widely between models. Global warming should in principle allow a northward expansion of rice-growing areas and a lengthening of the growing season now constrained by low temperatures. The expected increase in water-use efficiA^3381^Natural CO2 sinks in terrestrial and marine environments are important components of the global carbon cycle, yet the sign and magnitudes of key fluxes among them are unknown. The results of the Palmas Del Mar Workshop - Natural Sinks of CO2 presented in this special issue and its companion hard-bound volume of Water, Air, & Soil Pollution, provide a synthesis of current research on the carbon cycle, CO2 sinks and associated processes and fluxes, and critical research needs to assess the potential role of forest and land-use management in carbon sequestration. The papers in this volume present data, observations, and model simulations that demonstrate: 1) the existence of natural CO2 sinks that could mitigate a significant amount of CO2 emissions from fossil-fuel combustion; 2) probable, human-caused imbalances in C exchanges among vegetation, soils, and the atmosphere; 3) enhanced C storage in vegetation in response to excess atmospheric CO2; 4) strong interactions among carbon, nutrient and hydrological cycles; and 5) an excess of carbon production over consumption in several, large managed forests. Although it appears unlikely that the search for the "missing" C sink required to balance the C budget will end in the open ocean, new estimates of C storage in mangrove wood and peat, suggest that coastal ecosystems have the capacity to store significant amounts of carbon in vegetation and sediments. Convincing analyses are also presented indicating the technical and economical feasibility of managing existing lands to sequester additional carbon. Long-term field studies of CO2 fertilization effects and carbon cycling by plants and soils in geographically important systems, native forests, and coastal ecosystems will go a long way toward meeting the research needs identified at the workshop.273^1^Gregor,HD^1992^1^The potential role of temperate forests as sinks for co2 - examples from the german environmental-policy against global warming^94^64^1-2^197-212^^^^^Aug^^^^^3384 carbon, nutrient and hydrologA^3383^Among industrialized nations Germany ranks fourth in CO2 emissions. Most of these originate from the use of fossil fuels. Based on reports of a parliamentary study commission, established in 1987, and other expert groups in Germany this article adresses possible environmental effects of increasing atmospheric CO2, the sink potential of temperate forests and the influence of forest damage on this potential. A strategy for a 25 to 30% or 250 to 300 X 10(6) t yr-1 CO2 emissions reduction by 2005 (which Germany has itself committed to) is described in which measures to enhance C sequestration by forests play an important role. Expansion of forest area, a further increase of C storage by appropriate management and the restoration and protection of forest health impaired by air pollution would result in an additional storage of 17 to 20 x 10(6) t yr-1 of CO2, equaling 6 to 8% of the reduction target.ironmental-policy against global warming^94^64^1-2^197-212^^^^^Aug^^^^^3384 carbon, nutrient and hydrolog274^2^Handel,MD^Risbey,JS^1992^1^An annotated-bibliography on the greenhouse-effect and climate change^50^21^2^97-253^^^^^Jun^^^^^3386377^659^899^900^901^902^903^904^905^906^ssion, established in 1987, and other expert groups in Germany this article adresses possible environmental effects of increasing atmospheric CO2, the sink potential of temperate forests and the influence of forest damage on this potential. A strategy for a 25 to 30% or 250 to 300 X 10(6) t yr-1 CO2 emissions reduction by 2005 (which Germany has itself committed to) is described in which measures to enhance C sequestration by forests play an important role. Expansion of forest area, a further increase of C storage by appropriate management and the restoration and protection of forest health impaired by air pollution would result in an additional storage of 17 to 20 x 10(6) t yr-1 of CO2, equaling 6 to 8% of the reduction target.ironmental-policy against global warming^94^64^1-2^197-212^^^^^Aug^^^^^3384 carbon, nutrient and hydrologA^3385^The literature on climate change from an enhanced greenhouse effect is large and growing rapidly. The problems considered are increasingly interdisciplinary. For these reasons many workers will find useful pointers to the literature in the fields interacting with, but outside of, their own. We present here an annotated bibliography on issues relating to changes in the concentrations of Earth's greenhouse gases. The areas covered include theory and numerical modelling of climate change; cycles involving carbon dioxide and other radiatively important trace gases; observations of climate change and the problems associated with those observations; paleoclimatology as it relates to previous changes in the greenhouse gases; the impacts on and interactions with managed and natural ecosystems from climate change; policy issues related to climate change and to the limitation of climate change; history of the study of the greenhouse effect; and some other causes of climate change. Selection of papers has been made to facilitate rapid introduction to most of the important issues and findings in an area. Over 600 articles, reports, and books are discussed.275^1^Mortensen,LM^1992^1^Diurnal photosynthesis and transpiration of ficus-benjamina L as affected by length of photoperiod, co2 concentration and light level^200^42^2^100-105^^^^^Jun^^^^^3388348^364^374^441^527^529^92^ in the concentrations of Earth's greenhouse gases. The areas covered include theory and numerical modelling of climate change; cycles involving carbon dioxide and other radiatively important trace gases; observations of climate change and the problems associated with those observations; paleoclimatology as it relates to previous changes in the greenhouse gases; the impacts on and interactions with managed and natural ecosystems from climate change; policy issues related to climate change and to the limitation of climate change; history of the study of the greenhouse effect; and some other causes of climate change. Selection of papers has been mA^3387^The diurnal net photosynthesis of Ficus benjamina L., cultivar Cleo, was studied at different daylengths (12, 18 and 24 h day- 1), photosynthetic photon flux densities (40 and 120-mu-mol m-2 s-1 PPFD) and CO2 concentrations (350 and 700-mu-mol mol-1). Net photosynthesis increased to a maximum after 5-6 and 6-7 h of light at 12 and 18 h day-1 photoperiods, respectively, followed by a decrease towards the end of the photoperiod. At a photoperiod of 18 h day-1 similar diurnal curves were found at 350 and 700-mu-mol mol-1 CO2, and at 40 and 120-mu-mol m-2 s-1 PPFD. Five days after the photoperiod was changed from 18 to a 24 h day-1 the diurnal rhythm disappeared. Transpiration followed the same diurnal rhythm as that for photosynthesis. The water-use efficiency was enhanced by raising the CO2 concentration. A decrease in the CO2 concentration from 700 to 350-mu-mol mol-1 after six days at high CO2 first significantly decreased the photosynthesis, but three days later it reached the same level as that at high CO2.276^1^Muellerdombois,D^1992^1^Potential effects of the increase in carbon-dioxide and climate change on the dynamics of vegetation^94^64^1-2^61-79^^^^^Aug^^^^^3390664^672^907^908^909^910^911^912^913^914^ concentrations (350 and 700-mu-mol mol-1). Net photosynthesis increased to a maximum after 5-6 and 6-7 h of light at 12 and 18 h day-1 photoperiods, respectively, followed by a decrease towards the end of the photoperiod. At a photoperiod of 18 h day-1 similar diurnal curves were found at 350 and 700-mu-mol mol-1 CO2, and at 40 and 120-mu-mol m-2 s-1 PPFD. Five days after the photoperiod was changed from 18 to a 24 h day-1 the diurnal rhythm disappeared. Transpiration followed the same diurnal rhythm as that for photosynthesis. The water-use efficiency was enhanced by raising the CO2 concentration. A decrease in the CO2 concentration from 700 to 350-mu-mol mol-1 after six days at high CO2 first significantly decreased the photosynthesis, but three days later it reached the same level as that at hA^3389^The continued CO2 loading of the atmosphere appears to be responsible for inducing three new force factors controlling dynamic changes in the world's vegetation. They come from (1) enhanced fertilization with the single most important plant nutrient, (2) the widely expected global temperature increase, and (3) aggravated weather disturbances. Increased CO2 absorption may enhance plant growth but it may also increase soil-nutrient limitations. It surely will enhance the metabolism of forest trees similarly as global warming will enhance plant metabolism, but both factors may also shorten the lifespan of perennial plants. Increased weather disturbances can be expected to produce new physiological stresses on the standing vegetation, particularly on habitats with poor soils. Since wide-spread forest decline has been reported from both the Atlantic and Pacific region, it seems possible that the roughly synchronic mass mortality of trees during the past two decades is related to the global increase in CO2. The paper gives an overview of forest decline and dieback as known from past and present research and suggests how the changing atmospheric environment may interact in this widely observed contemporary Phenomenon of vegetation dynamics.277^2^Smith,RB^Skog,LJ^1992^1^Postharvest carbon-dioxide treatment enhances firmness of several cultivars of strawberry^170^27^5^420-421^^^^^May^^^^^3392418^874^A^3391^Various cultivars of strawberry (Fragaria xananassa Duch.) were stored for 42 h under an atmosphere of 15% CO2 to determine whether their firmness would be enhanced. Compared to initial samples and stored control samples, enhanced firmness was found in 21 of the 25 cultivars evaluated. The CO2 had no effect on color, as measured by Hunter 'L', 'a' and 'b', or on soluble solids concentration (SSC) or pH. There were significant differences among cultivars in firmness; Hunter color 'L', 'a', and 'b'; SSC; and pH.nic mass mortality of trees during the past two decades is related to the global increase in CO2.278^3^Winjum,JK^Dixon,RK^Schroeder,PE^1992^1^Estimating the global potential of forest and agroforest management-practices to sequester carbon^94^64^1-2^213-227^^^^^Aug^^^^^3394y observed contemporary Phenomenon of vegetation dynamics.277^2^Smith,RB^Skog,LJ^1992^1^Postharvest carbon-dioxide treatment enhances firmness of several cultivars of strawberry^170^27^5^420-421^^^^^May^^^^^3392418^874^A^3391^Various cultivars of strawberry (Fragaria xananassa Duch.) were stored for 42 h under an atmosphere of 15% CO2 to determine whether their firmness would be enhanced. Compared to initial samples and stored control samples, enhanced firmness was found in 21 of the 25 cultivars evaluated. The CO2 had no effect on color, as measured by Hunter 'L', 'a' and 'b', or on soluble solids concentration (SSC) or pH. There were significant differences among cultivars in firmness; Hunter color 'L', 'a', and 'b'; SSC; and pH.nic mass mortality of trees during the past two decades is related to the global increase in CO2.A^3393^Forests play a prominent role in the global C cycle. Occupying one-third of the earth's land area, forest vegetation and soils contain about 60% of the total terrestrial C. Forest biomass productivity can be enhanced by management practices, which suggests that, by this means, forests could store more C globally and thereby slow the increase in atmospheric CO2. The question is how much C can be sequestered by forest and agroforest management practices. To address the question, a global database of information was compiled to assess quantitatively the potential of forestry practices to sequester C. The database presently has information for 94 forested nations that represent the boreal, temperate and tropical latitudes. Results indicate that the most promising management practices are reforestation in the temperate and tropical latitudes, afforestation in the temperate regions, and agroforestry and natural reforestation in the tropics. Across all practices, the median of the mean C storage values for the boreal latitudes is 16 tCha-1 (n=46) while in the temperate and tropical latitudes the median values are 71 tCha-1 (n=401) and 66 tCha-1 (n=170), respectively. Preliminary projections are that if these practices were implemented on 0.6 to 1.2 x 10(9) ha of available land over a 50-yr period, approximately 50 to 100 GtC could be sequestered.279^2^Menard,C^Dansereau,B^1992^1^Influence of photosynthetic photon flux-density and planting scheme on growth and development of cultivar royalty roses^165^50^3^197-207^^^^^May^^^^^3396915^916^ quantitatively the potential of forestry practices to sequester C. The database presently has information for 94 forested nations that represent the boreal, temperate and tropical latitudes. Results indicate that the most promising management practices are reforestation in the temperate and tropical latitudes, afforestation in the temperate regions, and agroforestry and natural reforestation in the tropics. Across all practices, the median of the mean C storage values for tA^3395^The influence of photosynthetic photon flux density (PPFD) and planting scheme on growth, development, yield and quality of RosaXhybrida cultivar 'Royalty' was investigated. Three planting schemes (two, three, and four parallel rows) and three light treatments (ambient light and ambient light Plus supplemental lighting with either 50 or 100-mu-mol s-1 m-2 PPFD (high pressure sodium lamps) were studied. Generally, supplementary PPFD enhanced the vegetative and reproductive growth of the plants compared to plants grown in ambient light conditions. Marketable yield per plant was increased significantly by 79% (P< 0.05) for the crop period from 1 January to 24 March 1988 when a PPFD of 50-mu-mol s-1 m-2 was added to ambient light conditions. Carbon dioxide enrichment increased yield by 113% when a PPFD of 50-mu-mol s-1 m-2 was added to ambient light during the crop period of 1 January to 24 March, 1989. The number of flowers per plant in the superior classes (commercial classification: 'Select' and 'No. 1') was enhanced for this period compared with the same period the previous year when no supplemental carbon dioxide was provided. Generally the planting scheme of two parallel rows gave the best overall results.280^4^Peker,H^Srinivasan,MP^Smith,JM^McCoy,BJ^1992^1^Caffeine extraction rates from coffee beans with supercritical carbon-dioxide^201^38^5^761-770^^^^^May^^^^^3398917^918^919^ lamps) were studied. Generally, supplementary PPFD enhanced the vegetative and reproductive growth of the plants compared to plants grown in ambient light conditions. Marketable yield per plant was increased significantly by 79% (P< 0.05) for the crop period from 1 January to 24 March 1988 when a PPFD of 50-mu-mol s-1 m-2 was added to ambient light conditions. Carbon dioxide enrichment increased yield by 113% when a PPFD of 50-mu-mol s-1 m-2 was added to ambient light during the crop period of 1 January to 24 March, 1989. The number of flowers per plant in the superior classes (commercial classification: 'Select' and 'No. 1A^3397^The extraction of caffeine from whole coffee beans with supercritical carbon dioxide was studied in a continuous-flow extraction apparatus. Decaffeination rates were determined as a function of CO2 flow rate, temperature and pressure by continuously monitoring the caffeine in the effluent with aflame ionization detector. Soaking the raw beans in water prior to decaffeination enhanced the rate of extraction, which increased markedly with water content. Using CO2 saturated with water also increased the rate of extraction. The rate of decaffeination increased with pressure and temperature and was influenced by both intraparticle diffusion in the water-soaked beans and external mass transfer. A mathematical model based on a linear-driving-force approximation of mass transfer and partitioning of caffeine between the water and the supercritical CO2 describes the time-dependent process. The partition coefficient for caffeine distributed between water and supercritical CO2, the only parameter determined from the dynamic extraction rate data, increases with temperature and pressure.281^5^Goulart,BL^Hammer,PE^Evensen,KB^Janisiewicz,W^Takeda,F^1992^1^Pyrrolnitrin, captan + benomyl, and high co2 enhance raspberry shelf-life at 0C or 18C^154^117^2^265-270^^^^^Mar^^^^^3400920^ caffeine in the effluent with aflame ionization detector. Soaking the raw beans in water prior to decaffeination enhanced the rate of extraction, which increased markedly with water content. Using CO2 saturated with water also increased the rate of extraction. The rate of decaffeination increased with pressure and temperature and was influenced by both intraparticle diffusion in the water-soaked beans and external mass transfer. A mathematical model based on a linear-driving-force approximation of mass transfer and partitioning of caffeine between the water and the supercritical CO2 describes the time-dependent process. The partition coefficient for caffeine distributed between water and supercritical CO2, the only parameter determined from A^3399^The effects of preharvest applications of pyrrolnitrin (a biologically derived fungicide) on postharvest longevity of 'Bristol' black raspberry (Rubus occidentalis L.) and 'Heritage' red raspberry [R. idaeus L. var. strigosus (Michx.) Maxim] were evaluated at two storage temperatures. Preharvest fungicide treatments were 200 mg pyrrolnitrin/liter, a standard fungicide treatment (captan + benomyl or iprodione) or a distilled water control applied 1 day before first harvest. Black raspberries were stored at 18 or 0 +/- 1C in air or 20% CO2. Red raspberries were stored at the same temperatures in air only. Pyrrolnitrin-treated berries often had less gray mold (Botrytis cinerea Pers. ex Fr.) in storage than the control but more than berries treated with the standard fungicides. Storage in a modified atmosphere of 20% CO2 greatly improved postharvest quality of black raspberries at both storage temperatures by reducing gray mold development. The combination of standard fungicide or pyrrolnitrin, high CO2, and low temperature resulted in more than 2 weeks of storage with less than 5% disease on black raspberries; however, discoloration limited marketability after almost- equal-to 8 days under these conditions. Chemical names used: 3-chloro-4-(2'-nitro-3'-chlorophenyl)-pyrrole (pyrrolnitrin); N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (captan); methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate) (benomyl); 3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1- imidazolidinecarboxamide (Rovral, iprodione).282^1^Idso,SB^1992^1^Net photosynthesis - corrections required of leaf chamber measurements^107^58^1-2^35-42^^^^^Mar^^^^^3402130^546^921^922^923^924^d (Botrytis cinerea Pers. ex Fr.) in storage than the control but more than berries treated with the standard fungicides. Storage in a modified atmosphere of 20% CO2 greatly improved postharvest quality of black raspberries at both storage temperatures by reducing gray mold development. The combination of standard fungicide or pyrrolnitrin, high CO2, A^3401^Direct measurements of trunk and branch volumes and fine-root biomass confirm that the growth rate of sour orange trees supplied with an extra 300 cm3 of CO2 m-3 of air is approximately 2.8 times greater than that of similar trees growing in ambient air. Net CO2 exchange measurements made on individual leaves over three 24 h periods in May, June and July 1990, however, suggest a relative growth enhancement for the CO2-enriched trees of the order of five to seven, which is clearly impossible on the basis of the direct growth measurements. It is shown that this discrepancy is due to a problem inherent in the act of enclosing a leaf in a leaf chamber, but that its effects can be removed by means of a simple correction procedure.283^3^Schmid,R^Forster,R^Dring,MJ^1992^1^Circadian-rhythm and fast responses to blue-light of photosynthesis in ectocarpus (phaeophyta, ectocarpales) .2. Light and co2 dependence of photosynthesis^6^187^1^60-66^^^^^Apr^^^^^3404362^925^926^ fungicide or pyrrolnitrin, high CO2, A^3403^Photosynthesis of Ectocarpus siliculosus (Dillwyn) Lyngb. under continuous saturating red irradiation follows a circadian rhythm. Blue-light pulses rapidly stimulate photosynthesis with high effectiveness in the troughs of this rhythm but the effectiveness of such pulses is much lower at its peaks. In an attempt to understand how blue light and the rhythm affected photosynthesis, the effects of inorganic carbon on photosynthetic light saturation curves were studied under different irradiation conditions. The circadian rhythm of photosynthesis was apparent only at irradiances which were not limiting for photosynthesis. The same was found for blue- light-stimulated photosynthesis, although stimulation was observed also under very low red-light irradiances after a period of adaptation, provided that the inorganic-carbon concentration was not in excess. Double-reciprocal plots of light-saturated photosynthetic rates versus the concentration of total inorganic carbon (up to 10 mM total inorganic carbon) were linear and had a common constant for half-saturation (3.6 mM at pH 8) at both the troughs and the peaks of the rhythm and before and after blue-light pulses. Only at very low carbon concentrations was a clear deviation found from these lines for photosynthesis at the rhythm maxima (red and blue light), which indicated that the strong carbon limitation specifically affected photosynthesis at the peak phases of the rhythm. Very high inorganic carbon concentrations (20 mM) in the medium diminished the responses to blue light, although they did not fully abolish them. The kinetics of the stimulation indicate that the rate of photosynthesis is affected by two blue-light- dependent components with different time courses of induction and decay. The faster component seemed to be at least partially suppressed at red-light irradiances which were not saturating for photosynthesis. Lowering the pH of the medium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates that Ectocarpus takes up free CO2 only and not bicarbonate, although additional physiological mechanisms may enhance the availability of CO2.284^3^Olaizola,M^Duerr,EO^Freeman,DW^1991^1^Effect of co2 enhancement in an outdoor algal production system using tetraselmis^187^3^4^363-366^^^^^Dec^^^^^3406t), which indicated that the strong carbon limitation specifically affected photosynthesis at the peak phases of the rhythm. Very high inorganic carbon concentrations (20 mM) in the medium diminished the responses to blue light, although they did not fully abolish them. The kinetics of the stimulation indicate that the rate of photosynthesis is affected by two blue-light- dependent components with different time courses of induction and decay. The faster component seemed to be at least partially suppressed at red-light irradiances which were not saturating for photosynthesis. Lowering the pH of the medium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates A^3405^One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production. Our results suggest that through additions of CO2 gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO2 increased levels of dissolved CO2, total dissolved inorganic carbon (SIGMA-CO2), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM SIGMA-CO2 was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO2.dium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates 285^4^Carpenter,SR^Fisher,SG^Grimm,NB^Kitchell,JF^1992^1^Global change and fresh-water ecosystems^27^23^^119-139^927^928^929^930^931^932^933^934^935^936^286^2^Idso,SB^Balling,RC^1992^1^United-states drought trends of the past century^107^60^3-4^279-284^^^^^31 Aug^^^^^3409377^593^634^937^d algal production. Our results suggest that through additions of CO2 gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO2 increased levels of dissolved CO2, total dissolved inorganic carbon (SIGMA-CO2), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM SIGMA-CO2 was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO2.dium had the same effects as an increase of the carbon concentration to levels of approx. 10 mM. This indicates A^3408^One of the primary concerns about potential global change is that the steadily rising CO2 content of earth's atmosphere may lead to significant increases in the severity and frequency of drought, especially in the agricultural heartland of the USA (Manabe et al., 1981; Gleick, 1987; Manabe and Wetherald, 1986, 1987, McCabe et al., 1990). This consequence has been postulated to result from minor changes in the atmospheric supply of moisture (precipitation) and major changes in the atmospheric demand for moisture (potential evapotranspiration), as a result of increased surface temperatures. Waggoner (1989), for example, has shown how a 10% drop in precipitation can lead to a 46% increase in the frequency of drought; while Rind et al. (1990) have demonstrated that CO2-induced global warming, if it occurs as projected, could raise the frequency of severe drought in the USA from 5 to 50% by the year 2050. If drought is truly this responsive to changes in precipitation and potential evapotranspiration, and there is little reason to believe it is not, it could serve as a sensitive indicator of global warming and as a reliable test for identifying its onset. Hence, as the effective CO2 content of the atmosphere has already risen by nearly 50% above its pre-industrial level (Michaels, 1990; Houghton et al., 1990), studies of drought trends of the past century might even now provide evidence for the reality of global warming. However, there are three separate factors that could complicate this simple test.287^1^Leemans,R^1992^1^Modeling ecological and agricultural impacts of global change on a global scale^202^51^8-9^709-724^^^^^Aug-Sep^^^^^3411174^209^243^377^429^633^664^673^92^938^6% increase in the frequency of drought; while Rind et al. (1990) have demonstrated that CO2-induced global warming, if it occurs as projected, could raise the frequency of severe drought in the USA from 5 to 50% by the year 2050. If drought is truly this responsive to changes in precipitation and potential evapotranspiration, and A^3410^The changing composition of the atmosphere could lead to significant changes in regional and continental climate. The methodology to develop consistent climate-change scenarios and to link them to different impact-models is discussed. Results of both static and dynamic models are presented and the advantages and disadvantages of the different approaches are addressed. Examples are drawn from different impact studies on large-scale vegetation patterns, forest dynamics and agricultural systems. General conclusions of these studies are that vegetation and agricultural zones will shift on global, continental and regional scales, but that large uncertainties still exist in the timing, actual response and rate of change of the current zones. Despite these uncertainties, the direction of these models indicates future developments and could be used for policy purposes.288^1^Oeschger,H^1992^1^Atmospheric co2 - global change and regulation mechanisms^203^96^3^252-257^^^^^Mar^^^^^3413593^625^nspiration, and A^3412^For the estimate of the distribution in the carbon system of the CO2 emitted into the atmosphere due to human activities, the exchange of carbon between atmosphere and ocean, and between atmosphere and biosphere needs to be considered. Information on this spreading of excess CO2 can be obtained from measurements of a.o. CO2, C-13/C-12, C-14/C in the atmosphere, of natural and nuclear weapon produced C-14 in the ocean and in the biota and of other natural or anthropogenic tracers. - Based essentially on such information, models for the CO2 uptake by the carbon system have been developed which are capable of reproducing the result of the drop in the rate of increase of CO2 emissions from 4.5% to 2% per year following the oil-embargo in 1973. - Of special interest regarding the understanding of the carbon cycle and its role in controlling the climate of the Earth are the observations in polar ice cores covering the past 160.000 years, corresponding to one and a half glaciation cycles. They show variations of atmospheric CO2, CH4, and N2O parallel to the climatic variations. Measurements of C-13/C-12 in shells of foraminiferas support the hypothesis that these CO2 changes are caused by changes in the ocean's biological pump, i.e. the flux of detrital organic carbon from the surface to the deep ocean, which affects the total inorganic carbon in the surface ocean and the partial pressure of CO2.289^7^Shaver,GR^Billings,WD^Chapin,FS^Giblin,AE^Nadelhoffer,KJ^Oechel,WC^Rastetter,EB^1992^1^Global change and the carbon balance of arctic ecosystems^14^42^6^433-441^^^^^Jun174^227^30^362^57^691^739^791^92^939^290^3^Shugart,HH^Smith,TM^Post,WM^1992^1^The potential for application of individual-based simulation- models for assessing the effects of global change^27^23^^15-38^611^707^939^940^941^942^943^944^945^946^291^3^Barton,CVM^Lee,HSJ^Jarvis,PG^1993^1^A branch bag and co2 control-system for long-term co2 enrichment of mature sitka spruce [picea-sitchensis (bong) carr]^9^16^9^1139-1148^^^^^Dec^^^^^3417705^tionA^3416^This paper describes the construction and performance of branch bags and a CO2 control system used to fumigate branches of mature Sitka spruce trees with air enriched in CO2 (700 mu mol mol(-1)). It contains some examples of results obtained using the system over the course of the first two growing seasons. The branch bags have run continuously for 2 years with very few problems. CO2 concentrations were within 20 mu mol mol(-1) of the target concentration for more than 90% of the time. Temperatures within the bags were slightly higher than ambient (1-2 degrees C) and this had some effect on phenology. Attenuation of quantum flux density (photosynthetically active radiation) was 10-15%. The branch bag system has enabled investigation into the effects of elevated CO2 on mature tissue without the problems and expense of fumigating whole trees. Growth in elevated CO2 resulted in an increase in starch and a decrease in soluble protein content of needles. Stomatal conductance was higher in elevated CO2 grown needles, and there was some evidence of an increase in photosynthetic capacity.292^3^Combe,L^Bertolini,JM^Quetin,P^1993^1^Effects of carbon-dioxide and light on photosynthesis of primrose (primula-obconica hance)^146^73^4^1149-1161^^^^^Oct^^^^^3419130^360^363^372^376^384^434^528^792^92^A^3418^Net CO2 exchange rates were measured on a 1 m2 crop of Primula obconica placed in a closed loop growing chamber as a function of irradiation and CO2 concentration. Greenhouse cultivation with CO2 enrichment (700 ppm) or without (350 ppm) had only very little effect on dry weight or on flowering rate and did not modify photosynthetic capacity of primrose. Productivity differences between horticultural techniques, such as supplemental lighting and/or CO, enrichment, can be partly explained by study of photosynthesis curves: light increase is more efficient than carbon dioxide increase, the latter giving the best results with young primroses under strong irradiation.matal conductance was higher in elevated CO2 grow293^2^Comins,HN^McMurtrie,RE^1993^1^Long-term response of nutrient-limited forests to co2 enrichment - equilibrium behavior of plant-soil models^56^3^4^666-681^^^^^Nov^^^^^3421130^227^378^429^58^715^733^778^92^947^^146^73^4^1149-1161^^^^^Oct^^^^^3419130^360^363^372^376^384^434^528^792^92^A^3418^Net CO2 exchange rates were measured on a 1 m2 crop of Primula obconica placed in a closed loop growing chamber as a function of irradiation and CO2 concentration. Greenhouse cultivation with CO2 enrichment (700 ppm) or without (350 ppm) had only very little effect on dry weight or on flowering rate and did not modify photosynthetic capacity of primrose. Productivity differences between horticultural techniques, such as supplemental lighting and/or CO, enrichment, can be partly explained by study of photosynthesis curves: light increase is more efficient than carbon dioxide increase, the latter giving the best results with young primroses under strong irradiation.matal conductance was higher in elevated CO2 growA^3420^Established process-based models of forest biomass production in relation to atmospheric CO2 concentration (McMurtrie 1991) and soil carbon/nutrient dynamics (Parton et al. 1987) are integrated to derive the ''Generic Decomposition and Yield'' model (G'DAY). The model is used to describe how photosynthesis and nutritional factors interact to determine the productivity of forests growing under nitrogen-limited conditions. A simulated instantaneous doubling of atmospheric CO2 concentration leads to a growth response that is initially large (27% above productivity at current CO2) but declines to <10% elevation within 5 yr. The decline occurs because increases in photosynthetic carbon gain at elevated CO2 are not matched by increases in nutrient supply. Lower foliar N concentrations at elevated CO2 have two countervailing effects on forest production: decreased rates of N cycling between vegetation and soils (with negative consequences for productivity), and reduced rates of N loss through gaseous emission, fire, and leaching. Theoretical analysis reveals that there is an enduring response to CO2 enrichment, but that the magnitude of the long-term equilibrium response is extremely sensitive to the assumed rate of gaseous emission resulting from mineralization of nitrogen. Theory developed to analyze G'DAY is applicable to other published production-decomposition models describing the partitioning of soil carbon among compartments with widely differing decay-time constants.294^2^Conroy,J^Hocking,P^1993^1^Nitrogen nutrition of C-3 plants at elevated atmospheric co2 concentrations^37^89^3^570-576^^^^^Nov^^^^^3423204^229^243^312^360^376^409^433^436^92^e increases in photosynthetic carbon gain at elevated CO2 are not matched by increases in nutrient supply. Lower foliar N concentrations at elevated CO2 have two countervailing effects on forest production: decreased rates of N cycling between vegetation and soils (with negative consequences for productivity), and reduced rates of N loss through gaseous emissioA^3422^The atmospheric CO2 concentration has risen from the preindustrial level of approximately 290 mu 1 1(-1) to more than 350 mu 1 1(-1) in 1993. The current rate of rise is such that concentrations of 420 mu 1 1(-1) are expected in the next 20 years. For C-3 plants, higher CO2 levels favour the photosynthetic carbon reduction cycle over the photorespiratory cycle, resulting in higher rates of carbohydrate production and plant productivity. The change in balance between the two photosynthetic cycles appears to alter nitrogen and carbon metabolism in the leaf, possibly causing decreases in nitrogen concentrations in the leaf. This may result from increases in the concentration of storage carbohydrates of high molecular weight (soluble or insoluble) and/or changes in distribution of protein or other nitrogen containing compounds. Uptake of nitrogen may also be reduced at high CO2 due to lower transpiration rates. Decreases in foliar nitrogen levels have important implications for production of crops such as wheat, because fertilizer management is often based on leaf chemical analysis, using standards estimated when the CO2 levels were considerably lower. These standards will need to be re- evaluated as the CO2 concentration continues to rise. Lower levels of leaf nitrogen will also have implications for the quality of wheat grain produced, because it is likely that less nitrogen would be retranslocated during grain filling.295^3^Cruz,C^Lips,SH^Martinsloucao,MA^1993^1^The effect of nitrogen-source on photosynthesis of carob at high co2 concentrations^37^89^3^552-556^^^^^Nov^^^^^3425348^417^544^948^n concentrations in the leaf. This may result from increases in the concentration of storage carbohydrates of high molecular weight (soluble or insoluble) and/or changes in distribution of protein or other nitrogen containing compounds. Uptake of nitrogen may also be reduced at high CO2 due to lower transpiration rates. Decreases in foliar nitrogen levels have important implications for production of crops such asA^3424^Carob seedlings (Ceratonia siliqua L. cv. Mulata), fed with nitrate or ammonium, were grown in growth chambers containing two levels of CO2 (360 or 800 mu 1 1(-1)), three root temperatures (15, 20 or 25 degrees C), and the same shoot temperature (20/24 degrees C, night/day temperature). The response of the plants to CO2 enrichment was affected by environmental factors such as the type of inorganic nitrogen in the medium and root temperature. Increasing root temperature enhanced photosynthesis rate more in the presence of nitrate than in the presence of ammonium. Differences in photosynthetic products were also observed between nitrate- and ammonium-fed carob seedlings. Nitrate-grown plants showed an enhanced content of sucrose, while ammonium led to enhanced storage of starch. Increase in root temperature caused an increase in dry mass of the plants of similar proportions in both nitrogen sources. The enhancement of the rates of photosynthesis by CO2 enrichment was proportionally much larger than the resulting increases in dry mass production when nitrate was the nitrogen source. Ammonium was the preferred nitrogen source for carob at both ambient and high CO, concentrations. The level of photosynthesis of a plant is limited not only by atmospheric CO2 concentration but also by the nutritional and environmental conditions of the root.296^3^Cui,M^Miller,PM^Nobel,PS^1993^1^Co2 exchange and growth of the crassulacean acid metabolism plant opuntia-ficus-indica under elevated co2 in open-top chambers^8^103^2^519-524^^^^^Oct^^^^^3427130^243^310^374^376^377^401^434^508^58^erences in photosynthetic products were also observed between nitrate- and ammonium-fed carob seedlings. Nitrate-grown plants showed an enhanced content of sucrose, while ammonium led to enhanced storage of starch. Increase in root temperature caused an increase in dry mass of the plants of similar proportions in both nitrogen sources. The enhancement of the rates of photosynthesis by CO2 enrichment was proportionally much larger than the A^3426^CO2 uptake, water vapor conductance, and biomass production of Opuntia ficus-indica, a Crassulacean acid metabolism species, were studied at CO2 concentrations of 370, 520, and 720 muL L-1 in open-top chambers during a 23-week period. Nine weeks after planting, daily net CO2 uptake for basal cladodes at 520 and 720 muL L-1 Of CO2 was 76 and 98% higher, respectively, than at 370 muL L-1. Eight weeks after daughter cladodes emerged, their daily net CO2 uptake was 35 and 49% higher at 520 and 720 muL L-1 of CO2, respectively, than at 370 muL L-1. Daily water-use efficiency was 88% higher under elevated CO2 for basal cladodes and 57% higher for daughter cladodes. The daily net CO2 uptake capacity for basal cladodes increased for 4 weeks after planting and then remained fairly constant, whereas for daughter cladodes, it increased with cladode age, became maximal at 8 to 14 weeks, and then declined. The percentage enhancement in daily net CO2 uptake caused by elevated CO2 was greatest initially for basal cladodes and at 8 to 14 weeks for daughter cladodes. The chlorophyll content per unit fresh weight of chlorenchyma for daughter cladodes at 8 weeks was 19 and 62% lower in 520 and 720 muL L-1 Of CO2, respectively, compared with 370 muL L-1. Despite the reduced chlorophyll content, plant biomass production during 23 weeks in 520 and 720 muL L-1 of CO2 was 21 and 55% higher, respectively, than at 370 muL L-1. The root dry weight nearly tripled as the CO2 concentration was doubled, causing the root/shoot ratio to increase with CO2 concentration. During the 23-week period, elevated CO2 significantly increased CO2 uptake and biomass production of O. ficus-indica.297^3^Dufrene,E^Pontailler,JY^Saugier,B^1993^1^A branch bag technique for simultaneous co2 enrichment and assimilation measurements on beech (fagus-sylvatica L)^9^16^9^1131-1138^^^^^Dec^^^^^3429344^374^384^398^417^685^705^92^, and then declined. The percentage enhancement in daily net CO2 uptake caused by elevated CO2 was greatest initially for basal clA^3428^A cheap CO2 enrichment system was designed to perform continuous gas exchange measurements of branches of mature European beech trees (Fagus sylvatica L.). Branches were grown at ambient (350 cm(3) m(-3)) and elevated CO2 (700 cm(3) m(-3)) during the whole 1992 leafy period. Leaks resulting from airtightness defaults in the system appeared to be low enough to measure accurately net CO2 assimilation and transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C-3 photosynthetic pathway and the shade-tolerance of beech frees (85% increase). The A/C-a curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches. The pattern of daily transpiration rates remained the same for both control and enriched branches, hence we can assume that there was no visible CO2 effect on stomata.298^3^Eamus,D^Berryman,CA^Duff,GA^1993^1^Assimilation, stomatal conductance, specific leaf-area and chlorophyll responses to elevated co2 of maranthes corymbosa, a tropical monsoon rain-forest species^92^20^6^741-755^^^^^^^^^^3431131^188^243^341^344^361^705^743^757^92^ transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C-3 photosynthetic pathway and the shade-tolerance of beech frees (85% increase). The A/C-a curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches. The pattern of daily transpiA^3430^Seeds of Maranthes corymbosa Blume, a monsoon rain forest species of northern Australia, were sown under ambient or elevated CO2 concentrations in tropical Australia. Seedlings were grown under conditions of photon flux density, temperature and atmospheric vapour pressure deficit which followed ambient variations as closely as possible. Specific leaf area, chlorophyll, stomatal density, stomatal conductance and assimilation responses to photon flux density were measured after 30 weeks growth. Gas exchange characteristics were divided into morning and afternoon data sets and analysed separately. Stomatal density decreased and leaf area:dry weight ratio decreased in response to elevated CO2. In contrast there was no effect of elevated CO2 upon chlorophyll (total or ratio of a:b). Apparent quantum yield and rates of light saturated assimilation (A(max)) increased in response to elevated CO2. There was a significant decline in apparent quantum yield for both treatments between morning and afternoon. Stomatal conductance (g(s)) declined in response to elevated CO2. There was no significant difference in g(s) between morning and afternoon for ambient grown trees, but g(s) declined significantly between morning and afternoon for elevated CO2 grown trees. Instantaneous transpiration efficiency (ITE) was higher for elevated CO2 grown trees compared with control trees. There was a significant increase in ITE between morning and afternoon data for ambient grown trees; in contrast a significant decline in ITE was observed for elevated CO2 grown trees between morning anf afternoon data sets. The slope of the regression between assimilation rate and stomatal conductance increased for plants grown under elevated CO2. These data are discussed and compared with the responses of plants adapting to different photon flux densities.299^3^Ham,JM^Owensby,CE^Coyne,PI^1993^1^Technique for measuring air-flow and carbon-dioxide flux in large, open-top chambers^204^22^4^759-766^^^^^Oct-Dec^^^^^3433174^529^949^950^ternoon. StomaA^3432^Open-Top Chambers (OTCs) are commonly used to evaluate the effect of CO2, O3, and other trace gases on vegetation. A study was conducted to develop and test a new technique for measuring forced air flow and net CO2 flux from OTCs. Experiments were performed with a 4.5-m diam. OTC that had a sealed floor and a specialized air delivery system. Air flow through the chamber was computed with the Bernoulli equation using measurements of the pressure differential between the air delivery ducts and the chamber interior. An independent measurement of air flow was made simultaneously to calibrate and verify the accuracy of the Bernoulli relationship. The CO2 flux density was calculated as the product of chamber air flow and the difference in CO2 concentration between the air entering and exhausting from the OTC (C(in) - C(out)). Accuracy of the system was evaluated by releasing CO2 within the OTC at known rates to emulate respiration from the field surface. Data were collected with OTCs at ambient and elevated CO2 (almost-equal-to 700 mumol mol-1). Results showed that the Bernoulli equation, with a flow coefficient of 0.7, accurately measured air flow in the OTC to within +/- 5% regardless of flow rate and air duct geometry. Experiments in ambient OTCs showed that CO2 flux density (mumol m-2 s-1), computed from 2-min averages of air flow and C(in) - C(out), was typically within +/- 10% of actual flux, provided that the exit air velocity at the top of the OTC was greater than 0.6 m s-1. Obtaining the same level of accuracy in CO2- enriched OTCs, however, required a critical exit velocity near 1.2 m s-1 to minimize the incursion of ambient air and prevent contamination of the exit gas sample. When flux data were integrated over time to estimate daily CO2 flux (mumol m-2 d- 1), actual and measured values agreed to within +/- 2% for both ambient and CO2-enriched chambers, suggesting that accurate measurements of daily net C exchange are possible with this technique.a were collected with OTCs at ambient and elevated300^3^Masle,J^Hudson,GS^Badger,MR^1993^1^Effects of ambient co2 concentration on growth and nitrogen use in tobacco (nicotiana-tabacum) plants transformed with an antisense gene to the small-subunit of ribulose-1,5- bisphosphate carboxylase oxygenase^8^103^4^1075-1088^^^^^Dec^^^^^3435188^312^348^355^372^551^685^698^812^951^ir flow and C(in) - C(out), was typically within +/- 10% of actual flux, provided that the exit air velocity at the top of the OTC was greater than 0.6 m s-1. Obtaining the same level of accuracy in CO2- enriched OTCs, however, required a critical exit velocity near 1.2 m s-1 to minimize the incursion of ambient air and prevent contamination of the exit gas sample. When flux data were integrated over time to estimate daily CO2 flux