O2 concentration caused an increase (P < 0.05) in dry mass per needle, tree height and the concentration of the monoterpene alpha-pinene, but there were no direct effects of CO2 concentration on any of the other chemical measurements made. High nutrient availability increased cellulase digestibility of pine needles. There was a significant negative effect of the OTCs on protein precipitating capacity of the needle extracts in comparison to the open-air controls. Results suggest that predicted changes in atmospheric CO2 concentration will be insufficient to produce large changes in the concentration of condensed tannins and monoterpenes in Scots pine. Processes which are influenced by these compounds, such as decomposition and herbivore food selection; along with their effects on ecosystem functioning, are therefore unlikely to be directly affected through changes in these secondary metabolites.
tance in ecological interactions between pine and other organisms including herbivores and decomposers. Elevated C2032^2^Hodge,A^Millard,P^1998^1^Effect of elevated CO2 on carbon partitioning and exudate release from Plantago lanceolata seedlings^37^103^2^280-286^^^^^Jun^^^^^6830
1146^1334^1803^2364^2508^344^374^376^537^92^chemical measurements made. High nutrient availability increased cellulase digestibility of pine needles. There was a significant negative effect of the OTCs on protein precipitating capacity of the needle extracts in comparison to the open-air controls. Results suggest that predicted changes in atmospheric CO2 concentration will be insufficient to produce large changes in the concentration of condensed tannins and monoterpenes in Scots pine. Processes which are influenced by these compounds, such as decomposition and herbivore food selection; along with their effects on ecosystem functioning, are therefore unlikely to be directly affected through changes in these secondary metabolites.
tance in ecological interactions between pine and other organisms including herbivores and decomposers. Elevated CA^6829^Plantago lanceolata L. seedlings were grown in sand microcosm units over a 43-day experimental period under two CO2 regimes (800 or 400 mu mol mol(-1)) to investigate the effect of elevated atmospheric CO2 concentration on carbon partitioning and exudate release. Total organic carbon (TOC) content of the collected exudate material was measured throughout the experimental period. After 42 days growth the seedlings were labelled with [C-14]-CO2 and the fate of the label within the plant and its release by the roots monitored. Elevated CO2 significantly (P less than or equal to 0.001) enhanced shoot, root and total dry matter production although the R:S ratio was unaltered, suggesting no alteration in press carbon partitioning. The cumulative release of TOC (in mg C) over 0-42 days was unaltered by CO2 treatment however, when expressed as a percentage of net assimilated C, ambient-grown plants released a significantly (P less than or equal to 0.001) higher percentage from their roots compared to elevated CO2-grown plants (i.e. 8 vs 3%). The distribution of C-14-label was markedly altered by CO2 treatment with significantly (P less than or equal to 0.001) greater per cent label partitioned to the roots under elevated CO2. This indicates increased partitioning of recent assimilate belowground under elevated CO2 treatment although there was no significant difference in the percentage of C-14-label released by the roots. Comparison of plant C budgets based on C-14-pulse-chase methodology and TOC measurements is discussed.

2033^2^Jongen,M^Jones,MB^1998^1^Effects of elevated carbon dioxide on plant biomass production and competition in a simulated neutral grassland community^52^82^1^111-123^^^^^Jul^^^^^6832
1065^1684^1960^3107^344^349^436^506^507^92^release of TOC (in mg C) over 0-42 days was unaltered by CO2 treatment however, when expressed as a percentage of net assimilated C, ambient-grown plants released a significantly (P less than or equal to 0.001) higher percentage from their roots compared to elevatedA^6831^Using open-top chambers, four prominent species (Lolium perenne, Cynosurus cristatus, Holcus lanatus and Agrostis capillaris) of Irish neutral grasslands were grown at ambient and elevated (700 mu mol mol(-1)) atmospheric CO2 for a period of 8 months. The effects of interspecific competition on plant responses to CO2 enrichment were investigated by growing the species in a four-species mixture. The results indicate that the species differ in their ability to respond to elevated CO2. CO2-enrichment had the largest effect on the biomass production of H. lanatus, but substantial stimulations in biomass production were also found for the other three species. The CO2-stimulation of biomass production for H. lanatus was accompanied by increased tillering. In addition, reductions in specific leaf area were found for all species. Exposure to elevated CO2 increased the community biomass of the four- species mixture. This increase can be mainly attributed to a significant increase in the biomass of H. lanatus at elevated CO2. No statistically-significant changes in species composition of community biomass were found. However, H. lanatus did increase its share of community biomass at each of the harvests, with the other three species, mainly L. perenne, suffering losses in their shares at elevated CO2. The results show that: (1) the species varied in their response to elevated CO2; and (2) species composition in natural plant communities is likely to change at elevated CO2, but these changes may occur rather slowly. Much longer periods of exposure to elevated atmospheric CO2 may be required to permit detection of significant changes in species composition. (C) 1998 Annals of Botany Company.

2034^3^Knapp,AK^Conard,SL^Blair,JM^1998^1^Determinants of soil CO2 flux from a sub-humid grassland: Effect of fire and fire history^56^8^3^760-770^^^^^Aug^^^^^6834
1445^2512^2917^310^3108^3109^372^427^668^91^e four- species mixture. This increase can be mainly attributed to a significant increase in the biomass of H. lanatus aA^6833^Soil CO2 flux (J(CO2)) was measured at midday over a 2-yr period in undisturbed tallgrass prairie (Konza Prairie, Kansas, USA) to quantify seasonal and annual budgets, to evaluate temperature and moisture as determinants of soil CO2 flux, and to assess the effect of a common land management tool, spring fire, and fire history on soil respiration. We hypothesized that: (1) maximum rates and annual estimates of soil J(CO2) would be greater in more productive burned sites than in unburned sites, (2) soil J(CO2) would be greater in newly burned sites with a history of fire exclusion than in annually burned sites (consistent with differences in aboveground production), and (3) soil temperature and water availability would be primary abiotic determinants of soil J(CO2) in tallgrass prairie. A preliminary assessment of the effects of large herbivores on soil J(CO2) was included to evaluate the hypothesis that removal of aboveground biomass would reduce soil J(CO2). Results indicated that spring fire increased maximum monthly soil J(CO2) by 20-55% relative to unburned tallgrass prairie, with greatest monthly differences measured in April (fourfold higher in burned sites). In burned sites that differed in fire history, maximum monthly J(CO2) in annually burned prairie was 33% greater than in burned sites with a history of fire exclusion. Soil J(CO2) in these latter sites was still significantly higher than in unburned sites. Soil J(CO2) in sites grazed by bison was reduced by as much as 30% relative to adjacent ungrazed areas. Reduced root biomass and activity in grazed areas, unburned sites, and sites with a history of fire exclusion suggest that plants play a major role in determining soil J(CO2) in this grassland. Soil temperature at 5 cm was related strongly to midday J(CO2) in both annually burned sites (r(2) = 0.58) and unburned sites (r(2) = 0.71). In contrast, differences in soil moisture among sites, enhanced by comparing irrigated grassland to control areas, increased maximum monthly J(CO2) by only 8%. Thus, soil temperature was the primary abiotic determinant of soil J(CO2) during this study. Maximum monthly estimates of soil J(CO2) in tallgrass prairie ranged from 10.3 mu mol CO2 . m(-2) . s(-1) in unburned sites to 15.1 mu mol . m(-2) . s(-1) in annually burned irrigated sites, whereas annual estimates varied from 4.7 to 7.8 kg CO2/m(2). Over the 2-yr period, spring fire increased estimated annual soil J(CO2) by 38-51% relative to unburned sites, while irrigation increased annual soil J(CO2) by 13%. These estimates for tallgrass prairie are much higher than those reported for most temperate ecosystems but are similar to estimates for tropical forests. Characteristics of undisturbed tallgrass prairie that may lead to high levels of soil J(CO2) include: high above- and belowground productivity; a relatively high proportion of C stored belowground; levels of soil microbial biomass and activity that are among the highest in native ecosystems in the United States; and the lack of a single dominant factor such as temperature, moisture, or nutrient availability, that consistently limits biotic processes during the growing season. The sensitivity of soil J(CO2) in tallgrass prairie to different land use practices (fire and grazing) suggests that it is critical to include these factors in the development of grassland C budgets, as well as in regional models that estimate biogeochemical responses to land use change.

2035^6^Lutze,JL^Roden,JS^Holly,CJ^Wolfe,J^Egerton,JJG^Ball,MC^1998^1^Elevated atmospheric [CO2] promotes frost damage in evergreen tree seedlings^9^21^6^631-635^^^^^Jun^^^^^6836
130^perate ecosystems but are similar to estimates for tropical forests. Characteristics of undisturbed tallgrass prairie that may lead to high levels of soil J(CO2) include: high above- and belowground productivity; a relatively high proportion of C stored belowground; levels of soil microbial biomass and activity that are among the highest in native ecosystems in the United States; and the lack of a single dominant factor sucA^6835^Growth under elevated [CO2] promoted spring frost damage in field grown seedlings of snow gum (Eucalyptus pauciflora Sieb, ex Spreng,), one of the most frost tolerant of eucalypts, Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO2] (- 5.7 degrees C versus - 4.3 degrees C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO2 fertilization and may affect predictions of vegetation change based on increasing temperature.
latively high proportion of C stored belowground; levels of soil microbial biomass and activity that are among the highest in native ecosystems in the United States; and the lack of a single dominant factor suc2036^4^Moya,TB^Ziska,LH^Namuco,OS^Olszyk,D^1998^1^Growth dynamics and genotypic variation in tropical, field- grown paddy rice (Oryza sativa L.) in response to increasing carbon dioxide and temperature^127^4^6^645-656^^^^^Aug^^^^^6838
349^434^eing a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO2] (- 5.7 degrees C versus - 4.3 degrees C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO2 fertilization and may affect predictions of vegetation change based on increasing temperature.
latively high proportion of C stored belowground; levels of soil microbial biomass and activity that are among the highest in native ecosystems in the United States; and the lack of a single dominant factor sucA^6837^While previous studies have examined the growth and yield response of rice to continued increases in CO2 concentration and potential increases in air temperature, little work has focused on the long-term response of tropical paddy rice (i.e. the bulk of world rice production) in situ, or genotypic differences among cultivars in response to increasing CO2 and/or temperature. At the International Rice Research Institute, rice (cv IR72) was grown from germination until maturity for 4 field seasons, the 1994 and 1995 wet and the 1995 and 1996 dry seasons at three different CO2 concentrations (ambient, ambient + 200 and ambient + 300 mu L L-1 CO2) and two air temperatures (ambient and ambient + 4 degrees C) using open-top field chambers placed within a paddy site. Overall, enhanced levels of CO2 alone resulted in significant increases in total biomass at maturity and increased seed yield with the relative degree of enhancement consistent over growing seasons across both temperatures. Enhanced levels of temperature alone resulted in decreases or no change in total biomass and decreased seed yield at maturity across both CO2 levels. In general, simultaneous increases in air temperature as well as CO2 concentration offset the stimulation of biomass and grain yield compared to the effect of CO2 concentration alone. For either the 1995 wet and 1996 dry seasons, additional cultivars (N-22, NPT1 and NPT2) were grown in conjunction with IR72 at the same CO2 and temperature treatments. Among the cultivars tested, N-22 showed the greatest relative response of both yield and biomass to increasing CO2, while NPT2 showed no response and IR72 was intermediate. For all cultivars, however, the combination of increasing CO2 concentration and air temperature resulted in reduced grain yield and declining harvest index compared to increased CO2 alone. Data from these experiments indicate that (a) rice growth and yield can respond positively under tropical paddy conditions to elevated CO2, but that simultaneous exposure to elevated temperature may negate the CO2 response to grain yield; and, (b) sufficient intraspecific variation exists among cultivars for future selection of rice cultivars which may, potentially, convert greater amounts of CO2 into harvestable yield.

2037^2^Neilson,RP^Drapek,RJ^1998^1^Potentially complex biosphere responses to transient global warming^127^4^5^505-521^^^^^Jun^^^^^6840
1234^1637^174^3110^3111^3112^314^55^633^673^ with IR72 at the same CO2 and temperature treatments. Among the cultivars tested, N-22 showed the greatest relative response of both yield and biomass to increasing CO2, while NPT2 showed no response and IR72 was intermediate. For all cultivars, however, the combination of increasing CO2 concentration and air temperature resulted in reduced grain yield and declining harvest index compared to increased CO2 alone. Data from these experiments indicate that (a) rice growth and yield can respond positively under tropical paddy conditions to elevated CO2, but that simultaneous exposure to elevatA^6839^Feedback interactions between terrestrial vegetation and climate could alter predictions of the responses of both systems to a doubling of atmospheric CO2. Most previous analyses of biosphere responses to global warming have used output from equilibrium simulations of current and future climate, as compared to more recently available transient GCM simulations. We compared the vegetation responses to these two different classes of GCM simulation (equilibrium and transient) using an equilibrium vegetation distribution model, MAPSS. Average climatologies were extracted from the transient GCM simulations for current and doubled (2 x) CO2 concentrations (taken to be 2070-2099) for use by the equilibrium vegetation model. However, the 2 x CO2 climates extracted from the transient GCM simulations were not in equilibrium, having attained only about 65% of their eventual 2 x CO2 equilibrium temperature change. Most of the differences in global vegetation response appeared to be related to a very different simulated change in the pole to tropic temperature gradient. Also, the transient scenarios produced much larger increases of precipitation in temperate latitudes, commensurate with a minimum in the latitudinal temperature change. Thus, the (equilibrium) global vegetation response, under the transient scenarios, tends more to a greening than a decline in vegetation density, as often previously simulated. It may be that much of the world could become greener during the early phases of global warming, only to reverse in later, more equilibrial stages. However, whether or not the world's vegetation experiences large drought-induced declines or perhaps large vegetation expansions in early stages could be determined by the degree to which elevated CO2 will actually benefit natural vegetation, an issue still under debate. There may occur oscillations, perhaps on long timescales, between greener and drier phases, due to different frequency responses of the coupled ocean-atmosphere-biosphere interactions. Such oscillations would likely, of themselves, impart further reverberations to the coupled Earth System.

2038^3^Peisker,M^Heinemann,I^Pfeffer,M^1998^1^A study on the relationship between leaf conductance, CO2 concentration and carboxylation rate in various species^91^56^1^35-43^^^^^Apr^^^^^6842
1754^1918^243^256^348^372^374^384^665^923^reening than a decline in vegetation density, as often previously simulated. It may be that much of the world could become greener during the early phases of global warming, only to reverse in later, more equilibrial stages. However, whether or not the world's vegetation experiences large drought-induced declines or perhaps large vegetation expansions in early stages could be determined by the degree to which elevated CO2 will actually benefit natural vegetation, an issue still under debate. There may occur oscillations, perhaps on long timescales, between greener and drier phases, due to different frequency responses of the coupled ocean-atmosphere-biosphere interactions. Such oscillatioA^6841^Leaf conductance g(L) is strongly influenced by environmental factors like CO2, irradiance and air humidity. According to Ball et al. (1987), g(L) is correlated with an index calculated as the product of net CO2 exchange rate A and ambient water vapour concentration W-a, divided by ambient CO2 concentration c(a). However, this empirical model does not apply to high values of g(L) observed at c(a) below CO2 compensation concentration Gamma. Therefore, we applied modified indices in which A is replaced by estimates for the rate of carboxylation. Such estimates, P-1 and P-2, were determined by adding to A the quotient of Gamma and the sum of gas phase resistance r(g) and intracellular resistance for CO2 exchange r(i), P-1 = A+Gamma/(r(g) + r(i)). or the quotient of Gamma and r(i), P-2 = A + Gamma/r(i). If P-2 is chosen, c(a) in the Ball index has to be replaced by the intercellular CO2 concentration c(i). By using the modified indices P-1.W-a/c(a) and P-2.W-a/c(i), we analysed data from the C-3 species Nicotiana tabacum and Nicotiana plumbaginifolia, the C-3-C-4 intermediate species Diplotaxis tenuifolia, and the C-4 species Zea mays. The data were collected at widely varying levels of irradiance and CO2 concentration. For all species uniform relationships between g(L) and the new indices were found for the whole range of CO2 concentrations below and above Gamma. Correlations between g(L) and P-1.W-a/c(a) were closer than those between g(L) and P-2.W- a/c(i) because P-1/c(a) implicitly contains g(L). Highly significant correlations were also obtained for the relationships between g(L) and the ratios P-1/c(a) and P- 2/c(i).

2039^1^Poorter,H^1998^1^Do slow-growing species and nutrient-stressed plants respond relatively strongly to elevated CO2?^127^4^6^693-697^^^^^Aug^^^^^6844
224^229^243^341^344^361^437^57^682^975^chosen, c(a) in the Ball index has to be replaced by the intercellular CO2 concentration c(i). By using the modified indices P-1.W-a/c(a) and P-2.W-a/c(i), we analysed data from the C-3 species NA^6843^Mainly based on a simulation model, Lloyd & Farquhar (1996; Functional Ecology, 10, 4-32) predict that inherently slow- growing species and nutrient-stressed plants show a relatively strong growth response to an increased atmospheric CO2 concentration. Compiling published experiments, I conclude that these predictions are not supported by the available data. On average, inherently fast-growing species are stimulated proportionately more in biomass than slow-growing species and plants grown at a high nutrient supply respond more strongly than nutrient-stressed plants.

2040^6^Prior,SA^Torbert,HA^Runion,GB^Mullins,GL^Rogers,HH^Mauney,JR^1998^1^Effects of carbon dioxide enrichment on cotton nutrient dynamics^166^21^7^1407-1426^^^^^^^^^^6846
1334^361^374^434^456^685^881^977^24^229^243^341^344^361^437^57^682^975^chosen, c(a) in the Ball index has to be replaced by the intercellular CO2 concentration c(i). By using the modified indices P-1.W-a/c(a) and P-2.W-a/c(i), we analysed data from the C-3 species NA^6845^The rise in atmospheric carbon dioxide (CO2) concentration is predicted to have positive effects on agro-ecosystem productivity. However, an area which requires further study centers on nutrient dynamics of crops grown under elevated CO2 in the field. In 1989 and 1990, cotton [Gossypium hirsutum (L.) Deltapine 77'] was grown under two CO2 levels [370 mu mol mol(- 1)=ambient and 550 mu mol mol(-1)=free-air CO2 enrichment(FACE)]. At physiological maturity, nutrient concentration and content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) were determined for whole plant and individual plant organs. While the effects of added CO2 on whole plant nutrient concentrations and contents were consistent, some differences among plant organs were observed between years. FACE often decreased tissue nutrient concentration, but increased total nutrient accumulation. Results indicate that under elevated CO2, field grown cotton was more nutrient efficient in terms of nutrient retrieval from the soil and nutrient utilization in the plant. This implies more efficient fertilizer utilization, better economic return for fertilizer expenditures, and reduced environmental impact from agricultural fertilization practices in the future.

2041^1^Rosenthal,Y^1998^1^Variations of ecosystem gas exchange in the rain forest mesocosm at Biosphere 2 in response to elevated CO2^127^4^5^539-547^^^^^Jun^^^^^6848
312^314^360^entration and content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) were determined for whole plant and individual plant organs. While the effects of added CO2 on whole plant nutrient concentrations and contents were consistent, some differences among plant organs were observed between years. FACE often decreased tissue nutrient concentration, but increased total nutrient accumulation. Results indicate that under elevated CO2, field grown cotton was moreA^6847^The effects of elevated CO2 on tropical ecosystems were studied in the artificial rain forest mesocosm at Biosphere 2, a large- scale and ecologically diverse experimental facility located in Oracle, Arizona. The ecosystem responses were assessed by comparing the whole-system net gas exchange (NEE) upon changing CO2 levels from 900 to 450 ppmV. The day-NEE was significantly higher in the elevated CO2 treatment. In both experiments, the NEE rates were similar to values observed in natural analogue systems. Variations in night-NEE, reflecting both soil CO2 efflux and plants respiration, covaried with temperature but showed no clear correlation with atmospheric CO2 levels. After correcting for changes in CO2 efflux we show that the rain forest net photosynthesis increased in response to increasing atmospheric CO2. The photosynthetic enhancement was expressed in higher quantum yields, maximum assimilation rates and radiation use efficiency. The results suggest that photosynthesis in large tropical trees is CO2 sensitive, at least following short exposures of days to weeks. Taken at face value, the data suggest that as a result of anthropogenic emissions of CO2, tropical rain forests may shift out of steady state, and become a carbon sink at least for short periods. However, a better understanding of the unique conditions and phenomena in Biosphere 2 is necessary before these results are broadly useful.

2042^4^Saccardy,K^Pineau,B^Roche,O^Cornic,G^1998^1^Photochemical efficiency of Photosystem II and xanthophyll cycle components in Zea mays leaves exposed to water stress and high light^91^56^1^57-66^^^^^Apr^^^^^6850
164^2092^2885^3113^3114^3115^3116^3117^3118^713^c CO2 levels. After correcting for changes in CO2 efflux we show that the rain forest net photosynthesis increased in response to increasing atmospheric CO2. The photosynthetic enhancement was expressed in higher quantum yields, maximum assimilation rates and radiation use efficiency. The results suggest that photosynthesis in large tropical trees iA^6849^The effects of two light treatments (photosynthetically active photon flux density of either 650 or 1950 mu mol m(-2) s(-1)) on the photochemical efficiency of Photosystem II (PS II) (measured as variable to maximum fluorescence ratio) and on the xanthophyll cycle components was studied in wilted Zea mays leaves. For comparison, these parameters were followed under the same light conditions in well-hydrated leaves maintained either in normal or CO2-free air. The net CO2 assimilation of dehydrated leaves declined rapidly as their relative water content (RWC) decreased from 100 to 60% while the PS II efficiency measured after a prolonged dark period of 16 h declined only when RWC leaves was lower than 60%. Furthermore, drought caused an increase in the pool size of the xanthophyll cycle pigments and the presence of a sustained elevated level of zeaxanthin and antheraxanthin at the end of the long dark period. The leaf water deficit enhanced the sensitivity of PS II efficiency to light exposure. During illumination, strong inhibition of PS II efficiency and large violaxanthin deepoxidation was observed in wilted leaves even under moderate photon flux density compared to control leaves in the same conditions. After 2 h of darkness following the light treatment, the PS II efficiency that is dependent on the previous PPFD, decreased with leaf water deficit. Moreover, zeaxanthin epoxidation led to an accumulation of antheraxanthin in dehydrated leaves, All these drought effects on PS II efficiency and xanthophyll cycle components were also obtained in well-hydrated leaves by short-term CO2 deprivation during illumination. We conclude that the increased susceptibility of PS II efficiency to light in wilted maize leaves is mainly explained by the decrease of CO2 availability and the resulting low net CO2 assimilation.

2043^3^Saxe,H^Ellsworth,DS^Heath,J^1998^1^Tree and forest functioning in an enriched CO2 atmosphere^84^139^3^395-436^^^^^Jul^^^^^6852
1344^1633^3119^3120^3121^3122^3123^343^398^861^osure. During iA^6851^Forests exchange large amounts of CO2 with the atmosphere and can influence and be influenced by atmospheric CO2. There has been a recent proliferation of literature on the effects of atmospheric CO2 on forest trees. More than 300 studies of trees on five different continents have been published in the last five years. These include an increasing number of field studies with a long-term focus and involving CO2 x stress or environment interactions. The recent data on long-term effects of elevated atmospheric CO2 on trees indicate a potential for a persistent enhancement of tree growth for several years, although the only relevant long-term datasets currently available are for juvenile trees. The current literature indicates a significantly larger average long-term biomass increment under elevated CO2 for conifers (130%) than for deciduous trees (49%) in studies not involving stress components. However, stimulation of photosynthesis by elevated CO2 in long-term studies was similar for conifers (62 %) and deciduous trees (53 %). Recent studies indicate that elevated CO2 causes a more persistent stimulation of biomass increment and photosynthesis than previously expected. Results of seedling studies, however, might not be applicable to other stages of tree development because of complications of age- dependent and size-dependent shifts in physiology and carbon allocation, which are accelerated by elevated CO2. In addition, there are many possible avenues to down-regulation, making the predicted canopy CO2 exchange and growth of mature trees and forests in a CO2-rich atmosphere uncertain. Although, physiological down-regulation of photosynthetic rates has been documented in field situations, it is rarely large enough to offset entirely photosynthetic gains in elevated CO2. A persistent growth stimulation of individual mature trees has been demonstrated although this effect is more uncertain in trees in natural stands. Resource interactions can both constrain tree responses to elevated CO2 and be altered by them. Although drought can reduce gas-exchange rates and offset the benefits of elevated CO2, even in well watered trees, stomatal conductance is remarkably less responsive to elevated CO2 than in herbaceous species. Stomata of a number of tree species have been demonstrated to be unresponsive to elevated CO2. We conclude that positive effects of CO2 on leaf area can be at least as important in determining canopy transpiration as negative, direct effects of CO2 on stomatal aperture. With respect to nutrition, elevated CO2 has the potential to alter tree-soil interactions that might influence future changes in ecosystem productivity. There is continued evidence that in most cases nutrient limitations diminish growth and photosynthetic responses to elevated CO2 at least to some degree, and that elevated CO2 can accelerate the appearance of nutrient limitations with increasing time of treatment. In many studies, tree biomass responses to CO2 are artefacts in the sense that they are merely responses to CO2-induced changes in internal nutritional status of the tree. There are numerous interactions between CO2 and factors of the biotic and abiotic environment. The importance of increasing atmospheric CO2 concentrations for productivity is likely to be overestimated if these are not taken into account. Many interactions, however, are simply additive rather than synergistic or antagonistic. This appears to hold true for many parameters under elevated CO2 in combination with temperature, elevated O- 3, and other atmospheric pollutants. However, there is currently little evidence that elevated CO2 will counteract O-3 damage. When the foliage content of C, mineral nutrients and secondary metabolites is altered by elevated CO2, tree x insect interactions are modified. In most trees, mycorrhizal interactions might be less important for direct effects of CO2 than for alleviating general nutrient deficiencies. Since many responses to elevated CO2 and their interactions with stress show considerable variability among species/genotypes, one principal research need is for comparative studies of a large variety of woody species and ecosystems under realistic conditions. We still need more long-term experiments on mature trees and stands to address critical scaling issues likely to advance our understanding of responses to elevated CO2 at different stages of forest development and their interactions with climate and environment. The only tools available at present for coping with the consequences of rising CO2 are management of resources and selection of genotypes suitable for the future climate and environment.

2044^3^Serraj,R^Sinclair,TR^Allen,LH^1998^1^Soybean nodulation and N-2 fixation response to drought under carbon dioxide enrichment^9^21^5^491-500^^^^^May^^^^^6854
1530^2843^3124^3125^3126^384^386^506^859^92^might be less important for direct effects of CO2 than for alleviating general nutrient deficiencies. Since many responses to elevated CO2 and their interactions with stress show considerable variability among species/genA^6853^The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N-2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two shortterm experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 mu mol CO2 mol(-1). Under drought-stressed conditions, elevated [CO2] resulted in a delay in the decrease in Nz fixation rates associated,vith drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2], The total non-structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N-2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought- induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N-2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N-2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N-2 fixation.

2045^1^Sicher,RC^1998^1^Yellowing and photosynthetic decline of barley primary leaves in response to atmospheric CO2 enrichment^37^103^2^193-200^^^^^Jun^^^^^6856
1672^2423^341^343^385^409^434^493^618^92^tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N-2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N-2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by A^6855^The photosynthetic response of barley (Hordeum vulgare L. cv. Brant) primary leaves was studied as a function of chlorosis induced by CO2 enrichment. Leaf yellowing; measured as changes of chlorophyll a and b, was more extensive in controlled environments at elevated (680 +/- 17 mu l l(-1)) than at ambient (380 +/- 21 mu l l(-1)) CO2. Stomatal conductance of primary leaves was decreased by growth in elevated CO2 between 11 and 18 days after sowing (DAS) when measured at both 380 and 680 mu l l(-1) CO2. Internal leaf CO2 concentration (C-i) was also lower for elevated- compared to ambient-CO2-grown primary leaves between 11 and 14 DAS. Results suggest that non-stomatal factors were responsible for the decreased photosynthetic rates of elevated- compared to ambient-CO2-grown primary leaves 18 DAS. Various photochemical measurements, including quantum absorptance (alpha), minimal (F-0), maximal (F-m), and variable (F-v) chlorophyll fluorescence, as well as the F-v/F-m ratio, were significantly decreased 18 DAS in the elevated- compared to ambient-CO2 treatment. Photochemical (q(P)) and nonphotochemical (q(N)) chlorophyll fluorescence quenching: coefficients of 18-day-old primary leaves did not differ between CO2 treatments. Photosynthetic electron transport rates of photosystem II were slightly lower for elevated- compared to ambient-CO2-grown primary leaves 18 DAS. Concentrations of alpha-amino N (i.e. free amino acids) in barley primary leaves were increased by CO2 enrichment 10 DAS, but subsequently, alpha-amino N decreased in association with photosynthetic decline. Total acid protease activity was greater in elevated- than in ambient-CO2-grown leaves 18 DAS. The above findings suggest that photoinhibition and premature senescence were factors in the CO2-dependent yellowing of barley primary leaves.

2046^3^Staddon,PL^Graves,JD^Fitter,AH^1998^1^Effect of enhanced atmospheric CO2 on mycorrhizal colonization by Glomus mosseae in Plantago lanceolata and Trifolium repens^84^139^3^571-580^^^^^Jul^^^^^6858d 1096^137^2137^372^374^376^392^419^474^92^t-CO2 treatment. Photochemical (q(P)) and nonphotochemical (q(N)) chlorophyll fluorescence quenching: coefficients of 18-day-old primary leaves did not differ between CO2 treatments. Photosynthetic electron transport rates of photosystem II were slightly lower for elevated- compared to ambient-CO2-grown primary leaves 18 DAS. Concentrations of alpha-amino N (i.e. free amino acids) in barley primary leaves were increased by CO2 enrichment 10 DAS, but subsequently, alpha-amino N decreased in association with photosynthetic decline. Total acid protease activity was greater in elevated- than in ambient-CO2-grown leaves 18 DAS. The above findings suggest that photoinhibition and premature senescence were factors in the CO2-dependent yellowing of barley primary leaves.

2046^3^Staddon,PL^Graves,JD^Fitter,AH^1998^1^Effect of enhanced atmospheric CO2 on mycorrhizal colonization by Glomus mosseae in Plantago lanceolata and Trifolium repens^84^139^3^571-580^^^^^Jul^^^^^6858d A^6857^Plantage lanceolata L. and Trifolium repens L. were grown for 16 wk in ambient (360 mu mol mol(-1)) and elevated (610 mu mol mol(-1)) atmospheric CO2. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and given a phosphorus supply in the form of bonemeal, which would not be immediately available to the plants. Seven sequential harvests were taken to determine whether the effect of elevated CO2 on mycorrhizal colonization was independent of the effect of CO2 on plant growth. Plant growth analysis showed that both species grew faster in elevated CO2 and that P. lanceolata had increased carbon allocation towards the roots. Elevated CO, did not affect the percentage of root length colonized (RLC); although total colonized root length was greater, when plant size was taken into account this effect disappeared. This finding was also true for root length colonized by arbuscules. No CO2 effect was found on hyphal density (colonization intensity) in roots. The P content of plants was increased at elevated CO2, although both shoot and root tissue P concentration were unchanged. This was again as a result of bigger plants at elevated CO2. Phosphorus inflow was unaffected by CO2 concentrations. It is concluded that there is no direct permanent effect of elevated CO2, on mycorrhizal functioning, as internal mycorrhizal development and the mycorrhizal P uptake mechanism are unaffected. The importance of sequential harvests in experiments is discussed. The direction for future research is highlighted, especially in relation to C storage in the soil.

2047^4^Tognetti,R^Longobucco,A^Miglietta,F^Raschi,A^1998^1^Transpiration and stomatal behaviour of Quercus ilex plants during the summer in a Mediterranean carbon dioxide spring^9^21^6^613-622^^^^^Jun^^^^^6860
1285^2712^3127^3128^3129^343^344^372^384^91^is effect disappeared. This finding was also true for root length colonized by arbuscules. No CO2 effect was found on hyphal density (colonization intensiA^6859^Variations in the water relations and stomatal response of Quercus ilex were analysed under field conditions by comparing trees at two locations in a Mediterranean environment during two consecutive summers (1993 and 1994), We used the heat-pulse velocity technique to estimate transpirational water use of trees during a 5 month period from June to November 1994, At the end of sap flow measurements, the trees were harvested, and the foliage and sapwood area measured, A distinct environmental gradient exists between the two sites with higher atmospheric CO2 concentrations in the proximity of a natural CO, spring. Trees at the spring site have been growing for generations in elevated atmospheric CO2 concentrations. At both sites, maximum leaf conductance was related to predawn shoot water potential. The effects of water deficits on water relations and whole- plant transpiration during the summer drought were severe. Leaf conductance and water potential recovered after major rainfall in September to predrought values. Sap flow leaf conductance and predawn water potential decreased in parallel with increases in hydraulic resistance, reaching a minimum in mid- summer. These relationships are in agreement with the hypothesis of the stomatal control of transpiration to prevent desiccation damage but also to avoid 'runaway embolism'. Trees at the CO2 spring underwent less reduction in hydraulic resistance for a given value of predawn water potential. The decrease in leaf conductance caused by elevated CO2 was limited and tended to be less at high than at low atmospheric vapour pressure deficit. Mean land diurnal) sap flux were consistently higher in the control site trees than in the CO2 spring trees. The degree of reduction in water use between the two sites varied among the summer periods. The control site trees had consistently higher sap flow at corresponding values of either sapwood cross-sectional area or foliage area, Larger trees displayed smaller differences than smaller trees, between the control and the CO2 spring trees. A strong association between foliage area and sapwood cross-sectional area was found in both the control and the CO2 spring trees, the latter supporting a smaller foliage area at the corresponding sapwood stem cross- sectional area. The specific leaf area (SLA) of the foliage was not influenced by site. The results are discussed in terms of the effects of elevated CO2 on plant water use at the organ and whole-tree scale.

2048^2^Winter,K^Virgo,A^1998^1^Elevated CO2 enhances growth in the rain forest understory plant, Piper cordulatum, at extremely low light intensities^54^193^3^323-326^^^^^Jul^^^^^6862
2297^312^344^374^376^389^494^713^ site trees than in the CO2 spring trees. The degree of reduction in water use between the two sites varied among the summer periods. The control site trees had consistently higher sap flow at corresponding values of either sapwood cross-sectional area or foliage area, Larger trees displayed smaller differences than smaller trees, between the control and thA^6861^Seedlings of the rain forest understory shrub Piper cordulatum were grown for several months at ambient and elevated concentrations of atmospheric CO2. Photon flux density (PFD) during 12-h photoperiods was maintained at extremely low levels (< 10 mu mol m(-2) s(-1)). Despite these low PFDs, dry matter accumulation and leaf area production were increased in air containing elevated (approximately twice-ambient) CO2 concentrations compared to ambient air. In leaves that had developed in deep shade and at ambient CO2, rates of net CO2 uptake, measured at 6 mu mol photons m(-2)s(-1), were 30% higher at elevated than at ambient CO2. Rates of net CO2 loss in the dark were 10% lower at elevated than at ambient CO2.

2049^3^Zanetti,S^Hartwig,UA^Nosberger,J^1998^1^Elevated atmospheric CO2 does not affect per se the preference for symbiotic nitrogen as opposed to mineral nitrogen of Trifolium repens L^9^21^6^623-630^^^^^Jun^^^^^6864
1292^1751^3065^3130^346^376^417^427^704^92^r trees, between the control and thA^6863^The objective of this investigation was to examine the effect of an elevated atmospheric CO2 partial pressure (pCO(2)) on the N-sink strength and performance of symbiotic N-2 fixation in Trifolium repens L. cv. Milkanova, After initial growth under ambient pCO(2) in a nitrogen-free nutrient solution, T. repens in the exponential growth stage was exposed to ambient and elevated pCO(2) (35 and 60 Pa) and two levels of mineral N (N- free and 7.5 mol m(-3) N) for 36 d in single pots filled with silica sand in growth chambers. Elevated pCO(2) evoked a significant increase in biomass production from day 12 after the start of CO2 enrichment. For plants supplied with 7.5 mol m(-3) N, the relative contribution of symbiotically fixed N (%N-sym) as opposed to N assimilated from mineral sources (N- 15-isotope-dilution method), dropped to 40%, However, in the presence of this high level of mineral N, %N-sym was unaffected by atmospheric pCO(2) over the entire experimental period. In plants fully dependent on N-2 fixation, the increase in N yield reflects a stimulation of symbiotic N-2 fixation that was the result of the formation of more nodules rather than of higher specific N-2 fixation. These results are discussed with regard to physiological processes governing symbiotic N-2 fixation and to the response of symbiotic N-2 fixation to elevated pCO(2) in field-grown T. repens.

2050^10^Ziska,LH^Moya,TB^Wassmann,R^Namuco,OS^Lantin,RS^Aduna,JB^Abao,E^Bronson,KF^Neue,HU^Olszyk,D^1998^1^Long-term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice^127^4^6^657-665^^^^^Aug^^^^^6866
1334^349^374^434^673^685^ CO2 enrichment. For plants supplied with 7.5 mol m(-3) N, the relative contribution of symbiotically fixed N (%N-sym) as opposed to N assimilated from mineral sources (N- 15-isotope-dilution method), dropped to 40%, However, in the presence of this high level of mineral N, %N-sym was unaffected by atmospheric pCO(2) over the entire experimental period. In plants fully dependent on N-2 fA^6865^Recent anthropogenic emissions of key atmospheric trace gases (e.g. CO2 and CH4) which absorb infra-red radiation may lead to an increase in mean surface temperatures and potential changes in climate. Although sources of each gas have been evaluated independently, little attention has focused on potential interactions between gases which could influence emission rates. In the current experiment, the effect of enhanced CO2 (300 mu L L-1 above ambient) and/or air temperature (4 degrees C above ambient) on methane generation and emission were determined for the irrigated tropical paddy rice system over 3 consecutive field seasons (1995 wet and dry seasons 1996 dry season). For all three seasons, elevated CO2 concentration resulted in a significant increase in dissolved soil methane relative to the ambient control. Consistent with the observed increases in soil methane, measurements of methane flux per unit surface area during the 1995 wet and 1996 dry seasons also showed a significant increase at elevated carbon dioxide concentration relative to the ambient CO2 condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO2 concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO2 alone. The observed increase in methane emissions were associated with a large, consistent, CO2-induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO2 concentration increases, methane emissions from tropical paddy rice could increase above current projections.

2051^6^Tuba,Z^Jones,MB^Szente,K^Nagy,Z^Garvey,L^Baxter,R^9UNKNOWN YEAR^1^Some ecophysiological and production responses of grasslands to long-term elevated CO2 under continental and atlantic climates^357^^^241-250^
312^344^348^399^5^641^665^674^778^92^962^
2052^4^Allen,LH^Valle,RR^Jones,JW^Jones,PH^1998^1^Soybean leaf water potential responses to carbon dioxide and drought^48^90^3^375-383^^^^^May-Jun^^^^^6869evate1337^230^264^348^386^431^434^537^57^642^o the ambient CO2 condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO2 concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO2 alone. The observed increase in methane emissions were associated with a large, consistent, CO2-induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO2 concentration increases, methane emissions from tropical paddy rice could increase above current projections.

2051^6^Tuba,Z^Jones,MB^Szente,K^Nagy,Z^Garvey,L^Baxter,R^9UNKNOWN YEAR^1^Some ecophysiological and production responses of grasslands to long-term elevated CO2 under continental and atlantic climates^357^^^241-250^
312^344^348^399^5^641^665^674^778^92^962^
2052^4^Allen,LH^Valle,RR^Jones,JW^Jones,PH^1998^1^Soybean leaf water potential responses to carbon dioxide and drought^48^90^3^375-383^^^^^May-Jun^^^^^6869evateA^6868^Rising CO2 can have direct effects on crop water relations and indirect effects on water available for growth. We studied the effects of elevated CO2 and drought on leaf water relations of soybean [Glycine max (L.) Merr. cv. Bragg] and considered the hypothesis of osmotic adjustment mediated by increased photosynthesis (Hypothesis 1) vs. the hypothesis of water conservation mediated by decreased stomatal conductance (Hypothesis 2) to explain improved water relations of plants growing under elevated CO2. In Exp. 1, soybean was grown at 330, 450, 660, and 800 mu mol mol(-1) CO2 in sunlit, closed- circulation, controlled-environment chambers under well-watered conditions. Leaf total water potential (WP), osmotic potential (OP), and turgor potential (TP) were measured at midday during V4 to R6 stages of development. In Exp. 2 (well-watered, R1-R3) and Exp. 3 (13-d drying cycle, R6 seed filling), soybean was grown at 330 and 660 mu mol mol(-1) CO2 and WP, OP, and TP were measured five times per day on sunlit and shaded leaves. In Exp. 3, stomatal conductance (g(s)) and transpiration rate (TR) of leaves were also measured. Experiments 1 and 2 showed that elevated CO2 increased TP and decreased OP, but did not affect leaf WP, thus favoring Hypothesis 1. In Exp. 3, leaf WP was higher in elevated than ambient CO2. Diurnal TP was higher in elevated than ambient CO2 at the beginning of drought, and was maintained longer each day as drought progressed. At the end of drought, TP and WP was higher in elevated than ambient CO2. Elevated CO2 leaves had lower TR because of lower g(s) than ambient CO2 counterparts. Thus, Exp. 3 supported Hypothesis 2, that both stressed and nonstressed plants in elevated CO2 have a better water status (e.g., higher TP) than plants in ambient CO2 due to water conservation mediated by decreased g(s). Remobilization of leaf nutrients during seed filling may limit the capability for osmotic adjustment. Regardless of the mechanisms, growth of plants in elevated CO2 should be less affected by drought than plants in ambient CO2.

2053^4^Arisi,ACM^Cornic,G^Jouanin,L^Foyer,CH^1998^1^Overexpression of iron superoxide dismutase in transformed poplar modifies the regulation of photosynthesis at low CO2 partial pressures or following exposure to the prooxidant herbicide methyl viologen^8^117^2^565-574^^^^^Jun^^^^^6871
1092^130^1569^1677^2369^2410^3131^440^493^713^ginning of drought, and was maintained longer each day as drought progressed. At the end of drought, TP and WP was higher in elevated than ambient CO2. Elevated CO2 leaves had lower TR because of lower g(s) than ambient CO2 counterparts. Thus, Exp. 3 supported Hypothesis 2, that both stressed and nonstressed plants in elevated CO2 have a better water status (e.g., higher TP) than plants in ambient CO2 due to water conservation mediated by decreased g(s). Remobilization of leaf nutrients during seed filling may limit the capability for osmotic adjustment. Regardless of the mechanisms, growth of plants in elevated CO2 should be less affected by dA^6870^Chloroplast-targeted overexpression of an Fe superoxide dismutase (SOD) from Arabidopsis thaliana resulted in substantially increased foliar SOD activities. Ascorbate peroxidase, glutathione reductase, and monodehydroascorbate reductase activities were similar in the leaves from all of the lines, but dehydroascorbate reductase activity was increased in the leaves of the FeSOD transformants relative to untransformed controls. Foliar H2O2, ascorbate, and glutathione contents were comparable in all lines of plants. Irradiance-dependent changes in net CO, assimilation and chlorophyll a fluorescence quenching parameters were similar in all lines both in air (21% O-2) and at low (1%) O-2. CO2-response curves for photosynthesis showed similar net CO2-exchange characteristics in all lines. In contrast, values of photochemical quenching declined in leaves from untransformed controls at intercellular CO2 (Ci) values below 200 mu L L-1 but remained constant with decreasing Ci in leaves of FeSOD transformants. When the O-2 concentration was decreased from 21 to 1%, the effect of FeSOD overexpression on photochemical quenching at limiting Ci was abolished. At high light (1000 mu mol m(-2) s(-1)) a progressive decrease in the ratio of variable (F-v) to maximal (F-m) fluorescence was observed with decreasing temperature. At 6 degrees C the high-light-induced decrease in the F-v/F-m ratio was partially prevented by low O-2 but values were comparable in all lines. Methyl viologen caused decreased F- v/F-m ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.

2054^2^Ball,AS^Drake,BG^1998^1^Stimulation of soil respiration by carbon dioxide enrichment of marsh vegetation^130^30^8-9^1203-1205^^^^^Aug
417^57^733^818^ols at intercellular CO2 (Ci) values below 200 mu L L-1 but remained constant with decreasing Ci in leaves of FeSOD transformants. Wh2055^5^Bandara,DC^Nobuyasu,H^Ofosu-Budu,KG^Ando,T^Fujita,K^1998^1^Effect of CO2 enrichment on biomass production, photosynthesis, and sink activity in soybean cv. Bragg and its supernodulating mutant nts 1007^316^44^2^179-186^^^^^Jun^^^^^6874
1096^2612^3132^3133^3134^3135^417^427^57^92^decreasing temperature. At 6 degrees C the high-light-induced decrease in the F-v/F-m ratio was partially prevented by low O-2 but values were comparable in all lines. Methyl viologen caused decreased F- v/F-m ratios, but this was less marked in the FeSOD transformants than in the untransformed controls. These observations suggest that the rate of superoxide dismutation limits flux through the Mehler-peroxidase cycle in certain conditions.

2054^2^Ball,AS^Drake,BG^1998^1^Stimulation of soil respiration by carbon dioxide enrichment of marsh vegetation^130^30^8-9^1203-1205^^^^^Aug
417^57^733^818^ols at intercellular CO2 (Ci) values below 200 mu L L-1 but remained constant with decreasing Ci in leaves of FeSOD transformants. WhA^6873^Soybean (Glycine max L. Merr.) cv. Bragg and its supernodulating mutant nts 1007 were grown in pots containing vermiculite with a N-free nutrient solution in order to examine the effect of elevated CO2 concentration (100+20 Pa CO2) on biomass production, photosynthesis, and biological nitrogen fixation. The whole plant weight increase in Bragg was higher than in the mutant at a high CO2 concentration. Apparent photosynthetic activities of the upper leaves in both Bragg and the mutant increased up to 14 d after treatment initiation by the CO2 enrichment and thereafter decreased to some extent. Both leaf area and leaf thickness of Bragg increased more than in nts 1007. With the elevated CO2 concentration, biological nitrogen fixation (BNF) also responded in the same manner as biomass production in both Bragg and nts 1007. The increase of BNF in Bragg was largely due to an increase in nodule weight. Starch contents in the leaves of both Bragg and the mutant increased significantly by CO2 enrichment, with a higher increase in Bragg than in its mutant. Sugar content in leaf differed only slightly in both Bragg and the mutant. N content in leaf decreased in both Bragg and its mutant, with the decrease being more pronounced in Bragg. However, in other plant parts (roots, stem, and petiole + pods), N content increased in the mutant while in Bragg, it decreased in the pod. N accumulation rate was higher in Bragg than in the mutant and increased more in Bragg than in the mutant by CO2 enrichment. The ureide content in leaf decreased in Bragg but increased in the mutant by elevated CO2 concentration. In the nodules, ureide content increased in both Bragg and the mutant by CO2 enrichment. Based on these results, it is suggested that in terms of biomass production and photosynthetic rate, Bragg responded more to elevated CO2 concentration than its mutant nts 1007. The alleviation of the stunted vegetative growth of the mutant by CO2 enrichment was limited despite the significant increase in the photosynthetic activity, presumably due to the limitation of sink activity in the growing parts and not to insufficient supply of N through BNF.

2056^1^Colinvaux,PA^1998^1^A new vicariance model for Amazonian endemics^175^7^2^95-96^^^^^Mar^^^^^6876
3136^
A^6875^It is unlikely that ice age climates of the Amazon were sufficiently arid to fragment the forest as required by the Haffer refugial hypothesis. However, glacial Amazon climates were colder and had reduced CO2 concentrations that would have had their strongest effects on the biota in the elevated areas stipulated to have been refugia. If local endemicity of butterflies or birds records Pleistocene speciation, this is because glacial climates provided cool, CO2 starved islands in a sea of continuous forest.

2057^4^Cook,AC^Tissue,DT^Roberts,SW^Oechel,WC^1998^1^Effects of long-term elevated [CO2] from natural CO2 springs on Nardus stricta: Photosynthesis, biochemistry, growth and phenology^9^21^4^417-425^^^^^Apr^^^^^6878
1121^2347^30^360^361^374^376^377^417^691^etic activitA^6877^Plants of Nardus stricta growing near a cold, naturally emitting CO2 spring in Iceland were used to investigate the long-term (> 100 years) effects of elevated [CO2] on photosynthesis, biochemistry, growth and phenology in a northern grassland ecosystem. Comparisons were made between plants growing in an atmosphere naturally enriched with CO2 (approximate to 790 mu mol mol(-1)) near the CO2 spring and plants of the same species growing in adjacent areas exposed to ambient CO2 concentrations (approximate to 360 mu mol mol(-1)). Nardus stricta growing near the spring exhibited earlier senescence and reductions in photosynthetic capacity (approximate to 25%), Rubisco content (approximate to 26%), Rubisco activity (approximate to 40%), Rubisco activation state (approximate to 23%), chlorophyll content (approximate to 33%) and leaf area index (approximate to 22%) compared,vith plants growing away from the spring. The potential positive effects of elevated [CO2] on grassland ecosystems in Iceland are likely to be reduced by strong down-regulation in the photosynthetic apparatus of the abundant N, stricta species.

2058^3^Cotrufo,MF^Briones,MJI^Ineson,P^1998^1^Elevated CO2 affects field decomposition rate and palatability of tree leaf litter: Importance of changes in substrate quality^130^30^12^1565-1571^^^^^Oct^^^^^6880
2364^3137^374^377^417^57^750^92^approximate to 790 mu mol mol(-1)) near the CO2 spring and plants of the same species growing in adjacent areas exposed to ambient CO2 concentrations (approximate to 360 mu mol mol(-1)). Nardus stricta growing near the spring exhibited earlier senescence and reductions in photosynthetic capacity (approximate to 25%), Rubisco content (approximate to 26%), Rubisco activity (approximate to 40%), Rubisco activation state (approximate to 23%), chlorophyll content (approximate to 33%) and leaf area index (approximate to 22%) compared,vith plants growing away from the spring. The potential positive effects of elevated [CO2] on grassland ecosystems in Iceland are likelyA^6879^Field decomposition rates of ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) leaf litters were measured for litters grown at ambient and elevated concentration of atmospheric CO2 inside solar domes. Litter raised at 600 mu l l(-1) CO2 retained significantly more mass at the end of the first year of field decomposition than material raised at 350 mu l l(-1). This reduction in decomposition could be related to changes in tissue quality resulting from growing the plants at higher CO2 concentrations, with C-to-N ratios and lignin contents being significantly increased. The elevated CO2 treatment also affected the rate of consumption of ash leaf litter by Oniscus asellus L. (Isopoda: Oniscoidea), with significantly less (-16%) material being consumed for litter derived from the high CO2 regime. Our results indicate that changes in litter quality, which we may expect under elevated CO2, may affect litter palatability for soil fauna. (C) 1998 Elsevier Science Ltd. All rights reserved.
kely2059^2^Cowling,SA^Sage,RF^1998^1^Interactive effects of low atmospheric CO2 and elevated temperature on growth, photosynthesis and respiration in Phaseolus vulgaris^9^21^4^427-435^^^^^Apr^^^^^6882
1260^1980^2575^312^348^360^384^417^423^914^600 mu l l(-1) CO2 retained significantly more mass at the end of the first year of field decomposition than material raised at 350 mu l l(-1). This reduction in decomposition could be related to changes in tissue quality resulting from growing the plants at higher CO2 concentrations, with C-to-N ratios and lignin contents being significantly increased. The elevated CO2 treatment also affected the rate of consumption of ash leaf litter by Oniscus asellus L. (Isopoda: Oniscoidea), with significantly less (-16%) material being consumed for litter derived from the high CO2 regime. Our results indicate that changes in litter quality, which we may expect under elevated CO2, may affect litter palatability for soil fauna. (C) 1998 Elsevier Science Ltd. All rights reserved.
kelyA^6881^For most of the past 250 000 years, atmospheric CO, has been 30-50% lower than the current level of 360 mu mol CO2 mol-l air. Although the effects of CO2 on plant performance are well recognized, the effects of low CO2 in combination with abiotic stress remain poorly understood. In this study, a growth chamber experiment using a two-by-two factorial design of CO2 (380 mu mol mol(-1), 200 mu mol mol(-1)) and temperature (25/20 degrees C day/night, 36/29 degrees C) was conducted to evaluate the interactive effects of CO2 and temperature variation on growth, tissue chemistry and leaf gas exchange of Phaseolus vulgaris. Relative to plants grown at 380 pmol mol(-1) and 25/20 degrees C, whole plant biomass was 36% less at 380 mu mol mol(-1) x 36/29 degrees C, and 37% less at 200 mu mol mol(-1) x 25/20 degrees C, Most significantly, growth at 200 mu mol mol(- 1) x 36/29 degrees C resulted in 77% less biomass relative to plants grown at 380 pmol mol(-1) x 25/20 degrees C, The net CO2 assimilation rate of leaves grown in 200 mu mol mol(-1) x 25/20 degrees C was 40% lower than in leaves from 380 pmol mol(-1) x 25/20 degrees C, but similar to leaves in 200 mu mol mol(-1) x 36/29 degrees C. The leaves produced in low CO2 and high temperature respired at a rate that was double that of leaves from the 380 mu mol mol(-1) x 25/20 degrees C treatment. Despite this, there was little evidence that leaves at low CO2 and high temperature were carbohydrate deficient, because soluble sugars, starch and total non-structural carbohydrates of leaves from the 200 mu mol mol(-1) x 36/29 degrees C treatment were not significantly different in leaves from the 380 mu mol mol(-1) x 25/20 degrees C treatment. Similarly, there was no significant difference in percentage root carbon, leaf chlorophyll and leaf/root nitrogen between the low CO2 x high temperature treatment and ambient CO2 controls. Decreased plant growth was correlated with neither leaf gas exchange nor tissue chemistry. Rather, leaf and root growth were the most affected responses, declining in equivalent proportions as total biomass production. Because of this close association, the mechanisms controlling leaf and root growth appear to have the greatest control over the response to heat stress and CO2 reduction in P. vulgaris.

2060^2^Gallardo,A^Merino,J^1998^1^Soil nitrogen dynamics in response to carbon increase in a Mediterranean shrubland of SW Spain^130^30^10-11^1349-1358^^^^^Sep^^^^^6884
1298^20^2102^3138^3139^362^417^535^672^733^s, starch and total non-structural carbohydrates of leaves from the 200 mu mol mol(-1) x 36/29 degrees C treatment were not significantly different in leaves from the 380 mu mol mol(-1) x 25/20 degrees C treatment. Similarly, there was no significant difference in percentage root carbon, leaf chlorophyll and leaf/root nitrogen between the low CO2 x high temperature treatment and ambient CO2 controls. Decreased plant growth was correlated with neither leaf gas exchange nor tissue chemistry. Rather, leaf and root growth were the most affected rA^6883^Most models predict that high atmospheric CO2 concentrations will lead to an increase in the C-to-N ratio of litter production in terrestrial ecosystems. The effect of an increase in the soil C-to-N ratio on the nitrogen dynamics in a Mediterranean shrubland was simulated by mixing with the lifter layer wood shavings with a high C-to-N ratio. Samples of mineral soil, taken subsequently eight times during 404 d, were analyzed for total C, total N, total soil carbohydrates, potential net N mineralization, potential net nitrification and microbial biomass-N. We found significant increases in the concentration of total carbohydrates, C-to-N ratio and microbial biomass N in amended soils during the experiment, while potential net N mineralization rate and net nitrification rate significantly decreased; amounts of available nitrogen (NH4+-N + NO3-N) were unaffected by the amendment treatment. However, by the end of the experiment, no significant differences between amended and control soil samples were found. The total carbohydrates-to-K2SO4-extractable total-N ratio was the best predictor of both net mineralization rate and microbial biomass N, showing that the available C-to- available-N ratio is a better indicator of N dynamics than the total C to total N ratio. Our results support the hypothesis that increasing C availability in soils leads to a decrease in N availability for plants through the immobilization of N in microbial biomass and to an increase in the temporal heterogeneity of soil properties in a Mediterranean shrubland. (C) 1998 Elsevier Science Ltd. All rights reserved.

2061^2^Gao,Q^Yu,M^1998^1^A model of regional vegetation dynamics and its application to the study of Northeast China Transect (NECT) responses to global change^137^12^2^329-344^^^^^Jun^^^^^6886
227^243^2589^2762^3140^51^633^696^700^738^ailable nitrogen (NH4+-N + NO3-N) were unaffected by the amendment treatment. However, by the end of the experiment, no significant differences between amended and control soil samples were founA^6885^We developed a dynamic regional vegetation model to address problems of responses of regional vegetation to elevated ambient CO2 and climatic change. The model takes into consideration both local ecosystem processes within a patch or grid cell, such as plant growth and death, and mass and energy flow, such as plant migration, across adjacent grid cells. The model is able to couple vegetation structure dynamics and primary production processes. The normalized differential vegetation index from meteorological satellite AVHRR was used to parameterize the model. Plant migration rates were derived based on effective seedling distribution around parent plants. The model was applied to Northeast China Transect at a spatial resolution of 10 min latitude by 10 min longitude per grid cell and a temporal resolution of 1 month. The results indicated that with doubled CO2 concentration, a 20% increase in precipitation and a 4 degrees C increase in temperature, the model predicted that net primary productivity (NPP) of Larix forests, conifer-broadleaf mixed forests, Aneurolepidium chinense steppes, Stipa grandis steppes, and wetland and salty meadows would decrease by 15% to 20%. However, NPP of deciduous broadleaf forests, woodland and shrubs, Stipa baicalensis meadow steppes, and desert grasslands would increase by 20% to 115%, as predicted by the model for the same climatic scenario. The average NPP of natural vegetation over the whole transect would decrease slightly, largely because of the compensation between the positive effects of increased CO2 and precipitation and the negative effect of increased evapotranspiration induced by increased temperature.

2062^9^Geiger,M^Walch-Liu,P^Engels,C^Harnecker,J^Schulze,ED^Ludewig,F^Sonnewald,U^Scheible,WR^Stitt,M^1998^1^Enhanced carbon dioxide leads to a modified diurnal rhythm of nitrate reductase activity in older plants, and a large stimulation of nitrate reductase activity and higher levels of amino acids in young tobacco plants^9^21^3^253-268^^^^^Mar^^^^^6888ty (NPP1437^2249^229^3141^372^376^448^504^57^92^d forests, Aneurolepidium chinense steppes, Stipa grandis steppes, and wetland and salty meadows would decrease by 15% to 20%. However, NPP of deciduous broadleaf forests, woodland and shrubs, Stipa baicalensis meadow steppes, and desert grasslands would increase by 20% to 115%, as predicted by the model for the same climatic scenario. The average NPP of natural vegetation over the whole transect would decrease slightly, largely because of the compensation between the positive effects of increased CO2 and precipitation and the negative effect of increased evapotranspiration induced by increased temperature.

2062^9^Geiger,M^Walch-Liu,P^Engels,C^Harnecker,J^Schulze,ED^Ludewig,F^Sonnewald,U^Scheible,WR^Stitt,M^1998^1^Enhanced carbon dioxide leads to a modified diurnal rhythm of nitrate reductase activity in older plants, and a large stimulation of nitrate reductase activity and higher levels of amino acids in young tobacco plants^9^21^3^253-268^^^^^Mar^^^^^6888ty (NPPA^6887^Higher rates of nitrate assimilation are required to support faster growth in enhanced carbon dioxide. To investigate how this is achieved, tobacco plants were grown on high nitrate and high light in ambient and enhanced (700 mu mol mol(-1)) carbon dioxide. Surprisingly, enhanced carbon dioxide did not increase leaf nitrate reductase (MR) activity in the middle of the photoperiod. Possible reasons for this anomalous result were investigated. (a) Measurements of biomass, nitrate, amino acids and glutamine in plants fertilized once and twice daily with 12 mol m(-3) nitrate showed that enhanced carbon dioxide did not lead to a nitrate limitation in these plants. (b) Enhanced carbon dioxide modified the diurnal regulation of NR activity in source leaves. The transcript for nia declined during the light period in a similar manner in ambient and enhanced carbon dioxide. The decline of the transcript correlated with a decrease of nitrate in the leaf, and was temporarily reversed after re-irrigating with nitrate in the second part of the photoperiod. The decline of the transcript was not correlated with changes of sugars or glutamine. NR activity and protein decline in the second part of the photoperiod, and NR is inactivated in the dark in ambient carbon dioxide. The decline of NR activity was smaller and dark inactivation was partially reversed in enhanced carbon dioxide, indicating that post- transcriptional or post-translational regulation of NR has been modified. The increased activation and stability of NR in enhanced carbon dioxide was correlated with higher sugars and lower glutamine in the leaves. (c) Enhanced carbon dioxide led to increased levels of the minor amino acids in leaves. (d) Enhanced carbon dioxide led to a large decrease of glycine and a small decrease of serine in leaves of mature plants. The glycine:serine ratio decreased in source leaves of older plants and seedlings. The consequences of a lower rate of photorespiration for the levels of glutamine and the regulation of nitrogen metabolism are discussed. (e) Enhanced carbon dioxide also modified the diurnal regulation of NR in roots. The nia transcript increased after nitrate fertilization in the early and the second part of the photoperiod. The response of the transcript was not accentuated in enhanced carbon dioxide. NR activity declined slightly during the photoperiod in ambient carbon dioxide, whereas it increased 2-fold in enhanced carbon dioxide. The increase of root NR activity in enhanced carbon dioxide was preceded by a transient increase of sugars, and was followed by a decline of sugars, a faster decrease of nitrate than in ambient carbon dioxide, and an increase of nitrite in the roots. (f) To interpret the physiological significance of these changes-in nitrate metabolism, they were compared with the current growth rate of the plants. (g) In 4-5-week-old plants, the current rate of growth was similar in ambient and enhanced carbon dioxide (approximate to 0.4 g(-1) d(-1)). Enhanced carbon dioxide only led to small changes of NR activity, nitrate decreased, and overall amino acids were not significantly increased. (h) Young seedlings had a high growth rate (0.5 g(-1) d(-1)) in ambient carbon dioxide, that was increased by another 20% in enhanced carbon dioxide. Enhanced carbon dioxide led to larger increases of NR activity and NR activation, a 2-3-fold increase of glutamine, a 50% increase of glutamate, and a 2-3-fold increase in minor amino acids. It also led to a higher nitrate level. It is argued that enhanced carbon dioxide leads to a very effective stimulation of nitrate uptake, nitrate assimilation and amino acid synthesis in seedlings. This will play an important role in allowing faster growth rates in enhanced carbon dioxide at this stage.

2063^6^Hodge,A^Paterson,E^Grayston,SJ^Campbell,CD^Ord,BG^Killham,K^1998^1^Characterisation and microbial utilisation of exudate material from the rhizosphere of Lolium perenne grown under CO2 enrichment^130^30^8-9^1033-1043^^^^^Aug^^^^^6890
1096^1262^1803^2364^312^361^57^733^738^778^ NR aA^6889^The effects of elevated atmospheric CO2 concentration on alterations, both qualitatively and quantitatively, of exuded compounds from the roots of Lolium perenne seedlings were investigated by growing plants in a sterilised sand microcosm unit. In addition, the effect of CO2 treatment on carbon substrate utilisation of microbial populations extracted from the rhizosphere of L. perenne seedlings grown in soil microcosm units was examined and alterations on microbial activity and diversity assessed using a commercially-available redox-based sole C source utilisation test (Biolog(R)) including additional exudate compounds. Both types of microcosm units (sand and soil) were maintained at specific growth conditions under two CO2 regimes (450 and 720 mu mol mol(-1)). Growth of L. perenne seedlings from both types of microcosm units was enhanced under elevated atmospheric CO2 although the root-to-shoot ratios were not significantly altered, indicating no gross change in dry matter partitioning. Cumulative total organic carbon (TOC) release in the exudate material over the duration of the experiment was significantly (P less than or equal to 0.05) higher from ambient-grown seedlings despite a significant (P less than or equal to 0.05) increase in the dry weight of roots of the elevated CO2 grown seedlings as determined at harvest. Over the individual sampling periods TOC release was significantly (P less than or equal to 0.05) higher from elevated CO2 grown seedlings on only one occasion (21 d). Qualitative differences, measured between d 1-6 and 14-18, also occurred with elevated CO2 treatment decreasing the amount of phenolic acids and total sugars at the latter sampling period compared to ambient CO2 seedlings. Total numbers of bacteria were significantly (P less than or equal to 0.05) decreased under elevated CO2 although culturable numbers significantly (P less than or equal to 0.05) increased. This increase in culturable microorganisms may explain the faster carbon source utilisation rates of the elevated CO2 treatment. No change in morphotypes of microbial colonies were observed suggesting a quantitative difference due to elevated CO2 treatment only. (C) 1998 Elsevier Science Ltd. All rights reserved.

2064^3^Hu,SJ^Firestone,MK^Chapin,FS^1998^1^Elevated atmospheric CO2 and soil biota^32^281^5376^518^^^^^24 Jul

2065^2^Kellomaki,S^Wang,KY^1998^1^Daily and seasonal CO2 exchange in Scots pine grown under elevated O-3 and CO2: experiment and simulation^331^136^2^229-248^^^^^Jun^^^^^6893
2035^273^312^3142^3874^395^444^446^493^602^etween d 1-6 and 14-18, also occurred with elevated CO2 treatment decreasing the amount of phenolic acids and total sugars at the latter sampling period compared to ambient CO2 seedlings. Total numbers of bacteria were significantly (P less than or equal to 0.05) decreased under elevated CO2 although culturable numbers significantly (P less than or equal to 0.05) increased. This increase in culturable microorganisms may explain the faster carbon source utilisation rates of the elevated A^6892^Starting in early spring of 1994, naturally regenerated, 30- year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers and exposed in situ to doubled ambient O-3, doubled ambient CO2 and a combination of O-3 and CO2 from 15 April to 15 September. To investigate daily and seasonal responses of CO2 exchange to elevated O-3 and CO2, the CO2 exchange of shoots was measured continuously by an automatic system for measuring gas exchange during the course of one year (from 1 Januray to 31 December 1996). A process-based model of shoot photosynthesis was constructed to quantify modifications in the intrinsic capacity of photosynthesis and stomatal conductance by simulating the daily CO2 exchange data from the field. Results showed that on most days of the year the model simulated well the daily course of shoot photosynthesis. Elevated O-3 significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O-3 also led to a delay in onset of photosynthetic recovery in early spring and an increase in the sensitivity of photosynthesis to environmental stress conditions. The combination of elevated O-3 and CO2 had an effect on photosynthesis and stomatal conductance similar to that of elevated O-3 alone, but significantly reduced the O-3 induced depression of photosynthesis. Elevated CO2 significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O-3 alone and the combination of elevated O-3 and CO2 decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO2 increased the annual total of net photosynthesis by 13%.
l the daily course of shoot photosynthesis. Elevated O-3 significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O-3 also led to a delay in on2066^4^Kurschner,WM^Stulen,I^Wagner,F^Kuiper,PJC^1998^1^Comparison of palaeobotanical observations with experimental data on the leaf anatomy of durmast oak [Quercus petraea (Fagaceae)] in response to environmental change^52^81^5^657-664^^^^^May^^^^^6895
1627^2460^312^344^372^376^708^745^746^92^ the O-3 induced depression of photosynthesis. Elevated CO2 significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O-3 alone and the combination of elevated O-3 and CO2 decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO2 increased the annual total of net photosynthesis by 13%.
l the daily course of shoot photosynthesis. Elevated O-3 significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O-3 also led to a delay in onA^6894^To test whether stomatal density measurements on oak leaf remains are reliable tools for assessing palaeoatmospheric carbon dioxide concentration [CO2], under changing Late Miocene palaeoenvironmental conditions, young seedings of oak (Quercus petraea, Liebl.) were grown at elevated vs. ambient atmospheric [CO2] and at high humidity combined with an increased air temperature. The leaf anatomy of the young oaks was compared with that of fossil leaves of the same species. In the experiments, stomatal density and stomatal index were significantly decreased at elevated [CO2] in comparison to ambient [CO2]. Elevated [CO2] induced leaf cell expansion and reduced the intercellular air space by 35%. Leaf cell size or length were also stimulated at high air humidity and temperature. Regardless of a temperate or subtropical palaeoclimate, leaf cell size in fossil oak was not enhanced, since neither epidermal cell density nor length of the stomatal apparatus changed. The absence of these effects may be attributed to the phenological response of trees to climatic changes that balanced temporal changes in environmental variables to maintain leaf growth under optimal and stable conditions. Quercus petraea, which evolved under recurring depletions in the palaeoatmospheric [CO2], may possess sufficient phenotypic plasticity to alter stomatal frequency in hypostomatous leaves allowing high maximum stomatal conductance and high assimilation rates during these phases of low [CO2]. (C) 1998 Annals of Botany Company.

2067^3^Liakatas,A^Roussopoulos,D^Whittington,WJ^1998^1^Controlled-temperature effects on cotton yield and fibre properties^178^130^^463-471^^^^^Jun^^^^^6897
348^361^372^685^cellular air space by 35%. Leaf cell size or length were also stimulated at high air humidity and temperature. Regardless of a temperate or subtropical palaeoclimate, leaf cell size in fossil oak was not enhanced, since neither epidermal cell density nor length of the stomatal apparatus changed. The absence of these effects may be attributeA^6896^Temperature effects on cotton yield and fibre properties of three cotton cultivars were determined. Plants were grown in pots maintained in growth rooms at varying day and night temperatures representing seasonally constant or varying (C) or daily varying (V) regimes. Yield and fibre characters responded to variation of daily mean and amplitude of temperature. Mean temperature reduction improved yield components, but fibre length, uniformity, strength and micronaire were increased by high, particularly high day, temperatures. A large daily temperature amplitude produced an intermediate number of flowers and the lowest retention percentage. Fruiting and yield were increased by reduction in temperature down to the threshold mean temperature of 22 degrees C. However, V-regimes with a low minimum temperature acted as a further drop (below 22 degrees C) of temperature and adversely affected these characters, An adverse effect of low minimum temperature combined with a moderate day temperature was observed also on lint percentage and fibre properties. Varietal differences were more pronounced for highly heritable characters such as fibre properties, for which significant interactions between varieties and temperature also occurred. Differences in reproductive development were not sufficient to be of much practical importance.

2068^10^Ludewig,F^Sonnewald,U^Kauder,F^Heineke,D^Geiger,M^Stitt,M^Muller-Rober,BT^Gillissen,B^Kuhn,C^Frommer,WB^1998^1^The role of transient starch in acclimation to elevated atmospheric CO2^358^429^2^147-151^^^^^12 Jun^^^^^6899
1351^1584^1871^243^312^3144^3145^441^788^845^mber of flowers and the lowest retention percentage. Fruiting and yield were increased by reduction in temperature down to the threshold mean temperature of 22 degrees C. However, V-regimes with a low minimum temperature acted as a further drop (below 22 degrees C) of temperature and adversely affected these characters, An adverse effect of low minimum temperature combined with a moderate day temperature was observed A^6898^Although increased concentrations of CO2 stimulate photosynthesis, this stimulation is often lost during prolonged exposure to elevated carbon dioxide, leading to an attenuation of the potential gain in yield. Under these conditions, a wide variety of species accumulates non-structural carbohydrates in leaves, It has been proposed that starch accumulation directly inhibits photosynthesis, that the rate of sucrose and starch synthesis limits photosynthesis, or that accumulation of sugars triggers changes in gene expression resulting in loser activities of Rubisco and inhibition of photosynthesis. To distinguish these explanations, transgenic plants unable to accumulate transient starch due to leaf mesophyll-specific antisense expression of AGP B were grown at ambient and elevated carbon dioxide. There was a positive correlation between the capacity for starch synthesis and the rate of photosynthesis at elevated CO2 concentrations, showing that the capability to synthesize leaf starch is essential for photosynthesis in elevated carbon dioxide, The results show that in elevated carbon dioxide, photosynthesis is restricted by the rate of end product synthesis, Accumulation of starch is not responsible for inhibition of photosynthesis, Although transgenic plants contained increased levels of hexoses, transcripts of photosynthetic genes were not downregulated and Rubisco activity was not decreased arguing against a role of sugar sensing in acclimation to high CO2, (C) 1998 Federation of European Biochemical Societies.

2069^2^Monje,O^Bugbee,B^1998^1^Adaptation to high CO2 concentration in an optimal environment: radiation capture, canopy quantum yield and carbon use efficiency^9^21^3^315-324^^^^^Mar^^^^^6901
1290^130^348^372^374^389^409^422^685^692^P B were grown at ambient and elevated carbon dioxide. There was a positive correlation between the capacity for starch synthesis and the rate of photosynthesis at elevated CO2 concentrations, showing that the capability to synthesize leaf starch is essential for pA^6900^The effect of elevated [CO2] on wheat (Triticum aestivum L, Veery 10) productivity was examined by analysing radiation capture, canopy quantum yield, canopy carbon use efficiency, harvest index and daily C gain, Canopies were grown at either 330 or 1200 mu mol mol(-1) [CO2] in controlled environments, where root and shoot C fluxes were monitored continuously from emergence to harvest. A rapidly circulating hydroponic solution supplied nutrients, water and root zone oxygen, At harvest, dry mass predicted from gas exchange data was 102.8 +/- 4.7% of the observed dry mass in six trials. Neither radiation capture efficiency nor carbon use efficiency were affected by elevated [CO2], but yield increased by 13% due to a sustained increase in canopy quantum yield. CO2 enrichment increased root mass, tiller number and seed mass. Harvest index and chlorophyll concentration were unchanged, but CO2 enrichment increased average life cycle net photosynthesis (13%, P < 0.05) and root respiration (24%, P < 0 05). These data indicate that plant communities adapt to CO2 enrichment through changes in C allocation. Elevated [CO2] increases sink strength in optimal environments, resulting in sustained increases in photosynthetic capacity, canopy quantum yield and daily C gain throughout the life cycle.

2070^1^Mortensen,LM^1998^1^Effects of elevated CO2 concentration on growth of Betula pubescens Ehrh. in different climatic conditions^108^13^2^197-203^^^^^^^^^^6903
1262^243^3146^344^348^361^376^402^430^528^ dry mass predicted from gas exchange data was 102.8 +/- 4.7% of the observed dry mass in six trials. Neither radiation capture efficiency nor carbon use efficiency were affected by elevated [CO2], but yield increased by 13% due to a sustained increase in canopy quantum yield. CO2 enrichment increased root mass, tiller number and seed mass. Harvest index and chlorophyll concentration were unchanged, but CO2 enrichment increased average life cycle net photosynthesis (13%, P < 0.05) and root respiration (24%, P < 0 05). TheA^6902^Seedlings of Betula pubescens Ehrh. (mountain birch) were grown at ambient and elevated CO2 concentrations in environment- controlled growth chambers, and in chambers or wind tunnels in the field. In the two preliminary experiments in a controlled environment, CO2 enrichment increased the dry weights of six birch provenances grown at a daily mean temperature (MT) of 17 degrees C and 15 provenances grown at 12.5 degrees C MT by 27 and 7%. respectively. In more realistic conditions in field chambers (13.9 degrees C MT), the shoot dry weight of plants grown for 65 days was not significantly affected by the elevated CO2 concentration. In a parallel experiment, CO2 enrichment increased the shoot dry weight by 36% in both unheated (14.7 degrees C MT) and heated (18.1 degrees C MT) wind tunnels. In a final experiment over two seasons in open- top chambers at 850 m a.s.l., elevated CO2 concentrations increased the root (42%) but not the shoot dry weight. The results are discussed in relation to variable climatic conditions.

2071^1^Norby,RJ^1998^1^Nitrogen deposition: a component of global change analyses^84^139^1^189-200^^^^^May^^^^^6905
1103^243^372^374^377^400^483^58^715^741^or wind tunnels in the field. In the two preliminary experiments in a controlled environment, CO2 enrichment increased the dry weights of six birch provenances grown at a daily mean temperature (MT) of 17 degrees C and 15 provenances grown at 12.5 degrees C MT by 27 and 7%. respectively. In more realistic conditions in field chambers (13.9 degrees C MT), the shoot dry weight of plants grown for 65 days was not significantly affected by the elevated CO2 concentration. In a parallel experiment, CO2 enrichment increased the shoot dry weight by 36% in both unheated (14.7 degrees C MT) and heated (18.1 degrees C MT) wind tunnels. In a final experiment over two seasons in open- top chambers at 850 m a.s.l., elevated CO2 concentrations increased the root (42%) but not the shoot dry weight. The results are discussed in relation to variable climaA^6904^The global cycles of carbon and nitrogen are being perturbed by human activities that increase the transfer from large pools of non-reactive forms of the elements to reactive forms that are essential to the functioning of the terrestrial biosphere. The cycles are closely linked at all scales, and global change analyses must consider C and N cycles together. The increasing amount of N originating from fossil fuel combustion and deposited to terrestrial ecosystems as nitrogen oxides could increase the capacity of ecosystems to sequester C, thereby removing some of the excess carbon dioxide from the atmosphere and slowing the development of greenhouse warming. Several global and ecosystem models have calculated the amount of C sequestration that can be attributed to N deposition, based on assumptions about the allocation of N among ecosystem components with different C:N ratios. They support the premise that, since industrialization began, N deposition has been responsible for an increasing terrestrial C sink, but there is great uncertainty whether ecosystems will continue to retain exogenous N. Whether terrestrial ecosystems continue to sequester additional C will depend in part on their response to increasing concentrations of atmospheric carbon dioxide, widely thought to be constrained by limited N availability. Ecosystem models generally support the conclusion that responses to increasing concentrations of carbon dioxide will be greater, and the range of possible responses will be wider, in ecosystems where increased N inputs originate as atmospheric deposition. The interactions between N deposition and increasing carbon dioxide concentrations could be altered considerably, however, by additional factors, including N saturation of ecosystems, changes in community composition, and climate change, Nitrogen deposition is also linked to global change issues through the volatile losses of nitrous oxide, which is a potent greenhouse gas, and the role of nitrogen oxides in the production of tropospheric ozone, which could interact with plant responses to elevated carbon dioxide. Any consideration of the role of N deposition in global change issues must also balance the projected responses against the serious detrimental impact of excess N on the environment.

2072^9^Osborne,CP^LaRoche,J^Garcia,RL^Kimball,BA^Wall,GW^Pinter,PJ^LaMorte,RL^Hendrey,GR^Long,SP^1998^1^Does leaf position within a canopy affect acclimation of photosynthesis to elevated CO2? Analysis of a wheat crop under free-air CO2 enrichment^8^117^3^1037-1045^^^^^Jul^^^^^6907
1093^2455^264^3147^341^344^384^417^57^92^teractions between N deposition and increasing carbon dioxide concentrations could be altered considerably, however, by additional factors, including N saturation of ecosystems, changes in community composition, and climate change, Nitrogen deposition is also linked to global change issues through the volatile losses of nitrous oxide, which is a potent greenhouse gas, and the role of nitrogen oxides in the production of tropospheric ozone,A^6906^Previous studies of photosynthetic acclimation to elevated CO2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation in a vertical profile of leaves through a canopy of wheat (Triticum aestivum L.). The crop was grown at an elevated CO2 partial pressure of 55 Pa within a replicated field experiment using free-air CO2 enrichment. Cas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of ribulose-1,5- bisphosphate-limited photosynthesis. Net photosynthetic CO2 uptake was measured for leaves in situ within the canopy. Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2 uptake remained higher under elevated CO2. Acclimation at elevated CO2 was accompanied by decreases in both Rubisco and total leaf N contents and an increase in LHC content. Elevated CO2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO2 therefore depended on both vertical position within the canopy and the developmental stage.

2073^2^Peng,CH^Apps,MJ^1998^1^Simulating carbon dynamics along the Boreal Forest Transect Case Study (BFTCS) in central Canada - 2. Sensitivity to climate change^137^12^2^393-402^^^^^Jun^^^^^6909
1106^178^3050^3148^3149^372^374^697^700^715^ Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2 uptake remained higher under elevated CO2. Acclimation at elevA^6908^The effects of climate change and doubling atmospheric CO2 on carbon dynamics of the boreal forest in the area of the Boreal Forest Transect Case Study in central Canada were investigated using the process-based plant-soil model CENTURY 4.0. The results presented here suggest that (1) across the transect climate change would result in increased total carbon in vegetation biomass but decreased overall carbon in soil; (2) increased atmospheric CO2 concentration under current climatic patterns would result in increased total carbon in vegetation and in soil organic matter; and (3) combined climate change and elevated CO2 would increase both net primary productivity and decomposition rates relative to the current climate condition, but their combined action would be a reduction of soil carbon losses relative to those due to climate change alone. The interactive effects of climate change and elevated CO2, however, are not a simple additive combination of the individual responses. The responses to climate change and elevated CO2 vary across the climate gradient from southern to northern sites on the transect. The present simulations indicate that the northern sites are more sensitive to climate change than the southern sites are, but these simulations do not consider likely changes in the disturbance regime or changes in forest species distribution.

2074^2^Rey,A^Jarvis,PG^1998^1^Long-term photosynthetic acclimation to increased atmospheric CO2 concentration in young birch (Betula pendula) trees^13^18^7^441-450^^^^^Jul^^^^^6911
1121^1437^2453^256^2965^374^385^398^417^92^matter; and (3) combined climate change and elevated CO2 would increase both net primary productivity and decomposition rates relative to the current climate condition, but their combined action would be a reduction of soil carbon losses relative to those due to climate change alone. The interactive effects of climate change and elevated CO2, however, are not a simple additive combination of the individual responses. The responses to climate cA^6910^To study the long-term response of photosynthesis to elevated atmospheric CO2 concentration in silver birch (Betula pendula Roth.), 18 trees were grown in the field in open-top chambers supplied with 350 or 700 mu mol mol(-1) CO2 for four consecutive growing seasons. Maximum photosynthetic rates, stomatal conductance and CO2 response curves were measured over the fourth growing season with a portable photosynthesis system. The photosynthesis model developed by Farquhar et al. (1980) was fitted to the CO2 response curves. Chlorophyll, soluble proteins, total nonstructural carbohydrates, nitrogen and Rubisco activity were determined monthly. Elevated CO2 concentration stimulated photosynthesis by 33% on average over the fourth growing season. However, comparison of maximum photosynthetic rates at the same CO2 concentration (350 or 700 mu mol mol(-1)) revealed that the photosynthetic capacity of trees grown in an elevated CO2 concentration was reduced. Analysis of the response curves showed that acclimation to elevated CO2 concentration involved decreases in carboxylation efficiency and RuBP regeneration capacity. No clear evidence for a redistribution of nitrogen within the leaf was observed. Down-regulation of photosynthesis increased as the growing season progressed and appeared to be related to the source-sink balance of the trees. Analysis of the main leaf components revealed that the reduction in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll (10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance in response to the elevated CO2 treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO2 treatment. Thus, after four growing seasons exposed to an elevated CO2 concentration in the field, the trees maintained increased photosynthetic rates, although their photosynthetic capacity was reduced compared With trees grown in ambient CO2.

2075^2^Rouhier,H^Read,DJ^1998^1^The role of mycorrhiza in determining the response of Plantago lanceolata to CO2 enrichment^84^139^2^367-373^^^^^Jun^^^^^6913
1096^1334^1850^1983^2070^2467^312^474^672^733^ysis of the main leaf components revealed that the reduction in photosynthetic capacity was accompanied by an accumulation of starch in leaves (100%), which was probably responsible for the reduction in Rubisco activity (27%) and to a lesser extent for reductions in other photosynthetic components: chlorophyll (10%), soluble protein (9%), and N concentrations (12%) expressed on an area basis. Despite a 21% reduction in stomatal conductance in response to the elevated CO2 treatment, stomatal limitation was significantly less in the elevated, than in the ambient, CO2 treatment. Thus, after four growing seasons exposed to an elevated CO2 concentration in the field, the treesA^6912^Plantago lanceolata L. was grown for 104 d with (M) or without (NM) arbuscular mycorrhizal colonization under conditions of ambient (C-AMB = 350 mu l l(-1)) and elevated (C-ELEV = 540 mu l l(-1)) CO2. Sequential harvests (H) were taken at 41 (H-1), 76 (H-2) and 104 d (H-3) to determine the time-course of mycorrhizal influence on the response of the plant to CO2 enrichment. Total yields of M plants were greater than those of NM from H-2 onwards. Plants in the M-ELEV treatment were significantly larger than those in the M-AMB at 104 d. There were significant but much smaller differences in yield between NMELEV and NMAMB. The differences in total yield arose through impact of C-ELEV on both shoots and roots. Total root length was greater in M-ELEV than in M-AMB only at H-3, but total length of mycorrhizal root was greater at H-2 and H-3. The percentages of root length colonized and that occupied by arbuscules and vesicles were greater in M-ELEV than in M-AMB at the last two harvests, indicating increased sequestration of carbon in internal fungal structures. Though extraradical hyphal lengths were greater in M-ELEV than in M-AMB at H-2 and H-3, the differences were not significant. Phosphorus inflow and P content of M plants were higher than those of NM plants at H-2 and H-3, and were higher in M-ELEV than in M-AMB at H-3. ANOVA revealed no significant interactions between CO2 and mycorrhizal treatment. The results are discussed in relation to carbon sequestration in mycorrhizal systems and likely impacts of CO2 enrichment on P. lanceolata grown under field conditions. The importance of sequential harvesting for realistic determination of responses to CO2 is stressed.

2076^5^Spunda,V^Kalina,J^Cajanek,M^Pavlickova,H^Marek,MV^1998^1^Long-term exposure of Norway spruce to elevated CO2 concentration induces changes in photosystem II mimicking an adaptation to increased irradiance^4^152^4-5^413-419^^^^^May^^^^^6915
1092^1871^243^312^344^348^360^384^493^92^in M-AMB at the last two harvests, indicating increasedA^6914^Fifteen-year-old Norway spruces (Picea abies [L.] Karst.) were grown in open top chambers (OTC) at ambient (A) and elevated (i.e. ambient + 350 mu mol(CO2)mol(-1)) concentrations of CO2 (E) for four growing seasons (1992-1995). During this time period several examples of the depression of photosynthetic activities were observed for E needles. In order to better characterize the nature of this depression the gas exchange and fluorescence parameters were analyzed on current year needles during the last season (July 1995). The photon flux density response curves of CO2 uptake (P-N) revealed a significantly reduced stimulation of P-N for E needles as compared with short-term exposure to doubled CO2. Moreover, the sudden exposure of E shoots to 350 mu mol(CO2)mol(-1) at saturating irradiance revealed a depression of both P-Nmax (by 20 %) and quantum yield of PS II (by 32 %) compared with A shoots measured at 350 mu mol(CO2)mol(-1). The data supporting the diminished light harvesting system of photosystem II (PS II) in E shoots compared with A shoots were obtained from pigment analysis, low temperature fluorescence spectra and Chl a fluorescence induction kinetics. The relative proportion of inactive reaction centres of PS II determined from F-pl of the fluorescence induction was 20 % higher for E needles. These changes found for E needles mimicked an adaptation of PS II to increased irradiance compared with A needles. As the irradiance exposure was the same for the examined needles from both E and A spruces we suggest that these changes reported for E needles resulted from the feed-back limitation of photochemical reactions due to suppressed electron transport through the plastoquinone pool.

2077^4^Tognetti,R^Johnson,JD^Michelozzi,M^Raschi,A^1998^1^Response of foliar metabolism in mature trees of Quercus pubescens and Quercus ilex to long-term elevated CO2^173^39^3^233-245^^^^^Jun^^^^^6917
1120^1144^130^1342^243^3150^345^376^377^384^The data supporting the diminished light harvesting system of photosystem IA^6916^Long-term effects on and adaptations of the carbon physiology of long-lived trees exposed to increasing atmospheric levels of CO2 are unknown. We compared two indigenous Quercus species, Q. ilex and Q. pubescens, growing in a natural CO2 spring located in central Italy and at a nearby control site. In May, 1995 photosynthetic rate at least doubled when measured with supplemental CO2 in both species and sites. Dark respiration was much higher at the CO2 spring site in both species. Foliar sugar and starch concentrations in Q. ilex exhibited significant site and diurnal differences (May and September). In July, 1995 there was little difference in the water potential values of the measured trees at the different sites over the diurnal period. Photosynthetic rate was higher for both species in the CO2 spring, particularly in the early morning and late afternoon. Mid-day stomatal closure reduced photosynthesis to similar levels. In the morning leaf conductance and transpiration were generally lower in the CO2 spring trees, contributing to higher instantaneous water use efficiency for both species. Isoprene emission rates were higher in Q. pubescens trees growing in the CO2 spring. The maximum difference between control and CO2 spring trees occurred in late afternoon. In contrast, Q. ilex exhibited isoprene emission near background level. Foliage and branch carbon and nitrogen status showed increased concentrations of starch and tannins in Q. ilex and of soluble sugars in Q. pubescens in the elevated CO2 environment, while nitrogen concentration decreased in both species. Wood gravity increased 6 and 3% in Q. ilex and Q. pubescens, respectively, growing in the CO2 spring. Q. ilex exhibited afternoon recovery of water potential compared to Q. pubescens which had better night-time recovery. Q. ilex and e. pubescens exposed to elevated CO2 for prolonged periods exhibit different mechanisms for dealing with additional reduced carbon and do maintain an altered carbon physiology, even in midst of the region's characteristic summer drought. (C) 1998 Elsevier Science B.V. All rights reserved.

2078^1^Uprety,DC^1998^1^Carbon dioxide enrichment technology: Open top chambers a new tool for global climate research^202^57^5^266-270^^^^^May^^^^^6919
 trees occurred in late afternoon. In contrast, Q. ilex exhibited isoprene emission near background level. Foliage and branch carbon and nitrogen status showed increased concentrations of starch and tannins in Q. ilex and of soluble sugars in Q. pubescens in the elevated CO2 environment, while nitrogen concentration decreased in both species. Wood gravity increased 6 and 3% in Q. ilex and Q. pubescens, respectively, growing in the CO2 spring. Q. ilex exhibited afternoon recovery of water potential compared to Q. pubescens which had better night-time recovery. Q. ilex and e. pubescens exposed to elevated CO2 for prolonged periods exhibit different mechanisms for dealing with additional reduced carbon and do maintain an altered carbon physiology, even in midst of the region's characA^6918^There are many technical difficulties in conducting crop response studies for elevated carbon dioxide. Available facilities include green house, leaf cuvettes, phytotron, and air exclusion systems. The environmental control on these systems induces uncertainity in the extrapolation of results to the variable natural environments. However, open top chamber technology does not modify the micro-climate and induces realistic natural conditions. Open top chambers are cylindrical, aluminium frames with clear flexible covering and frustrum to reduce the incursion of external air. CO2 enriched air is introduced into the chamber through a perforated spurt with the help of a blower to distribute CO2 uniformly. A relatively simpler design and construction of open top chambers make them the most likely method to be used in the near future for long-term elevated CO2 exposures of crops and other ecosystems.
additional reduced carbon and do maintain an altered carbon physiology, even in midst of the region's charac2079^3^Verburg,PSJ^Gorissen,A^Arp,WJ^1998^1^Carbon allocation and decomposition of root-derived organic matter in a plant-soil system of Calluna vulgaris as affected by elevated CO2^130^30^10-11^1251-1258^^^^^Sep^^^^^6921
1334^310^344^362^374^376^538^57^672^92^ainity in the extrapolation of results to the variable natural environments. However, open top chamber technology does not modify the micro-climate and induces realistic natural conditions. Open top chambers are cylindrical, aluminium frames with clear flexible covering and frustrum to reduce the incursion of external air. CO2 enriched air is introduced into the chamber through a perforated spurt with the help of a blower to distribute CO2 uniformly. A relatively simpler design and construction of open top chambers make them the most likely method to be used in the near future for long-term elevated CO2 exposures of crops and other ecosystems.
additional reduced carbon and do maintain an altered carbon physiology, even in midst of the region's characA^6920^The effect of elevated CO2 on C allocation in plant and soil was assessed using soil cores planted with 1-y-old heather (Calluna vulgaris (L.) Hull). Plants were pulse-labeled with (CO2)-C-14 at ambient and elevated CO2 and two nitrogen regimes (low and high). After harvesting the plants, the soil was incubated to monitor total respiration and decomposition of C- 14-labeled rhizodeposits. Total and shoot biomass increased at high N but were not affected by CO2. Root biomass was not affected by either N or CO2 treatments. Total C-14 uptake and shoot-C-14 increased upon adding N and elevating CO2 but the N effect was strongest. Total C-14 uptake per unit shoot mass decreased with N, but increased with CO2. Root-C-14 content was not significantly affected by the N or CO2 treatment. Total soil-C-14 slightly increased at elevated CO2 whereas microbial C-14 increased due to high N. C allocation to shoots increased at the expense of roots, soil and respiration at high N but was not affected by the CO2 treatment. Variation in C-14 distribution within each treatment was small compared to variation in total C-14 amounts in each plant-soil compartment. Initially, C-14 respiration from rhizodeposits correlated well with root-C-14, total soil-C-14, soil solution-C-14 and microbial C-14, at harvest time and was increased by elevated CO2. By the end of the incubation, however, decomposition of labeled organic matter was not affected by the treatments whereas total (=C-12+C-14) respiration was lowest for the elevated-CO2 soils. We speculate that initially, respiration is dominated by decomposition of fresh root exudates whereas in the longer term, respiration originates from decomposition of more recalcitrant root material that had been formed during the entire experiment. The increased net C-14 uptake and unchanged distribution pattern, combined with an increased decomposition of easily-decomposable compounds and a decreased decomposition of more recalcitrant root-derived material indicated a small sink function of a Calluna plant-soil system under elevated CO2. (C) 1998 Elsevier Science Ltd. All rights reserved.

2080^1^Ziska,LH^1998^1^The influence of root zone temperature on photosynthetic acclimation to elevated carbon dioxide concentrations^52^81^6^717-721^^^^^Jun^^^^^6923
344^348^374^376^417^92^ time and was increased by elevated CO2. By the end of the incubation, however, decomposition of labeled organic matter was not affected by the treatments whereas total (=C-12+C-14) respiration was lowest for the elevated-CO2 soils. We speculate that initially, respiration is dominated by decomposition of fresh root exudates whereas in the longer term, respiration originates from decomposition of more recalcitrant root material that had been formed during the entire experiment. The increased net C-14 uptake and unchanged distribution pattern, combined with an increased decomposition of easily-decomposable compounds and a decreased decomposition of more recalcitrant root-derived material indicated a small sink function of a CA^6922^Soybean (Glycine max 'Clark') was grown from germination to 21 d after sowing (DAS) at ambient (similar to 360 mu mol mol(-1)) or elevated (similar to 720 mu mol mol(-1)) carbon dioxide (CO2) at either one of two soil temperatures, 25 or 30 degrees C to determine the influence of root zone temperature on root growth and photosynthetic stimulation at ambient and elevated concentrations of carbon dioxide. Although the photosynthetic rate became less stimulate over time, a significant stimulation of whole plant photosynthesis and plant dry weight was observed at the elevated CO2 concentration during the experimental period irrespective of soil temperature. At neither carbon dioxide concentration did the warmer soil temperature (30 degrees C) stimulate whole plant growth compared to a soil temperature of 25 degrees C, but it did increase root growth relative to shoot (top) growth with a subsequent increase in root/shoot ratio. Increasing soil temperature at either carbon dioxide concentration also significantly stimulated whole plant photosynthetic rate. However, the degree of stimulation was reduced with time irrespective of carbon dioxide concentration so that at 21 DAS no difference in photosynthesis between ambient and elevated soil temperatures was observed. Data from this experiment indicate that for soybean, a higher soil temperature stimulates root/shoot ratio and enhances photosynthetic response to elevated carbon dioxide in the short-term (i.e. days), but increasing root/shoot ratios does not provide a satisfactory explanation of long-term stimulation of photosynthesis at elevated levels of carbon dioxide. (C) 1988 Annals of Botany Company.

2081^3^Bransby,DI^McLaughlin,SB^Parrish,DJ^1998^1^A review of carbon and nitrogen balances in switchgrass grown for energy^310^14^4^379-384^^^^^^^^^^6925
 of 25 degrees C, but it did increase root growth relative to shoot (top) growth with a subsequent increase in root/shoot ratio. Increasing soil temperature at either carbon dioxide concentration also signifiA^6924^Increased atmospheric CO2, caused partly by burning fossil fuels, is assumed to elevate the risk of global warming, while nitrate contamination of surface runoff and groundwater from fertilizer and agricultural wastes constitutes a serious environmental hazard on a regional scale. Switchgrass (Panicum virgatum L.) grown as an energy crop could reduce atmospheric CO2 accumulation by replacing fossil fuels and sequestering C. It could also improve soil productivity by C sequestration, and reduce NO3-1 contamination of water by absorbing N lost from fertilizer and agricultural waste if planted in filter strips on adjacent land. The objective of this study was to assess potential impacts of switchgrass on C and N balances by reviewing and synthesizing information from current literature, unpublished data and on-going research. Replacing fossil fuels with switchgrass, or any other biomass, will have a much greater effect on atmospheric CO2 than C sequestration. This is because replacing fossil fuels provides a cumulative effect, while C sequestration offers only a one-time benefit. Furthermore, switchgrass will provide net gains in C sequestration only if it replaces annual row crops, but not if it replaces grazed pasture. Nitrogen recovery by switchgrass in an Alabama study was 65.6%, which compares favorably with the 50% recovery frequently quoted as the norm for wheal (Triticum aestivum L.) and corn (Zea mays L). (C) 1998 Elsevier Science Ltd. All rights reserved.

2082^3^Bryant,J^Taylor,G^Frehner,M^1998^1^Photosynthetic acclimation to elevated CO2 is modified by source : sink balance in three component species of chalk grassland swards grown in a free air carbon dioxide enrichment (FACE) experiment^9^21^2^159-168^^^^^Feb^^^^^6927
230^244^245^2575^344^348^384^745^from current literature, unpublished data and on-going research. Replacing fossil fuels with switchgrass, or any other biomass, will have a much greater effect on atmospheric CO2 than C sequestration. This is because replacing fossil fuels providA^6926^Artificial chalk grassland swards were exposed to either ambient air or air enriched to 600 mu mol mol(-1) CO2, using free-air CO2 enrichment technology, and subjected to an 8 week simulated grazing regime. After 14 months of treatment, ribulose-1,5-bisphosphate carboxylase (Rubisco) activity (V- c,V-max) and electron transport mediated ribulose-1,5- bisphosphate (RuBP) regeneration capacity (J(max)), estimated from leaf gas exchange, were significantly lower in fully expanded leaves of Anthyllis vulneraria L. (a legume) and Sanguisorba minor Scop, grown in elevated CO2. After a change in source:sink balance brought about by defoliation, photosynthetic capacity was fully restored in A. vulneraria and S. minor, but acclimation continued in the grass Bromopsis erecta (Hudson) Fourr. Changes in net photosynthesis (P-n) with growth at elevated CO2 ranged from a 1.6% reduction in precut leaves of A. vulneraria to a 47.1% stimulation in postcut leaves of S. minor. Stomatal acclimation was observed in leaves of A. vulneraria (reduced stomatal density) and B. erecta (reduced stomatal conductance). The results are discussed in terms of whole-plant resource-use optimization and chalk grassland community competitive interactions at elevated CO2.

2083^2^Cannell,MGR^Thornley,JHM^1998^1^N-poor ecosystems may respond more to elevated [CO2] than N- rich ones in the long term. A model analysis of grassland^127^4^4^431-442^^^^^Apr^^^^^6929
1103^1262^344^362^376^384^392^512^715^977^fully expanded leaves of Anthyllis vulneraria L. (a legume) and Sanguisorba minor Scop, grown in elevated CO2. After a change in source:sink balance brought about by defoliation, photosynthetic capacity was fully restored in A. vulneraria and S. minor, but acclimation continued in the grass Bromopsis erecta (Hudson) Fourr. Changes in net photosynthesis (P-n) with growth at elevated CO2 ranged from a 1.6% reduction in precut leaves of A. vulneraria to a 47.1% stimulation in postcut leaves of S. minor. Stomatal acclimation was observed in leavesA^6928^The Hurley Pasture Model was used to examine the short and long-term responses of grazed grasslands in the British uplands to a step increase from 350 to 700 mu mol mol(-1) CO2 concentration ([CO2]) with inputs of 5 or 100 kg N ha(-1) y(- 1). In N-rich grassland, [CO2] doubling quickly increased net primary productivity (NPP), total carbon (C-sys) and plant biomass by about 30%. By contrast, the N-poor grassland underwent a prolonged 'transient', when there was little response, but eventually NPP, C-sys and plant biomass more than doubled. The 'transient' was due to N immobilization and severe depletion of the soil mineral N pool. The large long-term response was due to slow N accumulation, as a result of decreased leaching, decreased gaseous N losses and increased N- 2-fixation, which amplified the CO2 response much more in the N-poor than in the N-rich grassland. It was concluded that (i) ecosystems use extra carbon fixed at high [CO2] to acquire and retain nutrients, supporting the contention of Gifford et al. (1996), (ii) in the long term, and perhaps on the real timescale of increasing [CO2], the response (in NPP, C-sys and plant biomass) of nutrient-poor ecosystems may be proportionately greater than that of nutrient-rich ones, (iii) short-term experiments on nutrient-poor ecosystems may observe only the transient responses, (iv) the speed of ecosystem responses may be limited by the rate of nutrient accumulation rather than by internal rate constants, and (v) ecosystem models must represent processes affecting nutrient acquisition and retention to be able to simulate likely real-world CO2 responses.

2084^5^Entry,JA^Runion,GB^Prior,SA^Mitchell,RJ^Rogers,HH^1998^1^Influence of CO2 enrichment and nitrogen fertilization on tissue chemistry and carbon allocation in longleaf pine seedlings^206^200^1^3-11^^^^^Mar^^^^^6931
1086^1096^1262^3151^347^362^407^58^733^92^d. It was concluded that (i) ecosystems use extra carbon fixed at high [CO2] to acquire and retain nutrients, supporting the contention of GiA^6930^One-year old, nursery-grown longleaf pine (Pinus palustris Mill.) seedlings were grown in 45-L pots containing a coarse sandy medium and were exposed to two concentrations of atmospheric CO2 (365 or 720 mu mol(-1)) and two levels of nitrogen (N) fertility (40 or 400 kg N ha(-1) yr(-1)) within open top chambers for 20 months. At harvest, needles, stems, coarse roots, and fine roots were separated and weighed. Subsamples of each tissue were frozen in liquid N, lyophilized at -50 degrees C, and ground to pass a 0.2 mm sieve. Tissue samples were analyzed for carbon (C), N, nonpolar extractives (fats, waxes, and oils = FWO), nonstructural carbohydrates (total sugars and starch), and structural carbohydrates (cellulose, lignin, and tannins). Increased dry weights of each tissue were observed under elevated CO2 and with high N; however, main effects of CO2 were significant only on belowground tissues. The high N fertility tended to result in increased partitioning of biomass aboveground, resulting in significantly lower root to shoot ratios. Elevated CO2 did not affect biomass allocation among tissues. Both atmospheric CO2 and N fertility tended to affect concentration of C compounds in belowground, more than aboveground, tissues. Elevated CO2 resulted in lower concentrations of starch, cellulose, and lignin, but increased concentrations of FWO in root tissues. High N fertility increased the concentration of starch, cellulose, and tannins, but resulted in lower concentrations of lignin and FWO in roots. Differences between CO2 concentrations tended to occur only with high N fertility. Atmospheric CO2 did not affect allocation patterns for any compound; however the high N treatment tended to result in a lower percentage of sugars, cellulose, and lignin belowground.
s of each tissue were observed under elevated CO2 and with high N; however, main effects of CO2 were significant only on belowground tissues. The high N fertility tended to result in increased partitioning of biomass aboveground, resulting in signifi2085^8^Fernandez,MD^Pieters,A^Donoso,C^Tezara,W^Azkue,M^Herrera,C^Rengifo,E^Herrera,A^1998^1^Effects of a natural source of very high CO2 concentration on the leaf gas exchange, xylem water potential and stomatal characteristics of plants of Spatiphylum cannifolium and Bauhinia multinervia^84^138^4^689-697^^^^^Apr^^^^^6933
1208^2060^243^344^348^376^398^431^92^968^ fertility increased the concentration of starch, cellulose, and tannins, but resulted in lower concentrations of lignin and FWO in roots. Differences between CO2 concentrations tended to occur only with high N fertility. Atmospheric CO2 did not affect allocation patterns for any compound; however the high N treatment tended to result in a lower percentage of sugars, cellulose, and lignin belowground.
s of each tissue were observed under elevated CO2 and with high N; however, main effects of CO2 were significant only on belowground tissues. The high N fertility tended to result in increased partitioning of biomass aboveground, resulting in signifiA^6932^The effect of a very high CO2 mole fraction (27 000-35 000 mu mol mol(-1)) on photosynthesis and water relations was studied during the dry and the rainy season in plants of Spatiphylum cannifolium (Dryand.) Schott and Bauhinia multinervia (H.B.K.) DC. growing near natural cold CO2 springs. Xylem water potential in plants of both species was lowered by drought, high CO2 growth-concentration decreasing it further in S. cannifolium. In plants of both species growing under high CO2 concentration photosynthetic rates measured at a CO2 mole fraction of 1000 mu mol mol(-1) were higher than in plants growing at ambient CO2 mole fraction and measured at 350 mu mol mol(-1). The response was the result of a direct effect of CO2 on the photosynthetic machinery. Changes in carboxylation efficiency in response to high CO2 were found during the rainy season, with an increase in S. cannifolium and a decrease in B. multinervia; a significant interaction between growth CO2 concentration and season in B. multinervia resulted from significant effects of both factors. An increase in intrinsic water-use efficiency due to high CO2 was determined in both species by an increase in photosynthetic rate as well as a decrease in leaf conductance. In high-CO2 plants of S. cannifolium a 71 % decrease in stomatal density and 73 % in stomatal index suggested that CO2 affected stomatal initiation, whereas in B. multinervia an 85 % decrease in stomatal index and a 72 % decrease in stomatal density indicated that CO2 influenced stomatal initiation as well as epidermal cell expansion. Our results indicate that very high CO2 concentrations did not inhibit photosynthesis in these species, and that growth under high CO2 allowed plants to attain carbon balances higher than those of plants growing under low CO2. This was particularly so during the dry season, since the photosynthetic rates at the corresponding ambient concentration were higher in plants nearer the springs, and carboxylation efficiency and some stomatal characteristics of both species apparently acclimated to high CO2, but patterns were not consistent and bore no obvious relationship to photosynthetic capacity.

2086^2^Garcia-Ibilcieta,D^Pushnik,JC^1997^1^Differential gene displays from Pinus ponderosa seedlings experiencing elevated CO2 stress^359^11^9^A1104^^^^^31 Jul

2087^3^Grodzinski,B^Jiao,JR^Leonardos,ED^1998^1^Estimating photosynthesis and concurrent export rates in C-3 and C-4 species at ambient and elevated CO2^8^117^1^207-215^^^^^May^^^^^6936
130^1538^2600^3152^348^385^632^788^n as well as epidermal cell expansion. Our results indicate that very high CO2 concentrations did not inhibit photosynthesis in these species, and that growth under high CO2 allowed plants to attain carbon balances higher than those of plants growing under low CO2. This was particularly so during the dry season, since the photosynthetic rates at the corresponding ambient concentration were higher in plants nearer the springs, and carboxylation efficiency and some stomatal characteristics of both sA^6935^The ability of 21 C-3 and C-4 monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO2 levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state (CO2)-C-14-labeling procedure. At ambient CO2 photosynthesis and export rates for C-3 species were 5 to 15 and 1 to 10 mu mol C m(-2) s(-1), respectively, and 20 to 30 and 15 to 22 mu mol C m(-2) s(-1), respectively, for C-4 species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C-3 dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C-4 species. At high CO2 photosynthetic and export rates were only slightly altered in C, species, and photosynthesis increased but export rates did not in all C(3)species. The C-3 species that had high efflux rates relative to photosynthesis at ambient CO2 exported at rates comparable to those of C-4 species on both an absolute basis and as a percentage of photosynthesis. At ambient CO2 there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO2 the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated.

2088^3^Hunt,HW^Morgan,JA^Read,JJ^1998^1^Simulating growth and root-shoot partitioning in prairie grasses under elevated atmospheric CO2 and water stress^52^81^4^489-501^^^^^Apr^^^^^6938
137^2139^230^314^374^407^423^427^494^57^t produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C-4 species. At high CO2 photosynthetic and export rates were only slightly altered in C, species, and photosynthesis increased but export rates did not in all C(3)species. TA^6937^We constructed a model simulating growth, shoot-root partitioning, plant nitrogen (N) concentration and total nonstructural carbohydrates in perennial grasses. Carbon (C) allocation was based on the concept of a functional balance between root and shoot growth, which responded to variable plant C and N supplies. Interactions between the plant and environment were made explicit by way of variables for soil water and soil inorganic N. The model was fitted to data on the growth of two species of perennial grass subjected to elevated atmospheric CO2 and water stress treatments. The model exhibited complex feedbacks between plant and environment, and the indirect effects of CO2 and water treatments on soil water and soil inorganic N supplies were important in interpreting observed plant responses. Growth was surprisingly insensitive to shoot-root partitioning in the model, apparently because of the limited soil N supply, which weakened the expected positive relationship between root growth and total N uptake. Alternative models for the regulation of allocation between shoots and roots were objectively compared by using optimization to find the least squares fit of each model to the data. Regulation by various combinations of C and N uptake rates, C and N substrate concentrations, and shoot and root biomass gave nearly equivalent fits to the data, apparently because these variables were correlated with each other. A partitioning function that maximized growth predicted too high a root to shoot ratio, suggesting that partitioning did not serve to maximize growth under the conditions of the experiment (C) 1998 Annals of Botany Company.

2089^2^Johnsen,KH^Major,JE^1998^1^Black spruce family growth performance under ambient and elevated atmospheric CO2^360^15^3^271-281^^^^^May^^^^^6940
10^2529^3153^361^374^384^546^705^prisingly insensitive to shoot-root partitioning in the model, apparently because of the limited soil N supply, which weakened the expected positive relationship between root growth and total N uptaA^6939^Seedlings from 20 families of black spruce (Picea mariana (Mill.) B.S.P.), representing a large range in field productivity, were subjected to a greenhouse retrospective test under ambient (409 ppm - year 1, 384 ppm - year 2) and high (686 ppm - year 1, 711 ppm - year 2) atmospheric CO2 environments. After one and two growth cycles, seedling height and diameter growth significantly increased under elevated CO2. At the end of the experiment, seedlings grown under high CO2 had a mean above-ground dry weight of 48.77 g as compared to 26.36 g for seedlings grown under ambient atmospheric CO2. Families were a significant source of variation for all growth parameters. Although the family x CO2 environment interaction was not a statistically significant source of variation in the analysis of variance, the correlation between greenhouse and IS-year field height growth was weaker (r = 0.29, p = 0.2177) under elevated CO2 compared to ambient CO2 (r = 0.51, p = 0.0223) following the first growth cycle. However, following the second growth cycle, greenhouse-field correlations were similar between the two CO2 environments (ambient CO2: r = 0.55, p = 0.0115; elevated CO2: r = 0.56, p = 0.0101). Thus, with this set of families, growth performance ranking after two years appears relatively stable under ambient and elevated CO2.

2090^3^Kainulainen,P^Holopainen,JK^Holopainen,T^1998^1^The influence of elevated CO2 and O-3 concentrations on Scots pine needles: changes in starch and secondary metabolites over three exposure years^2^114^4^455-460^^^^^May^^^^^6942
1064^1951^2688^2993^361^362^447^690^753^92^ CO2. Families were a significant source of variation for all growth parameters. Although the family x CO2 environment interaction was not a statistically significant source of variation in the analysis of variance, the correlation between greenhouse and IS-year field height growth was weaker (r = 0.29, p = 0.2177) under elevated CO2 compared to ambient CO2 (r = 0.51, p = 0.0223) following the first growth cycle. However, A^6941^Scots pine (Pinus sylvestris L.) trees, aged about 20 years old, growing on a natural pine heath were exposed to two concentrations of CO2 (ambient CO2 and double-ambient CO2) and two O-3 regimes (ambient O-3 and double-ambient O-3) and their combination in open-top chambers during growing seasons 1994, 1995 and 1996. Concentrations of foliar starch and secondary compounds are reported in this paper. Starch concentrations remained unaffected by elevated CO2 and/or O-3 concentrations during the first 2 study years. But in the autumn of the last study year, a significantly higher concentration of starch was found in current-year needles of trees exposed to elevated CO2 compared with ambient air. There were large differences in concentrations of starch and secondary compounds between individual trees. Elevated concentrations of CO2 and/or O-3 did not have any significant effects on the concentrations of foliar total monoterpenes, total resin acids or total phenolics. Significantly higher concentrations of monoterpenes and resin acids and mostly lower concentrations of starch were found in trees growing without chambers than in those growing in open-top chambers, while there were no differences in concentrations of total phenolics between trees growing without or in chambers. The results suggest that elevated concentrations of CO2 might increase foliar starch concentrations in Scots pine, while secondary metabolites remain unaffected. Realistically elevated O-3 concentrations do not have clear effects on carbon allocation to starch and secondary compounds even after 3 exposure years.

2091^1^Kerstiens,G^1998^1^Shade-tolerance as a predictor of responses to elevated CO2 in trees^37^102^3^472-480^^^^^Mar^^^^^6944
2163^2489^2640^2715^3154^3155^341^344^512^587^nd secondary compounds between individual trees. Elevated concentrations of CO2 and/or O-3 did not have any significant effects on the concentrations of foliar total monoterpenes, total resin acids or total phenolics. Significantly higher concentrations oA^6943^Evidence from 10 studies comparing angiosperm trees and 5 studies comparing conifers or differing shade-tolerance was analysed. The number of intraphyletic comparisons in which the more shade-tolerant species showed the greater relative increase of biomass in elevated CO2 was significantly higher than would be expected by chance alone. It is suggested that more shade-tolerant species are inherently better disposed. in terms of plant architecture and partitioning of biomass and nitrogen, to utilise resources (light, water, nutrients) that are potentially limiting in elevated CO2 and that these traitu are responsible for the interaction between shade-tolerance and CO2 concentration. Compared with less shade-tolerant angiosperm trees, more shade-tolerant angiosperm species generally have a lower lear area ratio in ambient CO2 and show a smaller relative reduction in elevated CO2. Furthermore, leaf nitrogen content is usually lower in more shads-tolerant angiosperm species and tends to be more strongly reduced by elevated CO2 in those species. Within angiosperm trees, more shade-tolerant species showed a stronger stimulation of net leaf photosynthetic I ate in most experiments, but this trend was not significant.

2092^4^Klironomos,JN^Ursic,M^Rillig,M^Allen,MF^1998^1^Interspecific differences in the response of arbuscular mycorrhizal fungi to Artemisia tridentata grown under elevated atmospheric CO2^84^138^4^599-605^^^^^Apr^^^^^6946
1019^1030^1983^2467^312^376^474^547^711^984^ss and nitrogen, to utilise resources (light, water, nutrients) that are potentially limiting in elevated CO2 and that these traitu are responsible for the interaction between shade-tolerance and CO2 concentration. Compared with less shade-tolerant angiosperm trees, more shade-tolerant angiosperm species generally have a lower lear area ratio in ambient CO2 and show a smaller relative reduction in elevated CO2. Furthermore, leaf nitrogen content is usually lower in more shads-tolerant angiosperm species and tends to be more strongly reA^6945^Arbuscular mycorrhizal (AM) fungi form mutualistic symbioses with the root systems of most plant species. These mutualisms regulate nutrient exchange in the plant-soil interface and might influence the way in which plants respond to increasing atmospheric CO2. In other experiments, mycorrhizal responses to elevated CO2 have been variable, so in this study we test the hypothesis that different genera of AM fungi differ in their response, and in turn alter the plant's response, to elevated CO2. Four species from three genera of AM fungi were tested. Artemisia tridentata Nutt. seedlings were inoculated with either Glomus intraradices Schenck & Smith, Glomus etunicatum Becker & Gerdemann, Acaulospora sp. or Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders and grown at either ambient CO2 (350 ppm) or elevated CO2 (700 ppm). Several significant inter-specific responses were detected. Elevated CO2 caused percent arbuscular and hyphal colonization to increase for the two Glomus species, but not for Acaulospora sp. or S. calospora. Vesicular colonization was not affected by elevated CO2 for any fungal species. In the extra-radical phase, the two Glomus species produced a significantly higher number of spores in response to elevated CO2, whereas Acaulospora sp. and S. calospora developed significantly higher hyphal lengths. These data show that AM fungal taxa differ in their growth allocation strategies and in their responses to elevated CO2, and that mycorrhizal diversity should not be overlooked in global change research.

2093^4^Ledergerber,S^Leadley,PW^Stocklin,J^Baur,B^1998^1^Feeding behaviour of juvenile snails (Helix pomatia) to four plant species grown at elevated atmospheric CO2^318^19^1^89-95^^^^^Jan-Feb^^^^^6948
1142^1997^338^374^874^) Walker & Sanders and grown at either ambient CO2 (350 ppm) or elevated CO2 (700 ppm). Several significant inter-specific responses were detected. Elevated CO2 caused percent arbuscular and hyphal colonization to increase for the two Glomus species, but not for AA^6947^The feeding behaviour of juveniles of the land snail Helix pomatia was examined in model plant communities consisting of Trifolium repens, Hieracium pilosella, Bromus erectus and Prunella vulgaris that are common species in extensively managed calcareous grasslands in the Swiss Jura mountains. The plant communities were grown either at ambient (350 ppm) or elevated (600 ppm) CO2 concentrations. Leaves of T. repens and P. vulgaris grown in elevated atmospheric CO2 had a lower specific leaf area, and leaves of T. repens had lower percentage N on a dry weight basis than leaves grown under ambient CO2 concentration. Snails fed on all four plant species, but showed a overwhelming preference for T. repens (percentages of total biomass consumed were 91.9 % at 350 ppm and 97.6 % at 600 ppm). The species-specific feeding intensity of juvenile H. pomatia did not differ between the two treatments. The total dry weight of T. repens consumed by the snails was marginally greater (P = 0.06) at elevated CO2, but there were no significant differences in leaf N or leaf area eaten. These findings are similar to numerous other studies showing that invertebrates increase their consumption of plant material to balance reductions in plant N concentrations at elevated CO2 treatments. Helix pomatia that fed on plants grown at elevated CO2 atmosphere showed a larger increase in relative wet weight than those that fed on plants from ambient CO2 conditions. However, the weight gain of H. pomatia was poorly correlated with amount of plant tissue consumed, so we suggest that the effect of CO2 on weight gain in H. pomatia was due to a change in the quality of T. repens leaves. (C) Elsevier, Paris.

2094^5^Morgan,JA^LeCain,DR^Read,JJ^Hunt,HW^Knight,WG^1998^1^Photosynthetic pathway and ontogeny affect water relations and the impact of CO2 on Bouteloua gracilis (C-4) and Pascopyrum smithii (C-3)^2^114^4^483-493^^^^^May^^^^^6950
312^3156^3157^3158^372^374^384^385^431^750^ snails was marginally greater (P = 0.06) at elevated CO2, but therA^6949^The eastern Colorado shortgrass steppe is dominated by the C-4 grass, Bouteloua gracilis, but contains a mixture of C-3 grasses as well, including Pascopyrum smithii. Although the ecology of this region has been extensively studied, there is little information on how increasing atmospheric CO2 will affect it. This growth chamber study investigated gas exchange, water relations, growth, and biomass and carbohydrate partitioning in B. gracilis and P. gracilis grown under present ambient and elevated CO2 concentrations of 350 mu l l(-1) and 700 mu l l(-1), respectively, and two deficit irrigation regimes. The experiment was conducted in soil-packed columns planted to either species over a 2-month period under summer- like conditions and with no fertilizer additions. Our objective was to better under stand how these species and the functional groups they represent will respond in future CO2-enriched environments. Leaf CO2 assimilation (A(n)), transpiration use efficiency (TUE, or A(n)/transpiration), plant growth, and whole-plant water use efficiency (WUE, or plant biomass production/water evapotranspired) of both species were greater at elevated CO2, although responses were more pronounced for P. smithii. Elevated CO2 enhanced photosynthesis, TUE, and growth in both species through higher soil water content (SWC) and leaf water potentials (Psi) and stimulation of photosynthesis. Consumptive water use was greater and TUE less for P. smithii than B. gracilis during early growth when soil water was more available. Declining SWC with time was associated with a steadily increased sequestering of total non-structural carbohydrates (TNCs), storage carbohydrates (primarily fructans for P. Smithii) and biomass in belowground organs of P. smithii, but not B. gracilis. The root:shoot ratio of P. smithii also increased at elevated CO2 while the root:shoot ratio of B. gracilis was unresponsive to CO2. These partitioning responses may be the consequence of different ontogenetic strategies of a cool-season and warm-season grass entering a warm, dry summer period; the cool-season P. smithii responds by sequestering TNCs belowground in preparation for summer dormancy, while resource partitioning of the warm-season B. gracilis remains unaltered. One consequence of greater partitioning of resources into P. smithii belowground organs in the present study was maintenance of higher Psi and A(n) rates. This, along with differences in photosynthetic pathway, may have accounted for the greater responsiveness of P. smithii to CO2 enrichment compared to B. gracilis.

2095^1^Niklaus,PA^1998^1^Effects of elevated atmospheric CO2 on soil microbiota in calcareous grassland^127^4^4^451-458^^^^^Apr^^^^^6952
1239^1781^312^374^467^547^57^661^738^99^und organs of P. smithii, but not B. gracilis. The root:shoot ratio of P. smithii also increased at elevated CO2 while the root:shoot ratio of B. gracilis was unresponsive to CO2. These partitioning responses may be the consequence of different ontogenetic strategies of a cool-season and warm-seasonA^6951^Microbial responses to three years of CO2 enrichment (600 mu L L-1) in the field were investigated in calcareous grassland. Microbial biomass carbon (C) and soil organic C and nitrogen (N) were not significantly influenced by elevated CO2. Microbial C:N ratios significantly decreased under elevated CO2 (-15%, P = 0.01) and microbial N increased by + 18% (P = 0.04). Soil basal respiration was significantly increased on one out of 7 sampling dates (+ 14%, P = 0.03; December of the third year of treatment), whereas the metabolic quotient for CO2 (qCO(2) = basal respiration/microbial C) did not exhibit any significant differences between CO2 treatments. Also no responses of microbial activity and biomass were found in a complementary greenhouse study where intact grassland turfs taken from the field site were factorially treated with elevated CO2 and phosphorus (P) fertilizer (1 g P m(-2) y(-1)). Previously reported C balance calculations showed that in the ecosystem investigated growing season soil C inputs were strongly enhanced under elevated CO2. It is hypothesized that the absence of microbial responses to these enhanced soil C fluxes originated from mineral nutrient limitations of microbial processes. Laboratory incubations showed that short- term microbial growth (one week) was strongly limited by N availability, whereas P was not limiting in this soil. The absence of large effects of elevated CO2 on microbial activity or biomass in such nutrient-poor natural ecosystems is in marked contrast to previously published large and short-term microbial responses to CO2 enrichment which were found in fertilized or disturbed systems. It is speculated that the absence of such responses in undisturbed natural ecosystems in which mineral nutrient cycles have equilibrated over longer periods of time is caused by mineral nutrient limitations which are ineffective in disturbed or fertilized systems and that therefore microbial responses to elevated CO2 must be studied in natural, undisturbed systems.
son soil C inp2096^4^Osorio,J^Osorio,ML^Chaves,MM^Pereira,JS^1998^1^Water deficits are more important in delaying growth than in changing patterns of carbon allocation in Eucalyptus globulus^13^18^6^363-373^^^^^Jun^^^^^6954
1272^1859^243^3032^361^372^514^57^642^748^ microbial growth (one week) was strongly limited by N availability, whereas P was not limiting in this soil. The absence of large effects of elevated CO2 on microbial activity or biomass in such nutrient-poor natural ecosystems is in marked contrast to previously published large and short-term microbial responses to CO2 enrichment which were found in fertilized or disturbed systems. It is speculated that the absence of such responses in undisturbed natural ecosystems in which mineral nutrient cycles have equilibrated over longer periods of time is caused by mineral nutrient limitations which are ineffective in disturbed or fertilized systems and that therefore microbial responses to elevated CO2 must be studied in natural, undisturbed systems.
son soil C inpA^6953^Potted cuttings of three Eucalyptus globulus Labill, clones (AR3, CN44, MP11) were either well watered or subjected to one of two soil water deficit regimes for six months in a greenhouse. Reductions in lateral branching, leaf production and leaf expansion were the leading contributors to the large differences observed in biomass production between well-watered and water-stressed plants. Although no significant differences among clones were observed in dry matter accumulation or in the magnitude of the response to soil water deficits, sensitivity of lateral branching, leaf initiation and whole-plant foliage to water stress was significantly lower in CN44 than in AR3 and MP11. When the confounding effect of differences in plant size resulting from the different watering regimes was removed, allometric analysis indicated that the genotypes differed in biomass allocation patterns. In addition to a drought-induced reduction in leaf number, water deficits also resulted in smaller leaves because leaf expansion was inhibited during dehydration events. Resumption of leaf expansion following stress relief occurred in all of the clones, but was particularly evident in severely stressed plants of Clone AR3, possibly as a result of the osmotic adjustment observed in this genotype.

2097^3^Pan,Q^Wang,Z^Quebedeaux,B^1998^1^Responses of the apple plant to CO2 enrichment: changes in photosynthesis, sorbitol, other soluble sugars, and starch^92^25^3^293-297^^^^^^^^^^6956
1163^312^3159^372^529^546^92^ the magnitude of the response to soil water deficits, sensitivity of lateral branching, leaf initiation and whole-plant foliage to water stress was significantly lower in CN44 than in AR3 and MP11. When the confounding effect of differences in plant size resulting from the different watering regimes was removed, allometric analysis indicated that the genotypes differed in biomass allocation patterns. In addition to a drought-induced reduction in leaf number, water deficits also resulted in smaller leaves because leaf expansA^6955^There is no information on the effects of elevated [CO2] on whole-plant photosynthesis and carbohydrate metabolism in apple (Malus domestica Borkh.) and other sorbitol-translocating plants. Experiments were conducted in controlled growth chambers to evaluate how increases in [CO2] affect plant photosynthesis and carbon partitioning into soluble sugars and starch in apple leaves. Apple plants (cv, Gala), 1-year-old, were exposed to [CO2] of 200, 360, 700, 1000, and 1600 mu L L-1 up to 8 d. Whole-plant net photosynthetic rates were analysed daily after [CO2] treatments. Newly expanded mature leaves were sampled at 1, 2, 4, and 8 d after [CO2] treatments for sorbitol, sucrose, glucose, fructose, and starch analysis. Midday whole-plant net photosynthetic rates increased linearly with increasing [CO2], but the differences in whole-plant photosynthesis between CO2-enrichment and ambient [CO2] treatments were less significant as apple plants acclimated to high atmospheric [CO2] for 8 d. Increases in [CO2] significantly increased sorbitol and starch, but did not affect sucrose concentrations. As a result, the ratios of starch to sorbitol and starch to sucrose at 8 d after [CO2] treatments were increased from 0.05 and 0.06 to 0.8 and 1.6 as [CO2] increased from ambient [CO2] (360 mu L L-1) to 1000 mu L L-1 [CO2], respectively. The sorbitol to sucrose ratio also increased from 1.3 to 2.2 as [CO2] increased from 360 to 1000 mu L L-1. Elevated [CO2] enhanced the photosynthesis of apple plants and altered carbohydrate accumulation in mature leaves in favour of starch and sorbitol over sucrose.

2098^11^Pan,YD^Melillo,JM^McGuire,AD^Kicklighter,DW^Pitelka,LF^Hibbard,K^Pierce,LL^Running,SW^Ojima,DS^Parton,WJ^Schimel,DS^1998^1^Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)^2^114^3^389-404^^^^^Apr^^^^^6958
1298^137^1660^2487^312^3160^384^508^697^700^d. Increases in [CO2] siA^6957^Although there is a great deal of information concerning responses to increases in atmospheric CO2 at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO2 is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO2. In this study, we analyze the responses of net primary production (NPP) to doubled CO2 from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO2 causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO2 and the mean annual temperature aid annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO2 for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO2 for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO2 is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO2 is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO2 is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainly about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO2.

2099^2^Reid,CD^Fiscus,EL^1998^1^Effects of elevated [CO2] and/or ozone on limitations to CO2 assimilation in soybean (Glycine max)^78^49^322^885-895^^^^^May^^^^^6960
1364^256^312^3161^344^384^435^444^448^728^es in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO2 isA^6959^Soybean (Glycine max) was grown in open-top field chambers at ambient (360 mu mol mol(-1)) or doubled [CO2] either in charcoal-filtered air (20 nmol mol(-1) [O-3]) or in non- filtered air supplemented to 1.5 x ambient [O-3] (70 nmol mol(- 1)) to determine the major limitations to assimilation under conditions of elevated [CO2] and/or [O-3]. Through plant ontogeny, assimilation versus intercellular CO2 concentration (A/Ci) responses were measured to assess the limitations to assimilation imposed by the capacity for Rubisco carboxylation, RuBP regeneration, and stomatal diffusion. In the vegetative stages, no significant treatment effects of elevated [CO2] and/or [O-3] were observed on Rubisco carboxylation efficiency (CE), light and CO2-saturated assimilation capacity (A(max)), and chlorophyll content (Chl). However, for plants grown in elevated [CO2], the assimilation rate at growth [CO2] (A) was 60% higher than at ambient [CO2] up to the seed maturation stage, and the potential rate of assimilation by Rubisco capacity (A(p)) was increased. Also in elevated [CO2]: A was 51% of A(p); the relative stomatal limitation (%Stomata) was 5%; and the relative RuBP regeneration limitation (%RuBP) was 44%. In ambient [CO2], O-3 gradually decreased A per unit leaf area, but had little effect on A, and the relative limitations to assimilation where A remained 51% of A(p), %Stomata was 27%, and %RuBP was 22%. During reproduction, CE declined for plants grown in elevated [CO2] and/or [O-3]; A(p) was unaffected by elevated [CO2], but was reduced by [O-3] at ambient [CO2]; A increased to 72% of A(p) in elevated [CO2] and/or [O-3]- fumigated air; the %Stomata increased; and the %RuBP decreased, to become non significant in elevated [CO2] from the beginning of seed growth on, and in O-3-fumigated air at ambient [CO2] at the seed maturation stage. The decrease in %RuBP occurred concomitantly with an increase in A(max) and Chl. Significant [CO2] x [O-3] interactions support the lack of an O-3 effect on assimilation and its limitations at elevated [CO2] during seed maturation. These data suggest that elevated [CO2] alleviated some of the effects of O-3 on photosynthesis.

2100^6^Rogers,GS^Gras,PW^Batey,IL^Milham,PJ^Payne,L^Conroy,JP^1998^1^The influence of atmospheric CO2 concentration on the protein, starch and mixing properties of wheat flour^92^25^3^387-393^^^^^^^^^^6962
130^1366^2733^312^372^386^434^439^57^724^22%. During reproduction, CE declined for plants grown in elevated [CO2] and/or [O-3]; A(p) was unaffected by elevated [CO2], but was reduced by [O-3] at ambient [CO2]; A increased to 72% of A(p) in elevated [CO2] and/or [O-3]- fumigated air; the %Stomata increased; and the %RuBP decreased, to become non significant in elevated [CO2] from the beginning of seed growth on, and in O-3-fumigated air at ambient [CO2] at the seed maturation stage. The decrease in %RuBP occurred concomitantly with an increase in A(max) and Chl. Significant [CO2] x [O-3] interactions support the lack of an O-3 effect on assimilation and its lA^6961^Wheat (Triticum aestivum L.) cultivars Hartog and Rosella were grown at CO2 concentrations of 280 mu L L-1 (representing the pre-industrial CO2 concentration), 350 mu L L-1 (ambient) and 900 mu L L-1 tan extreme projection of atmospheric CO2 concentration). The plants were grown in naturally lit glasshouses in 7 L pots containing soil to which basal nutrients had been added and the pH adjusted to 6.5, Hartog yielded 2.4 g of grain per plant when grown at 280 mu L CO2 L- 1. This yield was increased by 38% and 75% at CO2 concentrations of 350 mu L L-1 and 900 mu L L-1 respectively. These changes were due to increases in both grain number and individual grain weight as the level of CO2 was raised. The yield of Rosella was unaffected by altering the CO2 concentration. Increasing the CO2 concentration reduced grain protein concentration of cv. Hartog from 17.4% at 280 mu L CO2 L-1 to 16.5% and 16% at CO2 concentrations of 350 mu L L-1 and 900 mu L L-1 respectively. The grain protein concentration of cv. Rosella was reduced from 10.7% to 10.2% by increasing the CO2 concentration from 280 mu L L-1 to 350 mu L L-1; however, an additional increase in the CO2 concentration to 900 mu L L-1 had no effect on grain protein concentration. In Hartog flour, the highest proportion of polymeric protein in the flour (7.7%) occurred at 280 mu L CO2 L-1. This was reduced to 6.3% at 350 mu L CO2 L-1 but then increased again to 7.0% at 900 mu L CO2 L-1. These changes in concentration of polymeric protein were correlated (r(2)=0.58) with changes in mixing properties, The mixing time required to produce optimum dough strength was greatest at 900 mu L CO2 L-1 (181 s), then 141 s and 151 s at 350 mu L CO2 L-1 and 280 mu L CO2 L-1 respectively. These changes in mixing time could not be explained by changes in grain protein concentration. The proportion of 'B' starch granules (<10 mu m diameter) increased from 25% of total weight of starch at 280 mu L CO2 L-1 to 30% at CO2 concentrations 350 and 900 mu L L-1. There were generally no effects of CO2 concentration on dough mixing properties or starch granule size distribution for Rosella.

2101^4^Roth,S^Lindroth,RL^Volin,JC^Kruger,EL^1998^1^Enriched atmospheric CO2 and defoliation: effects on tree chemistry and insect performance^127^4^4^419-430^^^^^Apr^^^^^6964
1085^2534^2562^3162^3163^417^57^690^702^703^ L CO2 L-1. This was reduced to 6.3% at 350 mu L CO2 L-1 but then increased again to 7.0% at 900 mu L CO2 L-1. These changes in concentration of polymeric protein were correlated (r(2)=0.58) with changes in mixing properties, The mixing time required to produce optimum dough strength was greatest at 900 mu L CO2 L-1 (181 s), then 141 s and 151 s at 350 mu L CO2 L-1 and 280 mu L CO2 L-1 respectively. These changes in mixing time could not be explained by changes in grain protein concentration. The proportion of 'B' starch granules (<10 mu m diameter) increased from 25% of total weight of starch at 280 mu L CO2 L-1 to 30% at CO2 concentrations 350 and 900 mu L L-1. There were generally no A^6963^We examined the effects of CO2 and defoliation on tree chemistry and performance of the forest tent caterpillar, Malacosoma disstria. Quaking aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees were grown in open-top chambers under ambient or elevated concentrations of CO2. During the second year of growth, half of the trees were exposed to free-feeding forest tent caterpillars, while the remaining trees served as nondefoliated controls. Foliage was collected weekly for phytochemical analysis. Insect performance was evaluated on foliage from each of the treatments. At the sampling date coincident with insect bioassays, levels of foliar nitrogen and starch were lower and higher, respectively, in high CO2 foliage, and this trend persisted throughout the study. CO2-mediated increases in secondary compounds were observed for condensed tannins in aspen and gallotannins in maple. Defoliation reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. Similarly, defoliation induced accumulations of secondary compounds in aspen but not in maple. Larvae fed foliage from the enriched CO2 or defoliated treatments exhibited reduced growth and food processing efficiencies, relative to larvae on ambient CO2 or nondefoliated diets, but the patterns were host species-specific. Overall, CO2 and defoliation appeared to exert independent effects on foliar chemistry and forest tent caterpillar performance.

2102^2^Schier,GA^McQuattie,CJ^1998^1^Effects of carbon dioxide enrichment on response of mycorrhizal pitch pine (Pinus rigida) to aluminum: growth and mineral nutrition^252^12^6^340-346^^^^^May^^^^^6966
1096^1967^1983^224^3164^372^419^456^680^791^r and higher, respectively, in high CO2 foliage, and this trend persisted throughout the study. CO2-mediated increases in secondary compounds were observed for condensed tannins in aspen and gallotannins in maple. Defoliation reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. SimilA^6965^Carbon dioxide enrichment may increase the Al tolerance of trees by increasing root growth, root exudation and/or mycorrhizal colonization. The effect of elevated CO2 on the response of mycorrhizal pitch pine (Pinus rigida Mill.) seedlings to Al was determined in two experiments with different levels of nutrients, 0.1- or 0.2-strength Clark solution. During each experiment, seedlings inoculated with the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch were grown 13 weeks in sand irrigated with nutrient solution (pH 3.8) containing 0, 6.25, 12.5, or 25 mg/l Al (0, 232, 463, or 927 mu M Al) in growth chambers fumigated with 350 (ambient) or 700 (elevated) mu l/l CO2. At ambient CO2 in the absence of Al, mean total dry weights (DW) of seedlings at the high nutrient level were 164% higher than those at the low level. Total DW at elevated CO2, in the absence of Al, was significantly greater than that in ambient CO2 at the low (+34%) and high (+16%) nutrient levels. Root and shoot DW at both nutrient levels decreased with increasing Al concentrations with Al reducing root growth more than shoot growth. Although visible symptoms of Al toxicity in roots and needles were reduced by CO2 enrichment, there were no significant CO2 x Al interactions for shoot or root DW. The percentage of seedling roots that became mycorrhizal was negatively related to nutrient level and was greater at elevated than at ambient CO2 levels. Generally, elevated CO2 had little effect on concentration of mineral nutrients in roots and needles. Aluminum reduced concentrations of most nutrients by inhibiting uptake.

2103^4^Sehmer,L^Fontaine,V^Antoni,F^Dizengremel,P^1998^1^Effects of ozone and elevated atmospheric carbon dioxide on carbohydrate metabolism of spruce needles. Catabolic and detoxification pathways^37^102^4^605-611^^^^^Apr^^^^^6968
1064^1676^174^1865^2083^2369^367^417^425^446^nce of Al, was significantly greater than that in ambient CO2 at the low (+34%) and high (+16%) nutrient levels. Root and shoot DW at boA^6967^We have studied the effects of ozone, carbon dioxide and ozone combined with carbon dioxide fumigations on catabolic and detoxification pathways in spruce (Picea abies [L.] Karst.) needles. The results obtained showed an increase in the activities of three enzymes involved in the detoxification pathway, superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (AscPOD, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) when trees were exposed to ozone and to ozone- carbon dioxide treatments. In these two treatments, the fraction of SOD activity due to the chloroplastic isoform was increased (1.5-fold). In the needles of trees exposed to ozone and to ozone-carbon dioxide fumigation, an increase in the activities of glucose-6-phosphate dehydrogenase (G-6-PDH, EC 1.1.1.49) showed that the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 4.2.1.2], phosphofructokinase [PFK, EC 7.1.1] and phosphoenolpyruvate carboxylase [PEPC, EC 4.1.1.31]), was also observed making it possible for the cell to provide the reducing power necessary for detoxification as well as energy and carbon skeletons involved in the repair processes. When carbon dioxide alone was applied, no effects could be detected on these enzyme activities. However, when carbon dioxide was combined with ozone, the effect of ozone on trees was less than that induced by ozone alone, suggesting that elevated atmospheric carbon dioxide concentrations may to some extent protect plants from ozone injury.

2104^3^Seneweera,SP^Ghannoum,O^Conroy,J^1998^1^High vapour pressure deficit and low soil water availability enhance shoot growth responses of a C-4 grass (Panicum coloratum cv. Bambatsi) to CO2 enrichment^92^25^3^287-292^^^^^^^^^^6970
372^923^at the cell had the capacity to produce more NADPH necessary for the detoxification. Stimulation of other enzymes of catabolic pathways (fumarase [EC 4.2.1.2], phosphofructokinase [PFK, EC 7.1.1] and phosphoenolpyruvA^6969^The hypothesis that shoot growth responses of C-4 grasses to elevated CO2 are dependent on shoot water relations was tested using a C-4 grass, Panicum coloratum (NAD-ME subtype). Plants were grown for 35 days at CO2 concentrations of 350 or 1000 mu L CO2 L-1. Shoot water relations were altered by growing plants in soil which was brought daily to 65, 80 or 100% field capacity (FC) and by maintaining the vapour pressure deficit (VPD) at 0.9 or 2.1 kPa. At 350 mu L CO2 L-1, high VPD and lower soil water content depressed shoot dry mass, which declined in parallel at each VPD with decreasing soil water content. The growth depression at high VPD was associated with increased shoot transpiration, whereas at low soil water, leaf water potential was reduced. Elevated CO2 ameliorated the impact of both stresses by decreasing transpiration rates and raising leaf water potential. Consequently, high CO2 approximately doubled shoot mass and leaf length at a VPD of 2.1 kPa and soil water contents of 65 and 80% FC but had no effect on unstressed plants. Water use efficiency was enhanced by elevated CO2 under conditions of stress but this was primarily due to increases in shoot mass. High CO2 had a greater effect on leaf growth parameters than on stem mass. Elevated CO2 increased specific leaf area and leaf area ratio, the latter at high VPD only. We conclude that high CO2 increases shoot growth of C-4 grasses by ameliorating the effects of stress induced by either high VPD or low soil moisture. Since these factors limit growth of field-grown C-4 grasses, it is likely that their biomass will be enhanced by rising atmospheric CO2 concentrations.

2105^3^Sims,DA^Seemann,JR^Luo,Y^1998^1^The significance of differences in the mechanisms of photosynthetic acclimation to light, nitrogen and CO2 for return on investment in leaves^43^12^2^185-194^^^^^Apr^^^^^6972
1914^3165^3166^3167^372^376^526^665^699^92^y, high CO2 approximately doubled shoot mass and leaf length at a VPD of 2.1 kPa and soil water contents of 65 and 80% FC bA^6971^1. We report changes in photosynthetic capacity of leaves developed in varying photon flux density (PFD), nitrogen supply and CO2 concentration. We determined the relative effect of these environmental factors on photosynthetic capacity per unit leaf volume as well as the volume of tissue per unit leaf area. We calculated resource-use efficiencies from the photosynthetic capacities and measurements of leaf dry mass, carbohydrates and nitrogen content. 2. There were clear differences between the mechanisms of photosynthetic acclimation to PFD, nitrogen supply and CO2. PFD primarily affected volume of tissue per unit area whereas nitrogen supply primarily affected photosynthetic capacity per unit volume. CO2 concentration affected both of these parameters and interacted strongly with the PFD and nitrogen treatments. 3. Photosynthetic capacity per unit carbon invested in leaves increased in the low PFD, high nitrogen and low CO2 treatments. Photosynthetic capacity per unit nitrogen was significantly affected only by nitrogen supply. 4. The responses to low PFD and low nitrogen appear to function to increase the efficiency of utilization of the limiting resource. However, the responses to elevated CO2 in the high PFD and high nitrogen treatments suggest that high CO2 can result in a situation where growth is not limited by either carbon or nitrogen supply. Limitation of growth at elevated CO2 appears to result from internal plant factors that limit utilization of carbohydrates at sinks and/or transport of carbohydrates to sinks.

2106^4^Torbert,HA^Prior,SA^Rogers,HH^Runion,GB^1998^1^Crop residue decomposition as affected by growth under elevated atmospheric CO2^115^163^5^412-419^^^^^May^^^^^6974
2087^312^376^408^57^centration affected both of these parameters and interacted strongly with the PFD and nitrogen treatments. 3. Photosynthetic capacity per unit carbon invested in leaves increased in the low PFD, high nitrogen and low CO2 treatments. Photosynthetic capacity per unit nitrogen was significantly affeA^6973^Increasing atmospheric CO2 level has led to concerns about process changes in the biosphere. Elevated atmospheric CO2 concentration has been Shown to increase plant biomass, resulting in greater amounts of residue returned to soil. However, the effects on long-term storage of C in soil are highly debated. Changes in both quantity and quality of plant residue, as well as residue management, may alter soil C and N dynamics that will, in turn, affect the ability of soil to store C. Plant residues were collected from an experiment using open top chambers to increase CO2 levels under field conditions. A soil incubation study was conducted with a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults) to examine the effect of residue additions to two crop species (soybean, Glycine max (L.) Merr. and grain sorghum, Sorghum bicolor (L.) Moench), grown at two CO2 concentrations (ambient and twice ambient), and two incorporation treatments (incorporated or surface placement) on potential C and N mineralization. The difference in biomass inputs between plants grown in ambient and elevated atmospheric CO2 was also considered. Simulated residue incorporation reduced inorganic N concentration but had no effect on C mineralization. Both inorganic N content and C mineralization were higher with soybean than with grain sorghum. Although changes to both plant residue quality and quantity caused by elevated CO2 concentration affected C cycling in soil, residue quality may be more important for determining C storage. Nitrogen cycling in soil may be a controlling factor for C storage in terrestrial ecosystems.

2107^3^Warwick,KR^Taylor,G^Blum,H^1998^1^Biomass and compositional changes occur in chalk grassland turves exposed to elevated CO2 for two seasons in FACE^127^4^4^375-385^^^^^Apr^^^^^6976
2070^230^312^3168^344^374^376^384^673^977^m bicolor (L.) Moench), grown at two CO2 concentrations (ambient and twice ambient), and two incorporation treatments (incorporated or surface placement) on potential C and N mA^6975^Artificial turves composed of 7 chalk grassland species (Festuca ovina L; Briza media L.; Bromopsis erecta (Hudson) Fourr.; Plantago media L; Sanguisorba minor Scop.; Anthyllis vulneraria L. and Lotus corniculatus L.) were grown from seed and exposed to two seasons of elevated (600 mu mol mol(-1)) and ambient (340 mu mol mol(-1)) CO2 concentrations in free air CO2 enrichment (ETH-FACE, Zurich). The turves were clipped regularly to a height of 5 cm and assessed for above ground biomass production and relative abundance based on accumulated clipped dry biomass as well as by point quadrat recording. Below ground biomass production was assessed with root in- growth bags during the second season of growth. Increases in total biomass (> 30%) were noted in elevated CO2, but the differences did not become significant until the second season of growth. Individual species' biomass varied in response to elevated CO2, with significant increases in biomass in elevated CO2 turves for both legume species, and no significant CO2 effect on S. minor or P. media. An initial positive CO2 effect on biomass of combined grass species was reversed by the end of the experiment with less biomass and a significantly smaller proportion of total biomass present in elevated CO2, which was attributed primarily to changes in proportion of F. ovina. Species relative abundance was significantly affected by elevated CO2 in the final 4 of the 6 clip events, with the legume species increasing in proportion at the expense of the other species, particularly the grasses. Root length and dry weight were both significantly increased in elevated CO2 (77% and 89%, respectively), and these increases were greater than increases in shoot biomass (36%) from the same period. Species responses to elevated CO2, within the model community, were not consistent with predictions made from data on individual species, leading to the conclusion that responses to elevated CO2, at the community level, and species within the community level, are the result of direct physiological effects and indirect competitive effects. These conclusions are discussed with respect to the ecological responses of natural communities, and the chalk grassland community in particular, to elevated CO2.

2108^3^Wayne,PM^Reekie,EG^Bazzaz,FA^1998^1^Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modeling climate-induced geographic range shifts^2^114^3^335-342^^^^^Apr^^^^^6978
2017^230^310^312^344^361^402^605^669^867^ expense of the other species, particularly the grasses. Root length and dry weight were both significantly increased in elevated CO2 (77% and 89%, respectively), and these increases were greater than increases in shoot biomass (36%) from the same period. Species responses to elevated CO2, within the model community, were not consistent with predictions made from data on individual species, leading to the conclusion that responses to elevated CO2, at the community level, and species within the community level, are the result of direA^6977^Despite predictions that both atmospheric CO2 concentrations and air temperature will rise together, very limited data are currently available to assess the possible interactive effects of these two global change factors on temperate forest tree species. Using yellow birch (Betula alleghaniensis) as a model species, we studied how elevated CO2 (800 vs. 400 mu l l(-1)) influences seedling growth and physiological responses to a 5 degrees C increase in summer air temperatures (31/26 vs. 26/21 degrees C day/night), and how both elevated CO2 and air temperature during the growing season influence seedling ability to survive freezing stress during the winter dormant season. Our results show that while increased temperature decreases seedling growth, temperature-induced growth reductions are significantly lower at elevated CO2 concentrations (43% vs. 73%). The amelioration of high- temperature stress was related to CO2-induced reductions in both whole-shoot dark respiration and transpiration. Our results also show that increased summer air temperature, and to a lesser degree CO2 concentration, make dormant winter buds less susceptible to freezing stress. We show the relevance of these results to models used to predict how climate change will influence future forest species distribution and productivity, without considering the direct or interactive effects of CO2.

2109^3^Barrett,DJ^Richardson,AE^Gifford,RM^1998^1^Elevated atmospheric CO2 concentrations increase wheat root phosphatase activity when growth is limited by phosphorus^92^25^1^87-93^^^^^^^^^^6980
243^312^3169^3170^360^376^407^438^738^867^e seedling ability to survive freezing stress during the winter dormant season. Our results show that while increased temperature decreases seedling growth, temperature-induced growth reductions are significantly lower at elevated CO2 concentrations (43% vs. 73%). The amelioration of high- temperature stress was related to CO2-induced reductions in both whole-shoot dark respiration and transpiration. Our results alA^6979^Wheat seedlings were grown in solution culture under adequate and limited phosphorus treatments at current ambient and elevated (approximately 2X ambient) CO2 concentrations. Acid phosphomonoesterase ('phosphatase') activity of root segments was measured using p-nitrophenyl phosphate as substrate. When plant growth was P-limited, elevated CO2 concentrations increased phosphatase activity more than at ambient CO2. This result (1) was evident when expressed on a unit root dry weight or root length basis, indicating that increased root enzyme activity was unlikely to be associated with CO2-induced changes in root morphology; (2) occurred when plants were grown aseptically, indicating that the increase in phosphatase activity originated from root cells rather than root-associated microorganisms; (3) was associated with shoot P concentrations below 0.18%; (4) occurred only when wheat roots were grown under P deficiency but not when a transient P deficiency was imposed; and (5) suggest that a previously reported increase in phosphatase activity at elevated CO2 by an Australian native pasture grass (Gifford, Lutze and Barrett 1996; Plant and Soil 187, 369-387) was also a root mediated response. The observed increase in phosphatase activity by plant roots at elevated CO2, if confirmed for a wide range of field pasture and crop species, is one factor which may increase mineralisation of soil organic P as the anthropogenic increase of atmospheric CO2 concentrations continues. But, whether a concomitant increase in plant uptake of P occurs will depend on the relative influence of root and microbial phosphatases, and soil geochemistry in determining the rate of mineralisation of soil organic P for any given soil.

2110^3^Bartak,M^Nijs,I^Impens,I^1998^1^The susceptibility of PS II of Lolium perenne to a sudden fall in air temperature - response of plants grown in elevated CO2 and/or increased air temperature^173^39^1^85-95^^^^^Feb^^^^^6982
1092^1240^243^312^3171^3172^348^493^633^713^(5) suggest that a previously repA^6981^The effect of a sudden fall in air temperature from 20 to 5 degrees C on fast kinetics of chlorophyll fluorescence, maximum yield of the photosystem II photochemical reactions (Fv/Fm), quantum yield of the photosystem II electron transport (Phi(II)) coefficients of photochemical (qP), non-photochemical quenching (qN) was studied in Lolium perenne using a modulated chlorophyll fluorescence technique. Before fluorescence measurement, the plants were cultivated in the treatments simulating the likely future climate characterized with elevated air temperature and CO2 concentration and combination of both. On fast kinetics curves the risetimes of the I and D points characterizing the redox state of Q(A) were affected by lowering the air temperature. At 5 degrees C both the I and D points were reached later than at 20 degrees C. Also the I to D risetime was prolonged at 5 degrees C and it was found significantly longer in plants cultivated in ambient + 4 degrees C temperature. While a significant difference was found in the area over the rising part of the fluorescence curve between 20 and 5 degrees C, no difference was found in area over the relaxation curve part. Lowering of air temperature to 5 degrees C had no effect on Fv/Fm values in control plants and in the plants cultivated in elevated CO2 but brought significant decrease in plants cultivated in the ambient + 4 degrees C air temperature. Both Phi(II) and qP decreased with the temperature lowered to 5 degrees C while the values of qN increased. The changes in fluorescence parameters indicated altered functioning of PS II at low temperature. The changes in parameters are discussed as a consequense of decreased enzymatic activity, decreased turnover of plastoquinone pool and photoinhibition. (C) 1998 Elsevier Science B.V. All rights reserved.

2111^1^Beerling,DJ^1997^1^Carbon isotope discrimination and stomatal responses of mature Pinus sylvestris L trees exposed in situ for three years to elevated CO2 and temperature^318^18^6^697-712^^^^^^^^^^6984rence1208^1628^2911^3120^3173^376^3874^399^605^665^the fluorescence curve between 20 and 5 degrees C, no difference was found in area over the relaxation curve part. Lowering of air temperature to 5 degrees C had no effect on Fv/Fm values in control plants and in the plants cultivated in elevated CO2 but brought significant decrease in plants cultivated in the ambient + 4 degrees C air temperature. Both Phi(II) and qP decreased with the temperature lowered to 5 degrees C while the values of qN increased. The changes in fluorescence parameters indicated altered functioning of PS II at low temperature. The changes in parameters are discussed as a consequense of decreased enzymatic activity, decreased turnover of plastoquinone pool and photoinhibition. (C) 1998 Elsevier Science B.V. All rights reserved.

2111^1^Beerling,DJ^1997^1^Carbon isotope discrimination and stomatal responses of mature Pinus sylvestris L trees exposed in situ for three years to elevated CO2 and temperature^318^18^6^697-712^^^^^^^^^^6984renceA^6983^The Climate Change Experiment (CLIMEX) is a unique large scale facility in which an entire undisturbed catchment of boreal vegetation has been exposed to elevated CO2 (560 ppm) and temperature (+3 degrees C summer, +5 degrees C winter) for the past three years with all the soil-plant-atmosphere linkages intact. Here, carbon isotope composition end stomatal density have been analysed from sequential year classes of needles of mature Scots pine trees (Pinus sylvestris L.) to investigate the response of time-integrated water-use efficiency (WUE) and stomatal density to CO2 enrichment and climate change. Cal bon isotope discrimination decreased and WUE increased in cohorts of needles developing under increased CO2 and temperature, compared to needles on the same trees developing in pretreatment years. Mid-season instantaneous gas exchange, measured on the same trees for the past four pears, indicated that these responses resulted from higher needle photosynthetic rates and reduced stomatal conductance. Needles of P. sylvestris developing under increased CO2 and temperature had consistently lower stomatal densities than their ambient grown counterparts on the same trees. The stomatal density of P. sylvestris needles was inversely correlated with delta(13)C- derived WUE, implying some effect of this morphological response on leaf gas exchange. Future atmospheric CO2 and temperature increases are therefore likely to improve the water economy of P. sylvestris, at least at the scale of individual needles, by affecting stomatal density and gas exchange processes.

2112^3^Borkhsenious,ON^Mason,CB^Moroney,JV^1998^1^The intracellular localization of ribulose-1,5-bisphosphate carboxylase/oxygenase in Chlamydomonas reinhardtii^8^116^4^1585-1591^^^^^Apr^^^^^6986
1247^1552^243^502^553^veloping in pretreatment years. Mid-season instantaneous gas exchange, measured on the same trees for the past four pears, indicated that these responses resulted from higher needle photosynthetic rates and reduced stomatal conductance. NeA^6985^The pyrenoid is a proteinaceous structure round in the chloroplast of most unicellular algae. Various studies indicate that ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is present in the pyrenoid, although the fraction of Rubisco localized there remains controversial. Estimates of the amount of Rubisco in the pyrenoid of Chlamydomonas reinhardtii range from 5% to nearly 100%. Using immunolocalization, the amount of Rubisco localized to the pyrenoid or to the chloroplast stroma was estimated for C. reinhardtii cells grown under different conditions. It was observed that the amount of Rubisco in the pyrenoid varied with growth condition; about 40% was in the pyrenoid when the cells were grown under elevated CO2 and about 90% with ambient CO2. In addition, it is likely that pyrenoidal Rubisco is active in CO2 fixation because in vitro activity measurements showed that most of the Rubisco must be active to account for CO2-fixation rates observed in whole cells. These results are consistent with the idea that the pyrenoid is the site of CO2 fixation in C. reinhardtii and other unicellular algae containing CO2-concentrating mechanisms.

2113^1^Bunce,JA^1998^1^Effects of environment during growth on the sensitivity of leaf conductance to changes in humidity^127^4^3^269-274^^^^^Mar^^^^^6988
174^243^245^312^314^374^674^ pyrenoid of Chlamydomonas reinhardtii range from 5% to nearly 100%. Using immunolocalization, the amount of Rubisco localized to the pyrenoid or to the chloroplast stroma was estimated for C. reinhardtii cells grown under different conditions. It was observed that the amount of Rubisco in the pyrenoid varied with growth condition; about 40% was in the pyrenoid when the cells were grown under elevated CO2 and about 90% with ambient CO2. In addition, it is likely that pyrenoidal Rubisco is active in CO2 fixation because in vitro activity measurements showed that most of the Rubisco must be active to account for CO2-fixation rates observed in whole cells. These results are consistent wiA^6987^Soybeans (Glycine max) and grain amaranth (Amaranthus hypochondriacus) were grown at a range of temperatures, carbon dioxide concentrations and light conditions in controlled environment chambers, and the response of leaf conductance to water vapour to changes in humidity was then measured under a standard set of conditions. The sensitivity of conductance was analysed in terms of (i) the absolute sensitivity of conductance to changes in leaf to air water vapour pressure difference (LAVPD), (ii) the sensitivity of conductance relative to the absolute value of conductance, and (iii) the slope of the relationship between conductance and an index incorporating assimilation rate, carbon dioxide concentration and relative humidity. The sensitivity of conductance varied substantially with growth conditions for all three analyses in both species. The growth temperature of 25 degrees C increased the sensitivity of conductance by all three measures compared with growth at 20 or 30 degrees C in amaranth, with little difference between 25 and 30 degrees C in soybean. Growth at elevated carbon dioxide decreased sensitivity in amaranth by all three measures, and decreased the absolute but not the relative sensitivity in soybean. Growth at reduced photon flux density and growth at high stand density reduced sensitivity in amaranth by all three measures. In soybean, growth at high stand density reduced sensitivity by all three measures, but growth at low photon flux density increased the relative sensitivity. The sensitivity of leaf conductance to changes in humidity varied by a factor of two or more with growth environment by all measures of sensitivity in both the C3 and the C4 species.

2114^3^Crookshanks,M^Taylor,G^Dolan,L^1998^1^A model system to study the effects of elevated CO2 on the developmental physiology of roots: the use of Arabidopsis thaliana^78^49^320^593-597^^^^^Mar^^^^^6990
1155^1361^3174^374^376^92^ty of conductance by all three measures compared with growth at 20 or 30 degrees C in amaranth, with liA^6989^Three developmental changes were observed in the roots of Arabidopsis thaliana (Columbia) when shoots were exposed to elevated CO2, (i) The allometric coefficient, k, was enhanced significantly (P<0.001), (ii) primary root length and root extension rate were enhanced (P<0.001), Accelerated cortical cell expansion contributed to this effect and was associated with increased cell wall extensibility, measured as % plasticity. (iii) Lateral root formation and extension were also increased in elevated CO2 (P<0.05). These results illustrate that root growth and structure was altered following exposure to elevated CO2, The changes observed suggest that Arabidopsis provides a useful model which should, in future, be amenable to study using appropriate mutants allowing the genetic basis of the responses to be identified.
e of Arabidopsis thaliana^78^49^320^593-597^^^^^Mar^^^^^6990
1155^1361^3174^374^376^92^ty of conductance by all three measures compared with growth at 20 or 30 degrees C in amaranth, with li2115^4^Devakumar,AS^Shayee,MSS^Udayakumar,M^Prasad,TG^1998^1^Effect of elevated CO2 concentration on seedling growth rate and photosynthesis in Hevea brasiliensis^246^23^1^33-36^^^^^Mar^^^^^6992
130^264^312^344^360^376^434^
A^6991^To study the effect of elevated CO2 concentration on plant growth and photosynthesis, two clones of Hevea brasiliensis were grown in polybags and exposed to elevated concentration (700+/-25 ppm) for 60 days. There was higher biomass accumulation, leaf area and better growth when compared to ambient air grown plants. From A/Ci curves it is clear that photosynthetic rates increases with increase in CO2 concentrations. After 60 days of exposure to higher CO2 concentration, a decrease in the carbon assimilation rate was noticed.

2116^2^Hikosaka,K^Hirose,T^1998^1^Leaf and canopy photosynthesis of C-3 plants at elevated CO2 in relation to optimal partitioning of nitrogen among photosynthetic components: theoretical prediction^81^106^2-3^247-259^^^^^1 Mar^^^^^6994 C in amaranth, with li130^314^3175^344^348^360^423^467^639^666^M^Prasad,TG^1998^1^Effect of elevated CO2 concentration on seedling growth rate and photosynthesis in Hevea brasiliensis^246^23^1^33-36^^^^^Mar^^^^^6992
130^264^312^344^360^376^434^
A^6991^To study the effect of elevated CO2 concentration on plant growth and photosynthesis, two clones of Hevea brasiliensis were grown in polybags and exposed to elevated concentration (700+/-25 ppm) for 60 days. There was higher biomass accumulation, leaf area and better growth when compared to ambient air grown plants. From A/Ci curves it is clear that photosynthetic rates increases with increase in CO2 concentrations. After 60 days of exposure to higher CO2 concentration, a decrease in the carbon assimilation rate was noticed.

2116^2^Hikosaka,K^Hirose,T^1998^1^Leaf and canopy photosynthesis of C-3 plants at elevated CO2 in relation to optimal partitioning of nitrogen among photosynthetic components: theoretical prediction^81^106^2-3^247-259^^^^^1 Mar^^^^^6994 C in amaranth, with liA^6993^Effects of changes in the organization of photosynthetic components on leaf photosynthesis under contrasting atmospheric CO2 conditions (35 and 70 Pa) are evaluated using an optimization model, in which the photosynthetic rate is limited either by the capacity of ribulose bisphosphate carboxylase (RuBPCase) to consume ribulose bisphosphate (RuBP) or by the capacity of RuBP regeneration. The nitrogen cost of photosynthetic components to carry out each process is calculated for the optimal partitioning of nitrogen among the components. The model predicts that nitrogen allocation to the components carrying out RuBP regeneration should be increased with reduction in allocation to RuBPCase to maximize daily photosynthesis at 70 Pa CO2. Al a temperature of 25 degrees C, doubling the current CO2 level increases daily photosynthesis by 60% with optimal reallocation of the nitrogen partitioning while the increase without reallocation of nitrogen is 40%. However, at lower growth irradiance, the advantage in daily photosynthesis due to the reallocation decreases with increasing nitrogen content. The ratio of photosynthesis at 70 Pa to that at 35 Pa increases with increasing temperature. The effects of CO2 levels on photosynthesis of a canopy in which nitrogen is optimally allocated among leaf layers are also examined. At 25 degrees C, canopy photosynthesis at the doubled CO2 level is predicted to increase 60 and 40% with and without the optimization of nitrogen partitioning among photosynthetic components, respectively. Doubling the CO2 level does not affect the optimal nitrogen distribution among leaf layers in the canopy irrespective of optimization of nitrogen partitioning among photosynthetic components. (C) 1998 Elsevier Science B.V. All rights reserved.

2117^5^Huxman,TE^Hamerlynck,EP^Jordan,DN^Salsman,KJ^Smith,SD^1998^1^The effects of parental CO2 environment on seed quality and subsequent seedling performance in Bromus rubens^2^114^2^202-208^^^^^Apr^^^^^6996
1030^2484^372^374^376^417^423^92^dvantage in daiA^6995^Seeds were collected and compared from parent plants of Bromus rubens L. (Poaceae), an exotic Mojave Desert annual grass, grown in ambient (360 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) CO2 to determine if parental CO2 growth conditions affected seed quality. Performance of seeds developed on the above plants was evaluated to determine the influence of parental CO2 growth conditions on germination, growth rate, and leaf production, Seeds of B. rubens developed oil parents grown in elevated CO2 had a larger pericarp surface area, higher C:N ratio, and less total mass than ambient-developed seeds, Parental CO2 environment did not have an effect on germination percentage or mean germination timer as determined by radicle emergence. Seedlings from elevated-CO2-developed seeds had a reduced relative growth rate and achieved smaller final mass over the same growth period. Elevated-CO2-developed seeds had smaller seed reset-yes than ambient seeds, as determined by growing seedlings in sterile media and monitoring senescence. It appears that increased seed C:N ratios associated with plants grown under elevated CO2 may have a major effect on seed quality (morphology, nutrition) and seedling performance (e.g., growth rate and leaf production). Since the invasive success of B. rubens is primarily due to its ability to rapidly germinate, increase leaf area and maintain a relatively high growth rate compared to native annuals and perennial grasses, reductions in seed duality and seedling performance in elevated CO2 may have significant impacts on future community composition in the Mojave Desert.

2118^7^Johnson,DW^Thomas,RB^Griffin,KL^Tissue,DT^Ball,JT^Strain,BR^Walker,RF^1998^1^Effects of carbon dioxide and nitrogen on growth and nitrogen uptake in ponderosa and loblolly pine^204^27^2^414-425^^^^^Mar-Apr^^^^^6998
1044^1747^1967^2087^3003^372^374^456^669^672^e same growth period. Elevated-CO2-developed seeds had smaller seed reset-yes than ambient seeds, as determined by growing seedlings in sterile media aA^6997^The purpose of this paper is to summarize the results of a series of greenhouse and open-top chamber studies on the effects of N and elevated atmospheric CO2 on ponderosa and loblolly pine (Pinus ponderosa Laws, and P. taeda L.) to evaluate common patterns of response. Growth response to elevated CO2 ranged from zero to more than 1000%, depending largely upon N status, In both species, growth response to CO2 was greater under moderate N deficiency than under extreme N deficiency or N sufficiency/excess. Elevated CO2 generally caused lowered tissue N concentrations in many (but not all) cases, which in turn resulted in smaller increases in N uptake than in biomass. Growth response to N ranged from -50 (in ponderosa pine) to more than 1000%, depending upon the N status of the control medium. Growth response to N was enhanced by elevated CO2 when N was in the extreme deficiency range but not when N was in the moderate deficiency range. In two separate studies, ponderosa pine responded negatively to high N inputs, and in each case this response was mitigated by elevated CO2. Collectively, these results show that (i) N deficiency is a continuum rather than a step function, (ii) responses to elevated CO2 vary across this continuum of N deficiency, and (iii) elevated CO2 greatly enhances growth response to N additions when N is initially in the extremely deficient range.

2119^15^Jones,TH^Thompson,LJ^Lawton,JH^Bezemer,TM^Bardgett,RD^Blackburn,TM^Bruce,KD^Cannon,PF^Hall,GS^Hartley,SE^Howson,G^Jones,CG^Kampichler,C^Kandeler,E^Ritchie,DA^1998^1^Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems^32^280^5362^441-443^^^^^17 Apr^^^^^7000
1262^1327^1334^1850^1983^3176^372^407^56^778^from -50 (in ponderosa pine) to more than 1000%, depending upon the N status of the control medium. Growth response to N was enhanced by elevated CO2 when N was in the extreme deficiency range but not when N was in the moderate deficiency range. In two separate studies, ponderosa pine responded negatively to high A^6999^In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.

2120^5^Kampichler,C^Kandeler,E^Bardgett,RD^Jones,TH^Thompson,LJ^1998^1^Impact of elevated atmospheric CO2 concentration on soil microbial biomass and activity in a complex, weedy field model ecosystem^127^4^3^335-346^^^^^Mar^^^^^7002derosa pine responded negatively to high 1298^2087^230^312^3177^374^376^545^56^855^tained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.

2120^5^Kampichler,C^Kandeler,E^Bardgett,RD^Jones,TH^Thompson,LJ^1998^1^Impact of elevated atmospheric CO2 concentration on soil microbial biomass and activity in a complex, weedy field model ecosystem^127^4^3^335-346^^^^^Mar^^^^^7002derosa pine responded negatively to high A^7001^Although soil organisms play an essential role in the cycling of elements in terrestrial ecosystems, little is known of the impact of increasing atmospheric CO2 concentrations on soil microbial processes. We determined microbial biomass and activity in the soil of multitrophic model ecosystems housed in the Ecotron (NERC Centre for Population Biology, Ascot, UK) under two atmospheric CO2 concentrations (ambient vs. ambient + 200 ppm). The model communities consist of four annual plant species which naturally co-occur in weedy fields and disturbed ground throughout southern England, together with their herbivores, parasitoids and soil biota. At the end of two experimental runs lasting 9 and 4.5 months, respectively, root dry weight and quality showed contradictory responses to elevated CO2 concentrations, probably as a consequence of the different time-periods (and hence number of plant generations) in the two experiments. Despite significant root responses no differences in microbial biomass could be detected. Effects of CO2 concentration on microbial activity were also negligible. Specific enzymes (protease and xylanase) showed a significant decrease in activity in one of the experimental runs. This could be related to the higher C:N ratio of root tissue. We compare the results with data from the literature and conclude that the response of complex communities cannot be predicted on the basis of oversimplified experimental set-ups.

2121^2^LeCain,DR^Morgan,JA^1998^1^Growth, gas exchange, leaf nitrogen and carbohydrate concentrations in NAD-ME and NADP-ME C-4 grasses grown in elevated CO2^37^102^2^297-306^^^^^Feb^^^^^7004
130^243^312^3178^3179^344^360^374^376^417^erimental runs lasting 9 and 4.5 months, respectively, root dry weight and quality showed contradictory responses to elevated CO2 concentrations, probably as a consequence of the different time-periods (and hence number of plant generations) in the two experiments. Despite significant root responses no differences in microbial biomass could be A^7003^Plants with the C-4 photosynthetic pathway have predominantly one of three decarboxylation enzymes in their bundle sheath cells. Within the grass family (Poaceae) bundle sheath leakiness to CO2 is purported to be lowest in the nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME, EC 1.1.1.40) group, highest in the NAD-ME (EC 1.1.1.39) group and intermediate in the phosphoenolpyruvate carboxykinase (PCK, EC 4.1.1.32) group. We investigated the hypothesis that growth and photosynthesis of NAD-ME C-4 grasses would respond more to elevated CO2 treatment than NADP-ME grasses. Plants were frown in 8-1 pots in growth chambers with ample water and fertilizer for 39 days at a continuous CO2 concentration of either 350 or 700 mu l 1(-1). NAD-ME species included Bouteloua gracilis Lag. ex Steud (Blue grama), Buchloe dactyloides (Nutt.) Engelm. (Buffalo grass) and Panicum virgatum L. (Switchgrass) and the NADP-ME species were Andropogon gerardii Vittman (Big bluestem), Schizachyrium scoparium (Michx.) Nash (Little bluestem), and Sorghastrum mutans (L.) Nash (Indian grass). Contrary to our hypothesis, growth of the NADP-ME grasses was generally greater under elevated CO2 (significant for A. gerardii and S. mutans), while none of the NAD-ME grasses had a significant growth response. Increased leaf total non- structural carbohydrate (TNC) was associated with greater growth responses of NADP-ME grasses. Decreased leaf nitrogen in NADP-ME species grown at elevated CO2 was found to be an artifact of TNC dilution. Assimilation (A) vs intercellular CO2 (C-i) curves revealed that leaf photosynthesis was not saturated at 350 mu l 1(-1) CO2, in any of these C-4 grasses. Assimilation of elevated CO2-grown A. gerardii was higher than in plants grown in ambient CO2. In contrast, B. gracilis grown in elevated CO2 displayed lower A, a trait more commonly reported in C-3 plants. Photosynthetic acclimation is B. gracilis was not related to leaf TNC or nitrogen concentrations, but A:C-i curves suggest a reduction in activity of both phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39). Some adaptation of stomatal functioning was also seen in B. gracilis and A. gerardii leaves grown in elevated CO2. Our study shows that C-4 grasses have the capacity for increased growth and photosynthesis under elevated CO2 even when water and nutrients are non-limiting. While it was the NADP-ME species which had significant responses in the present study, we have previously reported significant growth increases in elevated CO2 for B. gracilis.

2122^1^Morison,JIL^1998^1^Stomatal response to increased CO2 concentration^78^49^^443-452^^^^^Mar^^^^^7006
130^243^344^348^384^398^399^465^550^92^ plants grown in ambient CO2. In contrast, B. gracilis grown in elevated CO2 displayed lower A, a trait more commonly reported in C-3 plants. Photosynthetic acclimation is B. gracilis was not related to leaf TNC or nitrogen concentrations, but A:C-i curves suggest a reduction in activA^7005^The stomatal response to CO2 is important in understanding stomatal physiology, and important in understanding vegetation- atmosphere exchanges at all scales from the individual plant up to global vegetation. Despite the long history of experiments on stomatal responses to CO2 there are still considerable uncertainties in both these tasks. The difficulty in understanding differences in stomatal conductance between plants grown for any length of time in different CO2 atmospheres is stressed because of the many other possible changes in the plants' carbohydrate, nutrient and water relations. The other key issues that are highlighted are: whether stomata acclimate to CO2 either in parallel with any mesophyll photosynthetic acclimation or independently of changes in the mesophyll; whether stomata on different leaf surfaces respond to CO2 similarly; and whether reported changes in stomatal frequency are important to leaf gas exchange. The need for direct examination of stomatal sensitivity of plants grown in different CO2 concentrations is stressed.

2123^2^Porte,A^Loustau,D^1998^1^Variability of the photosynthetic characteristics of mature needles within the crown of a 25-year-old Pinus pinaster^13^18^4^223-232^^^^^Apr^^^^^7008
1265^256^312^3180^356^372^665^687^713^714^ponses to CO2 there are still considerable uncertainties in both these tasks. The difficulty in understanding differences in stomatal conductance between plants grown for any length of time in different CO2 atmospheres is stressed because of the many other possible changes in the plants' carbohydrate, nutrient and water relations. The other key issues that are highlighted are: whether stomata acclimate to CO2 either in parallel with any mesophyll photosynthetic acclimation or independently of changes in the mesophyll; whether stomata on different leaf surfaces respond to CO2 similarly; and whether reported changes in stomatal frequency are important to leaf gas exchange. The need for direct examination of stomatal sensitivity of plants grown A^7007^Photosynthetic characteristics of 1- and 2-year-old needles were determined in excised shoots of maritime pine (Pinus pinaster Ait.) with an open gas exchange system. We used the nonlinear least mean squares method to derive values for quantum yield of electron transport (alpha), maximum carboxylation velocity (V-cmax), and maximum electron transport rate (J(max)), from photosynthetic response curves to light and CO2. Crown height had no significant effect on any of the parameters; however, V-cmax and J(max), as well as a were 43, 26 and 35% higher, respectively, in 1-year-old needles than in 2-year-old needles. The main effect of irradiance on needles was a small decline in leaf concentrations of nitrogen and phosphorus from the top to the bottom of the canopy. Only J(max) demonstrated a linear relationship with both nitrogen content (R-2 = 0.42) and irradiance at the shoot level. Because needle age accounted for most of the variability in photosynthesis, we incorporated needle age into the photosynthesis model of Farquhar et al. (1980). The modified model underestimated the daily assimilation rate of 1-year-old needles in the field, especially when assimilation rates were high.

2124^5^Reddy,KR^Robana,RR^Hodges,HF^Liu,XJ^McKinion,JM^1998^1^Interactions of CO2 enrichment and temperature on cotton growth and leaf characteristics^173^39^2^117-129^^^^^Apr^^^^^7010
312^3181^344^348^372^374^417^745^757^784^to light and CO2. Crown height had no significant effect on any of the parameters; however, V-cmax and J(max), as well as a were 43, 26 and 35% higher, respectively, in 1-year-old needles than in 2-year-old needles. The main effect of irradiance on needles was a small decline in leaf concentrations of nitrogen and phosphorus from the top to the bottom of the canopy. Only J(max) demonstrated a linear relationship with both nitrogen content (R-2 = 0.42) and irradiance at the shoot level. Because needle age accounted for most of the variability in photosynthesis, we incorporated needle age into the photosyntA^7009^Studies on the interactive effects of atmospheric CO2 and temperature on growth and leaf morphology, particularly on stomatal index and density are limited. Upland cotton was grown in naturally-lit plant growth chambers al 30/22 degrees C day/night temperatures from planting until squaring or the fifth or sixth leaf emerged. Five growth chambers were maintained at ambient (350 mu l l(-1)) CO2 and another five at twice ambient (700 mu l l(-1)) CO2 throughout the experiment. Day/night temperature treatments of 20/12, 25/17, 30/22, 35/27 and 40/32 degrees C were imposed at each CO2 treatment for 42 days after squaring. The plants were irrigated with half- strength Hoagland's nutrient solution three times per day. Growth of plant parts was determined at the end of the experiment. Stomatal characteristics, nonstructural carbohydrates and specific leaf weight were measured on the fully expanded tenth mainstem leaf, Stomatal density and index were not affected by elevated CO2. Stomata and epidermal cell numbers pet leaf increased in high CO2 and were positively correlated with final leaf sizes irrespective of CO2 level. Our results suggest that plants do not acclimate to elevated CO2 by changing stomatal density within a single generation. Leaves had greater area and accumulated more biomass when grown in high CO2. Growth stimulation expressed as dry weight at 700 mu l l(-1) over dry weight al 350 mu l l(-1) CO2 was uniform across temperatures. Temperature optimum for vegetative and reproductive growth was 30/22 degrees C and was not altered by CO2 enrichment. Fruit retention was severely curtailed at the two higher temperatures compared to 30/22 degrees C in both CO2 environments. increased carbohydrate storage in leaves may be an added advantage for initiation and growth of vegetative structures such as branches at all temperatures. However, it is unlikely that high temperature effects on flower abortion will be ameliorated by high CO2. Species/cultivars that retain fruits at high temperatures would be more productive both in the present-day cotton producing environments and are even more desirable in the future warmer world. (C) 1998 Elsevier Science B.V. All rights reserved.

2125^4^Rillig,MC^Allen,MF^Klironomos,JN^Field,CB^1998^1^Arbuscular mycorrhizal percent root infection and infection intensity of Bromus hordeaceus grown in elevated atmospheric CO2^98^90^2^199-205^^^^^Mar-Apr^^^^^7012
1334^1983^243^374^376^417^427^442^cross temperatures. Temperature optimum for vegetative and reproductive growth was 30/22 degrees C and was not altered by CO2 enrichment. Fruit retention was severely curtailed at the two higher temperatures compared to 30/22 degrees C in both CO2 environments. increased carbohydrate storage in leaves may be an added advantage for initiation and growth of vegetative structures such as branches at all temperatures. However, it is unlikely that high temperature effects on flower abortion will be ameliorated by high CO2. Species/cultivars that retain fruits at high temperatures would be more pA^7011^Using Bromus hordeaceus, a grass from a Mediterranean annual grassland in California, we measured changes in infection intensity, rather than the more traditional % root infection, as an indicator of response to elevated atmospheric CO2 and soil nutrient enrichment. Intensity was measured as the number of intraradical hyphae intersecting a microscope cross-hair for specific root diameter size classes. We found an increase in intensity of infection when plants were exposed to elevated CO2, and we found a decrease in infection intensity when plants were fertilized. This finding is significant in that it provides evidence for an increase in carbon allocation to the mycobiont under elevated CO2 even in the absence of change in percent infection, or mycorrhizal root length. Previous studies may therefore have overlooked an important response of arbuscular mycorrhizal fungi to this treatment, leading to an underestimation of the importance of mycorrhizae under elevated CO2. Infection intensity may also change in response to many other treatments and environmental variables that the symbiosis is exposed to, high-lighting the potential usefulness of intensity as a response variable in mycorrhizal research.

2126^2^Roberntz,P^Stockfors,J^1998^1^Effects of elevated CO2 concentration and nutrition on net photosynthesis, stomatal conductance and needle respiration of field-grown Norway spruce trees^13^18^4^233-241^^^^^Apr^^^^^7014
3182^344^348^360^376^384^417^425^57^742^ts were exposed to elevated CO2, and we found a decrease in infection intensity when plants were fertilized. This finding is significant in that it provides evidence for an increase in carbon allocation to the mycobiont under elevated CO2 even in the absence of change in percent infection, or mycorrhizal root length. Previous studies may therefore have overlooked an important response of arbuscular mycorrhizal fungi to this treatment, leading to an underestimation of the importance of mycorrhizae under elevated CO2. Infection intensity may also chanA^7013^To study the effects of elevated CO2 on gas exchange, nonstructural carbohydrate and nutrient concentrations in current-year folia,ae of 30-year-old Norway spruce (Picea abies (L.) Karst.) trees, branches were enclosed in ventilated, transparent plastic bags and flushed with ambient air (mean 370 mu mol CO2 mol(-1); control) or ambient air + 340 mu mol CO2 mol(-1) (elevated CO2) during two growing seasons. One branch bag was installed on each of 24 selected trees From control and fertilized plots. To reduce the effect of variation among trees, results from each treated branch were compared with those from a control branch on the same whorl of the same tree. Elevated CO2 increased rates of light-saturated photosynthesis on average by 55% when measured at the treatment CO2 concentration. The increase was larger in shoots with high needle nitrogen concentrations than in shoots with low needle nitrogen concentrations. However, shoots grown in elevated CO2 showed a decrease in photosynthetic capacity compared with shoots grown in ambient CO2. When measured at the internal CO2 concentration of 200 mu mol CO2 mol(-1), photosynthetic rates of branches in the elevated CO2 treatments were reduced by 8 to 32%. The elevated CO2 treatment caused a 9 to 20% reduction in carboxylation efficiency and an 18% increase in respiration rates. In response to elevated CO2, starch, fructose and glucose concentrations in the needles increased on average 33%, whereas concentrations of potassium, nitrogen, phosphorus, magnesium and boron decreased. Needle nitrogen concentrations explained 50-60% of the variation in photosynthesis and CO2 acclimation was greater at low nitrogen concentrations than at high nitrogen concentrations. We conclude that the enhanced photosynthetic rates found in shoots exposed to elevated CO2 increased carbohydrate concentrations, which may have a negative feedback on the photosynthetic apparatus and stimulate cyanide-resistant respiration. We also infer that the decrease in nutrient concentrations of needles exposed to elevated CO2 was the result of retranslocation of nutrients to other parts of the branch or tree.

2127^3^Robinson,MF^Heath,J^Mansfield,TA^1998^1^Disturbances in stomatal behaviour caused by air pollutants^78^49^^461-469^^^^^Mar^^^^^7016
1224^1754^2185^2387^312^3183^3184^383^461^602^ease in respiration rates. In response to elevated CO2, starch, fructose and glucose concentrations in the needles increased on average 33%, whereas concentrations of potassium, nitrogen, phosphorus, magnesium and boron decreased. Needle nitrogen concentrations explained 50-60% of the variation in photosynthesis and CO2 acclimation was greater at low nitrogen concentrations than at high nitrogen concentrations. We conclude that the enhanced photosynthetic rates found in shoots exposed to elevated CO2 increased carbohydrate concentrations, which may have a negative feedback on the photosynthetic apparatus and stimulate cyanide-resistant respiration. We also infer that the decrease in nutrient concentrations of neeA^7015^Many atmospheric pollutants, even when present at relatively low concentrations, may interfere with the control of stomatal aperture, and they thus have the potential to upset the water balance of the leaf or the whole plant. Although at high concentrations pollutants such as SO2 and O-3 usually cause stomatal closure, at low concentrations stomatal conductance is often increased. As well as creating a risk of loss of control of water relations, this is likely to increase the dose of the pollutant entering the mesophyll. It is, however, difficult to generalize about the nature of the physiological disturbances caused by pollutants because of variation in the responses between plants. In some cases the effects may be peculiar to one, or just a few, species. Two mechanisms underlying the interference with stomatal control have recently been identified, one involving O-3 and the other CO2. In Aster tripolium (sea aster) stomata in detached epidermal strips close as the external Na+ concentration is increased, and it has been proposed that this phenomenon is involved in the regulation of salt loading of shoot tissues. Ozone has been shown to have the capacity to interfere with Na+-induced stomatal closure, and the possibility that it therefore disrupts an aspect of salinity tolerance in this species is worthy of further research. Elevated CO2, on the other hand, has been found to interfere with the control of water relations of beech (Fagus sylvatica): for a given degree of drought, stomatal conductance and rates of soil water depletion were significantly higher in elevated CO2 than in ambient air. It is normally assumed that atmospheric CO2-enrichment will lead to increased plant productivity and improved water economy, while also providing some protection against other atmospheric pollutants through partial stomatal closure. However, the response of beech indicates that in some species there may also be detrimental effects of CO2-enrichment on plant-water relations.
the external Na+ concentration is incre2128^3^Sims,DA^Seemann,JR^Luo,YQ^1998^1^Elevated CO2 concentration has independent effects on expansion rates and thickness of soybean leaves across light and nitrogen gradients^78^49^320^583-591^^^^^Mar^^^^^7018
1272^130^243^360^376^388^417^427^610^91^n aspect of salinity tolerance in this species is worthy of further research. Elevated CO2, on the other hand, has been found to interfere with the control of water relations of beech (Fagus sylvatica): for a given degree of drought, stomatal conductance and rates of soil water depletion were significantly higher in elevated CO2 than in ambient air. It is normally assumed that atmospheric CO2-enrichment will lead to increased plant productivity and improved water economy, while also providing some protection against other atmospheric pollutants through partial stomatal closure. However, the response of beech indicates that in some species there may also be detrimental effects of CO2-enrichment on plant-water relations.
the external Na+ concentration is increA^7017^The rate and extent of leaf thickness and development are important determinants of plant photosynthetic capacity, The interactive effects of photon flux density (PFD), nitrogen supply and CO2 concentration on leaf expansion rate were measured as well as final leaf size and thickness of soybean, Leaf thickness and final area were not correlated with leaf relative expansion rate (RER) suggesting that these parameters are controlled by different mechanisms and that final leaf dimensions are determined by the duration rather than the rate of leaf expansion, Carbohydrate supply did not explain the variation ii? leaf RER since RER increased with increasing CO2 concentration, but decreased with increasing PFD. Leaf thickness and final area were related to resource supply but not in a simple fashion, Both positive and negative correlations between leaf thickness and carbohydrate and nitrogen concentrations were obtained depending on the environmental variable responsible for the variation. In contrast, there was a simple proportional relationship between whole plant relative growth rate and a correlate of leaf thickness (leaf water content per unit area), suggesting that leaf thickness responds to the balanced supply of all resources, in the same fashion as RGR, rather than to any individual resource.

2129^2^Smith,PHD^Jones,TH^1998^1^Effects of elevated CO2 on the chrysanthemum leafminer, Chromatomyia syngenesiae: a greenhouse study^127^4^3^287-291^^^^^Mar^^^^^7020
1282^
A^7019^Although feeding behaviour of Chromatomyia syngenesiae on plants grown in elevated CO2 (ambient + 200ppm) was unaffected, leaf-miner development was slower in elevated compared to ambient CO2 atmospheres. Pupal weight was lower at high CO2 and correlated with the area of leaf mined; no such correlation existed in ambient CO2. There appears to be no compensatory feeding by the leaf-miner for the reduced food quality of plants growing in elevated CO2. The implications of these findings are discussed.
for the variation. In contrast, there2130^3^Uprety,DC^Dwivedi,N^Mohan,R^1998^1^Characterization of CO2 responsiveness in a Brassica oxycamp interspecific hybrid^161^180^1^7-13^^^^^Mar^^^^^7022
243^374^92^
A^7021^A study of the characterization of CO2 responsiveness in Brassica oxycamp and its parents Brassica oxyrrhina and Brassica campestris was done using open top chamber technology. The response of the X. B. oxycamp (hybrid) to elevated CO2 was significantly positive in respect of photosynthesis and growth and similar to that of its parent B. campestris is. X B. oxycamp and B. campestris with greater sink potential responded significantly, whereas B. oxyrrhina with a poor sink did not respond to CO2 enrichment. Photosynthetic changes at elevated CO2 levels in the hybrid and parents are partially attributed to the CO2 effects on stomatal conductance and chlorophyll fluorescence.
e leaf-miner for the reduced food quality of plants growing in elevated CO2. The implications of these findings are discussed.
for the variation. In contrast, there2131^4^Williams,M^Robertson,EJ^Leech,RM^Harwood,JL^1998^1^Lipid metabolism in leaves from young wheat (Triticum aestivum cv. Hereward) plants grown at two carbon dioxide levels^78^49^320^511-520^^^^^Mar^^^^^7024
130^1936^2619^2620^344^372^434^724^741^751^ parents Brassica oxyrrhina and Brassica campestris was done using open top chamber technology. The response of the X. B. oxycamp (hybrid) to elevated CO2 was significantly positive in respect of photosynthesis and growth and similar to that of its parent B. campestris is. X B. oxycamp and B. campestris with greater sink potential responded significantly, whereas B. oxyrrhina with a poor sink did not respond to CO2 enrichment. Photosynthetic changes at elevated CO2 levels in the hybrid and parents are partially attributed to the CO2 effects on stomatal conductance and chlorophyll fluorescence.
e leaf-miner for the reduced food quality of plants growing in elevated CO2. The implications of these findings are discussed.
for the variation. In contrast, thereA^7023^Lipid synthesis was studied in primary leaves from 7-d-old wheat plants which had been grown at either ambient CO2 concentration (350 mu mol mol(-1)) or elevated CO2 (650 mu mol mol(-1)) by incubating tissue samples with [1-C-14]acetate, Growth at different CO2 concentrations did not affect the total incorporation of radiolabel into lipids but it did influence the relative labelling of individual lipid classes, such as diacylglycerol. The leaf basal segment was also studied separately and growth in an enriched CO2 atmosphere was associated with a dramatic increase (over 6-fold) in diphosphatidylglycerol (cardiolipin) labelling, indicating an increased rate of mitochondrial membrane biogenesis, Immunocytological observations correlated with this metabolic result. Both leaf samples showed significant decreases in pigment and surface wax labelling caused by growth at elevated CO2. Growth at different CO2 concentrations also influenced fatty acid labelling patterns, particularly those of the major labelled membrane lipids of the primary leaf whereby there were changes in their ratios of radiolabelled 16 carbon to 18 carbon fatty acids. Phosphatidylglycerol was characterized, for instance, by increased palmitate labelling after wheat was grown in elevated CO2 concentrations, In contrast, phosphatidylcholine was marked by a dramatic decrease in palmitate labelling but a corresponding increase in labelling of its 18 carbon unsaturated fatty acids, The diacylglycerol fraction showed increased unsaturation of its C18 fatty acids. In addition, changes to the fatty acid moieties from the basal segment lipids were also associated with changes in the amount of labelling of the polyenoic fatty acids of monogalactosyldiacylglycerol. Possible reasons for these changes in lipid labelling are discussed. The data show that growth in elevated atmospheric CO2 concentrations causes significant changes in the metabolism of leaf lipids as well as increasing mitochondrial biogenesis.
rns, particularly those of the major labelle2132^3^Williams,RS^Lincoln,DE^Norby,RJ^1998^1^Leaf age effects of elevated CO2-grown white oak leaves on spring-feeding lepidopterans^127^4^3^235-246^^^^^Mar^^^^^7026
1080^2445^3185^3186^3187^341^483^764^774^92^abelling after wheat was grown in elevated CO2 concentrations, In contrast, phosphatidylcholine was marked by a dramatic decrease in palmitate labelling but a corresponding increase in labelling of its 18 carbon unsaturated fatty acids, The diacylglycerol fraction showed increased unsaturation of its C18 fatty acids. In addition, changes to the fatty acid moieties from the basal segment lipids were also associated with changes in the amount of labelling of the polyenoic fatty acids of monogalactosyldiacylglycerol. Possible reasons for these changes in lipid labelling are discussed. The data show that growth in elevated atmospheric CO2 concentrations causes significant changes in the metabolism of leaf lipids as well as increasing mitochondrial biogenesis.
rns, particularly those of the major labelleA^7025^Folivorous insect responses to elevated CO2-grown tree species may be complicated by phytochemical changes as leaves age. For example, young expanding leaves in tree species may be less affected by enriched CO2-alterations in leaf phytochemistry than older mature leaves due to shorter exposure times to elevated CO2 atmospheres. This, in turn, could result in different effects on early vs. late instar larvae of herbivorous insects. To address this, seedlings of white oak (Quercus alba L.), grown in open-top chambers under ambient and elevated CO2, were fed to two important early spring feeding herbivores; gypsy moth (Lymantria dispar L.), and forest tent caterpillar (Malacosoma disstria Hubner). Young, expanding leaves were presented to early instar larvae, and older fully expanded or mature leaves to late instar larvae. Young leaves had significantly lower leaf nitrogen content and significantly higher total nonstructural carbohydrate:nitrogen ratio as plant CO2 concentration rose, while nonstructural carbohydrates and total carbon-based phenolics were unaffected by plant CO2 treatment. These phytochemical changes contributed to a significant reduction in the growth rate of early instar gypsy moth larvae, while growth rates of forest tent caterpillar were unaffected. The differences in insect responses were attributed to an increase in the nitrogen utilization efficiency (NUE) of early instar forest tent caterpillar larvae feeding on elevated CO2-grown leaves, while early instar gypsy moth larval NUE remained unchanged among the treatments. Later instar larvae of both insect species experienced larger reductions in foliage quality on elevated CO2-grown leaves than earlier instars, as the carbohydrate:nitrogen ratio of leaves substantially increased. Despite this, neither insect species exhibited changes in growth or consumption rates between CO2 treatments in the later instar. An increase in NUE was apparently responsible for offsetting reduced foliar nitrogen for the late instar larvae of both species.
2133^1^Woodward,A^1998^1^Relationships among environmental variables and distribution of tree species at high elevation in the Olympic mountains^61^72^1^10-22^^^^^Feb^^^^^7028
17^227^3188^3189^937^th larvae, while growth rates of forest tent caterpillar were unaffected. The differences in insect responses were attributed to an increase in the nitrogen utilization efficiency (NUE) of early instar forest tent caterpillar larvae feeding on elevated CO2-grown leaves, while early instar gypsy moth larval NUE remained unchanged among the treatments. Later instar larvae of both insect species experienced larger reductions in foliage quality on elevated CO2-grown leaves than earlier instars, as the carbohydrate:nitrogen ratio of leaves substantially increased. Despite this, neither insect species exhibited changes in growth or consumption rates between CO2 treatments in the later instar. An increase in NUE was apparently responsible for offsetting reduced foliar nitrogen for the late instar larvae of both species.
A^7027^Relationships among environmental variables and occurrence of tree species were investigated at Hurricane Ridge in Olympic National Park, Washington, USA. A transect consisting of three plots was established down one north-and one south-facing slope in stands representing the typical elevational sequence of tree species. Tree species included subalpine fir (Abies lasiocarpa), Douglas-fir (Pseudotsuga menziesii), mountain hemlock (Tsuga mertensiana), and Pacific silver fir (Abies amabilis). Air and soil temperature, precipitation, and soil moisture were measured during three growing seasons. Snowmelt patterns, soil carbon and moisture release curves were also determined. The plots represented a wide range in soil water potential, a major determinant of tree species distribution (range of minimum values = -1.1 to -8.0 MPa for Pacific silver fir and Douglas-fir plots, respectively). Precipitation intercepted at plots depended on topographic location, storm direction and storm type. Differences in soil moisture among plots was related to soil properties, while annual differences at each plot were most often related to early season precipitation. Changes in climate due to a doubling of atmospheric CO2 will likely shift tree species distributions within, but not among aspects. Change will be buffered by innate tolerance of adult trees and the inertia of soil properties.

2134^5^Andalo,C^Raquin,C^Machon,N^Godelle,B^Mousseau,M^1998^1^Direct and maternal effects of elevated CO2 on early root growth of germinating Arabidopsis thaliana seedlings^52^81^3^405-411^^^^^Mar^^^^^7030
130^1364^1378^2124^3190^376^377^409^547^874^ soil carbon and moisture release curves were also determined. The plots represented a wide range in soil water potential, a major determinant of tree species distribution (range of minimum values = -1.1 to -8.0 MPa for Pacific silver fir and Douglas-fir plots, respectively). Precipitation intercepted at plots depended on topographic location, storm direction and storm type. Differences in soil moA^7029^Individuals of Arabidopsis thaliana, collected in different natural populations, were grown in controlled and elevated CO2 in a glasshouse. Following germination, root growth of progeny of different lines of these populations was studied in control and elevated atmospheric CO2. No significant direct effect of atmospheric CO2 concentration could be demonstrated on root growth. An important parental effect was apparent, namely that root length and branching were decreased in seeds collected from a mother plant which had been grown in elevated CO2. This was correlated with smaller seeds, containing less nitrogen. These parental effects were genetically variable. We conclude that CO2 may affect plant fitness via parental effects on seed size and early root growth and that the genetic variability shown in our study demonstrates that Arabidopsis populations will evolve in the face of this new selective pressure. (C) 1998 Annals of Botany Company.
tion, storm direction and storm type. Differences in soil mo2135^4^Arp,WJ^Van Mierlo,JEM^Berendse,F^Snijders,W^1998^1^Interactions between elevated CO2 concentration, nitrogen and water: effects on growth and water use of six perennial plant species^9^21^1^1-11^^^^^Jan^^^^^7032
245^312^3191^360^376^386^434^436^439^442^levated atmospheric CO2. No significant direct effect of atmospheric CO2 concentration could be demonstrated on root growth. An important parental effect was apparent, namely that root length and branching were decreased in seeds collected from a mother plant which had been grown in elevated CO2. This was correlated with smaller seeds, containing less nitrogen. These parental effects were genetically variable. We conclude that CO2 may affect plant fitness via parental effects on seed size and early root growth and that the genetic variability shown in our study demonstrates that Arabidopsis populations will evolve in the face of this new selective pressure. (C) 1998 Annals of Botany Company.
tion, storm direction and storm type. Differences in soil moA^7031^Two experiments are described in which plants of six species mere grown for one full season in greenhouse compartments with 350 or 560 mu mol mol(-1) COL. In the first experiment two levels of nitrogen supply were applied to study the interaction between CO2 and nitrogen, In the second experiment two levels of mater supply were added to the experimental set-up to investigate the three-way interaction between CO2, nitrogen and water, Biomass and biomass distribution were determined at harvests, while water use and soil moisture were monitored throughout the experiments, In both experiments a positive effect of CO2 on growth was found at high nitrogen concentrations but not at low nitrogen concentrations, However, plants used much less water in the presence of low nitrogen concentrations, Drought stress increased the relative effect of elevated CO2 on growth, Available soil moisture was used more slowly at high CO2 during drought or at high nitrogen concentrations, while at low nitrogen concentrations decreased water use resulted in an increase in soil moisture, The response to the treatments was similar in all the species used, Although potentially faster growing species appeared to respond better to high CO2 when supplied with a high level of nitrogen, inherently slow-growing species were more successful at low nitrogen concentrations.

2136^2^Battaglia,M^Sands,PJ^1998^1^Process-based forest productivity models and their application in forest management^45^102^1^13-32^^^^^3 Mar^^^^^7034
2099^3192^3193^3194^3195^372^434^513^586^811^re monitored throughout the experiments, In both experiments a positive effect of CO2 on growth was found at high nitrogen concentrations but not at low nitrogen concentrations, However, plants used much less water in the presence of low nitrogen concentrations, Drought stress increased the relative effect of elevated CO2 on growth, Available soil moisture was used more slowly at high CO2 during drought or at high nitrogen concentrations, while at low nitrogen concentrations dA^7033^Few process-based forest productivity models have become incorporated into forest management systems. The prevalent perception is that process-based models are suited only for research applications and that management questions will be solved only by using descriptive empirical models. This is despite the fact that the latter can neither deal satisfactorily with changing environmental and management conditions nor answer all questions currently asked by managers. This paper develops the proposition that the end-use specifies the design and scale of forest simulation models, and that given the range of questions now asked in forest management a range of models is required. The spatial and temporal resolution, and the input and output data required to address typical forest management questions is examined. A survey of recent literature examines in which areas, and by whom, existing forest productivity models are being applied. It is concluded that many current management questions can be adequately answered using models in which a phenomenological approach is applied to predict annual forest growth at the stand-scale. Lumped-parameter process-based models and hybrid models provide the most immediate means through which our understanding of the biological processes underlying forest growth can be included in forest management systems. However, more detailed process-based models can Flay an important role in validating simpler models, in the development of generalizations applicable over long time scales and for testing hypotheses about the way trees function and respond to interacting stresses. Guidelines are also given on model structures appropriate for different classes of management questions. (C) 1998 Elsevier Science B.V.

2137^4^Beerling,DJ^Woodward,FI^Lomas,M^Jenkins,AJ^1997^1^Testing the responses of a dynamic global vegetation model to environmental change: a comparison of observations and predictions^175^6^6^439-450^^^^^Nov^^^^^7036
1167^130^137^2911^3120^3173^344^372^669^699^ be adequately ansA^7035^Dynamic global vegetation - biogeochemistry models are required to predict the likely responses of the terrestrial biosphere to anticipated future global environmental change and for improved representation of an active vegetation surface within general circulation models of the Earth's global climate system. Testing the predictions of such models is essential to their development prior to use in a predictive capacity. The climate change experiment (CLIMEX) has exposed an entire catchment of boreal vegetation to elevated CO2 (560 ppmv) and temperature (+3 degrees C in summer, +5 degrees C in winter) for the past three years and has a considerable archive of pre-and posttreatment measurements of both CO2 and water vapour fluxes of the vegetation, catchment runoff and soil nutrient status. These data have been used to test the predictions of the University of Sheffield dynamic global vegetation model (SDGVM) for the same site using historical records of climate as input. Comparisons of observations and predictions at the scale of individual leaves and whole ecosystems are generally favourable, increasing our confidence in the application of the model to forecasting the responses of the terrestrial biosphere to various global change scenarios. The SDGVM has been used to predict the future responses of the ecosystem at the site into the year 2003AD. The results indicate rather small changes in leaf area index and catchment runoff but quite large increases in net primary productivity. The model predictions are now open to testing further as the CO2 and temperature treatments continue in the CLIMEX greenhouse.

2138^2^Bunce,JA^Ziska,LH^1998^1^Decreased hydraulic conductance in plants at elevated carbon dioxide^9^21^1^121-126^^^^^Jan^^^^^7038
1030^1323^2866^3196^344^347^376^386^434^92^ent status. These data have been used to test the predictions of the University of Sheffield dynamic global vegetation model (SDGVM) for the same site using historical records of climate as input. Comparisons of observations and A^7037^Previous work indicated that long-term exposure to elevated carbon dioxide levels can reduce hydraulic conductance in some species, but the basis of the response was not determined, In this study, hydraulic conductance was measured at concentrations of both 350 and 700 cm(3) m(-3) carbon dioxide for plants grown at both concentrations, to determine the reversibility of the response, In Zea mays and Amaranthus hypochondriacus, exposure to the higher carbon dioxide concentration for several hours reduced whole-plant transpiration rate by 22-40%, without any consistent change in leaf water potential, indicating reversible reductions in hydraulic conductance at elevated carbon dioxide levels, Hydraulic conductance in these species grown at both carbon dioxide concentrations responded similarly to measurement concentration of carbon dioxide, indicating that the response was reversible, In Glycine max, which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide levels, and in Abutilon theophrasti, no short- term changes in hydraulic conductance with measurement concentration of carbon dioxide were found, despite lower transpiration rates at elevated carbon dioxide, In G. max and Medicago sativa, growth at high dew-point temperature reduced transpiration rate and decreased hydraulic conductance, The results indicate that both reversible and irreversible decreases in hydraulic conductance can occur at elevated carbon dioxide concentrations, and that both could be responses to reduced transpiration rate, rather than to carbon dioxide concentration itself.

2139^2^Cao,MK^Woodward,FI^1998^1^Net primary and ecosystem production and carbon stocks of terrestrial ecosystems and their responses to climate change^127^4^2^185-198^^^^^Feb^^^^^7040
1103^2137^243^3197^344^407^429^51^547^56^ration of carbon dioxide, indicating that the response was reversible, In Glycine max, which in earlier work had shown a long-term decrease in hydraulic conductance at elevated carbon dioxide lA^7039^Evaluating the role of terrestrial ecosystems in the global carbon cycle requires a detailed understanding of carbon exchange between vegetation, soil, and the atmosphere. Global climatic change may modify the net carbon balance of terrestrial ecosystems, causing feedbacks on atmospheric CO2 and climate. We describe a model for investigating terrestrial carbon exchange and its response to climatic variation based on the processes of plant photosynthesis, carbon allocation, litter production, and soil organic carbon decomposition. The model is used to produce geographical patterns of net primary production (NPP), carbon stocks in vegetation and soils, and the seasonal variations in net ecosystem production (NEP) under both contemporary and future climates. For contemporary climate, the estimated global NPP is 57.0 Gt C y(-1), carbon stocks in vegetation and soils are 640 Gt C and 1358 Gt C, respectively, and NEP varies from -0.5 Gt C in October to 1.6 Gt C in July. For a doubled atmospheric CO2 concentration and the corresponding climate, we predict that global NPP will rise to 69.6 Gt C y(-1), carbon stocks in vegetation and soils will increase by, respectively, 133 Gt C and 160 Gt C, and the seasonal amplitude of NEP will increase by 76%. A doubling of atmospheric CO2 without climate change may enhance NPP by 25% and result in a substantial increase in carbon stocks in vegetation and soils. Climate change without CO2 elevation will reduce the global NPP and soil carbon stocks, but leads to an increase in vegetation carbon because of a forest extension and NPP enhancement in the north. By combining the effects of CO2 doubling, climate change, and the consequent redistribution of vegetation, we predict a strong enhancement in NPP and carbon stocks of terrestrial ecosystems. This study simulates the possible variation in the carbon exchange at equilibrium state. We anticipate to investigate the dynamic responses in the carbon exchange to atmospheric CO2 elevation and climate change in the past and future.
2140^3^Case,AL^Curtis,PS^Snow,AA^1998^1^Heritable variation in stomatal responses to elevated CO2 in wild radish, Raphanus raphanistrum (Brassicaceae)^5^85^2^253-258^^^^^Feb^^^^^7042
1142^1208^251^312^344^348^376^384^417^92^l increase by 76%. A doubling of atmospheric CO2 without climate change may enhance NPP by 25% and result in a substantial increase in carbon stocks in vegetation and soils. Climate change without CO2 elevation will reduce the global NPP and soil carbon stocks, but leads to an increase in vegetation carbon because of a forest extension and NPP enhancement in the north. By combining the effects of CO2 doubling, climate change, and the consequent redistribution of vegetation, we predict a strong enhancement in NPP and carbon stocks of terrestrial ecosystems. This study simulates the possible variation in the carbon exchange at equilibrium state. We anticipate to investigate the dynamic responses in the carbon exchange to atmospheric CO2 elevation and climate change in the past and future.
A^7041^Rising atmospheric carbon dioxide may affect plant populations in the short term through effects on photosynthesis and carbon allocation, and over the long term as an agent of natural selection. To test for heritable effects of elevated CO2 on stomatal responses and plant fecundity in Raphanus raphanistrum, we grew plants from 12 paternal families in outdoor open-top chambers at ambient (35 Pa) or elevated (67 Pa) CO2. Contrary to results from a previous study of this species, total flower and fruit production were marginally lower under elevated CO2. Across families, stomatal index and guard cell length showed little response to CO2 enrichment, but these characters varied significantly among paternal families in both the direction and magnitude of their response to changing CO2. Although these family-by-CO2, interactions suggest that natural selection might affect stomatal characters when ambient CO2 levels increase, we found no significant correlation between either character and flower or fruit production. Therefore, our data suggest that while heritable variation for stomatal index and guard cell length exists in this population, selection due to increasing CO2 is not likely to act on these traits because they had no detectable effect on lifetime fecundity.

2141^3^Crookshanks,M^Taylor,G^Broadmeadow,M^1998^1^Elevated CO2 and tree root growth: contrasting responses in Fraxinus excelsior, Quercus petraea and Pinus sylvestris^84^138^2^241-250^^^^^Feb^^^^^7044
130^2393^3055^310^376^377^407^508^547^867^production were marginally lower under elevated CO2. Across families, stomatal index and guard cell length showed little response to CO2 enrichment, but these characters varied significantly among paternal families in both the direction and magnitude of their response to changing CO2. Although these family-by-CO2, interactions suggest that natural selection might affect stomatal characters when ambient CO2 levels increase, we found no significant correlation between either character and flower or fruit proA^7043^Root growth and respiration in elevated CO2 (700 mu mol mol(- 1)) was studied in three tree species, Fraxinus excelsior L., Quercus petraea. L. and Pinus sylvestris L. grown in open-top chambers (OTCs) during a long-term exposure (20 months), during which root systems were allowed to develop without restriction imposed by pots. Root growth, measured as root length using root in-growth bags was increased significantly in trees exposed to elevated CO2, although the magnitude of the response differed considerably between species and with time of sampling, the greatest effect observed after 6 months in ash (ratio of elevated:ambient, e:a; 3.40) and the smallest effect observed in oak (e:a; 1.95). This was accompanied by changes in specific root length, with a significant decrease in all species after 6 months, suggesting that root diameter or root density were increased in elevated CO2. Increases in root length might have resulted from an acceleration in root cell expansion, since epidermal cell size was significantly increased in the zone of elongation in ash root tips (P < 0.05). Contrasting effects of elevated CO2 were observed for root carbohydrates, with significant increases in soluble sugars for all species (P < 0.05), but both increases and decreases in starch content were observed, depending on species, and producing a significant interaction between species and CO2 (P < 0.001). Exposure to elevated CO2 increased the total root d. wt for whole trees of all three species after 8 months of exposure, although the magnitude of this effect, in contrast to the root in-growth study, was greatest in Scots pine and smallest in ash. No significant effect of elevated CO2 was observed on the root:shoot ratio. Further detailed analysis of whole root systems after 20 months confirmed that species differences in root responses to elevated CO2 were apparent, with increased coarse and fine root production in elevated CO2 for Scots pine and ash respectively. Lateral root number was increased in elevated CO2 for all species, as was mean root diameter. Root respiration rates were significantly reduced in elevated CO2 for all three species. These results provide firm evidence that exposure of trees to future CO2 concentrations will have large effects on root system development, growth, carbohydrate status and respiration. The magnitude and direction of such effects will differ, depending on species. The consequences of such responses for the three species studied are discussed.

2142^3^Gleadow,RM^Foley,WJ^Woodrow,IE^1998^1^Enhanced CO2 alters the relationship between photosynthesis and defence in cyanogenic Eucalyptus cladocalyx F. Muell^9^21^1^12-22^^^^^Jan^^^^^7046
1282^1871^360^384^57^665^690^733^742^92^:shoot ratio. Further detailed analysis of whole root systems after 20 months confirmed that species differences in root responses to elevated CO2 were apparent, with increased coarse and fine root production in elevated CO2 for Scots pine and ash respectively. Lateral root number was increased in elevated CO2 for all sA^7045^The effect of elevated CO2 and different levels of nitrogen on the partitioning of nitrogen between photosynthesis and a constitutive nitrogen-based secondary metabolite (the cyanogenic glycoside prunasin) was examined in Eucalyptus cladocalyx. Our hypothesis was that the expected increase in photosynthetic nitrogen-use efficiency of plants grown at elevated CO2 concentrations would lead to an effective reallocation of available nitrogen from photosynthesis to prunasin, Seedlings were grown at two concentrations of CO2 and nitrogen, and the proportion of leaf nitrogen allocated to photosynthesis, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), protein and prunasin compared, Up to 20% of leaf nitrogen was allocated to the cyanogenic glycoside, although this proportion varied with leaf age, position and growth conditions, Leaf prunasin concentration,vas strongly affected by nitrogen supply, but did not increase, on a dry weight basis, in the leaves from the elevated CO2 treatments, However, the proportion of nitrogen allocated to prunasin increased significantly, in spite of a decreasing pool of leaf nitrogen, in the plants grown at elevated concentrations of CO2. There was less protein in leaves of plants grown at elevated CO2 in both nitrogen treatments, while the concentration of active sites of Rubisco only decreased in plants from the low-nitrogen treatment. These changes in leaf chemistry may have significant implications in terms of the palatability of foliage and defence against herbivores.

2143^5^Griffiths,BS^Ritz,K^Ebblewhite,N^Paterson,E^Killham,K^1998^1^Ryegrass rhizosphere microbial community structure under elevated carbon dioxide concentrations, with observations on wheat rhizosphere^130^30^3^315-321^^^^^Mar^^^^^7048
1096^1781^2920^3198^374^376^407^504^797^92^ed with leaf age, position and growth conditions, Leaf prunasin concentration,vas strongly affected by nitrogen supply, but did not increase, on a dry weight basis, in the leaves from the elevated CO2 treatments, However, tA^7047^The structure of microbial communities in the rhizospheres of ryegrass and wheat, growing at an elevated atmospheric CO2 concentration, was investigated using broad-scale DNA techniques. Community DNA hybridisation and %G + C base profiling by thermal denaturation assess changes at the whole microbial community level. DNA analysis of the rhizosphere of ryegrass grown in soil microcosms for 28 or 42 d, showed only minor differences between plants grown at 450 or 720 mu l CO2 l(-1). In a second experiment with ryegrass, 5 of 10 replicate microcosms were pulse labelled with (CO2)-C-14 and 5 simultaneously sampled for DNA analysis. Carbon partitioning below ground showed changes due to the elevated CO2, notably an increased proportion of fi?ted carbon in non-microbial biomass residue in the rhizosphere. There was again no effect of elevated CO2 on rhizosphere microbial community structure. Community DNA hybridisation indicated that the rhizosphere communities under ambient and elevated CO2 were 86% similar (unlikely to be a biologically relevant change), with indistinguishable %G + C profiles. Wheat was grown to maturity (129 d) in a different soil microcosm design, and rhizosphere microbial communities from plants grown at 350 and 700 mu l CO2 l(-1) were identical according to the DNA analyses. In these experiments rhizosphere microbial community structure at the broad scale was unaffected by the interactions occurring below ground as a result of elevated concentrations of CO2. (C) 1998 Elsevier Science Ltd. All rights reserved.

2144^3^Hall,JM^Paterson,E^Killham,K^1998^1^The effect of elevated CO2 concentration and soil pH on the relationship between plant growth and rhizosphere denitrification potential^127^4^2^209-216^^^^^Feb^^^^^7050
1096^1146^243^264^374^376^377^507^535^57^esidue in the rhizosphere. There was again no effect of elevated CO2 on rhizosphere microbial community structure. Community DNA hybridisation indicated that the rhizosphere communities under ambient and elevated CO2 were 86% similaA^7049^The effect of CO2 concentration on plant growth and the size of the rhizosphere denitrifier population was investigated for ryegrass grown at 3 different soil pH values (pH 4.3, 5.9 and 7.0). Soil microcosms were planted with ryegrass and maintained under constant growth conditions at either ambient (450ppm) or elevated (720ppm) CO2 concentration. At harvest, the rhizosphere soil was collected and subjected to a potential denitrification assay to provide an estimate of the size of the denitrifier population present. Ryegrass dry matter production varied across the pH range studied and contrary to other studies, elevated CO2 concentration did not consistently increase growth. Plant growth was reduced by approximate to 35% and 23% at pH 4.3 and pH 5.9, respectively, under elevated CO2 concentration. At pH 7.0, however, plant growth was increased by approximate to 45% under elevated CO2. Potential denitrification rates within the rhizosphere followed a similar pattern to plant growth in the different treatments, suggesting that plant growth and the size of denitrifier population within the rhizosphere are coupled. This study investigates the relationship between plant growth and rhizosphere denitrification potential, thereby providing an estimate of the size of the denitrifier population under increased CO2 concentration and soil pH.

2145^3^Ineson,P^Coward,PA^Hartwig,UA^1998^1^Soil gas fluxes of N2O, CH4 and CO2 beneath Lolium perenne under elevated CO2: The Swiss free air carbon dioxide enrichment experiment^206^198^1^89-95^^^^^Jan^^^^^7052
1190^3019^344^d across the pH range studied and contrary to other studies, elevated CO2 concentration did not consistently increase growth. Plant growth was reduced by approximate to 35% and 23% at pH 4.3 and pH 5.9, respectively, under elevated CO2 concentration. At pH 7.0, however, plant growth was increased by approximate to 45% under elevated CO2. Potential denitrification rates within the rhizosphere followed a similar pattern to plant growth in the different treA^7051^Fluxes of nitrous oxide, methane and carbon dioxide were measured from soils under ambient (350 mu L L-1) and enhanced (600 mu L L-1) carbon dioxide partial pressures (pCO(2)) at the 'Free Air Carbon Dioxide Enrichment' (FACE) experiment, Eidgenossische Technische Hochschule (ETH), Eschikon, Switzerland in July 1995, using a GC housed in a mobile laboratory. Measurements were made in plots of Lolium perenne maintained under high N input. During the data collection period N fertiliser was applied at a rate of 14 g m(-2) of N. Elevated pCO(2) appeared to result in an increased (27%) output of N2O, thought to be the consequence of enhanced root-derived available soil C, acting as an energy source for denitrification. The climate, agricultural practices and soils at the FACE experiment combined to give rise to some of the largest N2O emissions recorded for any terrestrial ecosystem. The amount of CO2-C being lost from the control plot was higher (10%) than for the enhanced CO2 plot, and is the reverse of that predicted. The control plot oxidised consistently more CH4 than the enhanced plot, oxidising 25.5 +/- 0.8 mu g m(-2) hr(- 1) of CH4 for the control plot, with an average of 8.5 +/- 0.4 mu g m(-2) hr(-1) of CH4 for the enhanced CO2 plot. This suggests that elevated pCO(2) may lead to a feedback whereby less CH4 is removed from the atmosphere. Despite the limited nature of the current study (in time and space), the observations made here on the interactions of elevated pCO(2) and soil trace gas release suggest that significant interactions are occurring. The feedbacks involved could have importance at the global scale.

2146^4^Jackson,RB^Sala,OE^Paruelo,JM^Mooney,HA^1998^1^Ecosystem water fluxes for two grasslands in elevated CO2: a modeling analysis^2^113^4^537-546^^^^^Feb^^^^^7054
243^374^377^385^529^547^57^674^783^92^ largest N2O emissions recorded for any terrestrial ecosystem. The amount of CO2-C being lost from the control plot was higher (10%) than for the enhanced CO2 plot, and is the reverse of A^7053^The need to combine data from CO2 field experiments with climate data remains urgent, particularly because each CO2 experiment cannot run for decades to centuries. Furthermore, predictions for a given biome need to take into account differences in productivity and leaf area index (LAI) independent of CO2-derived changes. In this study, we use long- term weather records and field data from the Jasper Ridge CO2 experiment in Pale Alto, California, to model the effects of CO2 and climate variability on ecosystem water fluxes. The sandstone and serpentine grasslands at Jasper Ridge provide a range of primary productivity and LAI, with the sandstone as the more productive system. Modeled soil water availability agreed well with published observations of time-domain reflectometry in the CO2 experiment. Simulated water fluxes based on 10-year weather data (January 1985-December 1994) showed that the sandstone grassland had a much greater proportion of water movement through plants than did the serpentine; transpiration accounted for approximately 30% of annual fluxes in the sandstone and only 10% in the serpentine. Although simulated physiological and biomass changes were similar in both grasslands, the consequences of elevated CO2 were greater for the sandstone water budget. Elevated CO2 increased soil drainage by 20% in the sandstone, despite an approximately one-fifth increase in plant biomass; in the serpentine, drainage increased by <10% and soil evaporation was unchanged for the same simulated biomass change. Phenological changes, simulated by a 15-day lengthening of the growing season, had minimal impacts on the water budget. Annual variation in the timing and amount of rainfall was important for water fluxes in both grasslands. Elevated CO2 increased sandstone drainage > 50 mm in seven of ten years, but the relative increase in drainage varied from 10% to 300% depending on the year. Early-season transpiration in the sandstone decreased between 26% and 41%, with elevated CO2 resulting in a simulated water savings of 54-76 mm. Even in years when precipitation was similar (e.g., 505 and 479 mm in years 3 and 4), the effect of CO2 varied dramatically. The response of grassland water budgets to CO2 depends on the productivity and structure of the grassland, the amount and timing of rainfall, and CO2-induced changes in physiology. In systems with low LAT, large physiological changes may not necessarily alter total ecosystem water budgets dramatically.

2147^5^Lal,M^Singh,KK^Rathore,LS^Srinivasan,G^Saseendran,SA^1998^1^Vulnerability of rice and wheat yields in NW India to future changes in climate^107^89^2^101-114^^^^^Feb^^^^^7056
1221^130^3199^51^on in the timing and amount of rainfall was important for water fluxes in both grasslands. Elevated CO2 increased sandstone drainage > 50 mm in seven of ten years, but the relative increase in drainage varied from 10% to 300% depending on the year. Early-season transpiration in the sandstone decreased between 26% and 41%, with elevated CO2 resulting in a simulated wateA^7055^Agricultural sector is one of the sensitive areas which would be influenced by the projected global warming and associated climate change. In spite of the uncertainties about the precise magnitude of climate change on regional scales, an assessment of the possible impacts of changes in key climatic elements on our agricultural resources is important for formulating response strategies. In this study, vulnerability of wheat and rice crops in northwest India to the projected climate change is examined. CERES wheat and rice models adopted for the study were validated for their ability to reproduce yields at the selected NW Indian stations. The sensitivity experiments with these models showed higher yields for both wheat and rice (28% and 15% respectively for a doubling of CO2) under elevated CO2 levels. A 3 degrees C (2 degrees C) rise in air temperature nearly cancels out the positive effect of elevated CO2 on the wheat (rice) yields. While the wheat crops are found to be sensitive to increase in maximum temperature, the rice crops are vulnerable to increase in minimum temperature. The combined effect of enhanced CO2 and imposed thermal stress on the wheat (rice) crop is 21% (4%) increase in yield for the irrigation schedule presently practised in the region. While the adverse impacts of likely water shortage on wheat crops would be minimised to a certain extent under elevated CO2 levels, they would largely be maintained for the rice crops resulting in about 20% net decline in rice yields. In general, acute water shortage conditions combined with the thermal stress should adversely affect both the wheat and more severely the rice productivity in NW India even under the positive effects of elevated CO2 in the future. (C) 1998 Elsevier Science B.V.

2148^4^Li,A^Berntson,GM^Godbold,DL^Bazzaz,FA^1998^1^The dynamics of root production and loss in Betula papyrifera seedlings in response to elevated CO2 and an aluminium pulse^220^161^1^17-21^^^^^Feb^^^^^7058
1323^1334^3200^417^427^92^sitive to increase in maximuA^7057^Seedlings of Betula papyrifera were grown in sand/nutrient solution cultures in rhizotrone growth containers under elevated (700 ppm) or ambient (375 ppm) atmospheric CO2 concentrations for approximately 10 weeks. Thirty seven days after the begin of the experiment the plants were exposed to a 10 day pulse of 400 or 1200 mu M Al. Elevated atmospheric CO2 increased both root production and loss. Exposure to Al reduced root production and slightly reduced root loss. The reduced root production due to Al was amplified after the pulse had receded, resulting in a significantly lower net and gross root production at the end of the experiment. There were no clear CO2 x Al interactions.

2149^3^Luo,YQ^Sims,DA^Griffin,KL^1998^1^Nonlinearity of photosynthetic responses to growth in rising atmospheric CO2: an experimental and modelling study^127^4^2^173-183^^^^^Feb^^^^^7060
130^1522^264^312^348^360^372^376^448^665^ium pulse^220^161^1^17-21^^^^^Feb^^^^^7058
1323^1334^3200^417^427^92^sitive to increase in maximuA^7059^Nonlinear responses of photosynthesis to the CO2 concentration at which plants were grown (C-g) have been often reported in the literature. This study was designed to develop mechanistic understanding of the nonlinear responses with both experimental and modelling approaches. Soybean (Glycine max) was grown in five levels of C-g (280, 350, 525, 700, 1000 ppm) with either a high or low rate of nitrogen fertilization. When the rate of nitrogen fertilization was high, the photosynthetic rate measured at C-g was highest in plants from the 700 ppm CO2 treatment. When the rate of nitrogen fertilization was low, little variation was observed in the photosynthetic rates of plants from the different treatments measured at their respective C-g. Measurements of CO2-induced changes in mass- based leaf nitrogen concentration (n(m) an index of changes in biochemical processes) and leaf mass per unit area (h, an index of morphological properties) were used in a model and indicate that the nonlinearity of photosynthetic responses to C-g is largely determined by relative changes in photosynthetic sensitivity, biochemical downregulation, and morphological upregulation. In order to further understand the nonlinear responses, we compiled data from the literature on CO2-induced changes in n(m) and h. These compiled data indicate that h generally increases and n(m) usually decreases with increasing C-g, but that the trajectories and magnitudes of the changes in h and n(m) vary with species and growth environments. Integration of these variables (n(m) and h) into a biochemically based model of photosynthesis enabled us to predict diverse responses of photosynthesis to C-g. Thus a general mechanism is suggested for the highly variable, nonlinear responses of photosynthesis to C-g reported in the literature.

2150^2^Matysiak,B^Nowak,J^1998^1^Acclimatization and the growth of Ficus benjamina microcuttings as affected by carbon dioxide concentration^361^73^2^185-188^^^^^Mar^^^^^7062
1491^243^376^674^781^onlinearity of photosyntheA^7061^The influence of CO2 concentrations (350 and 1200 mu mol mol(- 1)) on the growth of Ficus benjamina microcuttings cv. Golden King and cv. Natasja, was investigated with reference to light levels (50 and 150 mu mol m(-2) s(-1) PPFD, Photosynthetic Photon Flux Density) and the nutrient solution concentrations (0.7, 1.4, 2.1 and 2.8 mS cm(-1) EC, electrical conductivity). Plants grown in peat + perlite at 1,200 mu mol mol(-1) CO2 concentration and simultaneously at high PPFD level (150 mu mol m(-2) s(-1)) had the highest shoot and root fresh weights and the highest leaf area. Elevation of CO2 concentration at low level of PPFD did not affect the growth of F. benjamina. Survival of F. benjamina microcuttings cultivated in rockwool was low (65-90%) and the growth rate was slow, irrespective of nutrient solution concentration. CO2 enrichment increased survival and accelerated the growth of these microcuttings. The best growth of F. benjamina microcuttings cultivated in rockwool was at 1,200 mu mol mol(-1) CO2 and the highest level of electrical conductivity (EC) 2.8 mS cm(-1).

2151^1^McElwain,JC^1998^1^Do fossil plants signal palaeoatmospheric CO2 concentration in the geological past?^190^353^1365^83-95^^^^^29 Jan^^^^^7064
1635^1807^227^3201^377^534^593^634^745^982^Density) and the nutrient solution concentrations (0.7, 1.4, 2.1 and 2.8 mS cm(-1) EC, electrical conductivity). Plants grown in peat + perlite at 1,200 mu mol mol(-1) CO2 concentration and simultaneously at high PPFD level (150 mu mol m(-2) s(-1)) had the highest shoot and root fresh weights and the highest leaf area. Elevation of CO2 concentration at low level of PPFD did not affect the growth of F. benjamina. Survival of F. benjamina microcuttings cultivated in rockwool was low (65-90%) and the growth rate was slow, irrespective of nutrient solution concentration. CO2 enrichment increased survival and accelerated the growth of these microcuttings. The best growth of F. benjamina microcuttings cultivated in rockwool was at 1,200 mu mol mol(-1) CA^7063^Fossil, subfossil, and herbarium leaves have been shown to provide a morphological signal of the atmospheric carbon dioxide (CO2) environment in which they developed by means of their stomatal density and index. An inverse relationship between stomatal density/index and atmospheric CO2 concentration has been documented for all the studies to date concerning fossil and subfossil material. Furthermore, this relationship has been demonstrated experimentally by growing plants under elevated and reduced CO2 concentrations. To date, the mechanism that controls the stomatal density response to atmospheric CO2 concentration remains unknown. However, stomatal parameters of fossil plants have been successfully used as a proxy indicator of palaeo-CO2 levels. This paper presents new estimates of palaeoatmospheric CO2 concentrations for the Middle Eocene (Lutetian), based on the stomatal ratios of fossil Lauraceae species from Bournemouth in England. Estimates of atmospheric CO2 concentrations derived from stomatal data from plants of the Early Devonian, Late Carboniferous, Early Permian and Middle Jurassic ages are reviewed in the light of new data. Semi-quantitative palaeo-CO2 estimates based on the stomatal ratio (a ratio of the stomatal index of a fossil plant to that of a selected nearest living equivalent) have in the past relied on the use of a Carboniferous standard. The application of a new standard based on the present-day CO2 level is reported here for comparison. The resultant ranges of palaeo-CO2 estimates made from standardized fossil stomatal ratio data are in good agreement with both carbon isotopic data from terrestrial and marine sources and long-term carbon cycle modelling estimates for all the time periods studied. These data indicate elevated atmospheric CO2 concentrations during the Early Devonian, Middle Jurassic and Middle Eocene, and reduced concentrations during the Late Carboniferous and Early Permian. Such data are important in demonstrating the long-term responses of plants to changing CO2 concentrations and in contributing to the database needed for general circulation model climatic analogues.

2152^7^Miglietta,F^Magliulo,V^Bindi,M^Cerio,L^Vaccari,FP^Loduca,V^Peressotti,A^1998^1^Free air CO2 enrichment of potato (Solanum tuberosum L.): development, growth and yield^127^4^2^163-172^^^^^Feb^^^^^7066
1261^130^131^137^312^348^372^409^417^442^tandard. The application of a new standard based on the present-day CO2 level is reported here for comparison. The resultant ranges of palaeo-CO2 estimates made from standardized fossil stomatal ratio data are in good agreement with both carbon isotopic data from terrestrial and marine sources and long-term carbon cycle modelling estimates for all the time periods studied. These data indicate elevated atmospheric CO2 concentrations during the Early Devonian, Middle Jurassic and Middle Eocene, and reduced concentrations during the Late Carboniferous and Early Permian. Such data are important in demonstrating the long-term responses of plants to changing COA^7065^A FACE (Free Air CO2 Enrichment) experiment was carried out on Potato (Solanum tuberosum L., cv. Primura) in 1995 in Italy. Three FACE rings were used to fumigate circular field plots of 8 m diameter while two rings were used as controls at ambient CO2 concentrations. Four CO2 exposure levels were used in the rings (ambient, 460, 560 and 660 mu mol mol-l). Phenology and crop development, canopy surface temperature, above-and below- ground biomass were monitored during the growing season. Crop phenology was affected by elevated CO2, as the date of flowering was progressively anticipated in the 660, 560, 460 mu mol mol(-1) treatments. Crop development was not affected significantly as plant height, leaf area and the number of leaves per plant were the same in the four treatments. Elevated atmospheric CO2 levels had, instead, a significant effect on the accumulation of total nonstructural carbohydrates (TNC = soluble sugars + starch) in the leaves during a sunny day. Specific leaf area was decreased under elevated CO2 with a response that paralleled that of TNC concentrations. This reflected the occurrence of a progressive increase of photosynthetic rates and carbon assimilation in plants exposed to increasingly higher levels of atmospheric CO2. Tuber growth and final tuber yield were also stimulated by rising CO2 levels. When calculated by regression of tuber yield vs. the imposed levels of CO(2)concentration, yield stimulation was as large as 10% every 100 mu mol mol(-1) increase, which translated into over 40% enhancement in yield under 660 mu mol mol(-1). This was related to a higher number of tubers rather than greater mean tuber mass or size. Leaf senescence was accelerated under elevated CO2 and a linear relationship was found between atmospheric CO2 levels and leaf reflectance measured at 0.55 mu m wavelength. We conclude that significant CO2 stimulation of yield has to be expected for potato under future climate scenarios, and that crop phenology will be affected as well.
f area was decreased unde2153^6^Mulholland,BJ^Craigon,J^Black,CR^Colls,JJ^Atherton,J^Landon,G^1998^1^Growth, light interception and yield responses of spring wheat (Triticum aestivum L.) grown under elevated CO2 and O-3 in open-top chambers^127^4^2^121-130^^^^^Feb^^^^^7068
2372^2373^243^2733^312^376^436^447^724^949^timulated by rising CO2 levels. When calculated by regression of tuber yield vs. the imposed levels of CO(2)concentration, yield stimulation was as large as 10% every 100 mu mol mol(-1) increase, which translated into over 40% enhancement in yield under 660 mu mol mol(-1). This was related to a higher number of tubers rather than greater mean tuber mass or size. Leaf senescence was accelerated under elevated CO2 and a linear relationship was found between atmospheric CO2 levels and leaf reflectance measured at 0.55 mu m wavelength. We conclude that significant CO2 stimulation of yield has to be expected for potato under future climate scenarios, and that crop phenology will be affected as well.
f area was decreased undeA^7067^Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO2) and two ozone (O-3) concentrations in open-top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO2 under ambient O-3 conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 mu mol mol(-1) CO2 treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 mu mol mol(-1) CO2, but senescence was delayed at 680 mu mol mol(-1) CO2. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 mu mol mol(-1) CO2 than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO2 were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 mu mol mol(-1) CO2 treatment, due to a combination of increases in the number of ears per m(- 2), grain number per ear and individual grain weight (IGW). Exposure to a seasonal mean (7 h d(-1)) of 84 nmol mol(-1) O-3 under ambient CO2 decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by approximate to 16%. Individual leaves senesced completely 7- 28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m(-2), the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO2 reduced the rate of O-3- induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO2 treatments in the absence of elevated O-3. Thus, although the presence of elevated CO2 reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O-3-induced injury during anthesis irrespective of the atmospheric CO2 concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed.

2154^3^Ong,BL^Koh,CKK^Wee,YC^1998^1^Effects of CO2 on growth and photosynthesis of Pyrrosia piloselloides (L.) Price gametophytes^79^35^1^21-27^^^^^^^^^^7070
256^2639^310^360^361^372^376^377^672^962^let and per ear and IGW. The presence of elevated CO2 reduced the rate of O-3- induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated COA^7069^The effects of CO2 concentration on spore germination, growth, and net photosynthetic rate (P-N) Of gametophytes of a tropical epiphytic fern, Pyrrosia piloselloides, were investigated over a 100-d period. Increasing CO2 concentration stimulated spore germination and enhanced gametophytic growth. The appearance of sexual organs and formation of sporophytes were accelerated with higher CO2 during growth. Radiant energy saturated P-N and dark respiration rate also increased with increasing CO2 concentrations during growth.

2155^2^Seneweera,SP^Conroy,JP^1997^1^Growth, grain yield and quality of rice (Oryza sativa L.) in response to elevated CO2 and phosphorus nutrition (Reprinted from Plant nutrition for sustainable food production and environment, 1997)^316^43^^1131-1136^^^^^Dec^^^^^7072
130^312^376^409^57^590^the maintenance of a higher green LAI during vegetative growth under ambient CO2 conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated COA^7071^The influence of rising atmospheric CO2 concentrations and phosphorus nutrition on growth, grain yield and quality of a early maturing rice cultivar (Oryza sativa L. cv. Jarrah) was investigated by growing plants in a range of phosphorus levels at tither 350 or 700 mu L CO2 L-1 in the growth chambers. Total above ground biomass and grain yield were greater at elevated CO2 concentrations and with increasing phosphorus supply. The CO2 response was evident at all but the lowest phosphorus treatments but its magnitude was greater at moderate phosphorus supplies. The increase in grain yield at high CO2 was due mainly to an enhancement of tiller number. The phosphorus concentration in the foliage was unaffected by CO2 enrichment and the critical concentration of 1.8 g kg(-1) dwt was the same as reported for field-grown rice. The concentration of calcium in the foliage was increased by high CO2 and the nitrogen concentration was reduced, Chemical analysis (amylose and mineral concentration) indicated that cooked rice grain from high-CO2-grown plants would be firmer and that concentrations of Zn and Fe, which are important in the diet of humans, will be lower. These results indicate that there is a need to plan for the inevitable rise in global CO2 concentrations by selecting cultivars which will be more productive and yet maintain suitable quality characteristics under elevated CO2 levels.

2156^3^Sharma-Natu,P^Khan,FA^Ghildiyal,MC^1997^1^Photosynthetic acclimation to elevated CO2 in wheat cultivars^79^34^4^537-543^^^^^^^^^^7074
2347^312^3202^3203^344^348^359^417^529^92^ increase in grain yield at high CO2 was due mainly to an enhancement of tiller number. The phosphorus concentration in the foliage was unaffected by CO2 enrichment and the critical concentration of 1.8 g kg(-1) dwt was the same as reported for field-grown rice. The concentration of calcium in the foliage was increased by high CO2 and the nitrogen concentration was reduced, Chemical analysis (amylose and mineral concentration) indicated that coA^7073^Wheat (T. aestivum) cvs. Kalyansona and Kundan grown under atmospheric (CA) and elevated CO2 concentrations (650-150 cm(3) m(-3) - CE) in open top chambers were examined for net photosynthetic rate (P-N), stomatal limitation (l(S)) of P-N, ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, and saccharide content of the leaves. The P-N values of both CA- and CE-grown plants compared at the same CO2 concentration showed a down regulation under CE at the post-anthesis stage. The negative acclimation of P-N appeared to be due to both stomatal and mesophyll components, and the RuBPC activity got also adjusted. There was a decrease in activation state of RuBPC under CE. In connection with this, an increased accumulation of saccharides in wheat leaf under CE was observed. Kalyansona, owing to its larger sink potential in terms of the number of grains, showed a greater enhancement under CE in both post-ear emergence dry matter production and grain yield. Under CE, this cultivar also showed a lower down regulation of P-N than Kundan.

2157^1^Thornley,JHM^1998^1^Dynamic model of leaf photosynthesis with acclimation to light and nitrogen^52^81^3^421-430^^^^^Mar^^^^^7076
1030^2756^32^348^372^416^417^423^444^92^N), stomatal limitation (l(S)) of P-N, ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, and saccharide content of the leaves. The P-N values of both CA- and CE-grown plants compared at the same CO2 concentration showed a down regulation under CE at the post-anthesis stage. The negative acclimation of P-N appeared to be due to both stomatal and mesophyll components, and the RuBPC activity got also adjusted. There was a decrease in activation state of RuBPC under CE. In connection with this, an increased accumulation of saccharides in wheat leaf under CE was observed. Kalyansona, owing to its larger sink potential in terms of the number of grains, showed a greater enhancement under CE in both post-ear emergence dry matter production and grain yield. Under CE, this cultivar also showed a lower down rA^7075^A simple model of photosynthesis in a mature C-3 leaf is described, based on a non-rectangular hyperbola: the model allows the high-light asymptote of that equation (P-max) to respond dynamically to light and nitrogen. This causes the leaf light response equation to acclimate continuously to the current conditions of light and N nutrition, which can vary greatly within a crop canopy, and through a growing season, with important consequences for gross production. Predictions are presented for the dynamics of acclimation, acclimated and non-acclimated photosynthetic rates are compared, and the dependence of leaf properties on light and N availability is explored. There is good correspondence of predictions with experimental results at the leaf level. The model also provides a mechanism for a down regulation of photosynthesis in response to increased carbon dioxide concentrations, whose magnitude will depend on conditions, particularly of nitrogen nutrition. (C) 1998 Annals of Botany Company.
wer down r2158^5^Tuba,Z^Csintalan,Z^Szente,K^Nagy,Z^Grace,J^1998^1^Carbon gains by desiccation-tolerant plants at elevated CO2^43^12^1^39-44^^^^^Feb^^^^^7078
243^310^3204^3205^3206^3207^3208^3209^344^348^mically to light and nitrogen. This causes the leaf light response equation to acclimate continuously to the current conditions of light and N nutrition, which can vary greatly within a crop canopy, and through a growing season, with important consequences for gross production. Predictions are presented for the dynamics of acclimation, acclimated and non-acclimated photosynthetic rates are compared, and the dependence of leaf properties on light and N availability is explored. There is good correspondence of predictions with experimental results at the leaf level. The model also provides a mechanism for a down regulation of photosynthesis in response to increased carbon dioxide concentrations, whose magnitude will depend on conditions, particularly of nitrogen nutrition. (C) 1998 Annals of Botany Company.
wer down rA^7077^1. There have been no reports of the long-term responses of the desiccation-tolerant (DT) plants to elevated CO2. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so-called poikilochlorophyllous desiccation-tolerant species (PDT), When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants. 2. However, the duration of:photosynthesis in X. scabria is prolonged by 300% when the measurements are: made at 700 as opposed to 350 p.p.m. CO2. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity, This response could have far-reaching implications for the success of such species in a future climate. 3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation, We show the desiccation responses of two common HDT species (Cladonia convoluta and Tortula ruralis) to elevated CO2 for comparison, Both HDT species showed increased net CO2 uptake in the material grown at high CO2 by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation- tolerant plants will be among the main beneficiaries of a high CO2 future.

2159^2^Vasseur,L^Potvin,C^1998^1^Natural pasture community response to enriched carbon dioxide atmosphere^331^135^1^31-41^^^^^Mar^^^^^7080
1684^1727^372^417^507^540^57^672^92^hen the measurements are: made at 700 as opposed to 350 p.p.m. CO2. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity, This response could have far-reaching implications for the success of such species in a future climate. 3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation, We show the desiccation responses of two common HDT species (Cladonia A^7079^We examined the response of a pasture community in southern Quebec (Canada) to long-term exposure of enriched atmospheric CO2 conditions. The study was conducted using open-top growth chambers directly placed on top of the natural pasture community. To investigate the change in the overall species composition in time and space, we used canonical correspondence analysis, a direct ordination method. Over the three years, the overall community responded significantly to enriched CO2. The analyses show that, after three years, CO2 was the most important environmental variable affecting the species composition. Initially the presence of the wall of the chambers influenced the composition but CO2 became more important by the third year. Soil and air temperatures only slightly influenced the community composition. The first two axes of the canonical correspondence analysis explained a large proportion of the variation in the three years and these trends appeared to increase with time. Species such as Agropyron repens appeared to be positively influenced by the presence of the wall (slightly warmer conditions). However, the analyses suggest that Phleum pratense and Trifolium repens, for example, were favored by the increase in atmospheric CO2. The variation in species composition in enriched versus ambient CO2 chambers suggests that the effect of the environmental factors, particularly CO2, were important in affecting the rate and pattern of succession. Furthermore, the temporal increase in importance of the variable CO2 in the present analyses indicates that there might be a time-lag in response to atmospheric enrichment.

2160^3^Volin,JC^Reich,PB^Givnish,TJ^1998^1^Elevated carbon dioxide ameliorates the effects of ozone on photosynthesis and growth: species respond similarly regardless of photosynthetic pathway or plant functional group^84^138^2^315-325^^^^^Feb^^^^^7082
1828^2034^2993^3210^344^360^376^389^444^587^ation in the three years and these trends appeared to increase with time. Species such as AgropyrA^7081^Due to their different physiological effects, elevated carbon dioxide and elevated ozone might have interactive impacts on plants, and differentially so on plants differing in photosynthetic pathway and growth rate. To test several hypotheses related to these issues, we examined the physiological, morphological and growth responses of six perennial species grown at various atmospheric concentrations of carbon dioxide and ozone. The species involved (two C-3 trees: Populus tremuloides Michx., Quercus rubra L.; two C-3 grasses: Agropyron smithii Rybd., Koeleria cristata L.; two C-4 grasses: Bouteloua curtipendula Michx., Schizachyrium scoparium Michx.) differed in growth form, stomatal conductance and photosynthetic pathway. In situ photosynthesis, relative growth rate (RGR) and its determinants (leaf area ratio, specific leaf area, leaf weight ratio and root weight ratio) were determined via sequential harvests of seedlings that were grown in all combinations of 366 or 672 mu mol mol(-1) CO2 and 3 or 95 nmol mol(-1) O-3 over a 101-d period. Elevated CO2 had minimal effect on either photosynthesis or RGR. By contrast, RGR for all six species was lower in high O-3 concentrations at ambient CO2, significantly so in A. smithii and P. tremuloides. Five of the six species also exhibited reductions in in situ photosynthesis at ambient CO2 in high-O-3-grown compared with low-O-3-grown plants. For all species, these O-3-induced reductions in RGR and photosynthesis were absent in the elevated CO2 environment. Root weight ratio was significantly reduced by elevated O-3 in A. smithii and P. tremuloides in ambient but not elevated CO2. Species with high stomatal conductance were the most susceptible to oxidant injury, while those with low stomatal conductance, such as the C-4 species and Q. rubra, were not as detrimentally affected by O-3. Elevated levels of CO2 will reduce stomatal conductance and O-3 uptake, and might therefore reduce the potential for oxidant damage. However, there was a stronger relationship of the percent reduction in whole-plant mass due to O-3, related to the ratio of photosynthesis to stomatal conductance. In general, results of this study of six functionally diverse plant species suggest that O-3 pollution effects on carbon balance and growth are likely to be ameliorated by elevated concentrations of atmospheric CO2.

2161^4^Walker,RF^Geisinger,DR^Johnson,DW^Ball,JT^1998^1^Atmospheric CO2 enrichment and soil N fertility effects on juvenile ponderosa pine: Growth, ectomycorrhizal development, and xylem water potential^45^102^1^33-44^^^^^3 Mar^^^^^7084
1334^2093^224^2426^3003^341^372^374^419^680^ not elevated CO2. Species with high stomatal conductance were the most susceptible to oxidant injury, while those with low stomatal conductance, such as the C-4 species and Q. rubra, were not as detrimentally affected by O-3. Elevated levels of CO2 will reduce stomatal conductance and O-3 uptake, and might therefore reduce the potential for oxidant damage. However, there was a stronger relationship of thA^7083^Interactive effects of elevated atmospheric CO2 and soil N fertility on above-and below-ground growth, mycorrhizal colonization, and water relations of juvenile ponderosa pine (Pious ponderosa Dougl. ex Laws.) were investigated. One-year- old seedlings were planted in undisturbed field soil within open-top chambers which permitted creation of atmospheres with 700 mu l l(-1), 525 mu l l(-1), or ambient CO2 concentrations. High and medium soil N treatments were imposed by incorporating sufficient (NH4)(2)SO4 to increase total N by 200 mu g g(-1) and 100 mu g g(-1), respectively, while unamended soil, which had a total N concentration of approximately 900 mu g g(-1), constituted the low N treatment. Following each of two consecutive field growing seasons, whole seedlings of every combination of CO2 and N treatment were harvest-ed to permit assessment of shoot and root growth and quantification of ectomycorrhizal development. Late in the second growing season, a simulated drought episode was imposed by withholding irrigation during which predawn and midday xylem water potential and soil water potential were measured. The initial harvest revealed that coarse and fine root weights were increased by CO2 enrichment during the first growing season. This result was most apparent in the 525 mu l l(-1) CO2 treatment and high soil N, which produced the greatest root volume as well. Shoot/root ratio decreased with increasing CO2 at the first harvest. After two growing seasons, elevated CO2 increased seedling diameter, shoot and root volume, and shoot and coarse root weight, again most prominently in high N. Unlike the initial results, however, stimulation of seedling growth by the 700 mu l l(-1) CO2 atmosphere exceeded that in 525 mu l l(-1) CO2 after two growing seasons, and shoot/root ratio was unaffected by either CO2 or N. At both harvests, seedlings grown in the enriched atmospheres generally had higher mycorrhizal counts and greater percentages of colonized root length, but differences among treatments in ectomycorrhizal development were nonsignificant regardless of quantification method. During the imposed drought episode, xylem water potential of seedlings grown in elevated CO2 descended below that of seedlings grown in the ambient atmosphere as soil water potential decreased, most notably in the predawn measurements. These results suggest that CO2 enrichment stimulates shoot and root growth of juvenile ponderosa pine under field conditions, a response somewhat dependent on soil N availability. However, below-ground growth is not increased proportionally more than that above ground, which may predispose this species to greater stress when soil water is limited. (C) 1998 Elsevier Science B.V.

2162^3^Williams,MW^Brooks,PD^Seastedt,T^1998^1^Nitrogen and carbon soil dynamics in response to climate change in a high-elevation ecosystem in the Rocky Mountains, USA^10^30^1^26-30^^^^^Feb^^^^^7086
1031^176^3211^3212^3213^3214^3215^669^reater percentages of colonized root length, but differences among treatments in ectomyA^7085^We have implemented a long-term snow-fence experiment at the Niwot Ridge Long-Term Ecological Research (NWT) site in the Colorado Front Range of the Rocky Mountains, U.S.A., to assess the effects of climate change on alpine ecology and biogeochemical cycles, The responses of carbon (C) and nitrogen (N) dynamics in high-elevation mountains to changes in climate ate investigated by manipulating the length and duration of snow cover with the 2.6 X 60 m snow fence, providing a proxy for climate change. Results from the first year of operation in 1994 showed that the period of continuous snow cover was increased by 90 d. The deeper and earlier snowpack behind the fence insulated soils from winter air temperatures, resulting in a 9 degrees C increase in annual minimum temperature at the soil surface. The extended period of snow cover resulted in subnivial microbial activity playing a major role in annual C and N cycling. The amount of C mineralized under the snow as measured by CO2 production was 22 g m(-2) in 1993 and 35 g m(- 2) in 1994, accounting for 20% of annual net primary aboveground production before construction of the snow fence in 1993 and 31% after the snow fence was constructed in 1994. In a similar fashion, maximum subnivial N2O flux increased 3-fold behind the snow fence, from 75 mu g N m(-2) d(-1) in 1993 to 250 mu g N m(-2) d(-1) in 1994. The amount of N lost from denitrification was greater than the annual atmospheric input of N in snowfall. Surface litter decomposition studies show that there was a significant increase in the litter mass loss under deep and early snow, with no significant change under medium and little snow conditions. Changes in climate that result in differences in snow duration, depth, and extent may therefore produce large changes in the C and N soil dynamics of alpine ecosystems.

2163^2^Yamauchi,N^Watada,AE^1998^1^Chlorophyll and xanthophyll changes in broccoli florets stored under elevated CO2 or ethylene-containing atmosphere^170^33^1^114-117^^^^^Feb^^^^^7088 m(-2)1246^1678^3216^454^601^
A^7087^Chlorophylls and xanthophylls were monitored in broccoli (Brassica oleracea L. var. italica Plen.) florets stored in air, air + 10 ppm ethylene, or 10% CO2 + 1% O-2 controlled atmosphere (CA) at 15 degrees C. Chlorophylls a and b, as measured with high-performance liquid chromatography, decreased in florets held in air. The decrease was accelerated by ethylene treatment and suppressed in CA. Chlorophyllide a and pheophorbide a were present in fresh broccoli florets, but the levels decreased significantly in all treatments during storage. The oxidized product of chlorophyll a, 13(2)- hydroxychlorophyll a, did not accumulate, Xanthophylls decreased, but new pigments, suggested to be esterified xanthophylls, formed with yellowing in stored florets. The chlorophyll degradative pathway in broccoli florets was not altered by ethylene or CA and differed from that reported for parsley (Petroselium crisum Nym.) and spinach (Spinacia oleracea L.) leaves.
^114-117^^^^^Feb^^^^^7088 m(-2)2164^6^Batts,GR^Ellis,RH^Morison,JIL^Nkemka,PN^Gregory,PJ^Hadley,P^1998^1^Yield and partitioning in crops of contrasting cultivars of winter wheat in response to CO2 and temperature in field studies using temperature gradient tunnels^178^130^^17-27^^^^^Feb^^^^^7090
1262^2344^243^312^376^467^57^58^590^977^matography, decreased in florets held in air. The decrease was accelerated by ethylene treatment and suppressed in CA. Chlorophyllide a and pheophorbide a were present in fresh broccoli florets, but the levels decreased significantly in all treatments during storage. The oxidized product of chlorophyll a, 13(2)- hydroxychlorophyll a, did not accumulate, Xanthophylls decreased, but new pigments, suggested to be esterified xanthophylls, formed with yellowing in stored florets. The chlorophyll degradative pathway in broccoli florets was not altered by ethylene or CA and differed from that reported for parsley (Petroselium crisum Nym.) and spinach (Spinacia oleracea L.) leaves.
^114-117^^^^^Feb^^^^^7088 m(-2)A^7089^Diverse cultivars of winter wheat (Triticum aestivum L.) were grown in the field in 1993/94 and 1994/95 at Reading UK in temperature gradient tunnels at normal atmospheric (c. 370) or elevated CO2 concentration (c. 700 mu mol CO2 mol(-1) air). In 1993/94, grain yield of cv. Avalon was insensitive to mean temperature (between 8.8 and 10.9 degrees C), while elevated CO2 increased yield by 1.3 t ha(-1) (12.6%). In all other cultivars, warming reduced grain yield and CO2 increased grain yield. In 1993/94, in cvs Galahad and Mercia the effects of CO2 and temperature on yield were additive. However, for cv. Hereward in both years and for cv. Soissons in 1994/95, there were negative interactions between the effects of CO2 and temperature on yield: the maximum benefit of doubling CO2 to grain yield, 4.5 and 2.7 t ha(-1) (65 and 29%) respectively, occurred at cooler temperatures; there was no benefit from doubling CO2 (i.e. 0%) once the temperature had increased above the seasonal mean by 2.2-2.6 degrees C in cv. Hereward and by 1.3 degrees C in cv. Soissons. The beneficial effect of doubling CO2 on grain yield in cvs Galahad, Hereward, Mercia and Soissons was negated by an increase in mean seasonal temperature of only 0.7-2.0 degrees C. Warming decreased root dry mass at anthesis in 1994/95 while it increased at elevated CO2 (49 and 186%, coolest and warmest regime, respectively). Carbon partitioned to roots declined progressively with warming, while at elevated CO2 there was an average of 56% increase in allocation to roots. The relative impacts of both CO2 and temperature were greater on root dry mass than on either grain yield or total above-ground biomass, while the effects on grain and biomass yield varied considerably between cultivars, suggesting that the impact of rising CO2 and temperature are likely to be dependent on cultivar.
pectively, occurred at cooler temperatures; there was no benefit from doubling CO2 (i.e. 0%) once the temperature had increased above the seasonal mean by 2.2-2.6 degrees C in 2165^6^Bucher,JB^Tarjan,DP^Siegwolf,RTW^Saurer,M^Blum,H^Hendrey,GR^1998^1^Growth of a deciduous tree seedling community in response to elevated CO2 and nutrient supply^362^36^4-5^777-782^^^^^Feb^^^^^7092
1234^376^672^2.0 degrees C. Warming decreased root dry mass at anthesis in 1994/95 while it increased at elevated CO2 (49 and 186%, coolest and warmest regime, respectively). Carbon partitioned to roots declined progressively with warming, while at elevated CO2 there was an average of 56% increase in allocation to roots. The relative impacts of both CO2 and temperature were greater on root dry mass than on either grain yield or total above-ground biomass, while the effects on grain and biomass yield varied considerably between cultivars, suggesting that the impact of rising CO2 and temperature are likely to be dependent on cultivar.
pectively, occurred at cooler temperatures; there was no benefit from doubling CO2 (i.e. 0%) once the temperature had increased above the seasonal mean by 2.2-2.6 degrees C in A^7091^In a FACE experiment, one year old alder, ash, beech, and oak seedlings were planted together in tubs containing calcareous sandy alluvial soil with or without a slow release NPK- fertilizer, and exposed to ambient and elevated CO2 concentrations (360 and 600 mu l mol(-1)) for 20 weeks. In addition to the fertilizer, all tubs received N-15-ammonium nitrate as a marker. Elevated CO2 significantly increased biomass production in alder, but had no effect on oak and ash. In beech, due to disease and mortality in all treatments, any possible effects were obscured. The addition of fertilizer had no effect on biomass production in alder, but increased production in oak and ash significantly. In oak a treatment synergism may be present. The non-appearance of a synergistic CO2 and fertilizer effect in alder may be explained by a fertilizer induced reduction of the N-fixing root-nodule biomass concurrent with a switch of the N-assimilation from atmospheric N to soil N supply, as the delta(15)N measurements in the leaves of alder as opposed to oak indicate. Although elevated CO2 resulted in a significant biomass increase in alder, it did not lead to an appreciable increase in the proportional presence of the species as measured on total plant biomass in the tub. Increasing the nutrient supply in the soil, however, did lead to appreciable gains in the proportional presence of oak and ash.

2166^5^Chen,K^Hu,GQ^Keutgen,N^Blanke,M^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. II. Leaf photosynthetic function^292^71^5-6^173-178^^^^^Dec^^^^^7094
312^344^374^417^493^508^ addition of fertilizer had no effect on biomass production in alder, but increased production in oak and ash significantly. In oak a treatment synergism may be present. The non-appearance of a synergistic CO2 and fertilizer effect in alder may be explained by a fertilizer induced reduction of the N-fixing root-nodule biomass concurrent with a switch of the N-assimilation from atmospheric N to soil N supply, as the delta(15)N measurements in tA^7093^Two-week-old strawberry (Fragaria x ananassa Duch, cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 days. An elevated CO2 concentration up to 750 ppm reduced total chlorophyll, chlorophyll a and chlorophyll b contents as well as the a/b ratio. Long-term CO2 enrichment induced leaf senescence and decreased photosynthetic efficiency as well as photochemical conversion efficiency of PS II. Intercellular CO2 concentration significantly increased with CO2 enrichment. Stomatal conductance, transpiration rate, and net photosynthesis rate of young leaves increased with raising CO2 concentrations. However, CO2 levels above 600 ppm markedly reduced net photosynthetic rate of adult and old leaves. High CO2 concentrations up to 900 ppm did not significantly affect dark respiration rate of the leaves. Photosynthetic water-use efficiency was highest in old leaves and lowest in young ones. Increased CO2 concentrations up to 600-750 ppm improved leaf photosynthetic capacity by increasing photosynthetic water-use efficiency.

2167^4^Chen,K^Hu,GQ^Keutgen,N^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. I. Plant Growth analysis^292^71^5-6^168-172^^^^^Dec^^^^^7096
3217^ total chlorophyll, chlorophyll a and chlorophyll b contents as well as the a/b ratio. Long-term CO2 enrichment induced leaf senescence and decreased photosynthetic efficiency as well as photochemical conversion efficiency of PS II. Intercellular CO2 concentration significantly increased with CO2 enrichment. Stomatal conductance, transpiration rate, and net photosynthesis rate of young leaves increased with raising CO2 concentrations. However, CO2 levels above 600 ppm markedly reduced net photosynthetic rate of adult and old leaves. High CO2 concentrations up to 900 ppm did not significantly affect dark respiration rate of the leaves. Photosynthetic water-use efficiency was highest in old leaves and lowest in young ones. Increased CO2 concentrations up to 600-750 ppm improved leA^7095^Two-week-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 days, Elevated CO2 promoted plant growth as indicated by a higher number of leaves, runners and daughter plants, larger leaf area index and dry mass per unit leaf area, increased total length of runners, plant height, canopy diameter, and enhanced daily growth of leaf area, runner and plant biomass. In contrast, specific leaf area and leaf area ratio of the plants decreased with increasing CO2 concentration, whereas neither average leaf area nor average runner length was significantly affected by CO2 enrichment. When compared with the 300 ppm CO2 treatment, 600 and 900 ppm CO2-treated plants led to a daily increment of 1.6 and 1.9 total leaf area, 1.1 and 1.8 total runner length, and 2.5 and 3.9 plant biomass, respectively, Increased CO2 concentration from 300 to 600 and 750 ppm markedly accelerated both relative growth rate and net assimilation rate of the plants. Leaf weight ratio and root weight ratio were significantly higher, while stem weight ratio was significantly lower above 600 ppm CO2 as a result of proportionally more biomass allocated to leaves and roots than to stems. Apart from an enhancement of plant growth, the long-term CO2 enrichment boosted vegetative propagation of strawberry plants as well. From an economical point of view, however, it is more efficient to use elevated CO2 concentrations of up to 600-750 ppm rather than 900 ppm for greenhouse cultivation of strawberry.

2168^4^Chen,K^Hu,GQ^Keutgen,N^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. III. Dry matter production and water consumption^292^71^5-6^179-182^^^^^Dec^^^^^7098
1096^374^377^417^672^ated plants led to a daily increment of 1.6 and 1.9 total leaf area, 1.1 and 1.8 total runner length, and 2.5 and 3.9 plant biomass, respectively, Increased CO2 concentration from 300 to 600 and 750 ppm markedly accelerated both relative growth rate and net aA^7097^Two-week-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 days. Elevated CO2 concentrations enhanced dry matter production, the root/shoot ratio and total water consumption of the plants. High CO2 promoted total dry matter increment and total leaf area increment of the plants, and improved dry matter- production efficiency and plant water-use efficiency. Water- consumption rate of plants and water-uptake efficiency of roots, however, declined at CO2-enriched conditions. In comparison with the 300 ppm CO2 treatment, 600 and 900 ppm CO2- grown plants increased dry matter-production efficiency by 37 % and 67 %, water-use efficiency by 137 % and 272 %, while reduced water-consumption rate by 39 % and 55 %, and water- uptake efficiency of roots by 53 % and 76 %, respectively. Increasing CO2 concentrations from 300 to 900 ppm enabled strawberry plants to produce dry matter more efficiently and to use soil water more economically because it reduced the impact of water stress on plant productivity.

2169^3^Chen,K^Hu,GQ^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. IV. Carbohydrate production and accumulation^292^71^5-6^183-188^^^^^Dec^^^^^7100
1096^312^376^ter consumption of the plants. High CO2 promoted total dry matter increment and total leaf area increment of the plants, and improved dry matter- production efficiency and plant water-use efficiency. Water- consumption rate of plants and water-uptake efficiency of roots, however, declined at CO2-enriched conditions. In comparison with the 300 ppm CO2 treatment, 600 and 900 ppm CO2- grown plants increased dry matter-production efficiency by 37 % and 67 %, water-use efficiency by 137 % and 272 %, while reduced water-consumption rate by 39 % and 55 %, and water- uptake efficiency of roots by 53 % and 76 %, respectively. Increasing CO2 concentrations from 300 to 900 ppm enabled strawberry plants to produce dry matter more efficiently and to A^7099^Two-week-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 days. Increasing CO2 concentration from 300 to 900 ppm promoted carbohydrate production of the plants, and subsequently increased carbohydrate accumulation in the plant organs, especially starch in leaves. Relative distribution of non- structural carbohydrates decreased in leaves and stems at 750 and 900 ppm CO2, increased in roots from 300 to 750 ppm CO2. Elevating CO2 concentration from 300 to 750 ppm reduced the proportions of glucose, fructose, and sucrose, but raised the proportion of starch in non-structural carbohydrates of the plants, as well as increased starch/sucrose ratio in leaves, stems, and whole plants. CO2 enrichment up to 900 ppm improved carbohydrate-production efficiency of the plants. This effect was particularly pronounced for starch. In comparison with 300 ppm CO2-grown plants, those treated by 600 and 900 ppm CO2 raised starch-, glucose-, fructose-, sucrose-, and non- structural carbohydrate-production efficiency by 2.6 and 16.1 fold, 1.6 and 2.1 fold, 0.6 and 1.0 fold, 0.8 and 1.6 fold, and 1.2 and 3.5 fold, respectively.

2170^3^Chen,K^Hu,GQ^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. V. Macronutrient uptake and utilization^292^71^5-6^189-194^^^^^Dec^^^^^7102
224^372^374^376^386^57^672^705^92^ non- structural carbohydrates decreased in leaves and stems at 750 and 900 ppm CO2, increased in roots from 300 to 750 ppm CO2. Elevating CO2 concentration from 300 to 750 ppm reduced the proportions of glucose, fructose, and sucrose, but raised the proportion of starch in non-structural carbohydrates of the plants, as well as increased starch/sucrose ratio in leaves, stems, and whole plants. CO2 enrichment up to 900 ppm improved carbohydrate-production efficiency of the plants. This effect was particularly pronounced for starch. In comparison with 300 ppm CO2-grown plants, those treated by 600 and 900 ppm CA^7101^Two-week-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 days. Raising CO2 concentration from 300 to 900 ppm promoted macronutrient accumulation in all organs of the plants, particularly in roots. It, however, reduced contents of macronutrients in most organs of the plants, especially in leaves, because of the dilution effect of larger amounts of carbohydrate accumulation in the plant organs. When compared with the 300 ppm CO2 treatment, 600 and 900 ppm CO2 increased accumulation of N by 93 % and 87 %, P by 113 % and 122 %, K by 98 % and 92 %, Ca by 212 % and 244 %, and Mg by 177 % and 200 %, respectively CO2 enrichment decreased the proportions of N and K, increased those of Ca and Mg, but did not affect the proportion of P in the plants. Increasing CO2 levels depressed macronutrient-uptake efficiency of the plant roots, but promoted macronutrient-use efficiency of the plants. In comparison with the 300 ppm CO2-treated plants, those treated with 600 and 900 ppm CO2 showed lower N-, P-, K-, Ca, and Mg- uptake efficiency of the roots and higher N-, P-, K-, Ca-, and Mg-use effficiency of the plants.

2171^3^Chen,K^Hu,GQ^Lenz,F^1997^1^Effects of CO2 concentration on strawberry. VI. Fruit yield and quality^292^71^5-6^195-200^^^^^Dec^^^^^7104
376^ents in most organs of the plants, especially in leaves, because of the dilution effect of larger amounts of carbohydrate accumulation in the plant organs. When compared with the 300 ppm CO2 treatment, 600 and 900 ppm CO2 increased accumulation of N by 93 % and 87 %, P by 113 % and 122 %, K by 98 % and 92 %, Ca by 212 % and 244 %, and Mg by 177 % and 200 %, respectively CO2 enrichment decreased the proportions of N and K, increased those of Ca and Mg, but did not affect the proportion of P in the plants. Increasing CO2 levels depressed macronutrient-uptake efficiency of the plant roots, but promoted macronutrient-use efficiency of the plants. In comparisoA^7103^Two-week-old strawberry (Fragaria x ananassa Duch. cv. 'Elsanta') plants were acclimatized to 300, 450, 600, 750 or 900 ppm CO2 in controlled environment chambers for 50 and 60 days during vegetative growth in late autumn of 1995 and reproductive growth in early spring of 1996. High CO2 promoted branch-crown and pedicel development as well as flower-bud differentiation. It also induced a second bloom. Flowering and fruit ripening started earlier and lasted for a longer period under high rather than low CO2 concentrations. CO2 enrichment shortened the periods of anthesis and single fruit growth but prolonged the periods of flowering and fruit harvest. Elevated CO2 concentrations enhanced fruit productivity as indicated by increases in pedicel number per plant, fruit setting per pedicel, fruit size, and dry matter content of the fruits. In comparison with the 300 ppm CO2 treatment, 450, 600, 750, and 900 ppm CO2 increased average fruit yield per plant by 0.7, 2.7, 3.6, and 4.1 fold, daily growth per fresh fruit by 0.4, 1.0, 1.1, and 1.3 fold, and growth rate of fruit biomass per plant by 1.0, 3.9, 5.5, and 6.9 fold, respectively. High CO2 tended to improve fruit quality as well. Raising CO2 concentrations accelerated dry matter increment and total sugar accumulation in the fruits, especially for sucrose, and decreased titratable acid content, resulting in a higher sugar/acid ratio of the fruits. Contents of starch and minerals in the fruits slightly decreased when CO2 rose.

2172^3^Cheng,SH^Moore,BD^Seemann,JR^1998^1^Effects of short- and long-term elevated CO2 on the expression of ribulose-1,5-bisphosphate carboxylase/oxygenase genes and carbohydrate accumulation in leaves of Arabidopsis thaliana (L) Heynh^8^116^2^715-723^^^^^Feb^^^^^7106
1026^1699^1826^1871^2000^243^2557^3218^3219^786^l, fruit size, and dry matter content of the fruits. In comparison with the 300 ppm CO2 treatment, 450, 600, 750, and 900 ppm CO2 increased average fruit yield per plant by 0.7, 2.7, 3.6, and 4.1 fold, daily growth per freA^7105^To investigate the proposed molecular characteristics of sugar- mediated repression of photosynthetic genes during plant acclimation to elevated CO2, we examined the relationship between the accumulation and metabolism of,nonstructural carbohydrates and changes in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) gene expression in leaves of Arabidopsis thaliana exposed to elevated CO2. Long-term growth of Arabidopsis at high CO2 (1000 mu L L-1) resulted in a 2-fold increase in nonstructural carbohydrates, a large decrease in the expression of Rubisco protein and in the transcript of rbcL, the gene encoding the large subunit of Rubisco (approximately 35-40%), and an even greater decline in mRNA of rbcS, the gene encoding the small subunit (approximately 60%). This differential response of protein and mRNAs suggests that transcriptional/posttranscriptional processes and protein turnover may determine the final amount of leaf Rubisco protein at high CO2. Analysis of mRNA levels of individual rbcS genes indicated that reduction in total rbcS transcripts was caused by decreased expression of all four rbcS genes. Short-term transfer of Arabidopsis plants grown at ambient CO2 to high CO2 resulted in a decrease in total rbcS mRNA by d 6, whereas Rubisco content and rbcL mRNA decreased by d 9. Transfer to high CO2 reduced the maximum expression level of the primary rbcS genes (1A and, particularly, 3B) by limiting their normal pattern of accumulation through the night period. The decreased nighttime levels of rbcS mRNA were associated with a nocturnal increase in leaf hexoses. We suggest that prolonged nighttime hexose metabolism resulting from exposure to elevated CO2 affects rbcS transcript accumulation and, ultimately, the level of Rubisco protein.

2173^2^Curtis,PS^Wang,XZ^1998^1^A meta-analysis of elevated CO2 effects on woody plant mass, form, and physiology^2^113^3^299-313^^^^^Feb^^^^^7108
1074^1342^1344^1633^1660^2489^256^377^419^595^protein at high CO2. Analysis of mRNA levels of individual rbcA^7107^Quantitative integration of the literature on the effect of elevated CO2 on woody plants is important to aid our understanding of forest health in coming decades and to better predict terrestrial feedbacks on the global carbon cycle. We used meta-analytic methods to summarize and interpret more than 500 reports of effects of elevated CO2 on woody plant biomass accumulation and partitioning, gas exchange, and leaf nitrogen and starch content. The CO2 effect size metric we used was the log-transformed ratio of elevated compared to ambient response means weighted by the inverse of the variance of the log ratio. Variation in effect size among studies was partitioned according to the presence of interacting stress factors, length of CO2 exposure, functional group status, pot size, and type of CO2 exposure facility. Both total biomass (WT) and net CO2 assimilation (A) increased significantly at about twice ambient CO2, regardless of growth conditions. Low soil nutrient availability reduced the CO2 stimulation of WT by half, from + 31 % under optimal conditions to + 16 %, while low light increased the response to + 52 %. We found no significant shifts in biomass allocation under high CO2. Interacting stress factors had no effect on the magnitude of responses of A to CO2, although plants grown in growth chambers had significantly lower responses (+ 19 %) than those grown in greenhouses or in open-top chambers (+ 54 %). We found no consistent evidence for photosynthetic acclimation to CO2 enrichment except in trees grown in pots < 0.51 (- 36 %) and no significant CO2 effect on stomatal conductance. Both leaf dark respiration and leaf nitrogen were significantly reduced under elevated CO2 (- 18 % and - 16 % respectively, data expressed on a leaf mass basis), while leaf starch content increased significantly except in low nutrient grown gymnosperms. Our results provide robust, statistically defensible estimates of elevated CO2 effect sizes against which new results may be compared or for use in forest and climate model parameterization.

2174^2^De Angelis,P^Scarascia-Mugnozza,GE^1998^1^Long-term CO2-enrichment in a Mediterranean natural forest: An application of large open top chambers^362^36^4-5^763-770^^^^^Feb^^^^^7110
227^312^372^374^529^660^672^de of responses of A to CO2, although plants grown in growth chambers had significantly lower responses (+ 19 %) than those grown in greenhouses or in open-top chambers (+ 54 %). We found no consistent evidence for photosynthetic acclimation to CO2 enrichment except in trees grown in pots < 0.51 (- 36 %) and no significant CO2 effect on stomatal conductance. Both leaf dark respiration and leaf nitrogen were significantly reduced under elevated CO2 (- 18 % and - 16 % respectively, data expressed on a leaf mass basis), while leaf starch content increased significantly except in low nutrient grown gymnosperms. Our results provide robust, statistically defensible estimates of elevated CO2 effect sizes against which new results may be compared or for use in forest and climate mA^7109^It is crucial to be able to anticipate the possible effects of environmental changes on the Mediterranean woodland communities given their essential role on protecting lands that are under a strong pressure by man and climate. Predictions of the effects of increasing CO2 concentration on plants have been inferred by short- and long-term studies, conducted at different scales and by different technologies. Open Top Chambers (OTCs) are experimental facilities that have been widely used to expose field grown plants to different pollutant gases, and more recently to elevated [CO2]. In this paper, we present the natural site and the experimental system (six large OTCs enclosing clumps of natural vegetation) that we have been utilizing for 3 years, to assess the impact of elevated [CO2] on a Mediterranean natural forest community. The results show that large OTCs can be usefully used to simulate CO2 doubling even under the harsh environmental conditions of the mediterranean region. (C) 1998 Elsevier Science Ltd.

2175^6^Elhottova,D^Triska,J^Santruckova,H^Kveton,J^Santrucek,J^Simkova,M^1997^1^Rhizosphere microflora of winter wheat plants cultivated under elevated CO2^206^197^2^251-259^^^^^Dec^^^^^7112
244^2689^3220^344^374^427^92^mate. Predictions of the effects of increasing CO2 concentration on plants have been inferred by short- and long-term studies, conducted at different scales and by different technologies. Open Top Chambers (OTCs) are experimental facilities that have been widely used to expose field grown plants to different pollutant gases, and more recently to elevated [CO2]. In this paper, we present the natural site and the experimental system (six large OTCs enclosing clumps of natural vegetation) that we have been utilizing for 3 years, to assess the impact of elevated [CO2] on a Mediterranean natural forest community. The results show that large OTCs can be usefully used to simulate CO2 doubling even under the harsh environmental conditions of the mediterranean region. (C) 1998 Elsevier ScienceA^7111^We studied an effect of elevated atmospheric CO2 on rhizosphere microorganisms in a hydroponics system where young wheat plants provided the only source of C for microorganisms. Plants were cultivated in mineral solution in sterile silica sand and exposed to control (ambient) and elevated (double) CO2 concentrations for periods of 13, 20, 25 and 34 days. Microbial biomass C (C content in fraction of size 0.3-2.7 mu m) was not affected by the elevated CO2 concentration during the first 25 days of plant growth and was increased after 34 days of plant growth. A content of poly-beta-hydroxybutyrate (PHB) reserve compounds (measured as derivatized product of 3-hydroxy-butyric acid and N-tert-butyldimethylsilyl-N-methyltrifluoracetamide using GC-MS) was lowered significantly (p<0.001) in the elevated CO2 after 25 and 34 days. It was accompanied with a shift of bacterial distribution towards the nutritional groups utilising more complex organic material (number of CFUs on media with different sources of C and N). A coincidence of several events connected with plant and microbial carbon economy (decrease of an assimilation rate and relative growth rate of plants, small increase of microbial biomass, PHB decrease and suppression within the bacterial nutritional group requiring the most readily available source of C and energy) was observed in the system under elevated CO2 on the 25th day. A modification of the CC-MS method for the detection of low levels of PHB compounds in natural samples was developed. We excluded the lipids fractionation step and we used EI MS/MS detection of the main fragment ions of the derivatized compound. This guarantees that the ion profiles have high signal-to-noise ratio at correct retention time. The detection limit is then about 30 pg g(-1) of sand or soil. The rhizosphere microflora responded very sensitively to the short- term changes in C partitioning in plants caused by the elevated CO2.
lising more complex organic material (number of CFUs on media with different sources of C an2176^4^Gary,C^Bertin,N^Frossard,JS^Le Bot,J^1998^1^High mineral contents explain the low construction cost of leaves, stems and fruits of tomato plants^78^49^318^49-57^^^^^Jan^^^^^7114
130^3221^3222^3223^372^389^521^662^867^92^in the bacterial nutritional group requiring the most readily available source of C and energy) was observed in the system under elevated CO2 on the 25th day. A modification of the CC-MS method for the detection of low levels of PHB compounds in natural samples was developed. We excluded the lipids fractionation step and we used EI MS/MS detection of the main fragment ions of the derivatized compound. This guarantees that the ion profiles have high signal-to-noise ratio at correct retention time. The detection limit is then about 30 pg g(-1) of sand or soil. The rhizosphere microflora responded very sensitively to the short- term changes in C partitioning in plants caused by the elevated CO2.
lising more complex organic material (number of CFUs on media with different sources of C anA^7113^The construction cost of plant tissues is used in crop models to convert the products of photosynthesis into biomass. As for other greenhouse crops, tomato tissues are specific in that they have a high mineral content. The consequences of this accumulation of minerals on the construction cost of the tissues and the possible interactions with the physiological age of the organs and with the CO2 concentration in the atmosphere was examined. For that purpose, three methods of estimating the construction cost were used and compared. Large quantities of minerals accumulated in the tissues of tomato plants (ranging from 0.05 in fruits to 0.26 g g(-1) DM in leaves). The subsequent dilution of the organic matter explained why the estimated construction cost of the dry matter (organic matter + minerals) was fairly low in comparison to that of other crop species. The construction cost was higher in fruits than in vegetative organs, partly because of a lower mineral content. It decreased by 7-12% from top to bottom of the canopy, following the increase in the physiological age of the tissues. This ontogenic drift was partly explained by the accumulation of minerals in the older organs. In the conditions of CO2 enrichment of a commercial greenhouse, no effect of CO2 concentration on the mineral content and on the construction cost of tissues was observed. Such a variability of the construction cost of tomato plant tissues due to the accumulation of minerals or to the ontogeny questions the use of standard values in crop models.

2177^3^Heagle,AS^Miller,JE^Booker,FL^1998^1^Influence of ozone stress on soybean response to carbon dioxide enrichment: I. Foliar properties^164^38^1^113-121^^^^^Jan-Feb^^^^^7116
1023^1025^1262^1702^3224^372^384^456^92^965^nstruction cost of the dry matter (organic matter + minerals) was fairly low in comparison to that of other crop species. The construction cost was higher in fruits than in vegetative organs, partly because of a lower mineral content. It decreased by 7-12% from top to botA^7115^Tropospheric O-3 can cause foliar injury, decreased growth, and decreased yield, whereas CO2 enrichment generally causes opposite effects. Little is known about plant response to mixtures of O-3 and CO2. Open-top field chambers were ere used to determine if foliar responses of soybean [Glycine max (L.) Merr.] to CO2 enrichment are affected by O-3 stress and vice versa. Plants were grown in 14-L pots and exposed to four CO2 and three O-3 concentrations in 12 combinations. The CO2 treatments were ambient (366 mu L L-1) and three treatments with CO2 added for 24 h d(-1) at approximately 1.3, 1.6, and 2.0 times ambient. The O-3 treatments were charcoal-filtered air (CF), nonfiltered air (NF), and NF with O-3 added for 12 h d(-1) (NF+), resulting in seasonal concentrations of approximately 20, 46, and 75 nL L-1. Foliar effects of CO2 enrichment were dependent on the amount of stress caused by O-3 In the CF treatment, plants were not stressed by O-3, and CO2 enrichment caused chlorosis and decreased chlorophyll. In the IVF and NF+ treatments, plants were stressed by O-3, and CO2 enrichment suppressed chlorosis and increased chlorophyll. Ozone decreased specific leaf weight, increased foliar N and C, and decreased C/N ratios, whereas CO2 caused opposite responses for these measures. Ozone increased foliar S and B but did not affect P or K concentrations. Conversely, CO2 enrichment suppressed foliar S, B, P, and K concentrations. These interactions between O-3 and CO2 emphasize a need to consider the amount of plant stress caused by O-3 in studies to measure effects of CO2 enrichment.

2178^3^Heagle,AS^Miller,JE^Pursley,WA^1998^1^Influence of ozone stress on soybean response to carbon dioxide enrichment: III. Yield and seed quality^164^38^1^128-134^^^^^Jan-Feb^^^^^7118
174^1828^264^580^92^ately 20, 46, and 75 nL L-1. Foliar effects of CO2 enrichment were dependent on the amount of stress caused by O-3 In the CF treatment, plants were not stressed by O-3, and CO2 enrichment caused chlorosis and decreased chloropA^7117^Ozone in the troposphere can cause plant stress, whereas elevated CO2 generally causes positive responses. Little is known of how these gases interact to affect plant response. Interactive effects on yield and seed quality of soybean [Glycine max (L.) Merr.] grown in 14-L pots were measured in open-top field chambers. Essex was tested in 1993, and Essex, Holladay, and NK 6955 were tested in 1994. Plants were exposed from emergence to maturity to four CO2 levels (ambient and 1.3, 1.6, and 2.0 times ambient) and three O-3 levels (0.4, 0.9, and 1.5 times ambient) in 12 combinations. Increasing O-3 suppressed growth and yield, whereas CO2 enrichment stimulated growth and yield. Carbon dioxide-induced stimulation was greater for plants stressed by O-3 than for non stressed plants. For example, CO2 at 2.0 times ambient increased 2-yr mean seed yield of Essex by 16, 24, and 81% at O-3 levels of O.4, 0.9, and 1.5 times ambient, respectively. Effects of O-3 and CO2 on seed oil content were variable with numerous cultivar differences. Seed protein content was never affected. Elevated O-3 suppressed oleic acid content in seeds, whereas CO2 increased it; the nature of the O-3 x CO2 interaction for oleic acid was similar to that observed for most yield measures. Carbon dioxide-induced stimulation of plants stressed by O-3 was apparently caused partly by amelioration of O-3 stress. Interactions between O-3 and CO2 must be considered for proper interpretation of cause-effect relationships in CO2 enrichment studies.

2179^10^Karnosky,DF^Podila,GK^Gagnon,Z^Pechter,P^Akkapeddi,A^Sheng,Y^Riemenschneider,DE^Coleman,MD^Dickson,RE^Isebrands,JG^1998^1^Genetic control of responses to interacting tropospheric ozone and CO2 in Populus tremuloides^362^36^4-5^807-812^^^^^Feb^^^^^7120
2054^264^3225^3226^344^423^58^633^738^92^ 2.0 times ambient increased 2-yr mean seed yield of Essex by 16, 24, and 81% at O-3 levels of O.4, 0.9, and 1.5 times ambient, respectively. Effects of O-3 and CO2 on seed oil content were variable with numeroA^7119^We exposed trembling aspen (Populus tremuloides Michx.) clones differing in tropospheric ozone (O-3) tolerance in various open-top chamber studies for three growing seasons, and examined the effects of O-3, CO2, and O-3 + CO2 on growth and physiological processes. Ozone in the range of 80 ppm hr (Sum 00) per growing season decreased height, diameter, and stem and leaf biomass slightly in a tolerant clone but severely in a sensitive clone. Elevated CO2 (150 ppm over ambient) did not compensate for the O-3 effects. Antioxidant enzyme analysis showed elevated SOD levels in the tolerant clone but not in the sensitive clone following O-3 exposure. Northern blot analysis indicated that the chloroplastic and cytosolic Cu/Zn SOD's were significantly increased in response to O-3 in the tolerant but not the sensitive clone. Currently, we are conducting molecular analysis to determine the functional significance of SOD's in regulating O-3 tolerance in aspen. (C) 1997 Elsevier Science Ltd.
e variable with numero2180^4^Kurz,C^Schmieden,U^Strobel,P^Wild,A^1998^1^The combined effect of CO2, ozone, and drought on the radical scavenging system of young oak trees (Quercus petraea) - A phytothron study^362^36^4-5^783-788^^^^^Feb^^^^^7122
1064^1262^2651^3227^3228^3229^361^425^443^446^
A^7121^In order to study the combined effects of CO2, ozone, and drought, we simulated in a controlled environment the climatic conditions of a German oak stand with high ozone (daytime: 80 ppb, control: 20 ppb) during one vegetative period under a regime of low and high CO2 concentration (370 vs 720 ppm) and drought (4 weeks < -800 hPa). To investigate the effects of CO2, ozone and drought on the radical scavenging system, we monitored the level of glutathione, ascorbate, and a- tocopherol. However, it is important that, under the regime of elevated CO2, the antioxidative behaviour of glutathione and ascorbate appears to be masked by their function as storage molecules for sulfur or carbon. (C)1998 Elsevier Science Ltd.
variable with numero2181^5^Lussenhop,J^Treonis,A^Curtis,PS^Teeri,JA^Vogel,CS^1998^1^Response of soil biota to elevated atmospheric CO2 in poplar model systems^2^113^2^247-251^^^^^Jan^^^^^7124
1096^1334^312^3230^3231^376^535^57^797^92^^^^^7122
1064^1262^2651^3227^3228^3229^361^425^443^446^
A^7121^In order to study the combined effects of CO2, ozone, and drought, we simulated in a controlled environment the climatic conditions of a German oak stand with high ozone (daytime: 80 ppb, control: 20 ppb) during one vegetative period under a regime of low and high CO2 concentration (370 vs 720 ppm) and drought (4 weeks < -800 hPa). To investigate the effects of CO2, ozone and drought on the radical scavenging system, we monitored the level of glutathione, ascorbate, and a- tocopherol. However, it is important that, under the regime of elevated CO2, the antioxidative behaviour of glutathione and ascorbate appears to be masked by their function as storage molecules for sulfur or carbon. (C)1998 Elsevier Science Ltd.
variable with numeroA^7123^We tested the hypotheses that increased belowground allocation of carbon by hybrid poplar saplings grown under elevated atmospheric CO2 would increase mass or turnover of soil biota in bulk but not in rhizosphere soil. Hybrid poplar saplings (Populus x euramericana cv. Eugenei) were grown for 5 months in open-bottom root boxes at the University of Michigan Biological Station in northern, lower Michigan. The experimental design was a randomized-block design with factorial combinations of high or low soil N and ambient (34 Pa) or elevated (69 Pa) CO2 in five blocks. Rhizosphere microbial biomass carbon was 1.7 times greater in high-than in low-N soil, and did not respond to elevated CO2. The density of protozoa did not respond to soil N but increased marginally (P < 0.06) under elevated CO2. Only in high-N soil did arbuscular mycorrhizal fungi and microarthropods respond to CO2. In high-N soil, arbuscular mycorrhizal root mass was twice as great, and extramatrical hyphae were 11% longer in elevated than in ambient CO2 treatments. Microarthropod density and activity were determined in situ using minirhizotrons. Microarthropod density did not change in response to elevated CO2, but in high-N soil, microarthropods were more strongly associated with fine roots under elevated than ambient treatments. Overall, in contrast to the hypotheses, the strongest response to elevated atmospheric CO2 was in the rhizosphere where (1) unchanged microbial biomass and greater numbers of protozoa (P < 0.06) suggested faster bacterial turnover, (2) arbuscular mycorrhizal root length increased, and (3) the number of microarthropods observed on fine roots rose.

2182^4^Manderscheid,R^Bender,J^Schenk,U^Weigel,HJ^1997^1^Response of biomass and nitrogen yield of white clover to radiation and atmospheric CO2 concentration^173^38^2^131-143^^^^^Nov^^^^^7126
1262^1345^1958^1960^2742^312^372^431^507^728^ to CO2. In high-N soil, arbuscular mycorrhizal root mass was twice as great, and extramatrical hyphae were 11% longer in elevated thanA^7125^The objectives of the present study were to test (i) whether the effect of season-long CO2 enrichment on plant dry matter production of white clover (Trifolium repens cv. Karina) depends on the temperature or can solely be explained by changes in radiation use efficiency, and (ii) whether the atmospheric CO2 concentration affects the relationship between tissue %N and plant biomass. Plants were grown in pots with adequate nutrient and water supply and were exposed to ambient and above ambient CO2 concentrations (approximately + 80 ppm, + 160 ppm, + 280 ppm) in open-top chambers for two seasons. Nitrogen fertilizer was given only before the experiment started to promote N-2 fixation. Plants were clipped to a height of 5 cm, when the canopy had reached a height of about 20 cm and when the CO2 effect had not been diminished due to self-shading of the leaves. Photon exposure (400-700 nm) measured above the canopy was linearly related to the above ground biomass, the leaf area index and the nitrogen yield (r(2)>0.94). The slopes of the curves depended on the CO2 concentration. Since most of the radiation (>90%) was absorbed by the foliage, the slopes were used to calculate the CO2 effect on the radiation use efficiency of biomass production, which is shown to increase curvilinearly between 380 and 660 ppm CO2 from 2.7 g MJ(-1) to 3.9 g MJ(-1). CO2 enrichment increased above ground biomass by increasing the leaf number, the individual leaf weight and the leaf area; specific leaf weight was not affected. The relative CO2 response varied between harvests; there was a slight but not significant positive relationship with mean daytime temperature. At the beginning of the season, plant nitrogen concentration in the above ground biomass was decreased by CO2 enrichment. However, at later growth stages, when the plants depended solely on N-2 fixation, nitrogen concentration was found to be increased when the nitrogen concentration value was adjusted for the decrease due to the higher biomass of the plants exposed to elevated CO2. (C) 1997 Elsevier Science B.V.

2183^2^Meier,M^Fuhrer,J^1997^1^Effect of elevated CO2 on orchard grass and red clover grown in mixture at two levels of nitrogen or water supply^173^38^3^251-262^^^^^Dec^^^^^7128
1021^2394^2742^312^3232^344^376^386^436^506^urvilinearly between 380 and 660 ppm CO2 from 2.7 g MJ(-1) to 3.9 g MJ(-1). CO2 enrichment increased above ground biomass by increasing the leaf number, the individual leaf weight and the leaf area; specific leaf weight was not affected. The relative CO2 response varied between harvests; there was a slight but not significant positive relationship with mean daytime temperature. At the beginning of the season, plant nitrogen concentration in the above ground biomass was decreased by CO2 enrichment. However, at later growth stages, when the plants depended solely on N-2 fixation, nitrogen concentration was found to be increased when the nitrogen concentration value was adjusted for the decrease due to the higher biomass of the plants exposed to eA^7127^A mixture of orchard grass (Dactylis glomerata L.) and red clover (Trifolium pratense L.) was grown in microcosms at either ambient (40 Pa) or elevated CO2 (78 Pa) and supplied with two levels of nitrogen (N) or two levels of irrigation. The aim was to study how reduced N or water supply affect the CO2 response of shoot and root growth, in relationship to changes in the plant C/N ratio. Plant growth was monitored non- destructively, and shoot dry mass was determined after 41 days (first growth period) and after 67 days (second growth period). Stubble and root dry mass, and C/N ratios in roots and shoots were measured only after regrowth. Elevated CO2 continuously stimulated growth of the mixture, and increased the shoot biomass in the absence of N or water limitations without changing the shoot/root dry weight ratio, nor the C/N ratio. The CO2-effect on orchard grass tended to be stronger than the effect on red clover, and was more pronounced during the first as compared to the second growth period. At low N, yield of red clover showed the stronger CO2 response, whereas with reduced water supply the relative CO2-stimulation of shoot biomass in orchard grass was more pronounced. Both low-N and reduced water supply decreased shoot, root, and stubble biomass, decreased the shoot/root ratio, and increased the C/N ratio. Elevated CO2 reduced negative effects of limited N or water supply on shoot growth, but the positive CO2 effect at low N declined with time. The interaction between CO2 and N was most pronounced for stubble mass, whereas the interaction between CO2 and reduced water supply was only significant for root mass. It is concluded that changes in shoot/root ratio are mainly caused by low N and reduced water supply via changes in the N-status of the plant, and that elevated CO2 has little effect on the shoot/root ratio, but tends to reduce negative effects of limiting N and water on growth. (C) 1997 Published by Elsevier Science B.V.
ounced during the first as compared to the second growth period. A2184^5^Miglietta,F^Bettarini,I^Raschi,A^Korner,C^Vaccari,FP^1998^1^Isotope discrimination and photosynthesis of vegetation growing in the Bossoleto CO2 spring^362^36^4-5^771-776^^^^^Feb^^^^^7130
427^ced water supply decreased shoot, root, and stubble biomass, decreased the shoot/root ratio, and increased the C/N ratio. Elevated CO2 reduced negative effects of limited N or water supply on shoot growth, but the positive CO2 effect at low N declined with time. The interaction between CO2 and N was most pronounced for stubble mass, whereas the interaction between CO2 and reduced water supply was only significant for root mass. It is concluded that changes in shoot/root ratio are mainly caused by low N and reduced water supply via changes in the N-status of the plant, and that elevated CO2 has little effect on the shoot/root ratio, but tends to reduce negative effects of limiting N and water on growth. (C) 1997 Published by Elsevier Science B.V.
ounced during the first as compared to the second growth period. AA^7129^The Bossoleto CO2 spring emits CO2 which has a stable carbon isotopic ratio (delta(13)C = -8 parts per thousand). We determined delta(13)C on leaves of several individual species growing in Bossoleto and in a nearby control site at ambient CO2. delta(13)C was 6% more negative in leaves of species collected from the grassland community of Bossoleto, indicating increased discrimination (Delta) against the heavy carbon isotope. No such changes were found in ruderal species growing in the same spring, suggesting that photosynthetic capacity was much less affected. Delta was substantially increased under elevated CO2 in leaves of Quercus pubescens but not in Quercus ilex, which also did not show any increase in non-structural carbohydrates. Gas-exchange measurements made on Plantago lanceolata, supported the view that photosynthetic capacity is decreased in plants grown under elevated CO2 and on poor soils. (C) 1998 Elsevier Science Ltd.

ounced during the first as compared to the second growth period. A2185^3^Miller,JE^Heagle,AS^Pursley,WA^1998^1^Influence of ozone stress on soybean response to carbon dioxide enrichment: II. Biomass and development^164^38^1^122-128^^^^^Jan-Feb^^^^^7132
1262^344^580^92^to and in a nearby control site at ambient CO2. delta(13)C was 6% more negative in leaves of species collected from the grassland community of Bossoleto, indicating increased discrimination (Delta) against the heavy carbon isotope. No such changes were found in ruderal species growing in the same spring, suggesting that photosynthetic capacity was much less affected. Delta was substantially increased under elevated CO2 in leaves of Quercus pubescens but not in Quercus ilex, which also did not show any increase in non-structural carbohydrates. Gas-exchange measurements made on Plantago lanceolata, supported the view that photosynthetic capacity is decreased in plants grown under elevated CO2 and on poor soils. (C) 1998 Elsevier Science Ltd.

ounced during the first as compared to the second growth period. AA^7131^Previous research has shown that elevated CO2 concentrations can increase plant growth, whereas the air pollutant O-3 is phytotoxic. Because elevated concentrations of these gases will co-occur, the objective of our experiment was to determine if estimates of plant growth response to future levels of CO2 and O-3 require experiments to test the gases in combination. Soybean plants [Glycine max (L.) Merr. cv. Essex) were exposed in open-top chambers to combinations of O-3 and CO2 from plant emergence through physiological maturity. Ozone treatments were charcoal-filtered air (CF), nonfiltered sir (NF), and NF with O-3 added for 12 h d(-1) (NF+) (seasonal mean 12 h d(-1) O-3 concentrations of 20, 50, or 79 nL L-1, respectively). Carbon dioxide exposures were for 24 h d(-1) giving seasonal mean 12 h d(-1) concentrations of 370, 482, 599, or 713 mu L L-1 Over the season, elevated CO2 usually stimulated growth and O-3 suppressed growth. Elevated CO2 usually increased partitioning of biomass to branches, decreased partitioning to pods, increased specific leaf weight, and decreased leaf area ratio. Ozone suppressed leaf and root weight ratios, increased pod weight ratios, and decreased specific leaf weight. Toward the end of the season, both O-3 and CO2 accelerated reproductive development. Elevated CO2 moderated suppression of growth by O- 3, and the highest CO2 concentration completely ameliorated O-3 effects on main stem biomass, root biomass, and leaf area. Ozone, however, limited some positive growth responses to CO2, especially at less than a doubling of CO2 concentrations. These results indicate that in order to understand the future impacts of atmospheric gases such as elevated CO2 and O-3 On crop growth, their combined effects should be determined.

2186^5^Rillig,MC^Allen,MF^Klironomos,JN^Chiariello,NR^Field,CB^1998^1^Plant species-specific changes in root-inhabiting fungi in a California annual grassland: responses to elevated CO2 and nutrients^2^113^2^252-259^^^^^Jan^^^^^7134 biomass to branches, dec1334^1675^1781^1981^1983^376^377^433^778^849^c leaf weight, and decreased leaf area ratio. Ozone suppressed leaf and root weight ratios, increased pod weight ratios, and decreased specific leaf weight. Toward the end of the season, both O-3 and CO2 accelerated reproductive development. Elevated CO2 moderated suppression of growth by O- 3, and the highest CO2 concentration completely ameliorated O-3 effects on main stem biomass, root biomass, and leaf area. Ozone, however, limited some positive growth responses to CO2, especially at less than a doubling of CO2 concentrations. These results indicate that in order to understand the future impacts of atmospheric gases such as elevated CO2 and O-3 On crop growth, their combined effects should be determined.

2186^5^Rillig,MC^Allen,MF^Klironomos,JN^Chiariello,NR^Field,CB^1998^1^Plant species-specific changes in root-inhabiting fungi in a California annual grassland: responses to elevated CO2 and nutrients^2^113^2^252-259^^^^^Jan^^^^^7134 biomass to branches, decA^7133^Five co-occurring plant species from an annual mediterranean grassland were grown in monoculture for 4 months in pots inside open-top chambers at the Jasper Ridge Biological Preserve (San Mateo County, California). The plants were exposed to elevated atmospheric CO2 and soil nutrient enrichment in a complete factorial experiment. The response of root-inhabiting non- mycorrhizal and arbuscular mycorrhizal fungi to the altered resource base depended strongly on the plant species. Elevated CO2 and fertilization altered the ratio of non-mycorrhizal to mycorrhizal fungal colonization for some plant species, but not for others. Percent root infection by non-mycorrhizal fungal increased by over 500% for Linanthus parviflorus in elevated CO2, but decreased by over 80% for Bromus hordeaceus. By contrast, the mean percent infection by mycorrhizal fungi increased in response to elevated CO2 for all species, but significantly only for Avena barbata and B. hordeaceus. Percent infection by mycorrhizal fungi increased, decreased, or remained unchanged for different plant hosts in response to fertilization. There was evidence of a strong interaction between the two treatments for some plant species and non- mycorrhizal and mycorrhizal fungi. This study demonstrated plant species-and soil fertility-dependent shifts in belowground plant resource allocation to different morphogroups of fungal symbionts. This may have consequences for plant community responses to elevated CO2 in this California grassland ecosystem.

2187^2^Rusterholz,HP^Erhardt,A^1998^1^Effects of elevated CO2 on flowering phenology and nectar production of nectar plants important for butterflies of calcareous grasslands^2^113^3^341-349^^^^^Feb^^^^^7136
2584^3233^3234^342^345^374^376^377^489^92^ecreased by over 80% for Bromus hordeaceus. By contrast, the mean percent infection by mycorrhizal fungi increased in response to elevated CO2 for all species, but significantly only for Avena barbata and B. hordeaceus. Percent infection by mycorrhizal fungi increasA^7135^Effects of elevated CO2 on flowering phenology and nectar production were investigated in Trifolium pratense, Lotus corniculatus, Scabiosa columbaria, Centaurea jacea and Betonica officinalis, which are all important nectar plants for butterflies. In glasshouse experiments, juvenile plants were exposed to ambient (350 mu l l(-1)) and elevated (660 mu l l(- 1)) CO2 concentrations for 60-80 days. Elevated CO2 significantly enhanced the development of flower buds in C. jacea. B. officinalis flowered earlier and L. corniculatus produced more flowers under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar per flower was not affected by elevated CO2 in the tested legumes (T. pratense and L. corniculatus), but was significantly reduced (!) in the other forbs. Elevated CO2 did not significantly affect nectar sugar concentration and composition. However, S. columbaria and C. jacea produced significantly less total sugar under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species, whereas the total of amino acids produced per flower was reduced in all non-legumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as most butterflies which have no alternative food resources to nectar. Changes in nectar production due to elevated CO2 could also have generally detrimental effects on the interactions of flowers and their pollinators.

2188^5^Sgherri,CLM^Quartacci,MF^Menconi,M^Raschi,A^Navari-Izzo,F^1998^1^Interactions between drought and elevated CO2 on alfalfa plants^4^152^1^118-124^^^^^Jan^^^^^7138
264^2821^3235^377^546^829^92^significantly reduced (!) in the other forbs. Elevated CO2 did not significantly affect nectar sugar concentration and composition. However, S. columbaria and C. jacea produced significantly less total sugar under elevated CO2. The nectar amino acid conA^7137^Alfalfa (Medicago sativa L.) plants were grown in open top chambers at ambient (340 ppm) and high (600 ppm) CO2 concentrations. Twenty-five days after the first cutting one set of both plants was subjected to water deficit conditions by withholding water for 5 days. A chamber effect on proteolytic activity, monogalactosyl diacylglycerol to digalactosyl diacylglycerol molar ratio, total non-structural carbohydrates and soluble protein contents occurred. In contrast, no change in leaf water potential was observed between plants grown outdoors and inside the chambers. Plants grown at high CO2 concentration showed a lower decrease in leaf water potential in comparison with plants grown at atmospheric CO2 when subjected to water stress. Under high CO2 concentration leaf nitrogen content decreased whereas starch accumulation and a higher proteolytic activity were recorded. Following water depletion, CO2-enriched plants showed a decrease in total non- structural carbhydrates and soluble proteins. In thylakoid membranes high CO2 caused an increase in chlorophyll and lipid contents and a degradation of monogalactosyl diacylglycerol. A higher degree of unsaturation in the main thylakoid lipids was also observed. CO2-enriched plants were less affected by water stress as shown by reduced chlorophyll degradation and a higher membrane stability.

2189^2^Usuda,H^Shimogawara,K^1998^1^The effects of increased atmospheric carbon dioxide on growth, carbohydrates, and photosynthesis in radish, Raphanus sativus^231^39^1^1-7^^^^^Jan^^^^^7140
130^2194^230^349^372^384^409^434^ the chambers. Plants grown at high CO2 concentration showed a lower decrease in leaf water potential in comparison with plants grown at atmospheric CO2 when subjected to water stress. Under high CO2 concentration leaf nitrogen content decreased whereas starch accumulation and a higher proteolytic activity were recorded. Following water depletion, CO2-enriched plants showed a decrease in total non- structural carbhydrates and soluble proteins. In thylakoiA^7139^The effects of sink capacity on the regulation of the acclimation of photosynthetic capacity to elevated levels of carbon dioxide are important from a global perspective. We investigated the effeocts of elevated (750 mu mol mol(-1)) and ambient (350 mu mol mol(-1)) atmospheric CO2 on growth, carbohydrate levels, and photosynthesis in radish seedlings from 15 to 46 d after planting. In radish, a major sink is the storage root, and its thickening is initiated early. Elevated CO2 increased the accumulation of dry matter by 111% but had no effect on the acclimation of the rate of photosynthesis or on the levels of carbohydrates in leaves at dawn, Elevated CO2 increased the dry weight in storage roots by 105% by 46 d after planting, apparently enhancing the sink capacity, This enhanced capacity seemed to be responsible for absorption of elevated levels of photosynthate and to result in the absence of any over-accumulation of carbohydrates in source leaves and the absence of negative acclimation of photosynthetic capacity at the elevated level of CO2.

2190^2^Utriainen,J^Holopainen,T^1998^1^Ultrastructural and growth responses of young Scots pine seedlings (Pinus sylvestris) to increasing carbon dioxide and ozone concentrations^362^36^4-5^795-800^^^^^Feb^^^^^7142
1064^1076^1633^1828^1951^2173^372^385^73^ohydrate levels, and photosynthesis in radish seedlings from 15 to 46 d after planting. In radish, a major sink is the storage root, and its thickening is initiated early. Elevated CO2 increased the accumulation of dry matter by 111% but had no effect on the acclimation of the rate of photosynthesis or on the levels of carbohydrates in leaves at dawn, Elevated CO2 increased the dry weight in storage roots by 105% by 46 d after planting, apparently enhancing the sink capacity, This enhanced capacity seemed to be responsible for absorption of elevated levels of photosynthate and to result in the absence of any over-accumulation of carbohydrates in source leaves and the absence of negative acclimation of photosynA^7141^Three-year-old Scots pine seedlings were exposed to ambient or elevated (2 x ambient) O-3 and CO2 levels, singly and in combination, during one growth period in open-top field chambers. Growth measurements showed increased shoot length and needle width in response to CO2 enrichment, whereas O-3 exposure resulted in visible injury (chlorotic mottling and increased yellowing of previous year needles). At the ultrastructural level, O-3 caused increased electron density of chloroplast stroma and increased number of cytoplasmic ribosomes at both CO2 levels. CO2 enrichment also resulted in an increase in the size of starch grains in chloroplasts. In general, simultaneous exposure to elevated O-3 reduced the impact of elevated CO2. (C)1998 Elsevier Science Ltd.
k capacity, This enhanced capacity seemed to be responsible for absorption of elevated levels of photosynthate and to result in the absence of any over-accumulation of carbohydrates in source leaves and the absence of negative acclimation of photosyn2191^4^Williams,RS^Thomas,RB^Strain,BR^Lincoln,DE^1997^1^Effects of elevated CO2, soil nutrient levels, and foliage age on the performance of two generations of Neodiprion lecontei (Hymenoptera : Diprionidae) feeding on loblolly pine^238^26^6^1312-1322^^^^^Dec^^^^^7144
1065^229^2530^312^3236^344^488^57^764^92^resulted in visible injury (chlorotic mottling and increased yellowing of previous year needles). At the ultrastructural level, O-3 caused increased electron density of chloroplast stroma and increased number of cytoplasmic ribosomes at both CO2 levels. CO2 enrichment also resulted in an increase in the size of starch grains in chloroplasts. In general, simultaneous exposure to elevated O-3 reduced the impact of elevated CO2. (C)1998 Elsevier Science Ltd.
k capacity, This enhanced capacity seemed to be responsible for absorption of elevated levels of photosynthate and to result in the absence of any over-accumulation of carbohydrates in source leaves and the absence of negative acclimation of photosynA^7143^We investigated how changes in loblolly Dine needle phytochemistry caused by elevated CO2, leaf age, and soil nutrient levels affected the performance of 2 individual generations of the multivoltine folivorous insect pest Neodiprion lecontei (Fitch). In 2 feeding trials, mature needles produced in the previous (spring) and current (fall) year from seedlings grown in open-topped chambers under 4 CO2 and 2 soil nutrient levels were fed to 2 separate generations of redheaded pine sawfly larvae. Strong seasonal differences (i.e., spring versus fall) in leaf nutritional and defensive constituents resulted in significant between-generation differences in the growth, consumption, and growth efficiency of sawfly larvae, Enriched CO2-grown needles had higher levels of starch and starch/nitrogen ratios in older, overwintering spring needles, which were lower in leaf nitrogen and monoterpenes than younger, current year needles (fall). Overall, larval growth was higher and consumption lower on the fall needles, presumably because of higher levels of leaf nitrogen compared with the spring needles. The plant CO2 concentration significantly contributed to the larval consumption responses between seasons (significant CO2 X season interaction), demonstrating that the 2 sawfly generations were affected differently by CO2-induced phytochemical alterations in spring versus fall needles. The data presented here suggests that when investigating multivoltine folivorous insect responses to elevated CO2-grown tree seedlings in which multiple leaf flushes within a growing season expose insects to an array of leaf phytochemical changes, >1 insect generation should be investigated.

2192^2^Zebian,KJ^Reekie,EG^1998^1^The interactive effects of atmospheric carbon dioxide and light on stem elongation in seedlings of four species^52^81^2^185-193^^^^^Feb^^^^^7146
310^372^374^376^417^568^669^705^740^92^d monoterpenes than younger, current year needles (fall). Overall, larval growth was higher and consumption lower on the fall needles, pA^7145^Four species, Sinapis alba L., Medicago saliva L., Gypsophila paniculata L, and Picea abies (L.) Karsten, were grown in three light regimes: darkness, low light (25 mu mol m(-2) s(-1) for 10 min d(-1)) and high light (120 mu mol m(-2) s(-1) for 12 h d(-1)) and four levels of carbon dioxide: 0, 350, 700 and 1400 +/- 50 mu l l(-1). Germination was not affected by any of the treatments. The effects of carbon dioxide on stem elongation were identical in low and high light: stem length increased at a decreasing rate with level of carbon dioxide in all species. Level of carbon dioxide also affected stem elongation in complete darkness, but the pattern was more complex and varied among species. Total weight did not vary with level of carbon dioxide to any significant extent in either darkness or low light, but increased with level of carbon dioxide at high light in all four species. Due to the absence of any effect of carbon dioxide on growth in darkness and low light, we suggest the effects of carbon dioxide on stem elongation are independent of effects on growth and may be due to a direct interaction with developmental processes. In contrast, level of carbon dioxide had little effect on allocation patterns in the dark and low light experiments, but had marked effects in high light. Therefore, the effect of carbon dioxide on allocation was probably due to the effects of carbon dioxide on growth rather than to any direct interaction between carbon dioxide and development. An understanding of the mechanisms by which carbon dioxide affects development may help us understand the often variable effects of carbon dioxide upon plants. (C) 1998 Annals of Botany Company.

2193^2^Ziska,LH^Bunce,JA^1997^1^Influence of increasing carbon dioxide concentration on the photosynthetic and growth stimulation of selected C-4 crops and weeds^91^54^3^199-208^^^^^Dec^^^^^7148
130^349^360^372^374^417^434^750^e to the absence of any effect of carbon dioxide on growth in darkness and low light, we suggest the effects of carbon dioxidA^7147^Plants of six weedy species (Amaranthus retroflexus, Echinochloa crus-galli, Panicum dichotomiflorum, Setaria faberi, Setaria viridis, Sorghum halapense) and 4 crop species (Amaranthus hypochondriacus, Saccharum officinarum, Sorghum bicolor and Zea mays) possessing the C-4 type of photosynthesis were,at-own at ambient (38 Pa) and elevated (69 Pa) carbon dioxide during early development (i.e. up to 60 days after sowing) to determine: (a) if plants possessing the C-4 photosynthetic pathway could respond photosynthetically or in biomass production to future increases in global carbon dioxide and (b) whether differences exist between weeds and crops in the degree of response. Based on observations in the response of photosynthesis (measured as A, CO2 assimilation rate) to the growth CO2 condition as well as to a range of internal CO2 (C- i) concentrations, eight of ten C-4 species showed a significant increase in photosynthesis. The largest and smallest increases observed were for A. retroflexus (+30%) and Z. mays (+5%), respectively. Weed species (+19%) showed approximately twice the degree of photosynthetic stimulation as that of crop species (+10%) at the higher CO2 concentration. Elevated carbon dioxide also resulted in significant increases in whole plant biomass for four C-4 weeds (A. retroflexus, E. crus-galli, P. dichotomiflorum, S viridis) relative to the ambient CO2 condition. Leaf water potentials for three selected species (A. retroflexus, A. hypochondriacus, Z. mays) indicated that differences in photosynthetic stimulation were not due solely to improved leaf water status. Data from this study indicate that C-4 plants may respond directly to increasing CO2 concentration, and in the case of some C-4 weeds (e.g. A. retroflexus) may show photosynthetic increases similar to those published for C-3 species.
ange of internal CO2 (C- i) concentrations, eight of ten C-4 species showed a significant increase in photosynthesis. The largest and smallest increases observed were for A. retroflexus (+30%) an2194^7^Chagvardieff,P^Dimon,B^Souleimanov,A^Massimino,D^Le Bras,S^Pean,M^Louche-Teissandier,D^9UNKNOWN YEAR^1^Effects of modified atmosphere on crop productivity and mineral content^363^^^1971-1974^^^^^^^^^^7150
130^131^312^409^5^559^741^92^ses in whole plant biomass for four C-4 weeds (A. retroflexus, E. crus-galli, P. dichotomiflorum, S viridis) relative to the ambient CO2 condition. Leaf water potentials for three selected species (A. retroflexus, A. hypochondriacus, Z. mays) indicated that differences in photosynthetic stimulation were not due solely to improved leaf water status. Data from this study indicate that C-4 plants may respond directly to increasing CO2 concentration, and in the case of some C-4 weeds (e.g. A. retroflexus) may show photosynthetic increases similar to those published for C-3 species.
ange of internal CO2 (C- i) concentrations, eight of ten C-4 species showed a significant increase in photosynthesis. The largest and smallest increases observed were for A. retroflexus (+30%) anA^7149^Wheat, potato, pea and tomato crops were cultivated from seeding to harvest in a controlled and confined growth chamber at elevated CO2 concentration (3700 mu L.L-1) to examine the effects on biomass production and edible part yields. Different responses to high CO2 were recorded, ranging from a decline in productivity for wheat, to slight stimulation for potatoes, moderate increase for tomatoes, and very large enhancement for pea. Mineral content in wheat and pea seeds was not greatly modified by the elevated CO2. Short-term experiments (17 d) were conducted on potato at high (3700 mu L.L-1) and very high (20,000 mu L.L-1) CO2 concentration and/or low O-2 partial pressure (similar to 20,600 mu L.L-1 or 2 kPa). Low O-2 was more effective than high CO2 in total biomass accumulation, but development was affected: Low O-2 inhibited tuberization, while high CO2 significantly increased production of tubers. (C) 1997 COSPAR. Published by Elsevier Science Ltd.
ases observed were for A. retroflexus (+30%) an2195^3^Grotenhuis,T^Reuveni,J^Bugbee,B^9UNKNOWN YEAR^1^Super-optimal CO2 reduces wheat yield in growth chamber and greenhouse environments^363^^^1901-1904^^^^^^^^^^7152
5^560^examine the effects on biomass production and edible part yields. Different responses to high CO2 were recorded, ranging from a decline in productivity for wheat, to slight stimulation for potatoes, moderate increase for tomatoes, and very large enhancement for pea. Mineral content in wheat and pea seeds was not greatly modified by the elevated CO2. Short-term experiments (17 d) were conducted on potato at high (3700 mu L.L-1) and very high (20,000 mu L.L-1) CO2 concentration and/or low O-2 partial pressure (similar to 20,600 mu L.L-1 or 2 kPa). Low O-2 was more effective than high CO2 in total biomass accumulation, but development was affected: Low O-2 inhibited tuberization, while high CO2 significantly increased production of tubers. (C) 1997 COSPAR. Published by Elsevier Science Ltd.
ases observed were for A. retroflexus (+30%) anA^7151^Seven growth chamber trials (six replicate trials using 0.035, 0.12, and 0.25 % CO2 in air and one trial using 0.12, 0.80, and 2.0% CO2 in air) and three replicate greenhouse trials (0.035, 0.10, 0.18, 0.26, 0.50, and 1.0% CO2 in air) compare the effects of super-optimal CO2 on the seed yield, harvest index, and vegetative growth rate of wheat (Triticum aestivum L. cvs. USU-Apogee and Veery-10). Plants in the growth chamber trials were grown hydroponically under fluorescent lamps, while the greenhouse trials were grown under sunlight and high pressure sodium lamps and in soilless media. Plants in the greenhouse trials responded similarly to those in the growth chamber trials; maximum yields occurred near 0.10 and 0.12 % CO2 and decreased significantly thereafter. This research indicates that the toxic effects of elevated CO2 are not specific to only one environment and has important implications for the design of bio-regenerative life support systems in space, and for the future of terrestrial agriculture. (C) 1997 COSPAR. Published by Elsevier Science Ltd.

2196^5^Wheeler,RM^Mackowiak,CL^Stutte,GW^Yorio,NC^Berry,WL^9UNKNOWN YEAR^1^Effect of elevated carbon dioxide on nutritional quality of tomato^363^^^1975-1978^^^^^^^^^^7154
174^5^ir) compare the effects of super-optimal CO2 on the seed yield, harvest index, and vegetative growth rate of wheat (Triticum aestivum L. cvs. USU-Apogee and Veery-10). Plants in the growth chamber trials were grown hydroponically under fluorescent lamps, while the greenhouse trials were grown under sunlight and high pressure sodium lamps and in soilless media. Plants in the greenhouse trials responded similarly to those in the growth chamber trials; maximum yields occurred near 0.10 and 0.12 % CO2 and decreased significantly thereafter. This research indicates that the toxic effects of elevated CO2 are not specific to only one environment and has important implications for the design of bio-regenerative life support systems in space, and for the future of terrestrial agriculA^7153^Tomato (Lycopersicon esculentum Mill.) cvs. Red Robin (RR) and Reimann Philipp (RP) were grown hydroponically for 105 d with a 12 h photoperiod, 26 degrees C /22 degrees C thermoperiod, and 500 mu mol.m(-2).s(-1) PPF at either 400, 1200, 5000, or 10,000 mu mol.mol(-1) (0.04, 0.12, 0.50, 1.00 kPa) CO2. Harvested fruits were analyzed for proximate composition, total dietary fiber, nitrate, and elemental composition. No trends were apparent with regard to CO2 effects on proximate composition, with fruit from all treatments and both cultivars averaging 18.9% protein, 3.6% fat, 10.2% ash, and 67.2% carbohydrate. In comparison, average values for field-grown fruit are 16.6% protein, 3.8% fat, 8.1% ash, and 71.5% carbohydrate (Duke and Atchely, 1986). Total dietary fiber was highest at 10,000 mu mol.mol(-1) (28.4% and 22.6% for RR and RP) and lowest at 1000 mu mol.mol(-1) (18.2% and 15.9% for RR and RP), but showed no overall trend in response to CO2. Nitrate values ranged from 0.19% to 0.35% and showed no trend with regard to CO2. K, Mg, and P concentrations showed no trend in response to CO2 but Ca levels increased from 198 and 956 ppm in RR and RP at 400 mu mol.mol(-1), to 2537 and 2825 ppm at 10,000 mu mol.mol(-1). This increase in Ca caused an increase in fruit Ca/P ratios from 0.07 and 0.37 for RR and RP at 400 mu mol.mol(-1). to 0.99 and 1.23 for RR and RP at 10,000 mu mol.mol(-1), suggesting that more dietary Ca should be available from high CO2-grown fruit. Published by Elsevier Science Ltd on behalf of COSPAR.

2197^3^Awmack,CS^Harrington,R^Leather,SR^1997^1^Host plant effects on the performance of the aphid Aulacorthum solani (Kalt.) (Homoptera : Aphididae) at ambient and elevated CO2^127^3^6^545-549^^^^^Dec^^^^^7156
2534^344^374^376^423^430^489^490^764^797^iber was highest at 10,000 mu mol.mol(-1) (28.4% and 22.6% for RR and RP) and lowest at 1000 mu mol.mol(-1) (18.2% and 15.9% for RR and RP), but showed no overall trend in response to CO2. Nitrate values ranged from 0.19% to 0.35% and showed no tA^7155^In future elevated CO2 environments, chewing insects are likely to perform less well than at present because of the effects of increased carbon fixation on their host plants. When the aphid, Aulacorthum solani was reared on bean (Vicia faba) and tansy (Tanacetum vulgare) plants under ambient and elevated CO2, performance was enhanced on both hosts at elevated CO2. The nature of the response was different on each plant species suggesting that feeding strategy may influence an insect's response to elevated CO2. On bean, the daily rate of production of nymphs was increased by 16% but there was no difference in development time, whereas on tansy, development time was 10% shorter at elevated CO2 but the rate of production of nymphs was not affected. The same aphid clone therefore responded differently to elevated CO2 on different host plants. This increase in aphid performance could lead to larger populations of aphids in a future elevated CO2 environment.
values ranged from 0.19% to 0.35% and showed no t2198^3^Berntson,GM^Wayne,PM^Bazzaz,FA^1997^1^Below-ground architectural and mycorrhizal responses to elevated CO2 in Betula alleghaniensis populations^43^11^6^684-695^^^^^Dec^^^^^7158
1103^1646^361^376^377^407^419^540^679^92^d on bean (Vicia faba) and tansy (Tanacetum vulgare) plants under ambient and elevated CO2, performance was enhanced on both hosts at elevated CO2. The nature of the response was different on each plant species suggesting that feeding strategy may influence an insect's response to elevated CO2. On bean, the daily rate of production of nymphs was increased by 16% but there was no difference in development time, whereas on tansy, development time was 10% shorter at elevated CO2 but the rate of production of nymphs was not affected. The same aphid clone therefore responded differently to elevated CO2 on different host plants. This increase in aphid performance could lead to larger populations of aphids in a future elevated CO2 environment.
values ranged from 0.19% to 0.35% and showed no tA^7157^1. Replicate populations of crowded, regenerating stands of Betula alleghaniensis were grown in ambient and elevated (700 p.p.m.) atmospheric CO2 concentrations in monoliths of forest soil. Early in the second year the seedlings were harvested and detailed measurements of individual plant root architectural parameters and ectomycorrhizal colonization were made. 2. Comparing the average responses of individual plants within the populations, elevated CO2 had no significant effects on architectural parameters that improve a plant's ability to forage for and acquire soil resources. In contrast, the intensity and magnitude of mycorrhizal colonization, and whole plant C/N ratios were significantly enhanced with elevated CO2. 3. The allometric scaling relationship between total plant biomass and root biomass was not affected by CO2, suggesting that relative allocation between roots and shoots was not affected. However, the allometric scaling relationships between root architectural parameters and plant biomass, and between fine root biomass and woody root biomass were significantly altered by elevated CO2. For all of these relationships, elevated CO2 reduced the 'size bias' of architectural components in relation to plant size within the populations; in elevated CO2 root architectural size (e.g. root length) per unit biomass was more similar between the smallest and largest individuals within the population than was the case for ambient CO2. 4. Overall, the results of this study suggest that the average individual seedling biomass and architectural growth responses within populations of plants exposed to elevated atmospheric CO2 levels may be unresponsive, but that mycorrhizal responses and interactions among plants within populations may be altered significantly. These findings have important implications for how we make predictions about plant growth responses to elevated CO2 in natural ecosystems. Significant increases in mycorrhizal infection rates and architecture-biomass allometries suggest that below-ground competitive interactions within plant populations may be reduced in elevated CO2. Alterations in competitive interactions may lead to shifts in productivity and plant population structure.

2199^3^Bettarini,I^Vaccari,FP^Miglietta,F^1998^1^Elevated CO2 concentrations and stomatal density: observations from 17 plant species growing in a CO2 spring in central Italy^127^4^1^17-22^^^^^Jan^^^^^7160
1030^312^344^348^374^384^465^634^705^73^. 4. Overall, the results of this study suggest that the average individual seedling biomass and architectural growth responses within populations of plants exposed to elevated atmospheric CO2 levels may be unresponsive, but that mycorrhizal responses and interactions among plants within populations may be altered significantly. These findings have important implications for how we make predictions about plant growth responses to elevated CO2 in natural ecosystems. Significant increases in mycorrhizal infection rates and architecture-biomass allometries suggest that below-groA^7159^Stomatal density (SD) and stomatal conductance (g(s)) can be affected by an increase of atmospheric CO2 concentration. This study was conducted on 17 species growing in a naturally enriched CO2 spring and belonging to three plant communities. Stomatal conductance, stomatal density and stomatal index (SI) of plants from the spring, which were assumed to have been exposed for generations to elevated [CO2], and of plants of the same species collected in a nearby control site, were compared. Stomatal conductance was significantly lower in most of the species collected in the CO2 spring and this indicated that CO2 effects on g, are not of a transitory nature but persist in the long term and through plant generations. Such a decrease was, however, not associated with changes in the anatomy of leaves: SD was unaffected in the majority of species (the decrease was only significant in three out of the 17 species examined), and also SI values did not vary between the two sites with the exception of two species that showed increased SI in plants grown in the CO2-enriched area. These results did not support the hypothesis that long-term exposure to elevated [CO2] may cause adaptive modification in stomatal number and in their distribution.

2200^2^Brooks,GL^Whittaker,JB^1998^1^Responses of multiple generations of Gastrophysa viridula, feeding on Rumex obtusifolius, to elevated CO2^127^4^1^63-75^^^^^Jan^^^^^7162
1142^2976^312^3187^3237^3238^384^489^774^92^lected in a nearby control site, were compared. Stomatal conductance was significantly lower in most of the species collected in the CO2 spring and this indicated that CO2 effects on g, are not of a transitory nature but persist in the long term and through plant generations. Such a decrease was, however, not associated with changes in the anatomy of leaves: SD was unaffected in the majority of species (the decrease was only significant in three out of the 17 species examined), and also SI values did not vary between the two sites with the exception of two species A^7161^Rumex obtusifolius plants and three generations of the tri- voltine leaf beetle Gastrophysa viridula were simultaneously exposed to elevated CO2 (600 ppm) to determine its effect on plant quality and insect performance. This exposure resulted in a reduction in leaf nitrogen, an increase in the C/N ratio and lower concentrations of oxalate in the leaves than in ambient air (350 ppm). Despite these changes in food quality, the effect of elevated CO2 on larvae of Gastrophysa viridula over three generations was minimal. However, the effect of CO2 did differ slightly between the generations of the insect. For the first generation, the results obtained were different from many of the published results in that elevated CO2 had no measurable effects on performance, except that third instar larvae showed compensatory feeding. Food quality, including leaf nitrogen content, declined over time in material grown in both ambient and elevated CO2. The results obtained for the second generation were similar to the first except that first instar larvae showed reduced relative growth rate in elevated CO2. Development time from hatching to pupation decreased over each generation, probably as a result of increasing temperatures. Measurements of adult performance showed that fecundity at the end of the second generation was reduced relative to the first, in line with the reduction in food quality. In addition at the end of the second generation, but not at the end of the first generation, adult females in elevated CO2 laid 30% fewer eggs per day and the eggs laid were 15% lighter than those in ambient conditions. These lighter eggs, coupled with no effect of elevated CO2 on growth during the third generation, meant that the larvae were consistently smaller in elevated CO2 during this generation. These results offer further insights into the effect that elevated CO2 will have on insect herbivores and provide a more detailed basis for population predictions.
he results obtained for the second generation were similar to the fi2201^3^Chen,SG^Impens,I^Ceulemans,R^1997^1^Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers (vol 3, pg 97, 1997)^127^3^6^550^^^^^Dec

2202^3^Cotrufo,MF^Ineson,P^Scott,A^1998^1^Elevated CO2 reduces the nitrogen concentration of plant tissues^127^4^1^43-54^^^^^Jan^^^^^7165
1344^2184^229^2489^2533^3003^377^457^789^966^the second generation, but not at the end of the first generation, adult females in elevated CO2 laid 30% fewer eggs per day and the eggs laid were 15% lighter than those in ambient conditions. These lighter eggs, coupled with no effect of elevated CO2 on growth during the third generation, meant that the larvae were consistently smaller in elevated CO2 during this generation. These results offer further insights into the effect that elevated CO2 will have on insect herbivores and provide a more detailed basis for population predictions.
he results obtained for the second generation were similar to the fiA^7164^We summarize the impacts of elevated CO2 on the N concentration of plant tissues and present data to support the hypothesis that reductions in the quality of plant tissue commonly occur when plants are grown under elevated CO2. Synthesis of existing data showed an average 14% reduction of N concentrations in plant tissue generated under elevated CO2 regimes. However, elevated CO2 appeared to have different effects on the N concentrations of different plant types, as the reported reductions in N have been larger in C3 plants than in C4 plants and N-2-fixers. Under elevated CO2 plants changed their allocation of N between above-and below-ground components: root N concentrations were reduced by an average of 9% compared to a 14% average reduction for above-ground tissues. Although the concentration of CO2 treatments represented a significant source of variance for plant N concentration, no consistent trends were observed between them.
he results obtained for the second generation were similar to the fi2203^2^Deng,X^Woodward,FI^1998^1^The growth and yield responses of Fragaria ananassa to elevated CO2 and N supply^52^81^1^67-71^^^^^Jan^^^^^7167
341^344^409^436^437^439^541^57^ commonly occur when plants are grown under elevated CO2. Synthesis of existing data showed an average 14% reduction of N concentrations in plant tissue generated under elevated CO2 regimes. However, elevated CO2 appeared to have different effects on the N concentrations of different plant types, as the reported reductions in N have been larger in C3 plants than in C4 plants and N-2-fixers. Under elevated CO2 plants changed their allocation of N between above-and below-ground components: root N concentrations were reduced by an average of 9% compared to a 14% average reduction for above-ground tissues. Although the concentration of CO2 treatments represented a significant source of variance for plant N concentration, no consistent trends were observed between them.
he results obtained for the second generation were similar to the fiA^7166^Strawberry plants (Fragaria ananassa Duchesne var. Elsanta) were grown in pots at two concentrations of carbon dioxide (partial pressures of 39 and 56 Pa) and with three rates of nitrogen supply (0.04, 0.4 and 4 mM as nutrient solution) to study their individual and interactive effects on plant growth and fruit yield. Nitrogen deficiency reduced total dry biomass and relative growth rate (RGR), mainly through reductions in leaf area ratio (LAR) and plant N concentration (PNC), although both the net assimilation rare (NAR) and root weight ratio (RWR) increased. Elevated CO2 increased the N productivity (NP) but reduced the LAR. High CO2 increased the fruit yield by 42% at high N supply and by 17% at low N supply. The CO2 yield enhancement occurred through an increase in the flower and fruit number of individual plants. This resulted in an increase in the fruit weight ratio (FWR) of plants at high CO2. Nitrogen deficiency reduced the fruit yield by about 50% through decreases in fruit size, fruit set and the number of fruits. However, N deficiency increased the proportion of total plant dry biomass allocated to fruits. There were no significant interactions between CO2 and N supply on yield. (C) 1998 Annals of Botany Company.

2204^5^Dury,SJ^Good,JEG^Perrins,CM^Buse,A^Kaye,T^1998^1^The effects of increasing CO2 and temperature on oak leaf palatability and the implications for herbivorous insects^127^4^1^55-61^^^^^Jan^^^^^7169
1080^1142^2172^2534^2950^417^489^628^703^733^ion (PNC), although both the net assimilation rare (NAR) and root weight ratio (RWR) increased. Elevated CO2 increased the N productivity (NP) but reduced the LAR. High CO2 increased the fruit yield by 42% at high N supply and by 17% at low N supply. The CO2 yield enhancement occurred through an increase in the flower and fruit number of individual plants. This resulted in an increase in the fruit weight ratio (FWR) of plants at high CO2. Nitrogen deficiency reduced the fruit yield by about 50% through decreases in fruit size, fruit set anA^7168^Rising levels of atmospheric CO2 are expected to perturb forest ecosystems, although the extent to which specific ecological interactions will be modified is unclear. This research evaluates the effects of elevated CO2 and temperature, alone and in combination, on the leaf nutritional quality of Pendunculate oak (Qeurcus robur L.), and the implications for herbiverous insect defoliators are discussed. A 3 degrees C temperature rise reduced leaf nutritional quality, by reducing foliar nitrogen concentration and increasing condensed tannin content. Doubling atmospheric CO2 temporarily increased total phenolics, but also reduced leaf toughness. The nutritional quality of the second leaf flush (lammas growth) was considerably reduced at elevated CO2. It is concluded that larval development of spring-feeding defoliators and hence adult fecundity may be adversely affected by increased temperatures.
h CO2. Nitrogen deficiency reduced the fruit yield by about 50% through decreases in fruit size, fruit set an2205^3^Goettel,MS^Duke,GM^Goerzen,DW^1997^1^Pathogenicity of Ascosphaera larvis to larvae of the alfalfa leafcutting bee, Megachile rotundata^364^129^6^1059-1065^^^^^Nov-Dec^^^^^7171
3239^
A^7170^Laboratory assays and field surveys showed that Ascosphaera larvis (Bissett) is a pathogen of alfalfa leafcutting bee larvae, capable of causing high mortality in commercial populations. In one population over 21% of bees were found to be infected by A. larvis. However, overall levels of the disease are low and it is unlikely that this pathogen poses an immediate threat to commercial leafcutting bee populations in Canada. The LD50 was determined to be 1.9 x 10(5) spores/bee. Elevated levels of CO2 are required for in vitro spore germination. The disease can easily be diagnosed within bee cells by X-ray radiography, thereby enabling disease levels to be monitored using conventional methods utilized by the industry to monitor leafcutting bee quality.
it yield by about 50% through decreases in fruit size, fruit set an2206^1^Hikosaka,K^1997^1^Modelling optimal temperature acclimation of the photosynthetic apparatus in C-3 plants with respect to nitrogen use^52^80^6^721-730^^^^^Dec^^^^^7173
1265^2197^3240^3241^3242^356^372^384^552^635^ld surveys showed that Ascosphaera larvis (Bissett) is a pathogen of alfalfa leafcutting bee larvae, capable of causing high mortality in commercial populations. In one population over 21% of bees were found to be infected by A. larvis. However, overall levels of the disease are low and it is unlikely that this pathogen poses an immediate threat to commercial leafcutting bee populations in Canada. The LD50 was determined to be 1.9 x 10(5) spores/bee. Elevated levels of CO2 are required for in vitro spore germination. The disease can easily be diagnosed within bee cells by X-ray radiography, thereby enabling disease levels to be monitored using conventional methods utilized by the industry to monitor leafcutting bee quality.
it yield by about 50% through decreases in fruit size, fruit set anA^7172^A new hypothesis for temperature acclimation by the photosynthetic apparatus is presented. An optimization model is developed to examined effects of changes in the organization of photosynthetic components on leaf photosynthesis under various growth temperatures where the photosynthetic apparatus is not damaged. In this model, photosynthetic rate is limited either by the capacity of ribulose bisphosphate carboxylase (RuBPCase) to consume ribulose bisphosphate (RuBP), or by the capacity of RuBP regeneration. For temperature dependence of the RuBPCase activity, data from Spinacia oleracea L., which have a temperature optimum of 30 degrees C, are used. For temperature dependence of the capacity of RuBP regeneration, two contrasting curves that have temperature optima of 30 degrees C (Eucalyptus pauciflora Sieb. ex Spreng) and 40 degrees C (Larrea divaricata Cav.) are applied. The temperature dependence of each process is fixed for respective species, but the rate of each process varies with changes in the amounts of components. The cost of proteins, in terms of nitrogen, required to carry out each process is calculated when nitrogen is partitioned differently among photosynthetic components. The optimal nitrogen partitioning that maximizes daily photosynthesis at a given temperature is obtained. The predicted temperature optimum of the photosynthetic rate in Larrea divaricata exhibits large shifts with changes in target temperature, while shifts are negligible in Eucalyptus pauciflora. It is suggested that the shift in temperature optimum of photosynthetic rate is large when the temperature dependences of the capacities of RuBPCase and RuBP regeneration differ from each other. (C) 1997 Annals of Botany Company.

2207^4^Hopkins,DW^Chudek,JA^Webster,EA^Barraclough,D^1997^1^Following the decomposition of ryegrass labelled with C-13 and N-15 in soil by solid-state nuclear magnetic resonance spectroscopy^365^48^4^623-631^^^^^Dec^^^^^7175
1185^3243^3244^3245^3246^372^534^535^600^658^ess varies with changes in thA^7174^Investigating the biogeochemistry of plant material decomposition in soil has been restricted by difficulties extracting and identifying organic compounds. In this study the decomposition of C-13- and N-15-labelled Lolium perenne leaves mixed with mineral soil has been investigated over 224 days of incubation under laboratory conditions. Decomposition was followed using short-term rates of CO2 evolution, the amounts of C-13 and N-15 remaining were determined by mass spectrometry, and C-13 and N-15 solid-state nuclear magnetic resonance (NMR) spectroscopy was used to characterize chemically the plant material as it decomposed. After 224 days 48% of the added C-13 had been lost with a rapid period of CO2 evolution over the first 56 days. The fraction of cross- polarization magic angle spinning (CP MAS) C-13 NMR spectra represented by O-alkyl-C signal probably in carbohydrates (chemical shift, 60-90 p.p.m.) declined from 60 to 20% of the spectrum (chemical shift, 0-200 p.p.m.) over 224 days. The rate of decline of the total C-13 exceeded that of the 60-90 p.p.m. signal during the first 56 days and was similar thereafter. The fraction of the CP MAS C-13 NMR spectra represented by the alkyl- and methyl-C (chemical shift, 10-45 p.p.m.) signal increased from 5 to 14% over the first 14 days and was 19% after 224 days. CP MAS C-13 NMR of C-13- and N-15-L. perenne contained in 100-mu m aperture mesh bags incubated in the soil for 56 days indicated that the remaining material was mainly carbohydrate but there was an increase in the alkyl-and methyl- C associated with the bag's contents. After 224 days incubation of the labelled C-13- and N-15-L. perenne mixed with the soil, 40% of the added N-15 had been lost. Throughout the incubation there was only one signal centred around 100 p.p.m, detectable in the CP MAS N-15 NMR spectra. This signal corresponded to amide N-15 in peptides and may have been of plant or microbial origin or both. Although there had been substantial interaction between the added N-15 and the soil microorganisms, the associated redistribution of N-15 from plant to microbial tissues occurred within the amide region. The feasibility of following some of the component processes of plant material decomposition in soil using NMR has been demonstrated in this study and evidence that microbial synthesis contributes to the increase in alkyl- and methyl-C content of soil during decomposition has been represented.

2208^2^John-McKay,ME^Colman,B^1997^1^Variation in the occurrence of external carbonic anhydrase among strains of the marine diatom Phaeodactylum tricornutum (Bacillariophyceae)^249^33^6^988-990^^^^^Dec^^^^^7177
1538^1545^1619^174^1858^2871^3247^739^e soil, 40% of the added N-15 had been lost. Throughout the incubation there was only one signal centred around 100 p.p.m, detectable in the CP MAS N-15 NMR spectra. This signal corresponded to amide N-15 in peptides and may have been of plant or microbial origin or both. Although there had been substantial interaction between the added N-15 and the soiA^7176^Eleven different strains of Phaeodactylum tricornutum Bohlin were obtained from three culture collections and were examined for the presence of external and internal carbonic anhydrase (CA). Cells of all strains, grown in standing culture at alkaline pH and low dissolved inorganic carbon had internal CA, but only eight were found to have external CA. External CA activity was reduced when cultures were bubbled with air and was completely repressed when they were grown on 5% CO2. Expression of external CA activity appears to be regulated by CO2 concentration in the growth medium, but within one species, there appears to be a variation in occurrence of external CA and consequently in the mode of inorganic carbon acquisition.

2209^3^Keller,T^Guiot,J^Tessier,L^1997^1^Climatic effect of atmospheric CO2 doubling on radial tree growth in south eastern France^134^24^6^857-864^^^^^Nov^^^^^7179
plant or microbial origin or both. Although there had been substantial interaction between the added N-15 and the soiA^7178^The climatic effect of a doubling of atmospheric CO2 on radial growth of trees was studied in ten populations of three species in south eastern France using an Atmospheric General Circulation Model (AGCM) predicting a 3 degrees C increase of mean temperature and a light rise of precipitation. Results are based on empirical growth climate models, involving an Artificial Neural Network (ANN) technique. Only two of the studied populations, on the boundaries of their ecological area, are sensitive to the climatic variations. One is the larch (Larix decidua Mill.) population located at 2300m on elevation (near the timberline) which shows a radial growth increase. The other is the most southern French Scots pine (Pinus sylvestris L.) population which reacts with a severe growth rate reduction.

2210^2^Kellomaki,S^Wang,KY^1997^1^Effects of long-term CO2 and temperature elevation on crown nitrogen distribution and daily photosynthetic performance of Scots pine^45^99^3^309-326^^^^^15 Dec^^^^^71815 and the soi2068^229^3180^3248^360^376^384^687^714^92^ atmospheric CO2 on radial growth of trees was studied in ten populations of three species in south eastern France using an Atmospheric General Circulation Model (AGCM) predicting a 3 degrees C increase of mean temperature and a light rise of precipitation. Results are based on empirical growth climate models, involving an Artificial Neural Network (ANN) technique. Only two of the studied populations, on the boundaries of their ecological area, are sensitive to the climatic variations. One is the larch (Larix decidua Mill.) population located at 2300m on elevation (near the timberline) which shows a radial growth increase. The other is the most southern French Scots pine (Pinus sylvestris L.) population which reacts with a severe growth rate reduction.

2210^2^Kellomaki,S^Wang,KY^1997^1^Effects of long-term CO2 and temperature elevation on crown nitrogen distribution and daily photosynthetic performance of Scots pine^45^99^3^309-326^^^^^15 Dec^^^^^71815 and the soiA^7180^Single Scots pines (Pinus sylvestris L.), aged 20-25 years, were grown in open-top chambers and exposed to elevated temperature (Elev. T), elevated CO2 (Elev. C) and a combination of elevated CO2 and temperature (Elev. C + T) for 3 years. The vertical distribution of needle nitrogen concentration was measured simultaneously with gas exchange of attached shoots. Based on the measurements, the dependencies on needle nitrogen concentrations of four photosynthetic parameters, i.e., RuP2 (ribulose 1,5-bisphosphate)-saturated rate of carboxylation (V- cmax), maximum potential electron transport (J(max)), the rate of respiration in the light (R-d) and light-use-efficiency factor (delta), were determined. Using a crown multilayer model, the performance of daily crown photosynthesis in Scots pine was predicted. Compared to the control treatment, the mean concentration of nitrogen in the foliage decreased by 20% and by 17% for trees grown under Elev. C and under Elev. C + T, respectively, but increased by 4% for trees grown under Elev. T. However, the total content of foliage nitrogen per unit ground area increased by 25% for trees grown under Elev. C, by 19% for trees grown under Elev. C + T and by 6% for trees grown under Elev. T; these were due to the increase in the total needle area index. Regressions showed that the foliage grown under Elev. C and Elev. C + T had steeper slopes representing the responses of V-cmax, and R-d and delta to leaf nitrogen concentrations, while Elev. C + T and Elev. T had steeper slopes representing the response of J(max) to needle nitrogen concentrations. Predictions showed that, on a typical sunny day, the daily total of crown photosynthesis increased 22% and 27%, separately for Elev. C and Elev. C + T, and by only 9% for Elev. T alone. Furthermore, the increased daily crown photosynthesis, resulting from treatments involving elevated CO2, can be attributed mainly to an increase in the ambient CO2 concentration and the needle area index, while modification of the intrinsic photosynthetic capacity had only a marginal effect. Based on the current pattern of crown nitrogen allocation, the prediction showed also that the relationship between daily crown photosynthesis and crown nitrogen content was strongly dependent on the daily incident PAR and air temperature. The CO2-elevated treatments led to an increase in the sensitivity of daily crown photosynthesis to changes in crown nitrogen content, daily incident PAR and temperature, while the temperature-elevated treatment had the opposite effect on the sensitivity. (C) 1997 Elsevier Science B.V.

2211^9^Kirschbaum,MUF^Medlyn,BE^King,DA^Pongracic,S^Murty,D^Keith,H^Khanna,PK^Snowdon,P^Raison,RJ^1998^1^Modelling forest-growth response to increasing CO2 concentration in relation to various factors affecting nutrient supply^127^4^1^23-41^^^^^Jan^^^^^7183
1234^130^2116^312^3148^361^372^376^429^811^ CO2, can be attributed mainly to an increase in the ambient CO2 concentration and the needle area index, while modification of the intrinsic photosA^7182^It is well recognized that photosynthesis of C3 plants is highly responsive to CO2 concentration. However, in natural ecosystems, plants are subject to a range of feedback effects that can interact with increased photosynthetic carbon gain in different ways so that it is not clear to what extent increased photosynthesis will translate into increased growth. To assess the probable growth response of nutrient-limited forests to increasing CO2 concentration, we use a previously developed modelling framework and apply it under conditions where the supply of nutrients is affected by a range of different factors. Our analysis indicates that forest growth is likely to be highly stimulated by increasing CO2 concentration in forests with high fertility, in forests with nitrogen fixing plants, in those subject to fire or where nitrogen in wood is effectively removed from the biologically active cycle either through physical removal of stems in harvesting or through continued stem growth over long time periods. Forest growth is likely to be stimulated by CO2 concentration in both phosphorus-and sulphur-limited forests provided nutrients in heartwood of trees are removed from the active nutrient cycle. Without this removal from the cycling system, however, sulphur-limited forests should show little response to increasing CO2. In phosphorus-limited forests without phosphorus removal, the response to increasing CO2 depends further on the equilibration state of the large pool of unavailable secondary phosphorus. Considered over periods of centuries during which the secondary pool has equilibrated, growth of phosphorus-limited forests is likely to be only weakly stimulated by increasing CO2 concentration. However, over shorter periods, increasing CO2 concentration should lead to a substantial increase in productivity. In general, it can be concluded that systems that are more open with respect to nutrient gains and losses are likely to be more responsive to increasing CO2 concentration than systems where the amount of available nutrients is less variable. In more open systems, operation at a lower internal nutrient concentration as a result of increasing atmospheric CO2 concentration can lead to reduced nutrient losses per unit carbon gain. Our analysis shows that the effect of increasing CO2 on forest growth can differ substantially between forests due to interactions with a range of factors that affect nutrient supply. The response of a particular forest to increasing CO2 concentration can only be predicted if the main factors controlling nutrient supply and growth in that forest are understood and incorporated into an assessment.

2212^6^Klironomos,JN^Rillig,MC^Allen,MF^Zak,DR^Kubiske,M^Pregitzer,KS^1997^1^Soil fungal-arthropod responses to Populus tremuloides grown under enriched atmospheric CO2 under field conditions^127^3^6^473-478^^^^^Dec^^^^^7185
1096^1334^137^1981^1983^312^372^547^57^672^o nutrient gains and losses are likely to be more responsive to increasing CO2 concentration than systems where the amount of aA^7184^We investigated the influence of elevated CO2 and soil N availability on the growth of arbuscular mycorrhizal and non- mycorrhizal fungi, and on the number of mycophagous soil microarthropods associated with the roots of Populus tremuloides. CO2 concentration did not significantly affect percentage infection of Populus roots by mycorrhizal or non- mycorrhizal fungi. However, the extra-radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interaction between CO2 and soil N availability. Under N-poor soil. conditions, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fungi, but depressed growth by non-mycorrhizal fungi. There was no CO2 effect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated with the increase in non-mycorrhizal fungi. Results indicate a strong interaction between CO2 concentration and soil N availability on mycorrhizal functioning and on fungal-based soil food webs.

2213^3^Kwa,SH^Wee,YC^Kumar,PP^1997^1^Ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase activities of photoautotrophic callus of Platycerium coronarium (Koenig ex OF Muell.) Desv. under CO2 enrichment^177^50^2^75-82^^^^^^^^^^7187
1643^1644^243^3249^344^360^372^710^845^948^ extra-radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interaction between CO2 and soil N availability. Under N-poor soil. conditions, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fungi, but depressed growth by non-mycorrhizal fungi. There was no CO2 effect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated with the increase in non-mycorrhizal fungi. Results indicate a strong interaction between CO2 concentratiA^7186^The in vitro activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) were measured in cell-free extracts of Platycerium coronarium callus cultured for up to 42 days under photoautotrophic conditions with CO2 enrichment. With an increase in CO2 in the culture environment to 10% (v/v) at low light, the apparent photoautotrophic fixation of CO2 by Rubisco declined, whereas the non-photoautotrophic CO2 fixation by PEPC activity was enhanced. Hence, photosynthesis appears to play a lesser role in providing carbon skeletons and energy with prolonged culture in a CO2-enriched environment. Instead, the anaplerotic supply of C-skeletons by PEPC may be important under such a situation. Short-term (HCO3-)-C-14 fixation experiments indicated that photoautotrophic callus cultured for 3 weeks with 10% CO2 enrichment assimilated less (CO2)-C-14 than the control (0.03% CO2). Analyses of C-14-metabolites indicated that about 50% of the total soluble (CO2)-C-14 fixed was in the organic acid fraction and 35% in the amino acid fraction. Despite the changes in the in vitro Rubisco/PEPC activity-ratio, no significant change in the C-14 distribution pattern was apparent in response to increasing sucrose or CO2 concentrations. The suppression of Rubisco activity and total chlorophyll content in high sucrose or elevated CO2 concentrations suggests an inhibition of the capacity for photoautotrophic callus growth under these conditions.

2214^5^Luo,Y^Chen,JL^Reynolds,JF^Field,CB^Mooney,HA^1997^1^Disproportional increases in photosynthesis and plant biomass in a Californian grassland exposed to elevated CO2: a simulation analysis^43^11^6^696-704^^^^^Dec^^^^^7189
310^374^376^672^699^783^791^92^a situation. Short-term (HCO3-)-C-14 fixation experiments indicated that photoautotrophic callus cultured for 3 weeks with 10% CO2 enrichment assimilated less (CO2)-C-14 than the control (0.03% CO2). Analyses of C-14-metabolites indicated that about 50% of the total soluble (CO2)-C-14A^7188^1. Elevated CO2 concentrations often lead to increased photosynthetic carbon uptake in plants, but this does nor necessarily result in a proportional increase in plant biomass. We examined this paradox for grasslands in northern California that have been exposed to elevated CO2 since 1992. We evaluated the effects of physiological adjustments on plant growth and carbon balance of the dominant species, Avena barbata, using a plant growth model. 2. Without physiological adjustments, an observed 70% increase in leaf photosynthesis in elevated CO2 was predicted to increase plant biomass by 97% whereas experimental measurements suggested 5 and 13% decreases in 1992 and 1993, respectively, and a 40% increase in 1994. 3. Simulations with an increase in carbon allocation to roots by 29%, or leaf death rate by 80%, or non-structural carbohydrate storage by 60%, or leaf mass per unit area by 25% each predicted an approximately 40% increase in plant biomass in 1994 under elevated CO2. It follows that greater suppression of the biomass responses to elevated CO2, in 1992 and 1993 resulted from variable combinations of these physiological adjustments. 4. This modelling study concludes that (a) an increase in carbon loss or (b) a decrease in carbon-use efficiency or (c) an increase in carbon allocation to root growth will result in an increase in biomass growth that is less than that in leaf photosynthesis under elevated CO2. Alternatively, if carbon loss is reduced (e.g, depressed respiration) and/or carbon allocation to leaf growth is increased, biomass growth may be stimulated more than leaf photosynthesis by atmospheric CO2 concentration. Moreover, this modelling exercise suggests that physiological adjustments may have substantial effects on ecosystem carbon processes by varying ecosystem carbon influx, litterfall and Litter quality.
l carbohydrate storage by 60%, or leaf mass per unit area by 25% each predicted an approximately 40% increase in plant biomass in 1994 under elevated CO2. It follows that greater sup2215^4^Navas,ML^Sonie,L^Richarte,J^Roy,J^1997^1^The influence of elevated CO2 on species phenology, growth and reproduction in a Mediterranean old-field community^127^3^6^523-530^^^^^Dec^^^^^7191
1208^130^230^2419^341^344^374^423^429^434^se efficiency or (c) an increase in carbon allocation to root growth will result in an increase in biomass growth that is less than that in leaf photosynthesis under elevated CO2. Alternatively, if carbon loss is reduced (e.g, depressed respiration) and/or carbon allocation to leaf growth is increased, biomass growth may be stimulated more than leaf photosynthesis by atmospheric CO2 concentration. Moreover, this modelling exercise suggests that physiological adjustments may have substantial effects on ecosystem carbon processes by varying ecosystem carbon influx, litterfall and Litter quality.
l carbohydrate storage by 60%, or leaf mass per unit area by 25% each predicted an approximately 40% increase in plant biomass in 1994 under elevated CO2. It follows that greater supA^7190^We studied the effects on the phenology, growth and reproduction of 19 Mediterranean species, of elevating the atmospheric CO2 concentration ([CO2]) to twice-ambient. Intact monoliths were taken from an old-field and put, during a six month growing season, into growth chambers in which external climatic conditions were mimicked and [CO2] was regulated. Fruit set time was significantly changed in six species under elevated [CO2] and leaf and branch senescence accelerated in most species. Grasses had fewer leaves and legumes were more branched at peak production under elevated [CO2] than under ambient. Plant seed number was not significantly changed under elevated [CO2], whereas the reproductive effort of grasses was significantly depressed. Reproductive and vegetative characteristics showed related responses to [CO2], as species with enhanced biomass had a hastened fruit set time, a higher number of fruits per plant and a higher reproductive biomass under elevated [CO2] than under ambient conditions, while species with depressed biomass had a delayed fruit set time, a lower number of fruits per plant and a lower reproductive biomass. Our results also show a high interspecific variability in [CO2] response, but some trends emerged at the family level: the production of vegetative and reproductive modules were depressed in grasses and slightly stimulated in legumes.

2216^2^Berntson,GM^Bazzaz,FA^1998^1^Regenerating temperate forest mesocosms in elevated CO2: belowground growth and nitrogen cycling^2^113^1^115-125^^^^^Jan^^^^^7193
1044^2520^2522^2523^361^374^377^407^547^715^evated [CO2] than under ambient. Plant seed number was not significantly changed under elevated [CO2], whereas the reproductive effort of grasses was significantly depressed. Reproductive and vegetative characteristics showed related responses to [CO2], as species with enhanced biomass had a hastened fruit set time, a higher number of fruits per plant and a higher reproductive biomass under elevated [CO2] than under ambient conditions, wA^7192^The response of temperate forest ecosystems to elevated atmospheric CO2 concentrations is important because these ecosystems represent a significant component of the global carbon cycle. Two important but not well understood processes which elevated CO2 may substantially alter in these systems are regeneration and nitrogen cycling. If elevated CO2 leads to changes in species composition in regenerating forest communities then the structure and function of these ecosystems may be affected. In most temperate forests, nitrogen appears to be a limiting nutrient. If elevated CO2 leads to reductions in nitrogen cycling through increased sequestration of nitrogen in plant biomass or reductions in mineralization rates, long-term forest productivity may be constrained. To study these processes, we established mesocosms of regenerating forest communities in controlled environments maintained at either ambient (375 ppm) or elevated (700 ppm) CO2 concentrations. Mesocosms were constructed from intact monoliths of organic forest soil. We maintained these mesocosms for 2 years without any external inputs of nitrogen and allowed the plants naturally present as seeds and rhizomes to regenerate. We used N-15 pool dilution techniques to quantify nitrogen fluxes within the mesocosms at the end of the 2 years. Elevated atmospheric CO2 concentration significantly affected a number of plant and soil processes in the experimental regenerating forest mesocosms. These changes included increases in total plant biomass production, plant C/N ratios, ectomycorrhizal colonization of tree fine roots, changes in tree fine root architecture, and decreases in plant NH4+ uptake rates, gross NH4+ mineralization rates, and gross NH4+ consumption rates. In addition, there was a shift in the relative biomass contribution of the two dominant regenerating tree species; the proportion of total biomass contributed by white birch (Betula papyrifera) decreased and the proportion of total biomass contributed by yellow birch (B. alleghaniensis) increased. However, elevated CO2 had no significant effect on the total amount of nitrogen in plant and soil microbial biomass. In this study we observed a suite of effects due to elevated CO2, some of which could lead to increases in potential long term growth responses to elevated CO2, other to decreases. The reduced plant NH4+ uptake rates we observed are consistent with reduced NH4+ availability due to reduced gross mineralization rates. Reduced NH4+ mineralization rates are consistent with the increases in C/N ratios we observed for leaf and fine root material. Together, these data suggest the positive increases in plant root architectural parameters and mycorrhizal colonization may not be as important as the potential negative effects of reduced nitrogen availability through decreased decomposition rates in a future atmosphere with elevated CO2.
of total biomass contributed by white birch (Betula papyrifera) decreased and the proportion of total biomass contributed by yellow birch (B. alleghaniensis) incre2217^3^Cruz,C^Lips,SH^Martins-Loucao,MA^1997^1^Changes in the morphology of roots and leaves of carob seedlings induced by nitrogen source and atmospheric carbon dioxide^52^80^6^817-823^^^^^Dec^^^^^7195
2231^243^3174^3250^349^372^374^417^433^92^erm growth responses to elevated CO2, other to decreases. The reduced plant NH4+ uptake rates we observed are consistent with reduced NH4+ availability due to reduced gross mineralization rates. Reduced NH4+ mineralization rates are consistent with the increases in C/N ratios we observed for leaf and fine root material. Together, these data suggest the positive increases in plant root architectural parameters and mycorrhizal colonization may not be as important as the potential negative effects of reduced nitrogen availability through decreased decomposition rates in a future atmosphere with elevated CO2.
of total biomass contributed by white birch (Betula papyrifera) decreased and the proportion of total biomass contributed by yellow birch (B. alleghaniensis) increA^7194^Carob seedlings were grown hydroponically for 9 weeks under 360 and 800 mu l l(-1) CO2. One of two nitrogen sources, nitrate or ammonium, was added to the nutrient medium at concentrations of 3 mol m(-3). Root systems of the developing plants supplied with nitrate compared to those supplied with ammonium were characterized by: (a) more biomass on the lower part of the root; (b) fewer lateral roots of first and second order; (c) longer roots; (d) higher specific root length; (e) a smaller root diameter. The morphology of the root systems of nitrate- fed plants changed in the presence of elevated carbon dioxide concentrations, resembling, more closely, that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate- fed plants. Nitrate-fed plants had greater total leaf area in the presence of high carbon dioxide than in normal CO2, due to an increase in epidermal cell size that led to development of larger leaflets with lower stomatal frequency. The observed changes in the morphology of roots and shoots agreed with the results observed for total biomass production. Nitrate-fed plants increased their biomass production by 100% in the presence of elevated CO2 compared to 15% in ammonium-fed plants, indicating that the response of carob to high CO2 concentrations is very dependent on the nitrogen source. Under elevated CO2, nitrate grown plants had a larger content of sucrose in both roots and shoots, while no significant difference was observed in the content of sucrose in ammonium- grown plants, whether in ambient or enriched carbon dioxide. Hence, the differences in soluble carbohydrate contents can, at least partly, account for differences in root and shoot morphology. (C) 1997 Annals of Botany Company.

2218^3^Gebauer,RLE^Strain,BR^Reynolds,JP^1998^1^The effect of elevated CO2 and N availability on tissue concentrations and whole plant pools of carbon-based secondary compounds in loblolly pine (Pinus taeda)^2^113^1^29-36^^^^^Jan^^^^^7197
1080^1142^1652^1997^244^338^56^57^841^92^ologyA^7196^We examined the extent to which carbon investment into secondary compounds in loblolly pine (Pinus taeda L.) is changed by the interactive effect of elevated CO2 and N availability and whether differences among treatments are the result of size-dependent changes. Seedlings were grown for 138 days at two CO2 partial pressures (35 and 70 Pa CO2) and four N solution concentrations (0.5, 1.5, 3.5, and 6.5 mmol l(-1) NO3NH4) and concentrations of total phenolics and condensed tannins were determined four times during plant development in primary and fascicular needles, stems and lateral and tap roots. Concentrations of total phenolics in lateral roots and condensed tannins in tap roots were relatively high regardless of treatment. In the smallest seedlings secondary compound concentrations were relatively high and decreased in the initial growth phase. Thereafter condensed tannins accumulated strongly during plant maturation in all plant parts except in lateral roots, where concentrations did not change. Concentrations of total phenolics continued to decrease in lateral roots while they remained constant in all other plant parts. At the final harvest plants grown at elevated CO2 or low N availability showed increased concentrations of condensed tannins in aboveground parts. The CO2 effect, however, disappeared when size differences were adjusted for, indicating that CO2 only indirectly affected concentrations of condensed tannins through accelerating growth. Concentrations of total phenolics increased directly in response to low N availability and elevated CO2 in primary and fascicular needles and in lateral roots, which is consistent with predictions of the carbon-nutrient balance (CNB) hypothesis. The CNB hypothesis is also supported by the strong positive correlations between soluble sugar and total phenolics and between starch and condensed tannins. The results suggest that predictions of the CNB hypothesis could be improved if developmentally induced changes of secondary compounds were included.
ange. C2219^2^Hattenschwiler,S^Korner,C^1998^1^Biomass allocation and canopy development in spruce model ecosystems under elevated CO2 and increased N deposition^2^113^1^104-114^^^^^Jan^^^^^7199
1064^146^1654^2012^229^312^344^400^715^798^f condensed tannins in aboveground parts. The CO2 effect, however, disappeared when size differences were adjusted for, indicating that CO2 only indirectly affected concentrations of condensed tannins through accelerating growth. Concentrations of total phenolics increased directly in response to low N availability and elevated CO2 in primary and fascicular needles and in lateral roots, which is consistent with predictions of the carbon-nutrient balance (CNB) hypothesis. The CNB hypothesis is also supported by the strong positive correlations between soluble sugar and total phenolics and between starch and condensed tannins. The results suggest that predictions of the CNB hypothesis could be improved if developmentally induced changes of secondary compounds were included.
ange. CA^7198^Ecosystem-level experiments on the effects of atmospheric CO2 enrichment and N deposition on forest trees are urgently needed. Here we present data for nine model ecosystems of spruce (Picea abies) on natural nutrient-poor montane forest soil (0.7 m(2) of ground and 350 kg weight). Each system was composed of six 7-year-old (at harvest) trees each representing a different genotype, and a herbaceous understory layer (three species). The model ecosystems were exposed to three different CO2 concentrations (280, 420, 560 mu l l(-1)) and three different rates of wet N deposition (0, 30, 90 kg ha(-1) year(- 1)) in a simulated annual course of Swiss montane climate for 3 years. The total ecosystem biomass was not affected by CO2 concentration, but increased with increasing N deposition. However, biomass allocation to roots increased with increasing CO2 leading to significantly lower leaf mass ratios (LMRs) and leaf area ratios (LARs) in trees grown at elevated CO2. In contrast to CO2 enrichment, N deposition increased biomass allocation to the aboveground plant parts, and thus LMR and LAR were higher with increasing N deposition. We observed no CO2 x N interactions on growth, biomass production, or allocation, and there were also no genotype x treatment interactions. The final leaf area index (LAI) of the spruce canopies was 19% smaller at 420 and 27% smaller at 560 than that measured at 280 mu l CO2 l(-1), but was not significantly altered by increasing N deposition. Lower LAIs at elevated CO2 largely resulted from shorter branches (less needles per individual tree) and partially from increased needle litterfall. Independently of N deposition, total aboveground N content in the spruce communities declined with increasing CO2 (-18% at 420 and -31% at 560 compared to 280 mu l CO2 l(-1)). N deposition had the opposite effect on total above ground N content (+18% at 30 and +52% at 90 compared to 0 kg N ha(-1) year(-1)). Our results suggest that under competitive conditions on natural forest soil, atmospheric CO2 enrichment may not lead to higher ecosystem biomass production, but N deposition is likely to do so. The reduction in LAI under elevated CO2 suggests allometric down-regulation of photosynthetic carbon uptake at the canopy level. The strong decline in the tree nitrogen mass per unit ground area in response to elevated CO2 may indicate CO2- induced reductions of soil N availability.

2220^3^Luscher,A^Hendrey,GR^Nosberger,J^1998^1^Long-term responsiveness to free air CO2 enrichment of functional types, species and genotypes of plants from fertile permanent grassland^2^113^1^37-45^^^^^Jan^^^^^7201
1239^1292^130^1777^374^398^507^57^792^92^ition, total aboveground N content in the spruce communities declined with increasing CO2 (-18% at 420 and -31% at 560 compared to 280 mu l CO2 l(-1)). N deposition had the opposite effect on total above ground N content (+18% at 30 and +52% at 90 compared to 0 kg N ha(-1) year(-1)). Our results suggest that under competitive conditions on natural forest soil, atmospheric CO2 eA^7200^To test inter- and intraspecific variability in the responsiveness to elevated CO2, 9-14 different genotypes of each of 12 perennial species from fertile permanent grassland were grown in Lolium perenne swards under ambient (35 Pa) and elevated (60 Pa) atmospheric partial pressure of CO2 (pCO(2)) for 3 years in a free air carbon dioxide enrichment (FACE) experiment. The plant species were grouped according to their functional types: grasses (L. perenne, L. multiflorum, Arrhenatherum elatius, Dactylis glomerata, Festuca pratensis, Holcus lanatus, Trisetum flavescens), non-legume dicots (Rumex obtusifolius, R. acetosa, Ranunculus friesianus), and legumes (Trifolium repens, T. pratense). Yield (above a cutting height of 4.5 cm) was measured three times per year. The results were as follow. (1) There were highly significant differences in the responsiveness to elevated pCO(2) between the three functional types; legumes showed the strongest and grasses the weakest yield increase at elevated pCO(2). (2) There were differences in the temporal development of responsiveness to elevated pCO(2) among the functional types. The responsiveness of the legumes declined from the first to the second year, while the responsiveness of the non-legume dicots increased over the 3 years. During the growing season, the grasses and the non- legume dicots showed the strongest response to elevated pCO(2) during reproductive growth in the spring. (3) There were no significant genotypic differences in responsiveness to elevated pCO(2). Our results suggest that, due to interspecific differences in the responsiveness to elevated pCO(2), the species proportion within fertile temperate grassland may change if the increase in pCO(2) continues. Due to the temporal differences in the responsiveness to elevated pCO(2) among species, complex effects of elevated pCO(2) on competitive interactions in mixed swards must be expected. The existence of genotypic variability in the responsiveness to elevated pCO(2), on which selection could act, was not found under our experimental conditions.

2221^2^Bishop,DL^Bugbee,BG^1998^1^Photosynthetic capacity and dry mass partitioning in dwarf and semi-dwarf wheat (Triticum aestivum L.)^4^153^5-6^558-565^^^^^Nov^^^^^7203
2575^3251^3252^3253^348^356^384^435^724^783^ears. During the growing season, the grasses and the non- legume dicots showed the strongest response to elevated pCO(2) during reproductive growth in the spring. (3) There were no significant genotypic differences in responsiveness to elevated pCO(2). Our results suggest that, due to interspecific differences in the responsiveness to elevated pCO(2), the species proportion within fertile temperate grassland may change if the increase in pCO(2) continues. Due to the temporal differences in the responsiveness to elevated pCO(2) among species, complex effects of elevated pCO(2) on competitive interactions in mixed swards must be expected. The existence of genotypic variability in the responsiveness to elevated pCO(2), on which selection could act, was A^7202^Efficient use of space and high yields are critical for long- term food production aboard the International Space Station. The selection of a full dwarf wheat (less than 30 cm tall) with high photosynthetic and yield potential is a necessary prerequisite for growing wheat in the controlled, volume- limited environments available aboard long-term spaceflight missions. This study evaluated the photosynthetic capacity and carbon partitioning of a full-dwarf wheat cultivar, Super Dwarf, which is routinely used in spaceflight studies aboard U.S. space shuttle and NASA/Mir missions and made comparisons with other dwarf and semidwarf wheat cultivars utilized in other ground-based studies in plant space biology. Photosynthetic capacity of the flag leaf in two dwarf (Super Dwarf, BB-19), and three semi-dwarf (Veery-10, Yecora Rojo, IBWSN 199) wheat cultivars (Triticum aestivum L.) was assessed by measuring: net maximum photosynthet ic rate, RuBP carboxylation efficiency, chlorophyll concentration and flag leaf area. Dry mass partitioning of carbohydrates to the leaves, sheaths, stems and ear was also assessed. Plants were grown under controlled environmental conditions in three replicate studies: slightly enriched CO2 (370 mu mol mol(-1)), high photosynthetic photon flux (1000 mu mol m(-2) s(-1); 58 mol m(-2) d(-1)) for a 16 h photoperiod, 22/15 degrees C day/night temperatures, ample nutrients and water provided by one-half strength Hoagland's nutrient solution (Hoagland and Amen, 1950). Photosynthetic capacity of the flag leaf was determined at anthesis using net CO2 exchange rate versus internal CO2 concentration curves measured under saturating light (2000 mu mol m(-2) s(-1)) and CO2 (1000 mu mol mol(-1)). Dwarf wheat cultivars had greater photosynthetic capacities than the taller semi-dwarfs, they averaged 20 % higher maximum net photosynthetic rates compared to the taller semi-dwarfs, but these higher rates occurred only at anthesis, had slightly greater carboxylation efficiencies and significantly increased chlorophyll concentrations per unit leaf area. The reduced- height wheat had significantly less dry mass fraction in the stem but greater dry mass partitioned to the ear than the taller semi-dwarfs (Yecora rojo, IBWSN-199). Studies with detached heads confirm that the head is a significant sink in the shorter wheat cultivars.

2222^2^Lootens,P^Heursel,J^1998^1^Irradiance, temperature, and carbon dioxide enrichment affect photosynthesis in Phalaenopsis hybrids^170^33^7^1183-1185^^^^^Dec^^^^^7205
174^188^2577^3254^3255^348^374^749^763^779^t anthesis using net CO2 exchange rate versus internal CO2 concentration curves measured under saturating light (2000 mu mol m(-2) s(-1)) and CO2 (1000 mu mol mol(-1)). Dwarf wheat cultivars had greater photosynthetic capacities than the taller semi-dwarfs, they averaged 20 % higher maximum net photosynthetic rates compared to the taller semi-dwarfs, but these higher rates occurred only at anthesis, had slightly greater carboxylation efficiencies and significantly increaseA^7204^The short-term effects of photosynthetic photon flux (PPF), day/night temperatures and CO2 concentration on CO2 exchange were determined for two Phalaenopsis hybrids. At 20 degrees C, the saturating PPF for photosynthesis was 180 mu mol.m(-2).s(- 1). At this PPF and ambient CO2 level (380 mu L.L-1), a day/night temperature of 20/15 degrees C resulted in the largest daily CO2 uptake. Higher night temperatures probably increased the respiration rate and lowered daily CO2 uptake in comparison with 20/15 degrees C. An increase in the CO2 concentration from 380 to 950 mu L.L-1 increased daily CO2 uptake by 82%.

2223^4^Murphy,KP^Santamaria,JM^Davies,WJ^Lumsden,PJ^1998^1^Ventilation of culture vessels. I. Increased growth in vitro and survival ex vitro of Delphinium^361^73^6^725-729^^^^^Nov^^^^^7207
1323^1491^1869^312^3256^349^560^781^nthetic rates compared to the taller semi-dwarfs, but these higher rates occurred only at anthesis, had slightly greater carboxylation efficiencies and significantly increaseA^7206^Inclusion of small circular apertures covered with filters in the sides of plastic culture vessels led to a small but significant increase in the multiplication rate of Delphinium cultured in vitro and greater survival following transfer ex vitro. Filters had no effect on the multiplication rate and survival of Hosta. In vessels with apertures there was a large increase in the rate of water loss, but relative humidity was greater than 95% in both intact vessels and in vessels with filters. It is suggested that in vessels with apertures there was an increase in the flow of water vapour from the vessel atmosphere to the external atmosphere, due to a reduced diffusive resistance. The improved performance of Delphinium plants could have resulted from an increase in transpiration and movement of water (and therefore some nutrients) through the plants.

2224^3^Roussopoulos,D^Liakatas,A^Whittington,WJ^1998^1^Cotton responses to different light-temperature regimes^178^131^^277-283^^^^^Nov^^^^^7209ly increase1285^264^310^348^546^643^674^687^92^ertures covered with filters in the sides of plastic culture vessels led to a small but significant increase in the multiplication rate of Delphinium cultured in vitro and greater survival following transfer ex vitro. Filters had no effect on the multiplication rate and survival of Hosta. In vessels with apertures there was a large increase in the rate of water loss, but relative humidity was greater than 95% in both intact vessels and in vessels with filters. It is suggested that in vessels with apertures there was an increase in the flow of water vapour from the vessel atmosphere to the external atmosphere, due to a reduced diffusive resistance. The improved performance of Delphinium plants could have resulted from an increase in transpiration and movement of water (and therefore some nutrients) through the plants.

2224^3^Roussopoulos,D^Liakatas,A^Whittington,WJ^1998^1^Cotton responses to different light-temperature regimes^178^131^^277-283^^^^^Nov^^^^^7209ly increaseA^7208^A series of experiments investigating the interactive effects of light and temperature on vegetative growth, earliness, fruiting, yield and fibre properties in three cultivars of cotton, was undertaken in growth rooms. Two constant day/night temperature regimes with a difference of 4 degrees C (30/20 and 26/16.5 degrees C) were used throughout the growing season in combination with two light intensities (75 and 52.5 W m(-2)). The results showed that significant interactions occurred for most of the characters studied. Although the development of leaf area was mainly temperature-dependent, plants at harvest had a larger leaf area when high temperature was combined with low rather than with high light intensity. Leaf area was least in the low temperature-low light regime. However, the plants grown under the high temperature-low light combination weighed the least. Variations in the number of nodes and internode length were largely dependent on temperature rather than light. Light did, however, affect the numbers of branches, sympodia and monopodia. The first two of these were highest in the high light-high temperature regime and the third in the low light- low temperature regime. All other characters, except time to certain developmental stages and fibre length, were reduced at the lower light intensity. Variation in temperature modified the light effect and vice versa, in a character-dependent manner. More specifically, square and boil dry weights, as well as seed cotton yield per plant, were highest in high light combined with low temperature, where the most and heaviest bells were produced. But flower production was favoured by high light and high temperature, suggesting increased boil retention at low temperature, especially when combined with low light. Low temperature and high light also maximized lint percentage. Fibres were shortest in the high temperature-high light regime, where fibre strength, micronaire index and maturity ratio were at a maximum. However, the finest and the most uniform fibres were produced when high light was combined with low temperature. Cultivar differences were significant mainly in leaf area and dry matter production at flowering.

2225^4^Schapendonk,AHCM^Stol,W^van Kraalingen,DWG^Bouman,BAM^1998^1^LINGRA, a sink/source model to simulate grassland productivity in Europe^314^9^2-3^87-100^^^^^Nov^^^^^7211
227^2476^3257^349^416^699^867^914^92^ a character-dependent manner. More specifically, square and boil dry weights, as well as seed cotton yield per plant, were highest in high light combined with low temperature, where the most and heaviest bells were produced. But flower production was favoured by high light and high temperature, suggesting increased boil retention at low temperature, especially when combined with low light. Low temperature and high light also maximized lint percentage. Fibres were shortest in the high temperature-high light regime, where fibre strength, micronaire index and maturity ratio were at a maximum. However, the finest and the most uniform fibres A^7210^A simulation model for the prediction of the productivity of Lolium perenne L. grasslands is described and validated. Simulated key processes are light utilization, leaf formation, leaf elongation, tillering, and carbon partitioning (storage, shoot, root). Source- and sink-limited growth are simulated independently. Sink-limited growth is characterized by temperature-dependent leaf expansion and tiller development, whereas source-limited growth is determined by photosynthetic light-use-efficiency of the canopy and the remobilization of stored carbohydrates in the stubble. At each integration step, commonly 1 day, the available amount of carbon from the source is compared with the carbon required by the sink. The actual growth is determined by the minimum value of either the sink or the source. If the source is in excess of the sink, the surplus is allocated to storage carbohydrates in the stubble. This storage carbon is available for remobilization at times that the sink requires more carbohydrates than are available from photosynthesis. In contrast to previous grassland models, LINGRA describes regrowth after defoliation in a mechanistic way, balanced by temperature-driven remobilization of stored carbohydrates. In order to validate LINGRA, an extensive set of experimental data was used, derived from measurements at 35 sites in Europe. The average error between the observed and predicted yields was 14% at the level of irrigated, and 19% at the level of non-irrigated, treatments for the whole of Europe. (C) 1998 Elsevier Science B.V. All rights reserved.

2226^4^Akimoto,M^Shirai,A^Ohtaguchi,K^Koide,K^1998^1^Carbon dioxide fixation and polyunsaturated fatty acid production by the red alga Porphyridium cruentum^366^73^2-3^269-278^^^^^May-Jun^^^^^7213
130^492^92^990^f either the sink or the source. If the source is in excess of the sink, the surplus is allocated to storage carbohydrates in the stubble. This storage carbon is available for remobilization at times that the sink requires more carbohydrates thA^7212^Focusing on CO2 fixation, photoautotrophic cultivation of the red alga Porphyridium cruentum was investigated by means of a batch culture under a 5% CO2-enriched atmosphere. The alg-al growth kinetics was successfully described with a logistic model, and simulation of a continuous culture under the optimum growth conditions (30 degrees C, 12 klux and 1.18 g-cells/L) showed that the algal CO2-fixation activity could reach 0.66 g- CO2/(L X d). Under the same growth conditions, eicosapentaenoic acid (20:5 n-3, EPA) and arachidonic acid (20:4 n-6, ARA) yields were similarly calculated to be 3.6 mg-EPA/(L X d) and 6.5 mg-ARA/(L X d), respectively.





2228^6^Wurr,DCE^Hand,DW^Edmondson,RN^Fellows,JR^Hannah,MA^Cribb,DM^1998^1^Climate change: a response surface study of the effects of CO2 and temperature on the growth of beetroot, carrots and onions^178^131^^125-133^^^^^Sep^^^^^7217
344^376^434^662^ble. This storage carbon is available for remobilization at times that the sink requires more carbohydrates thA^7216^Ten daylit, controlled-environment cabinets were used to investigate the possible impacts of global rises in atmospheric CO2 concentration and temperature on beetroot (Beta vulgaris L.), carrot (Daucus carota L.) and bulb onion (Allium cepa L.) plants. Their responses to CO2 concentrations of 350, 450, 550, 650 and 750 vpm and temperatures of 12, 13.5, 15, 16.5 and 18 degrees C were examined by using a fractional factorial design for the two treatment factors. Use of the daylit cabinets allowed the plants to be grown in natural light, common atmospheric humidities (vpd 0.7 kPa) and nonlimiting supplies of water and mineral nutrients. Polynomial models were used to summarize the whole plant dry weight and fresh weight yield responses and to indicate the potential impact of climate change. Additionally, the models were used to generate predictions of the percentage change in whole plant dry weight and plant fresh weight yield for the years 2025 and 2050 relative to 1992. Baseline values of 350 vpm for CO2 and a mean temperature of 13.5 degrees C for 1992 together with forecast CO2 values of 407 and 442 vpm and temperature increases of 0.7 and 1.1 C for 2025 and 2050 respectively were used. For 2025, fresh weight yield changes of + 19%, +9% and +13% were obtained for beetroot, carrot and onion crops respectively, while for 2050 the respective changes were + 32 %, + 13 % and +21 %. Measurements of the ratio of the maximum diameter of the bulb to the minimum diameter of the neck for onions showed that there was little or no influence of CO2, whereas the effect of temperature was substantial. Bulbing was accelerated by high temperature and was greatly delayed at low temperature. At temperatures < 15 degrees C, the delays to bulbing resulted in the development of undesirable, thick-necked onions which tended to remain green with erect leaves. These results suggest, therefore, that a warmer climate will be advantageous for the commercial production of bulb onions in Britain.
92. Baseline values of 350 vpm for C2229^1^Amthor,JS^1998^1^Perspective on the relative insignificance of increasing atmospheric CO2 concentration to crop yield^207^58^2^109-127^^^^^Aug^^^^^7219
1100^1203^227^243^312^3258^3259^374^376^409^sh weight yield changes of + 19%, +9% and +13% were obtained for beetroot, carrot and onion crops respectively, while for 2050 the respective changes were + 32 %, + 13 % and +21 %. Measurements of the ratio of the maximum diameter of the bulb to the minimum diameter of the neck for onions showed that there was little or no influence of CO2, whereas the effect of temperature was substantial. Bulbing was accelerated by high temperature and was greatly delayed at low temperature. At temperatures < 15 degrees C, the delays to bulbing resulted in the development of undesirable, thick-necked onions which tended to remain green with erect leaves. These results suggest, therefore, that a warmer climate will be advantageous for the commercial production of bulb onions in Britain.
92. Baseline values of 350 vpm for CA^7218^Average yield of most crops in many countries increased significantly during the past 50 to 100 years. Although atmospheric CO2 concentration, [CO2](a), also increased during that time period, and although crop growth and yield can respond positively to [CO2](a) increase, yield increases were due mainly to factors other than increasing [CO2](a). Similarly, some yield increases prior to 1900 were also associated primarily with factors other than changes in [CO2](a). In particular, past national average yield increases were the result chiefly of technological advances such as nitrogen fertilization; selection of genotypes with increased harvest index and disease resistance; mechanization of planting, cultivation, and harvesting; and chemical weed and pest control. If technology continues to increase average yields at recent rates, near-future increases in [CO2](a) will have only small impacts on yield in comparison to technology in many countries. Conversely, if future increases in [CO2](a) are the main drivers of future yield increases, those yield increases will be small. These points are demonstrated through a comparison of (i) long-term records of yield, (ii) data from key controlled-[CO2] experiments, and (iii) records of past [CO2](a). Finally, it is noted that continued [CO2](a) increase may bring with it climatic changes that could have negative or positive impacts on future yield. (C) 1998 Elsevier Science B.V. All rights reserved.

2230^4^Duquesnay,A^Breda,N^Stievenard,M^Dupouey,JL^1998^1^Changes of tree-ring delta C-13 and water-use efficiency of beech (Fagus sylvatica L.) in north-eastern France during the past century^9^21^6^565-572^^^^^Jun^^^^^7221
2703^3260^3261^362^384^504^539^586^627^745^ltivation, and harvesting; and chemical weed and pest control. If technology continues to increase average yields at recent rates, near-future increases in [CO2](a) will have only small impacts on yield in comparison to technology in many countries. Conversely, if future increases in [CO2](a) are the mainA^7220^We investigated variation in intrinsic water-use efficiency during the past century by analysing delta(13)C in tree rings of beech growing in north-eastern France. Two different silvicultural systems were studied: high forest and coppice- with-standards, We studied separately effects related to the age of the tree at the time the ring was formed and effects attributable to environmental changes. At young ages, delta(13)C shows an increase of more than 1 parts per thousand. However, age-related trends differ in high forest and coppice- with-standards. Changes in microenvironmental variables during stand maturation, and physiological changes related to structural development of the trees with ageing, could explain these results. During the past century, delta(13)C in tree rings shows a pattern of decline that is not paralleled by air delta(13)C changes. Isotopic discrimination has significantly decreased from 18.1 to 16.4 parts per thousand in high forest and varied insignificantly between 17.4 and 16.9 parts per thousand in coppice-with-standards, As a consequence, intrinsic water-use efficiency has increased by 44% in high forest and 23% in coppice-with-standards during the past century. These results accord with the increased water-use efficiency observed in controlled experiments under a CO2-enriched atmosphere. However other environmental changes, such as nitrogen deposition, may be responsible for such trends.





2232^4^Luxmoore,RJ^Hanson,PJ^Beauchamp,JJ^Joslin,JD^1998^1^Passive nighttime warming facility for forest ecosystem research^13^18^8-9^615-623^^^^^Aug-Sep^^^^^7225
137^310^312^3263^3264^3265^349^811^92^976^physiological changes related to structural development of the trees with ageing, could explain these results. During the past century, delta(13)C in tree rings shows a pattern of decline that is not paralleled by air delta(13)C changes. Isotopic discrimination has significantly decreased from 18.1 to 16.4 parts per thousand in high forest and varied insignificantly between 17.4 and 16.9A^7224^A nighttime warming experiment is proposed. Over the last four decades a significant rise in nighttime mini mum temperature has been determined from analysis of meteorological records from a global distribution of locations. The experiment involves nighttime deployment of infrared (IR) reflecting curtains around four sides of a forest canopy and across the top of the forest to mimic the top-down warming effect of cloud cover. The curtains are deployed with cable and pulley systems mounted on a tower and scaffolding structure built around the selected forest site. The trunk space is not enclosed except as an optional manipulation. The curtains reflect long-wave radiation emitted from the forest and ground back into the forest warming the trees, litter, and soil. Excellent infrared reflection can be obtained with commercially available fabrics that have aluminum foil bonded to one side. A canopy warming of 3 to 5 degrees C is expected on cloudless nights, and on cloudy nights, a warming of 1 to 3 degrees C is anticipated relative to a control plot. The curtains are withdrawn by computer control during the day and also at night during periods with precipitation or excessive wind. Examples of hypothesized ecosystem responses to nighttime warming include: (1) increase in tree maintenance respiration (decreasing carbon reserves and ultimately tree growth), (2) increase in the length of the growing season (increasing growth), (3) increase in soil respiration, (4) increase in litter decomposition, (5) increase in mineralization of N and other nutrients from soil organic matter, (6) increase in nutrient uptake (increasing growth), and (7) increase in N immobilization in litter. Hypothesis 1 has the opposite consequence for tree growth to Hypotheses 2 and 6, and thus opposite consequences for the feedback regulation that vegetation has on net greenhouse gas releases to the atmosphere. If Hypothesis 1 is dominant, warming could lead to more warming from the additional CO2 emissions. Site- specific meteorological, ecophysiological. and phenological measurements are obtained in the warming treatment and in a carefully selected control plot to investigate site-specific hypotheses, Measurements made on both plots for a baseline period and during the period of curtain deployment provide data to test the hypotheses statistically by the "before-after- control-impact" method applicable to unreplicated experiments. The enclosure has a modular design that can be adapted and combined with other forest-scale manipulation experiments such as free air CO2 enrichment and throughfall displacement.

2233^6^Bender,J^Hertstein,U^Fangmeier,A^van Oijen,M^Weigel,HJ^Jager,HJ^1998^1^The impact of climate change on yield of wheat in Europe: Results of the European stress physiology and climate experiment (ESPACE-wheat)^292^72^1-2^37-42^^^^^May^^^^^7227
1190^1262^1364^174^264^312^447^92^eleases to the atmosphere. If Hypothesis 1 is dominant, warming could lead to more warming from the additional CO2 emissions. Site- specific meteorological, eA^7226^The European Stress Physiology and Climate Experiment (ESPACE- wheat) was funded by the EU from 1994-1997. Major goals of the project were 1) to investigate by means of experiments the sensitivity of wheat growth, development and productivity to the combined effects of changes in CO2 concentration, climatic variables and other physiological stresses, 2) to use experimental data for extension and improvement of process- based wheat growth simulation models, and 3) to apply models to assess the influences on crops of climatic change, CO2 concentration and additional stresses in Europe. Experimental studies were performed at different sites in Europe through three consecutive seasons by means of open-top chambers according to a common standard protocol, and two simulation models were used for the analysis: AFRCWHEAT2 and LINTULCC. This paper summarizes the main findings of the effects of CO2 enrichment and other factors such as ozone, drought stress or nitrogen supply on the yield response of spring wheat (Triticum aestivum cv. Minaret). A comparison of the measured data with the main outputs of the LINTULCC model simulations is are presented. Generally, Minaret wheat did not respond significantly to ozone. CO2 enrichment had a positive influence on grain yield in almost all experiments, however, significant interactions between CO2 and other factors were not common. The average measured yield increase due to CO2 doubling was 35 % compared to grain yield measured at ambient CO2 concentrations, although there was a great variability in yield responses between sites and years. LINTULCC predicted a 42 % yield increase, but a much smaller variation between individual experiments. Although the effects of CO2 and O-2 on crop growth and yield were acceptably simulated, observed process-rates often showed variation not related to light intensity, temperature, CO2 or O-2, ie, not related to the main driving variables of the models. This unexplained variability in the measured datasets suggested a role of factors which were not accounted for in the models.

2234^2^Bertin,N^Gary,C^1998^1^Short and long term fluctuations of the leaf mass per area of tomato plants - Implications for growth models^52^82^1^71-81^^^^^Jul^^^^^7229
1608^243^341^348^662^ive influence on grain yield in almost all experiments, however, significant interactions between CO2 and other factors were not common. The average measured yield increase due to CO2 doubling was 35 % compared to grain yield measured at ambient CO2 concentrations, although there was a great variability in yield responses between sites and years. LINTULCC predicted a 42 % yield increase, but a much smaller variation between individual experiments. Although the effects of CO2 and O-2 on crop growth and yield were acceptably simulated, observed process-rates often showed variation not related to light intensity, temperature, CO2 or O-2, ie, not related to the main driving variables of the models. This unexplained variability in the measured datasets suggested a role of factors whiA^7228^The leaf mass per unit leaf area (LMA) is a key variable in many growth models, since it is often used to predict leaf area expansion from leaf dry weight increase, or vice versa. Influences of source-sink balance on leaf area, leaf dry weight, LMA, and leaf content in non-structural carbohydrates were investigated in glasshouse tomato crops. The source-sink balance was manipulated by artificial shading, CO2 enrichment or fruit removal using different tomato cultivars. Leaf area was hardly affected by competition for assimilates except under extreme conditions. Iri contrast, leaf dry weight, and consequently LMA, underwent large and rapid fluctuations in response to any factor that changed source and sink activities. A 60% reduction of photosynthetically active radiation involved a 24% decrease in LMA after 10 d. Carbon dioxide enrichment and fruit removal induced about a 45% and 15% increase in LMA, respectively, on plants with two fruiting trusses, but hardly affected LMA of producing plants. No significant cultivar effect could be identified. Changes in starch and soluble sugar content in leaves accounted for only 29% of diurnal variations in LMA, suggesting regular fluctuations of other components. We propose that structural LMA varies between a maximum and a minimum value according to the ratio of assimilate supply and demand during leaf development. Leaf area is independent of the supply of assimilates when the minimum structural LMA is realised. When the maximum structural LMA is attained, a storage pool of assimilates may accumulate in leaves during periods of high supply and low demand. We present a model including these hypotheses, which predicts structural and non- structural LMA variations of plants with different source-sink ratios. (C) 1998 Annals of Botany Company.

2235^3^Mitra,A^Dey,S^Sawarkar,SK^1998^1^Photoautotrophic in vitro multiplication of the orchid Dendrobium under CO2 enrichment^261^41^1^145-148^^^^^^^^^^7231
561^781^92^sses, but hardly affected LMA of producing plants. No sigA^7230^An attempt to reduce the production cost on tissue cultured plants, photoautotrophic culture of a high value orchid Dendrobium was established under CO2-enriched conditions. The shoot length and the number of leaves were almost equal in plantlets grown on medium with 2 % sucrose or without sucrose and under normal or enhanced (40 g m(-3)) CO2 concentration, whereas the fresh and dry masses were higher in cultures grown in sucrose containing media or under CO2 enrichment. Development of roots was observed only on media without sucrose, but CO2 enrichment did not have significant effects on in vitro rootings.

2236^2^Van Labeke,MC^Dambre,P^1998^1^Effect of supplementary lighting and CO2 enrichment on yield and flower stem quality of Alstroemeria cultivars^165^74^4^269-278^^^^^29 May^^^^^7233
1160^1161^1173^1485^1510^512^607^881^rophic in vitro multiplication of the orchid Dendrobium under CO2 enrichment^261^41^1^145-148^^^^^^^^^^7231
561^781^92^sses, but hardly affected LMA of producing plants. No sigA^7232^The effects of CO2 enrichment and supplementary lighting on the production and Rower stem quality of five Alstroemeria cultivars ('Barbara', 'Fiona', 'Helios', 'Mona Lisa' and 'Tiara') were studied. CO2 enrichment up to 900 mu l l(-1) alone was beneficial for an increase in the number of flower stems and flower stem quality regardless of the use of supplementary lighting. Supplementary lighting alone enhanced flower stem production and quality to a lower extent than CO2 enrichment. The combination of both supplementary lighting and CO2 enrichment resulted in superior flower stem production for Alstroemeria 'Fiona', 'Helios' and 'Mona Lisa', and flower stem quality for Alstroemeria 'Barbara', 'Fiona' and 'Mona Lisa'. (C) 1998 Elsevier Science B.V.





2238^3^Goodale,CL^Aber,JD^Farrell,EP^1998^1^Predicting the relative sensitivity of forest production in Ireland to site quality and climate change^288^10^1^51-67^^^^^9 Apr^^^^^7237
1660^2017^256^3266^3267^3268^3269^399^659^861^f producing plants. No sigA^7236^Most model-based predictions of climate change effects on forest ecosystems have used either potential or static descriptions of vegetation and site, removing the effects of direct management or land use. In this paper we use a previously developed and validated model of carbon and water balances in forest ecosystems (PnET-II) to assess the relative sensitivity of forest production in Ireland to predicted climate change and to ambient variability in site quality. After validating the model against measured productivity for 2 sets of stands, we ran the model using existing variation in site quality, represented as differences in foliar N concentration, and also for predicted changes in climate and atmospheric CO2. Resulting variations in productivity were compared with those due to potential errors in the specification of input parameters and to variation in current ambient climate across the region. The effects on net primary production (NPP) and wood production of either ambient variation in climate or predicted changes in temperature, precipitation and CO2 are quite small (0 to 30%) relative to the effects of ambient variability in site quality (up to 400%). The range of possible variation in other user-specified physiological parameters resulted in changes of less than 10% in model predictions. We conclude that site-specific conditions and management practices result in a range of forest productivity that is much greater than any likely to be induced by climate change or CO2 enrichment. We also suggest that it is essential to understand and map spatial variability in site quality, as well as to understand how the productive capacity of landscapes will change in response to management and pollution loading, if we are to predict the actual role that climate change will play in altering forest productivity and global biogeochemistry.

2239^1^Grant,RF^1998^1^Simulation in ecosys of root growth response to contrasting soil water and nitrogen^81^107^2-3^237-264^^^^^1 Apr^^^^^7239bient variation in climate 1069^1285^224^312^314^3270^3271^417^724^986^ation and CO2 are quite small (0 to 30%) relative to the effects of ambient variability in site quality (up to 400%). The range of possible variation in other user-specified physiological parameters resulted in changes of less than 10% in model predictions. We conclude that site-specific conditions and management practices result in a range of forest productivity that is much greater than any likely to be induced by climate change or CO2 enrichment. We also suggest that it is essential to understand and map spatial variability in site quality, as well as to understand how the productive capacity of landscapes will change in response to management and pollution loading, if we are to predict the actual role that climate change will play in altering forest productivity and global biogeochemistry.

2239^1^Grant,RF^1998^1^Simulation in ecosys of root growth response to contrasting soil water and nitrogen^81^107^2-3^237-264^^^^^1 Apr^^^^^7239bient variation in climate A^7238^If mathematical models of plant growth are to perform reliably under diverse conditions of soil and climate, then the effects of these conditions on root growth must be represented. A mathematical model of root and mycorrhizal growth is proposed to represent the effects of soil and climate on growth using the hypothesis that a functional equilibrium exists among root axes and shoot branches. In this model access to growth resources (C, N, P, water) by different axes or branches depends upon (1) proximity of the axis or branch to the point of resource acquisition, and (2) the rate at which resources are consumed by the axis or branch in relation to that by other axes or branches. This model was coupled to a plant growth model as part of the ecosystem simulation model ecosys, and its sensitivity to changes in model parameters and soil boundary conditions was tested. Simulated root growth was less sensitive to changes in soil water and nitrogen than was simulated shoot growth. This lower sensitivity allowed the model to simulate changes in root,shoot ratios with changes in soil water and nitrogen that were consistent with those commonly reported in the literature. Changes in soil water also caused changes in vertical distributions of root length density to be simulated that were also consistent with those reported. Changes in root,shoot partitioning and in root density distributions allowed improved access by plants in the model to limiting growth resources. The root model was parameterized from basic root growth studies conducted independently of the model, and without reference to site-specific patterns of seasonal root growth. Consequently the model is likely to be of general value in the simulation of root growth under diverse soil conditions, although such generality needs to be established through further testing under different soils, climates and crops. The precision of some of the model parameters is uncertain and the sensitivity of the model to this uncertainty is discussed. (C) 1998 Elsevier Science B.V. All rights reserved.

2240^1^Idso,SB^1998^1^CO2-induced global warming: a skeptic's view of potential climate change^288^10^1^69-82^^^^^9 Apr^^^^^7241
1020^3272^3273^3274^3275^3276^3277^349^377^899^ vertical distributions of root length density to be simulated that were also consistent with those reported. Changes in root,shoot partitioning and in root density distributions allowed improved access by plants in the model to limiting growth resources. The root model was parameterized from basic root growth studies conducted independently of the model, and without reference to site-specific patterns of seasonal root growth. Consequently the model is likely to be of general value in the simulation of root growth under diverse soil conditions, although such generality needs to be established through further testing under different soils, climates and crops. The precision of some of the model parameters is uncertain and the sensitivity of the model to this uncertainty is discussed. (C) 1998 Elsevier ScieA^7240^Over the course of the past 2 decades, I have analyzed a number of natural phenomena that reveal how Earth's near-surface air temperature responds to surface radiative perturbations. These studies all suggest that a 300 to 600 ppm doubling of the atmosphere's CO2 concentration could raise the planet's mean surface air temperature by only about 0.4 degrees C. Even this modicum of warming may never be realized, however, for it could be negated by a number of planetary cooling forces that are intensified by warmer temperatures and by the strengthening of biological processes that are enhanced by the same rise in atmospheric CO2 concentration that drives the warming. Several of these cooling forces have individually been estimated to be of equivalent magnitude, but of opposite sign, to the typically predicted greenhouse effect of a doubling of the air's CO2 content, which suggests to me that little net temperature change will ultimately result from the ongoing buildup of CO2 in Earth's atmosphere. Consequently, I am skeptical of the predictions of significant CO2-induced global warming that are being made by state-of-the-art climate models and believe that much more work on a wide variety of research fronts will be required to properly resolve the issue.

2241^3^King,SP^Badger,MR^Furbank,RT^1998^1^CO2 refixation characteristics of developing canola seeds and silique wall^92^25^3^377-386^^^^^^^^^^7243
1274^1275^1817^2625^3278^3279^424^493^554^739^d by a number of planetary cooling forces that are intensified by warmer temperatures and by the strengthening of biological processes that are enhanced by the same rise in atmospheric CO2 concentration that drives the warming. Several of these cooling forces have individually been estimated to be of equivalent magnitude, but of opposite sign, to the typically predicted greenhouse effect of a doubling of the air's CO2 content, which suggests to me that little net temperature change will ultimately result from the ongoing buildup of CO2 in Earth's atmosphere. ConsequA^7242^The potential for developing canola (Brassica napus L.) seeds and the interior silique (pod) wall to refix respired CO2 has been investigated. From ribulose-1,5-bisphosphate carboxylase- oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) activities, seeds were estimated to have a greater CO2, fixation capacity than silique wall endocarp during oil filling. The major component of seed fixation capacity was embryo Rubisco, which had a total activity of 6.3 nmol min(-1) embryo(-1) (3.7 mu mol min(-1) mg chlorophyll(-1)) at 28 days after anthesis (DAA) with smaller contributions from seed coat and embryo PEPC. Rubisco activities were probably maximal in vivo because of high silique cavity CO2 concentrations (0.8 to 2.5%). Seed chlorophyll content rapidly increased over 10-fold from 20 to 30 DAA and, with 20% of incident light transmitted through the silique wall, embryos demonstrated appreciable photosynthetic electron transport rates and most energy produced appeared to be used for Rubisco-catalysed CO2 fixation. Endocarp refixation capacity was less than seeds because chlorophyll content was not enriched and PEPC activities were relatively small. These data indicate that developing seeds and also endocarp refix respired CO2 and that embryo chlorophyll plays a critical role in this refixation.

2242^3^Linker,R^Seginer,I^Gutman,PO^1998^1^Optimal CO2 control in a greenhouse modeled with neural networks^367^19^3^289-310^^^^^Mar^^^^^7245
376^total activity of 6.3 nmol min(-1) embryo(-1) (3.7 mu mol min(-1) mg chlorophyll(-1)) at 28 days after anthesis (DAA) with smaller contributions from seed coat and embryo PEPC. Rubisco activities were probably maximal in vivo because of high silique cavity CO2 concentrations (0.8 to 2.5%). Seed chlorophyll content rapidly increased over 10-fold from 20 to 30 DAA and, with 20% of incident light transmitted through the silique wall, embryos demonstrated appreciable photosynthetic electron transport rates and most energy produced appeared to be used for Rubisco-caA^7244^CO, enrichment in warm climates requires a delicate balance between the need to ventilate and the desire to enrich. Model- based optimization can achieve this balance, but requires reliable models of the greenhouse environment and of the crop response. This study assumes that the crop response is known, and focuses on the greenhouse model. Neural network greenhouse models were trained using data collected over two summer months in a small greenhouse. The models were reduced to minimum size, by predicting separately the temperature and CO2 concentration, and by eliminating any unessential input. The resulting models not only fit the data well, they also seem qualitatively correct, and produce reasonable optimization results. Using these models, the effect of evaporative cooling on extending the enrichment duration is demonstrated. (C) 1998 Elsevier Science B.V. All rights reserved.
onstrated appreciable photosynthetic electron transport rates and most energy produced appeared to be used for Rubisco-ca2243^5^Mitra,A^Bhattacharya,PS^Dey,S^Sawarkar,SK^Bhattacharyya,BC^1998^1^Photoautotrophic in vitro culture of Chrysanthemum under CO2 enrichment^303^12^4^335-337^^^^^Apr^^^^^7247
781^
A^7246^Photoautotrophic culture of Chrysanthemum was established under CO2 enrichment (2% v/v). The shoot length and number of leaves were almost equal (2.7 cm and 14 respectively) both under photoautotrophic and photomixotrophic cultures, recorded after four weeks of incubation. Similarly, average dry mass of the plantlets were comparable (31 and 28 mg respectively) under both conditions. The number of branches and internode length which influence the number of propagule potential for mass propagation, were also identical. Nevertheless, photoautotrophic cultivation minimized the risk of contamination in cultures, which in turn will reduce the production cost.
998 Elsevier Science B.V. All rights reserved.
onstrated appreciable photosynthetic electron transport rates and most energy produced appeared to be used for Rubisco-ca2244^8^Pospisilova,J^Wilhelmova,N^Synkova,H^Catsky,J^Krebs,D^Ticha,I^Hanackova,B^Snopek,J^1998^1^Acclimation of tobacco plantlets to ex vitro conditions as affected by application of abscisic acid^78^49^322^863-869^^^^^May^^^^^7249
243^256^3280^3281^3282^3283^349^384^781^91^v). The shoot length and number of leaves were almost equal (2.7 cm and 14 respectively) both under photoautotrophic and photomixotrophic cultures, recorded after four weeks of incubation. Similarly, average dry mass of the plantlets were comparable (31 and 28 mg respectively) under both conditions. The number of branches and internode length which influence the number of propagule potential for mass propagation, were also identical. Nevertheless, photoautotrophic cultivation minimized the risk of contamination in cultures, which in turn will reduce the production cost.
998 Elsevier Science B.V. All rights reserved.
onstrated appreciable photosynthetic electron transport rates and most energy produced appeared to be used for Rubisco-caA^7248^Plantlets of Nicotiana tabacum L. cv, Petit Havana SR1 were grown in vitro on Murashige and Skoog medium containing 2% saccharose, and then transplanted ex vitro into pots with coarse sand and Hewitt nutrient solution, In the first day after transplantation, the antitranspirant abscisic acid (ABA; 0.01, 0.05 or 0.10 mM) was added to the substrate. Leaf stomatal conductance (g(s)), which was high in plants during the first days after transplantation similarly as in plantlets grown in vitro, was considerably decreased by ABA-treatment, However, in the further days g(s) decreased more quickly in control than in ABA-treated plants, and after 2 or 3 weeks g(s) was significantly lower than that of plantlets grown in vitro but similar in control and ABA-treated plants. Two weeks after transplantation, net photosynthetic rate, chlorophyll a + b content, maximal photochemical efficiency, and actual quantum yield of photosystem II in plant leaves were higher in comparison with those in plantlets grown in vitro. ABA- treatment had slight positive or insignificant effect on photosynthetic parameters and enhanced plant growth. Thus ABA application can alleviate 'transplant shock' and speed up acclimation of plantlets to ex vitro conditions.

2245^4^Saarnio,S^Alm,J^Martikainen,PJ^Silvola,J^1998^1^Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire^12^86^2^261-268^^^^^Apr^^^^^7251
1781^1930^209^243^312^3170^3284^376^673^99^as in plantlets grown in vitro, was considerably decreased by ABA-treatment, However, in the further days g(s) decreased more quickly in control than in ABA-treated plants, and after 2 or 3 weeks g(s) was significantly lower than that of plantlets grown in vitro but similar in control and ABA-treated plants. Two weeks after transplantation, net photosynthetic rate, chlorophyll a + b content, maximal photochemical efficiency, and actual quantum yield of photosystem II in plant leaves were higher in comparison with those in plantlets grown in vitro.A^7250^1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17-20 degrees C). The potential for CH4 production and oxidation was measured at the end of the emission experiment. 2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores ('Sphagnum') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6-12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17-20 degrees C). 4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.

2246^4^Tischler,CR^Polley,HW^Johnson,HB^Mayeux,HS^1998^1^Environment and seedling age influence mesquite response to epicotyl removal^319^51^3^361-365^^^^^May^^^^^7253
1531^3285^376^547^710^751^92^m the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the A^7252^Herbivory by small mammals is a major factor controlling survival of honey mesquite (Prosopis glandulosa Torr. var, glandulosa) seedlings. Clipping below the cotyledons is lethal; removal of the epicotyl may not be lethal but can severely limit seedling growth. Seedlings of other woody species sometimes compensate for epicotyl removal by prolonging the life of cotyledons. Also, projected future increases in atmospheric CO2 concentration could influence survival and growth after epicotyl removal. Objectives of this study were to determine effects of epicotyl removal at various seedling ages, atmospheric CO2 concentrations, and soil fertility, on (1) seedling survival, (2) cotyledonary leaf longevity, and (3) shoot and root growth of young seedlings. Mesquite seedlings were grown at 350, 700, and 1,000 mu L liter(-1) atmospheric CO2 concentration in nutrient poor and nutrient rich soils. All ages of seedlings survived epicotyl removal. Cotyledonary leaf fresh mass and chlorophyll content were higher in plants where epicotyls were clipped. Root and shoot mass of both clipped and unclipped plants generally increased at higher CO2 concentrations when mineral nutrition was adequate, but responded less to CO2 when soil fertility was low. Responses to epicotyl clipping in mesquite seedlings are complex, being strongly influenced by soil fertility, atmospheric CO2 concentration, seedling age at clipping, and interactions between these factors.

2247^1^Wellburn,AR^1998^1^Atmospheric nitrogenous compounds and ozone - is NOx fixation by plants a possible solution?^84^139^1^5-9^^^^^May^^^^^7255
349^374^433^92^spheric CO2 concentrations, and soil fertility, on (1) seedling survival, (2) cotyledonary leaf longevity, and (3) shoot and root growth of young seedlings. Mesquite seedlings were grown at 350, 700, and 1,000 mu L liter(-1) atmospheric CO2 concentration in nutrient poor and nutrient rich soils. All ages of seedlings survived epicotyl removal. Cotyledonary leaf fresh mass and chlorophyll content were higher in A^7254^Air quality thresholds for O-3 for the protection of human health and vegetation set by the European Union (EU) have been exceeded in Europe regularly in the 1990s. Because target reductions for oxides of nitrogen (NOx) set for the year 2000 are unlikely to be achieved, these O-3 exceedances are likely to continue into the next millenium. Improvements of plant tolerance towards O-3 are being investigated but very little work has been done to explore NOx tolerance and plant acclimation to NO2 and NO. However, it is clear that within the populations of some plant species there is wide variation, and some individuals can fix NOx, and use the nitrogen directly from the atmosphere, rather than rely upon, for example, root uptake of nitrate. It is possible that individuals capable of fixing NOx could be selected for a range of species, and genotypes with high rates of uptake could be of value as crops or for forestation in polluted areas (e.g. landscaping in the vicinity of motorways) to reduce tropospheric concentrations of NOx significantly and also to decrease the potential for O-3 production.

2248^6^He,P^Bader,KP^Radunz,A^Kahmann,U^Ruppel,GH^Schmid,GH^1998^1^Gas exchange characteristics in leaves of the Euphorbiacea Aleurites montana as consequence of growth under 700 ppm CO2 in air - A study on photosynthesis and photorespiration in the Chinese tung-oil tree^291^53^3-4^151-158^^^^^Mar-Apr^^^^^7257
1531^188^3286^ery little work has been done to explore NOx tolerance and plant acclimation to NO2 and NO. However, it is clear that within the populations of some plant species there is wide variation, and some individuals can fix NOx, and use the nitrogen directly from the atmosphere, rather than rely upon, for example, root uptake of nitrate. It is possible that individuals capable of fixing NOx could be selected for a range of species, and genotypes with high rates of uptake could be of value as crops or for forestation in polluted areas (e.g. landscaping in the vicinity of motorways) to reduce troposphericA^7256^Three months old plants of the Chinese tung-oil tree Aleurites montana (Euphorbiaceae) were cultivated for 4 months in air containing 700 ppm CO2. These plants, which grow substantially better in the CO2-enriched atmosphere, were analyzed by mass spectrometry for photosynthesis and photorespiration together with control plants grown all the lime in normal (350 ppm CO2) air. Thereafter part of the plants was subjected for two weeks to 0.3 ppm SO2 in the atmosphere and again analyzed for photosynthesis and photorespiration. Aleurites montana exhibits a strongly CO2-dependent photosynthesis which partially explains the observed stimulatory effect of 700 ppm CO2 on growth of the plant. In control plants grown in normal air, photorespiration measured simultaneously with photosynthesis via the uptake of O-18(2) in the light, is much lower than in C-3-plants like tobacco (He et at, 1995, Z. Naturforsch. 50c, 781-788). In Aleurites grown in 700 ppm CO2, however, photorespiration is completely absent in contrast to tobacco when grown under 700 ppm CO2. In tobacco, photorespiration is not inhibited to the extent of the in vitro experiments in which plants grown at 350 ppm CO2 are measured under the increased CO2 content of 700 ppm. Gas exchange measurements carried out by mass spectrometry show that the ratio of O-2 evolved to CO2 fixed is about 0.5. Apparently, part of the CO2 fixed is channelled into a metabolic path without concomitant O-2-evolution. Although the plant has no succulent appearance (its leaves somehow resemble maple leaves) apparently a Crassulacean type metabolism is performed. When Aleurites plants grown all the time in normal air with 350 ppm, are exposed for two weeks to 0.3 ppm SO2 the treatment completely inhibits this CO2-fixing portion which is tentatively attributed to a Crassulacean type of metabolism. This is demonstrated by a normal C-3-type ratio O-2 evolved/CO2 fixed of 1. When Aleurites plants, grown for 4 months in a CO2- enriched atmosphere of 700 ppm CO2, are subjected for two weeks to 0.3 ppm SO2, the features of control plants show up again. When these plants are tested under 350 ppm CO2 the Crassulacean type CO2-fixation apparently is not inhibited by SO2. Photorespiration, although low is present in the same activity as in the controls. Seemingly, an increased level of CO2 in air tends to alleviate the impact of the SO2 at least in the Chinese lung-oil tree.

2249^2^Knapp,PA^Soule,PT^1998^1^Recent Juniperus occidentalis (western juniper) expansion on a protected site in central Oregon^127^4^3^347-357^^^^^Mar^^^^^7259
227^312^3287^374^399^434^456^549^92^ormed. When Aleurites plants grown all the time in normal air with 350 ppm, are exposed for two weeks to 0.3 ppm SO2 the treatment completely inhibits this CO2-fixing portion which is tentatively attributed to a Crassulacean type of metabolism. This is demonstrated by a normal C-3-type ratio O-2 evolved/CO2 fixed of 1. When Aleurites plants, grown for 4 months in a CO2- enriched atmosphere of 700 ppm CO2, are subjected for two wA^7258^The expansion of Juniperus occidentalis (western juniper) has been extensive in the last century, and increases in density and cover have been linked with the indirect effects of domestic livestock grazing (i.e. cessation of periodic fires, increases of nurse-plant sites), and more favourable climatic conditions. In this study, we document changes in vegetation (including J. occidentalis) in central Oregon over a 23-year period and relate these changes to their probable causes. In June 1995 we returned to the Horse Ridge Research Natural Area (HRRNA), a site that has a history of minimal anthropogenic impacts, to replicate a 1972 vegetation survey. Using the canopy-intercept method, line intercept method, and aerial photography analysis to measure herbaceous cover, shrub cover and tree cover, respectively, we found significant changes had occurred in the 23-year period between studies. Relative changes of tree, shrub, and perennial herbaceous cover were 59%, 7%, and -38%, respectively. Relative increases in J. occidentalis density, as measured by the number of clumps and the number of stems, were 37% and 53%, respectively. Mean maximum height of J. occidentalis had increased by 10%. We examined the role of potentially confounding influences (e.g. fire, grazing, pathogens, climatic variability) and found that none of the traditional mechanisms implicated in J. occidentalis expansion adequately explained the observed changes. We suggest that the role of biological inertia of both anthropogenic and natural means may have had a profound effect on the J. occidentalis ecology of HRRNA.

2250^2^Raddatz,RL^Shaykewich,CF^1998^1^Impact of warm summers on the actual evapotranspiration from spring wheat grown on the eastern Canadian prairies^82^78^1^171-179^^^^^Feb^^^^^7261
1285^3288^508^727^nd tree cover, respectively, we found significant changes had occurred in the 23-year period between studies. Relative changes of tree, shrub, and perennial herbaceous cover were 59%, 7%, and -38%, respectively. Relative increaA^7260^How do warm summers (June-July-August) influence the actual evapotranspiration totals from cropped land sown to spring wheat on the eastern Canadian Prairies? The eastern Prairies is a semi-arid region where over 60% of the land is cultivated. Over a third of the cropped land is usually sown to spring wheat. A comparison of mean summer temperatures and modelled evapotranspiration, for the years 1988 to 1996, demonstrated that with the current environmental conditions and farming practices, warm summers have lower actual evapotranspiration totals from spring wheat than cool summers. The average daily actual evapotranspiration rate is generally higher in years with higher mean summer temperatures; however, the crop growth- period is shorter. The net effect is lower total actual evapotranspiration from spring wheat. This suggests that climate warming on the eastern Canadian Prairies, if the current trend continues and all other factors remain equal, will reduce, on average, the total actual evapotranspiration from spring wheat. A reduction in the growth-period actual evapotranspiration from lands sown to spring wheat will likely decrease the total actual evapotranspiration for the entire warm season as growth-period evapotranspiration currently makes up about three-quarters of the seasonal total. However, the magnitude and timing of the reduction is far from certain. The consequence for agriculture may be a reduction in the average spring wheat yield because yield is positively correlated with the actual evapotranspiration total from the crop.

2251^4^Sagi,M^Dovrat,A^Kipnis,T^Lips,H^1998^1^Nitrate reductase, phosphoenolpyruvate carboxylase, and glutamine synthetase in annual ryegrass as affected by salinity and nitrogen^166^21^4^707-723^^^^^^^^^^7263
1538^244^3289^361^386^427^439^618^639^92^piration from spring wheat. This suggests that climate warming on the eastern Canadian Prairies, if the current trend continues and all other factors remain equal, will reduce, on average, the total actual evapotranspirA^7262^The concentration of organic acids, organic nitrogen (N), nitrate (NO3), and total cations increased in annual ryegrass (Lolium multiflorum Lam.) with salinity and N concentration in the growth medium. Increasing salinity and N in the growth medium induced changes in the level of key enzymes of N assimilation and organic acids: nitrate reductase (NR, EC 1.6.6.1), phosphoenolpyruvate carboxylase (PEPc, EC 4.1.1.31), and glutamine synthetase (GS, EC 6.3.1.2). Plants grown in pots filled with sand were irrigated with nutrient solutions with an electroconductivity of 2 or 11.2 dS m(-1) and N applied as ammonium nitrate (NH4NO3), sodium nitrate (NaNO3), or ammonium applied as ammonium nitrate (NH4NO3), sodium nitrate (NaNO3), or ammonium (NH4) as ammonium sulfate [(NH4)(2)SO4] at concentrations of 0.5, 4.5 or 9.0 mM. Nitrate reductase, PEPc, and GS increased with salinity and N level. Shoot NR was highest in the presence of NH4NO3 irrespective of salinity level, while root NR activity responded best to NO3. Enhancement of PEPc activity in both shoots and roots was highest with NH4NO3 and lowest with NH4. Nitrogen source had no significant effect on GS activity in shoots or roots of ryegrass. Shoot NR activity increased with NO3 concentration in the tissue, as calculated from repression coefficients. The PEPc activity correlated positively with total cations and NO3 concentrations in the plants, irrespective of the salinity level, suggesting that the increase in total cations and NO3 induced by salinity may have triggered the changes in enzyme activities. The concentration of organic acids in both shoots and roots correlated positively with PEPc activity irrespectively of the salinity level. The PEPc activity was higher in roots than in shoots, while organic acid concentration was higher in shoots. These results suggest that a significant part of the organic acids produced in the roots were used as carbon skeleton for transamination reactions. The increased activity of NR, PEPc, and GS in roots may constitute part of an adaptation strategy of the plant to increasing salinity in the medium. These enzymes have an important role in the metabolism of amino acids and the synthesis of organic N in annual ryegrass irrigated with saline water, and boosting them with suitable N fertilizers could increase the nutritional value and protein content of the crop.

2252^5^Signora,L^Galtier,N^Skot,L^Lucas,H^Foyer,CH^1998^1^Over-expression of sucrose phosphate synthase in Arabidopsis thaliana results in increased foliar sucrose/starch ratios and favours decreased foliar carbohydrate accumulation in plants after prolonged growth with CO2 enrichment^78^49^321^669-680^^^^^Apr^^^^^7265
1116^1437^1442^2410^3034^3290^3291^344^366^635^was higher in roots than in shoots, while organic acid concentration was higher in shoots. These results suggest that a significant part of the organic acids produced in the roots were used as carbon skeleton for transamination reactions. The increased activity of NR, PEPc, and GS in roots may constitute A^7264^Arabidopsis thaliana ecotype Columbia was transformed with a maize sucrose phosphate synthase (SPS) cDNA under the control of the promoter for the small subunit of ribulose-l,5- bisphosphate carboxylase from tobacco (rbcS). The effects of SPS over-expression were compared in plants of the T-2 and T-3 generations grown either in air or with CO2 enrichment (700 mu l l(-1)) for either 4 or 10 weeks. Maximal extractable foliar SPS activities were three times those of the untransformed controls in the highest rbcS-SPS expressing line. In untransformed Arabidopsis leaves SPS activity was not subject to light/dark regulation, but was modified by incubation with either the inhibitor, orthophosphate, or the activator, mannose. Photosynthesis (A(max)) values were similar in all lines grown in air. After 10 weeks of CO, enrichment a decrease in A,,, in the untransformed controls, but not in the high SPS expressors, was observed. There was a strong correlation between the sucrose-to-starch ratio of the leaves and their SPS activity in both growth conditions. The total foliar carbohydrate contents of 4-week-old plants was similar in all lines whether plants were grown in air or with CO2 enrichment, After 10 weeks growth the leaves of the high rbcS-SPS expressors accumulated much less total carbohydrate than untransformed control leaves in both growth conditions. It was concluded that SPS overexpression causes increased foliar sucrose/starch ratios in Arabidopsis leaves and favours decreased foliar carbohydrate contents when plants are grown for long periods with CO2 enrichment.

2253^5^Kanechi,M^Ochi,M^Abe,M^Inagaki,N^Maekawa,S^1998^1^The effects of carbon dioxide enrichment, natural ventilation, and light intensity on growth, photosynthesis, and transpiration of cauliflower plantlets cultured in vitro photoautotrophically and photomixotrophically^154^123^2^176-181^^^^^Mar^^^^^7267
1055^1178^1901^3292^3293^781^788^801^ was observed. There was a strong correlation between the sucrose-to-starch ratio of the leaves andA^7266^The effects of natural ventilation and CO2 enrichment during the rooting stage on the growth and the rates of photosynthesis and transpiration of in vitro cauliflower (Brassica oleracea L.) plantlets were investigated. In vitro plantlets were established in airtight or ventilated vessels with or without CO2 supplied (approximate to 1200.mu g L-1) through gas permeable films attached to the vessel's cap for 15 days before transplanting ex vitro. Leaves generated in vitro in ventilated vessels had a higher photosynthetic rate than those produced in airtight vessels, which lead to greater leaf expansion and shoot and root dry matter accumulation during in vitro culture and acclimatization. Enhanced photosynthesis in leaves of ventilated plantlets was positively correlated with chlorophyll content. Increasing photosynthetically active radiation from 70 to 200 mu mol.m(-1)-s(-1) enhanced the growth of in vitro plantlets under ventilated conditions but it depressed photosynthesis of the leaves grown photomixotrophically with sugar and CO2 enrichment which might be due to the feedback inhibition caused by marked accumulations of sucrose and starch. Higher CO2 levels during in vitro culture enhanced photosynthesis under photoautotrophic conditions, but inhibited it under photomixotrophic conditions. Fifteen days after transplanting ex vitro, high photosynthetic ability and stomatal resistance to transpiratory water loss of ventilated plantlets in vitro had important contributions to rooting and acclimatization. Our findings show that the ventilated culture is effective for accelerating photoautotrophic growth of plantlets by increasing photosynthesis, suggesting that, especially for plantlets growing in vitro without sugar, CO2 enrichment may be necessary to enhance photosynthetic ability.
phyll content. Increasing photosynthetically active radiation from 70 to 200 mu mol.m(-1)-s(-1) enhanced the growth of in vitro plantlets under ventilated conditions but it depressed photosynthesis of the leaves grown photomi2254^3^Reddy,VR^Reddy,KR^Wang,Z^1997^1^Cotton responses to nitrogen, carbon dioxide, and temperature interactions (Reprinted from Plant nutrition for sustainable food production and environment, 1997)^316^43^^1125-1130^^^^^Dec^^^^^7269
376^397^431^438^674^687^91^der photomixotrophic conditions. Fifteen days after transplanting ex vitro, high photosynthetic ability and stomatal resistance to transpiratory water loss of ventilated plantlets in vitro had important contributions to rooting and acclimatization. Our findings show that the ventilated culture is effective for accelerating photoautotrophic growth of plantlets by increasing photosynthesis, suggesting that, especially for plantlets growing in vitro without sugar, CO2 enrichment may be necessary to enhance photosynthetic ability.
phyll content. Increasing photosynthetically active radiation from 70 to 200 mu mol.m(-1)-s(-1) enhanced the growth of in vitro plantlets under ventilated conditions but it depressed photosynthesis of the leaves grown photomiA^7268^Several studies were conducted to evaluate how increases in the global atmospheric carbon dioxide concentration [CO2] and temperature affect growth and development rates, dry matter production, photosynthesis, and water use efficiency of cotton and how these responses are influenced by leaf N levels. In one study, cotton (cv. DPL 50) plants were grown at four temperatures (20/12, 25/17, 30/22, and 35/27 degrees C day/night) until harvest at 70 days after emergence (DAE). Each temperature treatment was combined with [CO2] of 350 or 700 mu L L-1. In another study, cotton (cv. DES 119) grown at two [CO2] received five N treatments (0, 1, 2, 6, and 10 mM NO3 in Hoagland's nutrient solution) at 17 DAE and every 2 days thereafter. Canopy gross photosynthetic rates increased with increasing [CO2] and temperature. The increased photosynthesis resulted in higher plant growth and dry matter accumulation rates except at the highest temperature. At 70 DAE, the maximum canopy dry matter accumulation rate occurred in 30/22 degrees C. The 35/27 degrees C treatment induced fruit abortion, resulting in greater dry matter accumulation in vegetative structures. Increases in plant dry weights by CO2 enrichment were greater in the two high temperature regimes than in the two lower temperature regimes. Water-use efficiency increased with increased [CO2] and decreased with increased temperature. Increases in water-use efficiency were due mainly to increased photosynthesis and partly to reduced canopy transpiration. Increase in leaf N concentration increased cotton photosynthesis and vegetative growth rates, and the increases were higher at 700 mu L L-1 than at 350 mu L L-1 [CO2].

2255^6^Tanaka,M^Takamura,T^Watanabe,H^Endo,M^Yanagi,T^Okamoto,K^1998^1^In vitro growth of Cymbidium plantlets cultured under superbright red and blue light-emitting diodes (LEDs)^361^73^1^39-44^^^^^Jan^^^^^7271
243^2776^2837^874^accumulation rates except at the highest temperature. At 70 DAE, the maximum canopy dry matter accumulation rate occurred A^7270^The effects of light generated by superbright blue and red LEDs on the growth of Cymbidium plantlets cultured in vitro have been studied. Leaf growth, chlorophyll content and shoot and root weights were affected by different LED irradiations. Red light promoted leaf growth but decreased chlorophyll content. This was reversed by blue Light. The growth of Cymbidium plantlets in terms of increase in total shoot and root weights was comparable under red plus blue LEDs and the fluorescent systems. Generally, the response to different LED was similar for plantlets grown on sugar-free medium with or without CO2 enrichment and sugar-containing medium but without CO2 enrichment. The growth of Cymbidium plantlets was enhanced by CO2 enrichment. Our study demonstrates the effectiveness of a total irradiation system for Cymbidium plantlets growth in vitro. The significance of our findings in relation to the development of a suitable lighting system for plant tissue culture is discussed.
cumulation rate occurred 2256^4^Dhakhwa,GB^Campbell,CL^LeDuc,SK^Cooter,EJ^1997^1^Maize growth: assessing the effects of global warming and CO2 fertilization with crop models^107^87^4^253-272^^^^^1 Dec^^^^^7273
1138^130^137^374^376^377^413^434^508^58^erent LED irradiations. Red light promoted leaf growth but decreased chlorophyll content. This was reversed by blue Light. The growth of Cymbidium plantlets in terms of increase in total shoot and root weights was comparable under red plus blue LEDs and the fluorescent systems. Generally, the response to different LED was similar for plantlets grown on sugar-free medium with or without CO2 enrichment and sugar-containing medium but without CO2 enrichment. The growth of Cymbidium plantlets was enhanced by CO2 enrichment. Our study demonstrates the effectiveness of a total irradiation system for Cymbidium plantlets growth in vitro. The significance of our findings in relation to the development of a suitable lighting system for plant tissue culture is discussed.
cumulation rate occurred A^7272^Projected future climate change scenarios derived from two General Circulation Models (GCMs): Geophysical Fluid Dynamics Laboratory (GFDL) and United Kingdom Meteorological Office (UKMO), and two crop models: Crop Estimation through Resources and Environmental Synthesis (CERES), and Erosion/Productivity Impact Calculator (EPIC), were considered to assess the climate change impact on the yield and biomass of maize. Climate change scenarios included changes in temperature, precipitation and solar radiation from two GCMs interpolated to 1 degrees x1 degrees grid cells in the central Piedmont in North Carolina. Changes in mean monthly temperature and precipitation from the GCMs were used to adjust observed daily climate records from 1949-1988. There is convincing evidence that future temperature linked to global warming might be characterized by asymmetric change between daily daytime maxima and daily nighttime minima. Two hypotheses regarding how GCM temperature would alter observational record were examined. The first hypothesis assumed that daytime and nighttime warming occurs symmetrically, i.e., maximum and minimum temperatures are raised equally. The second hypothesis assumed that nighttime minima change is three times greater than daytime maxima change and the change in mean diurnal temperature range is approximately equal to the change in daily mean temperature. For the equal day-night warming scenario, when only the effects of climate change (i.e., changes in temperature, precipitation and solar radiation) were considered, simulations with CERES and EPIC indicated substantial losses in maize grain yield and total above ground biomass with both the GCM scenarios. For the asymmetric warming, the reduction in biomass and yield due to climate change was less than that obtained with symmetric warming. Simulated maize yield and biomass with CERES and EPIC increased when only effects due to CO2-fertilization were considered. The inclusion of CO2 fertilization effects with those due to climate change resulted in higher biomass and yield compared to values obtained with effects of climate change alone. When CERES was used with the GFDL scenario, and the effects of CO2 fertilization and the climate change were combined, no difference in simulated yield was found between the two hypotheses; only an 8% difference in aboveground biomass was found when the UKMO scenario was used. When EPIC was used, the differential day-night warming hypothesis resulted in 9-13% less reduction in biomass and yield than did the use of the equal day-night warming hypothesis. (C) 1997 Elsevier Science B.V.

2257^3^Holcroft,DM^Gil,MI^Kader,AA^1998^1^Effect of carbon dioxide on anthocyanins, phenylalanine ammonia lyase and glucosyltransferase in the arils of stored pomegranates^154^123^1^136-140^^^^^Jan^^^^^7275
1012^1234^174^322^3294^3295^3296^3297^3298^454^ biomass with CERES and EPIC increased when only effects due to CO2-fertilization were considered. The inclusion of CO2 fertilization effects with those due to climate change resultA^7274^Wonderful' Pomegranates (Punica granatum L.) were placed in jars ventilated continuously with air or air enriched with 10 or 20 kPa CO2 at 10 degrees C for 6 weeks. Samples were taken initially and after 1, 2, 4, and 6 weeks, and postharvest quality attributes were measured. The arils of the pomegranates stored in air were deeper red than the initial controls and than those stored in CO2-enriched atmospheres. This increased color was associated with increased anthocyanin concentration. Arils from fruit stored in air enriched with 10 kPa CO2 had a lower anthocyanin concentration than air-stored fruit, and atmospheres enriched with 20 kPa CO2 had even lower levels, possibly from suppressed anthocyanin biosynthesis. Anthocyanin concentration correlated well with the activity of phenylalanine ammonia lyase but not with glucosyltransferase activity. Moderate CO2 atmospheres (10 kPa) prolong the storage life and maintain quality of pomegranates, including adequate red color intensity of the arils.
e result2258^3^Kozai,T^Kubota,C^Jeong,BR^1997^1^Environmental control for the large-scale production of plants through in vitro techniques^177^51^1^49-56^^^^^^^^^^7277
188^2124^3299^3300^3301^349^566^781^802^and after 1, 2, 4, and 6 weeks, and postharvest quality attributes were measured. The arils of the pomegranates stored in air were deeper red than the initial controls and than those stored in CO2-enriched atmospheres. This increased color was associated with increased anthocyanin concentration. Arils from fruit stored in air enriched with 10 kPa CO2 had a lower anthocyanin concentration than air-stored fruit, and atmospheres enriched with 20 kPa CO2 had even lower levels, possibly from suppressed anthocyanin biosynthesis. Anthocyanin concentration correlated well with the activity of phenylalanine ammonia lyase but not with glucosyltransferase activity. Moderate CO2 atmospheres (10 kPa) prolong the storage life and maintain quality of pomegranates, including adequate red color intensity of the arils.
e resultA^7276^Leafy or chlorophyllous explants of a number of plant species currently micropropagated have been found to have high photosynthetic ability. Their growth and development have been promoted on sugar-free medium rather than on sugar-containing medium, provided that the environmental factors, such as CO2 concentration, light intensity and relative humidity, are controlled for promoting photosynthesis and transpiration of explants/shoots/plantlets in. vitro. Thus, environmental control is essential for promoting photosynthetic growth and development of in vitro plantlets. Several types of sugar-free (photoautotrophic) culture systems for large-scale micropropagation of plants have been developed. Advantages of sugar-free over conventional (heterotrophic or photomixotrophic) micropropagation systems are as follows: growth and development of plantlets in vitro are faster and more uniform, plantlets in vitro have less physiological and morphological disorders, biological contamination in vitro is less, plantlets have a higher percentage of survival during acclimatization ex vitro, and larger culture vessels could be used because of less biological contamination. Hence, production costs could be reduced and plant quality could be improved significantly with photoautotrophic micropropagation. Methods for the measurement and control of in vitro environments and the beneficial effects of environmental control on photosynthetic growth, development, and morphogenesis in large-scale production of micropropagated plantlets are presented.

2259^4^Kuhn,M^Niewohner,C^Isenbeck-Schroter,M^Schulz,HD^1998^1^Determination of major and minor constituents in anoxic thermal brines of deep sandstone aquifers in Northern Germany^368^32^2^265-274^^^^^Feb^^^^^7279
2301^3302^3303^3304^3305^3306^rophic) micropropagation systems are as follows: growth and development of plantlets in vitro are faster and more uniform, plantlets in vitro have less physiological and morphological disorders, biological contamination in vitro is less, plantA^7278^The common process of low energy geothermal exploitation is the doublet of production- and reinjection borehole. The quality of water reinjected into a elastic reservoir is essential for the reliability of an injection well. In order to estimate precipitation reactions it is necessary to obtain extensive reliable analysis data of the water for the use of thermodynamic modelling. For thermal anoxic brines, the analysis of major and especially minor ion content is difficult because of matrix effects and possible iron precipitation. A selection of analysing methods were applied to two anoxic thermal brines of deep sandstone aquifers of Northern Germany. Detection limits and measured data of the major constituents are presented of Na+, K+, NH4+, Ca2+, Mg2+, Ba2+, Sr2+, Fe- total, Mn2+, SiO44-, B(OH)(3), Zn2+, Pb2+, Cd2+, F-, Cl-, Br-, I-, SO42-, SO32-, S2-, PO43-, NO3-, NO2- and DOC. The measurements were done with ICP-OES, ionselective electrodes, photometry, polarography, titration methods, ion chromatography and TOC-analyzer. Except for SO(4)(2-)and Cl-, the anion analysis was done on-site, since the high iron content in the anoxic water requires acidification in order to prevent iron hydroxide precipitation. The minor constituents Zn2+, Pb2+, Cu2+, Cd2+, Cr3+, Sc3+, Co2+, Y3+, La3+, Ce3+, Al3+, were enriched by trace matrix separation using the cation exchange resin Chelex((R))100. The element concentrations in the acidic eluates of the Chelex((R))100 columns were measured using ICP- MS. The pH dependency of the exchange equilibrium at pH values of 4, 5 and 6 (buffered and unbuffered) as well as the relation to the salt content between 35 and 250 gl(-1) total dissolved solids of Na-K-Ca-Mg-Cl-SO4 were evaluated by sensitivity analysis. (C) 1998 Elsevier Science Ltd. All rights reserved.

2260^3^Reddy,KR^Hodges,HF^McKinion,JM^1997^1^A comparison of scenarios for the effect of global climate change on cotton growth and yield^92^24^6^707-713^^^^^^^^^^7281
1163^3181^341^344^374^tration methods, ion chromatoA^7280^If global surface temperatures change as projected because of radiative and physiological effects of a changing environment, we should expect important changes in crop production in the 21st Century. Experiments were conducted at ambient and twice ambient atmospheric CO2 concentrations at five temperatures. The 1995 temperature in Mississippi was used as a reference with the other temperatures being 1995 minus 2 degrees C, and 1995 plus 2, 5 and 7 degrees C. Daily and seasonal variation and amplitudes were maintained. Seedlings had 4-6 times as much leaf area and dry weight at 20 d after emergence when grown at 28 degrees C as at 23 degrees C (1995 ambient) average temperature during that growth period. Number of days to first square, flower, and open boil decreased as temperature increased. Double atmospheric CO2 did not affect these developmental rates. Temperatures above 28 degrees C, or 1995 average whole-season temperatures, were detrimental to mid-and late-season boil retention and growth. No fruits were retained to maturity at 1995 plus 5 or 7 degrees C. However, whole season vegetative growth was not significantly reduced by temperature 5-7 degrees C above the 1995 ambient conditions. Twice ambient CO2 caused about 40% increase in vegetative dry matter accumulation across temperatures. In a separate experiment, similar results were obtained on fruiting cotton grown at a range of temperatures based on long-term average US Midsouth July temperatures. Therefore, if global warming occurs as predicted, food and fibre production in such high- temperature and humid environments may be more limited to vegetative structures and the animals that consume vegetative structures.

2261^3^Schenk,U^Jager,HJ^Weigel,HJ^1997^1^The response of perennial ryegrass white clover mini-swards to elevated atmospheric CO2 concentrations: effects on yield and fodder quality^369^52^3^232-241^^^^^Sep^^^^^7283
1262^137^1684^1958^1960^312^376^507^57^975^s, were detrimental to mid-and late-season boil retention and growth. No frA^7282^In order to assess the effects of future elevated atmospheric CO2 concentrations on yield, mineral content and the nutritive value of mixed swards of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.). both species were grown as monocultures and as different mixtures and were exposed season-long to ambient (380 p.p.m.) and elevated (670 p.p.m.) CO2 concentrations in open-top chambers. Mini-swards were cut four times at about monthly intervals at a height of 5 cm, dry- matter yields were determined and content of macroelements (N, P, K, S, Mg, Ca, Na) and crude fibre, crude protein and ash content were measured. The CO2-related increase in seasonal yield amounted to 16-38% for white clover monocultures, 12-29% for mixed swards and 5-9% for ryegrass monocultures. The white clover content of all swards was significantly enhanced by elevated CO2. The K and Na content of total yield was decreased by high CO2 but did not fall below the minimum requirements for ruminants. As the Ca content of total yield was increased by elevated CO2 and the P content was not changed, the Ca/P ratio of total yield was increased and exceeded values required for animal nutrition. The crude protein content of total yield was reduced by high CO2 at thr beginning of the growing season only and was increased by elevated CO2 in the course of the experiment, whereas crude fibre content was decreased through out the season, sometimes falling below the minimum requirement for ruminants. Removal of N, P, S, Mg and Ca by cutting was significantly enhanced because of CO2 enrichment, The results show that, besides the positive effect of rising atmospheric CO2 on dry-matter yield of white clover/ryegrass swards, impacts on the nutritive value should be expected. Possible changes in species composition and implications for grassland management are briefly discussed.
 by elevated CO2. The K and Na content of total yield was decreased by high CO2 but did not fall below the minimum requirements for ruminants. As the Ca2262^2^Will,RE^Teskey,RO^1997^1^Effect of irradiance and vapour pressure deficit on stomatal response to CO2 enrichment of four tree species^78^48^317^2095-2102^^^^^Dec^^^^^7285
188^2489^2965^398^465^546^633^639^867^923^eld was reduced by high CO2 at thr beginning of the growing season only and was increased by elevated CO2 in the course of the experiment, whereas crude fibre content was decreased through out the season, sometimes falling below the minimum requirement for ruminants. Removal of N, P, S, Mg and Ca by cutting was significantly enhanced because of CO2 enrichment, The results show that, besides the positive effect of rising atmospheric CO2 on dry-matter yield of white clover/ryegrass swards, impacts on the nutritive value should be expected. Possible changes in species composition and implications for grassland management are briefly discussed.
 by elevated CO2. The K and Na content of total yield was decreased by high CO2 but did not fall below the minimum requirements for ruminants. As the CaA^7284^The stomatal response of seedlings grown in 360 or 720 mu mol mol(-1) to irradiance and leaf-to-air vapour pressure deficit (VPD) at both 360 and 720 mu mol mol(-1) CO2, was measured to determine how environmental factors interact with CO2 enrichment to affect stomatal conductance, Seedlings of four species with different conductances and life histories, Cercis canadensis (L.), Quercus rubra (L.), Populus deltoides (Bartr. ex Marsh.) x P. nigra (L.), and Pinus taeda (L.), were measured in hopes of identifying general responses, Conductance of seedlings grown at 360 and 720 mu mol mol-l CO2 were similar and responded in the same manner to measurement CO2 concentration, irradiance and VPD, Conductance was lower for all species where measured at 720 than when measured at 360 mu mol mol(-1) CO2 at both VPDs (similar to 1.5 and similar to 2.5 kPa) and all measured irradiances greater than zero (100, 300, 600, > 1600 mu mol m(-2) s(-1)). The average decrease in conductance due to measurement in elevated CO2 concentration was 32% for Cercis, 29% for Quercus, 26% for Populus, and 11% for Pinus, For all species, the absolute decrease in conductance due to measurement in CO2 enrichment decreased as irradiance decreased or VPD increased, The proportional decrease due to measurement in CO2 enrichment decreased in three of eight cases: from 0.46 to 0.10 in Populus and from 0.18 to 0.07 in Pinus as irradiance decreased from > 1600 to 100 mu mol m(-2) s(-1) and from 0.35 to 0.24 in Cercis as VPD increased from 1.3 to 2.6 kPa.

2263^2^Yokota,T^Hagihara,A^1998^1^Changes in the relationship between tree size and aboveground respiration in field-grown hinoki cypress (Chamaecyparis obtusa) trees over three years^13^18^1^37-43^^^^^Jan^^^^^7287
2155^2183^3307^349^520^945^han when measured at 360 mu mol mol(-1) CO2 at both VPDs (similar to 1.5 and similar to 2.5 kPa) and all measured irradiances greater than zero (100, 300, 600, > 1600 mu mol m(-2) s(-1)). The average decrease in conductance due to measurement in elevated CO2A^7286^Respiration measurements of aerial parts of 18-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) trees were made under field conditions over three years to study changing relationships with tree age between respiration and phytomass, phytomass increment, and leaf mass. The relationship between annual respiration (r(a)) and phytomass (w(T)) was approximated by a proportional function (r(a) = aw(T)), where the proportional constant (a) decreased year by year. The effect of time on the relationship between annual respiration and phytomass of each sample tree was fitted by a power function. Respiration of the tree suppressed by the canopy decreased year by year, but respiration of the other trees increased slightly with age. The relationship between annual respiration and leaf mass was also approximated by a generalized power function. Excluding the suppressed tree, the relationship between annual respiration (r(a)) and the annual increment of aboveground phytomass (Delta w(T)) was described by a proportional function (r(a) = 2.27 Delta w(T)), where the proportional constant, 2.27, was independent of sample tree and year, indicating that about 2.3 times of the annual aboveground phytomass increment equivalent was respired annually. For any tree. the time constant relationships between annual respiration and leaf mass and phytomass increment for different-sized trees were similar to the corresponding time continuum relationships. In contrast, the time continuum relationship between annual respiration and phytomass differed from the time constant relationship, indicating that respiration of less active woody tissue contributed significantly to aboveground respiration. Based on the relationship between tree size and annual respiration, annual aboveground stand respiration was estimated to be 25.0, 26.9, and 25.8 Mg-dm ha(-1) year(-1) for the three consecutive years, respectively, and the corresponding above-ground stand biomass was 60.0, 69.0, and 76.8 Mg-dm ha(-1).
ass (Delta w(T)) was des2264^6^He,ZL^von Caemmerer,S^Hudson,GS^Price,GD^Badger,MR^Andrews,TJ^1997^1^Ribulose-1,5-bisphosphate carboxylase/oxygenase activase deficiency delays senescence of ribulose-1,5-bisphosphate carboxylase/oxygenase but progressively impairs its catalysis during tobacco leaf development^8^115^4^1569-1580^^^^^Dec^^^^^7289
1604^2126^243^348^355^384^441^553^556^813^for different-sized trees were similar to the corresponding time continuum relationships. In contrast, the time continuum relationship between annual respiration and phytomass differed from the time constant relationship, indicating that respiration of less active woody tissue contributed significantly to aboveground respiration. Based on the relationship between tree size and annual respiration, annual aboveground stand respiration was estimated to be 25.0, 26.9, and 25.8 Mg-dm ha(-1) year(-1) for the three consecutive years, respectively, and the corresponding above-ground stand biomass was 60.0, 69.0, and 76.8 Mg-dm ha(-1).
ass (Delta w(T)) was desA^7288^Transgenic tobacco (Nicotiana tabacum L. cv W38) plants with an antisense gene directed against the mRNA of ribulose-1,5- biphosphate carboxylase/oxygenase (Rubisco) activase grew more slowly than wild-type plants in a CO2-enriched atmosphere, but eventually attained the same height and number of leaves. Compared with the wild type, the anti-activase plants had reduced CO2 assimilation rates, normal contents of chlorophyll and soluble leaf protein, and much higher Rubisco contents, particularly in older leaves. Activase deficiency greatly delayed the usual developmental decline in Rubisco content seen in wild-type leaves. This effect was much less obvious in another transgenic tobacco with an antisense gene directed against chloroplast-located gl