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 glyceraldehyde-3-phosphate dehydrogenase, which also had reduced photosynthetic rates and delayed development. Although Rubisco carbamylation was reduced in the anti-activase plants, the reduction was not sufficient to explain the reduced photosynthetic rate of older anti- activase leaves. Instead, up to a 10-fold reduction in the catalytic turnover rate of carbamylated Rubisco in vivo appeared to be the main cause. Slower catalytic turnover by carbamylated Rubisco was particularly obvious in high-CO2-grown leaves but was also detectable in air-grown leaves. Rubisco activity measured immediately after rapid extraction of anti- activase leaves was not much less than that predicted from its degree of carbamylation, ruling out slow release of an inhibitor from carbamylated sites as a major cause of the phenomenon. Nor could substrate scarcity or product inhibition account for the impairment. We conclude that activase must have a role in vivo, direct or indirect, in promoting the activity of carbamylated Rubisco in addition to its role in promoting carbamylation.

2265^1^Lal,R^1997^1^Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2-enrichment^370^43^1-2^81-107^^^^^1 Nov^^^^^7291in the reduced photosynthetic rate of 1104^2413^3308^3309^3310^3311^3312^3313^3314^3315^ld reduction in the catalytic turnover rate of carbamylated Rubisco in vivo appeared to be the main cause. Slower catalytic turnover by carbamylated Rubisco was particularly obvious in high-CO2-grown leaves but was also detectable in air-grown leaves. Rubisco activity measured immediately after rapid extraction of anti- activase leaves was not much less than that predicted from its degree of carbamylation, ruling out slow release of an inhibitor from carbamylated sites as a major cause of the phenomenon. Nor could substrate scarcity or product inhibition account for the impairment. We conclude that activase must have a role in vivo, direct or indirect, in promoting the activity of carbamylated Rubisco in addition to its role in promoting carbamylation.

2265^1^Lal,R^1997^1^Residue management, conservation tillage and soil restoration for mitigating greenhouse effect by CO2-enrichment^370^43^1-2^81-107^^^^^1 Nov^^^^^7291in the reduced photosynthetic rate of A^7290^This manuscript reviews the potential impact of residue management, conservation tillage and soil restoration on carbon sequestration in world soils. The greenhouse effect is among four principal ecological issues of global concern that include: (i) adequacy of land resources to meet needs of present and future generations; (ii) role of world soils and agricultural practices in the 'greenhouse' effect; (iii) potential of crop residue management, restoration of degraded soils, and conservation tillage in carbon sequestration in soil; and (iv) minimizing risks of soil degradation by enhancing soil resilience and soil quality. Annual increase in CO, concentration in the atmosphere is 3.2 x 10(15) g, and there exists a potential to mitigate this effect through C sequestration in soils. Just as world soils are an important active pool of organic carbon and play a major role in the global carbon cycle, crop residue is a major renewable resource which also has an important impact on the global carbon cycle. I have estimated the annual production of crop residue to be about 3.4 billion Mg in the world. If 15% of C contained in the residue can be converted to passive soil organic carbon (SOC) fraction, it may lead to C sequestration at the rate of 0.2 x 10(15) g/yr. Similarly restoring presently degraded soils, estimated at about 2.0 billion ha, and increasing SOC content by 0.01%/yr may lead C sequestration at the rate of 3.0 Pg C/yr. Conservation tillage is an important tool for crop residue management, restoration of degraded soil, and for enhancing C sequestration in soil. Conservation tillage, any tillage system that maintains at least 30% of the soil surface covered by residue, was practised in 1995 on about 40 x 10(6) ha or 35.5% of planted area in USA. It is projected that by the year 2020, conservation tillage may be adopted on 75% of cropland in USA (140 x 10(6) ha), 50% in other developed countries (225 x 10(6) ha), and 25% in developing countries (172 x 10(6) ha). The projected conversion of conventional to conservation tillage may lead to a global C sequestration by 2020 at a low estimate of 1.5 x 10(15) g, and at a high estimate of 4.9 x 10(15) g of C. These potentials of C sequestration can be realized through adoption of regional, national and global soil policy that stipulate appropriate use of world soil resources. (C) 1997 Elsevier Science B.V.

2266^4^Niu,G^Kozai,T^Hayashi,M^Tateno,M^1997^1^Time course simulations of CO2 concentration and net photosynthetic rates of potato plantlets cultured under different lighting cycles^256^40^6^1711-1718^^^^^Nov-Dec^^^^^7293
376^781^92^illage, any tillage system that maintains at least 30% of the soil surface covered by residue, was practised in 1995 on about 40 x 10(6) ha or 35.5% of planted area in USA. It is projected that by the year 2020, conservation tillage may be adopted on 75% of cropland in USA (140 x 10(6) ha), 50% in other developed countries (225 x 10(6) ha), and 25% in developing countries (172 x 10(6) ha). The projected conversion of conventioA^7292^Potato (Solanum tuberosum L. cv. Benimaru) plantlets were cultured under four lighting cycles with the same ratio of photo/dark period (16 h/8 h, 4 h/2 h, I h/0.5 h, and 0.25 h/0.125 h) photoautotrophically (without sugar-in the medium) and photomixotrophically (with sugar in the medium) in vitro for 28 days. Simulations of time courses of CO2 concentration in the vessel (C-i) for plantlets cultured photoautotrophically, and photomixotrophically and dry weight accumulations of the plantlets cultured photoautotrophically were conducted using the same model and parameter values as those in Niu and Kozai (1997). While underestimation and overestimation of the time courses of C-i in some treatments were observed the simulated values of C-i and the dry weight accumulation of the plantlets generally agreed with the measured values. The simulated responses of net photosynthetic rate of the plantlets to C-i indicated that in the early, culture period, plantlets have higher photosynthetic ability under photoautotrophic than under photomixotrophic culture conditions. The quantitative relationship between daily net photosynthetic rate (daily net production) and vessel ventilation rate per plantlet was simulated under various CO2 levels outside the vessel for given sizes of potato plantlets cultured in vitro photoautotrophically, to aid appropriate CO2 enrichment and vessel design in commercial micropropagation systems.

2267^2^Rey,A^Jarvis,PG^1997^1^Growth response of young birch trees (Betula pendula Roth.) after four and a half years of CO2 exposure^52^80^6^809-816^^^^^Dec^^^^^7295
229^3003^312^361^376^384^526^733^746^857^ile underestimation and overestimation of the time courses of C-i in some treatments were observed the simulated values of C-i and the dry weight accumulation of the plantlets generally agreed with the measured values. The simulated responses of net photosynthetic rate of the plantlets to C-i indicated that in the early, culture period, plantlets have higher photosynthetic ability under photoauA^7294^A field experiment consisting of 18 birch trees grown in open top chambers in ambient and elevated CO2 concentrations was set up with the aim of testing whether the positive growth response observed in many short-term studies is maintained after several growing seasons. We present the results of growth and biomass after 4.5 years of CO2 exposure, one of the longest studies so far on deciduous tree species. We found that elevated CO2 led to a 58% increase in biomass at the end of the experiment. However, estimation of stem mass during the growing season showed that elevated CO2 did not affect relative growth rate during the fourth growing season, and therefore, that the large accumulation of biomass was the result of an early effect on relative growth rate in previous years. Trees grown in elevated CO2 invested more carbon into fine roots and had relatively less leaf area than trees grown in ambient CO2, In contrast with previous studies, acceleration of growth did not involve a significant decline in nutrient concentrations of any plant tissue. It is likely that increased fine root density assisted the trees in meeting their nutrient demands. Changes in the species composition of the ectomycorrhizal fungi associated with the trees grown in elevated CO2 in favour of late successional species supports the hypothesis of an acceleration of the ontogeny of the trees in elevated CO2. (C) 1997 Annals of Botany Company.

2268^2^Sharma,A^Sengupta,UK^1997^1^Carbon allocation and partitioning in Vigna radiata (L.) Wilczek as affected by additional carbon gain^79^34^3^419-426^^^^^^^^^^7297
1531^1768^243^244^348^385^762^820^te during the fourth growing season, and therefore, that the large accumulation of biomass was the result of an early effect on relative growth rate in previous years. Trees grown in elevated CO2 invested more carbon into fine roots and had relatively less leaf area than trees grown in ambient CO2, In contrast with previous studies, acceleration of growth did not involve a significant decline in A^7296^Carbon allocation to the source leaf export and partitioning to the sink were studied in mungbean supplied by additional carbon from the source leaves subjected to high CO2 concentrations (600 and 900 cm(3) m(-3)) in three metabolic and functional source-sink combinations. The plants were pruned to a source- path-sink system. With CO2 enrichment there was an appreciable increase in net photosynthetic CO2 uptake in earlier formed and physiologically younger leaves. Most of the carbon fixed as a result of enrichment was translocated out of the source leaf within one diurnal cycle. The carbon remaining in the source leaf was unchanged. Partitioning of extra carbon into starch or sugar depended upon the amount of extra carbon synthesized. The unloading of the extra carbon into sinks depended on whether it was used for growth or stored. Under increased carbon content, the leaf as a sink was able to reorganize its metabolic reactions more rapidly to maintain the required gradient for unloading than the pod acting as the sink.

2269^5^Torbert,HA^Rogers,HH^Prior,SA^Schlesinger,WH^Runion,GB^1997^1^Effects of elevated atmospheric CO2 in agro-ecosystems on soil carbon storage^127^3^6^513-521^^^^^Dec^^^^^7299
1262^1334^2298^264^3316^376^442^534^538^57^unctional source-sink combinations. The plants were pruned to a source- path-sink system. With CO2 enrichment there was an appreciable increase in net photosynthetic CO2 uptake in earlier formed and physiologically younger leaves. Most of the carbon fixed as a result of enrichment was translocated out of the source leaf within one diurnal cycle. The carbon remaining in the source leaf was unchanged. Partitioning of extra carbon into starch or sugar depended upon the amount of extra carbon synthesized. The unloading of the extra carbon into sinks depended on whether it was used for growth or stored. Under increased carbon content, the leaf as a sink was able to reorganize its metabolic reactions more rapidly to maintain the required gradient for unloading than the pod A^7298^Increasing global atmospheric CO2 concentration has led to concerns regarding its potential effects on the terrestrial environment. Attempts to balance the atmospheric carbon (C) budget have met with a large shortfall in C accounting (approximate to 1.4 x 10(15) g C y(-1)) and this has led to the hypothesis that C is being stored in the soil of terrestrial ecosystems. This study examined the effects of CO2 enrichment on soil C storage in C3 soybean (Glycine max L.) Merr. and C4 grain sorghum (Sorghum bicolor L.) Moench. agroecosystems established on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split-plot design replicated three times with two crop species (soybean and grain sorghum) as the main plots and two CO2 concentration (ambient and twice ambient) as subplots using open top field chambers. Carbon isotopic techniques using delta(13)C were used to track the input of new C into the soil system. At the end of two years, shifts in delta(13)C content of soil organic matter carbon were observed to a depth of 30 cm. Calculated new C in soil organic matter with grain sorghum was greater for elevated CO2 vs. ambient CO2 (162 and 29 g m(-2), respectively), but with soybean the new C in soil organic matter was less for elevated CO2 vs. ambient CO2 (120 and 291 g m(-2), respectively). A significant increase in mineral associated organic C was observed in 1993 which may result in increased soil C storage over the long-term, however, little change in total soil organic C was observed under either plant species. These data indicate that elevated atmospheric CO2 resulted in changes in soil C dynamics in agro-ecosystems that are crop species dependent.

2270^3^Williams,RS^Lincoln,DE^Thomas,RB^1997^1^Effects of elevated CO2-grown loblolly pine needles on the growth, consumption, development, and pupal weight of red- headed pine sawfly larvae reared within open-topped chambers^127^3^6^501-511^^^^^Dec^^^^^7301
1080^1081^2530^3187^3317^489^546^628^764^774^13)C content of soilA^7300^Seedlings of loblolly pine, Pinus taeda, were grown in open- topped chambers under four levels of CO2: two ambient and two elevated. Larvae of the red-headed pine sawfly, Neoniprion lecontei, were reared from early instar to pupation, primarily on branches within chambers. Larval growth and mortality were assessed and leaf phytochemistry samples of immature and mature leaves collected weekly. Mature leaves grown under elevated CO2 had significant reductions in leaf nitrogen and increases in non-structural carbohydrate contents, resulting in foliage being a poorer food source for larvae, i.e. higher carbohydrate:nitrogen ratio. Nutritional constituents of immature needles were unaffected by seedling CO2 treatment. Volatile mono-and sesquiterpenes were unrelated to plant CO2 treatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO2 enrichment, while mature needle consumption was not different between the treatments. The average weight gain per larva significantly declined in late instar larvae consuming elevated CO2-grown needles. In spite of this reduced growth, neither the days to pupation nor pupal weights were different among the CO2 treatments. This study suggests that enriched CO2-induced alterations in pine needle phytochemistry can affect red-headed pine sawfly performance, However, compensatory measures by larvae, such as choosing to consume more nutritious immature needles, apparently helps offset enriched CO2-induced reductions in the leaf quality of mature needles.

2271^3^Bowden,RD^Newkirk,KM^Rullo,GM^1998^1^Carbon dioxide and methane fluxes by a forest soil under laboratory-controlled moisture and temperature conditions^130^30^12^1591-1597^^^^^Oct^^^^^7303
310^3318^3319^3320^374^416^429^57^672^reatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO2 enrichment, while mature needle consumption was not different between the treatments. The average weigA^7302^Carbon dioxide and methane are important greenhouse gases whose exchange rates between soils and the atmosphere are controlled strongly by soil temperature and moisture. We made a laboratory investigation to quantify the relative importance of soil moisture and temperature on fluxes of CO2 and CH4 between forest soils and the atmosphere. Forest floor and mineral soil material were collected from a mixed hardwood forest at the Harvard Forest. Long-Term Ecological Research Site (MA) and were incubated in the laboratory under a range of moisture (air-dry to nearly saturated) and temperature conditions (5-25 degrees C). Carbon dioxide emissions increased exponentially with increasing temperature in forest floor material, with emissions reduced at the lowest and highest soil moisture contents. The forest floor Q(10) of 2.03 (from 15-25 degrees C) suggests that CO2 emissions were controlled primarily by soil biological activity. Forest floor CO2 emissions were predicted with a multiple polynomial regression model (r(2) = 0.88) of temperature and moisture, but the fit predicting mineral soil respiration was weaker (r(2) = 0.59). Methane uptake was controlled strongly by soil moisture, with reduced fluxes under conditions of very low or very high soil moisture contents. A multiple polynomial model accurately described CH4 uptake by mineral soil material (r(2) = 0.81), but only weakly (r(2) = 0.45) predicted uptake by forest floor material. The mineral soil Q(10) of 1.11 for CH4 uptake indicates that methane uptake is controlled primarily by physical processes. Our work suggests that inclusion of both moisture and temperature can improve predictions of soil CO2 and CH4 exchanges between soils and the atmosphere. Additionally, global change models need to consider interactions of temperature and moisture in evaluating effects of global climate change on trace gas fluxes. (C) 1998 Elsevier Science Ltd. All rights reserved.
al activity. Forest floor CO2 emissions were predicted with a multiple polynomial regression2272^2^Dhakhwa,GB^Campbell,CL^1998^1^Potential effects of differential day-night warming in global climate change on crop production^50^40^3-4^647-667^^^^^Dec^^^^^7305
1138^1356^1386^3321^3322^377^434^633^857^92^
A^7304^Recent studies on the nature of global warming indicate the likelihood of an asymmetric change in temperature, where night- time minimum temperature increases more rapidly than the daytime maximum temperature. We used a physically based scenario of asymmetric warming combined with climate change scenarios from General Circulation Models (GCMs) outputs and the EPIC (Erosion Productivity Impact Calculator) plant process model to examine the effects of asymmetric temperature change on crop productivity. Our results indicated that the potential effects of global change on crop productivity may be less severe with asymmetric day-night warming than with equal day- night warming.
 Ltd. All rights reserved.
al activity. Forest floor CO2 emissions were predicted with a multiple polynomial regression2273^6^Falloon,PD^Smith,P^Smith,JU^Szabo,J^Coleman,K^Marshall,S^1998^1^Regional estimates of carbon sequestration potential: linking the Rothamsted Carbon Model to GIS databases^263^27^3^236-241^^^^^Jul^^^^^7307
174^179^227^454^udies on the nature of global warming indicate the likelihood of an asymmetric change in temperature, where night- time minimum temperature increases more rapidly than the daytime maximum temperature. We used a physically based scenario of asymmetric warming combined with climate change scenarios from General Circulation Models (GCMs) outputs and the EPIC (Erosion Productivity Impact Calculator) plant process model to examine the effects of asymmetric temperature change on crop productivity. Our results indicated that the potential effects of global change on crop productivity may be less severe with asymmetric day-night warming than with equal day- night warming.
 Ltd. All rights reserved.
al activity. Forest floor CO2 emissions were predicted with a multiple polynomial regressionA^7306^Soil organic matter (SOM) represents a major pool of carbon within the biosphere. It is estimated at about 1400 Pg globally, which is roughly twice that in atmospheric CO2. The soil can act as both a source and a sink for carbon and nutrients, Changes in agricultural land use and climate can lead to changes in the amount of carbon held in soils, thus, affecting the fluxes of CO2 to and from the atmosphere. Some agricultural management practices will lead to a net sequestration of carbon in the soil. Regional estimates of the carbon sequestration potential of these practices are crucial if policy makers are to plan future land uses to reduce national CO, emissions. In Europe, carbon sequestration potential has previously been estimated using data from the Global Change and Terrestrial Ecosystems Soil Organic Matter Network (GCTE SOMNET). Linear relationships between management practices and yearly changes in soil organic carbon were developed and used to estimate changes in the total carbon stock of European soils. To refine these semi-quantitative estimates, the local soil type, meteorological conditions and land use must also be taken into account. To this end, we have modified the Rothamsted Carbon Model, so that it can be used in a predictive manner. with SOMNET data. The data is then adjusted for local conditions using Geographical Information Systems databases. In this paper, we describe how these developments call be used to estimate carbon sequestration at the regional level using a dynamic simulation model linked to spatially explicit data. Some calculations of the potential effects of afforestation on soil carbon stocks in Central Hungary provide a simple example of the system in use.

2274^5^Foley,JA^Levis,S^Prentice,IC^Pollard,D^Thompson,SL^1998^1^Coupling dynamic models of climate and vegetation^127^4^5^561-579^^^^^Jun^^^^^7309
243^2491^2493^256^2762^3082^344^385^633^674^ices and yearly changes in soil organic carbon were developed and used to estimate changes in the total carbon stock of EuA^7308^Numerous studies have underscored the importance of terrestrial ecosystems as an integral component of the Earth's climate system. This realization has already led to efforts to link simple equilibrium vegetation models with Atmospheric General Circulation Models through iterative coupling procedures. While these linked models have pointed to several possible climate- vegetation feedback mechanisms, they have been limited by two shortcomings: (i) they only consider the equilibrium response of vegetation to shifting climatic conditions and therefore cannot be used to explore transient interactions between climate and vegetation; and (ii) the representations of vegetation processes and land-atmosphere exchange processes are still treated by two separate models and, as a result, may contain physical or ecological inconsistencies. Here we present, as a proof concept, a more tightly integrated framework for simulating global climate and vegetation interactions. The prototype coupled model consists of the GENESIS (version 2) Atmospheric General Circulation Model and the IBIS (version 1) Dynamic Global Vegetation Model. The two models are directly coupled through a common treatment of land surface and ecophysiological processes, which is used to calculate the energy, water, carbon, and momentum fluxes between vegetation, soils, and the atmosphere. On one side of the interface, GENESIS simulates the physics and general circulation of the atmosphere. On the other side, IBIS predicts transient changes in the vegetation structure through changes in the carbon balance and competition among plants within terrestrial ecosystems. As an initial test of this modelling framework, we perform a 30 year simulation in which the coupled model is supplied with modern CO2 concentrations, observed ocean temperatures, and modern insolation. In this exploratory study, we run the GENESIS atmospheric model at relatively coarse horizontal resolution (4.50 latitude by 7.5 degrees longitude) and IBIS at moderate resolution (2 degrees latitude by 2 degrees longitude). We initialize the models with globally uniform climatic conditions and the modern distribution of potential vegetation cover. While the simulation does not fully reach equilibrium by the end of the run, several general features of the coupled model behaviour emerge. We compare the results of the coupled model against the observed patterns of modern climate. The model correctly simulates the basic zonal distribution of temperature and precipitation, but several important regional biases remain. In particular, there is a significant warm bias in the high northern latitudes, and cooler than observed conditions over the Himalayas, central South America, and north-central Africa. In terms of precipitation, the model simulates drier than observed conditions in much of South America, equatorial Africa and Indonesia, with wetter than observed conditions in northern Africa and China. Comparing the model results against observed patterns of vegetation coves shows that the general placement of forests and grasslands is roughly captured by the model. In addition, the model simulates a roughly correct separation of evergreen and deciduous forests in the tropical, temperate and boreal zones. However, the general patterns of global vegetation cover are only approximately correct: there are still significant regional biases in the simulation. In particular, forest cover is not simulated correctly in large portions of central Canada and southern South America, and grasslands extend too far into northern Africa. These preliminary results demonstrate the feasibility of coupling climate models with fully dynamic representations of the terrestrial biosphere. Continued development of fully coupled climate-vegetation models will facilitate the exploration of a broad range of global change issues, including the potential role of vegetation feedbacks within the climate system, and the impact of climate variability and transient climate change on the terrestrial biosphere.
s shows that the general placem2275^5^Hobbie,JE^Kwiatkowski,BL^Rastetter,EB^Walker,DA^McKane,RB^1998^1^Carbon cycling in the Kuparuk basin: Plant production, carbon storage, and sensitivity to future changes^278^103^D22^29065-29073^^^^^27 Nov^^^^^7311
137^146^174^314^362^374^660^681^715^over are only approximately correct: there are still significant regional biases in the simulation. In particular, forest cover is not simulated correctly in large portions of central Canada and southern South America, and grasslands extend too far into northern Africa. These preliminary results demonstrate the feasibility of coupling climate models with fully dynamic representations of the terrestrial biosphere. Continued development of fully coupled climate-vegetation models will facilitate the exploration of a broad range of global change issues, including the potential role of vegetation feedbacks within the climate system, and the impact of climate variability and transient climate change on the terrestrial biosphere.
s shows that the general placemA^7310^The Marine Biological Laboratory General Ecosystem Model was calibrated for an arctic tussock tundra system using data from long-term observations and experiments at Toolik Lake, Alaska. These experiments include the effects of changes in temperature, light, CO2, and nutrients, so the model could be applied to five regions comprising the entire Kuparuk River basin. Met primary production, averaged for the entire basin, was 92 g C m(-2) yr(-1). A 150 year simulation of carbon storage under a doubling of CO2 (slow ramp-up) and a temperature increase of 3.5 degrees C gave an estimate of +400 g C m(-2) when soil moisture increased and +500 g C m(-2) when soil moisture decreased. Drier soils stimulated decomposition producing an increase in nitrogen availability; the increased N led to increased net primary production. If this result is applicable to other arctic ecosystems, then it is unlikely that warming will enhance carbon loss to the atmosphere to further enhance warming.
hows that the general placem2276^2^Johnston,KM^Schmitz,OJ^1997^1^Wildlife and climate change: Assessing the sensitivity of selected species to simulated doubling of atmospheric CO2^127^3^6^531-544^^^^^Dec^^^^^7313
1019^1167^3323^3324^673^727^lude the effects of changes in temperature, light, CO2, and nutrients, so the model could be applied to five regions comprising the entire Kuparuk River basin. Met primary production, averaged for the entire basin, was 92 g C m(-2) yr(-1). A 150 year simulation of carbon storage under a doubling of CO2 (slow ramp-up) and a temperature increase of 3.5 degrees C gave an estimate of +400 g C m(-2) when soil moisture increased and +500 g C m(-2) when soil moisture decreased. Drier soils stimulated decomposition producing an increase in nitrogen availability; the increased N led to increased net primary production. If this result is applicable to other arctic ecosystems, then it is unlikely that warming will enhance carbon loss to the atmosphere to further enhance warming.
hows that the general placemA^7312^We explored, using computer simulations, the sensitivity of four mammal species (elk, Cervus canadensis; white-tailed deer, Odocoileus virginianus; Columbian ground squirrel, Spermophilus columbianus; and chipmunk, Tamias striatus) within the continental USA to the effect of anticipated levels of global climate change brought about by a doubling of atmospheric CO2. Sensitivity to the direct effects of climate change were evaluated using a climate-space approach to delineate the range of thermal conditions tolerable by each species. Sensitivity to indirect effects were evaluated by quantifying the association of each species to the current vegetation distribution within the continental USA and using this association to assess whether wildlife species distributions might shift in response to vegetation shifts under climate change. Results indicate that altered thermal conditions alone should have little or no effect on the wildlife species' distributions as physiological tolerance to heat load would allow them to survive. Analyses of the effects of vegetation change indicate that deer and chipmunks should retain their current distributions and possibly expand westward in the USA. For Elk and ground squirrels, there is a possibility that their current distributions would shrink and there is little possibility that each species would spread to new regions. This work emphasizes that the distributions of the four mammalian species are likely to be influenced more by vegetation changes than by thermal conditions. Future efforts to understand the effects of global change on wildlife species should focus on animal-habitat and climate-vegetation linkages.

2277^4^Lal,M^Whetton,PH^Pittock,AB^Chakraborty,B^1998^1^Simulation of present-day climate over the Indian subcontinent by general circulation models^371^9^1^69-96^^^^^Mar^^^^^7315
130^174^2095^2675^312^3325^633^812^ed thermal conditions alone should have little or no effect on the wildlife species' distributions as physiological tolerance to heat load would allA^7314^There continues to be some improvement in the ability of general circulation models to simulate the present-day climate on large scales although further improvements in the model resolution and parameterization of physical processes are still needed for the realistic simulation of regional climates. Quantitative assessment of the magnitude of climate change on a regional scale and its implications are essential for understanding, planning and management of resources at national/regional levels. In developing countries like India, where the economy is largely regulated by variability in summer monsoon rainfall, the consideration of measures for reducing the impacts of global change should begin as soon as possible, particularly with regard to floods and droughts, cyclone disaster preparedness, hydrological planning in semi-arid regions and coastal zone management issues. With this in view, we examine here the skill of a range of global climate models in simulating the regional climatology of the Indian subcontinent. This is a necessary first step in preparing climate change scenarios for the region. The simulation of the current broad scale patterns of mean sea level pressure, temperature and precipitation over the northern hemisphere and over the Indian subcontinent in particular are assessed for a broad range of global climate modelling experiments. The experiments included both slab ocean and coupled ocean experiments. Five experiments are identified as having a fairly realistic simulation and may be considered acceptable for use in regional climate change assessments. All of these are of relatively high resolution and use a Q-flux correction (in the slab ocean experiments) or a flux correction (in the coupled ocean experiments). A further four experiments, with somewhat poorer regional climate simulations, are acceptable but only to a moderate degree of confidence. However, some six experiments have such marked deficiencies in their simulation of present- day regional climatology that we consider them unacceptable for regional climate change assessment.

2278^1^Mosier,AR^1998^1^Soil processes and global change^263^27^3^221-229^^^^^Jul^^^^^7317
1106^3019^312^32^3326^3327^3328^3329^669^990^nd precipitation over the northern hemisphere and over the Indian subcontinent in particular are assessed for a broad range of global climate modelling experiments. The experiments included both slab ocean and coupled ocean experiments. Five experiments are identified as having a fairly realistic simulation and may be considered acceptable for use in regional climate change assessments. All of these are of relatively high resolution and use a Q-flux correction (in the slab ocean experiments) or a flux correction (in the coupled ocean experiments). A further four experiments, with somewhat poorer regional climate simulations, are acceptable but only to a moderate degree of confidence. However, some six experiments have such marked deficiencies in their simulation of present- day regional climatology that we consider themA^7316^Contributors to the Intergovernmental Panel on Climate Change (IPCC) generally agree that increases in the atmospheric concentration of greenhouse trace gases (i.e., CO2, CH4, N2O, O-3) since preindustrial times, about the year 1750, have led to changes in the earth's climate. During the past 250 years the atmospheric concentrations of CO2, CH4, and N2O have increased by 30, 145, and 15%, respectively. A doubling of preindustrial CO2 concentrations by the end of the twenty-first century is expected to raise global mean surface temperature by about 2 degrees C and increase the frequency of severe weather events. These increases are attributed mainly to fossil fuel use, land-use change, and agriculture. Soils and climate changes are related by bidirectional interactions. Soil processes directly affect climatic changes through the production and consumption of CO2, CH4, and N2O and, indirectly, through the production and consumption of NH,, NO,, and CO. Although CO2 is primarily produced through fossil fuel combustion, land-use changes, conversion of forest and grasslands to agriculture, have contributed significantly to atmospheric increase of CO2. Changes in land use and management can also result in the net uptake, sequestration, of atmospheric CO2. CH4 and N2O are produced (30% and 70%, respectively) in the soil, and soil processes will likely regulate future changes in the atmospheric concentration of these gases. The soil-atmosphere exchange of CO2, CH4, and N2O are interrelated, and changes in one cycle can im part changes in the N cycle and resulting soil-atmosphere exchange of N2O. Conversely, N addition increases C sequestration. On the other hand, soil processes are influenced by climatic change through imposed changes in soil temperature, soil water, and nutrient competition. Increasing concentrations of atmospheric CO2 alters plant response to environmental parameters and frequently results in increased efficiency in use of N and water. In annual crops increased CO2 generally leads to increased crop productivity. In natural systems, the long-term impact of increased CO2 on ecosystem sustainability is not known. These changes may also-result in altered CO2, CH4, and N2O exchange with the soil. Because of large temporal and spatial variability in the soil-atmosphere exchange of trace gases, the measurement of the absolute amount and prediction of the changes of these fluxes, as they are impacted by global change on regional and global scales, is still difficult. in recent years, however, much progress has been made in decreasing the uncertainty of field scale flux measurements, and efforts are being directed to large scale field and modeling programs. This paper briefly relates soil process and issues akin to the soil-atmosphere exchange of CO2, CH4, and N2O. The impact of climate change, particularly increasing atmospheric CO2 concentrations, on soil processes is also briefly discussed.
esults in increased efficiency in use of N and water. In annual crops increased CO2 generally leads to increased2279^5^Oechel,WC^Vourlitis,GL^Hastings,SJ^Ault,RP^Bryant,P^1998^1^The effects of water table manipulation and elevated temperature on the net CO2 flux of wet sedge tundra ecosystems^127^4^1^77-90^^^^^Jan^^^^^7319
1234^137^179^189^2930^31^312^3330^673^681^the soil-atmosphere exchange of trace gases, the measurement of the absolute amount and prediction of the changes of these fluxes, as they are impacted by global change on regional and global scales, is still difficult. in recent years, however, much progress has been made in decreasing the uncertainty of field scale flux measurements, and efforts are being directed to large scale field and modeling programs. This paper briefly relates soil process and issues akin to the soil-atmosphere exchange of CO2, CH4, and N2O. The impact of climate change, particularly increasing atmospheric CO2 concentrations, on soil processes is also briefly discussed.
esults in increased efficiency in use of N and water. In annual crops increased CO2 generally leads to increasedA^7318^lit situ manipulations were conducted in a naturally drained lake on the arctic coastal plain near Prudhoe Bay, Alaska (70 degrees 21.98' N, 148 degrees 33.72' W) to assess the potential shortterm effects of decreased water table and elevated temperature on net ecosystem CO2 flux. The experiments were conducted over a 2-year period, and during that time, water table depth of drained plots was maintained on average 7 cm lower than the ambient water table, and surface temperatures of plots exposed to elevated temperature were increased on average 0.5 degrees C. Water table drainage, and to a lesser extent elevated temperature, resulted in significant increases in ecosystem respiration (ER) rates, and only small and variable changes in gross ecosystem productivity (GEP). As a result, drained plots were net sources of approximate to 40 gC m(-2) season(-1) over both years of manipulation, while control plots were net sinks of atmospheric CO2 of about 10 gC m(-2) season(- 1) (growing season length was an estimated 125 days). Control plots exposed to elevated temperatures accumulated slightly more carbon than control plots exposed to ambient temperatures. The direct effects of elevated temperature on net CO2 flux, ER, and GEP were small, however, elevated temperature appeared to interact with drainage to exacerbate the amount of net carbon loss. These data suggest that many currently saturated or nearly saturated wet sedge ecosystems of the north slope of Alaska may become significant sources of CO2 to the atmosphere if climate change predictions of increased evapotranspiration and reduced soil water status are realized. There is ample evidence that this may be already occurring in arctic Alaska, as a change in net carbon balance has been observed for both tussock and wet-sedge tundra ecosystems over the last 2-3 decades, which coincides with a recent increase in surface temperature and an associated decrease in soil water content. In contrast, if precipitation increases relatively more than evapotranspiration, then increases in soil moisture content will likely result in greater carbon accumulation.





2281^2^Scurlock,JMO^Hall,DO^1998^1^The global carbon sink: a grassland perspective^127^4^2^229-233^^^^^Feb^^^^^7323
137^2100^2487^327^3331^344^454^58^661^672^
A^7322^The challenge to identify the biospheric sinks for about half the total carbon emissions from fossil fuels must include a consideration of below-ground ecosystem processes as well as those more easily measured above-ground. Recent studies suggest that tropical grasslands and savannas may contribute more to the 'missing sink' than was previously appreciated, perhaps as much as 0.5 Pg (= 0.5 Gt) carbon per annum. The rapid increase in availability of productivity data facilitated by the Internet will be important for future scaling-up of global change responses, to establish independent lines of evidence about the location and size of carbon sinks.
 in soil water content. In contrast, if precipitation increases relatively more than evapotranspiration,2282^21^Sellers,PJ^Hall,FG^Kelly,RD^Black,A^Baldocchi,D^Berry,J^Ryan,M^Ranson,KJ^Crill,PM^Lettenmaier,DP^Margolis,H^Cihlar,J^Newcomer,J^Fitzjarrald,D^Jarvis,PG^Gower,ST^Halliwell,D^Williams,D^Goodison,B^Wickland,DE^Guertin,FE^1997^1^BOREAS in 1997: Experiment overview, scientific results, and future directions^278^102^D24^28731-28769^^^^^26 Dec^^^^^7325
2092^2912^312^3332^3333^344^529^659^783^888^
A^7324^The goal of the Boreal Ecosystem-Atmosphere Study (BOREAS) is to improve our understanding of the interactions between the boreal forest biome and the atmosphere in order to clarify their roles in global change. This overview paper describes the science background and motivations for BOREAS and the experimental design and operations of the BOREAS 1994 and BOREAS 1996 field years. The findings of the 83 papers in this journal special issue are reviewed, In section 7, important scientific results of the project to date are summarized and future research directions are identified.




 than evapotranspiration,2284^3^Tian,H^Hall,CAS^Qi,Y^1998^1^Modeling primary productivity of the terrestrial biosphere in changing environments: Toward a dynamic biosphere model^183^17^5^541-557^^^^^^^^^^7329
1117^1134^137^1467^1637^1660^3084^3148^344^392^^BOREAS in 1997: Experiment overview, scientific results, and future directions^278^102^D24^28731-28769^^^^^26 Dec^^^^^7325
2092^2912^312^3332^3333^344^529^659^783^888^
A^7324^The goal of the Boreal Ecosystem-Atmosphere Study (BOREAS) is to improve our understanding of the interactions between the boreal forest biome and the atmosphere in order to clarify their roles in global change. This overview paper describes the science background and motivations for BOREAS and the experimental design and operations of the BOREAS 1994 and BOREAS 1996 field years. The findings of the 83 papers in this journal special issue are reviewed, In section 7, important scientific results of the project to date are summarized and future research directions are identified.




 than evapotranspiration,A^7328^There is a widespread perception that the atmosphere and the climate are beginning to change, and that these changes could have profound impacts on the primary productivity of the terrestrial biosphere. The terrestrial biosphere is a dynamic system that interacts with the atmosphere and climate principally through the exchanges of energy, water, and elements. Due to the limitations of equilibrium terrestrial biosphere models, new generation models - dynamic biosphere models, are critically needed for assessing and predicting the primary production and biogeochemical cycles of the terrestrial biosphere in changing global environment. The goal of dynamic biosphere modeling is to model terrestrial ecosystem dynamics induced by natural and anthropogenic disturbances, as well as the interactions of energy, water, and carbon cycles within the terrestrial biosphere and between the terrestrial biosphere and the atmosphere. The critical gaps in developing such a terrestrial biosphere model are not our inability to construct model code but instead the poorly developed links between empiricism and the concepts we used to construct our models, especially a lack of data that would help to make our models mechanistic, an incomplete fundamental knowledge about how complex terrestrial ecosystems work, a poor understanding of how to scale up what we do know and of how to validate such a model. The interaction among data, model structure, parameter sets, and predictive uncertainty will Bead to important progress in the development of dynamic biosphere models.

2285^4^Woodbury,PB^Smith,JE^Weinstein,DA^Laurence,JA^1998^1^Assessing potential climate change effects on loblolly pine growth: A probabilistic regional modeling approach^45^107^1-3^99-116^^^^^17 Aug^^^^^7331
1167^146^174^312^3334^3335^447^633^705^ctions of energy, water, and carbon cycles within the terrestrial biosphere and between the terrestrial biosphere and the atmosphere. The critical gaps in developing such a terrestrial biosphere model are not our inabilitA^7330^Most models of the potential effects of climate change on forest growth have produced deterministic predictions. However, there are large uncertainties in data on regional forest condition, estimates of future climate, and quantitative relationships between environmental conditions and forest growth rate. We constructed a new model to analyze these uncertainties along with available experimental results to make probabilistic estimates of climate change effects on the growth of loblolly pine (Pinus taeda L.) throughout its range in the USA. Complete regional data sets were created by means of spatial interpolation, and uncertainties in these data were estimated. A geographic information system (GIS) was created to integrate current and predicted climate data with regional data including forest distribution, growth rate, and stand characteristics derived from USDA Forest Service data. A probabilistic climate change scenario was derived from the results of four different general circulation models (GCM). Probabilistic estimates of forest growth were produced by linking the GIS to a Latin Hypercube carbon (C) budget model of forest growth. The model estimated a greater than 50% chance of a decrease in loblolly pine growth throughout most of its range. The model also estimated a 10% chance that the total regional basal area growth will decrease by more than 24 X 10(6) m(2) yr(-1) (a 92% decrease), and a 10% chance that basal area growth will increase by more than 62 X 10(6) m(2) yr(-1) (a 142% increase above current rates). The most influential factor at all locations was the relative change in C assimilation. Of climatic factors, CO2 concentration was found to be the most influential factor at all locations. Substantial regional variation in estimated growth was observed, and probably was due primarily to variation in historical growth rates and to the importance of historical growth in the model structure. (C) 1998 Elsevier Science B.V.

GCO2

GC3

GC4

GO2

GCH4
different general circulation models (GCM).2286^3^Yeates,G W^Newton,P C D^Ross,D J^1999^1^Response of soil nematode fauna to naturally elevated CO2 levels influenced by soil pattern^372^1^^285-293^^^^^Jun^^^^^7338
312^344^535^56^a decrease in loblolly pine growth throughout most of its range. The model also estimated a 10% chance that the total regional basal area growth will decrease by more than 24 X 10(6) m(2) yr(-1) (a 92% decrease), and a 10% chance that basal area growth will increase by more than 62 X 10(6) m(2) yr(-1) (a 142% increase above current rates). The most influential factor at all locations was the relative change in C assimilation. Of climatic factors, CO2 concentration was found to be the most influential factor at all locations. Substantial regional variation in estimated growth was observed, and probably was due primarily to variation in historical growth rates and to the importance of historical growth in the model structure. (C) 1998 Elsevier Science B.V.

GCO2

GC3

GC4

GO2

GCH4
different general circulation models (GCM).A^7337^As experimental elevation of CO2 in short-term experiments may produce organic matter with decomposition characteristics different from those produced under long-term equilibrated conditions, we sampled the soil nematode fauna near a natural CO2 vent in Northland, New Zealand. Various indices of the nematode fauna showed significant effects, with all being significantly correlated with soil pH, microbial carbon and atmospheric CO2 across the 33 sampling points. There was a general decrease in nematode abundance and diversity, but an increase in dominance and proportion of bacterial-feeding nematodes with increasing atmospheric CO2 concentration. However, when the nematode data from gley and organic soils present at the site were differentiated most of the significant correlations were with soil microbial carbon; they were positive in the organic soil but negative in the gley soil. That these responses can be related to soil carbon and to microbial carbon demonstrates that any general response to long-term CO2 enrichment represents an integration of specific responses by the soil biota in the various soils present.

2287^7^Balaguer,L^Manrique,E^de los Rios,A^Ascaso,C^Palmqvist,K^Fordham,M^Barnes,J D^1999^1^Long-term responses of the green-algal lichen Parmelia caperata to natural CO2 enrichment^2^119^2^166-174^^^^^May^^^^^7340
1998^243^3206^3336^3337^372^417^529^539^92^tly correlated with soil pH, microbial carbon and atmospheric CO2 across the 33 sampling points. There was a general decrease in nematode abundance and diversity, but an increase in dominance and proportion of bacterial-feeding nematodes with increasing atmospheric CO2 concentration. However, when the nematode data from gley and organic soils present at the site were differentiated most of the significant correlations were with soil microbial carbon; they were positive in the organic soil but negative in the gley soil. That these responses can be related to soil carbon and to microbial carbon demonstrates that any general response to long-A^7339^Acclimation to elevated CO2 was investigated in Parmelia caperata originating from the vicinity of a natural CO2 spring, where the average daytime CO2 concentration was 729 +/- 39 mu mol mol(-1) dry air. Thalli showed no evidence of a down- regulation in photosynthetic capacity following long-term exposure to CO2 enrichment in the field; carboxylation efficiency, total Ribulose bisphosphate carboxylase/oxygenase (Rubisco) content, apparent quantum yield of CO2 assimilation, and the light-saturated rate of CO2 assimilation (measured under ambient and saturating CO2 concentrations) were similar in thalli from the naturally CO2 enriched site and an adjacent control site where the average long-term CO2 concentration was about 355 mu mol mol(-1). Thalli from both CO2 environments exhibited low CO2 compensation points and early saturation of CO2 uptake kinetics in response to increasing external CO2 concentrations, suggesting the presence of an active carbon- concentrating mechanism. Consistent with the lack of significant effects on photosynthetic metabolism, no changes were found in the nitrogen content of thalli following prolonged exposure to elevated CO2. Detailed intrathalline analysis revealed a decreased investment of nitrogen in Rubisco in the pyrenoid of algae located in the elongation zone of thalli originating from elevated CO2, an effect associated with a reduction in the percentage of the cell volume occupied by lipid bodies and starch grains. Although these differences did not affect the photosynthetic capacity of thalli, there was evidence of enhanced limitations to CO2 assimilation in lichens originating from the CO2-enriched site. The light-saturated rate of CO2 assimilation measured at the average growth CO2 concentration was found to be significantly lower in thalli originating from a CO2-enriched atmosphere compared with that of thalli originating and measured at ambient CO2, At lower photosynthetic photon flux densities, the light compensation point of net CO2 assimilation was significantly higher in thalli originating from elevated CO2 and this effect was associated with higher usnic acid content.

2288^2^McConnaughay,K D M^Coleman,J S^1999^1^Biomass allocation in plants: Ontogeny or optimality? A test along three resource gradients^11^80^8^2581-2593^^^^^Dec^^^^^7342
1312^1315^1527^2552^314^372^374^492^803^92^vated CO2, an effect associated with a reduction in the percentage of the cell volume occupied by lipid bodies and starch grains. Although these differences did not affect the photosynthetic capacity of thalli, there was evidence of enhanced limitations to CO2 assimilation in lichens originating from the CO2-enriched site. The light-saturated rate of CO2 assimilation measured at the average growth CO2 concentration was found to be significantly lower in thalli originating from a CO2-enriched atmosphere compared with that of thalli originating and measured at ambient CO2, At lower photosynthetic photon flux densities, the light compensation point of net CO2 assimilation was significantA^7341^We examined biomass allocation patterns throughout the entire vegetative growth phase for three species of annual plants along three separate gradients of resource availability to determine whether observed patterns of allocational plasticity are consistent with optimal partitioning theory. Individuals of the annual plant species Abutilon theophrasti, Chenopodium album, and Polygonum pensylvanicum were grown from locally field-gathered seed in controlled greenhouse conditions across gradients of light, nutrients, and water. Frequent harvests were used to determine the growth and allocation (root vs. shoot, and leaf area vs. biomass) responses of these plants over a 57-d period. Growth analysis revealed that each species displayed significant plasticity in growth rates and substantial amounts of ontogenetic drift in root: shoot biomass ratios and ratios of leaf area to biomass across each of the three resource gradients. Ontogenetically controlled comparisons of root : shoot and leaf area ratios across light and nutrient gradients were generally consistent with predictions based on optimal partitioning theory; allocation to roots decreased and leaf area increased under low light and high nutrient conditions. These trends were confirmed, though were less dramatic, in allometric plots of biomass allocation throughout ontogeny. These species did not alter biomass allocation (beyond ontogenetic drift) in response to the broadly varying water regimes. Furthermore, many of the observed differences in biomass allocation were limited to a given time during growth and development. We conclude that, for these rapidly growing annual species, plasticity in biomass allocation patterns is only partially consistent with optimal partitioning theory, and that these plastic responses are ontogenetically constrained. Further, while these species did adjust biomass allocation patterns in response to light and nutrient availability, they did not adjust biomass allocation in response to water availability, despite dramatic plasticity in growth rates along all three resource gradients. Our results support a developmentally explicit model of plasticity in biomass allocation in response to limiting resources.

2289^3^Inubushi,K^Cheng,W G^Chander,K^1999^1^Carbon dynamics in submerged soil microcosms as influenced by elevated CO2 and temperature^316^45^4^863-872^^^^^Dec^^^^^7344
344^534^535^57^ation (beyond ontogenetic drift) in response to the broadly varying water regimes. Furthermore, many of the observed differences in biomass allocation were limited to a given time during growth and development. We conclude that, for these rapidly growing annual species, plasticity in biomass allocation patterns is only partially consistent with optimal partitioning theory, and that these plastic responses are ontogenetically constrained. Further, while these species did adjust biomass allocation patterns in response to light and nutrient availability, they did not adjust biomass allocation in response to water availability, despite dramatic plaA^7343^A 45-d incubation experiment was conducted under controlled laboratory conditions to study the interactive effects of elevated CO2 and temperature on the dynamics of microbial biomass C and organic C in hooded paddy soil microcosms amended or unamended with rice straw. The microcosms with the two treatments were transferred separately to four growth chambers to incubate them under 16 h/8 h light and dark conditions. Two of the growth chambers set at 25 and 35 degrees C provided a continuous how of elevated CO2 (equivalent to 800 mu L L-1). Similarly the other two growth chambers were run under near ambient CO2 (400 mu L L-1) conditions at each of the two temperatures. The amounts of soluble carbon, microbial biomass C, chlorophyll-type compounds, and organic C in the surface (0- 1 cm) and sub-surface (below 1 cm) soil layers were measured at 15, 30, and 45 d after incubation. The amount of soluble carbon in the straw-amended soil gradually decreased throughout the incubation period, while no significant differences were detected among the four different conditions. The interactive effects of both elevated CO2 and temperature were found to be positive in terms of the size of the microbial biomass in surface soil, although no significant differences were detected in the subsurface. However, the amount of total soil organic C was larger in the soils incubated at a lower temperature. The amounts of chlorophyll-type compounds doubled in the surface soil when the soils were incubated under elevated CO2 conditions, indicating that the higher incubation concentration of CO2 promoted the growth of algae in surface soil.

2290^4^Reddy,K R^Davidonis,G H^Johnson,A S^Vinyard,B T^1999^1^Temperature regime and carbon dioxide enrichment alter cotton roll development and fiber properties^48^91^5^851-858^^^^^Sep-Oct^^^^^7346
1163^3338^3339^467^614^92^easured at 15, 30, and 45 d after incubation. The amount of soluble carbon in the straw-amended soil gradually decreased throughout the incubation period, while no significaA^7345^Temperature and atmospheric carbon dioxide concentration [CO2] affect cotton (Gossypium hirsutum L.) growth and development, but the interaction of these two factors on boil and fiber properties has not been studied. An experiment aas conducted in naturally lit plant growth chambers to determine the influence of temperature and atmospheric [CO2] on cotton (cv. DPL-51) boll and fiber growth parameters. Five temperature regimes were evaluated: the 1995 temperature at Mississippi State, MS; the 1995 temperature minus 2 degrees C; and the 1995 temperature plus 2, 5, and 7 degrees C. Daily and seasonal variation and amplitudes were maintained. Atmospheric [CO2] treatments were 360 (ambient) and 720 mu L L-1. Boll number, bell growth, and fiber properties were measured. Boll size and maturation periods decreased as temperature increased. Boll growth increased with temperature to 25 degrees C and then declined at the highest temperature. Boll maturation period, size, and growth rates were not affected by atmospheric [CO2]. The most temperature-sensitive aspect of cotton development is boll retention. Almost no bells were retained to maturity at 1995 plus 5 or 7 degrees C, but squares and bells were continuously produced even at those high temperatures. Therefore, the upper limit for cotton boil survival is 32 degrees C, or 5 degrees C warmer than the 1995 U.S. Mid-South ambient temperatures. The 720 mu L L-1 atmospheric [CO2] had about 40% more squares and bells across temperatures than the 360 mu L L-1 [CO2], Fibers were longer when bells grew at less than optimal temperatures (25 degrees C) for boll growth. As temperature increased, fiber length distributions were more uniform. Fiber fineness and maturity increased linearly with the increase in temperature up to 26 degrees C, but decreased at 32 degrees C. Short-fiber content declined linearly from 17 to 26 degrees C, but was higher at higher temperature. As for boll growth and developmental parameters, elevated atmospheric [CO2] did not affect any of the fiber parameters. Changes in temperature, however, had a dramatic effect on boll set and tiber properties. The relationships between temperature and boll growth and developmental rate functions and fiber properties provide the necessary functional parameters to build fiber models under optimum water and nutrient conditions.

2291^2^Rouhier,H^Read,D J^1999^1^Plant and fungal responses to elevated atmospheric CO2 in mycorrhizal seedlings of Betula pendula^173^42^3^231-241^^^^^Dec^^^^^7348
1983^2034^243^3340^376^423^430^437^57^92^ when bells grew at less than optimal temperatures (25 degrees C) for boll growth. As temperature increased, fiber length distributions were more uniform. Fiber fineness and maturity increased linearly with the increase in temperature up to 26 degrees C, but decreased at 32 degrees C. Short-fiber content declined linearly from 17 to 26 degrees C, but was higher at higher temperature. As for boll growth and developmental parameters, elevated atmospheric [CO2] did not affect any of the fibA^7347^The effects of elevated CO2 concentrations upon carbon allocation in mycorrhizal (M) and non-mycorrhizal (NM) birch (Betula pendula) seedlings were investigated. M plants, colonised by the fungus Paxillus involutus, and NM plants, were exposed for 3 months to ambient (350 mu l 1(-1)) or elevated (700 mu l 1(-1)) CO2 environments. The assimilation and distribution of carbon within the different compartments of the plant-substrate-fungal system were investigated using radioactive carbon as a tracer. In addition, the impact of elevated CO2 upon extension growth of the ectomycorrhizal mycelium of the fungus was determined in transparent observation chambers. Yields of whole plants and of shoots were significantly decreased under elevated CO2 whether they were grown with or without their fungal symbionts. Neither the dry mass production of roots of mycorrhizal plants, nor the amount of carbon allocated to shoots, roots and mycorrhizal tips were affected by elevated CO2. While the number of mycorrhizal root tips was decreased with CO2 enrichment, their relative importance in the total root system was unchanged. There was a significant increase in the extent of development of the external mycelium under elevated CO2. A greater proportion of the radioactive carbon was allocated to the soil compartment under elevated CO2. This increase, probably arising through increased rhizodeposition, was greater in NM than M plants. The responses are discussed in terms of nutrient availability in the growth media and the possible role of increased carbon allocation to mycorrhizal mycelium in nature. (C) 1999 Elsevier Science B.V. All rights reserved.

2292^3^Ziska,L H^Teasdale,J R^Bunce,J A^1999^1^Future atmospheric carbon dioxide may increase tolerance to glyphosate^253^47^5^608-615^^^^^Sep-Oct^^^^^7350
245^3341^3342^349^417^662^r the dry mass production of roots of mycorrhizal plants, nor the amount of carbon allocated to shoots, roots and mycorrhizal tips were affected by elevated CO2. While the number of mycorrhizal rootA^7349^We tested whether the efficacy of chemical weed control might change as atmospheric CO2 concentration [CO2] increases by determining if tolerance to a widely used, phloem mobile, postemergence herbicide, glyphosate, was altered by a doubling of [CO2]. Tolerance was determined by following the growth of Amaranthus retroflexus L. (redroot. pigweed), a C-4 species, and Chenopodium album L. (common lambsquarters), a C-3 species, grown at near ambient (360 mu mol mol(-1)) and twice ambient (720 mu mol mol(-1)) [CO2] for 14 d following glyphosate application at rates of 0.00 (control), 0.112 kg ai ha(-1) (0.1 x the commercial rate), and 1.12 kg ai ha(-1) (1.0 x the commercial rare) in four separate trials. Irrespective of [CO2], growth of the C-4 species, A. retroflexus, was significantly reduced and was eliminated altogether at glyphosate application rates of 0.112 and 1.12 kg ai ha(-1), respectively. However, in contrast to the ambient [CO2] treatment, an application rate of 0.112 kg ai ha(-1) had no effect on growth, and a 1.12 kg ai ha(-1) rate reduced but did not eliminate growth in elevated [CO2]-grown C. album. Although glyphosate tolerance does increase with plant size at the time of application, differences in glyphosate tolerance between CO2 treatments in C. album cannot be explained by size alone. These data indicate that rising atmospheric [CO2] could increase glyphosate tolerance in a C-3 weedy species. Changes in herbicide tolerance at elevated [CO2] could limit chemical weed control efficacy and increase weed-crop competition.

2293^4^Schortemeyer,M^Atkin,O K^McFarlane,N^Evans,J R^1999^1^The impact of elevated atmospheric CO2 and nitrate supply on growth, biomass allocation, nitrogen partitioning and N-2 fixation of Acacia melanoxylon^92^26^8^737-747^^^^^^^^^^7352
2601^2742^312^3343^3344^361^376^384^429^672^ether at glyphosate application rates of 0.112 and 1.12 kg ai ha(-1), respectively. However, in contrast to the ambient [CO2] treatment, an application rate of 0.112 kg ai ha(-1) had no effeA^7351^The interactive effects of nitrate supply and atmospheric CO2 concentration on growth, N-2 fixation, dry matter and nitrogen partitioning in the leguminous tree Acacia melanoxylon R. Br. were studied. Seedlings were grown hydroponically in controlled-environment cabinets for 5 weeks at seven N-15- labelled nitrate levels, ranging from 3 to 6400 mmol m(-3). Plants were exposed to ambient (similar to 350 mu mol mol(-1)) or elevated (similar to 700 mu mol mol(-1)) atmospheric CO2 for 6 weeks. Total plant dry mass increased strongly with nitrate supply. The proportion of nitrogen derived from air decreased with increasing nitrate supply. Plants grown under either ambient or elevated CO2 fixed the same amount of nitrogen per unit nodule dry mass (16.6 mmol N per g nodule dry mass) regardless of the nitrogen treatment. CO2 concentration had no effect on the relative contribution of N2 fixation to the nitrogen yield of plants. Plants grown with greater than or equal to 50 mmol m(-3) N and elevated CO2 had approximately twice the dry mass of those grown with ambient CO2 after 42 days. The rates of net CO2 assimilation under growth conditions were higher per unit leaf area for plants grown under elevated CO2. Elevated CO2 also decreased specific foliage area, due to an increase in foliage thickness and density. Dry matter partitioning between plant organs was affected by ontogeny and nitrogen status of the plants, but not by CO2 concentration. In contrast, plants grown under elevated CO2 partitioned more of their nitrogen to roots. This could be attributed to reduced nitrogen concentrations in foliage grown under elevated CO2.

2294^4^Aben,S K^Seneweera,S P^Ghannoum,O^Conroy,J P^1999^1^Nitrogen requirements for maximum growth and photosynthesis of rice, Oryza sativa L-cv. Jarrah grown at 36 And 70 Pa CO2^92^26^8^759-766^^^^^^^^^^7354
2072^348^360^372^409^417^439^442^448^ contribution of N2 fixation to the nitrogen yield of plants. Plants grown with greater than or equal to 50 mmol m(-3) N and elevated CO2 had apA^7353^The hypothesis that growth of rice (Oryza sativa L. cv. Jarrah) at elevated atmospheric CO2 partial pressure alters leaf nitrogen (N) concentrations required to support maximum dry mass production and photosynthetic rates during the period of rapid tiller initiation was tested by growing plants for 30 days in unstirred sand/hydroponic culture with N concentrations of 5, 20, 40, 60 and 100 mg N L-1. Maximum growth and photosynthetic potential was greater at 70 than 36 Pa CO2 at all N concentrations in the solution. Elevated CO2 reduced leaf N concentrations required to support 90% of maximum growth and photosynthetic rates (critical concentration) from 40 to 27 g kg(-1) for growth and from 45 to 30 g kg(-1) for photosynthesis. Morphological changes at elevated CO2 included increased tiller numbers and reduced leaf area ratio. The latter could be explained by lower plant N concentrations which occurred at high CO2 at each N concentration in the solution, primarily due to lower leaf blade and root N concentrations. Changes in tiller numbers at high CO2 were unrelated to leaf or plant N but were strongly correlated with leaf soluble carbohydrate concentrations. We conclude that elevated CO2 alters the nutritional physiology of rice during the rapid tillering phase in a way that increases the efficiency of N utilisation for growth and photosynthesis.

2295^2^Kellomaki,S^Wang,K Y^1999^1^Short-term environmental controls of heat and water vapour fluxes above a boreal coniferous forest: model computations compared with measurements by eddy correlation^81^124^2-3^145-173^^^^^13 Dec^^^^^7356
256^2712^3345^3346^3347^3348^372^3874^586^605^itical concentration) from 40 to 27 g kg(-1) for growth and from 45 to 30 g kg(-1) for photosynthesis. Morphological changes at elevated CO2 included increased tiller numbers and reduced leaf area ratio. The latter could be explained by lower plant N concentrations which occurred at high CO2 at each N concentration in the solution, primarily due to lower leaf blade and root N concA^7355^Eddy correlation and stern how measurements were coupled with detailed microclimate and soil measurements made in a boreal Scots pine forest in the late growing season of 1998 to determine sensible and latent heat fluxes from the soil and the canopy separately. A 'resistance/energy' model is constructed and parametrized in order to reproduce the dynamics of water and heat exchange between the soil, the canopy and the atmosphere as a part of a larger forest ecosystem model (FinnFor; Kellomaki and Vaisanen, 1997). Unique features of the present model are that (1) energy flux equations are expressed in terms of conceptual resistances and their solutions are obtained by closing two surface energy budget equations defined separately for canopy and soil surface; (2) the forest canopy is divided into shaded and sunlit fractions in the radiation transfer submodel and the canopy resistance submodels; (3) a numerical integrating solutions are derived separately for net radiation absorption in the canopy, bulk canopy resistance and the bulk aerodynamic resistances of the forest; and (4) iterative determinations of canopy water potential based on a classical one-dimensional water how model enable the model to represent explicitly the interaction between the above-ground and the below-ground water dynamics. The model is validated against 19-day flux measurements. In general, the total system sensible heat flux (H), total system latent heat flux (lambda E), canopy latent heat flux (lambda E-c), and soil surface heat flux (G(s)) computed by the model matched well with the measured data. Based on 1/2 h flux measurements, daily lambda E varied from 0.50-7.38 MW m(-2), H from 0.64-8.3 MW m(-2): and lambda E-c from 0.30-6.93 MW m(-2). The Bowen ratio (H/lambda E) ranged from -4.5 to 9.8, but 82% of the values for the Bowen ratio were within 0.5-2.5. The model computations showed that daily lambda E-c and H-c accounted for 21-64% and 43-66% of the daily total system flux, respectively. Daily soil latent heat (lambda E,) and soil sensible heat (H-s) fluxes accounted for 0.02-4.5% and 0.05-7.6%, respectively, and the daily energy storage within the canopy (S-c) and G(s) accounted for 0.1-7.2% and 0.8-5.6%, respectively. Plotting of 1/2 h flux data against a single environmental factor indicated that a 68% change in lambda E-c and a 72% change in H-c can be explained by a change in canopy radiation absorption (R-nc) at the 5% probability level. The high correlation between the canopy fluxes and R-nc could be related to the moderate weather conditions and high soil water content during the selected days, whereas lambda E- s, H-s, S-c and G(s) give no significant correlation with R-n. As expected. lambda E-c was strongly dependent on canopy resistance (r(cs)), but less impact on aerodynamic resistances during most of the measuring time. The proportion of energy partitioning in H and lambda E exhibited a clear diurnal trend and was mainly controlled by the system total resistance and the vapour pressure deficit, but less related to changes in soil water content. (C) 1999 Elsevier Science B.V. All rights reserved.

2296^2^Medlyn,B E^Jarvis,P G^1999^1^Design and use of a database of model parameters from elevated [CO2] experiments^81^124^1^69-83^^^^^1 Dec^^^^^7358
605^gle environmental factor indicated that a 68% change in lambda E-c and a 72% change in H-c can be explained by a change in canopy radiation absorption (R-nc) at the 5% probability level. The high correlation between the canopy fluxes and R-nc could be related to the moderate weather conditions and high soil water content during the selected days, whereas lambda E- s, H-s, S-c and G(s) give no significant correlation with R-n. As expected. lambda E-c was strongly dependent on canopy resistance (r(cs)), but less impact on aerodynamic resistances during most of the measuring time. The proportion of energy partitioning in H and lambda E exhibited a clear diurnal trend and was mainly controlled by the system total resistance and the vapour pressure deficit, but less related to A^7357^This paper describes a new approach for linking experiments and models: a searchable database of model parameter values obtained directly from experiments. The experiments were carried out as part of a major European project studying the long-term effects of elevated [CO2] on European forest species. To ensure that the information obtained from these experiments was fully utilised in the modelling component of the project, a database was used to store and synthesise experimental data. Key features of the database include: (1) Data is stored as model parameters rather than raw experimental data, which aids transfer of information from experiments to models. (2) Extensive meta-data is stored, which is crucial for correct interpretation of parameter values. (3) The database has a relational structure, which facilitates data retrieval. In this paper, we document the structure of the database. The structure is flexible and generic and could easily be adapted to suit other fields of research. We illustrate the use of the database with examples from the project. (C) 1999 Elsevier Science B.V. All rights reserved.

2297^4^Brooks,P D^Campbell,D H^Tonnessen,K A^Heuer,K^1999^1^Natural variability in N export from headwater catchments: snow cover controls on ecosystem N retention^324^13^14-15^2191-2201^^^^^Oct^^^^^7360
174^19^1986^3211^3212^3214^3349^3350^3351^669^experiments was fully utilised in the modelling component of the project, a database was used to store and synthesise experimental data. Key features of the database include: (1) Data is stored as model parameters rather than raw experimental data, which aids transfer of information from experiments to models. (2) Extensive meta-data is stored, which is crucial for correct interpretation of parameter values. (3) The database has a relational structure, which facilitates data retrieval. In this paper, we document the structure of the database. The structure is flexible and generic and could easily be adapted to suit other fields of research. We illustrate A^7359^The causes of natural variability in catchment scale N export need to be understood and quantified before the effects of increased N deposition in high elevation catchments can be evaluated. This study evaluates controls on the size of the leachable soil N pool concurrent with the spring hydrologic flush that is primarily responsible for the transport of N to surface water. In high elevation catchments in the western United States, sources of N during this snowmelt flush include both atmospheric N deposition stored in the snowpack until melt and mobile soil N pools, and sinks are dominated by biogeochemical processes that occur in soil under snow cover. Because soil processes may serve either as a source or sink for N, controls on the amount of inorganic N leached from soil during the snowmelt period were evaluated in the major landscape types in four catchments in Colorado. Measurements of leached N were inversely related to measurements of over-winter CO2 flux at all sites, indicating that N was immobilized in soil heterotrophic biomass. Because over-winter soil heterotrophic activity is controlled primarily by the depth and timing of snow accumulation, the importance of these plot scale measurements to catchment scale N export were evaluated using a long-term record of winter precipitation, N deposition, and N export from Loch Vale in Rocky Mountain National Park. This data set identified a strong, linear relationship (r(2) = 0.68) between catchment scale N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identified at the plot scale. These results indicate that the winter snow pack is the major control both on hydrologic N export and on soil source/sink relationships for N concurrent with this transport mechanism. The effect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the effects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersheds. In these systems, changes in surface water chemistry are likely to occur in high deposition, snow-covered sites during low snow years before terrestrial vegetation is affected. Copyright (C) 1999 John Wiley & Sons, Ltd.

2298^2^Barton,C V M^Jarvis,P G^1999^1^Growth response of branches of Picea sitchensis to four years exposure to elevated atmospheric carbon dioxide concentration^84^144^2^233-243^^^^^Nov^^^^^7362
1323^256^349^423^425^439^639^685^705^984^e N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identified at the plot scale. These results indicate that the winter snow pack is the major control both on hydrologic N export and on soil source/sink relationships for N concurrent with this transport mechanism. The effect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the effects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersA^7361^Branch bags were used to expose branches on mature Sitka spruce trees to either ambient [CO2] (A) or elevated [CO2] (E) for 4 yr. This paper reports the effects of this treatment on the growth, development and phenology of the branches, including shoot expansion, shoot numbers, needle dimensions, needle numbers and stomatal density. The effect of elevated [CO2] on the relationship between leaf area and sapwood area was investigated. Exposure to elevated [CO2] doubled photosynthetic rates in current-fear shoots and, despite some downregulation, 1-yr-old E shoots also had higher rates of photosynthesis than their A counterparts. Thus, the amount of assimilate fixed by E branches was substantially more than that fixed by A branches; hen-ever, this increase in the local production of assimilate did not lead to an increase in non-structural carbohydrate or stimulate growth or meristematic activity within the E branches. There was a very consistent relationship between leaf area and stem cross-sectional area that was not influenced by [CO2]. However, unbagged branches had thicker stems than bagged branches, resulting in a slightly lower ratio of leaf area to cross-sectional area. The implications of the results for the modelling of growth and allocation and the potential utility of the branch bag technique are discussed.

2299^3^Rodriguez,D^Van Oijen,M^Schapendonk,A H M C^1999^1^LINGRA-CC: a sink-source model to simulate the impact of climate change and management on grassland productivity^84^144^2^359-368^^^^^Nov^^^^^7364
1098^130^243^3352^3353^372^409^431^507^92^oots also had higher rates of photosynthesis than their A counterparts. Thus, the amount of assimilate fixed by E branches was substantially more than that fixed by A branches; hen-ever, this increase in the local production of assimilate did not lead to an increase in non-structural carbohydrate or stimulate growth or meristematic activity within the E branches. There was a very consistent relationship between leaf area and stem cross-sectional areA^7363^A simulation model for the prediction of grassland (Lolium perenne) productivity under conditions of climate change is described and validated for grass growing in the Wageningen Rhizolab, Wageningen, The Netherlands. In this work the model was used to study the impact of different management strategies on the productivity of grassland under present and increased atmospheric CO2 concentrations. In LINGRA-CC simulated key processes are light utilization, leaf formation, leaf elongation, tillering and carbon partitioning. The daily growth rate is determined by the minimum of a sink and a source term. As in a previous model (LINGRA), the potential growth of the sink depends on the mean daily temperature, and can be modified by the effects of the availability of assimilates on tillering. The growth of roots is calculated from the amount of carbohydrates the shoot is unable to utilize when the number or activity of the sinks is small (overflow hypothesis). The main difference between LINGRA and LINGRA-CC is the way the source of assimilates for growth is calculated. Assimilate production depends on intercepted radiation, and a photosynthetic light- use efficiency (LUE) calculated as a function of CO2, temperature, light intensity and the Rubisco concentration of upper leaves. Other differences are that in LINGRA-CC, the specific shoot area for new growth depends on the level of reserves. Data from two independent experiments with L, perenne swards, grown in enclosures at two levels of CO2 during 1994 and 1995, were used to calibrate and validate the model, respectively. The model predicted well the observed amounts of harvested biomass, and the dynamics of the leaf area index, tiller number and specific shoot area. LINGRA-CC was used to stud? the effects of different combinations of cutting interval and cutting height on biomass production, at ambient (350 mu mol mol(-1) CO2) and double (700 mu mol mol(-1) CO2) CO2 conditions. Under both ambient and doubled CO2, maximum biomass was produced with cuttings of leaf area index >1, and at cutting intervals of 20 and 17 d for ambient and increased CO2 environments, respectively. Under high CO2 conditions the curling interval for maximum yield was 15% shorter than at ambient CO2. However, the gain in harvested biomass obtained by reducing the cutting interval by 3 d under high CO2 conditions was negligible.

2300^2^Crick,S G^McConchie,R^1999^1^Ethanol vapour reduces leaf blackening in cut flower Protea 'Pink Ice' stems^259^17^3^227-231^^^^^Nov^^^^^7366
1460^3354^ 1995, were used to calibrate and validate the model, respectively. The model predicted well the observed amounts of harvested biomass, and the dynamics of the leaf area index, tiller number and specific shoot area. LINGRA-CC was used to stud? the effects of different combinations of cutting interval and cutting height on biomass production, at ambient (350 mu mol mol(-1) CO2) and double (700 mu mol mol(-1) CO2) CO2 conditions. Under both ambient and doubled CO2, maximum biomass was produced with cuttings of lA^7365^The effect of ethanol vapour on postharvest leaf blackening of Protea susannae X compacta 'Pink Ice' stems stored in plastic bags under darkness at 20 degrees C (+/- 1 degrees C) was assessed over a 19 day period. Application of ethanol vapour to the stems significantly reduced leaf blackening. Stems exposed to 5.6 g ethanol kg(-1) stem weight, had the least amount of leaf blackening with less than 20% of leaves blackened by day 14. In contrast, the control stems had 50% of leaves blackened by day 9, and 100% by day 15. The highest ethanol treatment at 11.2 g ethanol kg(-1) stem weight caused substantial blackening within the first 24 h of the treatment being applied. Ethanol vapour concentrations in the bag head space decreased rapidly in comparison with the bags with no stems, suggesting that ethanol was rapidly taken up by the stems. Only the highest ethanol treatment had detectable levels of ethanol in the bags after 17 days, and ethanol vapour had no effect on CO2 concentration in the bag head space. Carbon dioxide concentrations ranged between 1.0 and 2.5%. The rate of leaf blackening on the bagged stems without ethanol was significantly less than on stems not in bags, suggesting that elevated CO2 levels may have contributed to reduced blackening. (C) 1999 Elsevier Science B.V. All rights reserved.

2301^2^Favis-Mortlock,D T^Guerra,S J T^1999^1^The implications of general circulation model estimates of rainfall for future erosion: a case study from Brazil^373^37^3-4^329-354^^^^^Oct^^^^^7368
1251^137^1448^1449^1451^3355^3356^3357^372^374^reatment at 11.2 g ethanol kg(-1) stem weight caused substantial blackening within the first 24 h of the treatment being applied. Ethanol vapour concentrations in the bag head space decreased rapidly in comparison with the bags with no stems, suggesting that ethanol was rapidly taken up by the stems. Only the highest ethanol treatment had detectable levels of ethanol in the bags after 17 days, and ethanol vapour had no effect on CO2 concentration in the bag head spA^7367^One consequence of global change will be shifts in the probability of occurrence of soil erosion by water. This could have serious consequences for those areas of the world which are present-day 'hotspots' for erosion. By means of a case study, this paper suggests an approach to quantifying the change in risk of serious erosion for sites in such areas. The case study focuses on future erosion under intensive soya bean cultivation in the Mate Grosso area of Brazil. On the area's highly erodible latosols, current erosion problems are severe. Scenarios of change future climate change are taken from general circulation models (GCMs) and used to perturb current- climate weather data. These are input to an erosion model (water erosion prediction project (WEPP)-CO2), together with local knowledge regarding current and probable future land use, in order to estimate future changes in erosion rates. WEPP- simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, reflecting the range of uncertainty in predictions of future rainfall. Using the 'best-guess' climate scenario from the UK Meteorological Office's HADCM2 GCM, the increase in mean annual sediment yield is 27%. Increases are disproportionately greater in wetter years. Average rates for individual months increase by over 100%. Erosion increases most on those parts of the hillslope profile which are currently hardest-hit by erosion. At present, an annual sediment yield of 5 t ha(-1) is currently exceeded in about 1 year in 2. The HADCM2 simulations suggest that an equal or greater rate will occur in about 70% of years by around 2050. A rate of at least 10 t ha(-1) yr(-1) is currently exceeded in about 1 year in 5. The HADCM2 simulations suggest that this will rise, to about 1 year in 4. (C) 1999 Elsevier Science B.V. All rights reserved.
and use, in order to estimate future changes in erosion rates. WEPP- simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, r2302^7^Newman,J A^Gibson,D J^Hickam,E^Lorenz,M^Adams,E^Bybee,L^Thompson,R^1999^1^Elevated carbon dioxide results in smaller populations of the bird cherry-oat aphid Rhopalosiphum padi^283^24^4^486-489^^^^^Nov
1965^3358^344^349^360^373^374^417^423^849^
2303^1^Drake,S R^1999^1^Quality of 'Bosc' pears as influenced by elevated carbon dioxide storage^214^22^4^417-425^^^^^Oct^^^^^7371
1234^1416^ are currently hardest-hit by erosion. At present, an annual sediment yield of 5 t ha(-1) is currently exceeded in about 1 year in 2. The HADCM2 simulations suggest that an equal or greater rate will occur in about 70% of years by around 2050. A rate of at least 10 t ha(-1) yr(-1) is currently exceeded in about 1 year in 5. The HADCM2 simulations suggest that this will rise, to about 1 year in 4. (C) 1999 Elsevier Science B.V. All rights reserved.
and use, in order to estimate future changes in erosion rates. WEPP- simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, rA^7370^'Bosc' pears (Pyrus communis L.) were placed in a purge-type controlled-atmosphere (CA) storage immediately after harvest (<24 h) and held for 180 days at IC. Oxygen in all atmospheres was 1.5% and CO2 was 1%, 3% or 5%. Pears were evaluated immediately after removal from CA storage and after ripening for an additional 7 days at 21 C. Pears stored in 3% CO2 were firmer, had a superior finish, with significantly reduced decay and internal breakdown than pears stored in 1% CO2. In 3% CO2, pears retained the ability to ripen after long-term storage. A 10 day delay in atmosphere establishment had little or no influence on the long-term keeping quality or ripening ability of 'Bosc 'pears. Firmness, soluble solids content and starch either alone or together were good indices of maturity for 'Bosc 'pears.
ce B.V. All rights reserved.
and use, in order to estimate future changes in erosion rates. WEPP- simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, r2304^9^Grant,R F^Black,T A^den Hartog,G^Berry,J A^Neumann,H H^Blanken,P D^Yang,P C^Russell,C^Nalder,I A^1999^1^Diurnal and annual exchanges of mass and energy between an aspen-hazelnut forest and the atmosphere: Testing the mathematical model Ecosys with data from the BOREAS experiment^278^104^D22^27699-27717^^^^^27 Nov^^^^^7373
1599^178^3359^3360^3361^3362^349^398^614^977^, had a superior finish, with significantly reduced decay and internal breakdown than pears stored in 1% CO2. In 3% CO2, pears retained the ability to ripen after long-term storage. A 10 day delay in atmosphere establishment had little or no influence on the long-term keeping quality or ripening ability of 'Bosc 'pears. Firmness, soluble solids content and starch either alone or together were good indices of maturity for 'Bosc 'pears.
ce B.V. All rights reserved.
and use, in order to estimate future changes in erosion rates. WEPP- simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, rA^7372^There is much uncertainty about the net carbon (C) exchange of boreal forest ecosystems, although this exchange may be an important part of global C dynamics. To resolve this uncertainty, net C exchange has been measured at several sites in the boreal forest of Canada as part of the Boreal Ecosystem- Atmosphere Study (BOREAS). One of these sites is the Southern Old Aspen site at which diurnal CO2 and energy (radiation, latent, and sensible heat) fluxes were measured during 1994 using eddy correlation techniques at different positions within a mixed 70 year old aspen-hazelnut forest. These measurements were used to test a complex ecosystem model "ecosys" in which mass and energy exchanges between terrestrial ecosystems and the atmosphere are simulated hourly under diverse conditions of soil, management, and climate. These simulations explained between 70% and 80% of diurnal variation in ecosystem CO2 and energy fluxes measured during three 1 week intervals in late April, early June, and mid-July. Total annual CO2 fluxes indicated that during 1994, aspen was a net sink of 540 (modeled) versus 670 (measured) g C m(-2) yr(-1), while hazelnut plus soil were a net source of 472 (modeled) versus 540 (measured) g C m(-2) yr(-1). The aspen-hazelnut forest at the BOREAS site was therefore estimated to be a net sink of about 68 (modeled) versus 130 (measured) g C m(-2) yr(-1) during 1994. Long-term simulations indicated that this sink may be larger during cooler years and smaller during warmer years because C fixation in the model was less sensitive to temperature than respiration. These simulations also indicated that the magnitude of this sink declines with forest age because respiration increases with respect to fixation as standing phytomass grows. Confidence in the predictive capabilities of ecosystem models at decadal or centennial timescales is improved by well-constrained tests of these models at hourly timescales.
fluxes measured during three 1 week intervals in late April, early June, and mid-July. Total2305^1^Haszpra,L^1999^1^On the representativeness of carbon dioxide measurements^278^104^D21^26953-26960^^^^^20 Nov^^^^^7375
1136^1258^314^344^891^894^
A^7374^On the basis of the measurements at two monitoring sites located close to each other (220 km) in plain regions in Hungary, the representativeness of low-elevation continental CO2 measurements is estimated. It is shown that under such conditions only the measurements carried out in the early afternoon hours can be considered as regionally representative for the CO2 content of the planetary boundary layer (PBL). Filtering the data in this way, it is calculated that the characteristic CO2 mixing ratio in the PBL may be about 2.5 ppm higher over this part of Europe than at the Mauna Loa Observatory (National Oceanic and Atmospheric Administration), Hawaii.

2306^4^Wait,D A^Jones,C G^Wynn,J^Woodward,F I^1999^1^The fraction of expanding to expanded leaves determines the biomass response of Populus to elevated CO2^2^121^2^193-200^^^^^Nov^^^^^7377-July. Total1871^243^2489^341^344^360^361^528^57^92^tiveness of carbon dioxide measurements^278^104^D21^26953-26960^^^^^20 Nov^^^^^7375
1136^1258^314^344^891^894^
A^7374^On the basis of the measurements at two monitoring sites located close to each other (220 km) in plain regions in Hungary, the representativeness of low-elevation continental CO2 measurements is estimated. It is shown that under such conditions only the measurements carried out in the early afternoon hours can be considered as regionally representative for the CO2 content of the planetary boundary layer (PBL). Filtering the data in this way, it is calculated that the characteristic CO2 mixing ratio in the PBL may be about 2.5 ppm higher over this part of Europe than at the Mauna Loa Observatory (National Oceanic and Atmospheric Administration), Hawaii.

2306^4^Wait,D A^Jones,C G^Wynn,J^Woodward,F I^1999^1^The fraction of expanding to expanded leaves determines the biomass response of Populus to elevated CO2^2^121^2^193-200^^^^^Nov^^^^^7377-July. TotalA^7376^We examined whether the effects of elevated CO2 on growth of 1- year old Populus deltoides saplings was a function of the assimilation responses of particular leaf developmental stages. Saplings were grown for; 100 days at ambient (approximately 350 ppm) and elevated (ambient + 200 ppm) CO2 in forced-air greenhouses. Biomass, biomass distribution, growth rates, and leaf initiation and expansion rates were unaffected by elevated CO2. Leaf nitrogen (N), the leaf C:N ratio, and leaf lignin concentrations were also unaffected. Carbon gain was significantly greater in expanding leaves of saplings grown at elevated compared to ambient CO2. The Rubisco content in expanding leaves was not affected by CO2 concentration. Carbon gain and Rubisco content were significantly lower in fully expanded leaves of saplings grown at elevated compared to ambient CO2, indicating CO2-induced down-regulation in fully expanded leaves. Elevated CO2 likely had no overall effect on bio mass accumulation due to the more rapid decline in carbon gain as leaves matured in saplings grown at elevated compared to ambient CO2. This decline in carbon gain has been documented in other species and shown to be related to a balance between sink/source balance and acclimation. Our data suggest that variation in growth responses to elevated CO2 can result from differences in leaf assimilation responses in expanding versus expanded leaves as they develop under elevated CO2.

2307^5^Lewis,C E^Peratoner,G^Cairns,A J^Causton,D R^Foyer,C H^1999^1^Acclimation of the summer annual species, Lolium temulentum, to CO2 enrichment^6^210^1^104-114^^^^^Nov^^^^^7379
243^2957^3363^3364^3365^3366^344^372^388^430^nt in expanding leaves was not affected by CO2 concentration. Carbon gain and Rubisco content were significantly lower in fully expanded leaves of saplings grown at elevated compared to ambient CO2, indicating CO2-induced down-regulation in fully expanded leaves. Elevated CO2 likely had no overall effect on bio mass accumulation due to the more rapid declA^7378^Lolium temulentum L. Ba 3081 was grown hydroponically in air (350 mu mol mol(-1) CO2) and elevated CO2 (700 mu mol mol(-1) CO2) at two irradiances (150 and 500 mu mol m(-2) s(-1)) for 35 days at which point the plants were harvested. Elevated CO2 did not modify relative growth rate or biomass at either irradiance. Foliar carbon-to-nitrogen ratios were decreased at elevated CO2 and plants had a greater number of shorter tillers, particularly at the lower growth irradiance. Both light-limited and light-saturated rates of photosynthesis were stimulated. The amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) protein was increased at elevated CO2, but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation stale was found with CO2 enrichment, particularly at the higher growth irradiance. Elevated-CO2- induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO2- dependent effects on fructan biosynthesis were observed. Leaf respiration rates were increased by 68% in plants grown with CO2 enrichment and low light. We conclude that high CO2 will only result in increased biomass if total light input favourably increases the photosynthesis-to-respiration ratio. At low irradiances, biomass is more limited by increased rates of respiration than by CO2-induced enhancement of photosynthesis.

2308^3^Maroco,J P^Edwards,G E^Ku,M S B^1999^1^Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide^6^210^1^115-125^^^^^Nov^^^^^7381
1376^204^230^3367^344^348^376^384^508^813^protein was increased at elevated CO2, but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation stale was found with CO2 enrichment, particularly at the higher growth irradiance. Elevated-CO2- induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO2- deA^7380^The effects of elevated CO2 concentrations on the photochemistry, biochemistry and physiology of C-4 photosynthesis were studied in maize (Zea mays L.). Plants were grown at ambient (350 mu L L-1) or ca. 3 times ambient (1100 mu L L-1) CO2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO2 levels, plants grown under elevated CO2 accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO2 concentration of growth, mature leaves of high-CO2-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use efficiency (225%) and higher dark respiration rates (100%). High-CO2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO2, and lower leaf protein contents (22%). Activities of a number of C-3 and C-4 cycle enzymes decreased on a leaf-area basis in the high-CO2-grown plants by 5-30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose 1,6- bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO2 condition (8% and 36%, respectively). These data show that the C-4 plant maize may benefit from elevated CO2 through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and starch, and to utilize these endproducts of photosynthesis to produce extra energy by respiration, may contribute to the enhanced growth of maize under elevated CO2.

2309^1^Cebrian,J^1999^1^Patterns in the fate of production in plant communities^16^154^4^449-468^^^^^Oct^^^^^7383
268^2799^3368^3369^338^372^534^57^672^699^rates (100%). High-CO2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO2, and lower leaf protein contents (22%). Activities of a number of C-3 and C-4 cycle enzymes decreased on a leaf-area basis in the high-CO2-grown plants by 5-30%, with NADP-malate dehydrogenase exhibiting the greatest decreA^7382^I examine, through an extensive compilation of published reports, the nature and variability of carbon flow (i.e., primary production, herbivory, detrital production, decomposition, export, and biomass and detrital storage) in a range of aquatic and terrestrial plant communities. Communities composed of more nutritional plants (i.e., higher nutrient concentrations) lose higher percentages of production to herbivores, channel lower percentages as detritus, experience faster decomposition rates, and, as a result, store smaller carbon pools. These results suggest plant palatability as a main limiting factor of consumer metabolical and feeding rates across communities. Hence, across communities, plant nutritional qualify may be regarded as a descriptor of the importance of herbivore control on plant biomass ("top-down" control), the rapidity of nutrient and energy recycling, and the magnitude of carbon storage. These results contribute to an understanding of how much and why the trophic routes of carbon flow, and their ecological implications, vary across plant communities. They also offer a basis to predict the effects of widespread enhancement of plant nutritional quality due to large-scale anthropogenic eutrophication on carbon balances in ecosystems.

2310^1^Sicher,R C^1999^1^Photosystem-II activity is decreased by yellowing of barley primary leaves during growth in elevated carbon dioxide^104^160^5^849-854^^^^^Sep^^^^^7385
113^131^1347^1672^2415^243^417^456^529^618^e faster decomposition rates, and, as a result, store smaller carbon pools. These results suggest plant palatability as a main limiting factor of consumer metabolical and feeding rates across communities. Hence, across communities, plant nutritional qualify may be regarded as a descriptor of the importance of herbivore control on plant biomass ("top-down" control), the rapidity of nutrient and energy recycling, and the magnitude of carbon storage. These results contribute to an understanding of how much and why the trophic routes of carbon fA^7384^Leaf yellowing was studied in 10-18-d-old barley seedlings (Houdeum vulgare L. cv. Brant) grown at ambient (38 Pa) and at elevated (68, 100, and 140 Pa) CO2 partial pressures in controlled-environment chambers. Maximal total chlorophyll (Chl) concentrations of primary leaves from all four CO2 growth treatments were 0.36 +/- 0.01 g m(-2), and these concentrations were observed 10-12 d after sowing (DAS). Total Chi levels in primary leaves were 35%, 64%, and 78% below maximal levels in the 38, 68, and 100 Pa CO2 growth treatments, respectively, when measured 18 DAS. Losses of Chi in 18-d-old primary leaves were similar in the 100 and 140 Pa CO2 treatments. Decreases of Chi d and Chi b in response to CO2 enrichment were comparable in isolated chloroplast preparations and in intact 18-d-old barley primary leaves of plants grown at 38 and 68 Pa CO2. Total thylakoid membrane proteins, the Chi alb binding protein (LHC-II), and D1 protein levels were also lower in chloroplast preparations from plants grown in the elevated compared to the ambient CO2 treatment. Both ferricyanide reduction and whole- chain electron-transport rates (H2O --> methylviologen) were significantly lower for chloroplasts from plants grown at 68 Pa CO2 compared with those grown at 38 Pa CO2. However, photosystem-I-dependent chloroplast photoreductions did not differ between CO2 treatments. The results indicated that the CO2-dependent yellowing of barley primary leaves adversely affected photosystem-II activity. Growth in elevated CO2 may have increased the susceptibility of photosystem-II to light damage.

2311^2^Watt,M^Evans,J R^1999^1^Linking development and determinancy with organic acid efflux from proteoid roots of white lupin grown with low phosphorus and ambient or elevated atmospheric CO2 concentration (vol 120, pg 705, 1999)^8^121^3^1057^^^^^Nov

2312^1^Kirschbaum,M U F^1999^1^Modelling forest growth and carbon storage in response to increasing CO2 and temperature^257^51^5^871-888^^^^^Nov^^^^^7388preparations from plants grown in137^1645^3050^310^3370^344^359^362^372^715^eatment. Both ferricyanide reduction and whole- chain electron-transport rates (H2O --> methylviologen) were significantly lower for chloroplasts from plants grown at 68 Pa CO2 compared with those grown at 38 Pa CO2. However, photosystem-I-dependent chloroplast photoreductions did not differ between CO2 treatments. The results indicated that the CO2-dependent yellowing of barley primary leaves adversely affected photosystem-II activity. Growth in elevated CO2 may have increased the susceptibility of photosystem-II to light damage.

2311^2^Watt,M^Evans,J R^1999^1^Linking development and determinancy with organic acid efflux from proteoid roots of white lupin grown with low phosphorus and ambient or elevated atmospheric CO2 concentration (vol 120, pg 705, 1999)^8^121^3^1057^^^^^Nov

2312^1^Kirschbaum,M U F^1999^1^Modelling forest growth and carbon storage in response to increasing CO2 and temperature^257^51^5^871-888^^^^^Nov^^^^^7388preparations from plants grown inA^7387^The response of plant growth to increasing climate change remains one of the unresolved issues in understanding the future of the terrestrial biosphere. It was investigated here by using the comprehensive forest growth model CenW 1.0.5 which integrates routines for the fluxes of carbon and water, interception of radiation and the cycling of nutrients. It was run with water and/or nutrient limitations on a background of naturally observed climate at Canberra, Australia. It was parameterised for Pinus radiata, the commercially most important plantation species in Australia. The simulations showed that under water-limited conditions, forest growth was highly sensitive to doubling CO2, with growth increases of over 50% on average and even greater increases in dry years. In contrast, when water supply was adequate, but nutrients were limiting, growth increases were smaller, with an initial increase of about 15% during the first year after CO2 was doubled. This growth increase diminished further over subsequent years so that after 20 years, there was virtually no remaining effect. This diminishing response was due to developing nutrient limitations caused by extra carbon input which immobilised nutrients in the soil. When both water and nutrients were adequate, growth was increased by about 15-20% with no decrease over time. Increasing ambient temperature had a positive effect on growth under nutrient limited conditions by stimulating nitrogen mineralisation rates, but had very little effect when nutrients were non-limiting. Responses were qualitatively similar when conditions were changed gradually. In response to increasing CO2 by 2 mu mol mol(-1) yr(-1) over 50 years, growth was increased by only 1% under nutrient- limited condition but by 16% under water-limited conditions. When temperature and CO2 were both changed to emulate conditions between 1950 and 2030, growth was enhanced between 5-15% over the 80-year period due to the effect of CO2 on photosynthesis and water economy especially under water-limited conditions, and due to the effect of increasing temperature in mineralising greater amounts of nutrients. These results show that there is not one universally applicable biological growth response to increasing temperature and CO2, but that they interact in complex ways with a number of other growth limiting factors. Any response factor of plants to CO2 can only be quantified if the important interacting factors can be independently characterised for different situations.

2313^2^Davies,S J^Unam,L^1999^1^Smoke-haze from the 1997 Indonesian forest fires: effects on pollution levels, local climate, atmospheric CO2 concentrations, and tree photosynthesis^45^124^2-3^137-144^^^^^6 Dec^^^^^7390
1134^1547^312^3371^3372^372^417^738^893^92^but by 16% under water-limited conditions. When temperature and CO2 were both changed to emulate conditions between 1950 and 2030, growth was enhanced between 5-15% over the 80-year period due to the effect of CO2 on photosynthesis and water economy especially under water-limiteA^7389^Atmospheric composition, local climate and sapling gas exchange were monitored to assess the short-term effects of smoke-haze from the 1997 Indonesian forest fires. Atmospheric concentrations of particulate matter, SO2, CO, CH4 and CO2, and relative humidity were elevated, and photosynthetically active radiation and ambient temperature were reduced by the smoke- haze. Despite elevated CO2 levels, photosynthesis in three tree species was reduced by the smoke-haze, both indirectly through reduced PAR levels, and directly through elevated aerosol and atmospheric pollutant levels. (C) 1999 Elsevier Science B.V. All rights reserved.

2314^3^White,A^Cannell,M G R^Friend,A D^1999^1^Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment^233^9^^S21-S30^^^^^^^^^^7392
243^256^428^429^57^660^661^669^674^727^ions between 1950 and 2030, growth was enhanced between 5-15% over the 80-year period due to the effect of CO2 on photosynthesis and water economy especially under water-limiteA^7391^Climate output from the UK Hadley Centre's HadCM2 and HadCM3 experiments for the period 1860 to 2100, with IS92a greenhouse gas forcing, together with predicted patterns of N deposition and increasing CO2, were input (offline) to the dynamic vegetation model, Hybrid v4.1 (Friend et al., 1997; Friend and White, 1999). This model represents biogeochemical, biophysical and biogeographical processes, coupling the carbon, nitrogen and water cycles on a sub-daily timestep, simulating potential vegetation and transient changes in annual growth and competition between eight generalized plant types in response to climate. Global vegetation carbon was predicted to rise from about 600 to 800 PgC (or to 650 PgC for HadCM3) while the soil carbon pool of about 1100 PgC decreased by about 8%. By the 2080s, climate change caused a partial loss of Amazonian rainforest, C-4 grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompanied by a decrease in net primary productivity (NPP) of vegetation in many tropical areas, southern Europe and eastern USA tin response to warming and a decrease in rainfall), but an increase in NPP of boreal forests. Global NPP increased from 45 to 50 PgC y(-1) in the 1990s to about 65 PgC y(-1) in the 2080s (about 58 PgC y(-1) for HadCM3). Global net ecosystem productivity (NEP) increased from about 1.3 PgC y(-1) in the 1990s to about 3.6 PgC y(-1) in the 2030s and then declined to zero by 2100 owing to a loss of carbon from declining forests in the tropics and at warm temperate latitudes - despite strengthening of the carbon sink at northern high latitudes. HadCM3 gave a mon erratic temporal evolution of NEP than HadCM2, with a dramatic collapse in NEP in the 2050s. (C) 1999 Elsevier Science Ltd. All rights reserved.
 partial loss of Amazonian rainforest, C-4 grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompa2315^5^Grams,T E E^Anegg,S^Haberle,K H^Langebartels,C^Matyssek,R^1999^1^Interactions of chronic exposure to elevated CO2 and O-3 levels in the photosynthetic light and dark reactions of European beech (Fagus sylvatica)^84^144^1^95-107^^^^^Oct^^^^^7394
1064^1076^1240^2057^2489^2993^312^3373^344^493^ the 2080s (about 58 PgC y(-1) for HadCM3). Global net ecosystem productivity (NEP) increased from about 1.3 PgC y(-1) in the 1990s to about 3.6 PgC y(-1) in the 2030s and then declined to zero by 2100 owing to a loss of carbon from declining forests in the tropics and at warm temperate latitudes - despite strengthening of the carbon sink at northern high latitudes. HadCM3 gave a mon erratic temporal evolution of NEP than HadCM2, with a dramatic collapse in NEP in the 2050s. (C) 1999 Elsevier Science Ltd. All rights reserved.
 partial loss of Amazonian rainforest, C-4 grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompaA^7393^Young trees of European beech (Fagus sylvatica) acclimated for one growing season to ambient (c. 367 mu l l(-1)) or elevated CO2 levels (c. 660 mu l l(-1)) were exposed during the subsequent year to combinations of the same CO2 regimes and ambient or twice-ambient ozone (O-3) levels (generated from the database of a rural site). By the end of June, before the development of macroscopic leaf injury, the raised O-3 levels had not affected the light and dark reactions of photosynthesis. However, acclimation to elevated CO2 had resulted in lowered chlorophyll and nitrogen concentrations, whereas photosynthetic performance, examined over a wide range of parameters from light and dark reactions, remained unchanged or showed only slight reductions (e.g. apparent electron transport rate, ETR; apparent quantum yield of CO2 gas exchange, Phi(CO2); apparent carboxylation efficiency, CE; and photosynthetic capacity at light and CO2 saturation, PC). In August, after the appearance of leaf necroses, plants grown under ambient CO2 and twice-ambient O-3 conditions declined in both the photosynthetic light reactions (optimum electron quantum yield, Fv/F-m, non-photochemical energy quenching, NPQ, reduction state of Q(A), apparent electron quantum yield, Phi(PSI)I, maximum electron transport rates) and the dark reactions as reflected by CE, Phi(CO2), as well as the maximum CO2 uptake rate (i.e. PC). CE, Phi(CO2) and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO2 and O-3 levels. By contrast, plants exposed to twice-ambient O-3 and elevated CO2 levels maintained a photosynthetic performance similar to individuals grown either under ambient CO2 and ambient O-3, or elevated CO2 and ambient O-3 conditions. The long-term exposure to elevated CO2 therefore tended to counteract adverse chronic effects of enhanced O-3 levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed.
In August, after the appearance of leaf necroses, plants grown un2316^4^Sild,E^Younis,S^Pleijel,H^Sellden,G^1999^1^Effect of CO2 enrichment on non-structural carbohydrates in leaves, stems and ears of spring wheat^37^107^1^60-67^^^^^Sep^^^^^7396
1010^1364^2051^243^344^359^372^374^724^92^n quantum yield, Phi(PSI)I, maximum electron transport rates) and the dark reactions as reflected by CE, Phi(CO2), as well as the maximum CO2 uptake rate (i.e. PC). CE, Phi(CO2) and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO2 and O-3 levels. By contrast, plants exposed to twice-ambient O-3 and elevated CO2 levels maintained a photosynthetic performance similar to individuals grown either under ambient CO2 and ambient O-3, or elevated CO2 and ambient O-3 conditions. The long-term exposure to elevated CO2 therefore tended to counteract adverse chronic effects of enhanced O-3 levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed.
In August, after the appearance of leaf necroses, plants grown unA^7395^Field-grown spring wheat (Triticum aestivum L, cv, Dragon) was exposed to ambient and elevated CO2 concentrations (15 and 2 times ambient) in open-top chambers. Contents of non-structural carbohydrates mere analysed enzymatically in leaves, stems and ears six times during the growing season. The impact of elevated CO2 on wheat carbohydrates was non-significant in most harvests. However, differences in the carbohydrate contents due to elevated CO2 were found in all plant compartments. Before anthesis, at growth stage (GS) 30 (the stem is 1 cm to the shoot apex), the plants grown in elevated CO2 contained significantly more mater soluble carbohydrates (WSC), fructans, starch and total non-structural carbohydrates (TNC) in the leaves in comparison with the plants groan in ambient CO2. It is hypothesised that the plants from the treatments with elevated CO2 were sink-limited at GS30, After anthesis, the leaf WSC and TNC contents of the plants from elevated CO2 started to decline earlier than those of the plants from ambient CO2. This may indicate that the leaves of plants grown in the chambers with elevated CO2 senesced earlier. Elevated CO2 accelerated grain development: 2 weeks after anthesis, the plants groan in elevated CO2 contained significantly more starch and significantly less fructans in the ears compared to the plants grown in ambient CO2. Elevated CO2 had no effect on ear starch and TNC contents at the final harvest. Increasing the CO2 concentration from 360 to 520 mu mol mol(-1) had a larger effect on wheat nonstructural carbohydrates than the further increase from 520 to 680 mu mol mol(-1). The results are discussed in relation to the effects of elevated CO2 on yield and yield components.

2317^3^De Luis,I^Irigoyen,J J^Sanchez-Diaz,M^1999^1^Elevated CO2 enhances plant growth in droughted N-2-fixing alfalfa without improving water status^37^107^1^84-89^^^^^Sep^^^^^7398
1292^130^243^360^374^376^377^407^58^632^ contents of the plants from elevated CO2 started to decline earlier than those of the A^7397^The long-term interaction between elevated CO2 and soil mater deficit was analysed in N-2-fixing alfalfa plants in order to assess the possible drought tolerance effect of CO2. Elevated CO2 could delay the onset of drought stress by decreasing transpiration rates, but this effect was avoided by subjecting plants to the same soil water content. Nodulated alfalfa plants subjected to ambient (400 mu mol mol(-1)) or elevated (700 mu mol mol(-1)) CO2 were either men watered or partially watered by restricting water to obtain 30% of the water content at field capacity (approximately 0.55 g water cm(-3)). The negative effects of sop water deficit on plant growth were counterbalanced by elevated CO2. In droughted plants, elevated CO2 stimulated carbon fixation and, as a result, biomass production was even greater than in well-watered plants grown in ambient CO2. Below-ground production was preferentially stimulated by elevated CO2 in droughted plants, increasing nodule biomass production and the availability of photosynthates to the nodules. As a result, total nitrogen content in droughted plants was higher than in well-watered plants grown in ambient CO2. The beneficial effect of elevated CO2 was not correlated with a better plant water status. It is concluded that elevated CO2 enhances growth of droughted plants by stimulating carbon fixation, preferentially increasing the availability of photosynthates to below-ground production (roots and nodules) without improving water status. This means that elevated CO2 enhances the ability to produce more biomass in N-2-fixing alfalfa under given soil water stress, improving drought tolerance.

2318^2^Peng,C H^Apps,M J^1999^1^Modelling the response of net primary productivity (NPP) of boreal forest ecosystems to changes in climate and fire disturbance regimes^81^122^3^175-193^^^^^20 Oct^^^^^7400
1298^178^2762^3084^3197^3374^3375^3376^344^372^ion was preferentially stimulated by elevated CO2 in droughted plants, increasing nodule biomass production and the availability A^7399^This study reports on the use of the process-based ecosystem model CENTURY 4.0 to investigate the patterns of net primary productivity (NPP) along a transect across the boreal forests of central Canada and the influence of climate change, CO2 fertilization and changing fire disturbance regimes on changes in NPP over time. Simulated NPP was tested against observed NPP data from northern sites near Thompson (Manitoba) and southern sites near Prince Albert (Saskatcheuan) and shown to be consistent with the data. The temporal dynamics of NPP were very different for the southern, central and northern sites, consistent with the hypothesis that different climate-driven processes regulate forest growth in the various regions of the boreal forest transect case study (BFTCS). The simulations suggest that climate change would result in increased NPP for most sites across the transect. According to the model results, increases in atmospheric CO2 also show increased NPP. The combined influence of climate change and elevated CO2 appear to interact in a positive, but non-linear manner. Statistical analysis of the simulation results indicate that changes in NPP are also positively correlated with changes in net N mineralization (R-2 = 0.89). This supports the conclusion that feedback via N cycling - a coupling of aboveground production with changes in belowground decomposition - is very important for understanding the NPP dynamics of the boreal forest under a changing climate. It was also found that NPP increases with greater fire frequency under current climate conditions, at least over the range of fire return intervals considered (50- 200 years). The influence of other changes in disturbance regimes (e.g. altered fire severity and concurrent changes in climate or CO2 fertilization), however, were not considered. (C) 1999 Elsevier Science B.V. All rights reserved.
ites across the transect. According to the model results, increases in atmospheric CO2 also show increased NPP. The combined influence of climate change an2319^3^Ceulemans,R^Janssens,I A^Jach,M E^1999^1^Effects of CO2 enrichment on trees and forests: Lessons to be learned in view of future ecosystem studies^52^84^5^577-590^^^^^Nov^^^^^7402
178^2426^2489^3377^3378^341^605^685^728^733^is supports the conclusion that feedback via N cycling - a coupling of aboveground production with changes in belowground decomposition - is very important for understanding the NPP dynamics of the boreal forest under a changing climate. It was also found that NPP increases with greater fire frequency under current climate conditions, at least over the range of fire return intervals considered (50- 200 years). The influence of other changes in disturbance regimes (e.g. altered fire severity and concurrent changes in climate or CO2 fertilization), however, were not considered. (C) 1999 Elsevier Science B.V. All rights reserved.
ites across the transect. According to the model results, increases in atmospheric CO2 also show increased NPP. The combined influence of climate change anA^7401^Because of their prominent role in global bioproductivity and because of their complex structure and function, forests and tree species deserve particular attention in studies on the likely impact of elevated atmospheric CO2 on terrestrial vegetation. Besides a synoptic review of some of the most prominent above-ground response processes, particular attention is given to below-ground responses of trees to elevated atmospheric CO2, while some feedback processes and interactions with Various biotic and abiotic factors are also briefly summarized. At the leaf level there is little evidence of the long-term loss of sensitivity to CO2 that was suggested by earlier experiments with tree seedlings in pots. Future studies on photosynthesis measurements will probably not alter our conclusions about acclimation, but should focus more on respiration under elevated CO2, which is still poorly understood. At the tree level, the increase in growth observed in elevated CO2 results from an increase in both leaf area and leaf photosynthetic rate (per unit leaf area). Tree growth enhancement is generally larger at high rates of nutrient supply; when nutrient supply rates do not meet growth rates, tree nutrient status declines and nutrients become limiting. In many studies at the canopy level, a shift in whole-tree carbon allocation pattern towards below-ground parts has been associated with increased atmospheric CO2 concentrations. At the ecosystem level, a larger amount of carbon being allocated below-ground could show up by either (1) more root growth and turnover, (2) enhanced activity of root-associated microorganisms, (3) larger microbial biomass pools and enhanced microbial activity, or (4) increased losses of soil carbon through soil respiration. Fine root production is generally enhanced, but it is not clear whether this response would persist in a forest. As elevated CO2 stimulates biomass production, litterfall and rhizodeposition also increase. This increased delivery of labile organic matter to the soil could influence soil microbial communities and subsequent decomposition rates, nutrient availability and carbon storage in soil. There are, however, contradictory hypothesis about the direction in which nutrient availability will be affected. Knowledge of the response of these and other ecophysiological processes to elevated CO2 is the key to understanding the functioning of the whole forest ecosystem. Our current knowledge is sufficiently large with regard to how the carbon uptake process and individual tree growth respond under atmospheric changes, but more emphasis should be put in future experiments on the interactions between various processes, such as the carbon and nitrogen cycles, and on below-ground responses. (C) 1999 Annals of Botany Company.
 production is generally enhanced, but it is not clear whether this response would persist in a forest. As elevated CO2 stimulates biomass production, litterfall and rhizodeposition also increase. This increased delivery of labile organic matter to the soil could i2320^5^Geiger,M^Haake,V^Ludewig,F^Sonnewald,U^Stitt,M^1999^1^The nitrate and ammonium nitrate supply have a major influence on the response of photosynthesis, carbon metabolism, nitrogen metabolism and growth to elevated carbon dioxide in tobacco^9^22^10^1177-1199^^^^^Oct^^^^^7404
1351^229^230^2530^2832^384^448^456^483^857^ the key to understanding the functioning of the whole forest ecosystem. Our current knowledge is sufficiently large with regard to how the carbon uptake process and individual tree growth respond under atmospheric changes, but more emphasis should be put in future experiments on the interactions between various processes, such as the carbon and nitrogen cycles, and on below-ground responses. (C) 1999 Annals of Botany Company.
 production is generally enhanced, but it is not clear whether this response would persist in a forest. As elevated CO2 stimulates biomass production, litterfall and rhizodeposition also increase. This increased delivery of labile organic matter to the soil could iA^7403^The effect of elevated [CO2] on biomass, nitrate, ammonium, amino acids, protein, nitrate reductase activity, carbohydrates, photosynthesis, the activities of Rubisco and Sig other Calvin cycle enzymes, and transcripts for Rubisco small subunit, Rubisco activase, chlorophyll a binding protein, NADP-glyceraldehyde-3-phosphate dehydrogenase, aldolase, transketolase, plastid fructose-1,6-bisphosphatase and ADP- glucose pyrophosphorylase was investigated in tobacco growing an 2, 6 and 20 mM nitrate and 1, 3 and 10 mM ammonium nitate. (i) The growth stimulation in elevated [CO2] was attenuated in intermediate and abolished in low nitrogen. (ii) Elevated [CO2] led to a decline of nitrate, ammonium, amino acids especially glutamine, and protein in low nitrogen and a dramatic decrease in intermediate nitrogen, but not in high nitrogen. (iii) Elevated [CO2] led to a decrease of nitrate reductase activity in low, intermediate and high ammonium nitrate and in intermediate nitrate, but not in high nitrate, (iii) At low nitrogen, starch increased relative to sugars. Elevated [CO2] exaggerated this shift. ADP-glucose pyrophosphorylase transcript increased in low nitrogen, and in elevated [CO2]. (iv) In high nitrogen, sugars rose in elevated [CO2], but there was no acclimation of photosynthetic rate, only a small decrease of Rubisco and no decrease of other Calvin cycle enzymes and no decrease of the corresponding transcripts. In lower nitrogen, there was a marked acclimation of photosynthetic rate and a general decrease of Calvin cycle enzymes, even though sugar levels did not increase. The decreased activities were due to a general decrease of leaf protein. The corresponding transcripts did not decrease except at very low nitrogen. (v) It is concluded that many of the effects of elevated [CO2] on nitrate metabolism, photosynthate allocation, photosynthetic acclimation and growth are due to a shift in nitrogen status.
 intermediate and high ammonium nitrate and in intermediate nitrate, but not in high nitrate, (iii) 2321^3^Grimmer,C^Bachfischer,T^Komor,E^1999^1^Carbohydrate partitioning into starch in leaves of Ricinus communis L-grown under elevated CO2 is controlled by sucrose^9^22^10^1275-1280^^^^^Oct^^^^^7406
1351^1584^312^3379^417^559^d [CO2], but there was no acclimation of photosynthetic rate, only a small decrease of Rubisco and no decrease of other Calvin cycle enzymes and no decrease of the corresponding transcripts. In lower nitrogen, there was a marked acclimation of photosynthetic rate and a general decrease of Calvin cycle enzymes, even though sugar levels did not increase. The decreased activities were due to a general decrease of leaf protein. The corresponding transcripts did not decrease except at very low nitrogen. (v) It is concluded that many of the effects of elevated [CO2] on nitrate metabolism, photosynthate allocation, photosynthetic acclimation and growth are due to a shift in nitrogen status.
 intermediate and high ammonium nitrate and in intermediate nitrate, but not in high nitrate, (iii) A^7405^Ricinus communis plants were grown. under normal (350 ppm) and elevated (700 ppm) CO2 atmosphere and the growth and carbohydrate status of leaf 2 (first leaf above the pair of primary leaves) was studied. Elevated carbon dioxide stimulated the growth of leaves 1.7-fold. The glucose and fructose concentrations exhibited the same diurnal rhythm under both growth conditions. The sucrose concentrations stayed relatively constant and at 700 ppm were one-third higher than at 350 ppm. The starch content increased steadily during the day and disappeared overnight at 350 ppm CO2, but remained partially in plants at 700 ppm CO2, Consequently at 700 ppm CO2, the leaves accumulated starch continuously over their life time, The rate of starch synthesis was correlated to the activity of ADP- glucose pyrophosphorylase, which was related to the sucrose concentration in the leaf, It is concluded that sucrose controls the expression of ADP-glucose pyrophosphorylase, leading to a shift of carbohydrate partitioning into starch when more sucrose is produced than consumed or exported, a situation which is especially pertinent at elevated CO2, These results show that the previously experimentally observed transscriptional regulation of starch synthesis by sucrose occurs in vivo in the daily life of a leaf.

2322^5^Olszyk,D M^Centeno,H G S^Ziska,L H^Kern,J S^Matthews,R B^1999^1^Global climate change, rice productivity and methane emissions: comparison of simulated and experimental results^107^97^2^87-101^^^^^18 Oct^^^^^7408
130^1528^174^2676^3380^3381^417^434^812^92^ared overnight at 350 ppm CO2, but remained partially in plants at 700 ppm CO2, Consequently at 700 ppm CO2, the leaves accumulated starch continuously over their life time, The rate of starch synthesis was correlated to the activity of ADP- glucose pyrophosphorylase, which was related to the sucrose concentration in the leaf, It is concluded that sucrose controls the expression of ADP-glucose pyrophosphorylase, leading to a shift of carbohydrate partitioning into A^7407^Irrigated rice production is a major food source for a large portion of the world's population, and a major anthropogenic source of the greenhouse gas methane (CH4). Potential impacts of global climate change [elevated carbon dioxide (CO2) and/or elevated temperature] on rice can be predicted with simulation models, but experiments are necessary to determine how well these models mimic the responses of the field crop. This paper compares grain yield, biomass, and methane emissions from experiments at the international Rice Research Institute (IRRI) at Los Banos, the Philippines, with potential responses based on simulations using the ORYZA1 process model and the climate data from those experiments. Yield and biomass were compared for the 1995 and 1996 dry seasons (DS) and the 1994 wet season (WS). Emissions of CH4 from rice fields were evaluated for the 1995 WS and 1996 DS, Simulated and experimental responses (adjusted for effects of the open-top chambers on plant growth) differed with climate change scenario, response parameter, and season Under current climate conditions (ambient CO2 and ambient temperature), simulated grain yield was 14% lower than the adjusted experimental grain yield in the 1996 DS, but was 17 and 37% higher than experimental grain yield in the 1995 DS and 1994 WS, respectively. With current climate, simulations underestimated experimental aboveground, belowground, and total biomass. The simulated CH4 emissions were the same as the experimental emissions, assuming CH4 emissions were 2.9% of the simulated total biomass carbon. With elevated CO7 and ambient temperature, simulations predicted greater increases (compared with current climate) in grain yield, aboveground biomass, and total biomass, but generally smaller increases in belowground biomass and CH4 emissions than the significant (at p < 0.05) increases that were found experimentally. With ambient CO2 and elevated temperature, both simulations and experiments generally showed either no change or a decrease in grain yield and biomass, but none of the responses in the experiments wen statistically significant. Simulated ambient CO2 and elevated temperature resulted in a smaller decrease in CH4 emissions than the significant decrease found in the experiments. For both elevated CO2 and elevated temperature, simulated grain yield increased in all three seasons, whereas there were no significant effects on experimental grain yield. The simulations predicted smaller increases in belowground biomass and CH4 emissions with elevated CO2 and elevated temperature than the significant increases in the experiments. To better correspond to experimental results, this study suggested that current simulation models could be improved in terms of effects of temperature on grain yield and use of belowground biomass to estimate CH4 emissions. (C) 1999 Elsevier Science B.V. All rights reserved.
xperimentally. With ambient CO2 and elevated temperature, both simulations and experiments generally showed either no change or a decrease in grain yield and 2323^2^Lake,J C^Hughes,L^1999^1^Nectar production and floral characteristics of Tropaeolum majus L. grown in ambient and elevated carbon dioxide^52^84^4^535-541^^^^^Oct^^^^^7410
10^2078^2584^33^3382^3383^3384^374^547^57^e experiments. For both elevated CO2 and elevated temperature, simulated grain yield increased in all three seasons, whereas there were no significant effects on experimental grain yield. The simulations predicted smaller increases in belowground biomass and CH4 emissions with elevated CO2 and elevated temperature than the significant increases in the experiments. To better correspond to experimental results, this study suggested that current simulation models could be improved in terms of effects of temperature on grain yield and use of belowground biomass to estimate CH4 emissions. (C) 1999 Elsevier Science B.V. All rights reserved.
xperimentally. With ambient CO2 and elevated temperature, both simulations and experiments generally showed either no change or a decrease in grain yield and A^7409^Tropaeolum majus (nasturtiums) were grown from seed in growth cabinets, under 380 and 750 ppmv CO2. Elevated CO2 significantly increased nectar secretion rate, both in flowers milked of nectar daily and in once sampled, 3-d-old flowers. Elevated CO2 did not affect time to flowering, total number of flowers produced, pollen to ovule ratio, or the total or individual concentrations of nectar amino acids. The dry weight and longevity of individual flowers was also unchanged. Nectar sugar content was unchanged by elevated CO2 in a subset of flowers used to assess the 3-d-old nectar volume. This subset did not show the same increase in nectar volume under elevated CO2 as the full set, resulting in the concentration of sugars remaining unchanged. Overall, the quantity rather than the quality of the nectar changed under elevated CO2 while flower characteristics remained constant, implying that the identity of pollinators may remain the same while foraging behaviour (e.g. number of visits per plant, distance travelled) may change in the future. (C) 1999 Annals of Botany Company.

2324^5^Tognetti,R^Longobucco,A^Raschi,A^Miglietta,F^Fumagalli,I^1999^1^Responses of two Populus clones to elevated atmospheric CO2 concentration in the field^374^56^6^493-500^^^^^Aug-Sep^^^^^7412
312^3385^361^376^423^514^685^746^91^92^owers produced, pollen to ovule ratio, or the total or individual concentrations of nectar amino acids. The dry weight and longevity of individual flowers was also unchanged. Nectar sugar content was unchanged by elevated CO2 in a subset of flowers used to assess the 3-d-old nectar volume. This subset did not show the same increase in nectar volume under elevated CO2 as the full set, resulting in the concentration of sugars remaining unchanged. Overall, the quantity rather than the quality of the nectar changed under elevated CO2 while flower characteristics remained constant, implying that the identity of pollinators may remain the same while foraging behaviour (e.g. number of visits per plant, distance A^7411^Two poplar clones, hybrid Populus deltoides Bartr. Ex Marsh x Populus nigra L. (Populus x euramericana), clone I-214, and Populus deltoides, clone Lux, were grown from clonal hardwood cuttings for one growing season in either ambient (360 mu mol mol(-1)) or elevated (560 mu mol mol(-1)) [CO2] in FACE-system rings at Rapolano Terme (Siena, Italy). Both clones I-214 and Lux exhibited a higher above-ground biomass, photosynthesis at light saturation and instantaneous transpiration efficiency (ITE) in CO2-enriched air. The elevated [CO2]-induced responses of clone I-214 included increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO2]-induced responses of clone Lux included an increase in the number of branches and leaf area (which might result in a higher leaf area index, LAI). Photosynthetic acclimation under elevated [CO2] was found only during the early morning and only in clone I-214. Stomatal conductance and transpiration ton a leaf area basis) decreased under elevated [CO2] particularly in clone Lux and at the end of the experiment. The effects of elevated [CO2] on leaf osmotic potential were limited, at least in conditions of non-limiting water availability. Clonal differences in response to elevated [CO2] should be taken in account when planning future poplar plantations in the forecast warmer and drier Mediterranean sites. ((C) Inra/Elsevier, Paris.).

2325^2^Rotter,R^Van de Geijn,S C^1999^1^Climate change effects on plant growth, crop yield and livestock^50^43^4^651-681^^^^^Dec^^^^^7414
1102^3386^3387^374^398^400^402^456^508^724^uded increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO2]-induced responses of clone Lux included an increase in the number of branches and leaf area (which might result in a higher leaf area index, LAI). Photosynthetic acclimation under elevated [CO2] was found only during the early morning and only in clone I-214. Stomatal conductance and transpiration ton a leaf area basis) decreased under elA^7413^A review is given of the state of knowledge in the field of assessing climate change impacts on agricultural crops and livestock. Starting from the basic processes controlling plant growth and development, the possible impacts and interactions of climatic and other biophysical variables in different agro- environments are highlighted. Qualitative and quantitative estimations of shifts in biomass production and water relations, inter-plant competition and crop species adaptability are discussed. Special attention is given to the problems encountered when scaling up physiological responses at the leaf- and plant level to yield estimates at regional to global levels by using crop simulation models in combination with geo-referenced, agro-ecological databases. Some non-linear crop responses to environmental changes and their relations to adaptability and vulnerability of agro-ecosystems are discussed.
nd only in clone I-214. Stomatal conductance and transpiration ton a leaf area basis) decreased under el2326^3^Jones,M H^Macdonald,S E^Henry,G H R^1999^1^Sex- and habitat-specific responses of a high arctic willow, Salix arctica, to experimental climate change^15^87^1^129-138^^^^^Oct^^^^^7416
3388^3389^372^384^422^91^92^ssible impacts and interactions of climatic and other biophysical variables in different agro- environments are highlighted. Qualitative and quantitative estimations of shifts in biomass production and water relations, inter-plant competition and crop species adaptability are discussed. Special attention is given to the problems encountered when scaling up physiological responses at the leaf- and plant level to yield estimates at regional to global levels by using crop simulation models in combination with geo-referenced, agro-ecological databases. Some non-linear crop responses to environmental changes and their relations to adaptability and vulnerability of agro-ecosystems are discussed.
nd only in clone I-214. Stomatal conductance and transpiration ton a leaf area basis) decreased under elA^7415^Dioecious plant species and those occupying diverse habitats may present special analytical problems to researchers examining effects of climate change. Here we report the results from two complementary studies designed to determine the importance of sex and habitat on gas exchange and growth of male and female individuals of a dioecious, circumpolar willow, Salix arctica, in the Canadian High Arctic. In field studies, male and female willows from dry and wet habitats were subjected to passively enhanced summer temperature (similar to 1.3 degrees C) using small open-top chambers over three years. Peak season gas exchange varied significantly by willow sex and habitat. Overall net assimilation was higher in the dry habitat than in the wet, and higher in females than in males. In the dry habitat, net assimilation of females was enhanced by experimental warming, but decreased in males. In the wet habitat, net assimilation of females was substantially depressed by experimental warming, while males showed an inconsistent response. Development and growth of male and female catkins were enhanced by elevated temperature more than leaf fascicles, but leaf fascicle development and growth varied more between the two habitats, particularly in males. In a controlled environment study, male and female willows from these same wet and dry habitats were grown in a 2x2 factorial experiment including 1 x or 2 x ambient [CO2] and 5 or 12 degrees C. The sexes responded very differently to the experimental treatments, but we found no effect of original habitat. Net assimilation in males was affected by the interaction of temperature and CO2, but in females by CO2 only. Our results demonstrate (a) significant intraspecific and intersexual differences in arctic willow physiology and growth, (b) that these differences are affected by environmental conditions expected to accompany global climate change, and (c) that sex- and habitat-specific responses should be explicitly accounted for in studies of dioecious species.
es showed 2327^5^Kytoviita,M M^Pelloux,J^Fontaine,V^Botton,B^Dizengremel,P^1999^1^Elevated CO2 does not ameliorate effects of ozone on carbon allocation in Pinus halepensis and Betula pendula in symbiosis with Paxillus involutus^37^106^4^370-377^^^^^Aug^^^^^7418
1064^1633^2386^2426^2530^2651^2777^2937^344^384^rom these same wet and dry habitats were grown in a 2x2 factorial experiment including 1 x or 2 x ambient [CO2] and 5 or 12 degrees C. The sexes responded very differently to the experimental treatments, but we found no effect of original habitat. Net assimilation in males was affected by the interaction of temperature and CO2, but in females by CO2 only. Our results demonstrate (a) significant intraspecific and intersexual differences in arctic willow physiology and growth, (b) that these differences are affected by environmental conditions expected to accompany global climate change, and (c) that sex- and habitat-specific responses should be explicitly accounted for in studies of dioecious species.
es showed A^7417^The effect of 700 mu mol CO2 mol(-1), 200 mmol ozone mol(-1) and a combination of the two on carbon allocation was examined in Pinus halepensis co-cultured with Betula pendula in symbiosis with the ectomycorrhizal fungus Paxillus involutus, The results show that under low nutrient and ozone levels, elevated CO2 has no effect on the growth of B. pendula or P. halepensis seedlings nor on net carbon partitioning between plant parts. Elevated CO2 did not enhance the growth of the fungus in symbiosis with the birch, On the other hand, ozone had a strong negative effect on the growth of the birch, which corresponded with the significantly reduced growth rates of the fungus. Exposure to elevated CO2 did not ameliorate the negative effects of ozone on birch; in contrast, it acted as an additional stress factor. Neither ozone nor CO2 had significant effects on biomass accumulation in the pine seedlings, Ozone stimulated the spread of mycorrhizal infection from the birch seedlings to neighbouring pines and had no statistically significant effects on phosphoenolpyruvate carboxylase (PEPC) or ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity in the pine needles or on PEPC activity in pine roots.

2328^3^Reid,C D^Fiscus,E L^Burkey,K O^1999^1^Effects of chronic ozone and elevated atmospheric CO2 concentrations on ribulose-1,5-bisphosphate in soybean (Glycine max)^37^106^4^378-385^^^^^Aug^^^^^7420
1828^243^3390^3391^348^417^435^550^557^686^O2 did not enhance the growth of the fungus in symbiosis with the birch, On the other hand, ozone had a strong negative effect on the growth of the birch, which corresponded with the significantly reduced growth rates of the fungus. Exposure to elevated CO2 did not ameliorate the negative effects of ozone on birch; in contrast, it acted as an additional stress factor. Neither ozone nor CO2 had significant effects on biomass accumulation in the pine seedlings, Ozone stimulated the spread of mycorrhizal infection from the birch seedlings to neighbouring pines and had A^7419^Ribulose-1,5-bisphosphate (RuBP) pool size was determined at regular intervals during the growing season to understand the effects of tropospheric ozone concentrations, elevated atmospheric carbon dioxide concentrations and their interactions on the photosynthetic limitation by RuBP regeneration. Soybean (Glycine max [L.] Merr, cv, Essex) was grown from seed to maturity in open-top field chambers in charcoal-filtered air (CF) either without (22 nmol O-3 mol(-1)) or with added O-3 (83 nmol mol(-1)) at ambient (AA, 369 mu mol CO2 mol(-1)) or elevated CO, (710 mu mol mol(-1)). The RuBP pool size generally declined with plant age in all treatments when expressed on a unit leaf area and in all treatments but CF-AA when expressed per unit ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4,1,1,39) binding site, Although O-3 in ambient CO2 generally reduced the RuBP pool per unit leaf area, it did not change the RuBP pool per unit Rubisco binding site, Elevated CO2, in CF or O-3-fumigated air, generally had no significant effect on RuBP pool size, thus mitigating the negative O-3 effect. The RuBP pools were below 2 mol mol(-1) binding site in all treatments for most of the season, indicating limiting RuBP regeneration capacity. These low RuBP pools resulted in increased RuBP regeneration Fia faster RUBP turnover, but only in CF air and during vegetative and flowering stages at elevated CO2. Also, the low RuBP pool sizes did not always reflect RuBP consumption rates or the RuBP regeneration limitation relative to potential carboxylation (%RuBP). Rather, %RuBP increased linearly with decrease in the RuBP pool turnover lime. These data suggest that amelioration of damage from O-3 by elevated atmospheric CO2 to the RuBP regeneration may be in response to changes in the Rubisco carboxylation.

2329^2^Loiseau,P^Soussana,J F^1999^1^Elevated [CO2], temperature increase and N supply effects on the accumulation of below-ground carbon in a temperate grassland ecosystem^206^212^2^123-134^^^^^^^^^^7422d air, gen2476^2487^344^362^376^442^535^56^57^660^pool size, thus mitigating the negative O-3 effect. The RuBP pools were below 2 mol mol(-1) binding site in all treatments for most of the season, indicating limiting RuBP regeneration capacity. These low RuBP pools resulted in increased RuBP regeneration Fia faster RUBP turnover, but only in CF air and during vegetative and flowering stages at elevated CO2. Also, the low RuBP pool sizes did not always reflect RuBP consumption rates or the RuBP regeneration limitation relative to potential carboxylation (%RuBP). Rather, %RuBP increased linearly with decrease in the RuBP pool turnover lime. These data suggest that amelioration of damage from O-3 by elevated atmospheric CO2 to the RuBP regeneration may be in response to changes in the Rubisco carboxylation.

2329^2^Loiseau,P^Soussana,J F^1999^1^Elevated [CO2], temperature increase and N supply effects on the accumulation of below-ground carbon in a temperate grassland ecosystem^206^212^2^123-134^^^^^^^^^^7422d air, genA^7421^The effects of elevated [CO2] (700 mu l l(-1) [CO2]) and temperature increase (+3 degrees C) on carbon accumulation in a grassland soil were studied at two N-fertiliser supplies (160 and 530 kgN ha(-1) year(-1)) in a long-term experiment (2.5 years) on well established ryegrass swards (Lolium perenne L.,) supplied with the same amounts of irrigation water. For all experimental treatments, the C:N ratio of the top soil organic matter fractions increased with their particle size. Elevated CO2 concentration increased the C:N ratios of the below-ground phytomass and of the macro-organic matter. A supplemental fertiliser N or a 3 degrees C increase in elevated [CO2] reduced it. At the last sampling date, elevated [CO2] did not affect the C:N ratio of the soil organic matter fractions, but increased significantly the accumulation of roots and of macro- organic matter above 200 mu m (MOM). An increased N-fertiliser supply stimulated the accumulation of the non harvested plant phytomass and of the OM between 2 and 50 mu m, without positive effect on the macro-organic matter > 200 mu m. Elevated [CO2] increased C accumulation in the OM fractions above 50 mu m by +2.1 tC ha(-1), on average, whereas increasing the fertiliser N supply led to an average supplemental accumulation of +0.8 tC ha(-1). There was no significant effect of a 3 degrees C temperature increase under elevated [CO2] on C accumulation in the OM fractions above 50 mu m.

2330^1^Bolin,B^1999^1^Effect on the biosphere of elevated atmospheric CO2 (pg 1851)^32^286^5440^684^^^^^22 Oct

2331^9^Fowler,D^Cape,J N^Coyle,M^Flechard,C^Kuylenstierna,J^Hicks,K^Derwent,D^Johnson,C^Stevenson,D^1999^1^The global exposure of forests to air pollutants^94^116^1-2^5-32^^^^^Nov^^^^^7425
1076^1172^327^3392^3393^3394^3395^362^529^57^tter fractions, but increased significantly the accumulation of roots and of macro- organic matter above 200 mu m (MOM). An increased N-fertiliser supply stimulated the accumulation of the non harvested plant phytomass and of the OM between A^7424^The tall, aerodynamically rough surfaces of forests provide for the efficient exchange of heat and momentum between terrestrial surfaces and the atmosphere. The same properties of forests also provide for large potential rates of deposition of pollutant gases, aerosols and cloud droplets. For some reactive pollutant gases, including SO2, HNO3 and NH3, rates of deposition may be large and substantially larger than onto shorter vegetation and is the cause of the so called "filtering effect" of forest canopies. Pollutant inputs to moorland and forest have been compared using measured ambient concentrations from an unpolluted site in southern Scotland and a more polluted site in south eastern Germany. The inputs of S and N to forest at the Scottish site exceed moorland by 16% and 31% respectively with inputs of 7.3 kg S ha(-1) y and 10.6 kg N ha(-1) y(-1). At the continental site inputs to the forest were 43% and 48% larger than over moorland for S and N deposition with totals of 53.6 kg S ha(-1) y(-1) and 69.5 kg N ha(-)1 y(- )1 respectively. The inputs of acidity to global forests show that in 1985 most of the areas receiving > 1 kg H+ ha(-1) y(-1) as S are in the temperate latitudes, with 8% of total global forest exceeding this threshold. By 2050, 17% of global forest will be receiving > 1 kg H-1 ha(-1) as S and most of the increase is in tropical and sub-tropical countries. Forests throughout the world are also exposed to elevated concentrations of ozone. Taking 60 ppb O-3 as a concentration likely to be phytotoxic to sensitive forest species, a global model has been used to simulate the global exposure of forests to potentially phytotoxic O-3 concentrations for the years 1860, 1950, 1970, 1990 and 2100. The model shows no exposure to concentrations in excess of 60 ppb in 1860, and of the 6% of global forest exposed to concentrations > 60 ppb in 1950, 75% were in temperate latitudes and 25% in the tropics. By 1990 24% of global forest is exposed to O-3 concentrates > 60 ppb, and this increases to almost 50% of global forest by 2100. While the uncertainty in the future pollution climate of global forest is considerable, the likely impact of O-3 and acid deposition is even more difficult to assess because of interactions between these pollutants and substantial changes in ambient CO2 concentration, N deposition and climate over the same period, but the effects are unlikely to be beneficial overall.

2332^2^Rennenberg,H^Gessler,A^1999^1^Consequences of N deposition to forest ecosystems - Recent results and future research needs^94^116^1-2^47-64^^^^^Nov^^^^^7427
1951^2471^2584^2957^2993^3392^3396^3397^372^460^of forests to potentially phytotoxic O-3 concentrations for the years 1860, 1950, 1970, 1990 and 2100. The model shows no exposure to concentrations in excess of 60 ppb in 1860, and of the 6% of global forest exposed to concentrations > 60 ppb in 1950, 75% were in temperate latitudes and 25% in the tropics. By 1990 24% of global forest is exposed to O-3 concentrates > 60 ppb, and this increases to almostA^7426^Wet and dry deposition of atmospheric nitrogen (N) compounds into forest ecosystems and their effect on physical, chemical and microbial processes in the soil has attracted considerable attention for many years. Still the consequences of atmospheric N deposition on N metabolism of trees and its interaction with soil microbial processes has only recently been studied. Atmospheric N deposited to the leaves is thought to enter the general N metabolism of the leaves, but the processes involved, the interaction with different metabolic pathways, and the connection between injury by atmospheric N and its metabolic conversion are largely unknown. Laboratory and field experiments have shown that N of atmospheric NO2 and NH3, deposited to the leaves of trees, is subject to long-distance transport in the phloem to the roots. This allocation can result in considerable decline of N uptake by the roots. Apparently, the flux of N from the soil into the roots can be down-regulated to an extent that equals N influx into the leaves. This down-regulation is not mediated by generally enhanced amino-N contents, but by elevated levels of particular amino acids. Field experiments confirm these results from laboratory studies: Nitrate (NO3) uptake by the roots of trees at a field sites exposed to high loads of atmospheric N is negligible, provided concentrations of Gln in the roots are high. At the ecosystem level, consequences of reduced N uptake by the roots of trees exposed to high loads of atmospheric N are (1) an increased availability of N for soil microbial processes, (2) enhanced emission of gaseous N-oxides from the soil, and (3) elevated leaching of NO3 into the ground water. How recent forest management practices aimed at transforming uniform monocultures to more structured species-rich forests will interact with these processes remains to be seen. Possible implications of these forest management practices on N metabolism in trees and N conversion in the soil are discussed particularly in relation to atmospheric N deposition.

2333^2^McLaughlin,S^Percy,K^1999^1^Forest health in North America: Some perspectives on actual and potential roles of climate and air pollution^94^116^1-2^151-197^^^^^Nov^^^^^7429
1342^1654^3033^3398^3399^3400^3401^3402^3403^602^of trees at a field sites exposed to high loads of atmospheric N is negligible, provided concentrations of Gln in the roots are high. At the ecosystem level, consequences of reduced N uptake by the roots of trees exposed to high loads of atmospheric N are (1) an increased availability of N for soil microbial processes, (2) enhanced emission of gaseous N-oxides from the soil, and (3) elevated leaching of NO3 into the ground water. How recent forest management practices aimed at transforming uniform monocultures to more structured species-rich forests will interact with these processes remains to be seen. Possible implications of these forest management practices on N metabolism in trees and N conversion in the soil are discussed particularly in relation to atmospheric N dA^7428^The perceived health of forest ecosystems over large temporal and spatial scales can be strongly influenced by the frames of reference chosen to evaluate both forest condition and the functional integrity of sustaining forest processes. North American forests are diverse in range, species composition, past disturbance history, and current management practices. Therefore the implications of changes in environmental stress from atmospheric pollution and/or global climate change on health of these forests will vary widely across the landscape. Forest health surveys that focus on the average forest condition may do a credible job of representing the near-term trends in economic value while failing to detect fundamental changes in the processes by which these values are sustained over the longer term. Indications of increased levels of environmental stress on forest growth and nutrient cycles are currently apparent in several forest types in North America. Measurements of forest ecophysiological responses to air pollutants in integrated case studies with four forest types (southern pine, western pine, high elevation red spruce, and northeastern hardwoods) indicate that ambient levels of ozone and/or acidic deposition can alter basic processes of water, carbon, and nutrient allocation by forest trees. These changes then provide a mechanistic basis for pollutant stress to enhance a wider range of natural stresses that also affect and are affected by these resources. Future climatic changes may ameliorate (+ CO2) or axacerbate (+ temperature, + UV-B) these effects. Current projections of forest responses to global climate change do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use efficiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to evaluate responses at appropriate frequencies across gradients in both forest resources and the stresses that influence them. Such programs must also be accompanied by supplemental process -oriented and pattern -oriented investigations that more thoroughly test cause and effect relationships among stresses and responses of both forests and the biogeochemical cycles that sustain them.

2334^3^Broadmeadow,M S J^Heath,J^Randle,T J^1999^1^Environmental limitations to O-3 uptake - Some key results from young trees growing at elevated CO2 concentrations^94^116^1-2^299-310^^^^^Nov^^^^^7431
312^3129^3404^3405^344^376^384^417^633^861^do not consider important physiological changes induced by air pollutants that may amplify climatic stresses. These include reduced rooting mass, depth, and function, increased respiration, and reduced water use efficiency. Monitoring and understanding the relative roles of natural and anthropogenic stress in influencing future forest health will require programs that are structured to eA^7430^Elevated carbon dioxide concentrations and limited water supply have been shown to reduce the impact of ozone pollution on the growth and physiology of Quercus petraea in a long-term factorial experiment. These responses can be explained by observed reductions in stomatal conductance, and thus potential ozone exposure of 28% and 40% for CO2 and drought treatments respectively. However, parameterisation of a stomatal conductance model for Quercus robur and Fagus sylvatica grown under ambient and elevated CO2 concentrations in a separate experiment has demonstrated that elevated CO2 also reduces the responsiveness of stomata to both saturation deficit (LAVPD) and soil moisture deficit (psi) in beech, and to a lesser extent, in oak. Season-long model simulations of ozone fluxes suggest that LAVPD and psi conductance parameters derived at ambient CO2 concentrations will lead to these fluxes being underestimated by 24% and 2% for beech and oak respectively at 615 ppm CO2.
programs that are structured to e2335^12^Karnosky,D F^Mankovska,B^Percy,K^Dickson,R E^Podila,G K^Sober,J^Noormets,A^Hendrey,G^Coleman,M D^Kubiske,M^Pregitzer,K S^Isebrands,J G^1999^1^Effects of tropospheric O-3 on trembling aspen and interaction with CO2: Results from an O-3-gradient and a face experiment^94^116^1-2^311-322^^^^^Nov^^^^^7433
1705^243^312^3226^3406^3407^344^422^633^92^drought treatments respectively. However, parameterisation of a stomatal conductance model for Quercus robur and Fagus sylvatica grown under ambient and elevated CO2 concentrations in a separate experiment has demonstrated that elevated CO2 also reduces the responsiveness of stomata to both saturation deficit (LAVPD) and soil moisture deficit (psi) in beech, and to a lesser extent, in oak. Season-long model simulations of ozone fluxes suggest that LAVPD and psi conductance parameters derived at ambient CO2 concentrations will lead to these fluxes being underestimated by 24% and 2% for beech and oak respectively at 615 ppm CO2.
programs that are structured to eA^7432^Over the years, a series of trembling aspen (Populus tremuloides Michx.) clones differing in O-3 sensitivity have been identified from OTC studies. Three clones (216 and 271[(O- 3 tolerant] and 259 [O-3 sensitive]) have been characterized for O-3 sensitivity by growth and biomass responses, foliar symptoms, gas exchange, chlorophyll content, epicuticular wax characteristics, and antioxidant production. In this study we compared the responses of these same clones exposed to O-3 under field conditions along a natural O-3 gradient and in a Free-Air CO2 and O-3 Enrichment (FACE) facility. In addition, we examined how elevated CO2 affected O-3 symptom development. Visible O-3 symptoms were consistently seen (5 out of 6 years) at two of the three sites along the O-3 gradient and where daily one-hour maximum concentrations were in the range of 96 to 125 ppb. Clonal differences in O-3 sensitivity were consistent with our OTC rankings. Elevated CO2 (200 ppm over ambient and applied during daylight hours during the growing season) reduced visible foliar symptoms for all three clones from 31 to 96% as determined by symptom development in elevated O-3 versus elevated O-3 + CO2 treatments. Degradation of the epicuticular wax surface of all three clones was found at the two elevated O-3 gradient sites. This degradation was quantified by a coefficient of occlusion which was a measure of stomatal occlusion by epicuticular waxes. Statistically significant increases in stomatal occlusion compared to controls were found for all three clones and for all treatments including elevated CO2, elevated O-3, and elevated CO2 + O-3. Our results provide additional evidence that current ambient O- 3 levels in the Great Lakes region are causing adverse effects on trembling aspen. Whether or not elevated CO2 in the future will alleviate some of these adverse effects, as occurred with visible symptoms but not with epicuticular wax degradation, is unknown.
ings. Elevated CO2 (200 ppm over ambient and applied during daylight hours during2336^4^Houpis,J L J^Anderson,P D^Pushnik,J C^Anschel,D J^1999^1^Among-provenance variability of gas exchange and growth in response to long-term elevated CO2 exposure^94^116^1-2^403-412^^^^^Nov^^^^^7435
1262^137^1985^2060^2160^243^312^344^348^376^found at the two elevated O-3 gradient sites. This degradation was quantified by a coefficient of occlusion which was a measure of stomatal occlusion by epicuticular waxes. Statistically significant increases in stomatal occlusion compared to controls were found for all three clones and for all treatments including elevated CO2, elevated O-3, and elevated CO2 + O-3. Our results provide additional evidence that current ambient O- 3 levels in the Great Lakes region are causing adverse effects on trembling aspen. Whether or not elevated CO2 in the future will alleviate some of these adverse effects, as occurred with visible symptoms but not with epicuticular wax degradation, is unknown.
ings. Elevated CO2 (200 ppm over ambient and applied during daylight hours duringA^7434^Genetic variability can have profound effects on the interpretation of results from elevated CO2 studies, and future forest management decisions. Information on which varieties are best suited to future atmospheric conditions is needed to develop future forest management practices. A large-scale screening study of the effects of elevated CO2 on 15 half- sibling sources of genetically superior ponderosa pine (Pinus ponderosa Dougl ex P. Laws.) is presented. These sources represent multiple elevations and latitudes throughout California. Among-provenance variability in the effects of elevated CO2 on gas exchange and growth, and their correlation with geographic origin were investigated in ponderosa pine seedlings subjected to ambient or elevated CO2 concentrations (525 mu mol mol(-1) CO2, and 700 mu mol mol(-1) CO2) for more than two years in open-top chambers. Substantial among- provenance variability in growth response to elevated CO2 was evident, with 8 sources demonstrating no significant growth response to elevated CO2 while 7 sources responded positively. For all sources, elevated CO2 increased photosynthesis (ranging from 19% increase at 525 mu mol mol(-1) CO2 to 49% increase at 700 mu mol mol(-1) CO2). A modest correlation existed between geographic origin and above ground growth response to elevated CO2.

2337^6^Pushnik,J C^Garcia-Ibilcieta,D^Bauer,S^Anderson,P D^Bell,J^Houpis,J L J^1999^1^Biochemical responses and altered genetic expression patterns in ponderosa pine (Pinus ponderosa Doug ex P. Laws) grown under elevated CO2^94^116^1-2^413-422^^^^^Nov^^^^^7437
2083^244^3408^341^348^361^423^610^647^705^ge and growth, and their correlation with geographic origin were investigated in ponderosa pine seedlings subjected to ambient or elevated CO2 concentrations (525 mu mol mol(-1) CO2, and 700 mu mol mol(-1) CO2) for more than two years in open-top chambers. Substantial among- provenance variability in growth response to elevated CO2 was evident, with 8 sources demonstrating no significant growth resA^7436^Biochemical and gene expression changes in response to elevated atmospheric CO2 were investigated in five maternal half-sibling breeding families of Ponderosa pine. Seedlings were grown in a common garden located at Lawrence Livermore National Laboratory, in open-topped chambers (OTC) for two years. Chamber atmospheres were maintained at ambient, ambient + 175 mu L L-1, CO2, or ambient + 350 mu L L-1CO2. Growth measurements showed significant increases in stem volumes and volume enhancement ratios in three of the five families studied when grown under elevated CO2. Biochemical and gene expression studies were undertaken to gain a mechanistic understanding of these phenotypic responses. Biochemical studies focused on sucrose phosphate synthase (SPS) specific activities at increase CO2 levels. Kinetic evaluations of SPS showed an increase in V-Max. Specific SPS probes revealed increases in the transcriptional levels of one SPS gene with exposure to increasing CO2. RT-PCR differential gene displays showed that overall only a small fraction of visualized gene transcripts responded to elevated CO2 (8-10%). There were also significant differences between the gene expression patterns of the different families, some of which correlated with alterations in growth at elevated CO2 levels.

2338^3^Tuba,Z^Proctor,M C F^Takacs,Z^1999^1^Desiccation-tolerant plants under elevated air CO2: A review^291^54^9-10^788-796^^^^^Sep-Oct^^^^^7439
1331^23^243^3206^3409^344^374^430^673^92^volumes and volume enhancement ratios in three of the five families studied when grown under elevated CO2. Biochemical and gene expression studies were undertaken to gain a mechanistic understanding of these phenotypic responses. Biochemical studies focused on sucrose phosphate synthase (SPS) specific activities at increase CO2 levels. Kinetic evaluations of SPS showed an increase in V-Max. Specific SPS probes revealed increases in the transcriptional levels of one SPS gene with exposure to increasing CO2. RT-PCR differential gene displays showeA^7438^This article summarises present knowledge of the ecophysiological responses to elevated atmospheric CO2 of desiccation tolerant (DT) plants. It deals primarily with lichens and bryophytes, as the most prominent groups of DT photosynthetic organisms, but includes some comment on algae and vascular DT plants. Results of research on DT plants are compared with those on desiccation sensitive vascular Cg plants, the most widely investigated group in the field of global change. Both DT and non-DT plants show an immediate positive response of photosynthesis to elevated CO2, but in both groups the longer term effect is generally reduced (or even reversed) by down-regulation or feedback inhibition of photosynthesis, or other limitations on production and growth. In bryophytes and lichens, enhanced short-term photosynthesis may or may not be reflected in increased production; bryophytes have limited source-sink differentiation, and lichens invest excess photosynthate in secondary metabolites. DT plants may gain some advantage from elevated CO2 at both low and excessive water contents. Neither theoretical considerations nor experimental results suggest that elevated atmospheric CO2 will lead to any substantial shift in the balance of advantage between DT and non-DT plants.

2339^4^Donnelly,A^Jones,M B^Burke,J I^Schnieders,B^1999^1^Does elevated CO2 protect grain yield of wheat from the effects of ozone stress?^291^54^9-10^802-811^^^^^Sep-Oct^^^^^7441
1076^1364^230^312^344^400^435^436^546^728^ and non-DT plants show an immediate positive response of photosynthesis to elevated CO2, but in both groups the longer term effect is generally reduced (or even reversed) by down-regulation or feedback inhibition of photosynthesis, or other limitations on production and growth. In bryophytes and lichens, enhanced short-term photosynthesis may or may not be reflected in increased production; bryophytes have limited source-sink differentiation, and lichens invest excess photosynthate in secondary metabolites. DT plants may gainA^7440^This study has investigated the effects of elevated CO2 and elevated O-3, both singly and in combination, on the yield of spring wheat (Triticum aestivum L., cv. Minaret). Plants were grown in open-top chambers and exposed to three CO2 concentrations (ambient, 510 and 680 ppmv) and two O-3 concentrations (ambient and ambient +50 or +90 ppbv) either from anthesis onwards or for the full growing season. To date, experiments that have investigated the interactive effects of these gases have shown a variety of responses, ranging from an amelioration of the damaging effects of high O-3 to a greater sensitivity to O-3, at elevated CO2. The effects on grain yield and yield components were determined. Our results confirm that elevated CO2 provides some protection to a wheat crop against the damaging effects of O-3 On grain yield. However, the level of protection varies from one growing season to the next and also appears to be related particularly to the timing of exposure to elevated O-3.
DT plants may gain2340^3^Schmitt,V^Kussmaul,A^Wild,A^1999^1^Interaction of elevated CO2 and ozone concentrations and irrigation regimes on leaf anatomy and carbohydrate status of young oak (Quercus petraea) trees^291^54^9-10^812-823^^^^^Sep-Oct^^^^^7443
1901^312^344^348^360^376^417^632^692^92^
A^7442^Young sessile oak (Quercus petraea) trees were exposed for one vegetation period in closed environmental chambers in a crossed factorial study on effects to varied CO2 concentrations, ozone concentrations and irrigation treatments. Elevated CO2 concentrations (ambient + 350 mu mol mol(-1)) caused a significant increase in biomass production, alterations in leaf anatomy and chloroplast ultrastructure as well as an increase in leaf starch content, as compared to ambient CO2 concentrations. The effects of elevated O-3 concentrations and drought stress were far less distinct. The leaf starch content was influenced by CO2 and O-3 in a synergistic manner.
ated particularly to the timing of exposure to elevated O-3.
DT plants may gain2341^5^Heilman,J L^Cobos,D R^Heinsch,F A^Campbell,C S^McInnes,K J^1999^1^Tower-based conditional sampling for measuring ecosystem-scale carbon dioxide exchange in coastal wetlands^375^22^3A^584-591^^^^^Sep^^^^^7445
2317^264^3410^3411^372^416^431^504^662^687^6^417^632^692^92^
A^7442^Young sessile oak (Quercus petraea) trees were exposed for one vegetation period in closed environmental chambers in a crossed factorial study on effects to varied CO2 concentrations, ozone concentrations and irrigation treatments. Elevated CO2 concentrations (ambient + 350 mu mol mol(-1)) caused a significant increase in biomass production, alterations in leaf anatomy and chloroplast ultrastructure as well as an increase in leaf starch content, as compared to ambient CO2 concentrations. The effects of elevated O-3 concentrations and drought stress were far less distinct. The leaf starch content was influenced by CO2 and O-3 in a synergistic manner.
ated particularly to the timing of exposure to elevated O-3.
DT plants may gainA^7444^Long-term measurements of CO2 exchange between coastal wetlands and the atmosphere are necessary to improve our understanding of the role these ecosystems play in the global carbon cycle, and the response of these systems to environmental change. We conducted research to adapt and evaluate tower-based conditional sampling as a method for measuring net CO2 exchange (NCE) at the ecosystem scale on a continuous basis. With conditional sampling, NCE is determined from the product of the standard deviation of vertical wind velocity, the difference in CO2 concentration between updrafts and downdrafts in the constant flux portion of the boundary layer above the surface, and an empirical coefficient. We constructed a system that used a sonic anemometer to measure vertical wind velocity (w) and control a high-speed three-way valve that diverted air from updrafts and down,drafts into separate sample lines, depending on the direction of w. An infrared gas analyzer was used to measure the concentration difference. The conditional sampling system was installed and tested in a marsh in the Nueces River Delta near Corpus Christi, Texas, as part of a long-term study of effects of freshwater inflow on CO2 flux. System accuracy was evaluated by comparing conditional sampling measurements of water vapor flux with independent estimates obtained with the Bowen ratio method. Average daily flux estimates for the two methods agreed to within 13%. Measurements showed that freshwater inflow due to flooding of the Nueces River increased NCE by increasing CO2 assimilation and decreasing CO2 efflux. Over a 65-d period, daily NCE varied from a maximum gain of 0.16 mol CO2 m(-2) d(-1) during flooding to a maximum loss of - 0.14 mol CO2 m(-2) d(-1) when the marsh dried. Our study showed that conditional sampling was well suited for quantifying CO2 exchange in coastal wetlands on a diel, daily, and seasonal basis.
te sample lines, depending on the direction of w. An infrared gas analyzer was used to measure the concentration difference2342^3^Schaffer,B^Whiley,A W^Searle,C^1999^1^Atmospheric CO2 enrichment, root restriction, photosynthesis, and dry-matter partitioning in subtropical and tropical fruit crops^170^34^6^1033-1037^^^^^Oct
2489^341^348^372^417^444^57^813^857^92^
2343^2^Makino,A^Mae,T^1999^1^Photosynthesis and plant growth at elevated levels of CO2^231^40^10^999-1006^^^^^Oct^^^^^7448
3412^3413^343^356^377^384^462^550^635^665^ agreed to within 13%. Measurements showed that freshwater inflow due to flooding of the Nueces River increased NCE by increasing CO2 assimilation and decreasing CO2 efflux. Over a 65-d period, daily NCE varied from a maximum gain of 0.16 mol CO2 m(-2) d(-1) during flooding to a maximum loss of - 0.14 mol CO2 m(-2) d(-1) when the marsh dried. Our study showed that conditional sampling was well suited for quantifying CO2 exchange in coastal wetlands on a diel, daily, and seasonal basis.
te sample lines, depending on the direction of w. An infrared gas analyzer was used to measure the concentration differenceA^7447^In this review, we discuss the effects of elevated CO2 levels on photosynthesis in relation to the whole plant growth in terrestrial higher C-3 plants. Short-term CO2 enrichment stimulates the rate of photosynthesis. Plant mass is also enhanced by CO2 enrichment. However, the effects of long-term CO2 enrichment on photosynthesis are variable. Generally, the prolonged exposure to CO2 enrichment reduces the initial stimulation of photosynthesis in many species, and frequently suppresses photosynthesis. These responses are attributed to secondary responses related to either excess carbohydrate accumulation or decreased N content rather than direct responses to CO2. Accumulation of carbohydrates in leaves may lead to the repression of photosynthetic gene expression and excess starch seems to hinder CO2 diffusion. Therefore, the species which have the sink organs for carbohydrate accumulation do not show the suppression of photosynthesis. The suppression of photosynthesis by CO2 enrichment is always associated with decreases in leaf N and Rubisco contents. These decreases are not due to dilution of N caused by a relative increase in the plant mass but are the result of a decrease in N allocation to leaves at the level of the whole plant, and the decrease in Rubisco content is not selective. Leaf senescence and plant development are also accelerated by CO2 enrichment. However, they are independent of each other in some species. Thus, various responses to CO2 observed at the level of a single leaf result from manifold responses at the level of the whole plant grown under conditions of CO2 enrichment.

2344^3^Mitchell,K A^Bolstad,P V^Vose,J M^1999^1^Interspecific and environmentally induced variation in foliar dark respiration among eighteen southeastern deciduous tree species^13^19^13^861-870^^^^^Nov^^^^^7450
130^1314^2068^3266^3414^360^520^547^783^92^the sink organs for carbohydrate accumulation do not show the suppression of photosynthesis. The suppression of photosynthesis by CO2 enrichment is always associA^7449^We measured variations in leaf dark respiration rate (Rd) and leaf nitrogen (N) across species, canopy light environment, and elevation for 18 co-occurring deciduous hardwood species in the southern Appalachian mountains of western North Carolina. Our overall objective was to estimate leaf respiration rates under typical conditions and to determine how they varied within and among species. Mean dark respi ration rate at 20 degrees C (R- d,R-mass, mu mol CO2 (kg leaf dry mass)(-1) s(-1)) for all 18 species was 7.31 mu mol kg(-1) s(-1). Mean R-d,R-mass of individual species varied from 5.17 mu mol kg(-1) s(-1) for Quercus coccinea Muenchh, to 8.25 mu mol kg(-1) s(-1) for Liriodendron tulipifera L. Dark respiration rate varied by leaf canopy position and was higher in leaves collected from high- light environments. When expressed on an area basis, dark respiration rate (R-d,R-area, mu mol CO2 (kg leaf dry area)(-1) s(-1)) showed a strong linear relationship with the predictor variables leaf nitrogen (N-area, g N (m leaf area)(-2)) and leaf structure (LMA, g leaf dry mass (m leaf area)(-2)) (r(2) = 0.62). This covariance was largely a result of changes in leaf structure with canopy position; smaller thicker leaves occur at upper canopy positions in high-light environments. Mass-based expression of leaf nitrogen and dark respiration rate showed that nitrogen concentration (N-mass, mg N (g leaf dry mass)(- 1)) was only moderately predictive of variation in R-d,R-mass for all leaves pooled (r(2) = 0.11), within species, or among species. We found distinct elevational trends, with both R-d,R- mass and N-mass higher in trees originating from high- elevation, cooler growth environments. Consideration of interspecies differences, vertical gradients in canopy light environment, and elevation, may improve our ability to scale leaf respiration to the canopy in forest process models.

2345^3^Hu,S J^Firestone,M K^Chapin,F S^1999^1^Soil microbial feedbacks to atmospheric CO2 enrichment^57^14^11^433-437^^^^^Nov^^^^^7452a1298^2087^2758^3083^3415^3416^398^506^534^715^
A^7451^Increased atmospheric CO2 concentration often stimulates plant photosynthesis, enhances carbon (C) allocation belowground, increases plant nutrient uptake and improves the efficiency of plant water use. Recent studies suggest that microbial responses to CO2-induced alterations in soil C, water and nutrient availability play an important role in determining ecosystem feedback to CO2 elevation. However, to date, most of the published results have been obtained from short-term experiments or from studies using high-nutrient or disturbed soils. Information on microbial responses to CO2-induced changes in natural and/or mature ecosystems with nutrient limitations is critical to predict changes in terrestrial ecosystem C storage under future CO2 scenarios.

2346^4^Bezemer,T M^Knight,K J^Newington,J E^Jones,T H^1999^1^How general are aphid responses to elevated atmospheric CO2?^376^92^5^724-730^^^^^Sep^^^^^7454
1282^137^1752^2533^312^3417^3418^547^701^715^452aA^7453^We studied the impact of elevated CO2 on 2 aphid pest species, Myzus persicae and Brevicoryne brassicae (Homoptera: Aphididae), on a series of host plants in 3 independent studies each differing in experimental complexity. Measurements on individual aphids showed that host plant and aphid species significantly influenced the response to elevated CO2. These differences occurred not only in the level of responsiveness but also directionally. B. brassicae reared on Brassica oleracea produced significantly less offspring at elevated CO2, whereas the opposite was found for M. persicae on the same host. No response was found for M. persicae on Senecio vulgaris. When populations of B. brassicae and M. persicae were followed for a longer period, no differences were observed in population sizes, Comparisons between different experimental systems show that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids. The consequences of these findings for climate change research are discussed.

2347^1^Wang,D L^1999^1^Effect of elevated CO2 on CH4 emission^338^44^13^1153-1157^^^^^Jul^^^^^7456
1233^3000^312^374^376^
A^7455^Global CH4 emission may increase under CO2 enrichment condition, which is projected for the future. CO2 enrichment could affect CH4 emission in two ways: ( i) Photosynthesis of plants that also include plants in rice paddies and natural wetlands will be stimulated under CO2 enrichment condition. CH4 emission rate may be increased due to the accumulation of more plant biomass, root exudes and soil organic matters. ( ii) Combined with other global warming forces, CO2 enrichment may bring a change of atmospheric temperature and precipitation around the world. CH4 emission will also be changed with the variation of the area and distribution of rice paddies and natural wetlands.
that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids. The consequences of these findi2348^1^Lloyd,J^1999^1^The CO2 dependence of photosynthesis, plant growth responses to elevated CO2 concentrations and their interaction with soil nutrient status, II. Temperate and boreal forest productivity and the combined effects of increasing CO2 concentrations and increased nitrogen deposition at a global scale^43^13^4^439-459^^^^^Aug^^^^^7458
2762^312^314^3419^344^534^661^672^738^892^paddies and natural wetlands will be stimulated under CO2 enrichment condition. CH4 emission rate may be increased due to the accumulation of more plant biomass, root exudes and soil organic matters. ( ii) Combined with other global warming forces, CO2 enrichment may bring a change of atmospheric temperature and precipitation around the world. CH4 emission will also be changed with the variation of the area and distribution of rice paddies and natural wetlands.
that long-term population responses to elevated CO2 can not be reliably predicted from detailed measurements on individual aphids. The consequences of these findiA^7457^1. Appropriate rates of carbon acquisition by temperate and boreal forests are re-evaluatted, Based on continental-scale forestry data it is suggested that the productivity of temperate and boreal forests has been overestimated previously. 2, Using these values, a model of the integrated response of ecosystems to carbon dioxide concentration and soil nitrogen availability is presented. The model does not assume constant C/N ratios in plant or soil and considers effects of increases in atmospheric CO2 concentrations and nitrogen deposition separately or together. 3, For temperate-zone forests a co- occurrence of a CO2 increase and nitrogen deposition doubles the increase in net primary productivity and carbon sequestration that would be the case for nitrogen deposition occurring on its own. Considered separately, the effect of the atmospheric CO2 increase is less than even moderate rates of anthropogenic N deposition for temperate or boreal forests. By contrast, for tropical forests, the atmospheric CO2 increase is sufficient to induce large rates of carbon accumulation in plants and soil. 4, Application of the model at the global scale suggests large localized sinks for CO2 in either tropical rain forests or in forested or grassland areas of Europe and North America where appreciable N deposition occurs. Overall, the model suggests a terrestrial sink owing to CO2 fertilization and N deposition of about 0.2 Pmol C per year. About half of this is in the mid-latitudes of the northern hemisphere and about half in the tropics.

2349^2^Soule,P T^Knapp,P A^1999^1^Western juniper expansion on adjacent disturbed and near-relict sites^319^52^5^525-533^^^^^Sep^^^^^7460
1203^312^3287^3420^3421^413^456^92^tivity and carbon sequestration that would be the case for nitrogen deposition occurring on its own. Considered separately, the effect of the atmospheric CO2 increase is less than even moderate rates of anthropogenic N deposition for temperate or boreal forests. By contrast, for tropical forests, the atmospheric COA^7459^We determined rates of western juniper (Juniperus occidentalis spp. occidentalis Hook.) density and cover change during the period 1951 to 1994 at 3 adjacent sites with nearly identical elevation, slope, aspect, soils, plant communities, and climate, but different land-use histories. The 3 sites are located in central Oregon at the confluence of the Deschutes and Crooked Rivers. Two of the sites are typical of central Oregon rangelands in that they have a history of anthropogenic disturbance including active fire suppression and domestic livestock grazing. The third site is a relict mesa that is a protected Research Natural Area and has experienced minimal anthropogenic impacts. We used large scale aerial photography to determine cover and density of western juniper in 1951, 1956, 1961, 1972, 1982, and 1994. We found that western juniper density and cover during the last 4 decades increased at all sites, with changes on the relict site similar to those on one of the disturbed sites. We suggest that even though 2 of the traditionally cited causes of western juniper expansion since the late 1800s (altered fire regimes, domestic livestock grazing) may have contributed to expansion on our disturbed sites, these mechanisms can not explain expansion on the near- relict mesa. Further, we examined climatic changes since 1900 in the region and concluded that the data did not fully support a climate-driven mechanism for the expansion. In seeking to explain western juniper expansion on semiarid rangelands, we suggest that all potential causal mechanisms (e.g., fire history, biological inertia, climate, domestic grazing, atmospheric CO2 enrichment) be considered.

2350^4^Atkin,O K^Schortemeyer,M^McFarlane,N^Evans,J R^1999^1^The response of fast- and slow-growing Acacia species to elevated atmospheric CO2: an analysis of the underlying components of relative growth rate^2^120^4^544-554^^^^^Sep^^^^^7462
1030^312^3422^3423^400^417^669^705^867^lict site similar to those on one of the disturbed sites. We suggest that evA^7461^In this study we assessed the impact of elevated CO2 with unlimited water and complete nutrient on the growth and nitrogen economy of ten woody Acacia species that differ in relative growth rate (RGR). Specifically. we asked whether fast- and slow-growing species systematically differ in their response to elevated CO2. Four slow-growing species from semi- arid environments (Acacia aneura, A. colei, A. coriacea and A. tetragonophylla) and six fast-growing species from mesic environments (Acacia dealbata, A. implexa, A. mearnsii, A. melanoxylon, A. irrorata and A. saligna) were grown in glasshouses with either ambient (similar to 350 ppm) or elevated (similar to 700 ppm) atmospheric CO2. All species reached greater final plant mass with the exception of A. aneura, and RGR, averaged across all species, increased by 10% over a 12-week period when plants were exposed to elevated CO2. The stimulation of RGR was evident throughout the 12-week growth period. Elevated CO2 resulted in less foliage area per unit foliage dry mass, which was mainly the result of an increase in foliage thickness with a smaller contribution from greater dry matter content per unit fresh mass. The net assimilation rate (NAR, increase in plant mass per unit foliage area and time) of the plants grown at elevated CO2 was higher in all species (on average 30% higher than plants in ambient CO2) and was responsible for the increase in RGR. The higher NAR was associated with a substantial increase in foliar nitrogen productivity in all ten Acacia species. Plant nitrogen concentration was unaltered by growth at elevated CO2 for the slow-growing Acacia species, but declined by 10% for faster- growing species. The rate of nitrogen uptake per unit root mass was higher in seven of the species when grown under elevated CO2, and leaf area per unit root mass was reduced by elevated CO2 in seven of the species. The absolute increase in RGR due to growth under elevated CO2 was greater for fast- than for slow-growing Acacia species.
oliage area per unit2351^3^Cater,M^Simoncic,P^Batic,F^1999^1^Pre-dawn water potential and nutritional status of pedunculate oak (Quercus robur L.) in the north-east of Slovenia^262^39^4^13-21^^^^^^^^^^7464
1034^2040^243^3424^361^372^386^514^912^92^
A^7463^In the 1997 growth period monthly measurements of pre-dawn water potential, electrical resistance of the cambial zone, groundwater level and quality together with annual dynamics of macronutrive elements in leaves and heavy metals (Zn, Ph, Cd) were performed. Two plots having different groundwater tables and crown defoliation were studied in the pedunculate oak forest complex (Querco Roboris-Carpinetum M. Wraber) in the north-east of Slovenia. Results showed lower (more negative) values of pre-dawn water potential and higher values of cambial electrical resistance on the plot with greater crown defoliation, which also had a lower groundwater table. Groundwater seems to be the key factor in the process of oak decline.
than for slow-growing Acacia species.
oliage area per unit2352^2^Grams,T E E^Matyssek,R^1999^1^Elevated CO2 counteracts the limitation by chronic ozone exposure on photosynthesis in Fagus sylvatica L.: Comparison between chlorophyll fluorescence and leaf gas exchange^262^39^4^31-39^^^^^^^^^^7466
1064^1076^1828^312^3425^348^374^434^435^92^of pre-dawn water potential, electrical resistance of the cambial zone, groundwater level and quality together with annual dynamics of macronutrive elements in leaves and heavy metals (Zn, Ph, Cd) were performed. Two plots having different groundwater tables and crown defoliation were studied in the pedunculate oak forest complex (Querco Roboris-Carpinetum M. Wraber) in the north-east of Slovenia. Results showed lower (more negative) values of pre-dawn water potential and higher values of cambial electrical resistance on the plot with greater crown defoliation, which also had a lower groundwater table. Groundwater seems to be the key factor in the process of oak decline.
than for slow-growing Acacia species.
oliage area per unitA^7465^The interaction of elevated CO2 and enhanced chronic ozone (O- 3) impact was analysed throughout the growing season in the photosynthetic response (chlorophyll fluorescence and leaf gas exchange) of beech saplings (Fagus sylvatica) which had been acclimated to CO2 supply during the year prior to the experiment. Both light and dark reactions (i.e. electron transport rate and photosynthetic capacity) of plants grown at ambient CO2 and twice-ambient O-3 concentrations were distinctly reduced by August. The O-3-induced decline was counteracted by elevated CO2 supply (i.e. ambient +300 ppm). Plants grown at high CO2 supply and ambient or twice-ambient O- 3 concentrations displayed a photosynthetic performance similar to plants exposed to ambient CO2 and O-3 conditions. Responses in chlorophyll fluorescence were found to be consistent with those in leaf gas exchange.
ter table. Groundwater seems to be the key factor in the process of oak decline.
than for slow-growing Acacia species.
oliage area per unit2353^5^Almeida,J P F^Luscher,A^Frehner,M^Oberson,A^Nosberger,J^1999^1^Partitioning of P and the activity of root acid phosphatase in white clover (Trifolium repens L.) are modified by increased atmospheric CO2 and P fertilisation^206^210^2^159-166^^^^^^^^^^7468
1510^2140^224^2414^312^376^436^527^692^92^he experiment. Both light and dark reactions (i.e. electron transport rate and photosynthetic capacity) of plants grown at ambient CO2 and twice-ambient O-3 concentrations were distinctly reduced by August. The O-3-induced decline was counteracted by elevated CO2 supply (i.e. ambient +300 ppm). Plants grown at high CO2 supply and ambient or twice-ambient O- 3 concentrations displayed a photosynthetic performance similar to plants exposed to ambient CO2 and O-3 conditions. Responses in chlorophyll fluorescence were found to be consistent with those in leaf gas exchange.
ter table. Groundwater seems to be the key factor in the process of oak decline.
than for slow-growing Acacia species.
oliage area per unitA^7467^The growth response of white clover (Trifolium repens L.) to the expected increase in atmospheric partial pressure of CO2 (p(CO2)) may depend on P availability. A decrease in the rate of transpiration due to increased p(CO2) may reduce the amount of P transported to the shoot, thereby causing a change in the partitioning of P between the root and shoot. To test these hypotheses, four concentrations of P in the nutrient solution, combined with two p(CO2) treatments, were applied to nodulated white clover plants. Compared to ambient p(CO2) (35 Pa), twice ambient p(CO2) (70 Pa) reduced the rate of transpiration but did not impair the total P uptake per plant. However, at twice ambient p(CO2) and a moderate to high supply of P, concentrations of structural P and soluble P (Pi) were lower in the leaves and higher in the roots. The activity of root acid phosphatase was lower at twice ambient p(CO2) than at ambient p(CO2); it depended on the Pi concentration in the roots. At the highest P concentration, twice ambient p(CO2) stimulated photosynthesis and the growth rate of the plant without affecting the concentration of nonstructural carbohydrates in the leaves. However, at the lower P concentrations, plants at twice ambient p(CO2) lost their stimulation of photosynthesis in the afternoon, they accumulated nonstructural carbohydrates in the leaves and their growth rate was not stimulated; indicating C-sink limitation of growth. P nutrition will be crucial to the growth of white clover under the expected future conditions of increased p(CO2).

2354^2^Loiseau,P^Soussana,J F^1999^1^Elevated [CO2], temperature increase and N supply effects on the turnover of below-ground carbon in a temperate grassland ecosystem^206^210^2^233-247^^^^^^^^^^7470
1298^146^1768^178^2087^2604^3426^344^508^977^re lower in the leaves and higher in the roots. The activity of root acid phosphatase was lower at twice ambient p(CO2) than at ambient p(CO2); it depended on the Pi concentration in the roots. At the highest P concentration, twicA^7469^The effects of elevated [CO2] (700 mu l l(-1) CO2) and temperature increase (+3 degrees C) on carbon turnover in grassland soils were studied during 2.5 years at two N fertiliser supplies (160 and 530 kg N ha(-1) y(-1)) in an experiment with well-established ryegrass swards (Lolium perenne) supplied with the same amounts of irrigation water. During the growing season, swards from the control climate (350 mu l l(-1) [CO2] at outdoor air temperature) were pulse labelled by the addition of (CO2)-C-13. The elevated [CO2] treatments were continuously labelled by the addition of fossil-fuel derived CO2 (C-13 of -40 to -50 parts per thousand). Prior to the start of the experimental treatments, the carbon accumulated in the plant parts and in the soil macro-organic matter ('old' C) was at -32 parts per thousand. During the experiment, the carbon fixed in the plant material ('new' C) was at -14 and -54 parts per thousand in the ambient and elevated [CO2] treatments, respectively. During the experiment, the C-13 isotopic mass balance method was used to calculate, for the top soil (0-15 cm), the carbon turnover in the stubble and roots and in the soil macro-organic matter above 200 mu (MOM). Elevated [CO2] stimulated the turnover of organic carbon in the roots and stubble and in the MOM at N+, but not at N-. At the high N supply, the mean replacement time of 'old' C by 'new' C declined in elevated, compared to ambient [CO2], from 18 to 7 months for the roots and stubble and from 25 to 17 months for the MOM. This resulted from increased rates of 'new' C accumulation and of 'old' C decay. By contrast, at the low N supply, despite an increase in the rate of accumulation of 'new' C, the soil C pools did not turnover faster in elevated [CO2], as the rate of 'old' C decomposition was reduced. A 3 degrees C temperature increase in elevated [CO2] decreased the input of fresh C to the roots and stubble and enhanced significantly the exponential rate for the 'old' C decomposition in the roots and stubble. An increased fertiliser N supply reduced the carbon turnover in the roots and stubble and in the MOM, in ambient but not in elevated [CO2]. The respective roles for carbon turnover in the coarse soil OM fractions, of the C:N ratio of the litter, of the inorganic N availability and of a possible priming effect between C- substrates are discussed.

2355^2^Griffin,K L^Luo,Y Q^1999^1^Sensitivity and acclimation of Glycine max (L.) Merr. leaf gas exchange to CO2 partial pressure^173^42^2^141-153^^^^^Oct^^^^^7472
130^343^372^377^465^546^550^639^665^685^rates of 'new' C accumulation and of 'old' C decay. By contrast, at the low N supply, despite an increase in the rate of accumulation of 'new' C, the soil C pools did not turnover faster in elevated [CO2], as the rate of 'old' C decomposition was reduced. A 3 degrees C temperature increase in elevated [CO2] decreased the input of fresh C to the roots and stubble and enhanced significantly the exponential rate for the 'old' C decomposition in the roots and stubble. An increased fertilA^7471^Theoretical studies suggest that partitioning leaf photosynthetic responses to CO2 partial pressures into two components, sensitivity and acclimation, facilitates both scaling-up photosynthetic responses and predicting global terrestrial carbon influx. Here, we experimentally examine these two components by growing soybean (Glycine max) in two CO2 partial pressures, 35 and 70 Pa, and making a suite of ecophysiological measurements on expanding and fully expanded leaves. These CO2 treatments resulted in a variety of acclimation responses, including changes in net photosynthetic rate and capacity, stomatal conductance, transpiration, and respiration. These responses were strongly dependent on leaf age. Despite the wide variety of acclimation responses, the experimentally derived photosynthetic sensitivity did not vary with CO2 treatments or leaf age. In addition, the photosynthetic sensitivity to ambient CO2 partial pressure was consistent with the sensitivity to intercellular CO2 partial pressure, indicating little effect of stomatal conductance on photosynthetic sensitivity. This study supports the theoretical conclusion that photosynthetic sensitivity is independent of growth environment and leaf age, as well as photosynthetic acclimation, even though the latter varies with both environmental and developmental factors. Accordingly, photosynthetic sensitivity may be directly extrapolated from leaf to globe to predict the increment in terrestrial carbon influx stimulated by the yearly increase in atmospheric CO2, whereas the acclimation component must be used to adjust the overall global estimate. (C) 1999 Elsevier Science B.V. All rights reserved.

2356^5^McMaster,G S^LeCain,D R^Morgan,J A^Aiguo,L^Hendrix,D L^1999^1^Elevated CO2 increases wheat CER, leaf and tiller development, and shoot and root growth^161^183^2^119-128^^^^^Sep^^^^^7474
243^312^3427^360^376^434^435^529^57^724^etic sensitivity to ambient CO2 partial pressure was consistent with the sensitivity to intercellular CO2 partial pressure, indiA^7473^Whole-plant responses to elevated CO2 throughout the life cycle are needed to understand future impacts of elevated atmospheric CO2. In this study, Triticum aestivum L. leaf carbon exchange rates (CER) and carbohydrates, growth, and development were examined at the tillering, booting, and grain-filling stages in growth chambers with CO2 concentrations of 350 (ambient) or 700 thigh) mu mol mol(-1). Single-leaf CER values measured on plants grown at high CO2 were 50% greater than those measured on plants grown at ambient CO2 for all growth stages, with no photosynthetic acclimation observed at high CO2. Leaves grown in high CO2 had more starch and simple sugars at tillering and booting, and more starch at grain-filling, than those grown in ambient CO2. CER and carbohydrate levels were positively correlated with leaf appearance rates and tillering (especially third-, fourth- and fifth-order tillers). Elevated CO2 slightly delayed tiller appearance, but accelerated tiller development after appearance. Although high CO2 increased leaf appearance rates, final leaf number/culm was not effected because growth stages were reached slightly sooner. Greater plant biomass was related to greater tillering. Doubling CO2 significantly increased both shoot and root dry weight, but decreased the shoot to root ratio. High CO2 plants had more spikes plant(-1) and spikelets spike(-1), but a similar number of fertile spikelets spike(-1). Elevated CO2 resulted in greater shoot, root and spike production and quicker canopy development by increasing leaf and tiller appearance rates and phenology.

2357^3^Amiro,B D^MacPherson,J I^Desjardins,R L^1999^1^BOREAS flight measurements of forest-fire effects on carbon dioxide and energy fluxes^107^96^4^199-208^^^^^15 Sep^^^^^7476
1162^1234^23^3428^3429^3430^3431^535^672^888^vely correlated with leaf appearance rates and tillering (especially third-, fourth- and fifth-order tillers). Elevated CO2 slightly delayed tiller appearance, but accelerated tiller development after appearance. AltA^7475^Fire is the dominant stand-replacing agent in the Canadian boreal forest, but few quantitative measurements are available on the micrometeorological effects of fire. Airborne flux measurements during the BOREAS experiment were referenced to age of burn along a 500-km transect through Saskatchewan and Manitoba, Canada. These data for 1-, 5-, and 7-year-old burns were supplemented with 15- and 30-year-old-burn data from the BOREAS northern study site near Thompson, Manitoba. Data were available near midday only and included the June, July and September campaigns during 1994, and July of 1996. Surface radiometric temperature increased by up to 6 degrees C and remained elevated even 15 years after fire. Net radiation was largely unaffected whereas albedo decreased in the first year post-fire but recovered by the fifth year. Sensible heat flux increased by 10-20% for the first few years after the fire and then decreased. Latent heat flux slightly decreased after the fire, causing the Bowen ratio to increase by ca. 50% for 7 years post-fire. The CO2 flux was reduced for the 15-year period after fire with the greatest reduction to ca. 25% of control areas during the year following fire. However, diurnal and annual data are needed to determine the total impact of fire on the boreal-forest carbon balance. (C) 1999 Elsevier Science B.V. All rights reserved.

2358^4^Fritschi,F B^Boote,K J^Sollenberger,L E^Allen,L H^1999^1^Carbon dioxide and temperature effects on forage establishment: tissue composition and nutritive value^127^5^7^743-753^^^^^Oct^^^^^7478
1752^2434^2533^3178^3432^384^385^547^57^733^996. Surface radiometric temperature increased by up to 6 degrees C and remained elevated even 15 years after fire. Net radiation was largely unaffected whereas albedo decreased in the first year post-fire but recovered by the fifth year. Sensible heat flux increased by 10-20% for the first few years after the fire and then decreased. Latent heat flux slightly decreased after the fire, causing the Bowen ratio to increasA^7477^Atmospheric CO2 concentration ([CO2]) and temperature are likely to increase in the future and may change plant growth and composition characteristics. Rhizoma peanut (Arachis glabrata Benth.) and bahiagrass (Paspalum notatum Flugge) were grown on a natural field soil in temperature-gradient greenhouses to evaluate the effects of elevated [CO2] and temperature on tissue composition and digestibility during the establishment year. Carbon dioxide levels were maintained at 365 (ambient) and 640 mu L CO2 L-1 air. The temperature- gradient greenhouses were regulated to obtain air temperature sectors of 0.2, 1.5, 2.9, and 4.5 degrees C above ambient. Samples were taken of previously undefoliated herbage at 57, 86, 121, 148, and 217 days after planting and entire plots were harvested at 218 days after planting. Elevated [CO2] increased total nonstructural carbohydrate concentration in rhizoma peanut leaves by almost 50%. Rhizoma peanut leaf N concentration was 6% lower at elevated than at ambient [CO2]. The N concentration in new rhizomes of rhizoma peanut was increased by high [CO2], while the N concentration in bahiagrass was not affected by temperature or [CO2]. No effects of [CO2] and temperature were found on neutral detergent fibre in rhizoma peanut leaves or stems; however, elevated [CO2] increased neutral detergent fibre in bahiagrass leaves. Only at season end was in vitro organic matter digestion of rhizoma peanut higher at ambient (623 g kg(-1)) than at elevated [CO2] (609 g kg(-1)). Elevated [CO2] had a greater effect on tissue composition of rhizoma peanut than of bahiagrass. These data suggest that elevated temperature and CO2-induced changes in chemical composition of forage species adapted to humid subtropics will be relatively small, particularly for C4 species.

2359^4^Friedlingstein,P^Joel,G^Field,C B^Fung,I Y^1999^1^Toward an allocation scheme for global terrestrial carbon models^127^5^7^755-770^^^^^Oct^^^^^7480
1262^1312^1315^1660^2056^2060^3149^3433^3434^504^ed than at ambient [CO2]. The A^7479^The distribution of assimilated carbon among the plant parts has a profound effect on plant growth, and at a larger scale, on terrestrial biogeochemistry. Although important progress has been made in modelling photosynthesis, less effort has been spent on understanding the carbon allocation, especially at large spatial scales. Whereas several individual-level models of plant growth include an allocation scheme, most global terrestrial models still assume constant allocation of net primary production (NPP) among plant parts, without any environmental coupling. Here, we use the CASA biosphere model as a platform for exploring a new global allocation scheme that estimates allocation of photosynthesis products among leaves, stems, and roots depending on resource availability. The philosophy underlying the model is that-allocation patterns result from evolved responses that adjust carbon investments to facilitate capture of the most limiting resources, i.e. light, water, and mineral nitrogen. In addition, we allow allocation of NPP to vary in response to changes in atmospheric CO2. The relative magnitudes of changes in NPP and resource-use efficiency control the response of root:shoot allocation. For ambient CO2, the model produces realistic changes in above- ground allocation along productivity gradients. In comparison to the CASA standard estimate using fixed allocation ratios, the new allocation scheme tends to favour root allocation, leading to a 10% lower global biomass. Elevated CO2, which alters the balance between growth and available resources, generally leads to reduced water stress and consequently, decreased root:shoot ratio. The major exception is forest ecosystems, where increased nitrogen stress induces a larger root allocation.

2360^3^Kasurinen,A^Helmisaari,H S^Holopainen,T^1999^1^The influence of elevated CO2 and O-3 on fine roots and mycorrhizas of naturally growing young Scots pine trees during three exposure years^127^5^7^771-780^^^^^Oct^^^^^7482
1076^1983^243^264^374^376^377^407^483^92^A^7481^Young Scots pine trees naturally established at a pine heath were exposed to two concentrations of CO2 (ambient and doubled ambient) and two O-3 regimes (ambient and doubled ambient) and their combination in open-top field chambers during growing seasons 1994, 1995 and 1996 (late May to 15 September). Filtered ozone treatment and chamberless control trees were also included in the treatment comparisons. Root in-growth cores were inserted to the undisturbed soil below the branch projection of each tree at the beginning of the fumigation period in 1994 and were harvested at the end of the fumigation periods in 1995 and 1996. Root biomasses were determined from different soil layers in the ingrowth cores, and the infection levels of different mycorrhizal types were calculated. Elevated O-3 and CO2 did not have significant effects on the biomass production of Scots pine coarse (diameter >2 mm) or fine roots (diameter <2 mm) and roots of grasses and dwarf shrubs. Elevated O-3 caused a transient stimulation, observable in 1995, in the proportion of tuber-like mycorrhizas, total mycorrhizas and total short roots but this stimulation disappeared during the last study year. Elevated CO2 did not enhance carbon allocation to root,growth or mycorrhiza formation, although a diminishing trend in the mycorrhiza formation was observed. In the combination treatment increased CO2 inhibited the transient stimulating effect of ozone, and a significant increase of old mycorrhizas was observed. Our conclusion is that doubled CO2 is not able to increase carbon allocation to growth of fine roots or mycorrhizas in nutrient poor forest sites and realistically elevated ozone does not cause a measurable limitation to roots within a period of three exposure years.

2361^5^Hungate,B A^Dijkstra,P^Johnson,D W^Hinkle,C R^Drake,B G^1999^1^Elevated CO2 increases nitrogen fixation and decreases soil nitrogen mineralization in Florida scrub oak^127^5^7^781-789^^^^^Oct^^^^^7484
1684^2102^341^3435^344^359^417^506^859^975^ransient stimulationA^7483^We report changes in nitrogen cycling in Florida scrub oak in response to elevated atmospheric CO2 during the first 14 months of experimental treatment. Elevated CO2 stimulated above-ground growth, nitrogen mass, and root nodule production of the nitrogen-fixing vine, Galactia elliottii Nuttall. During this period, elevated CO2 reduced rates of gross nitrogen mineralization in soil, and resulted in lower recovery of nitrate on resin lysimeters. Elevated CO2 did not alter nitrogen in the soil microbial biomass, but increased the specific rate of ammonium immobilization (NH4+ immobilized per unit microbial N) measured over a 24-h period. Increased carbon input to soil through greater root growth combined with a decrease in the quality of that carbon in elevated CO2 best explains these changes. These results demonstrate that atmospheric CO2 concentration influences both the internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosystem nitrogen mass (nitrogen fixation and nitrate leaching) in Florida coastal scrub oak. If these changes in nitrogen cycling are sustained, they could cause long-term feedbacks to the growth responses of plants to elevated CO2. Greater nitrogen fixation and reduced leaching could stimulate nitrogen-limited plant growth by increasing the mass of labile nitrogen in the ecosystem. By contrast, reduced nitrogen mineralization and increased immobilization will restrict the supply rate of plant-available nitrogen, potentially reducing plant growth. Thus, the net feedback to plant growth will depend on the balance of these effects through time.

2362^4^Constable,J V H^Guenther,A B^Schimel,D S^Monson,R K^1999^1^Modelling changes in VOC emission in response to climate change in the continental United States^127^5^7^791-806^^^^^Oct^^^^^7486
312^3436^3437^3438^3439^3440^3441^372^669^92^ internal cycling of nitrogen (mineralization, immobilization, and nitrification) as well as the processes that regulate total ecosysA^7485^The alteration of climate is driven not only by anthropogenic activities, but also by biosphere processes that change in conjunction with climate. Emission of volatile organic compounds (VOCs) from vegetation may be particularly sensitive to changes in climate and may play an important role in climate forcing through their influence on the atmospheric oxidative balance, greenhouse gas concentration, and the formation of aerosols. Using the VEMAP vegetation database and associated vegetation responses to climate change, this study examined the independent and combined effects of simulated changes in temperature, CO2 concentration, and vegetation distribution on annual emissions of isoprene, monoterpenes, and other reactive VOCs (ORVOCs) from potential vegetation of the continental United States. Temperature effects were modelled according to the direct influence of temperature on enzymatic isoprene production and the vapour pressure of monoterpenes and ORVOCs. The effect of elevated CO2 concentration was modelled according to increases in foliar biomass per unit of emitting surface area. The effects of vegetation distribution reflects simulated changes in species spatial distribution and areal coverage by 21 different vegetation classes. Simulated climate warming associated with a doubled atmospheric CO2 concentration enhanced total modelled VOC emission by 81.8% (isoprene + 82.1%, monoterpenes + 81.6%, ORVOC + 81.1%), whereas a simulated doubled CO2 alone enhanced total modelled VOC emission by only + 11.8% (isoprene + 13.7%, monoterpenes + 4.1%, ORVOC + 11.7%). A simulated redistribution of vegetation in response to altered temperatures and precipitation patterns caused total modelled VOC emission to decline by 10.4% (isoprene -11.7%, monoterpenes -18.6%, ORVOC 0.0%) driven by a decline in area covered by vegetation classes emitting VOCs at high rates. Thus, the positive effect of leaf-level adjustments to elevated CO2 (i.e. increases in foliar biomass) is balanced by the negative effect of ecosystem-level adjustments to climate (i.e. decreases in areal coverage of species emitting VOC at high rates).

2363^1^Cowling,S A^1999^1^Simulated effects of low atmospheric CO2 on structure and composition of North American vegetation at the Last Glacial Maximum^377^8^2^81-93^^^^^Mar^^^^^7488
1103^1181^137^1980^256^372^399^539^625^659^d total modelled VOC emission by 81.8% (isoprene + 82.1%, monoterpenes + 81.6%, ORVOC + 81.1%), whereas a simulated doubled CO2 alone enhanced total modelled VOC emission by only + 11.8% (isoprene + 13.7%, monoterpenes + 4.1%, ORVOC + 11.7%). A simulated redistribution of vegetation in response to altered temperatures and precipitation patterns caused total modelled VOC emission to decline by 10.4% (isoprene -11.7%, monoterpenes -18.6%, ORVOC 0.0%) driven by a decline in area covered by vegetation classes emitting VOCs at high rates. Thus, the positive effect of leaf-level adjustments to elevated CO2 (i.e. increases in foliar biomass) is balanced by the negative effect of ecosystem-leA^7487^1. Physiological experiments have indicated that the lower CO2 levels of the last glaciation (200 mu mol mol(-1)) probably reduced plant water-use efficiency (WUE) and that they combined with increased aridity and colder temperatures to alter vegetation structure and composition at the Last Glacial Maximum (LGM). 2. The effects of low CO2 on vegetation structure were investigated using BIOME3 simulations of leaf area index (LAI), and a two-by-two factorial experimental design (modern/LGM CO2, modern/ LGM climate). 3. Using BIOME3, and a combination bf lowered CO2 and simulated LGM climate (from the NCAR-CCM1 model), results in the introduction of additional xeric vegetation types between open woodland and closed-canopy forest along a latitudinal gradient in eastern North America. 4. The simulated LAI of LGM vegetation was 25- 60% lower in many regions of central and eastern United States relative to modern climate, indicating that glacial vegetation was much more open than today. 5. Comparison of factorial simulations show that low atmospheric CO2 has the potential to alter vegetation structure (LAI) to a greater extent than LGM climate. 6. If the magnitude of LAI reductions simulated for glacial North America were global, then low atmospheric CO2 may have promoted atmospheric warming and increased aridity, through alteration of rates of water and heat exchange with the atmosphere.

2364^3^van Ginkel,J H^Whitmore,A P^Gorissen,A^1999^1^Lolium perenne grasslands may function as a sink for atmospheric carbon dioxide^204^28^5^1580-1584^^^^^Sep-Oct^^^^^7490
137^1660^178^314^372^429^535^547^56^893^from the NCAR-CCM1 model), results in the introduction of additional xeric vegetation types between open woodland and closed-canopy forest along a latitudinal gradient in eastern North America. 4. The simulated LAI of LGM vegetation was 25- 60% lower in many regions of central and eastern United States relative to modern climate, indicating that glacial vegetation was much more open than today. 5. Comparison of factA^7489^Model calculations and scenario studies suggest the existence of a considerable positive feedback between temperature and CO2 levels in the atmosphere. Rising temperatures are supposed to increase decomposition of soil organic C leading to increased production of CO2 and this extra CO2 induces a positive feedback by raising the temperature still further. Evidence was found that negative feedback mechanisms also exist: more primary production is allocated to roots as atmospheric CO2 rises and these roots decompose more slowly than roots grown at ambient CO2 levels. Experimental data partly obtained with C- 14-techniques were applied in a grassland C model. The model results show that at an atmospheric CO2 concentration of 700 mu L L-1 increased belowground C storage will be more than sufficient to balance the increased decomposition of soil organic C in a ryegrass (Lolium perenne L.) grassland soil. Once a doubling of the present atmospheric CO2 concentration has been reached, C equivalent to 55% of the annual CO2 increase above 1 ha ryegrass can be withdrawn from the atmosphere. This indicates that grassland soils represent a significant sink for rising atmospheric CO2.

2365^3^Yamashita,I^Dan,K^Shimomura,M^1999^1^Active modified atmosphere packaging storage of cabbage plug seedlings^180^68^5^1015-1021^^^^^Sep^^^^^7492
aising the temperature still further. Evidence was found that negative feedback mechanisms also exist: more primary production is allocated to roots as atmospheric CO2 rises and these roots decompose more slowly than roots grown at ambient CO2 levels. Experimental data partly obtained with C- 14-techniques were applied in a grassland C model. The model results show that at an atmospheric CO2 concentration of 700 mu L L-1 increased belowground C storage will be more than sufficient to balance the increased decomposition of soil organic C in a ryegrass (Lolium perenne L.) grassland soil. Once a doubling of the present atmospheric CO2 concentration has been reached, C equivalent to 55% of thA^7491^When cabbage plug seedlings were stored under a modified atmosphere packaging (MAP) at 15 degrees C in the dark for 2 weeks, a passive MAP did not create an environment to inhibit stem elongation of seedling in the 0.1mm thick polyethylene (PE) film pouch. An active MAP by adjusting N-2 rich air with 2% O-2 did not successfully retard elongation either. In the active MAP where the internal atmosphere was replaced with N-2 enriched air (2.5% O-2) with elevated CO2, the elongation was delayed as CO2 concentration increased. When 16% CO2 was introduced to the 0.08mm thick nylon/PE film pouch, the inhibit of stem elongation was most successful. Analysis of plant weight, total number of leaves, green color intensity, ascorbic acid content in the leaf blade and head weight of harvested cabbage revealed that the elevated CO2 active MAP is a favorable storage condition for cabbage plug seedlings. The elevated CO2 active MAP, however, caused CO2 injury when CO2 concentration exceeded 24%.
ivalent to 55% of th2366^3^Uselman,S M^Qualls,R G^Thomas,R B^1999^1^A test of a potential short cut in the nitrogen cycle: The role of exudation of symbiotically fixed nitrogen from the roots of a N-fixing tree and the effects of increased atmospheric CO2 and temperature^206^210^1^21-32^^^^^^^^^^7494
1292^2742^312^3442^3443^372^421^669^708^92^ccessfully retard elongation either. In the active MAP where the internal atmosphere was replaced with N-2 enriched air (2.5% O-2) with elevated CO2, the elongation was delayed as CO2 concentration increased. When 16% CO2 was introduced to the 0.08mm thick nylon/PE film pouch, the inhibit of stem elongation was most successful. Analysis of plant weight, total number of leaves, green color intensity, ascorbic acid content in the leaf blade and head weight of harvested cabbage revealed that the elevated CO2 active MAP is a favorable storage condition for cabbage plug seedlings. The elevated CO2 active MAP, however, caused CO2 injury when CO2 concentration exceeded 24%.
ivalent to 55% of thA^7493^N-fixing trees facilitate the growth of neighboring trees of other species. These neighboring species benefit from the simple presence of the N fixation symbiosis in their surroundings. Because of this phenomenon, it has been hypothesized that a change in atmospheric CO2 concentration may alter the role of N-fixing trees in their environment. It is thought that the role of N-fixing trees in ecosystems of the future may be more important since they may help sustain growth increases due to increased CO2 concentration in nitrogen limited forests. We examined: (1) whether symbiotically fixed N was exuded from roots, (2) whether a doubled atmospheric CO2 concentration would result in increased organic N exudation from roots, and (3) whether increased temperature or N availability affected N exudation from roots. This study analyzed exudation of dissolved organic N from the roots of seedlings of the N-fixing tree Robinia pseudoacacia L. in a full factorial design with 2 CO2 (35.0 and 70.0 Pa) x 2 temperature (26 or 30 degrees C during the day) x 2 N fertilizer (0 and 10.0 mM N concentration) levels. Trees with no other source of N except N fixation exuded about 1% to 2% of the fixed N through their roots as dissolved organic N. Increased atmospheric CO2 concentrations did not, however, increase N exudation rates on a per gram belowground biomass basis. A 4 degrees C increase in temperature and N fertilization did, however, significantly increase N exudation rates. These results suggest that exudation of dissolved organic N from roots or nodules of N-fixing trees could be a significant, but minor, pathway of transferring N to neighboring plants in a much more rapid and direct way than cycling through death, decomposition and mineralization of plant residues. And, while exudation rates of dissolved organic N from roots were not significantly affected by atmospheric CO2 concentration, the previously observed 'CO2 fertilization effect' on N-fixing trees suggests that N exudation from roots could play a significant but minor role in sustaining increases in forest growth, and thus C storage, in a CO2 enriched atmosphere.

2367^2^Matamala,R^Drake,B G^1999^1^The influence of atmospheric CO2 enrichment on plant-soil nitrogen interactions in a wetland plant community on the Chesapeake Bay^206^210^1^93-101^^^^^^^^^^7496
1044^243^3019^3327^341^372^378^507^56^968^is. A 4 degrees C increase in temperature and N fertilization did, however, significantly increase N exudation rates. These results suggest that exudation of dissolved organic N from roots or nodules of N-fixing trees could be a significant, but minor, pathway of transferring N to neighboring plants in a much more rapid and direct way than cycling through death, decomposition and mineralization of plant residues. And, while exudation rates of dissolved organic N from roots were not significantly affected by atmospheric CO2 concentration, the previously observed 'CO2 fertilization effect' on N-fixing trees suggests that N exudation from roots could play a significantA^7495^We investigated plant and soil nitrogen pools and soil processes in monospecific stands of the C-3 sedge Scirpus olneyi and the C-4 grass Spartina patens grown in the field in open top chambers in a brackish marsh on the Chesapeake Bay. Stands of S. olneyi responded to eight years of elevated CO2, by increased rates of net ecosystem gas exchange and a large stimulation of net ecosystem production. We conducted our study in the summer of 1994 and 1995 when soil cores were collected and aboveground biomass was estimated. Nitrogen concentration in elevated CO2 treatments was reduced 15% in stems of S. olneyi and 8% in the upper 10 cm of the soil profile. While total plant nitrogen per unit of land area remained the same between treatments, total soil nitrogen showed a non- significant tendency to decrease in the upper 10 cm of the soil profile in elevated CO2 both years of study. A significant decrease in soil bulk density largely contributed to the observed decrease in soil nitrogen. Exchangeable nitrogen and potential denitrification rates were also reduced in elevated CO2, but net nitrogen mineralization was unchanged by elevated CO2 treatment in S. olneyi both years. Plants and soils in a pure stand of the C-4 grass, S. patens, showed none of these effects of elevated CO2 treatment. Our data provides evidence of changes in nitrogen dynamics of an ecosystem exposed to elevated CO2 for eight years; however due to the variability in these data, we cannot say if or how these changes are likely to impact the effect of rising CO2 on primary production or carbon accumulation in this ecosystem in the future.

2368^12^Peterson,A G^Ball,J T^Luo,Y^Field,C B^Curtis,P S^Griffin,K L^Gunderson,C A^Norby,R J^Tissue,D T^Forstreuter,M^Rey,A^Vogel,C S^1999^1^Quantifying the response of photosynthesis to changes in leaf nitrogen content and leaf mass per area in plants grown under atmospheric CO2 enrichment^9^22^9^1109-1119^^^^^Sep^^^^^7498
130^264^314^348^360^384^398^665^705^728^ease in soil nitrogen. Exchangeable nitrogA^7497^Previous modelling exercises and conceptual arguments have predicted that a reduction in biochemical capacity for photosynthesis (A(area)) at elevated CO2 may be compensated by an increase in mesophyll tissue growth if the total amount of photosynthetic machinery per unit leaf area is maintained (i.e. morphological upregulation). The model prediction was based on modelling photosynthesis as a function of leaf N per unit leaf area (N-area), where N-area = N-mass x LMA. Here, N-mass is percentage leaf N and is used to estimate biochemical capacity and LMA is leaf mass per unit leaf area and is an index of leaf morphology. To assess the relative importance of changes in biochemical capacity versus leaf morphology we need to control for multiple correlations that are known, or that are likely to exist between CO2 concentration, N-area, N-mass, LMA and A(area). Although this is impractical experimentally, we can control for these correlations statistically using systems of linear multiple-regression equations. We developed a linear model to partition the response of A(area), to elevated CO2 into components representing the independent and interactive effects of changes in indexes of biochemical capacity, leaf morphology and CO2 limitation of photosynthesis. The model was fitted to data from three pine and seven deciduous tree species grown in separate chamber-based field experiments. Photosynthetic enhancement at elevated CO2 due to morphological upregulation was negligible for most species. The response of A(area), in these species was dominated by the reduction in CO2 limitation occurring at higher CO2 concentration. However, some species displayed a significant reduction in potential photosynthesis at elevated CO2 due to an increase in LMA that was independent of any changes in N-area. This morphologically based inhibition of A(area) combined additively with a reduction in biochemical capacity to significantly offset the direct enhancement of A(area) caused by reduced CO2 limitation in two species. This offset was 100% for Acer rubrum, resulting in no met effect of elevated CO2 on A(area) for this species, and 44% for Betula pendula. This analysis shows that interactions between biochemical and morphological responses to elevated CO2 can have important effects on photosynthesis.

2369^4^Sternberg,M^Brown,V K^Masters,G J^Clarke,I P^1999^1^Plant community dynamics in a calcareous grassland under climate change manipulations^331^143^1^29-37^^^^^Jul^^^^^7500
130^1658^3444^372^374^57^764^789^92^99^e response of A(area), in these species was dominated by the reduction in CO2 limitation occurring at higher CO2 concentration. However, some species displayed a significant reduction in potential photosynthesis at elevated CO2 due to an increase in LMA that was independent of any changes in N-area. This morphologically based inhibition of A(area) combined additively with a reduction in biochemical capacity to significantly offset the direct enhancement of A(area) caused by reduced CO2 limitation in two species. This ofA^7499^This study investigates the effects of field manipulations of local climate to determine the potential impact of climate change on plant community dynamics in a calcareous grassland. The experimental site is located in a grassland at the Wytham estate, Oxfordshire, UK. The one hectare study area is within a 10 ha abandoned arable field on Jurassic corallian limestone. Two climate change scenarios were used: warmer winters with increased summer rainfall and warmer winters with summer drought. Plant cover and species richness were significantly increased in plots receiving supplemented summer rainfall, while the amount of litter was significantly reduced. Litter formation was significantly increased by winter warming and drought. The responses of the plant community to the climate manipulations were related to the life-history attributes of the dominant species. Seedling recruitment was limited by microsite availability, which also varied in the different climate manipulations. The results are discussed in terms of successional dynamics. They suggest that warmer winters may delay succession, as gap formation in the sward will provide sites for colonisation of annuals, thereby enabling their persistence in the sward. Under wetter conditions during summer, perennial grasses tend to close the sward, thereby inhibiting the establishment of later successional species.

2370^2^Grimmer,C^Komor,E^1999^1^Assimilate export by leaves of Ricinus communis L. growing under normal and elevated carbon dioxide concentrations: the same rate during the day, a different rate at night^6^209^3^275-281^^^^^Sep^^^^^7502
243^344^360^417^632^788^92^ litter was significantly reduced. Litter formation was significantly increased by winter warming and drought. The responses of the plant community to the climate manipulations were related to the life-history attributes of the dominant species. Seedling recruitment was limited by microsite availability, which also varied in the different climate manipulations. The results are discussedA^7501^Castor bean (Ricinus communis L.) plants were grown for 5-7 weeks in a controlled environment at 350 mu l l(-1) or 700 mu l l(-1) CO2. Carbon assimilation, assimilate deposition, dark respiration and assimilate mobilization were measured in leaves 2, 3 and 4 (counted from the base of the plant), and a balance sheet of carbon input and export was elaborated for both CO2 concentrations. Carbon dioxide assimilation was nearly constant over the illumination period, with only a slight depression occurring at the end of the day in mature source leaves, not in young source leaves, Assimilation was ca. 40% higher at 700 mu l l(-1) than at 350 mu l l(-1) CO2. The source leaves increased steadily in weight per unit area during the first 3 weeks, more at 700 mu l l(-1) than at 350 mu l l(-1) CO2. On top of an irreversible weight increase, there was a large gain in dry weight during the day, which was reversed during the night. This reversible weight gain was constant over the life time of the leaf and ca. 80% higher at 700 mu l l(-1) than at 350 yl l(-1). Most of it was due to carbohydrates. The carbon content (as a percentage) was not altered by the CO2 treatment. Respiration was 25% higher in high-CO2 plants when based on leaf area, but the same when based on dry weight. The rate of carbon export via the phloem was the same during the daytime in plants grown at 350 mu l l(-1) and 700 mu l l(-1) CO2. During the night the low-CO2 plants had only 50% of the daytime export rate, in contrast to the high-CO2 plants which maintained the high export rate. It was concluded that the phloem loading system is saturated during the daytime in both CO2 regimes, whereas during the night the assimilate supply is reduced in plants in the normal CO2 concentration. Two-thirds of the carbon exported from the leaves was permanently incorporated as plant dry matter in the residual plant parts. This "assimilation efficiency" was the same for both CO2 regimes. It is speculated that under 350 mu l l(-1) CO2 the growing Ricinus plant operates at sink limitation during the day and at source limitation during the night.

2371^2^Cowling,S A^Sykes,M T^1999^1^Physiological significance of low atmospheric CO2 for plant- climate interactions^378^52^2^237-242^^^^^Sep^^^^^7504
1933^2349^243^3445^372^388^399^539^672^673^ carbon export via the phloem was the same during the daytime in plants grown at 350 mu l l(-1) and 700 mu l l(-1) CO2. During the night the low-CO2 plants had only 50% of the daytime export rate, in contrast to the high-CO2 plants which maintained the high export rate. It was concluded that the phloem loading system is saturated during the daytime in both CO2 regimes, whereas during the night the assimilate supply is reduced in plants in the normal CO2 concentration. Two-thirds of the carbon exported from the leaves was permanently incorporated as plant dry matter in the residual plant parts. This "assimilation efficiency" was the same for both CO2 regimes. It is speculated that under 350 mu l l(-1) CO2 the growing Ricinus plant operaA^7503^Methods of palaeoclimate reconstruction from pollen are built upon the assumption that plant-climate interactions remain the same through time or that these interactions are independent of changes in atmospheric CO2. The latter may be problematic because air trapped in polar ice caps indicates that atmospheric CO2 has fluctuated significantly over at least the past 400,000 yr, and likely the last 1.6 million yr, Three other points indicate potential biases for vegetation-based climate proxies. First, C-3-plant physiological research shows that the processes that determine growth optima in plants (photosynthesis, mitochondrial respiration, photorespiration) are all highly CO2-dependent, and thus were likely affected by the lower CO2 levels of the last glacial maximum. Second, the ratio of carbon assimilation per unit transpiration (called water-use efficiency) is sensitive to changes in atmospheric CO2 through effects on stomatal conductance and may have altered C-3-plant responses to drought, Third, leaf gas- exchange experiments indicate that the response of plants to carbon-depleting environmental stresses are strengthened under low CO2 relative to today. This paper reviews the scope of research addressing the consequences of low atmospheric CO2 for plant and ecosystem processes and highlights why consideration of the physiological effects of low atmospheric CO2 on plant function is recommended for any future refinements to pollen- based palaeoclimatic reconstructions. (C) 1999 University of Washington.

2372^5^Bolin,B^Canadell,J^Moore,B^Noble,I^Steffen,W^1999^1^Effect on the biosphere of elevated atmospheric CO2^32^285^5435^1851-1852^^^^^17 Sep

2373^2^DeLucia,E H^Schlesinger,W H^1999^1^Effect on the biosphere of elevated atmospheric CO2 - Response^32^285^5435^1852^^^^^17 Sep

2374^1^Robertson,G P^1999^1^Effect on the biosphere of elevated atmospheric CO2^32^285^5435^1852^^^^^17 Sep
n atmospheric CO2 through effects on stomatal conductance and may have altered C-3-plant responses to drought, Third, l2375^2^Herrick,J D^Thomas,R B^1999^1^Effects of CO2 enrichment on the photosynthetic light response of sun and shade leaves of canopy sweetgum trees (Liquidambar styraciflua) in a forest ecosystem^13^19^12^779-786^^^^^Oct^^^^^7509
2056^342^344^3446^384^398^483^484^546^794^m processes and highlights why consideration of the physiological effects of low atmospheric CO2 on plant function is recommended for any future refinements to pollen- based palaeoclimatic reconstructions. (C) 1999 University of Washington.

2372^5^Bolin,B^Canadell,J^Moore,B^Noble,I^Steffen,W^1999^1^Effect on the biosphere of elevated atmospheric CO2^32^285^5435^1851-1852^^^^^17 Sep

2373^2^DeLucia,E H^Schlesinger,W H^1999^1^Effect on the biosphere of elevated atmospheric CO2 - Response^32^285^5435^1852^^^^^17 Sep

2374^1^Robertson,G P^1999^1^Effect on the biosphere of elevated atmospheric CO2^32^285^5435^1852^^^^^17 Sep
n atmospheric CO2 through effects on stomatal conductance and may have altered C-3-plant responses to drought, Third, lA^7508^To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 mu l l(-1)) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum trees were naturally established in a 15-year-old forest dominated by loblolly pine (Pinus taeda L.). Measurements were made in early June and late August 1997 during the first full year of CO2 fumigation in the Duke Forest FACE experiment. Sun leaves had a 68% greater leaf mass per unit area, 63% more leaf N per unit leaf area, 27% more chlorophyll per unit leaf area and 77% greater light-saturated photosynthetic rates than shade leaves. Elevated CO2 strongly stimulated light-saturated photosynthesis of sun and shade leaves in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leaves was mon than double the relative enhancement of shade leaves. Elevated CO2 stimulated apparent quantum yield by 30%. but there was no interaction between CO2 and leaf position. Daytime leaf-level carbon gain extrapolated from photosynthetic light response curves indicated that sun leaves were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.
s in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leav2376^3^Centritto,M^Lee,H S J^Jarvis,P G^1999^1^Long-term effects of elevated carbon dioxide concentration and provenance on four clones of Sitka spruce (Picea sitchensis). I. Plant growth, allocation and ontogeny^13^19^12^799-806^^^^^Oct^^^^^7511
1482^243^344^3447^360^361^376^422^439^634^s were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.
s in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leavA^7510^Four clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) from two provenances, at 53.2 degrees N (Skidegate a and Skidegate b) and at 41.3 degrees N (North Bend a and North Bend b), were grown near Edinburgh (55.5 degrees N), U.K., for three growing seasons in ambient (similar to 350 mu mol mol(-1)) and elevated (similar to 700 mu mol mol(-1)) CO2 concentrations under conditions of non-limiting water and nutrient supply. Bud phenology was not affected by elevated [CO2] in the second growing season, but in the third year, the duration of shoot extension growth in three of the four clones (North Bend clones and Skidegate a) was significantly shortened, because of the suppression of lammas growth. Saplings in elevated [CO2] had significantly greater dry masses of all components than saplings in ambient [CO2]. However, comparison of relative component dry masses between plants of similar size showed no effect of [CO2] treatment on plant allometric relationships. This finding, and the observed suppression of lammas growth by high [CO2] during the third growing season suggests that the main effect of increasing [CO2] is to accelerate sapling development. Clonal provenance did not affect dry mass production in ambient [CO2]. However in elevated [CO2] the more southerly clones significantly out-performed the more northerly clones when grown at a latitude close to the latitudinal provenance of the Skidegate clones. As atmospheric carbon dioxide concentration rises, such changes in the relative performance of genotypes may be exploited for economic gain through appropriate selection of provenances for forest plantings.

2377^2^Centritto,M^Jarvis,P G^1999^1^Long-term effects of elevated carbon dioxide concentration and provenance on four clones of Sitka spruce (Picea sitchensis). II. Photosynthetic capacity and nitrogen use efficiency^13^19^12^807-814^^^^^Oct^^^^^7513
130^344^3448^360^361^384^417^439^639^813^no effect of [CO2] treatment on plant allometric relationships. This finding, and the observed suppressA^7512^Four clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) from two provenances, at 53.2 degrees N (Skidegate a and Skidegate b) and at 41.3 degrees N (North Bend a and North Bend b, were grown for three growing seasons in ambient (similar to 350 mu mol mol(-1)) and elevated (similar to 700 mu mol mol(- 1)) CO2 concentrations. The clones were grown in stress-free conditions (adequate nutrition and water) to assess the effect of elevated [CO2] on tree physiology. Growth in elevated [CO2] significantly increased instantaneous photosynthetic rates of the clonal Sitka spruce saplings by about 62%. Downward acclimation of photosynthesis (A) was found in all four clones grown in elevated [CO2]. Rubisco activity and total chlorophyll concentration were also significantly reduced in elevated [CO2]. Provenance did not influence photosynthetic capacity. Best-fit estimates of J(max) (maximum rate of electron transport), V-cmax (RuBP-saturated rate of Rubisco) and A(max) (maximum rate of assimilation) were derived from responses of A to intercellular [CO2] by using the model of Farquharetal.(1980). At any leaf N concentration, the photosynthetic parameters were reduced by growth in elevated [CO2]. However, the ratio between J(max) and V-cmax was unaffected by CO2 growth concentration, indicating a tight coordination in the allocation of N between thylakoid and soluble proteins. In elevated [CO2] the more southerly clones had a higher initial N use efficiency (more carbon assimilated per unit of leaf N) than the more northerly clones, so that they had more N available for those processes or organs that were most limiting to growth at a particular time. This may explain the initial higher growth stimulation by elevated [CO2] in the North Bend clones than in the Skidegate clones.

2378^4^Kellogg,E A^Farnsworth,E J^Russo,E T^Bazzaz,F^1999^1^Growth responses of C-4 grasses of contrasting origin to elevated CO2^52^84^3^279-288^^^^^Sep^^^^^7515
312^344^3449^3450^376^384^386^417^685^813^um rate of assimilation) were deriA^7514^Nine grass species representing three independent origins of the C-4 photosynthetic pathway were grown at ambient (350 ppm) and elevated (700 ppm) CO2 and were harvested after flowering. Setaria and Arundinella are both members of the subfamily Panicoideae, and represent a single origin of the pathway. Aristida and Stipagrostis are sister genera in the subfamily Aristidoideae (formerly classified in subfamily Arundinoideae), and represent a second origin. Sporobolus, a member of the subfamily Chloridoideae, represents the third. By investigating two genera each within Panicoideae and Aristidoideae, we test the hypothesis that genera sharing the same origin of C-4 respond similarly. To explore variation among congeneric species, five species of Setaria were also examined to test the hypothesis that congeneric species have similar responses. Plant height and numbers of tillers, branches and inflorescences were measured, both over time and at final harvest. Biomass of roots, shoots, and inflorescences was also measured. Members of the Aristidoideae were generally significantly larger in elevated CO2, as indicated by measurements of biomass and plant height, whereas representatives of the Panicoideae varied considerably in their response. The two subfamilies differed significantly in their responses to elevated CO2 and this effect outweighed any effect of CO2 alone. Sporobolus, though equally distantly related to Panicoideae and Aristidoideae, had a CO2 response similar to that of some panicoid species. Even within the genus Setaria, some species were significantly smaller at elevated than at ambient CO2, whereas others were larger. This may reflect diversity in internal regulation rather than acclimation or changes in source-sink allocation of carbon. The variation complicates any prediction of responses of C-4 plants to future atmospheric change. Comparison of closely related species, however, may well lead to intriguing new insights into how regulatory pathways of CO2 assimilation are modified during evolution. (C) 1999 Annals of Botany Company.

2379^2^Barrett,D J^Gifford,R M^1999^1^Increased C-gain by an endemic Australian pasture grass at elevated atmospheric CO2 concentration when supplied with non- labile inorganic phosphorus^92^26^5^443-451^^^^^^^^^^7517
243^2508^2590^3451^3452^3453^360^640^666^92^evated CO2 and this effect outweighed any effect of CO2 alone. Sporobolus, though equally distantly related to Panicoideae and Aristidoideae, had a CO2 response similar to that of some panicoid species. Even within the genus Setaria, some species were significantly smaller at elevated than at ambient CO2, whereas others were larger. This may reflect diversity in internal regulation rather than acclimation or changes in source-sink allocation of carbon. The variation complicates any prediction of responses of C-4 plants to future atmospheric change. Comparison of closely related species, however, may well lead to intriguing new insights into how regulatory pathways of CO2 assimilation are modified during evolA^7516^Limited phosphorus (P) availability in Australia's highly weathered soils may constrain an increase in terrestrial net primary productivity (NPP) with the globally increasing atmospheric CO2 concentration. We examined whether an Australian temperate pasture grass (Danthonia richardsonii) grown in sand culture and supplied solely with virtually insoluble Al- and Fe-phosphate was able to increase C-gain when exposed to elevated (731 mu mol mol(-1)) compared with ambient (379 mu mol mol(-1)) CO2 concentrations. When supplied with 8 mg kg(-1) insoluble P concentration, total citrate efflux by root systems (mu mol h(-1)), plant P uptake, shoot photosynthesis rates and plant mass were all significantly greater at elevated than at ambient CO2 after a growth period of between 55 and 63 days. In this treatment, although the P concentration of the rooting medium limited growth at ambient CO2, elevated CO2 increased P-uptake from the non-labile source, increased photosynthesis rates per unit shoot soluble-P and increased plant mass. At P concentrations lower than 8 mg kg(-1), plant mass, specific citrate efflux and maximum leaf carboxylation rates were limited by the amount of P available in the rooting medium and no CO2 effect was observed. In all treatments, carbon supply did not appear to limit citrate efflux. Where an increase in P uptake at elevated CO2 was achieved, it was due to an increase in root mass (indicative of a potentially larger soil volume explored) rather than to increased specific rates of citrate efflux. Above 8 mg kg(-1), the supplied P concentration was sufficient that minimal rates of specific citrate efflux alone solubilised enough P for growth and a strong CO2 effect on plant mass, photosynthesis and P uptake was observed.

2380^5^Oltchev,A^Ibrom,A^Morgenstern,K^Kreilein,H^Gravenhorst,G^1999^1^Evaluation of the response of a spruce forest ecosystem on climatic changes: Results of modelling experiments^379^24^1-2^103-110^^^^^^^^^^7519
349^377^425^nthesis rates per unit shoot soluble-P and A^7518^The physical and chemical environment of forests will change in the future. How forests will react to new conditions is not known yet. In order to get an idea of the sensitivity of present forests to possible atmospheric changes, it is helpful to investigate the physiological response of forest ecosystem to a change of key environmental parameters. In order to estimate the response of a mountain spruce forest to different atmospheric conditions during the summer a six-layer non- steady-state SVAT model (SLODSVAT) was used Eight scenarios were used for modelling energy and mass exchange during an eleven day summer period, combining different combinations of microclimatic conditions. All atmospheric scenarios were examined for three various CO2 mixing ratio levels: 350ppm (current condition), 450ppm and 550ppm. A scenario "0" assuming the current climatic features at different CO2 contents was considered as well. Structural and physiological adaptation of the forest to the new atmospheric conditions were not taken into account. For all scenarios the modelling results show increased net CO2 flux into the forest with increasing ambient CO2 concentration. Maximum net CO2 uptake was simulated for dry climate scenarios. Transpiration and evapotranspiration rates had similar trends independently of the ambient CO2 concentration used: at cold and wet conditions they decreased, while at warm and dry conditions transpiration and evapotranspiration rates increased The influence of CO2 concentrations on transpiration rates is of minor importance if compared to changes of temperature, water vapour pressure, cloud amount and atmospheric precipitation as considered in this investigation. (C) 1998 Elsevier Science Ltd. All rights reserved.

2381^6^de la Vina,G^Pliego-Alfaro,F^Driscoll,S P^Mitchell,V J^Parry,M A^Lawlor,D W^1999^1^Effects of CO2 and sugars on photosynthesis and composition of avocado leaves grown in vitro^184^37^7-8^587-595^^^^^Jul-Aug^^^^^7521
1247^1437^3454^417^424^441^448^781^801^845^ric conditions werA^7520^The effects of micropropagation conditions on avocado (Persea americana Mill.) have been measured in leaves and plants cultured in vitro. The consequences of the type and concentration of sugar in the medium and of carbon dioxide concentration in the atmosphere on the rates of photosynthesis and amounts of ribulose 1,5-biphosphate carboxylase-oxygenase (EC 4.1.1.39; Rubisco) and total soluble protein (TSP) were measured. At the highest sucrose supply (87.6 mM), Rubisco content was substantially decreased in leaves, and even more when elevated CO2 (1 000 mu mol mol(-1)) was supplied. Maximum photosynthetic rate (P-max) was significantly decreased when plants developed in high sucrose and elevated CO2. However, Rubisco concentration was significantly greater when glucose was supplied at the same molar concentration or when the concentration of sucrose was small (14.6 mM), and no differences were observed due to the CO2 concentration in the air in these treatments. The ratio of Rubisco to total soluble protein (Rubisco/TSP) was dramatically decreased in plants grown in the highest concentration of sucrose and with elevated CO2. Leaf area and ratio of leaf fresh weight/(stem + root) fresh weight, were greater in plants grown with CO2, enriched air. However, upon transplanting, survival was poorer in plants grown on low sucrose/high CO2 compared to those grown on high sucrose/high CO2. (C) Elsevier, Paris.

2382^3^Van der Kooij,T A W^De Kok,L J^Stulen,I^1999^1^Biomass production and carbohydrate content of Arabidopsis thaliana at atmospheric CO2 concentrations from 390 to 1680 mu l l(-1)^380^1^4^482-486^^^^^Jun^^^^^7523
243^244^2601^312^360^372^618^632^742^92^ants developed in high sucrose and elevated CO2. However, Rubisco concentration was significantly greater when glucose was supplied at the same molar concentration or when the concentration of sucrose was small (14.6 mM), and no differences were observed due to the CO2 concentration in the air in these treatments. The ratio of Rubisco to total soluble pA^7522^The concentration dependency of the impact of elevated atmospheric CO2 concentrations on Arabidopsis thaliana L. was studied. Plants were exposed to nearly ambient (390), 560, 810, 1240 and 1680 mu l l(-1) CO2 during the vegetative growth phase for 8 days. Shoot biomass production and dry matter content were increased upon exposure to elevated CO2. Maximal increase in shoot fresh and dry weight was obtained at 560 mu l l(-1) CO2, which was due to a transient stimulation of the relative growth rate for up to 3 days. The shoot starch content increased with increasing CO2 concentrations up to two-fold at 1680 mu l l(-1) CO2, whereas the contents of soluble sugars and phenolic compounds were hardly affected by elevated CO2. The chlorophyll and carotenoid contents were not substantially affected at elevated CO2 and the chlorophyll a/b ratio remained unaltered. There was no acclimation of photosynthesis at elevated CO2; the photosynthetic capacity of leaves, which had completely developed at elevated CO2 was similar to that of leaves developed in ambient air. The possible consequences of an elevated atmospheric CO2 concentration to Arabidopsis thaliana in its natural habitat is discussed.

2383^1^Mortensen,L M^1999^1^Effects of different carbon dioxide and ozone concentrations on shoot growth of Phleum pratense L. and Betula pubescens Ehrh. as influenced by day length and irradiance^200^49^1^50-56^^^^^Mar^^^^^7525
130^2259^243^3146^3455^361^374^376^417^o a transient stimulation of the relative growth rate for up to 3 days. The shoot starch content increased with increasing CO2 concentrations up to two-fold at 1680 mu l l(-1) CO2, whereas the contents of soluble sugars and phenolic compounds were hardly affected by elevated CO2. The chlorophyll and carotenoid contents were not substantially affected at elevated CO2 and the chlorophyll a/b ratio remained unaltered. There was no acclimation of photosynthesis at elevated CO2; the photosynthetic capacity of leaves, which had completely developed at elevated CO2 waA^7524^Seedlings of Phleum pratense L. (timothy) and Betula pubescens Ehrh. (mountain birch) were grown for 37 or 42 days at all combinations of two CO2 concentrations (350 and 700 mu mol mol(-1)), two O-3 concentrations (13 and 59 nmol mol(-1) in 8 h day(-1)), two day lengths (17 and 24 h DL) and two levels of supplementary lighting (150 and 210 mu mol m(-2) s(-1) photosynthetic photon flux, PPF) in 16 growth chambers placed in a greenhouse. Elevated CO2 concentration increased the mean shoot dry weight by 47% in timothy and by 39% in birch. No significant interactions were found between CO2 and O-3, DL or PPF with respect to shoot dry weight in the two species. The number of shoots in timothy was generally enhanced by CO2 enrichment. The number of branches in birch was strongly enhanced by elevated CO2 at 17 but not at 24 h DL, and the ratio of the fresh weight of branches to main shoot was significantly increased irrespective of DL, Increasing the O-3 concentration caused visible leaf injuries both in timothy (chlorosis/necrosis) and in birch (yellow stipples/brown spots), while the shoot weight was not significantly affected. The number of O-3-induced injuries in timothy was decreased by increasing the CO2 concentration or the total irradiance (increasing DL and/or PPF). The number of injuries in birch was slightly decreased by increasing PPF; however, CO2 enrichment had no effect.

2384^4^Mansfield,J L^Curtis,P S^Zak,D R^Pregitzer,K S^1999^1^Genotypic variation for condensed tannin production in trembling aspen (Populs tremuloides, Salicaceae) under elevated CO2 and in high- and low-fertility soil^5^86^8^1154-1159^^^^^Aug^^^^^7527
1142^2552^2975^344^3456^3457^3458^3459^373^690^ots in timothy was generally enhanced by CO2 enrichment. The number of branches in birch was strongly enhanced by elevated CO2 at 17 but not at 24 h DL, and the ratio of the fresh weight of branches to main shoot was significantly increased irrespective of DL, Increasing the O-3 concentration caused visible leaf injuries both in timA^7526^The carbon/nutrient balance hypothesis suggests that leaf carbon to nitrogen ratios influence the synthesis of secondary compounds such as condensed tannins. We studied the effects of rising atmospheric carbon dioxide on carbon to nitrogen ratios and tannin production. Six genotypes of Populus tremuloides were grown under elevated and ambient CO2 partial pressure and high- and low-fertility soil in field open-top chambers in northern lower Michigan, USA. During the second year of exposure, leaves were harvested three times (June, August, and September) and analyzed for condensed tannin concentration. The carbon/nutrient balance hypothesis was supported overall, with significantly greater leaf tannin concentration at high CO2 and low soil fertility compared to ambient CO2 and high soil fertility. However, some genotypes increased tannin concentration at elevated compared to ambient CO2, while others showed no CO2 response. performance of lepidopteran leaf miner (Phyllonorycter tremuloidiella) larvae feeding on these plants varied across genotypes, CO2, and fertility treatments. These results suggest that with rising atmospheric CO2, plant secondary compound production may vary within species. This could have consequences for plant-herbivore and plant-microbe interactions and for the evolutionary response of this species to global climate change.

2385^2^Zaller,J G^Arnone,J A^1999^1^Interactions between plant species and earthworm casts in a calcareous grassland under elevated CO2^11^80^3^873-881^^^^^Apr^^^^^7529
1073^2091^3460^3461^3462^374^427^672^977^r) and analyzed for condensed tannin concentration. The carbon/nutrient balance hypothesis was supported overall, with significantly greater leaf tannin concentration at high CO2 and low soil fertility compared to ambient CO2 and high soil fertility. However, some genotypes increased tannin concentration at elevated compared to ambient CO2, while others showed no CO2 response. performance of lepidopteran leaf miner (Phyllonorycter tremuloidiella) larvae feA^7528^We tested the hypothesis that the spatial proximity of a plant species to nutrient-rich earthworm casts (e.g., 100% more ammonium and 30% more phosphate than in adjacent soil) is an important determinant of a plant's responsiveness to elevated atmospheric CO2. In 1995 we mapped the location of both earthworm surface casts and plants in each of 16 1.2-m(2) plots in a species-rich calcareous grassland in northwestern Switzerland. Eight plots have been maintained under current ambient CO2 concentrations (350 mu L CO2/ L), and eight have been maintained at elevated CO2 (600 mu L CO2/L) since March 1994. in addition, total ramet production of each species, as a measure of performance, and cumulative cast production at each location (cell) were recorded at peak community biomass in 1995. Plant species within functional groups (graminoids, non- legume forbs, and legumes) differed markedly in their degree of association with casts; however, after two growing seasons elevated CO2 had no effect on plant species or functional group associations with casts. No statistically significant relationship could be demonstrated between plant-species response (i.e., ramet production) to elevated CO2 and the degree of association with casts within any of the functional groups. However, a positive relationship was observed between the mean response of graminoid species to elevated CO2 (measured as the percentage change in mean total ramet production of graminoid species, relative to mean total ramet production at ambient CO2) and their mean degree of association (%) with surface casts at ambient CO2. Thus, graminoid species more frequently associated with casts (e.g., Anthoxanthum odoratum and Carer caryophyllea) produced more ramets per square meter at elevated CO2 than those less frequently associated with casts (e.g., Agrostis tenuis and Danthonia decumbens). These results, along with the strong and significant positive correlations observed between ramet production and associated cumulative cast mass across CO2 treatments for most plant species in all functional groups demonstrate: (1) that plant species differ significantly in their degree of association with nutrient-rich earthworm surface casts, regardless of the relative abundance of plant species in the community; (2) that graminoid species that are more highly associated with casts may respond more strongly to rising CO2 than those less highly associated with casts; and (3) that nutrient-rich earthworm casts stimulate the growth (ramet production) of most plant species in these grassland communities, even at current levels of atmospheric CO2. The data further suggest that these species-specific relationships between plants and casts have helped define the current structure of these highly diverse grassland communities and will likely influence their future structure as global CO2 levels continue to rise.

2386^4^Kickert,R N^Tonella,G^Simonov,A^Krupa,S V^1999^1^Predictive modeling of effects under global change^35^100^1-3^87-132^^^^^^^^^^7531 mass across CO2 treatments 1134^1649^2925^3149^3463^3464^3465^372^377^696^demonstrate: (1) that plant species differ significantly in their degree of association with nutrient-rich earthworm surface casts, regardless of the relative abundance of plant species in the community; (2) that graminoid species that are more highly associated with casts may respond more strongly to rising CO2 than those less highly associated with casts; and (3) that nutrient-rich earthworm casts stimulate the growth (ramet production) of most plant species in these grassland communities, even at current levels of atmospheric CO2. The data further suggest that these species-specific relationships between plants and casts have helped define the current structure of these highly diverse grassland communities and will likely influence their future structure as global CO2 levels continue to rise.

2386^4^Kickert,R N^Tonella,G^Simonov,A^Krupa,S V^1999^1^Predictive modeling of effects under global change^35^100^1-3^87-132^^^^^^^^^^7531 mass across CO2 treatments A^7530^The status of computer simulation models from around the world for evaluating the possible ecological, environmental, and societal consequences of global change is presented in this paper. In addition, a brief synopsis of the state of the science of these impacts is included. Issues considered include future changes in climate and patterns of land use for societal needs, Models dis cussed relate to vegetation (e.g, crop), soil, bio-geochemistry, water, and wildlife responses to conventional, forecasted changes in temperature and precipitation. Also described are models of these responses, alone and interactively, to increased CO2, other air pollutants and UV-B radiation, as the state of the science allows. Further, models of land-use change are included. Additionally, global multiple sector models of environment, natural resources, human population dynamics, economics, energy, and political relations are reviewed for integrated impact assessment. To the extent available, information on computer software and hardware requirements is presented for the various models. The paper concludes with comments about using these technologies as they relate to ecological risk assessment for policy decision analysis. Such an effort is hampered by considerable uncertainties with the output of existing models, because of the uncertainties associated with input data and the definitions of their dose-response relationships. The concluding suggestions point the direction for new developments in modeling and analyses that are needed for the 21st century. (C) 1999 Elsevier Science Ltd. All rights reserved.

2387^4^Navas,M L^Garnier,E^Austin,M P^Gifford,R M^1999^1^Effect of competition on the responses of grasses and legumes to elevated atmospheric CO2 along a nitrogen gradient: differences between isolated plants, monocultures and multi- species mixtures^84^143^2^323-331^^^^^Aug^^^^^7533
1030^188^2070^3466^3467^376^738^92^957^e reviewed for integrated impact assessment. To the extent available, information on computer softwaA^7532^The responses to CO2 of perennial grasses (Danthonia richardsonii and Phalaris aquatica) and legumes (Lotus pedunculatus and Trifolium repens) were compared under controlled conditions for isolated plants, monoculture stands and mixed-species stands along a N gradient to test whether: plant-plant interactions between species in mixed stands changed with concentration of CO2; responses to CO2 of species in mixtures could be related to their responses as single stands; responses of mixtures to CO2 could be related to the responses of individual species to CO2 and to competition. Plants were grown for 60 d in sand, using nutrient solutions (six nitrate concentrations from 0.25 to 16 mM NO3), at ambient (c. 357 mu l l(-1)) or elevated CO2 (c. 712 mu l l(-1)). Species dominance in the mixtures depended more on the range of N than of CO2 concentration provided: T. repens and L. pedunculatus dominated at low concentrations of N; L. pedunculatus and P. aquatica performed better at high concentrations. Responses of species in mixtures to CO2 were related to their responses in monocultures but not to those of isolated plants. Species biomass proportions in mixtures under ambient CO2 determined the outcome of mixture responses to CO2 more than of individual species responses to CO2. These results emphasize the influence of plant-plant interactions on community responses to CO2, since mixture behaviour under elevated CO2 could not be scaled-up from responses by isolated plants in this experiment.

2388^2^Roberntz,P^Linder,S^1999^1^Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. II. Foliar chemistry^252^14^1^17-27^^^^^Jul^^^^^7535
2173^256^348^374^417^526^605^705^733^92^, at ambient (c. 357 mu l l(-1)) or elevated CO2 (c. 712 mu l l(-1)). Species dominance in the mixtures depended more on the range of N than of CO2 concentration provided: T. repens and L. pedunculatus dominated at low concentrations of N; L. pedunculatus and P. aquatica performed better at high concentrations. ResponsA^7534^Branches on 30-year-old Norway spruce trees [Picea abies (L.) Karst.] were exposed to ambient (AMB) or ambient plus 350 mu mol CO2 mol(-1) (EL) for 4 years (except winters), using the branch bag technique (BB). The trees were growing on plots with low (control) and high (irrigated-fertilised) availability of soil nutrients. The seasonal variation in foliar macronutrients and non-structural carbohydrates in current and 1-year-old shoots was monitored throughout the treatment period. When the branches were harvested at the end of treatment, macronutrients were analysed in five age classes of foliage. The concentration of all elements, except magnesium, generally increased in AMB, i.e. a 'bag effect', but decreased as an effect of EL, i.e. a 'CO2 effect'. At the final harvest K, P, N and S were reduced in young needles by EL, whereas Mg was reduced in older needles on both plots. A change in needle morphology by EL possibly caused a dilution effect in irrigated-fertilised needles, but not in control needles. Reductions in K and Mg are suggested to be an effect of increased phloem transport from the branch, in consequence of higher rates of carbon fixation in EL. Foliage in BBs had higher concentration of Ca, but there was no significant effect of the EL-treatment, indicating that elevated CO2 had no effect on stomatal conductance. Quinic acid concentration decreased, but shikimic acid concentration increased in BBs, independently of CO2 treatment. Concentrations of starch and sugars increased in the EL- treatment, but pinitol decreased.

2389^4^Herbert,D A^Rastetter,E B^Shaver,G R^Agren,G I^1999^1^Effects of plant growth characteristics on biogeochemistry and community composition in a changing climate^356^2^4^367-382^^^^^Jul-Aug^^^^^7537
146^1895^3468^3469^374^57^715^737^795^892^ P, N and S were reduced in young needles by EL, whereas Mg was reduced in older needles on both plots. A change in needle morphology by EL possibly caused a dilution effect in irrigated-fertilised needles, but not in control needA^7536^Vegetation growth characteristics influence ecosystem biogeochemistry and must be incorporated in models used to project biogeochemical responses to climate variations. We used a multiple-element limitation model (MEL) to examine how variations in nutrient use efficiency (NUE) and net primary production to biomass ratio (nPBR) affect changes in ecosystem C stocks after an increase in temperature and atmospheric CO2. nPBR influences the initial rates of response, but the magnitude and direction of long-term responses are determined NUE. MEL was used to simulate responses to climate change in communities composed of two species differing in nPBR and/or NUE. When only nPBR differed between the species, the high-nPBR species outgrew the low-nPBR species early in the simulations, but the shift in dominance was transitory because of secondary N limitations. High-NUE and were therefore favored under elevated CO2. Increased temperature stimulated N release from soil organic matter (SOM) and therefore favored low-NUE species. The combined release from C and N limitation under the combination of increased temperature and elevated CO2 favored high-NUE species. High C:N litter from high-NUE species limited the N-supply rate from SOM, which favors the dominance of the high-NUE species in the short term. However, in the long term increased litter production resulted in SOM accumulation, which reestablished a N supply rate favorable to the reestablishment and dominance of the low-NUE species. Conditions then reverted to a state favorable to the high-NUE species.

2390^2^Matsueda,H^Inoue,H Y^1999^1^Aircraft measurements of trace gases between Japan and Singapore in October of 1993, 1996, and 1997^65^26^16^2413-2416^^^^^15 Aug^^^^^7539
176^3470^3471^3472^3473^3474^3475^3476^3477^893^mulations, but the shift in dominance was transitory because of secondary N limitations. High-NUE and were therefore favored under elevated CO2. Increased temperature stimulated N release from soil organic matter (SOM) and therefore favored A^7538^Carbon dioxide (CO2) methane (CH4), and carbon monoxide (CO) mixing ratios were measured in discrete air samples from aircraft between Japan and Singapore in October. The mixing ratios of all trace gases at 9-12 km were enhanced over the South China Sea in 1997 compared with those in 1993 and 1996. Vertical distributions of all trace gases over Singapore in 1997 also showed largely elevated mixing ratios at all altitudes. These distributions indicate a wide outflow of trace gases from intense biomass burning in the southeast Asia regions in the very strong El Nino year. The enhanced trace gases showed a strong linear correlation between CH4 and CO, and between CO and CO2, with the regression slopes of 0.051 Delta CH(4)ppb/Delta COppb) and 0.089 (Delta COppb/Delta CO(2)ppb). The emission ratios are characteristic of fires with relatively lower combustion efficiency from the tropical rain forest and peat lands in Kalimantan and Sumatra of Indonesia.
from soil organic matter (SOM) and therefore favored 2391^3^Carter,E B^Theodorou,M K^Morris,P^1999^1^Responses of Lotus corniculatus to environmental change. 2. Effect of elevated CO2, temperature and drought on tissue digestion in relation to condensed tannin and carbohydrate accumulation^269^79^11^1431-1440^^^^^Aug^^^^^7541
1793^244^3478^3479^3480^3481^3482^3483^829^92^butions of all trace gases over Singapore in 1997 also showed largely elevated mixing ratios at all altitudes. These distributions indicate a wide outflow of trace gases from intense biomass burning in the southeast Asia regions in the very strong El Nino year. The enhanced trace gases showed a strong linear correlation between CH4 and CO, and between CO and CO2, with the regression slopes of 0.051 Delta CH(4)ppb/Delta COppb) and 0.089 (Delta COppb/Delta CO(2)ppb). The emission ratios are characteristic of fires with relatively lower combustion efficiency from the tropical rain forest and peat lands in Kalimantan and Sumatra of Indonesia.
from soil organic matter (SOM) and therefore favored A^7540^Clonal plants of three genotypes of Lotus corniculatus (cv Lee) were grown in eight controlled environments under combinations of two temperature regimes, two CO2 concentrations and two watering regimes. Condensed tannins (proanthocyanidins), in- vitro digestibility, initial rates of gas evolution las an indicator of the initial rates of fermentation of the substrate), volatile fatty acid evolution, and non-structural carbohydrate (NSC) levels were determined in leaves, stems and roots at full flowering. Under control conditions (average midsummer conditions in the United Kingdom) the total condensed tannin content of leaves varied six-fold between genotypes but condensed tannin contents in stems and roots were similar. Condensed tannin levels were significantly increased in leaves and stems of all three genotypes by doubling the CO2 concentration while raising the temperature towards the optimum for growth significantly reduced condensed tannin levels. Drought stress significantly reduced condensed tannin levels in leaves and, particularly, in roots. Nutritive value was inversely related to condensed tannin levels in leaves and a negative relationship was observed between condensed tannin concentrations of more than 25-30 g kg(-1) dry matter and the initial rates of gas evolution when subjected to in-vitro fermentation with rumen micro-organisms. In leaves, digestibility was significantly increased by drought and by increasing temperature but reduced by high CO2. In stems, digestibility was significantly increased by drought, but not significantly affected by increasing temperature, or by high CO2 alone. In roots, digestibility was significantly increased by drought, and decreased by increasing temperature or CO2. Increasing the growth temperature towards optimum growth reduced the content of NSC in all tissues with the greatest changes occurring in root tissue. Doubling the CO2 concentration increased NSC levels in leaves and stems with starch content more than doubled under high CO2 while, in roots, increased levels were only observed in combination with drought stress. There was a linear correlation between condensed tannin concentration and total NSC that was positive for leaves, neutral for stems and negative for roots. The relationship between carbohydrate levels and rates of gas production was negative for leaves and positive for stem and roots. (C) 1999 Society of Chemical Industry.

2392^3^Zhu,J^Goldstein,G^Bartholomew,D P^1999^1^Gas exchange and carbon isotope composition of Ananas comosus in response to elevated CO2 and temperature^9^22^8^999-1007^^^^^Aug^^^^^7543
1669^1859^188^243^310^362^58^749^779^92^, digestibility was significantly increased by drought, and decreased by increasing temperature or CO2. Increasing the growth temperature towards optimum growth reduced the content of NSC in all tissues with the greatest changes occurring in root tissue. Doubling the CO2 concentration increased NSC levels in leaves and stems with starch content more than doubled under high CO2 while, in roots, iA^7542^Ananas comosus L. (Merr.) (pineapple) was grown at three day/night temperatures and 350 (ambient) and 700 (elevated) mu mol mol(-1) CO2 to examine the interactive effects of these factors on leaf gas exchange and stable carbon isotope discrimination (Delta,parts per thousand). All data were collected on the youngest mature leaf for 24 h every 6 weeks. CO2 uptake (mmol m(-2) d(-1)) at ambient and elevated CO2, respectively, were 306 and 352 at 30/20 degrees C, 175 and 346 at 30/25 degrees C and 187 and 343 at 35/25 degrees C, CO2 enrichment enhanced CO2 uptake substantially in the day in all environments. Uptake at night at elevated CO2, relative to that at ambient CO2, was unchanged at 30/20 degrees C, but was 80% higher at 30/25 degrees C and 44% higher at 35/25 degrees C suggesting that phosphoenolpyruvate carboxylase was not CO2- saturated at ambient CO2 levels and a 25 degrees C night temperature. Photosynthetic water use efficiency (WUE) was higher at elevated than at ambient CO2. Leaf Delta-values were higher at elevated than at ambient CO2 due to relatively higher assimilation in the light, Leaf Delta was significantly and linearly related to the fraction of total CO2 assimilated at night. The data suggest that a simultaneous increase in CO2 level and temperature associated with global warming would enhance carbon assimilation, increase WUE, and reduce the temperature dependence of CO2 uptake by A. comosus.

2393^4^Hymus,G J^Ellsworth,D S^Baker,N R^Long,S P^1999^1^Does free-air carbon dioxide enrichment affect photochemical energy use by evergreen trees in different seasons? A chlorophyll fluorescence study of mature loblolly pine^8^120^4^1183-1191^^^^^Aug^^^^^7545
1812^1998^2402^343^348^3484^372^444^639^713^ higher at 30/25 degrees C and 44% higher at 35/25 degrees C suggesting that phosphoenolpyruvate carboxylase was not CO2- saturated at ambient CO2 levels and a 25 degrees C night temperature. Photosynthetic water use efficiency (WUE) was higher at elevated than at ambient CO2. Leaf Delta-valuA^7544^Previous studies of the effects of growth at elevated CO2 on energy partitioning in the photosynthetic apparatus have produced conflicting results. The hypothesis was developed and tested that elevated CO2 increases photochemical energy use when there is a high demand for assimilates and decreases usage when demand is low. Modulated chlorophyll a fluorescence and leaf gas exchange were measured on needles at the top of a mature, 12-m loblolly pine (Pinus taeda L.) forest. Trees were exposed to ambient CO2 or ambient plus 20 Pa CO2 using free-air CO2 enrichment. During April and August, periods of shoot growth, light-saturated photosynthesis and linear electron transport were increased by elevated CO2. In November, when growth had ceased but temperatures were still moderate, CO2 treatment had no significant effect on linear electron transport. In February, when low temperatures were likely to inhibit translocation, CO2 treatment caused a significant decrease in linear electron transport. This coincided with a slower recovery of the maximum photosystem II efficiency on transfer of needles to the shade, indicating that growth in elevated CO2 induced a more persistent photoinhibition. Both the summer increase and the winter decrease in linear electron transport in elevated CO2 resulted from a change in photochemical quenching, not in the efficiency of energy transfer within the photosystem II antenna. There was no evidence of any effect of CO2 on photochemical energy sinks other than carbon metabolism. Our results suggest that elevated CO2 may increase the effects of winter stress on evergreen foliage.

2394^3^van Oene,H^Berendse,F^de Kovel,C G F^1999^1^Model analysis of the effects of historic CO2 levels and nitrogen inputs on vegetation succession^56^9^3^920-935^^^^^Aug^^^^^7547
1660^227^2285^312^3485^372^600^669^672^92^linear electron transport. In February, when low temperatures were likely to inhibit translocation, CO2 treatment caused a significant decrease in linear electron transport. This coincidedA^7546^(S)imulation models are useful to analyze and predict the effects of changes in atmospheric CO2 concentration and N deposition on terrestrial ecosystems. The effects of such abiotic changes on ecosystem variables such as nitrogen mineralization and carbon accumulation can affect plant species composition, which in turn may affect various ecosystem processes. However, these interacting effects of plant species composition on ecosystem processes and vice versa are often not included in simulation models. In this paper, a model is developed that includes both plant competition and the flows of nutrients, carbon, and water through the ecosystem. Direct effects of changing atmospheric CO2 on biomass, plant nitrogen concentrations, and litter quantity and quality are simulated together with indirect effects through changes in plant species composition. This model is validated against data from a primary succession chronosequence sere of Dutch inland dunes. For this validation, historical N deposition and atmospheric CO2 concentration records are used. Simulated plant species biomass, organic matter C and N, and total C and N accumulation were found to correspond to measured data. The model simulated plant species replacement well at the different sites of the chronosequence even though the historic conditions differed much between the sites. Additional analyses of the effect of N deposition (preindustrial to present-day) and elevated CO2 (preindustrial to present-day) in this ecosystem showed that N deposition had a strong effect both on vegetation development and on C and N accumulation. Compared to this, the stimulating effects of elevated CO2 on vegetation development were relatively small. Elevated CO2 affected early vegetation development, but the long-term response of vegetation development is dependent on N availability. In old mature forest, N deposition had only small effects while elevated CO2 delayed forest aging. Indirect effects of CO2 on C and N accumulation through changing plant competitive relations may ultimately be larger than direct CO2 effects.

2395^5^Niewiadomska,E^Gaucher-Veilleux,C^Chevrier,N^Mauffette,Y^Dizengremel,P^1999^1^Elevated CO2 does not provide protection against ozone considering the activity of several antioxidant enzymes in the leaves of sugar maple^4^155^1^70-77^^^^^Jul^^^^^7549
1064^1677^2125^2369^2473^2938^3033^312^3486^417^f the effect of N deposition (preindustrial to present-day) and elevated CO2 (preindustrial to present-day) in this ecosystem showed that N deposition had a strong effect both on vegetation development and on C and N accumulation. Compared to this, the stimulating effects of elevated CO2 on vegetation development were relatively small. Elevated CO2 affected early vegetation development, but the long-term response of vegetation development is dependent on N availability. In old mature forest, N deposition had only small effects while elevated CO2 delayed forest aging. Indirect effects of CO2 on C and N accumulation through changing plant competitive relA^7548^Seedlings of sugar maple (Acer saccharum Marsch.) were exposed for 46 days to 700 ppm of CO2, 200 ppb of ozone, and 700 ppm of CO2 + 200 ppb of ozone. A significant increase in the activity of H2O2 scavenging enzymes, i.e. ascorbate peroxidase [EC 1.11.1.11] and catalase [EC 1.11.1.6], was measured due to the action of O-3 This increase was rather negatively affected by elevated CO2. A tendency of decreased activity of glutathione reductase [EC 1.6.4.2] and superoxide dismutase [EC 1.15.1.1] due to the action of O-3 was detected. Elevated CO2 does not provide enhanced tolerance to oxidative stress in the seedlings of sugar maple. Changes in the activity of antioxidant enzymes were more pronounced in the young leaves (developed during the experiment) than in the old leaves (developed before starting the experiment). Stimulation of chloroplastic FeSOD by elevated CO2 was observed, indicating oxidative stress in chloroplasts evoked by elevated CO2 level. This effect did not result in enhanced protection against the detrimental effect of ozone, most probably due to compartmentation of CO2 and O-3 effects within the cell.

2396^5^Vu,J C V^Gesch,R W^Allen,L H^Boote,K J^Bowes,G^1999^1^CO2 enrichment delays a rapid, drought-induced decrease in Rubisco small subunit transcript abundance^4^155^1^139-142^^^^^Jul^^^^^7551
2346^243^3487^3488^356^360^372^377^845^951^atively affected by elevated CO2. A tendency of decreased activity of glutathione reductase [EC 1.6.4.2] and superoxide dismutase [EC 1.15.1.1] due to the action of O-3 was detected. Elevated CO2 does not provide enhanced tolerance to oxidative stress in the seedlings of sugar maple. Changes in the activity of antioxidant enzymes were more pronounced in the young leaves (developed during the experiment) than in the old leaves (developed before starting the experiment). Stimulation of chloroplastic FeSOD by elevated CO2 was observed, indicating oxidative stress in chloroplasts evoked by elevated CO2 level. This effect did not result in enhanced protection A^7550^Rice (Oryza sativa L. cv. IR-72) was grown in sunlit chambers at 350 and 700 mu mol CO2 mol(-1) under conditions of continuous flooding (control) or drought which was imposed at panicle initiation, to evaluate the effects of CO2 enrichment and soil water deficit on photosynthesis and Rubisco gene expression. Leaf and canopy photosynthetic rates were enhanced by high [CO2] but reduced by drought. High [CO2] and severe drought both reduced rbcS transcript abundance, along with the activity, activation and protein content of Rubisco, but the K- m (CO2) was not affected. The transition from moderate to severe drought caused a rapid decline, within 24 h, in the rbcS transcript abundance. High [CO2], however, delayed the adverse effects of severe drought on rbcS transcript abundance and activities of Rubisco, and permitted photosynthesis to continue for an extra day during the drought-stress cycle.
ative stress in chloroplasts evoked by elevated CO2 level. This effect did not result in enhanced protection 2397^3^Roderick,M L^Berry,S L^Noble,I R^1999^1^The relationship between leaf composition and morphology at elevated CO2 concentrations^84^143^1^63-72^^^^^Jul^^^^^7553
312^344^348^3489^374^393^57^641^860^92^ evaluate the effects of CO2 enrichment and soil water deficit on photosynthesis and Rubisco gene expression. Leaf and canopy photosynthetic rates were enhanced by high [CO2] but reduced by drought. High [CO2] and severe drought both reduced rbcS transcript abundance, along with the activity, activation and protein content of Rubisco, but the K- m (CO2) was not affected. The transition from moderate to severe drought caused a rapid decline, within 24 h, in the rbcS transcript abundance. High [CO2], however, delayed the adverse effects of severe drought on rbcS transcript abundance and activities of Rubisco, and permitted photosynthesis to continue for an extra day during the drought-stress cycle.
ative stress in chloroplasts evoked by elevated CO2 level. This effect did not result in enhanced protection A^7552^The composition and morphology of leaves exposed to elevated [CO2] usually change so that the leaf nitrogen (N) per unit dry mass decreases and the leaf dry mass per unit area increases. However, at ambient [CO2], leaves with a high leaf dry mass per unit area usually have low leaf hi per unit dry mass. Whether the changes in leaf properties induced by elevated [CO2] follow the same overall pattern as that at ambient [CO2] has not previously been addressed. Here we address this issue by using leaf measurements made at ambient [CO2] to develop an empirical model of the composition and morphology of leaves. Predictions from that model are then compared with a global database of leaf measurements made at ambient [CO2]. Those predictions are also compared with measurements showing the impact of elevated [CO2]. In the empirical model both the leaf dry mass and liquid mass per unit area are positively correlated with leaf thickness, whereas the mass of C per unit dry mass and the mass of N per unit liquid mass are constant. Consequently, both the N:C ratio and the surface area:volume ratio of leaves are positively correlated with the liquid content. Predictions from that model were consistent with measurements of leaf properties made at ambient [CO2] from around the world. The changes induced by elevated [CO2] follow the same overall trajectory. It is concluded that elevated [CO2] enhances the rate at which dry matter is accumulated but the overall trajectory of leaf development is conserved.

2398^3^Roumet,C^Laurent,G^Roy,J^1999^1^Leaf structure and chemical composition as affected by elevated CO2: genotypic responses of two perennial grasses^84^143^1^73-81^^^^^Jul^^^^^7555
1304^1380^2087^2346^2601^312^344^376^791^975^O2]. Those predictions are also compared with measurements showing the impact of elevated [CO2]. In the empirical model both the leaf dry mass and liquid mass per unit area are positively correlated with leaf thickness, whereas the mass of C per unit dry mass and the mass of N per unit liquid mA^7554^Genotypic variability was studied in two Mediterranean grass species, Bromus erectus and Dactylis glomerata, with regard to the response to CO2 of leaf total non-structural carbohydrate concentration ([TNC](1f)), specific leaf area (SLA), and leaf carbon and nitrogen concentrations ([C](1f) and [N](1f), respectively). Fourteen genotypes of each species were grown together on intact soil monoliths at ambient and elevated CO2 concentrations (350 and 700 mu mol mol(-1), respectively). In both species, the most consistent effect of elevated CO2 was an increase in [TNC](1f) and a decrease in leaf nitrogen concentration when expressed either as total dry mass [N- m](1f), structural dry mass [N(m)st](1f) or leaf area [N- a](1f). The SLA decreased only in D, glomerata, due to an accumulation of total nonstructural carbohydrates and to an increase in leaf density. No genotypic variability was found for any variable in B. erectus, suggesting that genotypes responded in a similar way to elevated CO2. In D. glomerata, a genotypic variability was found only for [Cst], [N-m](1f), [N(m)st](1f) and [N-a](1f). Since [N-m](1f) is related to plant growth and is a strong determinant of plant-herbivore interactions, our results suggest evolutionary consequences of elevated CO2 through competitive interactions or herbivory.

2399^2^Poorter,H^De Jong,R^1999^1^A comparison of specific leaf area, chemical composition and leaf construction costs of field plants from 15 habitats differing in productivity^84^143^1^163-176^^^^^Jul^^^^^7557
1074^188^348^3490^3491^372^427^439^587^867^ease in [TNC](1f) and a decrease in leaf nitrogen concentration when expressed either as total dry mass [N- m](1f), structural dry mass [N(m)st](1f) or leaf area [N- a](1f). The SLA decreased only in D, glomerata, due to an accumulation of total nonstructural carbohydrates and to an increase in leaf density. No genotypic variability was found for any variable in B. erectus, suggesting that genotypes responded in a similar way to elevated CO2. In D. glomeA^7556^Laboratory experiments have shown a large difference in specific leaf area (SLA, leaf area:leaf mass) between species from nutrient-poor and nutrient-rich habitats, but no systematic difference in the construction costs (the amount of glucose required to construct 1 g biomass). We examined how far these patterns are congruent with those from field-grown plants. An analysis was made of the vegetation in a range of grasslands and heathlands differing in productivity. The SLA of the dominant species in 15 different habitats was determined, as well as chemical composition and construction costs of bulk samples of leaves. SLA in the field was generally lower than in the laboratory, but showed consistency in that the ranking across species remained the same. Species from highly productive habitats had higher SLA than those from sites of low productivity, although individual species sometimes deviated substantially from the general trend. Construction costs were similar for plants from different habitats. This was mainly due to the positive correlation between an expensive class of compounds (proteins) and a cheap one (minerals).

2400^3^Bailey,S^Rebbeck,J^Loats,K V^1999^1^Interactive effects of elevated ozone plus carbon dioxide on duckweeds exposed in open-top chambers^185^99^2^19-25^^^^^Apr^^^^^7559
1828^264^3225^344^395^417^461^550^741^92^se from field-grown plants. An analysis was made of the vegetation in a range of grasslands and heathlands differing in productivity. The SLA of the dominant species in 15 different habitats was determined, as well as chemical composition and construction costs of bulk samples of leaves. SLA in the field was generally lower than in the laboratory, but showed consistency in that the ranking across species remained the same. Species from highly productive habitats had higher SLA than those from sites of low productivity, although individual species sometimes deviated substantially from the general trend. Construction costs were similar for plants from different habitats. ThA^7558^The response of Lemna minor L. and Spirodela polyrhiza (L.) Schleiden to projected future ambient levels of O-3 and CO2 was studied under field conditions. The two duckweed species were treated with either charcoal-filtered air (CF), ambient O-3 (lXO(3)), tn ice ambient O-3 (2XO(3)), twice ambient CO2 plus twice ambient O-3 (2XCO(2)+2XO(3)), or chamberless open-air (OA). Two experiments were conducted. In Experiment I, L. minor was treated for 15 d with a cumulative O-3 exposure of 14.4 ppm.h. No O-3 effects were observed during Experiment I. Dry weight of individual fronds and photosynthesis per frond increased in L minor exposed to 2XCO(2)+2XO(3)(-) air. In Experiment II after 25 d of treatment (cumulative O-3 exposure of 16.2 ppm h), negative effects of 2XO(3) on the photosynthetic and growth rates of L. minor were observed. Dark respiration of L minor significantly increased in 2XO(3)-air compared with controls, but declined significantly in 2XCO(2)+2XO(3)-air compared to those grown in 2XO(3)-air. Photosynthesis and drg weight per frond increased in 2XCO(2)+2XO(3)-air when compared with all other treatments. Measurement of A/C-i (assimilation versus intercellular CO2 concentration) curves in L. minor showed a significant reduction in carboxylation efficiency and maximum rates of photosynthesis in 2XCO(2)+2XO(3)-air compared with other treatments when expressed per weight. No differences in carboxylation efficiency were detected between treatments when expressed per frond. After 25 d of treatment, photosynthesis (per frond) and dry weight of S. polyrhiza were reduced in 2XO(3)-air, but final frond number was unaffected. Dark respiration of S. polyrhiza was unaffected in 2XO(3)(-) air, but when exposed to 2XCO(2)+2XO(3)-air, it declined significantly. Although S. polyrhiza photosynthesis per frond increased in 2XCO(2)+2XO(3)-air, dry weight was unaffected when compared with all other treatments. Only when comparisons were made between S. polyrhiza grown in 2XCO(2)+2XO(3)-air and 2XO(3)-air, were significant increases in dry weight observed. The addition of 2XCO(2) to 2XO(3)-air resulted in amelioration of negative O-3 effects for most responses for both duckweed species.

2401^3^Hussain,M W^Allen,L H^Bowes,G^1999^1^Up-regulation of sucrose phosphate synthase in rice grown under elevated CO2 and temperature^91^60^2-3^199-208^^^^^May^^^^^7561
230^243^244^344^348^360^374^388^430^813^ifferences in carboxylation efficiency were detected between treatments when expressed per frond. After 25 d of treatment, photosynthesis (per frond) and dry weight of S. polyrhiza were reduced in 2XO(3)-air, but final frond number was unaffected. Dark respiration of S. polyrhiza was unaffected in 2XO(3)(-) air, but when exposed to 2XCO(2)+2XO(3)-air, it declined significantly. Although S. polyrhiza photosynthesis per frond increased in 2XCO(2)+2XO(3)-air, dry weight was unaffected when compared with all other treatments. Only when comparisons were made between S. polyrhiza grown in 2XCO(2)+2XO(3)-air and 2XO(3)-air, were signiA^7560^Rice (Oryza sativa L. cv. IR-30) was grown season-long in outdoor, controlled-environment chambers at 33 Pa CO2 with day/night/paddy-water temperatures of 28/21/25 degrees C, and at 66 Pa CO2 with five different day/night/paddy-water temperature regimes (25/18/21, 28/21/25, 31/24/28, 34/27/31 and 37/30/34 degrees C). Sucrose phosphate synthase (SPS) activities in leaf extracts at 21, 48 and 81 days after planting (DAP) were assayed under saturating and selective (limiting) conditions. Diel SPS activity data indicated that rice SPS was light regulated; with up to 2.2-fold higher rates during the day. Throughout the growth season, leaf SPS activities were up-regulated in the CO2-enriched plants, averaging 20 and 12% higher than in ambient-CO2 grown plants in selective and saturating assays, respectively. Similarly, SPS activities increased 2.4% for each 1 degrees C rise in growth temperature from 25 to 34 degrees C, but decreased 11.5% at 37 degrees C. Leaf sucrose content was higher, and mirrored SPS activity better, than starch, although starch was more responsive to CO2 treatment. Leaf sucrose and starch contents were significantly higher throughout the season in plants at elevated CO2, but the N content averaged 6.5% lower. Increasing growth temperatures from 25 to 37 degrees C caused a linear decrease (62%) in leaf starch content, but not in sucrose. Consequently, the starch:sucrose ratio declined with growth temperature. The data are consistent with the hypothesis that the up-regulation of leaf SPS may be an acclimation response of rice to optimize the utilization and export of organic-C with the increased rates of inorganic-C fixation in elevated CO2 or temperature growth regimes.

2402^6^Santruckova,H^Santrucek,J^Kveton,J^Simkova,M^Elhottova,D^Rohacek,K^1999^1^Carbon balance of a winter wheat-root microbiota system under elevated CO2^79^36^3^341-354^^^^^^^^^^7563
1334^1364^243^344^374^376^384^407^57^92^rees C, but decreased 11.5% at 37 degrees C. Leaf sucrose content was higher, and mirrored SPS aA^7562^We examined the carbon budget of young winter wheat plants and their associated microorganisms as affected by a doubling of the atmospheric CO2 concentration (700 mu mol mol(-1)). Plants were grown hydroponically in pre-sterilised sand at a controlled irradiance and temperature regime. Net photosynthesis (P-N) and respiration (R-D) rates of roots and shoots were measured continuously, plant growth and carbon distribution in the plant-root medium-associated microorganism system were determined destructively in interval-based analyses. P-N in elevated CO2 grown plants (EC) was 123 % of that in the control (AC) plants when averaged over the whole life span (39-d-old plants, 34 d in EC), but the percentage varied with the developmental stage being 115, 88, and 167 % in the pretillering, tillering, and posttillering phase, respectively. There was a transient depression of P-N, higher amplitude of day/night fluctuations of the chloroplast starch content, and depression of carbon content in rhizosphere of EC plants during the period of tillering. After 34 d in EC, carbon content in shoots,'roots, and in rhizodepositions was enhanced by the factors 1.05, 1.28, and 1.96, respectively. Carbon partitioning between above and belowground biomass was not affected by EC, however, proportionally more C in the belowground partitioning was allocated into the root biomass, Carbon flow from roots to rhizodepositions and rhizosphere microflora was proportional to P-N; its fraction in daily assimilated carbon decreased from young (17 %) to older (3-4 %) plants.

2403^2^Coviella,C E^Trumble,J T^1999^1^Effects of elevated atmospheric carbon dioxide on insect-plant interactions^106^13^4^700-712^^^^^Aug^^^^^7565
1081^1089^1282^137^3186^3492^3493^3494^483^857^ stage being 115, 88, and 167 % in the pretillering, tillering, and posttillering phase, respectively. There was a transient depression of P-N, higher amplitude of day/night fluctuations of the chloroplast starch content, and depression of carbon content in rhizosphere of ECA^7564^In the enriched carbon dioxide atmosphere expected in the next century, many, species of herbivorous insects will confront less nutritious host plants that will induce both lengthened larval developmental times and greater mortality The limited data currently available suggest that the effect of increased atmospheric CO2 on herbivory will be nor only highly species- specific brit also specific to each insect-plant system. Several scenarios can be predicted however. (1) local extinctions will occur; (2) the endangered species status as well as the pest status of some insect species will change; (3) geographic distributions for some insect species will shift with host-plant ranges; and (4) changes in the population dynamics of affected insect species will influence their interactions with other insects and plants. For insect conservation purposes, it is critical to begin long-term studies on the effects of enhanced CO2 levels on insect populations. An analysis of the available literature indicates that many orders containing insect species important for ecosystem conservation, and even those important as agricultural or medical pests, have not been examined. Without a major increase in research on this topic, we will be unprepared for the species changes that will occur, we will lose the opportunity to document just how some insects adapt to elevated CO2 levels, and we will lack the information necessary for effective conservation efforts.

2404^1^Whittaker,J B^1999^1^Impacts and responses at population level of herbivorous insects to elevated CO2^381^96^2^149-156^^^^^^^^^^7567
1142^137^1965^3495^377^442^489^490^580^92^utions for some insect species will shift with host-plant ranges; and (4) changes in the population dynamics of affected insect species will influence their interactions with other insects and plants. For insect conservation purposes, it is critical to begin long-term studies on the effects of enhanced CO2 levels on insect populations. An analysis of the available literature indicates that A^7566^Most studies of responses of insects to elevated carbon dioxide have been made using short-term exposures to treated food plants and have involved measurements of responses in growth, reproduction, food consumption and efficiencies of conversion at specific stages in the life cycle. These will be reviewed in the light of longer-term studies recently published where whole generations have been reared in chambers with simultaneous treatment of plants and where insects have been free to select their food and microenvironment. Factors such as seasonal change in plants, choice of food plant, mode of feeding, timing of exposure, temperature, the role of natural enemies are considered and the whole placed in the context of other aspects of climate change. It is concluded that in studies to date, the only feeding guild in which some species have shown increases in population density in elevated carbon dioxide are the phloem feeders. Chewing insects (both free-living,and mining) generally have shown no change or reduction in abundance, though relative abundance may be greatly affected. Compensatory feeding is common in these groups.

2405^3^Cramer,M D^Gao,Z F^Lips,S H^1999^1^The influence of dissolved inorganic carbon in the rhizosphere on carbon and nitrogen metabolism in salinity-treated tomato plants^84^142^3^441-450^^^^^Jun^^^^^7569
1096^174^2262^2957^3496^361^367^424^639^678^e generations have been reared in chambers with simultaneous treatment of plants and where insects have been free to select their food and microenvironment. Factors such as seasonal change in plants, choice of food plant, mode of feeding, timing of exposure, temperature, the role of natural enemies are considered and the whole placed in the context of other aspects of climate change. It is concluded that in studies to date, the only feeding guild in which some species have shown increases in population density in elevated carbon dioxide are the phloem feeders. Chewing insects (both free-living,and mining) generally have shown no change A^7568^The influence of variation in the concentration of dissolved inorganic carbon (DIC) in the form of CO2 and HCO3- in the root media on the C and N metabolism of Lycopersicon esculentum cv. F144 was investigated under both saline and non-saline conditions. Tomato seedlings were grown in hydroponic culture (pH 6.5) with or without NaCl, and the root solution was aerated with either ambient CO2 (360 mol mol(-1)) or CO2- enriched air (5000 mu mol mol(-1)). Nitrate uptake and root tissue NO3- concentrations were increased slightly by elevated rhizosphere DIC concentrations in both control and salinity- treated plants. This is associated with 46% higher nitrate reductase activity in the roots of control plants supplied with elevated DIC than in those supplied with ambient DIG. The activity of phosphoenolpyruvate carboxylase (PEPc) in vitro in control and salinity-treated plants was unaffected by the supply of elevated rhizosphere DIC concentrations. However, PEPc activity in vitro was considerably higher than the rates of PEPc activity in vivo reported previously, indicating that PEPc activity was not in itself a limitation on the provision of anaplerotic C. Therefore elevated DIC concentration in the rhizosphere stimulated the uptake of NO3- and provided alternative C skeletons for the assimilation of the NH4+ resulting from NO3- reduction into amino acids within the roots. Salinity stimulated root glutamine synthetase (GS) activity up to double that in control plants. Furthermore, elevated DIC caused an increase in leaf and root GS activity of control plants while inhibiting GS activity in the roots of salinity-treated plants. Glutamine:2-oxoglutarate aminotransferase (GOGAT) activity of salinity-treated plants was doubled by elevated rhizosphere DIC concentrations. These changes in GS and GOGAT activity must reflect changes in amino acid synthesis. Under saline conditions the xylem transport of NO3- is partly blocked and a larger root assimilation develops, requiring not only the transamination of 2-oxoglutarate to glutamate but also that of oxaloacetate to aspartate and the transamidation of aspartate to asparagine.

2406^2^Matthies,D^Egli,P^1999^1^Response of a root hemiparasite to elevated CO2 depends on host type and soil nutrients^2^120^1^156-161^^^^^Jul^^^^^7571
1142^1684^312^344^3497^540^92^ of the NH4+ resulting from NO3- reduction into amino acids within the roots. Salinity stimulated root glutamine synthetase (GS) activity up to double that in control plants. Furthermore, elevated DIC caused an increase in leaf and root GS activity of control plants while inhibiting GS activity in the roots of salinity-treated plants. Glutamine:2-oxoglutarate aminotransferase (GOGAT) activity of salinity-treated plants was doubled by elevated rhizosphere DIC concentrations. These changes in GS and GOGAT activity must reflect changes in amino acid synthesis. Under saline conditions the xylem transport of NO3- is partly blocked and a larger root assimilation develops, requiring not only the transamination of 2-oxoglutaA^7570^Although elevated CO2 may affect various forms of ecological interactions, the effect of elevated CO2 on interactions between parasitic plants and their hosts has received little attention. We examined the effect of elevated CO2 (590 mu l l(- 1)) at two nutrient (NPK) levels on the interactions of the facultative root hemiparasite Rhinanthus alectorolophus with two of its hosts, the grass Lolium perenne and the legume Medicago sativa. To study possible effects on parasite mediation of competition between hosts, the parasite was grown with each host separately and with both hosts simultaneously. In addition, all combinations of hosts were grown without the parasite. Both the parasite and the host plants responded to elevated CO2 with increased growth, but only at high nutrient levels. The CO2 response of the hemiparasite was stronger than that of the hosts, but depended on the host species available. With L. perenne and M. sativa simultaneously available as hosts, the biomass of the parasite grown at elevated CO2 was 5.7 times that of parasites grown at ambient CO2. Nitrogen concentration in the parasites was not influenced by the treatments and was not related to parasite biomass. The presence of the parasite strongly reduced both the biomass of the hosts and total productivity of the system. This effect was much stronger at low than at high nutrient levels, but was not influenced by CO2 level. Elevated CO2 did not influence the competitive balance between the two different hosts grown in mixture. The results of this study support the hypothesis that hemiparasites may influence community structure and suggest that these effects are robust to changes in CO2 concentration.

2407^3^Muschak,M^Willmitzer,L^Fisahn,J^1999^1^Gas-exchange analysis of chloroplastic fructose-1,6- bisphosphatase antisense potatoes at different air humidities and at elevated CO2^6^209^1^104-111^^^^^Jul^^^^^7573
1538^1754^1783^2185^243^3113^312^3498^383^92^tiva simultaneously available as hosts, the biomass of the parasite grown at eA^7572^Gas-exchange measurements were performed to analyze the leaf conductances and assimilation rates of potato (Solanum tuberosum L. cv. Desiree) plants expressing an antisense construct against chloroplastic fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11) in response to increasing photon flux densities, different relative air humidities and elevated CO2 concentrations. Assimilation rates (A) and transpiration rates (E) were observed during a stepwise increase of photon flux density. These experiments were carried out under atmospheric conditions and in air containing 500 mu mol mol(-1) CO2. In both gas atmospheres, two levels of relative air humidity (60- 70% and 70-80%) were applied in different sets of measurements. Intercellular CO2 concentration, leaf conductance, air-to-leaf vapour pressure deficit, and instantaneous water-use efficiency (A/E) were determined. As expected, assimilation rates of the FBPase antisense plants were significantly reduced as compared to the wild type. Saturation of assimilation rates in transgenic plants occurred at a photon flux density of 200 mu mol m(-2) s(-1), whereas saturation in wild type plants was observed at 600 mu mol m(-2) s(-1). Elevated ambient CO2 levels did not effect assimilation rates of transgenic plants. At 70- 80% relative humidity and atmospheric CO2 concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference. emerged at 60-70%. These differences in leaf conductance vanished at elevated levels of ambient CO2. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from mesophyll cells, whereas the intercellular CO2 concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control by environmental parameters and mesophyll photosynthesis.
sim2408^8^Tubiello,F N^Rosenzweig,C^Kimball,B A^Pinter,P J^Wall,G W^Hunsaker,D J^LaMorte,R L^Garcia,R L^1999^1^Testing CERES-wheat with free-air carbon dioxide enrichment (FACE) experiment data: CO2 and water interactions^48^91^2^247-255^^^^^Mar-Apr^^^^^7575
1251^130^137^3499^374^431^434^724^92^mospheric CO2 concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference. emerged at 60-70%. These differences in leaf conductance vanished at elevated levels of ambient CO2. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from mesophyll cells, whereas the intercellular CO2 concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control by environmental parameters and mesophyll photosynthesis.
simA^7574^Dynamic crop-growth models are used to project the effects of rising atmospheric CO2 concentration and associated climate change on crop yields. Such model predictions are largely untested in the field, for lack of experimental data. We tested the CERES-Wheat model, modified to include leaf-level photosynthesis response to elevated CO2, using field data from 2 yr of Free-Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Mariclopa, AZ. Two irrigation treatments (well-watered, WW; water-deficit stressed, WS) and two atmospheric CO2 concentrations (ambient, 350 mu mol mol(-1); elevated, 550 mu mol mol(-1)) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO2 conditions in both years. The model did not simulate the accelerated crop phenology (5-8 d at physiological maturity) observed in the WW and elevated CO2 treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO2 by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2-water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured: 3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: 9%). The ability to simulate CO2-water interactions, though it needs to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO2 and climate change.

2409^2^Tognetti,R^Johnson,J D^1999^1^The effect of elevated atmospheric CO2 concentration and nutrient supply on gas exchange, carbohydrates and foliar phenolic concentration in live oak (Quercus virginiana Mill.) seedlings^374^56^5^379-389^^^^^Jun-Jul^^^^^7577
1344^229^256^341^3500^3501^399^685^752^967^spiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2-water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured: 3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: 9%). The ability to simulate CO2-water interactions, thouA^7576^We determined the direct effects of atmospheric CO2 concentration ([CO2]) on leaf gas exchange, phenolic and carbohydrate allocation in live oak seedlings (Quercus virginiana Mill.) grown at present (370 mu mol.mol(-1)) or elevated (520 mu mol.mol(-1)) [CO2] for 6 months in open-top chambers. Two soil nitrogen (N) treatments (20 and 90 mu mol.mol(-1) total N, low N and high N treatments, respectively) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf-level photosynthesis were maintained in plants subjected to elevated [CO2] over the 6-month treatment period in both N treatments. A combination of increased rates of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated [CO2]. The sustained increase in photosynthetic rate was accompanied by decreased dark respiration in elevated [CO2]. Elevated [CO2] led to increased growth rates; while total non-structural carbohydrate (sugars and starch) concentrations were not significantly Affected by elevated [CO2] treatment. The concentration of phenolic compounds increased significantly under elevated [CO2]. ((C) Inra/Elsevier, Paris.).

2410^3^Gunn,S^Bailey,S J^Farrar,J F^1999^1^Partitioning of dry mass and leaf area within plants of three species grown at elevated CO2^43^13^^3-11^^^^^Jun^^^^^7579
130^310^376^377^423^57^778^803^962^991^ely) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf-level photosynthesis were maintained in plants subjected to elevated [CO2] over the 6-month treatment period in both N treatments. A combination of increased rates of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated [CO2]. The sustained increase in photosynthetic rate was accompanied by decreased dark respiration in elevated [CO2]. Elevated [CO2] led to increased growth rates; while total non-structural carbohydrate (sugars aA^7578^1. We tested the hypothesis that the net partitioning of dry mass and dry mass:area relationships is unaltered when plants are grown at elevated atmospheric CO2 concentrations. 2. The total dry mass of Dactylis glomerata, Bellis perennis and Trifolium repens was higher for plants in 700 compared to 350 mu mol CO2 mol(-1) when grown hydroponically in controlled- environment cabinets. 3. Shoot:root ratios were higher and leaf area ratios and specific leaf areas lower in all species grown at elevated CO2. Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO2. 4. Whilst these data suggest that CO2 alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO2. CO2 changed only two of a total of 12 allometric coefficients we calculated for the three species: v relating shoot to root dry mass was higher in D. glomerata, whilst v relating leaf area to total dry mass was lower in T. repens. 5. CO2 alone has very little effect on partitioning when the size of the plant is taken into account.

2411^5^Davey,P A^Parsons,A J^Atkinson,L^Wadge,K^Long,S P^1999^1^Does photosynthetic acclimation to elevated CO2 increase photosynthetic nitrogen-use efficiency? A study of three native UK grassland species in open-top chambers^43^13^^21-28^^^^^Jun^^^^^7581
1998^2072^3003^348^361^384^439^442^665^92^ratios and specific leaf areas lower in all species grown at elevated CO2. Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO2. 4. Whilst these data suggest that CO2 alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO2. CO2 changed only two of a total of 12 allometric coefficients we calculated for the three species: v relating shoot to root dry mass was higher in D. glomerata, whilst v relating leaf area to toA^7580^1, The photosynthetic response to elevated CO2 and nutrient stress was investigated in Agrostis capillaris, Lolium perenne and Trifolium repens grown in an open-top chamber facility for 2 years under two nutrient regimes. Acclimation was evaluated by measuring the response of light-saturated photosynthesis to changes in the substomatal CO2 concentration. 2. Growth at elevated CO2 resulted in reductions in apparent Rubisco activity in vivo in all three species, which were associated with reductions of total leaf nitrogen content on a unit area basis for A. capillaris and L. perenne. Despite this acclimation, photosynthesis was significantly higher at elevated CO2 for T. repens and A. capillaris, the latter exhibiting the greatest increase of carbon uptake at the lowest nutrient supply. 3. The photosynthetic nitrogen-use efficiency (the rate of carbon assimilation per unit leaf nitrogen) increased at elevated CO2, Mot purely owing to higher values of photosynthesis at elevated CO2, but also as a result of lower leaf nitrogen contents. 4. Contrary to most previous studies, this investigation indicates that elevated CO2 can stimulate photosynthesis under a severely limited nutrient supply. Changes in photosynthetic nitrogen-use efficiency may be a critical determinant of competition within low nutrient ecosystems and low input agricultural systems.

2412^4^Norton,L R^Firbank,L G^Gray,A J^Watkinson,A R^1999^1^Responses to elevated temperature and CO2 in the perennial grass Agrostis curtisii in relation to population origin^43^13^^29-37^^^^^Jun^^^^^7583
1262^1380^243^376^427^738^792^92^ne. Despite this acclimation, photosynthesis was significantly higher at elevated CO2 for T. repens and A. capillaris, the latter exhibiting the greatest increase of carbon uptake at the lowest nutrient supply. 3. The photosynthetic nitrogen-use efficiency (the rate of carbon assimilation per unit leaf nitrogen) increased at elevated CO2, Mot purely owing to higher values of photosynthesis at elevated CO2, but also as a result A^7582^1. Evolutionary responses to climate change will depend on the presence of heritable variation within species populations for traits that increase fitness under the changing conditions. Patterns of ecotypic differentiation in relation to latitude in some species suggest that such variation exists in relation to temperature responses. Response to elevated CO2, whether heritable or not, is not expected to be related to latitudinal or climatic differences within temperate regions. 2. To test these ideas, seeds were collected from 10 populations of the outbreeding perennial grass Agrostis curtisii across its range in Europe from south Wales to Portugal. Plants were grown under ambient and elevated temperature and CO2 conditions, in a factorial design, in solardomes; two half sibs from each population were planted in separate pots in each of the two replicate domes with each combination of treatments. One half sib was harvested at the end of the first summer, the second at the end of the second summer. 3. Survival was uniformly high and flowering uniformly low across treatments and populations. 4. Responses to temperature and CO2 treatments varied over time for almost all populations. Treatment effects were not significant on plants harvested in year 1, although there was a trend towards higher shoot biomass under the elevated temperature and CO2 treatment. Tn year 2 shoot biomass was significantly higher under the elevated temperature treatment across all populations and there was a strong trend towards decreased biomass under elevated CO2 5. There were no significant correlations of plant response to either CO2 or temperature with climate at origin. 6. These results warn of the dangers of extrapolating evolutionary plant responses to CO2 from short-term experiments.

2413^3^Norton,L R^Firbank,L G^Blum,H^1999^1^Effects of free-air CO2 Enrichment (FACE) on experimental grassland communities^43^13^^38-44^^^^^Jun^^^^^7585
2419^2742^3502^372^374^417^507^540^705^92^the second at the end of the second summer. 3. A^7584^1. Experimental grassland communities (turves) were exposed to elevated (60 Pa) and ambient (35 Pa) CO2 partial pressures (pCO(2)) in a Free-air Carbon Dioxide Enrichment (FACE) experiment between 30 March 1995 and 4 July 1996. The vegetation was cut once during the experiment prior to the final harvest (harvest 2). 2, No significant treatment effects on total plant biomass at the whole turf level were detected, although biomass was typically about 25% higher under fumigation in year 1 and about 15% higher in year 2, 3, Biomass for two of the six sown species was significantly higher at harvest 2 than at harvest 1. There were no significant differences between individual species biomass under the two CO2 treatments at either harvest I or 2 or in terms of overall cumulative biomass. However, in four of the five sown species in both years biomass tended to be higher in the fumigated than in the control rings (Cerastium holosteiodes, Phleum pratense, Plantago lanceolata and Poa trivialis). In contrast, Lolium perenne showed increased biomass under the control treatment relative to the fumigated treatment in both years. Owing to the high variance both within and between rings for each of the two treatments the statistical power of most, but not all, of the analyses carried out was poor. 4, The relative proportions of each species in the turves under fumigated and control treatments was broadly similar after the first summer, with differences in die second year being mainly owing to the negative response of L. perenne to CO2 fumigation.

2414^4^Caporn,S J M^Brooks,A L^Press,M C^Lee,J A^1999^1^Effects of long-term exposure to elevated CO2 and increased nutrient supply on bracken (Pteridium aquilinum)^43^13^^107-115^^^^^Jun^^^^^7587
243^2663^2664^57^92^n terms of overall cumulative biomass. However, in four of the five sown species in both years biomass tended to be higher in the fumigated than in the control rings (Cerastium holosteiodes, Phleum pratense, Plantago lanceolata and Poa trivialis). In contrast, LA^7586^1. Bracken (Pteridium aquilinum) is an important fern with a global distribution. Little is known of the response of this species to elevated CO2. We investigated the effects of high CO2 (570 compared with 370 mu mol mol(-1)) with and without an increased nutrient supply (a combined N, P, K application) on the growth and physiology of bracken, growing in containers in controlled-environment glasshouses, over two full growing seasons. Results of growth and physiology determinations are reported for the second season. 2. Elevated CO2 had little impact on the growth or allocation of dry mass in bracken. No significant changes were detected in dry mass of the total plant or any of the organs: rhizomes, roots and fronds. In contrast to the small effects of high CO2 the high nutrient treatment caused a three-fold stimulation of total plant dry mass and an increase in the allocation of dry mass to above ground when compared with low nutrient controls. 3. Net photosynthetic rates in saturating light were increased by both high CO2 and nutrient treatments, particularly in spring months (May and June). Growth in elevated CO2 did not cause a down- regulation in light-saturated rates of photosynthesis. The increased carbon gain in the high CO2 treatments was accompanied, in the low-nutrient plants, by higher concentrations of carbohydrates. However, in high-nutrient plants the CO2 treatment did not cause an accumulation of carbohydrates. The absence of a growth response to elevated CO2 in bracken despite significant increases in photosynthesis requires further investigation.

2415^3^Centritto,M^Lee,H S J^Jarvis,P G^1999^1^Increased growth in elevated [CO2]: an early, short-term response?^127^5^6^623-633^^^^^Aug^^^^^7589
1344^1985^2060^243^2601^310^344^360^427^740^f high CO2 the high nutrient treatment caused a three-fold stimulation of total plant dry mass and an increase in the allocation of dry mass to above ground when compared with low nutrient controls. 3. Net photosynthetic rates in saturating light were incrA^7588^Saplings of four clones of Sitka spruce and cherry were grown for three and two growing seasons, respectively, in open top chambers at two CO2 concentrations (approximate to 350 and approximate to 700 mu mol mol(-1)) to determine whether the increase in total biomass brought about by enhanced [CO2] is a result of a transient or persistent effect in nonlimiting conditions. Classical growth analysis was applied to both species and mean current relative growth rate of total dry mass (R-T) and leaf dry mass (R-L), and period relative growth rate of total dry mass (R-T(t)) and leaf dry mass (R-L(t)) were calculated. Sitka spruce saplings and cherry seedlings showed a positive growth response to elevated [CO2], and at the end of the experiments both species were approximate to 40% larger in elevated [CO2] than in ambient [CO2]. As a result, the period mean R-T(t) and R-L(t) were significantly higher in elevated [CO2]. The differences in plant dry mass at the end of the experiments were a consequence of the more rapid growth in the early phase of exposure to elevated [CO2]. After this initial phase mean R-T and R-L were similar or even lower in elevated [CO2] than in ambient [CO2]. NAR of both species was much higher in elevated [CO2], whereas both LAR, SLA, and LMR showed the opposite trend. The higher LAR and SLA of plants in ambient [CO2] contributed to a compensation by which they maintained R- T Similar to that of elevated [CO2] saplings despite lower NAR and photosynthetic rate. However, when the same size the trees were similar amongst the [CO2] treatments, indicating that one of the main effect of elevated [CO2] on tree growth is to speed-up early development in all aspects.

2416^5^Paterson,E^Hodge,A^Thornton,B^Millard,P^Killham,K^1999^1^Carbon partitioning and rhizosphere C-flow in Lolium perenne as affected by CO2 concentration, irradiance and below-ground conditions^127^5^6^669-678^^^^^Aug^^^^^7591
2032^2508^3503^362^374^376^436^57^733^92^ass at the end of the experiments were a consequence of the A^7590^Plant responses to increasing atmospheric CO2 concentrations have received considerable interest. However, major uncertainties in relation to interactive effects of CO2 with above- and below-ground conditions remain. This microcosm study investigated the impacts of CO2 concentration on plant growth, dry matter partitioning and rhizodeposition as affected by: (i) photon flux density (PFD), and (ii) growth matrix. Plants were grown in a sandy loam soil for 28 d under two photon flux densities: 350 (low PFD) and 1000 mu mol m(-2) s(-1) (high PFD) and two CO2 concentrations: 450 (low CO2) and 720 mu mol mol(- 1) (high CO2). Partitioning of recent assimilate amongst plant and rhizosphere C-pools was determined by use of (CO2)-C-14 pulse-labelling. In treatments with high PFD and/or high CO2, significant (P< 0.05) increases in dry matter production were found in comparison with the low PFD/low CO2 treatment. In addition, significant (P < 0.05) reductions in shoot %N and SLA were found in treatments imposing high PFD and/or high CO2. Root weight ratio (RWR) was unaffected by CO2 concentration, however, partitioning of C-14 to below ground pools was significantly (P< 0.05) increased. In a separate study, L. perenne was grown for 28 d in microcosms percolated with nutrient solution, in either a sterile sand matrix or nonsterile soil, under high or low CO2. Dry matter production was significantly (P< 0.01) increased for both sand and soil grown seedlings. Dry matter partitioning was affected by matrix type. C-14-allocation below ground was increased for sand grown plants. Rhizodeposition was affected by CO2 concentration for growth in each matrix, but was increased for plants grown in the soil matrix, and decreased for those in sand. The results illustrate that plant responses to CO2 are potentially affected by (i) PFD, and (ii) by feedbacks from the growth matrix. Such feedbacks are discussed in relation to soil nutrient status and interactions with the rhizosphere microbial biomass.
found in treatments imposing2417^3^Tjoelker,M G^Oleksyn,J^Reich,P B^1999^1^Acclimation of respiration to temperature and CO2 in seedlings of boreal tree species in relation to plant size and relative growth rate^127^5^6^679-691^^^^^Aug^^^^^7593
348^3504^3505^372^374^376^377^520^524^57^ nutrient solution, in either a sterile sand matrix or nonsterile soil, under high or low CO2. Dry matter production was significantly (P< 0.01) increased for both sand and soil grown seedlings. Dry matter partitioning was affected by matrix type. C-14-allocation below ground was increased for sand grown plants. Rhizodeposition was affected by CO2 concentration for growth in each matrix, but was increased for plants grown in the soil matrix, and decreased for those in sand. The results illustrate that plant responses to CO2 are potentially affected by (i) PFD, and (ii) by feedbacks from the growth matrix. Such feedbacks are discussed in relation to soil nutrient status and interactions with the rhizosphere microbial biomass.
found in treatments imposingA^7592^The role of acclimation of dark respiration to temperature and CO2 concentration and its relationship to growth are critical in determining plant response to predicted global change. We explored temperature acclimation of respiration in seedlings of tree species of the North American boreal forest. Populus tremuloides, Betula papyrifera, Larix laricina, Pinus banksiana, and Picea mariana plants were grown from seed in controlled-environments at current and elevated concentrations of CO2 (370 and 580 mu mol mol(-1)) in combination with three temperature treatments of 18/12, 24/18, and 30/24 degrees C (light/dark period). Specific respiration rates of roots and shoots acclimated to temperature, damping increases in rates across growth-temperature environments compared to short-term temperature responses. Compared at a standard temperature, root and shoot respiration rates were, on average, 40% lower in plants grown at the highest compared to lowest growth temperature. Broad-leaved species had a lower degree of temperature acclimation of respiration than did the conifers. Among species and treatment combinations, rates of respiration were linearly related to size and relative growth rate, and relationships were comparable among growth environments. Specific respiration rates and whole-plant respiratory CO2 efflux as a proportion of daily net CO2 uptake increased at higher growth temperatures, but were minimally affected by CO2 concentration. Whole-plant specific respiration rates were two to three times higher in broad-leaved than coniferous species. However, compared to faster-growing broad-leaved species, slower-growing conifers lost a larger proportion of net daily CO2 uptake as respiratory CO2 efflux, especially in roots. Interspecific variation in acclimation responses of dark respiration to temperature is more important than acclimation of respiration to CO2 enrichment in modifying tree seedling growth responses to projected increases in CO2 concentration and temperature.
eaved species had a lower de2418^4^Wand,S J E^Midgley,G F^Jones,M H^Curtis,P S^1999^1^Responses of wild C4 and C3 grass (Poaceae) species to elevated atmospheric CO2 concentration: a meta-analytic test of current theories and perceptions^127^5^6^723-741^^^^^Aug^^^^^7595
1057^2324^2489^3178^3179^364^505^508^692^728^ant respiratory CO2 efflux as a proportion of daily net CO2 uptake increased at higher growth temperatures, but were minimally affected by CO2 concentration. Whole-plant specific respiration rates were two to three times higher in broad-leaved than coniferous species. However, compared to faster-growing broad-leaved species, slower-growing conifers lost a larger proportion of net daily CO2 uptake as respiratory CO2 efflux, especially in roots. Interspecific variation in acclimation responses of dark respiration to temperature is more important than acclimation of respiration to CO2 enrichment in modifying tree seedling growth responses to projected increases in CO2 concentration and temperature.
eaved species had a lower deA^7594^C4 plants contribute approximate to 20% of global gross primary productivity, and uncertainties regarding their responses to rising atmospheric CO2 concentrations may limit predictions of future global change impacts on C4-dominated ecosystems. These uncertainties have not yet been considered rigorously due to expectations of C4 low responsiveness based on photosynthetic theory and early experiments. We carried out a literature review (1980-97) and meta-analysis in order to identify emerging patterns of C4 grass responses to elevated CO2, as compared with those of C3 grasses. The focus was on nondomesticated Poaceae alone, to the exclusion of C4 dicotyledonous and C4 crop species. This provides a clear test, controlled for genotypic variability at family level, of differences between the CO2-responsiveness of these functional types. Eleven responses were considered, ranging from physiological behaviour at the leaf level to carbon allocation patterns at the whole plant level. Results were also assessed in the context of environmental stress conditions (light, temperature, water and nutrient stress), and experimental growing conditions (pot size, experimental duration and fumigation method). Both C4 and C3 species increased total biomass significantly in elevated CO2, by 33% and 44%, respectively. Differing tendencies between types in shoot structural response were revealed: C3 species showed a greater increase in tillering, whereas C4 species showed a greater increase in leaf area in elevated CO2. At the leaf level, significant stomatal closure and increased leaf water use efficiency were confirmed in both types, and higher carbon assimilation rates were found in both C3 and C4 species (33% and 25%, respectively). Environmental stress did not alter the C4 CO2-response, except for the loss of a significant positive CO2-response for above-ground biomass and leaf area under water stress. In C3 species, stimulation of carbon assimilation rate was reduced by stress (overall), and nutrient stress tended to reduce the mean biomass response to elevated CO2. Leaf carbohydrate status increased and leaf nitrogen concentration decreased significantly in elevated CO2 only in C3 species. We conclude that the relative responses of the C4 and C3 photosynthetic types to elevated CO2 concur only to some extent with expectations based on photosynthetic theory. The significant positive responses of C4 grass species at both the leaf and the whole plant level demand a re-evaluation of the assumption of low responsiveness in C4 plants at both levels, and not only with regard to water relations. The combined shoot structural and water use efficiency responses of these functional types will have consequential implications for the water balance of important catchments and range lands throughout the world, especially in semiarid subtropical and temperate regions. It may be premature to predict that C4 grass species will lose their competitive advantage over C3 grass species in elevated CO2.
verall), and nutrient stress tended to redu2419^3^Tjoelker,M G^Reich,P B^Oleksyn,J^1999^1^Changes in leaf nitrogen and carbohydrates underlie temperature and CO2 acclimation of dark respiration in five boreal tree species^9^22^7^767-778^^^^^Jul^^^^^7597
240^243^3240^348^372^374^376^377^384^520^ elevated CO2 concur only to some extent with expectations based on photosynthetic theory. The significant positive responses of C4 grass species at both the leaf and the whole plant level demand a re-evaluation of the assumption of low responsiveness in C4 plants at both levels, and not only with regard to water relations. The combined shoot structural and water use efficiency responses of these functional types will have consequential implications for the water balance of important catchments and range lands throughout the world, especially in semiarid subtropical and temperate regions. It may be premature to predict that C4 grass species will lose their competitive advantage over C3 grass species in elevated CO2.
verall), and nutrient stress tended to reduA^7596^We tested the hypothesis that acclimation of foliar dark respiration to CO2 concentration and temperature is associated with adjustments in leaf structure and chemistry. Populus tremuloides Michx, Betula papyrifera Marsh, Larix laricina (Du Roi) K, Koch, Pinus banksiana Lamb., and Picea mariana (Mill,) B.S.P. were grown from seed in combined CO2 (370 or 580 mu mol mol(-1)) and temperature treatments (18/12, 24/18, or 30/24 degrees C), Temperature and CO2 effects were predominately independent. Specific respiration rates partially acclimated to warmer thermal environments through downward adjustment in the intercept, but not Q(10) of the temperature-response functions. Temperature acclimation of respiration was larger for conifers than broad-leaved species and was associated with pronounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Shortterm increases in CO2 concentration did not inhibit respiration. Growth in the elevated CO2 concentration reduced leaf nitrogen and increased non-structural carbohydrate concentrations. However, for a given nitrogen concentration, respiration was higher in leaves grown in the elevated CO2 concentration, as rates increased with increasing carbohydrates, Across species and treatments, respiration rates were a function of both leaf nitrogen and carbohydrate concentrations (R-2 = 0.71, P < 0.0001). Longterm acclimation of foliar dark respiration to temperature and CO2 concentration is largely associated with changes in nitrogen and carbohydrate concentrations.

2420^3^Randerson,J T^Thompson,M V^Field,C B^1999^1^Linking C-13-based estimates of land and ocean sinks with predictions of carbon storage from CO2 fertilization of plant growth^257^51^3^668-678^^^^^Jul^^^^^7599
1660^1804^1859^1919^2762^344^3506^362^57^625^nounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Shortterm increases in CO2 concentration did not inhibit respiration. Growth in the elevated CO2 concentration reduced leaf nitroA^7598^The residence times of carbon in plants, litter, and soils are required for partitioning land and ocean sinks using measurements of atmospheric delta(13)CO(2) and also for estimating terrestrial carbon storage in response to net primary production (NPP) stimulation by elevated levels of atmospheric CO2. While C-13-based calculations of the land sink decline with increasing estimates of terrestrial carbon residence times (through the fossil fuel-induced isotopic disequilibrium term in equations describing the global atmospheric budgets of (CO2)-C-13 and CO2), estimates of land sinks based on CO2 fertilization of plant growth are directly proportional to carbon residence times. Here we used a single model of terrestrial carbon turnover, the Carnegie Ames- Stanford Approach (CASA) biogeochemical model, to simultaneously estimate 1984-1990 terrestrial carbon storage using both approaches. Our goal was to identify the fraction of the (CO2)-C-13-based land sink attributable to CO2 fertilization. Uptake from CO2 fertilization was calculated using a beta factor of 0.46 to describe the response of NPP to increasing concentrations of atmospheric CO2 from 1765 to 1990. Given commonly used parameters in the C-13-based sink calculation and assuming a deforestation flux of 0.8 Pg C/yr, CO2 fertilization accounts for 54% of the missing terrestrial carbon sink from 1984 to 1990. CO2 fertilization can account for all of the missing terrestrial sink only when the terrestrial mean residence time (MRT) and the land isodisequilibrium forcing are greater than many recent estimates.

2421^3^Lovelock,C E^Posada,J^Winter,K^1999^1^Effects of elevated CO2 and defoliation on compensatory growth and photosynthesis of seedlings in a tropical tree, Copaifera aromatica^382^31^2^279-287^^^^^Jun^^^^^7601
1390^2072^2511^312^360^374^386^547^669^711^ously estimate 1984-1990 terrestrial carbon storage using both approaches. Our goal was to identify the fraction of the (CO2)-C-13-based land sink attributable to CO2 fertilization. Uptake fromA^7600^After defoliation by herbivores, some plants exhibit enhanced rates of photosynthesis and growth that enable them to compensate for lost tissue, thus maintaining their fitness relative to competing, undefoliated plants. Our aim was to determine whether compensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO2. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO2, but not under elevated CO2. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO2. In contrast, under elevated CO2, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO2. Growth of leaf area after defoliation was increased, particularly under elevated CO2. Despite this increase, defoliated plants grown under elevated CO2 were further from compensating for tissue lost during defoliation after 5-1/2 weeks than those grown under ambient CO2 concentrations.

2422^4^Li,A G^Wall,G W^Trent,A^Hou,Y S^1999^1^Free-air CO2 enrichment effects on apex dimensional growth of spring wheat^164^39^4^1083-1088^^^^^Jul-Aug^^^^^7603
130^2404^3507^57^ompensatory photosynthesis and growth would be altered by increasing concentrations of atmospheric CO2. Defoliation of developing leaflets on seedlings of a tropical tree, Copaifera aromatica, caused increases in photosynthesis under ambient CO2, but not under elevated CO2. An enhancement in the development of buds in the leaf axils followed defoliation at ambient levels of CO2. In contrast, under elevated CO2, enhanced development of buds occurred in undefoliated plants with no further enhancement in bud development due to exposure to elevated CO2. Growth of leaf area after defoliation was increased, particularly under elevated CO2. Despite this increase, defoliated plants grown under elevated CO2 were further from compensating for tissue lost during A^7602^Although primordium initiation in wheat (Triticum aestivum L,) has been extensively researched, a complete description of the growth dynamics of the apex at elevated CO2 concentrations is lacking. This study determined the rates of main stem and tiller apical elongation and widening in plants grown under two levels of CO2 concentration. Spring wheat was grown at the University of Arizona's Maricopa Agricultural Center at elevated (550 mu mol mol(-1)) or ambient (370 mu mol mol(-1)) CO2 concentrations. Individual plant samples were collected at different developmental stages and dissected. After dissection, the Lengths and widths of the spires of the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3), and secondary tillers (T00, T01, T02, T10, T11, and T12) were measured with a stage micrometer. Apex dimensions were fitted to an exponential model, Elevated CO2 increased the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikelet stages, and the apex widths of T2 at double ridge stage, and of T2, T3, T10, and T11 at the flag leaf appearance stage. Combining these results with a parallel study, the longer apices did not have more spikelet primordia, but wider apices had more floret primordia, Elevated CO2 changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and later formed tillers. Earlier-formed tillers were less responsive to elevated CO2 levels. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

2423^7^Marino,B D V^Mahato,T R^Druitt,J W^Leight,L^Lin,G H^Russell,R M^Tubiello,F N^1999^1^The agricultural biome of Biosphere 2: Structure, composition and function^383^13^1-4^199-234^^^^^Jun^^^^^7605
1142^174^179^230^3508^3509^409^58^881^885^del, Elevated CO2 increased the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikeleA^7604^The agricultural mesocosm of Biosphere 2, known as the Intensive Agricultural Biome (IAB), provided food for the inhabitants of the facility during two periods of material closure between 1991 and 1994 (Mission I, September 26, 1991 to September 26, 1993, eight-person crew; Mission II, March 6, 1994 to September 17, 1994, seven-person crew). The design and operation of the mesocosm and preliminary results for food production of the IAB are described for both periods. The overall rate of crop production for the 0.22 ha area (soil depth of 1 m; soil and atmospheric volumes of approximately 2000 m(3) and 38000 m(3), respectively) sustained both crews. Overall production rates in Biosphere 2 exceeded those characteristic of fertile agricultural land in the most efficient agrarian communities, despite comparatively lower light levels, lack of insect pollinators and unusually dense insect pests. Crop yields were markedly higher for Mission II than for Mission I due, in part, to experience and improvements based on the first closure. The health of the Biospherians is briefly discussed in the context of a low-calorie (1800-2200 kcal day(-1) per person for Mission I and 2200-2400 kcal day(- 1) for Mission II), nutrient-dense diet characteristic of the Biosphere 2 food paradigm. sigh productivity and biodiversity were due to many factors including high resolution climate control, hyper-intensive agricultural practices, selection and planting of food crops adapted to humid, tropical and sub- tropical conditions, nutrient recycling, intensive pest management, and the superambient levels of atmospheric CO2 (concentrations up to 4500 ppmv were reported during the 1991 to 1994 occupations). Radiation use efficiency (RUE) for wheat for both periods and a post-Mission II planting were comparable to RUEs observed in other experimental elevated CO2 settings such as Controlled Ecological Life Support-Systems (CELSS) and Free Air CO2 Enrichment studies (FACE) even though yields were comparatively lower due to low light levels. Integrated management of pests, soil conditions and agricultural practices were key factors in the sustainability of the IAB resulting in minimization of plant loss due to insect herbivory, nematode infestation and reduction in the quality of IAB soils. The use of soils rather than hydroponic systems for the IAB had significant consequences for CO2, N2O and O-2 concentrations in the Biosphere 2 atmosphere and rendered primary regeneration technologies ineffective over the periods of closure. The initial high organic carbon content of the IAB soils prescribed by the designers proved to be the largest single source of CO2 and the largest sink for O-2. The choice of a soil-based compared to a hydroponic-based agricultural system contributed to the accumulation of N2O to levels as high as 300 times current ambient levels (approximately 310 ppbv). The IAB of Biosphere 2 has the potential; with system improvement, to be a high-yielding, self-sustaining agricultural mesocosm suited for a variety of research endeavors. (C) 1999 Elsevier Science B.V. All rights reserved.

2424^5^Rosenthal,Y^Farnsworth,B^Romo,F V R^Lin,G H^Marino,B D V^1999^1^High quality, continuous measurements of CO2 in Biosphere 2 to assess whole mesocosm carbon cycling^383^13^1-4^249-262^^^^^Jun^^^^^7607
360^372^384^669^n hydroponic systems for the IAB had significant consequences for CO2, N2O and O-2 concentrations in the Biosphere 2 atmosphere and rendered primary regeneration technologies ineffective over the periods of closure. The initial high organic carbon content of the IAB soils prescribed by the designers proved to be the largest single source of CO2 and the largest sink for O-2. The choice of a soil-based compared to a hydroponic-based agricultural system contributed to the accumulation of N2O to levels as high as 300 times current ambient levels (approximately 310 ppbv). The IAB of Biosphere 2 has the potential; with system improvement, to be a high-yielding, self-sustaining agricultural mesocosm suited for a variety of research endeA^7606^Accurate measurements of atmospheric CO2 concentrations are performed routinely in a variety of experimental settings including open fields and forests, leaf gas-exchange chambers, phytotrons and specialized growth chambers. However, the accurate monitoring of large scale structurally and biologically complex experimental systems, operating as materially closed systems, is not widely reported. Here we report the design elements, material specifications and other details for high precision monitoring of CO2 in Biosphere 2, a large scale ecologically diverse experimental facility located in Oracle, AZ. The results are used to illustrate how carbon balance in a temporarily isolated sub-system of the facility is used to assess carbon dynamics under different environmental conditions such as variable atmospheric CO2 levels, temperature, light, and soil moisture. The analytical system described here should be applicable for any settings in which continuous, high accuracy measurements of CO2 in a complex system are needed for quantitative research. (C) 1999 Elsevier Science B.V. All rights reserved.

2425^4^Tubiello,F N^Lin,G^Druitt,J W^Marino,B D V^1999^1^Ecosystem-level evapotranspiration and water-use efficiency in the desert biome of Biosphere 2^383^13^1-4^263-271^^^^^Jun^^^^^7609
174^374^427^ biologically complex experimental systems, operating as materially closed systems, is not widely reported. Here we report the design elements, material specifications and other details for high precision monitoring of CO2 in Biosphere 2, a large scale ecologically diverse experimental facility located in Oracle, AZ. The results are used to illustrate how carbon balance in a temporarily isolated sub-system of the facility is used to assess carbon dynamics under different environmental conditions such as variable atmospheric CO2 levels, temperature, light, and soil moisture. The analytical system described here should be applicable for any settings in which continuous, high accuracy measurements of CO2 in a complex sysA^7608^We estimate whole-system water and carbon fluxes for the desert biome of Biosphere 2 under two different daily-mean CO2 concentrations: 450 ppmv and 850 ppmv. The desert mesocosm occupies an area of approximately 1500 m(2), has a total atmospheric Volume of about 25000 m(3) and contains a heterogeneous distribution of plants and soils. Atmospheric water content and CO2 concentrations were measured continuously using a variety of sensors, including a Li-cor 6262 for CO2 deployed within the experimental area. Daily carbon and water budgets were calculated in the desert biome, isolated from the rest of Biosphere 2 by deploying isolation curtains for 24-h periods. Data collected for six closure periods suggest that elevated CO2 concentration increased whole-system carbon uptake, while evapotranspiration remained constant. As a result, whole-system water-use efficiency (WUE, defined as net ecosystem carbon uptake per unit water transpired) in the Biosphere 2 desert increased by more than 40%. Our measurements investigate soil-plant processes at a medium scale, ideally bridging the gap between traditional controlled-environment growth chambers and open-held studies. (C) 1999 Elsevier Science B.V. All rights reserved.

2426^6^Tubiello,F N^Mahato,T^Morton,T^Druitt,J W^Volk,T^Marino,B D V^1999^1^Growing wheat in Biosphere 2 under elevated CO2: Observations and modeling^383^13^1-4^273-286^^^^^Jun^^^^^7611
1007^130^137^312^3510^374^376^724^867^92^rs, including a Li-cor 6262 for CO2 deployed within the experimental area. Daily carbon and water budgets were calculated in the desert biome, isolated from the rest of Biosphere 2 by deploying isolation curtains for 24-h periods. Data collected for six closure periods suggest that elevated CO2 concentration increased whole-system carbon uptake, while evapotranspiration remained constant. As a result, whole-system water-use efficiency (WUE, defined as net ecosystem carbon uptake per unit water transpired) in the Biosphere 2 desert increased by more than 40%. Our measuremeA^7610^Spring wheat (Triticum aestivum L., cv. Yecora Rojo) was grown in the intensive agricultural biome (IAB) of Biosphere 2 during the 1995-1996 winter/spring season. Environmental conditions were characterized by a day/night temperature regime of 27/17 degrees C, relative humidity (RH) levels around 45%, mean atmospheric CO2 concentration of 450 ppmv, and natural light conditions with mean intensities about half of outside levels. Weekly samples of above-ground plant matter were collected throughout the growing season and phenological events recorded. A computer model, CERES-Wheat, previously tested under both field and controlled conditions, was used to simulate the observed crop growth and to help in data analysis. We found that CERES-Wheat simulated the data collected at Biosphere 2 to within 10% of observed, thus suggesting that wheat growth inside the IAB was comparable to that documented in other environments. The model predicts phenological stages and final dry matter (DM) production within 10% of the observed data. Measured DM production rates, normalized for light absorbed by the crop, suggested photosynthetic efficiencies intermediate between those observed under optimal field conditions and those recorded in NASA-Controlled Ecological Life-Support Systems (CELSS). We suggest that such a difference can be explained primarily in terms of low light levels inside the IAB, with additional effects due to elevated CO2 concentrations and diffuse light fractions. (C) 1999 Elsevier Science B.V. All rights reserved.

2427^4^Cotrufo,M F^Raschi,A^Lanini,M^Ineson,P^1999^1^Decomposition and nutrient dynamics of Quercus pubescens leaf litter in a naturally enriched CO2 Mediterranean ecosystem^43^13^3^343-351^^^^^Jun^^^^^7613
1298^1531^2487^312^57^583^596^733^874^879^a collected at Biosphere 2 to within 10% of observed, thus suggesting that wheat growth inside the IAB was comparable to that documented in other environments. The model predicts phenological stages and final dry matter (DM) production within 10% ofA^7612^1. The chemical composition (i.e. N, P, C, lignin and polyphenol concentrations) of Quercus pubescens leaf litter derived from a natural CO2 spring in Tuscany (Italy) was analysed and compared to litter from a nearby reference site. Litter was incubated for 25 months at both the natural CO2 spring and the reference site, and monitored for decomposition rates, nutrient and lignin concentrations. 2. Long-term exposure to elevated CO2 concentrations from the natural spring was associated with a change in the chemical composition of the Oak leaf litter, with decreases in P and polyphenol concentrations and increases in lignin. No differences in N concentrations were observed between the enriched CO2 litter from the natural spring and the reference litter. 3. Decomposition was reduced in the CO2 spring, with the lower P concentration of the native litter, combined with the lack of soil fauna observed at that site, being the factors most probably responsible for the measured decreases in mass loss. However, litter from the CO2 spring and reference litter decomposed at the reference site showed similar rates of decomposition. 4. All litter showed similar N concentrations during decomposition, with N being mineralized throughout the incubation period from both litter regardless of the site of incubation. In contrast, P dynamics differed between litter, with P being immobilized in the litter derived from the spring, and mineralized from the reference litter. When the litter from the spring was incubated at the reference site, there was a trend for net P uptake from the surrounding environment. The chemical composition of decomposing litter from the spring appeared to match that of the reference litter after 3 months of incubation at the reference site. 5. The results from the CO2 spring suggest that litter decomposition may be retarded under elevated levels of atmospheric CO2. However, results from field surveys around CO2 vents should be viewed with caution because differences may relate to factors other than the known differences in CO2 concentrations.

2428^1^Arnone,J A^1999^1^Symbiotic N-2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2^43^13^3^383-387^^^^^Jun^^^^^7615
1239^2742^2843^344^374^376^384^421^653^99^od from both litter regardless of the site of incubation. In contrast, P dynamics differed between litter, with P being immobilized in the litter derived from the spring, and mineralized from the reference litter. When the litter from the spring was incubated at the reference site, there was a trend for net P uptake from the surrounding environment. The chemical composition of decomposing litter from the spring appeared to match that of the reference litter after 3 months of incubation at the reference site. 5. The results from the CO2 spring suggest that litter decomposition may be retarded under elevated levels of atmospheric CO2. However, results from field surveys around CO2 vents should be viewed with caution because differences may relate to factors other than thA^7614^1. Increasing carbon dioxide concentration (E: 680 mu l CO2 litre(-1) vs ambient, A: 355 mu l CO2 litre(-1)) around late- successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992-1995) had no detectable effect on symbiotic N-2 fixation in Trifolium alpinum-the sole N-2-fixing plant species in these communities (74 +/- 30 mg N m(-2) year(-1), A and E plots pooled). 2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above-ground biomass (4.4 +/- 1.7 g m(-2), A and E plots pooled, n = 24) or N content per unit land area (124 +/- 51 mg N m(-2), A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N-2 fixation (%Ndfa: 61.0 +/- 4.1 across A and E plots) estimated using the N-15 dilution method. 3. Thus, it appears that N inputs to this ecosystem via symbiotic N-2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise.

2429^5^Huang,Y S^Street-Perrott,F A^Perrot,R A^Metzger,P^Eglinton,G^1999^1^Glacial-interglacial environmental changes inferred from molecular and compound-specific delta C-13 analyses of sediments from Sacred Lake, Mt. Kenya^138^63^9^1383-1404^^^^^May^^^^^7617
2513^3287^344^3511^3512^3513^3514^3515^3516^534^ies in these communities (74 +/- 30 mg N m(-2) year(-1), A and E plots pooled). 2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above-ground biomass (4.4 +/- 1.7 g m(-2), A and E plots pooled, n = 24) or N content per unit land area (124 +/- 51 mg N m(-2), A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N-2 fixation (%Ndfa: 61.0 +/- 4.1 across A and E plots) estimated using the N-15 dilution method. 3. Thus, it appears that N inputs to this ecosystem via symbiotic N-2 fixation will not be dramatically affected in the foreseeable future even as atmosA^7616^Molecular Stratigraphic analyses, including lipid distributions and compound-specific delta(13)C measurements, have been performed at 15 levels in a sediment core from Sacred Lake, Mt. Kenya, a high-altitude (2350 m a.s.l.) freshwater lake with a record extending from the last glacial (>40,000 cal. yr BP) through the present interglacial; Terrestrial and aquatic organic-matter sources were independently assessed using source-specific biomarkers. delta(13)C values of long-chain n- alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts: those from the last glacial maximum (LGM) (-20 to -18 parts per thousand) indicate a terrestrial vegetation dominated by C-4 grasses or sedges, whereas those from the early Holocene (-34 to -27 parts per thousand) reflect recolonization of the catchment area by C-3 plants, consistent with a rapid rise in the upper treeline. Specific algal biomarkers, including five unsaturated hydrocarbons of novel structure ascribed to the microalga Botryococcus braunii, were abundant, as confirmed by scanning electronic microscopy (SEM). An extreme delta(13)C shift of over 25 parts per thousand is displayed by the algal biomarkers, an elevated value of -5.1 parts per thousand at the last glacial maximum (LGM) contrasting with a minimum value of -30.3 parts per thousand at the beginning of the Holocene. A major change in the molecular distributions of the algal biomarkers parallels this large delta(13)C shift, with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the Holocene. The low atmospheric partial pressure of CO2 (pCO(2)) at the LGM would favour photosynthetic organisms possessing CO2-concentrating mechanisms, including terrestrial C-4 grasses and freshwater green algae. Hence, glacial/interglacial changes in pCO(2), and in the CO2:O-2 ratio in particular, had a significant impact on both terrestrial and aquatic ecosystems on Mt. Kenya, in addition to the effects of climate and local environmental factors. Copyright (C) 1999 Elsevier Science Ltd.

2430^2^Hemming,J D C^Lindroth,R L^1999^1^Effects of light and nutrient availability on aspen: Growth, phytochemistry, and insect performance^112^25^7^1687-1714^^^^^Jul^^^^^7619
1344^2114^2163^229^2971^2975^3456^3457^3517^733^ing with a minimum value of -30.3 parts per thousand at the beginning of the Holocene. A major change in the molecular distributions of the algal biomarkers parallels this large delta(13)C shift, with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the Holocene. The low atmospheric partial pressure of CO2 (pCO(2)) at the LGM would favour photosynthetic organisms possessing CO2-concentrating mechanisms, including terrestrial C-4 grasses and freshwater green algae. Hence, glacial/interglacial changes in pCO(2), and in the CO2:O-2 ratio in particular, had a significant impact on both terrestrial and aquatic ecosystems on Mt. Kenya, in addition to the effects of climate and local environmental factorA^7618^This study explored the effect of resource availability on plant phytochemical composition within the framework of carbon- nutrient balance (CNB) theory. We grew quaking aspen (Populus tremuloides) under two levels of light and three levels of nutrient availability and measured photosynthesis, productivity, and foliar chemistry [water, total nonstructural carbohydrates (TNC), condensed tannins, and phenolic glycosides]. Gypsy moths (Lymantria dispar) and forest tent caterpillars (Malacosoma disstria) were reared on foliage from each of the treatments to determine effects on insect performance. Photosynthetic rates increased under high light, but were not influenced by nutrient availability. Tree growth increased in response to both the direct and interactive effects of light and nutrient availability. Increasing light reduced foliar nitrogen, while increasing nutrient availability increased foliar nitrogen. TNC levels were elevated under high light conditions, but were not influenced by nutrient availability. Starch and condensed tannins responded to changes in resource availability in a manner consistent with CNB theory; levels were highest under conditions where tree growth was limited more than photosynthesis (i.e., high light-low nutrient availability). Concentrations of phenolic glycosides, however, were only moderately influenced by resource availability. In general, insect performance varied relatively little among treatments. Both species performed most poorly on the high light-low nutrient availability treatment. Because phenolic glycosides are the primary factor determining aspen quality for these insects, and because levels of these compounds were minimally affected by the treatments, the limited response of the insects was not surprising. Thus, the ability of CNB theory to accurately predict allocation to defense compounds depends on the response of specific allelochemicals to changes in resource availability. Moreover, whether allelochemicals serve to defend the plant depends on the response of insects to specific allelochemicals. Finally, in contrast to predictions of CNB theory, we found substantial allocation to storage and defense compounds under conditions in which growth was carbon-limited (e.g., low light), suggesting a cost to defense in terms of reduced growth.

2431^2^Stitt,M^Krapp,A^1999^1^The interaction between elevated carbon dioxide and nitrogen nutrition: the physiological and molecular background^9^22^6^583-621^^^^^Jun^^^^^7621
1026^1351^3518^3519^448^456^550^620^647^650^availability treatment. Because phenolic glycosides are the primary factor determining aspen quality for these insects, and because levels of these compounds were minimally affected by the treatments, the limited response of the insects was not surprising. Thus, the ability of CNB theory to accurately predict allocation to defense compounds depends on the response of specific allelochemicals to changes in resource availability. Moreover, whether allelochemicals serve to defend the plant depends on the responseA^7620^This review first summarizes the numerous studies that have described the interaction between the nitrogen supply and the response of photosynthesis, metabolism and growth to elevated [CO2]. The initial stimulation of photosynthesis in elevated [CO2] is often followed by a decline of photosynthesis, that is typically accompanied by a decrease of ribulose-1,5- bisphosphate carboxylase/oxygenase (Rubisco), an accumulation of carbohydrate especially starch, and a decrease of the nitrogen concentration in the plant. These changes are particularly marked when the nitrogen supply is low, whereas when the nitrogen supply is adequate there is no acclimation of photosynthesis, no major decrease in the internal concentration of nitrogen or the levels of nitrogen metabolites, and growth is stimulated markedly. Second, emerging evidence is discussed that signals derived from nitrate and nitrogen metabolites such as glutamine act to regulate the expression of genes involved in nitrate and ammonium uptake and assimilation? organic acid synthesis and starch accumulation, to modulate the sugar- mediated repression of the expression of genes involved in photosynthesis, and to modulate whole plant events including shoot-root allocation, root architecture and flowering. Third, increased rates of growth in elevated [CO2] will require higher rates of inorganic nitrogen uptake and assimilation. Recent evidence is discussed that an increased supply of sugars can increase the rates of nitrate and ammonium uptake and assimilation, the synthesis of organic acid accepters, and the synthesis of amino acids. Fourth, interpretation of experiments in elevated [CO2] requires that the nitrogen status of the plants is monitored, The suitability of different criteria to assess the plant nitrogen status is critically discussed. Finally the review returns to experiments with elevated [CO2] and discusses the following topics: is, and if so how, are nitrate and ammonium uptake and metabolism stimulated in elevated [CO2], and does the result depend on the nitrogen supply? Is acclimation of photosynthesis the result of sugar- mediated repression of gene expression, end-product feedback of photosynthesis, nitrogen-induced senescence, or ontogenetic drift? Is the accumulation of starch a passive response to increased carbohydrate formation, or is it triggered by changes in the nutrient status? How do changes in sugar production and inorganic nitrogen assimilation interact in different conditions and at different stages of the life history to determine the response of whole plant growth and allocation to elevated [CO2]?

2432^7^Heineke,D^Kauder,F^Frommer,W^Kuhn,C^Gillissen,B^Ludewig,F^Sonnewald,U^1999^1^Application of transgenic plants in understanding responses to atmospheric change^9^22^6^623-628^^^^^Jun^^^^^7623
1826^2125^3520^3521^372^441^448^564^685^845^turns to experiments with elevated [CO2] and discusses the following topics: is, and if so how, are nitrate and ammonium uptake and metabolism stimulated in elevated [CO2], and does the result dA^7622^Acclimation of plants to an increase in atmospheric carbon dioxide concentration is a well described phenomenon, It is characterized by an increase in leaf carbohydrates and a degradation of ribulose 1,5-bisphosphate carboxylase protein (Rubisco) leading in the long term to a lower rate of CO2 assimilation than expected from the kinetic constants of Rubisco, This article summarizes studies with transgenic plants grown in elevated pCO(2) which are modified in their capacity of CO2 fixation, of sucrose and starch synthesis, of triosephosphate and sucrose transport and of sink metabolism of sucrose, These studies show that a feedback accumulation of carbohydrates in leaves play only a minor role in acclimation, because leaf starch synthesis functions as an efficient buffer for photoassimilates. There is some evidence that in elevated pCO(2), plants grow faster and senescence is induced earlier.
 if so how, are nitrate and ammonium uptake and metabolism stimulated in elevated [CO2], and does the result d2433^3^Jarvis,A J^Mansfield,T A^Davies,W J^1999^1^Stomatal behaviour, photosynthesis and transpiration under rising CO2^9^22^6^639-648^^^^^Jun^^^^^7625
1918^2489^312^344^372^374^465^639^698^888^of ribulose 1,5-bisphosphate carboxylase protein (Rubisco) leading in the long term to a lower rate of CO2 assimilation than expected from the kinetic constants of Rubisco, This article summarizes studies with transgenic plants grown in elevated pCO(2) which are modified in their capacity of CO2 fixation, of sucrose and starch synthesis, of triosephosphate and sucrose transport and of sink metabolism of sucrose, These studies show that a feedback accumulation of carbohydrates in leaves play only a minor role in acclimation, because leaf starch synthesis functions as an efficient buffer for photoassimilates. There is some evidence that in elevated pCO(2), plants grow faster and senescence is induced earlier.
 if so how, are nitrate and ammonium uptake and metabolism stimulated in elevated [CO2], and does the result dA^7624^The literature reports enormous variation between species in the extent of stomatal responses to rising CO2. This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short-term response of leaf gas exchange to increases in ambient CO2 concentration by developing the recently proposed stomatal model of Jarvis gr Davies (1998). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO2 on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO2 concentration and also drought will have important effects on the relative gains to be achieved under rising CO2.

2434^12^Drake,B G^Azcon-Bieto,J^Berry,J^Bunce,J^Dijkstra,P^Farrar,J^Gifford,R M^Gonzalez-Meler,M A^Koch,G^Lambers,H^Siedow,J^Wullschleger,S^1999^1^Does elevated atmospheric CO2 concentration inhibit mitochondrial respiration in green plants?^9^22^6^649-657^^^^^Jun^^^^^7627
1260^2069^3522^384^389^430^462^507^520^92^ies (1998). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO2 on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO2 concentration and also droughtA^7626^There is abundant evidence that a reduction in mitochondrial respiration of plants occurs when atmospheric CO2 (C-a) is increased. Recent reviews suggest that doubling the present C-a will reduce the respiration rate [per unit dry weight (DW)] by 15 to 18%. The effect has two components: an immediate, reversible effect observed in leaves, stems, and roots of plants as well as soil microbes, and an irreversible effect which occurs as a consequence of growth in elevated C-a and appears to be specific to C-3 species. The direct effect has been correlated with inhibition of certain respiratory enzymes, namely cytochrome-c-oxidase and succinate dehydrogenase, and the indirect or acclimation effect may be related to changes in tissue composition. Although no satisfactory mechanisms to explain these effects have been demonstrated, plausible mechanisms have been proposed and await experimental testing. These are carbamylation of proteins and direct inhibition of enzymes of respiration. A reduction of foliar respiration of 15% by doubling present ambient C-a would represent 3 Gt of carbon per annum in the global carbon budget.

2435^2^Morison,J I L^Lawlor,D W^1999^1^Interactions between increasing CO2 concentration and temperature on plant growth^9^22^6^659-682^^^^^Jun^^^^^7629
1364^3386^344^3523^359^372^430^508^724^728^le effect observed in leaves, stems, and roots of plants as well as soil microbes, and an irreversible effect which occurs as a consequence of growth in elevated C-a and appears to be specific to C-3 species. The direct effect has been correlated with inhibition of certain respiratory enzymes, namely cytochrome-c-oxidase and succinate dehydrogenase, and the indirect or acclimation effect may be related to changes in tissue composition. Although no satisfactory mechanisms to explain these effects have been demonstrated, plausible mechanisms have been proposed and await experimental testing. These are carbamylation of proteins and direct inhibition of enzymes of respiration. A reduction of foliar rA^7628^The global environment is changing with increasing temperature and atmospheric carbon dioxide concentration, [CO2]. Because these two factors are concomitant, and the global [CO2] rise will affect all biomes across the full global range of temperatures, it is essential to review the theory and observations on effects of temperature and [CO2] interactions on plant carbon balance, growth, development, biomass accumulation and yield, Although there are sound theoretical reasons for expecting a larger stimulation of net CO2 assimilation rates by increased [CO2] at higher temperatures, this does not necessarily mean that the pattern of biomass and yield responses to increasing [CO2] and temperature is determined by this response. This paper reviews the interactions between the effects of [CO2] and temperature on plants. There is little unequivocal evidence for large differences in response to [CO2] at different temperatures, as studies are confounded by the different responses of species adapted and acclimated to different temperatures, and the interspecific differences in growth form and development pattern. We conclude by stressing the importance of initiation and expansion of meristems and organs and the balance between assimilate supply and sink activity in determining the growth response to increasing [CO2] and temperature.

2436^5^Norby,R J^Wullschleger,S D^Gunderson,C A^Johnson,D W^Ceulemans,R^1999^1^Tree responses to rising CO2 in field experiments: implications for the future forest^9^22^6^683-714^^^^^Jun^^^^^7631
1660^2056^3035^3119^3524^3525^430^733^857^966^igher temperatures, this does not necessarily mean that the pattern of biomass and yield responses to increasing [CO2] and temperature is determined by this response. This paper reviews the interactions between the effects of [CO2] and temperature on plants. There is little unequivocal evidence for large differences in response to [CO2] at different temperatures, as studies are confounded by the different responses of species adapted and acclimA^7630^The need to assess the role of forests in the global cycling of carbon and how that role will change as the atmospheric concentration of CO2 increases has spawned many experiments over a range of scales. Experiments using open-top chambers have been established at many sites to test whether the short- term responses of tree seedlings described in controlled environments would be sustained over several growing seasons under field conditions. Here we review the results of those experiments, using the framework of the interacting cycles of carbon, water and nutrients, because that is the framework of the ecosystem models that are being used to address the decades-long response of forests. Our analysis suggests that most of what was learned in seedling studies was qualitatively correct, The evidence from field-grown trees suggests a continued and consistent stimulation of photosynthesis of about 60% for a 300 p.p.m, increase in [CO2], and there is little evidence of the long-term loss of sensitivity to CO2 that was suggested by earlier experiments with tree seedlings in pots. Despite the importance of respiration to a tree's carbon budget, no strong scientific consensus has yet emerged concerning the potential direct or acclimation response of woody plant respiration to CO2 enrichment. The relative effect of CO2 on above-ground dry mass was highly variable and greater than that indicated by most syntheses of seedling studies. Effects of CO2 concentration on static measures of response are confounded with the acceleration of ontogeny observed in elevated CO2. The trees in these open-top chamber experiments were in an exponential growth phase, and the large growth responses to elevated CO2 resulted from the compound interest associated with an increasing leaf area. This effect cannot be expected to persist in a closed-canopy forest where growth potential is constrained by a steady-state leaf area index, A more robust and informative measure of tree growth in these experiments is the annual increment in wood mass per unit leaf area, which increased 27% in elevated CO2. There is no support for the conclusion from many studies of seedlings that root-to- shoot ratio is increased by elevated CO2; the production of fine roots may be enhanced, but it is not clear that this response would persist in a forest. Foliar nitrogen concentrations were lower in CO2-enriched trees, but to a lesser extent than was indicated in seedling studies and only when expressed on a leaf mass basis, The prediction that leaf litter C/N ratio would increase was not supported in field experiments. Also contrasting with seedling studies, there is little evidence from the field studies that stomatal conductance is consistently affected by CO2; however, this is a topic that demands more study. Experiments with trees in open- top chambers under field conditions have provided data on longer-term, larger-scale responses of trees to elevated CO2 under field conditions, confirmed some of the conclusions from previous seedling studies, and challenged other conclusions. There remain important obstacles to using these experimental results to predict forest responses to rising CO2, but the studies are valuable nonetheless for guiding ecosystem model development and revealing the critical questions that must be addressed in new larger-scale CO2 experiments.

2437^1^Ellsworth,D S^1999^1^CO2 enrichment in a maturing pine forest: are CO2 exchange and water status in the canopy affected?^9^22^5^461-472^^^^^May^^^^^7633
1099^2489^256^361^374^398^444^483^514^92^io would increase was not supported in field experiments. Also contrasting with seedling studies, there is little evidence from the field studies that stomatal conductance is consistently affected by CO2; however, this is a topic that demands more study. Experiments with trees in open- top chambers under field conditions have provided data on longer-term, larger-scale responses of trees to elevated CO2 under field conditions, confirmed some of the conclusions from previous seedling studies, and challenged otA^7632^Elevated CO2 is expected to reduce forest water use as a result of CO2-induced stomatal closure, which has implications for ecosystem-scale phenomena controlled by water availability. Leaf-level CO2 and H2O exchange responses and plant and soil water relations were examined in a maturing loblolly pine (Pinus taeda L,) stand in a free-air CO2 enrichment (FACE) experiment in North Carolina, USA to test if these parameters were affected by elevated CO2, Current-year foliage in the canopy was continuously exposed to elevated CO2 (ambient CO2 + 200 mu mol mol(-1)) in free-air during needle growth and development for lip to 400 d. Photosynthesis in upper canopy foliage was stimulated by 50-60% by elevated CO2 compared with ambient controls. This enhancement was similar in current-year, ambient-grown foliage temporarily measured at elevated CO2 compared with long-term elevated CO2 grown foliage, Significant photosynthetic enhancement by CO2 was maintained over a range of conditions except during peak drought. There was no evidence of water savings in elevated CO2 plots in FACE compared to ambient plots under drought and non-drought conditions. This was supported by evidence from three independent measures. First, stomatal conductance was not significantly different in elevated CO2 versus ambient trees of P. taeda, Calculations of time-integrated c(i)/c(a) ratios from analysis of foliar delta(13)C showed that these ratios were maintained in foliage under elevated CO2. Second, soil moisture was not significantly different between ambient and elevated CO2 plots during drought. Third, pre-dawn and mid-day leaf water potentials were also unaffected by the seasonal CO2 exposure, as were tissue osmotic potentials and turgor loss points. Together the results strongly support the hypothesis that maturing P. taeda trees have low stomatal responsiveness to elevated CO2. Elevated CO2 effects on water relations in loblolly pine-dominated forest ecosystems may be absent or small apart from those mediated by leaf area. Large photosynthetic enhancements in the upper canopy of P. taeda by elevated CO2 indicate that this maturing forest may have a large carbon sequestration capacity with limiting water supply.

2438^3^Myers,D A^Thomas,R B^Delucia,E H^1999^1^Photosynthetic capacity of loblolly pine (Pinus taeda L.) trees during the first year of carbon dioxide enrichment in a forest ecosystem^9^22^5^473-481^^^^^May^^^^^7635
130^256^344^348^360^372^384^385^444^665^iage under elevated CO2. Second, soil moisture was not significantly different between ambient and elevated CO2 plots during drought. Third, pre-dawn and mid-day leaf water potentials were also unaffected by the seasonal CO2 exposure, as were tissue osmotic potentials and turgor loss points. Together the results strongly support the hypothesis that maturing P. taeda trees have low stomatal responsiveness to elevated CO2. Elevated CO2 effects on water relations in loblolly pine-dominated forest ecosystems may be absent or small apart from those mediated by leaf area. Large A^7634^Our objective was to assess the photosynthetic responses of loblolly pine trees (Pinus taeda L,) during the first full growth season (1997) at the Brookhaven National Lab/Duke University Free Air CO2 Enrichment (FACE) experiment. Gas exchange, fluorescence characteristics, and leaf biochemistry of ambient CO2 (control) needles and ambient + 20 Pa CO2 (elevated) needles were examined five times during the year. The enhancement of photosynthesis by elevated CO2 in mature loblolly pine trees varied across the season and was influenced by abiotic and biotic factors. Photosynthetic enhancement by elevated CO2 was strongly correlated with leaf temperature. The magnitude of photosynthetic enhancement was zero in March but was as great as 52% later in the season. In March, reduced sink demand and lower temperatures resulted in lower net photosynthesis, lower carboxylation rates and higher excess energy dissipation from the elevated CO2 needles than from control needles, The greatest photosynthetic enhancement by CO2 enrichment was observed in July during a period of high temperature and low precipitation, and in September during recovery from this period of low precipitation, In July, loblolly pine trees in the control rings exhibited lower net photosynthetic rates, lower maximum rates of photosynthesis at saturating CO2 and light, lower values of carboxylation and electron transport rates (modelled from A-C-i curves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO2 rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light- and CO2-saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first-year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimation to CO2 occurs in these canopy loblolly pine trees growing in a forest ecosystem.

2439^3^Leymarie,J^Lasceve,G^Vavasseur,A^1999^1^Elevated CO2 enhances stomatal responses to osmotic stress and abscisic acid in Arabidopsis thaliana^9^22^3^301-308^^^^^Mar^^^^^7637
1754^2130^312^3159^344^3526^399^749^873^rating CO2 and light, lower values of carboxylation and electron transport rates (modelled from A-C-i curves), lower total Rubisco activity, and lower photochemical quenching of fluorescence in comparison to other measurement periods. During this period of low precipitation trees in the elevated CO2 rings exhibited reduced net photosynthesis and photochemical quenching of fluorescence, but there was little effect on light- and CO2-saturated rates of photosynthesis, modelled rates of carboxylation or electron transport, or Rubisco activity. These first-year data will be used to compare with similar measurements from subsequent years of the FACE experiment in order to determine whether photosynthetic acclimaA^7636^Carbon dioxide and abscisic acid (ABA) are two major signals triggering stomatal closure. Their putative interaction in stomatal regulation was investigated in well-watered air-grown or double CO2-grown Arabidopsis thaliana plants, using gas exchange and epidermal strip experiments. With plants grown in normal air, a doubling of the CO2 concentration resulted in a rapid and transient drop in leaf conductance followed by recovery to the pre-treatment level after about two photoperiods. Despite the fact that plants placed in air or in double CO2 for 2 d exhibited similar levels of leaf conductance, their stomatal responses to an osmotic stress (0.16-0.24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO2, Similarly, the drop in leaf conductance triggered by 1 mu M ABA applied at the root level was stronger at double CO2. Identical experiments were performed with plants fully grown at double CO2, Levels of leaf conductance and carbon assimilation rate measured at double CO2 were similar for air-grown and elevated CO2-grown plants. An enhanced response to ABA was still observed at high CO2 in pre- conditioned plants. It is concluded that: (i) in the absence of stress, elevated CO2 slightly affects leaf conductance in A. thaliana; (ii) there is a strong interaction in stomatal responses to CO2 and ABA which is not modified by growth at elevated CO2.

2440^3^Huxman,K A^Smith,S D^Neuman,D S^1999^1^Root hydraulic conductivity of Larrea tridentata and Helianthus annuus under elevated CO2^9^22^3^325-330^^^^^Mar^^^^^7639
245^374^376^409^417^430^465^610^881^92^ to an osmotic stress (0.16-0.24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO2, Similarly, the drop in leaf conductance triggered by 1 mu M ABA applied at the root level was stronger at double CO2. Identical experiments were performed with plants fully grown at double CO2, Levels of leaf conductance and carA^7638^While investigations into shoot responses to elevated atmospheric CO2 are extensive, few studies have focused on how an elevated atmospheric CO2 environment might impact root functions such as water uptake and transport. Knowledge of functional root responses may be particularly important in ecosystems where water is limiting if predictions about global climate change are true. In this study we investigated the effect of elevated CO2 on the root hydraulic conductivity (L-p) of a C-3 perennial, Lawea tridentata, and a C-3 annual, Helianthus annuus. The plants were grown in a glasshouse under ambient (360 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) CO2. The L-p through intact root systems was measured using a hydrostatic pressure-induced flow system. Leaf gas exchange was also determined for both species and leaf water potential (psi(leaf)) was determined in L, tridentata, The L-p of L, tridentata roots was unchanged by an elevated CO2 growth environment. Stomatal conductance (g(s)) and transpiration (E) decreased and photosynthetic rate (A(net)) and psi(leaf) increased in L, tridentata, There were no changes in biomass, leaf area, stem diameter or root : shoot (R : S) ratio for L, tridentata. In H, annuus, elevated CO2 induced a nearly two- fold decrease in root L-p. There was no effect of growth under elevated CO2 on A(net), g(s), E, above- and below-ground dry mass, R : S ratio, leaf area, root length or stem diameter in this species. The results demonstrate that rising atmospheric CO2 can impact water uptake and transport in roots in a species-specific manner. Possible mechanisms for the observed decrease in root L-p in H, annuus under elevated CO2 are currently under investigation and may relate to either axial or radial components of root L-p.

2441^3^Lin,W H^Bai,K Z^Kuang,T Y^1999^1^Effects of elevated CO2 and high temperature on single leaf and canopy photosynthesis of rice^384^41^6^624-628^^^^^Jun^^^^^7641
312^376^674^evated CO2 growth environment. Stomatal conductance (g(s)) and transpiratA^7640^The increase of atmospheric CO2 concentration is indisputable. In such condition, photosynthetic response of leaf is relatively well studied, while the comparison of that between single leaf and whole canopy is less emphasized. The stimulation of elevated CO2 on canopy photosynthesis may be different from that on single leaf level.. In this study, leaf and canopy photosynthesis of rice (Oryza sativa L.) were studied throughout the growing season. High CO2 and temperature had. a synergetic stimulation on single leaf photosynthetic rate until grain filling. Photosynthesis of leaf was stimulated by high CO2, although the stimulation was decreased by higher temperature at grain filling stage. On the other hand, the simulation of elevated CO2 on canopy photosynthesis leveled off with time. Stimulation at canopy level disappeared by grain filling stage in both temperature treatments. Green leaf area index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. Leaf nitrogen content decreased with the increase of CO2 concentration although it was not statistically significant at maturity. Canopy respiration rate increased at flowering stage indicating higher carbon loss: Shading effect caused bu leaf development reached maximum at flowering stage. The CO2 stimulation on photosynthesis was greater in single leaf than in canopy, Since enhanced CO2 significantly increased biomass of rice stems and panicles, increase in canopy respiration caused diminishment of CO2 stimulation in canopy net photosynthesis. Leaf nitrogen in the canopy level decreased with CO2 concentration and may eventually hasten CO2 stimulation on canopy photosynthesis. Early senescence of canopy leaves in high CO2 is also a possible cause.

2442^3^Hedges,L V^Gurevitch,J^Curtis,P S^1999^1^The meta-analysis of response ratios in experimental ecology^11^80^4^1150-1156^^^^^Jun^^^^^7643
174^3528^ index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. LA^7642^Meta-analysis provides formal statistical techniques for summarizing the results of independent experiments and is increasingly being used in ecology. The response ratio (the ratio of mean outcome in the experimental group to that in the control group) and closely related measures of proportionate change are often used as measures of effect magnitude in ecology. Using these metrics for meta-analysis requires knowledge of their statistical properties, but these have not been previously derived. We give the approximate sampling distribution of the log response ratio, discuss why it is a particularly useful metric for many applications in ecology, and demonstrate how to use it in meta-analysis. The meta- analysis of response-ratio data is illustrated using experimental data on the effects of increased atmospheric CO2 on plant biomass responses.
ology^11^80^4^1150-1156^^^^^Jun^^^^^7643
174^3528^ index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. L2443^4^Kruijt,B^Barton,C^Rey,A^Jarvis,P G^1999^1^The sensitivity of stand-scale photosynthesis and transpiration to changes in atmospheric CO2 concentration and climate^385^3^1^55-69^^^^^Mar^^^^^7645
1103^130^230^314^3529^372^376^384^385^975^e control group) and closely related measures of proportionate change are often used as measures of effect magnitude in ecology. Using these metrics for meta-analysis requires knowledge of their statistical properties, but these have not been previously derived. We give the approximate sampling distribution of the log response ratio, discuss why it is a particularly useful metric for many applications in ecology, and demonstrate how to use it in meta-analysis. The meta- analysis of response-ratio data is illustrated using experimental data on the effects of increased atmospheric CO2 on plant biomass responses.
ology^11^80^4^1150-1156^^^^^Jun^^^^^7643
174^3528^ index was not significantly affected by CO2 at maturity, but greater in plants grown at higher temperature. LA^7644^The 3-dimensional forest model MAESTRO was used to simulate daily and annual photosynthesis and transpiration fluxes of forest stands and the sensitivity of these flutes to potential changes in atmospheric CO2 concentration ([CO2]), temperature, water stress and phenology. The effects of possible feed-backs from increased leaf area and limitations to leaf nutrition were simulated by imposing changes in leaf area and nitrogen content. Two different tree species were considered: Picea sitchensis (Bong.) Carr., a conifer with long needle longevity and large leaf area, and Betula pendula Roth., a broad-leaved deciduous species with an open canopy and small leaf area. Canopy photosynthetic production in trees was predicted to increase with atmospheric [CO2] and length of the growing season and to decrease with increased water stress. Associated increases in leaf area increased production further only in the B. pendula canopy, where the original leaf area was relatively small. Assumed limitations in N uptake affected B. pendula more than P. sitchensis. The effect of increased temperature was shown to depend on leaf area and nitrogen content. The different sensitivities of the two species were related to their very different canopy structure. increased [CO2] reduced transpiration, but larger leaf area, early leaf growth, and higher temperature all led to increased water use. These effects were limited by feedbacks from soil water stress. The simulations suggest that, with the projected climate change, there is some increase in stand annual 'water use efficiency', but that actual water losses to the atmosphere may not always decrease.

2444^2^Leung,L R^Ghan,S J^1999^1^Pacific northwest climate sensitivity simulated by a regional climate model driven by a GCM. Part II: 2xCO(2) simulations^126^12^7^2031-2053^^^^^Jul^^^^^7647
344^930^stress. Associated increases in leaf area increased production further only in the B. pendula canopy, where the original leaf area was relatively small. Assumed limitations in N uptakA^7646^Global climate change due to increasing concentrations of greenhouse gases has stimulated numerous studies and discussions about its possible impacts on water resources. Climate scenarios generated by climate models at spatial resolutions ranging from about 50 km to 400 km may not provide enough spatial specificity for use in impact assessment. In Parts I and II of this paper. the spatial specificity issue is addressed by examining what information on mesoscale and small- scale spatial features can be gained by using a regional climate model with a subgrid parameterization of orographic precipitation and land surface cover, driven by a general circulation model. Numerical experiments have been performed to simulate the present-day climatology and the climate conditions corresponding to a doubling of atmospheric CO2 concentration. This paper describes and contrasts the large-scale and mesoscale features of the greenhouse warming climate signals simulated by the general circulation modal and regional climate model over the Pacific Northwest. Results indicate that changes in the large-scale circulation exhibit strong seasonal variability. There is an average warming of about 2 degrees C, and precipitation generally increases over the Pacific Northwest and decreases over California. The precipitation signal over the Pacific Northwest is only statistically significant during spring, when both the change in the large- scale circulation and increase in water vapor enhance the moisture convergence toward the north Pacific coast. The combined effects of surface temperature and precipitation changes are such that snow cover is reduced by up to 50% on average, causing large changes in the seasonal runoff. This paper also describes the high spatial resolution (1.5 km) climate signals simulated by the regional climate model. Reductions in snow cover of 50%-90% are found in areas near the snow line of the control simulation. Analyses of the variations of the climate signals with surface elevation ranging from sea level to 4000 m over two mountain ranges in the Pacific Northwest show that because of changes in the alitude of the freezing level, strong elevation dependency is found in the surface temperature, rainfall. snowfall, snow cover, and runoff signals.

2445^2^Baxter,R^Farrar,J F^1999^1^Export of carbon from leaf blades of Poa alpina L-at elevated CO2 and two nutrient regimes^78^50^336^1215-1221^^^^^Jul^^^^^7649
130^189^244^3364^344^362^678^711^92^ease in water vapor enhance the moisture convergence toward the north Pacific coast. The combined effects of surface temperature and precipitation changes are such that snow cover is reduced by up to 50% on average, causing large changes in the seasonal runoff. This paper also describes the high spatial resolution (1.5 km) climate signals simulated by the regional climate model. Reductions in snow cover of 50%-90% are found in areas near the snow line of the control simulation. Analyses of the variations of the climate signals with surface elevation ranging from sea leveA^7648^The hypothesis was tested that, in plants of the alpine! meadow grass (Poa alpina L,) exposed to elevated CO2, net photosynthesis and export from source leaves is; reduced as a result of feedback from sinks. Nutrient supply was used as one way of reducing photosynthesis and export. Single plants were grown in sand culture under specified controlled environmental conditions for a period of 50 d at two levels of nitrogen and phosphorus ('low': 0.2 mol m(-3) N, 0.04 mol m(-3) P;'high': 2.5 mol m(-3) N, 0.5 mol m(-3) P). Compartmentation within, and export of carbon from, individual youngest fully expanded leaves of acclimated plants was determined using C-14 feeding and efflux plus mass balance calculations of carbohydrate export. Independent of treatment, the bulk of soluble carbohydrate (65-75%) was present as fructan, with most of the remainder being sucrose. Depending on nutrient supply, CO2 could alter export from source leaves either by a reduction in the amount of sucrose present in a readily available pool for transport, or by altering the rate constant describing phloem loading.

2446^3^Marilley,L^Hartwig,U A^Aragno,M^1999^1^Influence of an elevated atmospheric CO2 content on soil and rhizosphere bacterial communities beneath Lolium perenne and Trifolium repens under field conditions^386^38^1^39-49^^^^^Jul^^^^^7651
1096^2435^2467^2758^312^3435^3530^3531^376^92^nditions for a period of 50 d at two levels of nitrogen and phosphorus ('low': 0.2 mol m(-3) N, 0.04 mol m(-3) P;'high': 2.5 mol m(-3) N, 0.5 mol m(-3) P). Compartmentation within, and export of carbon from, individual youngest fully expanded leaves of acclimated plants was determined using C-14 feeding and efflux plus mass balance calculations of carbohydrate export. Independent of treatment, the bulk of soluble carbohydrate (65-75%) was present as fructan, with most of the remainder being sucrose. Depending on nutrient supply, CO2 could alter export from source leaves either by a reduction in the amount of sucrose present in a readily avaiA^7650^The increase in atmospheric CO2 content alters C-3 plant photosynthetic rate, leading to changes in rhizodeposition and other root activities. This may influence the activity, the biomass, and the structure of soil and rhizosphere microbial communities and therefore the nutrient cycling rates and the plant growth. The present paper focuses on bacterial numbers and on community structure. The rhizospheres of two grassland plants, Lolium perenne (ryegrass) and Trifolium repens (white clover), were divided into three fractions: the bulk soil, the rhizospheric soil, and the rhizoplaneendorhizosphere. The elevated atmospheric CO2 content increased the most probable numbers of heterotrophic bacteria in the rhizosphere of L. perenne. However, this effect lasted only at the beginning of the vegetation period for T. repens. Community structure was assessed after isolation of DNA, PCR amplification, and construction of cloned 16S rDNA libraries. Amplified ribosomal DNA restriction analysis (ARDRA) and colony hybridization with an oligonucleotide probe designed to detect Pseudomonas spp. showed under elevated atmospheric CO2 content an increased dominance of pseudomonads in the rhizosphere of L. perenne and a decreased dominance in the rhizosphere of T. repens. This work provides evidence for a CO2-induced alteration in the structure of the rhizosphere bacterial populations, suggesting a possible alteration of the plant-growth-promoting- rhizobacterial (PGPR) effect.

2447^5^Olszyk,D^Wise,C^VanEss,E^Apple,M^Tingey,D^1998^1^Phenology and growth of shoots, needles, and buds of Douglas- fir seedlings with elevated CO2 and (or) temperature^188^76^12^1991-2001^^^^^Dec^^^^^7653
3532^3533^374^377^425^608^705^708^ in the rhizosphere of L. perenne. However, this effect lasted only at the beginning of the vegetation period for T. repens. Community structure was assessed after isolation of DNA, PCR amplification, and construction of cloned 16S rDNA libraries. Amplified ribosomal DNA restriction analysis (ARDRA) and colony hyA^7652^Increased atmospheric CO2 and global warming may affect overall tree growth, but impacts of these combined stresses are largely unknown in terms of multiple growing season impacts on specific flushes. Thus, the effects of ambient or elevated CO2 (approximately 200 mu mol.mol(-1) above ambient) and ambient or elevated temperature (approximately 4 degrees C above ambient) were evaluated for both main and second (lammas) flushes of Douglas-fir (Pseudotsuga menziesii (Mirb.) France). Established seedlings were grown for three full growing seasons in outdoor, sunlit chambers, which maintained diel and seasonal variation in climate. A reconstructed forest soil was used with a seasonal wet and dry cycle and without added fertilizer. Compared with ambient CO2 elevated CO2 had no impact on overall phenology and growth of terminal shoots, needles, or buds. In contrast, compared with ambient temperature, elevated temperature resulted in higher shoot and needle growth rates early in the season; reduced final terminal shoot length; and either reduced, increased, or unchanged final needle length, depending on season. Initiation of the lammas flush was delayed and (or) decreased at elevated temperature. Leading terminal bud break and growth occurred earlier; however, resting bud length was reduced, and bud width tended to increase with elevated temperature. Thus, at least during early seedling growth, elevated temperatures may reduce both main- and lammas- flush growth, thereby altering tree productivity, whereas elevated CO2 may have little effect on main or lammas growth at either the current or elevated temperature.

2448^3^Jager,H J^Hertstein,U^Fangmeier,A^1999^1^The European Stress Physiology and Climate Experiment - project 1. wheat (ESPACE-wheat): introduction, aims and methodology^314^10^3-4^155-162^^^^^Apr^^^^^7655
1285^130^1828^312^344^372^374^434^447^92^n contrast, compared with ambient temperature, elevated temperature resulted in higher shoot and needle growth rates early in the season; reduced final termA^7654^The response of crops to CO2 enrichment represents an issue of major concern both for scientists and for policymakers. In a concerted programme funded by the Commission of the European Communities, a Europe-wide experimental and modeling study was carried out to investigate the effects of increasing atmospheric CO2 concentrations, and of environmental stresses such as ozone or water/nutrient shortage, under different climatic conditions on wheat (Triticum aestivum L.). This contribution describes the experimental network and the standard protocol set-up for the assessments which served to improve and to validate process-orientated wheat growth simulation models. (C) 1999 Elsevier Science B.V. All rights reserved.

2449^2^Ewert,F^Pleijel,H^1999^1^Phenological development, leaf emergence, tillering and leaf area index, and duration of spring wheat across Europe in response to CO2 and ozone^314^10^3-4^171-184^^^^^Apr^^^^^7657
1279^130^1364^2733^341^372^720^723^724^92^ly in the season; reduced final termA^7656^Phenological development, leaf emergence, tillering and leaf area index (LAI), and duration (LAD) of spring wheat cv. Minaret, grown in open-top chambers at different sites throughout Europe for up to 3 years at each site, were investigated in response to elevated CO2 (ambient CO2 x2) and ozone (ambient ozone x1.5) concentrations. Phenological development varied among experiments and was partly explained by differences in temperature among sites and years. There was a weak positive relationship between the thermal rate of development and the mean daylength for the period from emergence to anthesis. Main stems produced on average 7.7 leaves with little variation among experiments. Variation was higher for the thermal rate of leaf emergence, which was partly explained by differences in the rate of change of daylength at plant emergence among seasons. Phenological development, rate of leaf emergence and final leaf number were not affected by CO2 and ozone exposure. Responses of tillering and LAI to CO2 and ozone exposure were significant only in some experiments. However, the direction of responses was consistent for most experiments. The number of tillers and ears per plant, respectively, was increased as a result of CO2 enrichment by about 13% at the beginning of stem elongation (DC31), at anthesis and at maturity. Exposure to ozone had no effect on tillering. LAI was increased as a result of CO2 elevation by about 11% at DC31 and by about 14% at anthesis. Ozone exposure reduced LAI at anthesis by about 9%. No such effect was observed at DC31. There were very few interactive effects of CO2 and ozone on tillering and LAI. Variations in tillering and LAI, and their responses to CO2 and ozone exposure, were partly explained by single linear relationships considering differences in plant density, tiller density and the duration of developmental phases among experiments. Consideration of temperature and incident photosynthetically active radiation in this analysis did not reduce the unexplained variation. There was a negative effect of ozone exposure on leaf area duration at most sites. Direct effects of elevated CO2 concentration on leaf senescence, both positive and negative, were observed in some experiments. There was evidence in several experiments that elevated CO2 concentration ameliorated the negative effect of ozone on leaf area duration. It was concluded from these results that an analysis of the interactive effects of climate, CO2 and ozone on canopy development requires reference to the physiological processes involved. (C) 1999 Elsevier Science B.V. All rights reserved.

2450^5^Ommen,O E^Donnelly,A^Vanhoutvin,S^van Oijen,M^Manderscheid,R^1999^1^Chlorophyll content of spring wheat flag leaves grown under elevated CO2 concentrations and other environmental stresses within the 'ESPACE-wheat' project^314^10^3-4^197-203^^^^^Apr^^^^^7659
1364^243^312^344^384^434^447^546^724^728^n of temperature and incident photosynthetically active radiation in this analysis did not reduce the unexplained variation. TherA^7658^Spring wheat cv. Minaret was grown in open-top chambers at four sites across Europe. The effect of different treatments (CO2 enrichment, O-3 fumigation, drought stress and temperature) on the chlorophyll content of the flag leaf was investigated using the MINOLTA SPAD-502 meter. Under optimum growth conditions the maximum chlorophyll content, which was reached at anthesis, was consistent among the sites ranging from 460 to 500 mg chlorophyll m(-2). No significant effect of elevated CO2 or O-3 was observed at anthesis. Leaf senescence, indicated by the chlorophyll breakdown after anthesis, was relatively constant in the control chambers. Under control conditions, thermal time until 50% chlorophyll loss was reached was 600 degrees C day. Elevated CO2 caused a faster decline in chlorophyll content (thermal time until 50% chlorophyll loss was reduced to 500-580 degrees C day) indicating a faster rate of plant development at two experimental sites. The effect of ozone on chlorophyll content depended on the time and dose of O-3 exposure. During grain filling, high O-3 concentrations induced premature senescence of the flag leaves (up to -130 degrees C day). This deleterious effect was mitigated by elevated CO2. Drought stress led to faster chlorophyll breakdown irrespective of CO2 treatment. (C) 1999 Elsevier Science B.V. All rights reserved.

2451^10^Mitchell,R A C^Black,C R^Burkart,S^Burke,J I^Donnelly,A^de Temmmerman,L^Fangmeier,A^Mulholland,B J^Theobald,J C^van Oijen,M^1999^1^Photosynthetic responses in spring wheat grown under elevated CO2 concentrations and stress conditions in the European, multiple-site experiment 'ESPACE-wheat'^314^10^3-4^205-214^^^^^Apr^^^^^7661
130^1347^1998^417^58^chlorophyll loss was reached was 600 degrees C day. Elevated CO2 caused a faster decline in chlorophyll content (thermal time until 50% chlorophyll loss was reduced to 500-580 degrees C day) indicating a faster rate of plant development at two experimental sites. The effect of ozone on chlorophyll content depended on theA^7660^Spring wheat cv. Minaret crop stands were grown under ambient and elevated CO2 concentrations at seven sites in Germany, Ireland, the UK, Belgium and the Netherlands. Six of the sites used open-top chambers and one used a controlled environment mimicking field conditions. The effect of elevated CO2 for a range of N application regimes, O-3 concentrations, and growth temperatures on flag leaf photosynthesis was studied. Before anthesis, flag leaf photosynthesis was stimulated about 50% by 650 compared with 350 mu mol mol(-1) CO2 at all sites, regardless of other treatments. Furthermore, there was no evidence of a decrease in photosynthetic capacity of flag leaves due to growth at elevated CO2 before anthesis, even for low N treatments. However, photosynthetic capacity, particularly carboxylation capacity, of flag leaves was usually decreased by growth at elevated CO2 after anthesis, especially in low N treatments. Acclimation of photosynthesis to elevated CO2 therefore appears to occur only slowly, consistent with a response to changes in sink-source relationships, rather than a direct response. Effect of elevated CO2 on stomatal conductance was much more variable between sites and treatments, but on average was decreased by similar to 10% at 650 compared with 350 mu mol mol(-1) CO2. Carboxylation capacity of flag leaves was decreased by growth at elevated O-3 both before and after anthesis, regardless of CO2 concentration. (C) 1999 Elsevier Science B.V. All rights reserved.

2452^8^Fangmeier,A^De Temmerman,L^Mortensen,L^Kemp,K^Burke,J^Mitchell,R^van Oijen,M^Weigel,H J^1999^1^Effects on nutrients and on grain quality in spring wheat crops grown under elevated CO2 concentrations and stress conditions in the European, multiple-site experiment 'ESPACE-wheat'^314^10^3-4^215-229^^^^^Apr^^^^^7663
1064^1076^1279^1364^137^1998^2087^229^2993^3534^eased by growth at elevated CO2 after anthesis, especially in low N treatments. Acclimation of photosynthesis to elevated CO2 therefore appears to occur only slowly, conA^7662^Nutrient element concentrations and grain quality were assessed in spring wheat grown under elevated CO2 concentrations and contrasting levels of tropospheric ozone at different nitrogen supply rates at several European sites. Carbon dioxide enrichment proved to affect nutrient concentrations in a complex manner, In green leaves, all elements (with exception of phosphorus and iron) decreased. In contrast, effects on the element composition of grains were restricted to reductions in nitrogen, calcium, sulphur and iron. Ozone exposure resulted in no significant effects on nutrient element concentrations in different tissues in the overall analysis. The nitrogen demand of green tissues was reduced due to CO2 enrichment as shown by reductions in the critical leaf nitrogen concentration and also enhanced nitrogen use efficiency. Reductions in the content of ribulose-bisphosphate carboxylase/oxygenase and repression of the photorespiratory pathway and reduced nitrogen allocation to enzymes driving the photosynthetic carbon oxidation cycle were chiefly responsible for this effect. Thus, nitrogen acquisition by the crop did not match carbon acquisition under CO2 enrichment, Since crop nitrogen uptake from the soil was already completed at anthesis, nitrogen allocated to the grain after anthesis originated from vegetative poors-causing grain nitrogen concentrations to decrease under CO2 enrichment (on average by 15% when CO2 concentrations increased from 360 to 680 mu mol mol(-1)). Correspondingly, grain quality was reduced by CO2 enrichment. The Zeleny value, Hagberg value and dry/wet gluten content decreased significantly with increasing [CO2]. Despite the beneficial impact of CO2 enrichment on growth and yield of C-3 cereal crops, declines in flour quality due to reduced nitrogen content are likely in a future, [CO2]-rich world. (C) 1999 Elsevier Science B.V. All rights reserved.
e carboxylase/oxygenase and repression of the photorespiratory pathway and reduced nitrogen allocation to enzymes driving the photo2453^2^van Oijen,M^Ewert,F^1999^1^The effects of climatic variation in Europe on the yield response of spring wheat cv. Minaret to elevated CO2 and O-3: an analysis of open-top chamber experiments by means of two crop growth simulation models^314^10^3-4^249-264^^^^^Apr^^^^^7665
1262^312^is originated from vegetative poors-causing grain nitrogen concentrations to decrease under CO2 enrichment (on average by 15% when CO2 concentrations increased from 360 to 680 mu mol mol(-1)). Correspondingly, grain quality was reduced by CO2 enrichment. The Zeleny value, Hagberg value and dry/wet gluten content decreased significantly with increasing [CO2]. Despite the beneficial impact of CO2 enrichment on growth and yield of C-3 cereal crops, declines in flour quality due to reduced nitrogen content are likely in a future, [CO2]-rich world. (C) 1999 Elsevier Science B.V. All rights reserved.
e carboxylase/oxygenase and repression of the photorespiratory pathway and reduced nitrogen allocation to enzymes driving the photoA^7664^In the ESPACE-Wheat programme, 25 open-top chamber experiments were carried out in 1994, 1995 and 1996, on nine locations, divided over eight European countries. In most experiments, spring wheat cv. Minaret was subjected to two levels of atmospheric CO2 and two levels of ozone. Grain yields in the control treatments (ambient levels of CO2 and O-3) varied strongly between sites. Also, yield response to elevated CO2 and O-3 showed great variation. The present study was conducted to determine whether climatic differences between sites could account for the observed variation. Two simulation models were used for the analysis: AFRCWHEAT2-O3 and LINTULCC. AFRCWHEAT2- O3 simulates phenology, canopy development and photosynthesis in greater detail than LINTULCC. Both models account for the effects of radiation and temperature on crop growth. New algorithms were developed to simulate the effects of CO2 and O- 3. Weather data that were measured in the experiments were used as input, and simulated growth responses to CO2 and O-3 were compared with measurements. No attempt was made to merge the two models. Thus two independent tools for analysis of data related to climate change were developed and applied. The average measured grain yield in the control treatment, across all 25 experiments, was 5.9 tons per hectare (t ha(-1)), with a standard deviation (SD) of 1.9 t ha(-1). The models predicted similar average yields (5.5 and 5.8 t ha(-1) for AFRCWHEAT2-O3 and LINTULCC, respectively), but smaller variation (SD for both models: 1.2 t ha(-1)). Average measured yield increase due to CO2-doubling was 30% (SD 22%). AFRCWHEAT2-O3 expected a slightly lower value (24%, SD 9%), whereas LINTULCC overestimated the response (42%, SD 11%). The average measured yield decrease due to nearly-doubled O-3 levels was 9% (SD 11%). Both models showed similar results, albeit at lower variation (7% yield decrease at SDs of 6 and 4%). Simulations accounted well for the observation that, at elevated CO2, the percentage yield loss due to O-3 was lower than at ambient CO2. The models predicted lower variation among sites and years than was measured. Yield response to CO2 and O-3 was predicted to depend on the climate, with a predominant effect of temperature on the response to CO2. In the measurements, these climatic effects were indeed observed, but a greater part of the variation was not related to light intensity, temperature, CO2, or O-3. This unexplained variability in the measured dataset was probably caused by factors not accounted for in the models, possibly related to soil characteristics. We therefore conclude that even perfect information on the climate variables examined in ESPACE-Wheat, i.e. light intensity and temperature, by itself would be insufficient for accurate prediction of the response of spring wheat to future elevated levels of CO2 and O-3. (C) 1999 Elsevier Science B.V. All rights reserved.
ase at SDs of 6 and 4%). Simulations accounted well for the observation that, at elevated CO2, the percentage yield loss due to O-2454^5^Perruchoud,D^Joos,F^Fischlin,A^Hajdas,I^Bonani,G^1999^1^Evaluating timescales of carbon turnover in temperate forest soils with radiocarbon data^137^13^2^555-573^^^^^Jun^^^^^7667
1106^1197^137^3311^344^3535^372^454^57^672^esponse to CO2. In the measurements, these climatic effects were indeed observed, but a greater part of the variation was not related to light intensity, temperature, CO2, or O-3. This unexplained variability in the measured dataset was probably caused by factors not accounted for in the models, possibly related to soil characteristics. We therefore conclude that even perfect information on the climate variables examined in ESPACE-Wheat, i.e. light intensity and temperature, by itself would be insufficient for accurate prediction of the response of spring wheat to future elevated levels of CO2 and O-3. (C) 1999 Elsevier Science B.V. All rights reserved.
ase at SDs of 6 and 4%). Simulations accounted well for the observation that, at elevated CO2, the percentage yield loss due to O-A^7666^Timescales of soil organic carbon (SOC) turnover in forests were investigated with soil radiocarbon data. The C-12/C-14 ratios were measured by accelerated mass spectroscopy on soil sampled from a deciduous temperate forest in Switzerland during 1969-1995. The resulting Delta(14)C values (125-174 parts per thousand) were in line with previously published C-14 soil data. We applied FORCLIM-D, a model of nonliving organic matter decomposition including nine litter and two soil compartments to estimate SOC turnover times for this forest type. Carbon 14 aging in woody vegetation was explicitly accounted for. Parameters were calibrated to match radiocarbon ratios observed for forest soils at Meathop Wood, United Kingdom [Harkness et al., 1986]. We estimated that roughly 50-94% (best estimate, 49%) of foliar litter carbon and 11-74% (73%) of fine root litter carbon are eventually respired as CO2 at Meathop Wood; the rest is transferred to soil humus, where it undergoes further decomposition. Turnover times for the 0-20 cm mineral soil layer ranged from 9-50 years (25 years) for a fast overturning soil compartment comprising 38-74% (68%) of bulk SOC and 155-10,018 years (3,570 years) for a slowly overturning compartment. For the Swiss site, SOC turnover times were in the same range. Parameter uncertainties were correlated and induced by uncertainties in C-14 observations from small-scale spatial inhomogeneities, sample preparation and by lack of reliable C- 14 observations for the "prebomb" test period. Model-based estimates of soil organic C turnover derived from C-14 data must be used cautiously since they depend on the underlying model structure: bypassing litter in FORCLIM-D overestimated SOC turnover by a factor of 2.5. Such an error might remain undetected in studies lacking samples from the late 1960s and early 1970s. Thus litter C turnover should be included when estimating SOC turnover in temperate forests from C-14 data.
sferred to soil humus, where it undergoes further decomposition. Turnover times 2455^4^Ormrod,D P^Lesser,V M^Olszyk,D M^Tingey,D T^1999^1^Elevated temperature and carbon dioxide affect chlorophylls and carotenoids in douglas-fir seedlings^104^160^3^529-534^^^^^May^^^^^7669
1102^188^230^243^3269^348^3536^437^456^605^SOC turnover times were in the same range. Parameter uncertainties were correlated and induced by uncertainties in C-14 observations from small-scale spatial inhomogeneities, sample preparation and by lack of reliable C- 14 observations for the "prebomb" test period. Model-based estimates of soil organic C turnover derived from C-14 data must be used cautiously since they depend on the underlying model structure: bypassing litter in FORCLIM-D overestimated SOC turnover by a factor of 2.5. Such an error might remain undetected in studies lacking samples from the late 1960s and early 1970s. Thus litter C turnover should be included when estimating SOC turnover in temperate forests from C-14 data.
sferred to soil humus, where it undergoes further decomposition. Turnover times A^7668^The objective of this study was to determine whether increased temperature and CO2 concentration would decrease or increase the concentrations of foliar pigments in S-yr-old seedlings of Douglas-fir Pseudotsuga menziesii [Mirb,] France var, menziesii). Seedlings were grown for 3 yr in sunlit, controlled environment chambers under ambient conditions or with a 179 mu L L-1 elevation of CO2 and/or a 3.5 degrees C elevation of temperature. Current- and previous-year needles were extracted with methanol for determination of chlorophylls and b, total carotenoids, and UV-absorbing compounds. Interactive effects of elevated temperature and CO2 on the measured responses were not significant. Current-year needles from the elevated CO2 treatment had the lowest chlorophyll and carotenoid concentrations, whereas needles of both age classes in the elevated temperature treatment had the highest concentrations of chlorophylls; current-year needles had the highest carotenoid concentration at elevated temperature. Neither temperature nor CO2 affected the concentrations of UV-absorbing compounds or needle fresh mass significantly. Chlorophyll a was correlated with carotenoids across all treatments (r = 0.75- 0.89) in both needle age classes and with chlorophyll b in most treatments.

2456^4^Polley,H W^Johnson,H B^Tischler,C R^Torbert,H A^1999^1^Links between transpiration and plant nitrogen: Variation with atmospheric CO2 concentration and nitrogen availability^104^160^3^535-542^^^^^May^^^^^7671
1019^243^3537^3538^3539^372^416^431^ation of chlorophylls and b, total carotenoids, and UV-absorbing compounds. Interactive effects of elevated temperature and CO2 on the measured responses were not significant. Current-year needles from the elevated CO2 treatment had the lowest chlorophyll and carotenoid concentrations, whereas needles of both age classes in the elevated temperature treatment had the highest concentrations of chlorophylls; current-year needles had the highest carotenoid concentration at elevated temperature. NeitA^7670^Transpiration is closely linked to plans nitrogen (N) content, indicating that global or other changes that alter plant N accumulation or the relative requirements of plants for water and N will affect transpiration. We studied effects of N availability and atmospheric CO2 concentration, two components of global biogeochemistry that are changing, on relationships between whole-plant transpiration and N in two perennial C-3 species, Pseudoroegneria spicata (a tussock grass) and Gutierrezia microcephala ia half-shrub). Two indices of plant N requirement were used: N accretion (N in live and dead tissues) and N loss in litter (N in dead tissues). Transpiration was analyzed as the product of N accretion or loss by plants and the ratio of transpiration to N accretion or loss. The two indices of plant N requirement led to different conclusions as to the effects of N availability on plant use of water relative to N. Transpiration scaled proportionally with N accretion, but transpiration per unit of N loss declined at high N. Carbon dioxide enrichment had little effect on the ratio of transpiration to N accretion and no effect on transpiration per unit of N lass. The two species accumulated similar amounts of N, but the half-shrub used more than twice as much water as the grass. Nitrogen availability and CO2 concentration influenced whole-plant transpiration more by changing plant N accumulation than by altering the stoichiometry between transpiration and plant N. Species differences in total water use, by contrast, reflected differences in the scaling of transpiration to plant N. A better under standing of species differences in water and N dynamics may thus be required to predict transpiration reliably.

2457^3^Mishra,R S^Abdin,M Z^Uprety,D C^1999^1^Interactive effects of elevated CO2 and moisture stress on the photosynthesis, water relation and growth of Brassica species^161^182^4^223-229^^^^^Jun^^^^^7673
2841^344^361^400^409^434^scaled proportionally with N accretion, but transpiration per unit of N loss deA^7672^Interactive effects of elevated CO2 and moisture stress on photosynthesis, growth and water relation of Brassica species were studied using open top chamber technology. Brassica species responded to the elevated CO2 significantly under moisture stress condition. The adverse effect of moisture stress on the photosynthesis and plant water components were minimized by elevated levels of CO2. Drought susceptible species of B. campestris and B. nigra responded better to elevated CO2 compared to drought tolerant Brassica species such as B. carinata and B, juncea. The plant water potential significantly improved by elevated CO2 coupled with higher stomatal resistance and root growth.

2458^6^Groninger,J W^Johnsen,K H^Seiler,J R^Will,R E^Ellsworth,D S^Maier,C A^1999^1^Elevated carbon dioxide in the atmosphere - What might it mean for loblolly pine plantation forestry?^387^97^7^4-10^^^^^Jul^^^^^7675
1386^256^3540^361^384^416^444^641^92^998^oportionally with N accretion, but transpiration per unit of N loss deA^7674^Research with loblolly pine suggests that projected increases iii atmospheric CO2 concentration will accelerate early growth and could result in shouter rotation length, reduced time until first commercial thinning, higher optimal planting density, and possibly higher maximum stocking level in managed stands. We discuss some of the physiological processes and stand dynamics that underlie these changes, as well as silvicultural strategies that may serve to ensure sustainability of intensively managed forest systems in the face of increasing CO2 and possible climate change.

2459^2^Rillig,M C^Allen,M F^1999^1^What is the role of arbuscular mycorrhizal fungi in plant-to- ecosystem responses to Elevated atmospheric CO2?^265^9^1^1-8^^^^^Jun^^^^^7677
1096^1317^1983^2364^2742^312^3435^474^789^91^ atmosphere - What might it mean for loblolly pine plantation forestry?^387^97^7^4-10^^^^^Jul^^^^^7675
1386^256^3540^361^384^416^444^641^92^998^oportionally with N accretion, but transpiration per unit of N loss deA^7676^We advocate the concept of an arbuscular mycorrhiza (AM) as a temporally and spatially complex symbiosis representing a suite of hosts and fungi, as against the more traditional "dual organism" view. We use the hierarchical framework presented in Fig. 1 as a basis for organizing many unanswered questions, and several questions that have not been asked, concerning the role of AM in responses to elevated atmospheric CO2. We include the following levels: plant host, plant population, plant community, functional group and ecosystem. Measurements of the contributions of AM fungi at the various levels require the use of different response variables. For example, hyphal nutrient translocation rates or percent AM root infection may be important measures at the individual plant level, but hyphal biomass or glomalin production and turnover are more relevant at the ecosystem level. There is a discrepancy between our knowledge of the multifaceted role of AM fungi in plant and ecosystem ecology and most of the current research aimed at elucidating the importance of this symbiosis in global-change scenarios. Our framework for more integrated and multifactorial research on mycorrhizal involvement in regulating CO2 responses may also serve to enhance communication between researchers working at different scales on large global-change ecosystem projects.

2460^2^Jones,C G^Hartley,S E^1999^1^A protein competition model of phenolic allocation^15^86^1^27-44^^^^^Jul^^^^^7679
2069^229^2967^3541^3542^3543^3544^3545^690^733^unctional group and ecosystem. Measurements of the contributions of AM fungi at the various levels require the use of different response variables. For example, hyphal nutrient translocation rates or percent AM root infection may be important measures at the individual plant level, but hyphal biomass or glomalin production and turnover are more relevant at the ecosystem level. There is a discrepancy between our knowledge of the multifaceted role of AM fungi in plant and ecosystem ecology and most of the curA^7678^We present a Protein Competition Model (PCM) for predicting total phenolic allocation and concentration in leaves of terrestrial higher plants. In contrast to predictions based on the carbon composition of end products, the PCM is based on metabolic origins of pathway constituents, alternative fates of pathway precursors, and biochemical regulatory mechanisms. Protein and phenolic synthesis compete for the common, limiting resource phenylalanine, so protein and phenolic allocation are inversely correlated. Phenolic allocation can be predicted from the effects of development, inherent growth rate and environment on leaf functions that create competing demands for proteins or phenolics. We present the model general principles. We predict phenolic concentrations as leaves develop; in inherently fast versus slow growing species; and in response to the environment (nitrogen, light, phosphorus, heat shock, herbivore and pathogen injury, and carbon dioxide). Because predictions generally fit observed patterns, we argue that, for phenylalanine-derived phenolics, the mechanistically distinctive PCM complements the Growth Differentiation and Resource Availability Hypotheses, and is a viable, testable alternative to the Carbon Nutrient Balance Hypothesis.

2461^1^Roberntz,P^1999^1^Effects of long-term CO2 enrichment and nutrient availability in Norway spruce. I. Phenology and morphology of branches^252^13^4^188-198^^^^^May^^^^^7681
2017^256^312^3448^3546^372^374^439^444^92^ phenolic allocation are inversely correlated. Phenolic allocation can be predicted from the effects of development, inherent growth rate and environment on leaf functions that create competing demands for proteins or phenolics. We present the model general principles. We predict phenolic concentrations as leaves develop; in inherently fast versus slow growing species; and in response to the environment (nitrogen, light, phosphorus, heat shock, herbivore and pathogen injury, and carbon dioxide). Because predictions generally fit observed patternA^7680^Branches of 30-year-old Norway spruce [Picea abies (L.) Karst.] trees were enclosed in ventilated, transparent plastic bags and flushed with air containing ambient (A approximate to 370 mu mol CO2 mol(-1)) or ambient plus 340 mu mol CO2 mol(-1) (EL). Light-saturated photosynthesis was on average 56% higher in EL compared to A. Branch phenology and morphology were strongly related to nitrogen concentration (mg g(-1) dry mass) in the foliage and to elevated temperatures in the bags, but no direct effect of EL was found. In 1995, budbreak occurred on average 4 days earlier in the bags compared to the control branches, which was partly explained by the temperature elevation in the bags. No nutrient or EL effect on budbreak was found. Increases in temperature and nitrogen supply increased shoot growth: together they explained 76% of the variation in the extension rate, 63% of the variation in extension duration and 65% of the variation in final length of leading shoots. Shoot morphology was altered both by increased nitrogen availability and by the enclosure induced environmental changes inside the bags, leading to reduced mutual shading between needles. Specific needle area (SNA) was lower in EL, but this was related to lower nitrogen concentrations. Total dry mass of the branches was unaffected by EL. It is concluded that treating individual branches of Norway spruce with elevated CO2 does not increase branch growth. The nutrient status of the branch and climate determine its growth, i.e, its sink strength for carbon. Increased export of carbohydrates to the rest of the tree is probable in EL treated branches.

2462^2^Cairney,J W G^Meharg,A A^1999^1^Influences of anthropogenic pollution on mycorrhizal fungal communities^35^106^2^169-182^^^^^^^^^^7683
1064^1342^1848^2530^3547^3548^479^602^605^733^rowth: together they explained 76% of the variation in the extension rate, 63% of the variation in extension duration and 65% of the variation in final length of leading shoots. Shoot morphology was altered both byA^7682^Mycorrhizal fungi form complex communities in the root systems of most plant species and are thought to be important in terrestrial ecosystem sustainability. We have reviewed the literature relating to the influence of the major forms of anthropogenic pollution on the structure and dynamics of mycorrhizal fungal communities. All forms of pollution have been reported to alter the structure of below-ground communities of mycorrhizal fungi to some degree, although the extent to which such changes will be sustained in the longer term is at present not clear. The major limitation to predicting the consequences of pollution-mediated changes in mycorrhizal fungal communities to terrestrial habitats is our limited understanding of the functional significance of mycorrhizal fungal diversity. While this is identified as a priority area for future research, it is suggested that, in the absence of such data, an understanding of pollution-mediated changes in mycorrhizal mycelial systems in soil may provide useful indicators for sustainability of mycorrhizal systems. (C) 1999 Elsevier Science Ltd. All rights reserved.

2463^2^Loats,K V^Rebbeck,J^1999^1^Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow- poplar seedlings^35^106^2^237-248^^^^^^^^^^7685
1076^256^344^3549^3550^3551^384^444^602^966^e been reported to alter the structure of below-ground communities of mycorrhizal fungi to some degree, although the extent to which such changes will be sustained in the longer term is at present not clear. The major limitation to predicting the consequences of pollution-mediated changes in mycorrhizal fungal communities to terrestrial habitats is our limited understanding of the functional significance of mycorrhizal fungal diversity. While this is identified as a priority area for future research, it is suggested that, in the absence of such data, an understanding of pollution-mediated changes in mycorrhizal mycelial systems in soil may provide useful A^7684^Potted seedlings of black cherry (Prunus serotina Ehrh.) (BC), green ash (Fraxinus pennsylvanica Marsh.) (GA), and yellow- poplar (Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO2 (control); (2) twice ambient O-3 (2XO(3)); (3) twice ambient CO2 (650 mu l l(-1)) plus CF air (2xCO(2)); or (4) twice ambient CO2 (650 yl l(-1)) plus twice ambient O-3 (2XCO(2)+2XO(3)) The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O-3 and CO2 on the gas exchange of all three species were limited. The effects of elevated CO2 and O-3, singly and combined, on light-saturated net photosynthesis (A(max)) and stomatal conductance (g(s)) were inconsistent across species. In all three species, elevated O-3 had no effect on g(s). Elevated CO2 significantly increased A(max) in GA and YP foliage, and decreased g(s) in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2xCO(2). Elevated O-3 affected few of these parameters but any change that was observed was opposite to that fi-om exposure to 2xCO(2)-air. Interactive effects of CO2 and O-3 On light-response parameters were limited. Carboxylation efficiencies, derived from CO2-response curves (A/C-i curves) decreased only in YP foliage exposed to 2xCO(2)-air. In general, growth was significantly stimulated by 2xCO(2) in all three species; though there were few significant growth responses following exposure to 2xO(3) or the combination of 2xCO(2) plus 2xO(3). Results indicate that responses to interacting stressors such as O-3 and CO2 are species specific. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
n g(s). Elevated CO2 significantly incr2464^3^de Wild,H P J^Woltering,E J^Peppelenbos,H W^1999^1^Carbon dioxide and 1-MCP inhibit ethylene production and respiration of pear fruit by different mechanisms^78^50^335^837-844^^^^^Jun^^^^^7687
1000^1012^1068^1507^2524^2750^3552^3553^418^497^es when exposed to 2xCO(2). Elevated O-3 affected few of these parameters but any change that was observed was opposite to that fi-om exposure to 2xCO(2)-air. Interactive effects of CO2 and O-3 On light-response parameters were limited. Carboxylation efficiencies, derived from CO2-response curves (A/C-i curves) decreased only in YP foliage exposed to 2xCO(2)-air. In general, growth was significantly stimulated by 2xCO(2) in all three species; though there were few significant growth responses following exposure to 2xO(3) or the combination of 2xCO(2) plus 2xO(3). Results indicate that responses to interacting stressors such as O-3 and CO2 are species specific. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
n g(s). Elevated CO2 significantly incrA^7686^Ethylene production in relation to O-2 partial pressure of whole pear fruit stored at 2 degrees C could be described by a Michaelis-Menten equation. This was indicated by the use of a gas exchange model. The maximum ethylene production rate was strongly inhibited while the K-mO2 value (1.25 kPa) was not affected by elevated CO2. Ethylene production was also inhibited by 1-MCP, an inhibitor of ethylene perception. The reduction in ethylene production by CO2 was similar for 1-MCP treated and untreated pears. Elevated CO2, therefore, must have had an influence on ethylene production other than through ethylene perception. A possible site of inhibition by CO2 is the conversion of ACC to ethylene. The O-2 uptake rate in relation to O-2 partial pressure of whole pear fruit could be described by a Michaelis-Menten equation. The O-2 uptake rate was inhibited by elevated CO2 at a level similar to the inhibition of ethylene production. Again the K-mO2 value (0.68 kPa) was not affected by CO2. Using 1-MCP treatments it was shown that there was no direct effect of inhibited ethylene production on O-2 uptake rate.

2465^3^Staddon,P L^Fitter,A H^Robinson,D^1999^1^Effects of mycorrhizal colonization and elevated atmospheric carbon dioxide on carbon fixation and below-ground carbon partitioning in Plantago lanceolata^78^50^335^853-860^^^^^Jun^^^^^7689
1684^1982^243^2757^349^374^407^431^692^92^, an inhibitor of ethylene perception. The reduction in ethylene production by CO2 was similar for 1-MCP treated and untreated pears. Elevated CO2, therefore, must have had an influence on ethylene production other than through ethylene perception. A possible site of inhibition by CO2 is the conversion of ACC to ethylene. The O-2 uptake rate in relation to O-2 partial pressure of whole pear fruit could be described by a Michaelis-Menten equation. The O-2 uptake rate was inhibited by elevated CO2 at a level similar to the inhibition of ethylene production. Again the K-mO2 value (0.68 kPa) was not affected by CO2. Using 1-MCP treatmA^7688^Plantago lanceolata with or without the mycorrhizal fungus Glomus mosseae were grown over a 100 d period under ambient (380 +/- 50 mu mol mol(-1)) and elevated (600 +/- 150 mu mol mol(-1)) atmospheric CO2 conditions. To achieve similar growth, non-mycorrhizal plants received phosphorus in solution whereas mycorrhizal plants were supplied with bonemeal. Measures of plant growth, photosynthesis and carbon input to the soil were obtained, Elevated CO2 stimulated plant growth to the same extent in mycorrhizal and non-mycorrhizal plants, but had no effect on the partitioning of carbon between shoots and roots or on shoot tissue phosphorus concentration. Mycorrhizal colonization was low, but unaffected by CO2 treatment. Net photosynthesis was stimulated both by mycorrhizal colonization and elevated CO2, and there was a more than additive effect of the two treatments on net photosynthesis. Colonization by mycorrhizal fungi inhibited acclimation, in terms of net carbon assimilation, of plants to elevated CO2. C-13 natural abundance techniques were used to measure carbon input into the soil, although the results were not conclusive. Direct measurements of below-ground root biomass showed that elevated CO2 did stimulate carbon flow below-ground and this was higher in mycorrhizal than non-mycorrhizal plants. For the four treatment combinations, the observed relative differences in amount of below-ground carbon were compared with those expected from the differences in net photosynthesis. A considerable amount of the extra carbon fixed both as a result of mycorrhizal colonization and growth in elevated CO2 did not reveal itself as increased plant biomass, As there was no evidence for a substantial increase in soil organic matter, most of this extra carbon must have been respired by the mycorrhizal fungus and the roots or by the the plants as dark-respiration. The need for detailed studies in this area is emphasized.
























 acclimation, in terms of net carbon assimilation, of plants to elevated CO2.2472^3^Rillig,M C^Field,C B^Allen,M F^1999^1^Soil biota responses to long-term atmospheric CO2 enrichment in two California annual grasslands^2^119^4^572-577^^^^^Jun^^^^^7703
1298^1334^1981^2258^312^372^672^778^885^92^n flow below-ground and this was higher in mycorrhizal than non-mycorrhizal plants. For the four treatment combinations, the observed relative differences in amount of below-ground carbon were compared with those expected from the differences in net photosynthesis. A considerable amount of the extra carbon fixed both as a result of mycorrhizal colonization and growth in elevated CO2 did not reveal itself as increased plant biomass, As there was no evidence for a substantial increase in soil organic matter, most of this extra carbon must have been respired by the mycorrhizal fungus and the roots or by the the plants as dark-respiration. The need for detailed studies in this area is emphasized.
























 acclimation, in terms of net carbon assimilation, of plants to elevated CO2.A^7702^Root, arbuscular-mycorrhizal (AM), soil faunal (protozoa and microarthropods), and microbial responses to field exposure to CO2 for six growing seasons were measured in spring 1997 in two adjacent grassland communities. The grasslands showed contrasting root responses to CO2, enrichment: whereas root length was not affected in the sandstone grassland, it was greater in the serpentine grassland, as was specific root length. AM fungal hyphal lengths were greater in the sandstone, but were unaffected in the serpentine community. This lent support to the hypothesis that there may be a tradeoff in resource allocation to more fine roots or greater mycorrhizal extraradical hyphal length. AM root infection was greater in both communities at elevated CO2, as was the proportion of roots containing arbuscules. Our data on total hyphal lengths, culturable and active fungi, bacteria, and protozoa supported the hypothesis that the fungal food chain was more strongly stimulated than the bacterial chain. This study is one of the first to test these hypotheses in natural multi-species communities in the field.

2473^1^Lloyd,J^1999^1^Current perspectives on the terrestrial carbon cycle^257^51^2^336-342^^^^^Apr^^^^^7705
1660^224^230^2426^3554^3555^372^57^672^890^
A^7704^Over the last 5 or so years, there have been significant advances in the understanding of the current role of the terrestrial biosphere in the global carbon cycle, especially in terms of how pools and fluxes are affected by variations in climate (including interannual variability as well as longer- term climate change), increases in atmospheric CO, concentrations and changed rates of atmospheric nitrogen deposition. At the same time, significant advances have been made in terms of both direct. measurement of ecosystem productivity and in an understanding of the key underlying mechanisms modulating carbon fluxes from terrestrial systems. A brief synopsis of these advances is the subject of this paper.
rongly stimulated than the bacterial chain. This study i2474^4^Hendry,M J^Mendoza,C A^Kirkland,R A^Lawrence,J R^1999^1^Quantification of transient CO2 production in a sandy unsaturated zone^133^35^7^2189-2198^^^^^Jul^^^^^7707
1234^1434^23^2543^312^3556^3557^543^607^669^30^2426^3554^3555^372^57^672^890^
A^7704^Over the last 5 or so years, there have been significant advances in the understanding of the current role of the terrestrial biosphere in the global carbon cycle, especially in terms of how pools and fluxes are affected by variations in climate (including interannual variability as well as longer- term climate change), increases in atmospheric CO, concentrations and changed rates of atmospheric nitrogen deposition. At the same time, significant advances have been made in terms of both direct. measurement of ecosystem productivity and in an understanding of the key underlying mechanisms modulating carbon fluxes from terrestrial systems. A brief synopsis of these advances is the subject of this paper.
rongly stimulated than the bacterial chain. This study iA^7706^Temporal and spatial respiration rates were determined in a 5.7-m thick, sandy, unsaturated zone over a 550-day period using measured CO2 concentrations, CO2 fluxes to the atmosphere, moisture contents, and temperatures. Cyclical patterns in CO2 concentrations were measured in duplicate nests of nine gas samplers. Maximum CO2 gas concentrations occurred during the summer (0.85-1.22%), and minimum concentrations occurred during the winter (0.04-0.24%). CO2 gas concentrations decreased with increasing depth during the summer and increased with depth during the winter. A one-dimensional finite element model was developed to quantify transient respiration rates through the unsaturated zone. The model was calibrated to the measured CO2 concentrations. Temperature and moisture content variations were represented with an analytical expression and linear interpolation of field-measured values, respectively, in the model. Simulation results provided very good approximations to the field-measured CO2 concentrations, but predicted CO2 fluxes to the atmosphere were higher than measured. Respiration rates ranged from 5 mu g C g(-1) d(-1) in the soil horizon during the summer to about <10(-4) mu g C g(-1) d(-1) in unsaturated sections of the C horizon. A sensitivity analysis showed that the respiration rates in the C horizon must be <10(-3) mu g C g(-1) d(-1) and that the majority of the elevated CO2 concentrations in this thick unsaturated zone are the result of respiration in the soil horizon. Overall, roots contribute about 75% of the CO2 in the summer months. O-2 gas, microbial analyses, and the distribution of root biomass supported this conclusion. These observations also imply that although microorganisms are present in subsurface environments their in situ activity in this sandy unsaturated zone may be very low.

2475^4^Ferris,R^Wheeler,T R^Ellis,R H^Hadley,P^1999^1^Seed yield after environmental stress in soybean grown under elevated CO2^164^39^3^710-718^^^^^May-Jun^^^^^7709 the field-measured CO2 concentrat243^3104^3105^312^3558^3559^359^374^546^58^here were higher than measured. Respiration rates ranged from 5 mu g C g(-1) d(-1) in the soil horizon during the summer to about <10(-4) mu g C g(-1) d(-1) in unsaturated sections of the C horizon. A sensitivity analysis showed that the respiration rates in the C horizon must be <10(-3) mu g C g(-1) d(-1) and that the majority of the elevated CO2 concentrations in this thick unsaturated zone are the result of respiration in the soil horizon. Overall, roots contribute about 75% of the CO2 in the summer months. O-2 gas, microbial analyses, and the distribution of root biomass supported this conclusion. These observations also imply that although microorganisms are present in subsurface environments their in situ activity in this sandy unsaturated zone may be very low.

2475^4^Ferris,R^Wheeler,T R^Ellis,R H^Hadley,P^1999^1^Seed yield after environmental stress in soybean grown under elevated CO2^164^39^3^710-718^^^^^May-Jun^^^^^7709 the field-measured CO2 concentratA^7708^Episodes of high temperature and drought are predicted to occur more frequently under conditions of future climate change, This study investigated whether an episode of high air temperature (HT + 15 degrees C), water deficit (WD), or both (HTWD), for 8 d, had the same effects on the yield of soybean [Glycine max (L.) Merrill, cv. Fiskeby V] grown under either ambient (aCO(2); 360 mu mol mol(-1) CO2) or elevated (eCO(2); 700 mu mol mol(-1) CO2) CO2 concentrations. Plants were grown in a glasshouse at either aCO(2) or at eCO(2) until 52 d after sowing (DAS). The 8-d stress treatments were then imposed before the plants were returned to their original environments. Across harvests, total biomass was 41% greater under eCO(2) than under aCO(2) but reduced by HT, WD, and HTWD under both CO2 concentrations, The relative response of total biomass to HT,WD, and HTWD episodes was the same for plants grown under either aCO(2) or eCO(2). At maturity, seed dry weight and number per plant under eCO(2) were increased by an average of 32 and 22%, respectively, compared with aCO(2). The same parameters were reduced after HTWD by 29 and 30%, respectively, in aCO(2) and eCO(2), Seed filling was earlier under HT and HTWD The rate of change in harvest index was unaltered by CO2 while under HTWD, it decreased. Seed number explained 85% of the variation in yield, but yield was also related linearly to photosynthesis during seed filling, suggesting both are important determinants of yields under stress.

2476^7^Adamsen,F J^Pinter,P J^Barnes,E M^LaMorte,R L^Wall,G W^Leavitt,S W^Kimball,B A^1999^1^Measuring wheat senescence with a digital camera^164^39^3^719-724^^^^^May-Jun^^^^^7711
1320^1324^1890^434^662^724^867^iomass was 41% greater under eCO(2) than under aCO(2) but reduced by HT, WD, and HTWD under both CO2 concentrations, The relative response of total biomass to HT,WD, and HTWD episodes was the same for plants grown under either aCO(2) or eCO(2). At maturity, seed dry weight and number per plant under eCO(2) were increaseA^7710^Documenting crop senescence rates is often difficult because of the need for frequent sampling during periods of rapid change and the subjective nature of human visual observations. The purpose of this study was to determine the feasibility of using images produced by a digital camera to measure the senescence rate of wheat and to compare the results with changes in greenness determined by two established methods. Measurements were made as part of an experiment to determine the effects of elevated CO2 and limited soil nitrogen on spring wheat (Triticum aestivum L.) at the University of Arizona's Maricopa Agricultural Center, near Phoenix, AZ. "Greenness" measurements were made during senescence of the crop with a color digital camera, a hand-held radiometer, and a SPAD chlorophyll meter. The green to red (GIR) for each pixel in an image was calculated and the average GIR computed for cropped images from a digital camera representing 1 m(2) for each treatment and sample date. The normalized difference vegetation index (NDVI) was calculated from the red and near-infrared canopy reflectances measured with a hand held radiometer. A SPAD reading was obtained from randomly selected flag leaves. All three methods of measuring plant greenness showed similar temporal trends. The relationships between GIR with NDVI and SPAD were linear over most of the range of GIR. However, NDVI was more sensitive at low values than GIR. GIR was more sensitive above G/R values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while GIR responded to both chlorophyll concentration in the leaves as well as the number of leaves present. Color digital imaging appears useful for quantifying the senescence of crop canopies. The cost of color digital cameras is expected to decrease and the quality and convenience of use to improve.
GIR computed for cropped images from a digital camera representing 1 m(2) for each treatment and sample date. The normalized difference 2477^4^Heagle,A S^Miller,J E^Booker,F L^Pursley,W A^1999^1^Ozone stress, carbon dioxide enrichment, and nitrogen fertility interactions in cotton^164^39^3^731-741^^^^^May-Jun^^^^^7713
1262^269^344^3466^3560^3561^372^580^864^92^ greenness showed similar temporal trends. The relationships between GIR with NDVI and SPAD were linear over most of the range of GIR. However, NDVI was more sensitive at low values than GIR. GIR was more sensitive above G/R values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while GIR responded to both chlorophyll concentration in the leaves as well as the number of leaves present. Color digital imaging appears useful for quantifying the senescence of crop canopies. The cost of color digital cameras is expected to decrease and the quality and convenience of use to improve.
GIR computed for cropped images from a digital camera representing 1 m(2) for each treatment and sample date. The normalized difference A^7712^Ozone (O-3) in the troposphere can cause plant stress leading to foliar injury and suppressed growth and yield, whereas elevated CO2 generally enhances growth and yield. Numerous studies have been performed to determine effects of O-3 and CO2 separately, but relatively few have been performed to determine if O-3 can affect plant response to CO2 or vice versa. Open-top field chambers were used to determine if such interactions occur for cotton (Gossypium hirsutum L.), which is relatively sensitive to O-3. Nitrogen nutrition is especially important in cotton production so N nutrition was included as an experimental factor. Plants were grown in 14-L pots at low, medium, and high soil N levels and exposed to three CO2 and two or three O-3 treatments in all combinations during two seasons. The CO2 treatments were ambient (370 mu L L-1) and two treatments with CO2 added for 24 h d(-1) at approximately 1.5 and 2.0 Limes ambient. In 1995, the O-3 treatments were charcoal filtered air (CP), and nonfiltered air (NF) with O-3 added for 12 h d(-1) (NF+). In 1996, a NF treatment was also included to represent ambient O-3 conditions. The CF, NF, and NF+ treatments resulted in seasonal O-3 concentrations of approximately 23, 51, and 75 nL L-1. Carbon dioxide enrichment generally stimulated growth and yield whereas O-3 exposure suppressed growth. and yield. Stimulation induced by CO2 increased as O-3 stress increased. For example, in 1995 at medium N, the percentage increase in yield caused by doubling CO2 in CF air was 0%, but was 52% in NF+ air. Comparable values for 1996 were 23% in CF air and 140% in NF+ air. These interactions occurred for a range of soil N levels, and were probably caused by CO2-induced prevention of O-3 stress. The results emphasize the need to consider O-3 x CO2 interactions to ensure correct interpretation of cause-effect relationships in CO2 enrichment studies with crops that are sensitive to O-3.
 Limes ambient. In 1995, the O-3 treatments were charcoal filtered air (CP), and nonfiltered air2478^3^Sozzi,G O^Trinchero,G D^Fraschina,A A^1999^1^Controlled-atmosphere storage of tomato fruit: low oxygen or elevated carbon dioxide levels alter galactosidase activity and inhibit exogenous ethylene action^269^79^8^1065-1070^^^^^Jun^^^^^7715
1012^1246^3562^3563^3564^3565^386^829^ and yield whereas O-3 exposure suppressed growth. and yield. Stimulation induced by CO2 increased as O-3 stress increased. For example, in 1995 at medium N, the percentage increase in yield caused by doubling CO2 in CF air was 0%, but was 52% in NF+ air. Comparable values for 1996 were 23% in CF air and 140% in NF+ air. These interactions occurred for a range of soil N levels, and were probably caused by CO2-induced prevention of O-3 stress. The results emphasize the need to consider O-3 x CO2 interactions to ensure correct interpretation of cause-effect relationships in CO2 enrichment studies with crops that are sensitive to O-3.
 Limes ambient. In 1995, the O-3 treatments were charcoal filtered air (CP), and nonfiltered airA^7714^The effects of 3% O-2 and 20% CO2, both alone and together with 100 mu g g(-1) C2H4, on ethylene production, chlorophyll degradation, carotenoid biosynthesis and alpha- and beta- galactosidase activity in breaker tomato (Lycopersicon esculentum Mill) fruit were investigated. The low O-2 and high CO2 atmospheres prevented the rise in ethylene production, total carotenoid and lycopene biosynthesis and alpha- and beta- galactosidase activity and slowed down chlorophyll degradation and loss of firmness (P<0.05). These suppressive effects were not reversed, or only in part - in the case of chlorophyll breakdown - by addition of 100 mu g g(-1) C2H4 to said controlled atmospheres. After transfer from the various atmospheres to air, flesh firmness decreased and ethylene production, total carotenoids, lycopene and beta-galactosidase II activity increased but these parameters were, in all cases, still significantly different from those of fruit held in air. Keeping tomatoes in controlled atmospheres, even in the presence of ethylene, had marked residual effects. Results suggest an antagonism between elevated CO2/low O-2 and exogenous ethylene which could determine most of the ripening parameter behaviour under controlled-atmosphere storage, though a direct regulatory mechanism by O-2 and/or CO2 should not be discarded. (C) 1999 Society of Chemical Industry.

2479^3^Gouk,S S^He,J^Hew,C S^1999^1^Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2^173^41^3^219-230^^^^^Jun^^^^^7717
1096^1124^1901^374^376^377^493^561^781^92^chlorophyll breakdown - by addition of 100 mu g g(-1) C2H4 to said controlled atmospheres. After transfer from the various atmospheres to air, flesh firmness decreased and ethylene production, total carotenoids, lycopene and beta-galactosidase II activity increased but these parameters were, in all cases, still significantly different from those of fruit held in air. Keeping tomatoes in controlled atmospheres, even in thA^7716^The effects on growth in super-elevated (1%) CO2 in terms of photosynthetic capability and carbohydrate production were studied in an epiphytic CAM (Crassulacean acid metabolism) orchid plantlet, Mokara Yellow (Arachmis hookeriana x Ascocenda Madame Kenny). The growth of the plantlets was greatly enhanced after growing for 3 months at 1% CO2 compared with the control plantlets (0.035% CO2). CO2 enrichment produced more than a 2- fold increase in dry matter production. The enhanced root growth at 1% CO2 led to a higher root:shoot ratio. Plantlets grown at super-elevated CO2 had higher F-v/F-m values, a higher photochemical quenching (q(P)) and a relatively lower non- photochemical quenching (q(N)). CO2 at 1% appeared to enhance the utilization of captured light energy in the orchid plantlets. CO2 enrichment also increased contents of soluble sugars (glucose and sucrose) and starch in the orchid plantlets. The extra starch formed under 1% CO, did not cause a disruption of the chloroplasts. Chlorophyll content was higher and a clear granal stacking was evident in young leaves and roots of plantlets grown at 1% CO2. An extensive thylakoid system was observed in the young leaf chloroplasts of the CO2- enriched plantlets indicating an improved development of the photosynthetic apparatus when compared to that of the control plantlets. The increased photosynthetic capacity and enhanced growth of the epiphytic roots under CO, enrichment would facilitate the generation of more photoassimilates and acquisition of essential resources, thereby increasing the survival rate of orchid plantlets under stressful field conditions. (C) 1999 Elsevier Science B.V. All rights reserved.

2480^3^Staddon,P L^Graves,J D^Fitter,A H^1999^1^Effect of enhanced atmospheric CO2 on mycorrhizal colonization and phosphorus inflow in 10 herbaceous species of contrasting growth strategies^43^13^2^190-199^^^^^Apr^^^^^7719
137^1684^3566^374^376^398^419^439^474^803^rmed under 1% CO, did not cause a disruption of the chloroplasts. Chlorophyll cA^7718^1, Ten herbaceous species were grown over a 4-month period under ambient (360 mu mol mol(-1)) and elevated (610 mu mol mol(-1)) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus mosseae and given a phosphorus (P) supply which was not immediately available to the plants. 2. Multiple harvests were taken in order to determine whether the effect of elevated CO2 on mycorrhizal colonization and phosphorus inflow was independent of its effect on plant growth. 3, All species grew faster under elevated CO2 and carbon partitioning was altered, generally in favour of the shoots. All species responded similarly to elevated CO2. 4. Elevated CO2 did not affect the percentage of root length colonized by AM fungi, but the total amount of colonized root length was increased, because the plants were bigger. 5. Elevated CO2 increased total P content, but had little or no effect on P concentration. At a given age, P inflow was stimulated by elevated CO2, but when root length was taken into account the CO2 effect disappeared. 6. In these host species there is no evidence for a direct effect of elevated CO2 on mycorrhizal functioning, because both internal mycorrhizal colonization and P inflow are unaffected. 7. Future research should concentrate on the potential for carbon flow to the soil via the external mycelial network.

2481^2^Stocklin,J^Korner,C^1999^1^Interactive effects of elevated CO2, P availability and legume presence on calcareous grassland: results of a glasshouse experiment^43^13^2^200-209^^^^^Apr^^^^^7721
1600^1783^2742^3047^3567^417^613^699^766^975^y in favour of the shoots. All species responded similarly to elevated CO2. 4. Elevated CO2 did not affect the percentage of root length colonized by AM fungi, but the total amount of colonized root length was increased, because the plants were bigger. 5. Elevated CO2 increased total P content, but had little or no effect on P concentration. At a given age, P inflow was stimulated by elevated CO2, but when root lA^7720^1, We investigated the interactive effects of elevated CO2, supply of phosphorus (P) and legume presence in model communities of calcareous grassland. Half of the communities contained six graminoids and eight nan-legume forb species, In the other half, four non-legume forbs were replaced by legumes. 2, Ecosystem responses. Above-ground phytomass (>5 cm) hardly responded to elevated CO2 alone. However, when P and legumes were combined. the CO2 effect on above-ground community phytomass in year two was a stimulation of 45% (P < 0.001). Below-ground community dry matter was stimulated by elevated CO2 alone by + 36% (P < 0.01), but was only + 20% (P < 0.05) when legumes were present and P was added, At the final (late season) harvest the mean effect of elevated CO2 on total above- and below-ground phytomass was + 23% (P < 0.001) and revealed no significant interactions among treatment combinations, because above- and belowground effects of CO2 enrichment had opposite directions. 3, Functional group responses. When legumes were absent, graminoids increased their total above- and below-ground phytomass in elevated CO2 by 60% (P < 0.001) but there was no increase when legumes were present. The response of forbs to CO2 was nor significant, irrespective of co-treatment. Legumes. however, were significantly stimulated by P supply and their CO2 response was much larger when P was added (+ 55%, P < 0.01 vs + 25%, NS). 4, Species responses. CO2 effects on species ranged from highly positive (+ 143%) to moderately negative (- 43%). 5, Our results demonstrate that the effect of CO2 enrichment in such natural grassland communities will be low on above-ground phytomass and largely below-ground if no additional nutrients are provided. N-2- fixing legumes appear to be crucial for the community response to elevated CO2 but legume responsiveness is largely controlled by P availability.
s among treatment combinations, because above- and belowground effects of CO2 enrichment had opposite directions. 3, Functional group respo2482^3^Hattenschwiler,S^Buhler,S^Korner,C^1999^1^Quality, decomposition and isopod consumption of tree litter produced under elevated CO2^15^85^2^271-281^^^^^May^^^^^7723
1531^1823^2477^3035^344^348^3568^3569^3570^693^ nor significant, irrespective of co-treatment. Legumes. however, were significantly stimulated by P supply and their CO2 response was much larger when P was added (+ 55%, P < 0.01 vs + 25%, NS). 4, Species responses. CO2 effects on species ranged from highly positive (+ 143%) to moderately negative (- 43%). 5, Our results demonstrate that the effect of CO2 enrichment in such natural grassland communities will be low on above-ground phytomass and largely below-ground if no additional nutrients are provided. N-2- fixing legumes appear to be crucial for the community response to elevated CO2 but legume responsiveness is largely controlled by P availability.
s among treatment combinations, because above- and belowground effects of CO2 enrichment had opposite directions. 3, Functional group respoA^7722^Rising atmospheric CO2 is expected to alter plant tissue quality which in turn could affect litter quality, decomposition, and carbon and nutrient turnover. We tested this hypothesis using leaf litter of beech (Fagus sylvatica) and branchlets (wood + bark) of spruce (Picea abies) produced under contrasting CO2 concentrations in model ecosystems. Both types of litter produced under elevated CO2 had significantly lower N concentrations, but showed no CO2-related differences in carbon and lignin concentrations. Decomposition rates (mass loss) assessed in a natural temperate forest were significantly slower in litter produced at high CO2. However, this effect became stronger in beech leaves but gradually disappeared in spruce branchlets over the 331-d exposure period. Irrespective of CO2 treatment beech leaf litter lost 16% of its initial N content. Spruce branchlets produced at low CO2 lost 50% of their initial N content, and those produced at high CO2 lost 26%. Two isopod species representing native macro-decomposers consumed 36% more of the high CO2-produced beech litter than they did of low CO2-produced beech litter. Only small, and non- significant increases in consumption of high CO2-produced spruce branchlets were observed. Isopods feeding on high CO, litter also produced more feces than those feeding litter from low CO2. Our results indicate that CO2-induced litter quality changes influence only certain stages of decomposition. and that these stages differ between different litter types. Inhibitory effects of elevated CO2, however, may be compensated by the positive feed-back of intensified "litter processing" of low quality litter by macro-decomposers. Consequently, the entire cycle of litter production and decomposition must be included in the analysis of the potential effects of rising CO2 on litter decomposition. This includes both micro- and macro- decomposer specific effects.
ost 50% of their initial N content, and those produced at high CO2 lost 26%. Two isopod species representing native mac2483^2^Syvertsen,J P^Graham,J H^1999^1^Phosphorus supply and arbuscular mycorrhizas increase growth and net gas exchange responses of two Citrus spp. grown at elevated [CO2]^206^208^2^209-219^^^^^^^^^^7725
1983^312^344^3566^3571^3572^376^57^705^803^high CO, litter also produced more feces than those feeding litter from low CO2. Our results indicate that CO2-induced litter quality changes influence only certain stages of decomposition. and that these stages differ between different litter types. Inhibitory effects of elevated CO2, however, may be compensated by the positive feed-back of intensified "litter processing" of low quality litter by macro-decomposers. Consequently, the entire cycle of litter production and decomposition must be included in the analysis of the potential effects of rising CO2 on litter decomposition. This includes both micro- and macro- decomposer specific effects.
ost 50% of their initial N content, and those produced at high CO2 lost 26%. Two isopod species representing native macA^7724^We hypothesized that greater photosynthate supply at elevated [CO2] could compensate for increased below-ground C demands of arbuscular mycorrhizas. Therefore, we investigated plant growth, mineral nutrition, starch, and net gas exchange responses of two Citrus spp. to phosphorus (P) nutrition and mycorrhizas at elevated atmospheric [CO2]. Half of the seedlings of sour orange (C. aurantium L.) and `Ridge Pineapple' sweet orange (C. sinensis L. Osbeck) were inoculated with the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenck and Smith and half were non-mycorrhizal (NM). Plants were grown at ambient or 2X ambient [CO2] in unshaded greenhouses for 11 weeks and fertilized daily with nutrient solution either without added P or with 2 mM P in a low-P soil. High P supply reduced AM colonization whereas elevated [CO2] counteracted the depressive effect of P on intraradical colonization and vesicle development. Seedlings grown at either elevated [CO2], high P or with G. intraradices had greater growth, net assimilation of CO2 (A(CO2)) in leaves, leaf water-use efficiency, leaf dry wt/area, leaf starch and carbon/nitrogen (C/N) ratio. Root/whole plant dry wt ratio was decreased by elevated [CO2], P, and AM colonization. Mycorrhizal seedlings had higher leaf-P status but lower leaf N and K concentrations than nonmycorrhizal seedlings which was due to growth dilution effects. Starch in fibrous roots was increased by elevated [CO2] but reduced by G. intraradices, especially at low-P supply. In fibrous roots, elevated [CO2] had no effect on C/N, but AM colonization decreased C/N in both Citrus spp. grown at low-P supply. Overall, there were no species differences in growth or A(CO2). Mycorrhizas did not increase plant growth at ambient [CO2]. At elevated [CO2], however, mycorrhizas stimulated growth at both P levels in sour orange, the more mycorrhiza-dependent species, but only at low- P in sweet orange, the less dependent species. At low-P and elevated [CO2], colonization by the AM fungus increased A(CO2) in both species but more so in sour orange than in sweet orange. Leaf P and root N concentrations were increased more and root starch level was decreased less by AM in sour orange than in sweet orange. Thus, the additional [CO2] availability to mycorrhizal plants increased CO2 assimilation, growth and nutrient uptake over that of NM plants especially in sour orange under P limitation.

2484^6^Murchie,E H^Sarrobert,C^Contard,P^Betsche,T^Foyer,C H^Galtier,N^1999^1^Overexpression of sucrose-phosphate synthase in tomato plants grown with CO2 enrichment leads to decreased foliar carbohydrate accumulation relative to untransformed controls^184^37^4^251-260^^^^^Apr^^^^^7727
1437^1584^243^244^3034^360^372^427^57^845^se plant growth at ambient [CO2]. At elevated [CO2], however, mycorrhizas stimulated growth at both P levels in sour orange, the more mycorrhiza-dependent species, but only at low- P in sweet orange, the less dependent species. At low-P and elevated [CO2], colonization by the AM fungus increased A(A^7726^Tomato plants expressing the maize sucrose-phosphate synthase (SPS) cDNA under the control of the promoter of the small subunit of ribulose-1,5-bisphosphate carboxylase oxygenase (rbcS) promoter were grown 5 weeks in air (450 mu mol.m(-2) s(- 1) irradiance, 350 ppm CO2) and then either maintained in air or exposed to CO2 enrichment (1 000 ppm CO2) for 8 d. A linear relationship between the foliar sucrose to starch ratio and maximal extractable SPS activity was found both in air and high CO2. Starch accumulation was dramatically increased in all plants subjected to CO2 enrichment but the CO2-dependent increase in foliar starch accumulation was much lower in the leaves of the SPS transformants than in those of the untransformed controls in the same conditions. Maximal extractable ribulose-1,5-bisphosphate carboxylase/ oxygenase activity was reduced by growth at high CO2 to a similar extent in both plant types. The carbon/nitrogen ratios were similar in both plant lines in both growth conditions after 20 d exposure to high CO2. A small (5 %) increase in carbon export capacity was observed at high CO2 in the leaves of transformed plants compared to leaves from untransformed controls. Increased foliar SPS activity did not, however, prevent acclimation of photosynthesis in plants grown with long-term CO2 enrichment. (C) Elsevier, Paris.

2485^7^Grant,R F^Wall,G W^Kimball,B A^Frumau,K F A^Pinter,P J^Hunsaker,D J^Lamorte,R L^1999^1^Crop water relations under different CO2 and irrigation: testing of ecosys with the free air CO2 enrichment (FACE) experiment^107^95^1^27-51^^^^^31 May^^^^^7729
1692^256^3288^341^344^384^431^59^614^977^tarch accumulation was much lower in the leaves of the SPS transformants than in those of the untransformed controls in the same conditions. Maximal extractable ribulose-1,5-bisphosphate carboxylase/ oxygenase activity was reduced by growth at high CO2 to a similar extent in both plant types. The carbon/nitrogen ratios were similar in both plant lines in both growth conditions after 20A^7728^Increases in crop growth under elevated atmospheric CO2 concentration (C-A) have frequently been observed to be greater under water-limited versus non-limited conditions. Crop simulation models used in climate change studies should be capable of reproducing such changes in growth response to C-A with changes in environmental conditions. We propose that changes with soil water status in crop growth response to C-A can be simulated if stomatal resistance is considered to vary directly with air-leaf C-A gradient, inversely with leaf carboxylation rate, and exponentially with leaf turgor. Resistance simulated in this way increases with C-A relatively less, and CO2 fixation increases with C-A relatively more, under water-limited versus non-limited conditions. As part of the ecosystem model ecosys, this simulation technique caused changes in leaf conductance and CO2 fixation, and in canopy water potential, temperature and energy balance in a modelling experiment that were consistent with changes measured under 355 versus 550 mu mol mol(-1) C-A and low versus high irrigation in a free air CO2 enrichment (FACE) experiment on wheat. Changes with C-A in simulated crop water relations allowed the model to reproduce under 550 mu mol mol(-1) C-A and low versus high irrigation a measured increase of 20 versus 10% in seasonal wheat biomass, and a measured decrease of 2 versus 5% in seasonal evapotranspiration, The basic nature of the processes simulated in this model is intended to enable its use under a wide range of soil, management and climate conditions. (C) 1999 Elsevier Science B.V. All rights reserved.

2486^2^Vitousek,P M^Field,C B^1999^1^Ecosystem constraints to symbiotic nitrogen fixers: a simple model and its implications^26^46^1^179-202^^^^^Jul^^^^^7731
1103^1298^224^312^372^374^424^456^787^92^ys, this simulation technique caused changes in leaf conductance and CO2 fixation, and in canopy water potential, temperature and energy balance in a modelling experiment that were consistent with changes measured unA^7730^The widespread occurrence of N limitation to net primary production (NPP) and other ecosystem processes, despite the ubiquitous occurrence of N-fixing symbioses, remains a significant puzzle in terrestrial ecology. We describe a simple simulation model for an ecosystem containing a generic nonfixer and a symbiotic N fixer, based on: (1) a higher cost for N acquisition by N fixers than nonfixers; (2) growth of fixers and fixation of N only when low N availability limits the growth of nonfixers, and other resources are available; and (3) losses of fixed N from the system only when the quantity of available N exceeds plant and microbial demands. Despite the disadvantages faced by the N fixer under these conditions, N fixation and loss adjust N availability close to the availability of other resources, and biomass and NPP in this simple model can be substantially but only transiently N limited. We then modify the model by adding: (1) losses of N in forms other than excess available N (e.g., dissolved organic N, trace gases produced by nitrification); and (2) constraints to the growth and activity of N fixers imposed by differential effects of shading, P limitation, and grazing. The combination of these processes is sufficient to describe an open system, with input from both precipitation and N fixation, that is nevertheless strongly N-limited at equilibrium. This model is useful for exploring causes and consequences of constraints to N fixation, and hence of N limitation, and we believe it will also be useful for evaluating how N fixation and limitation interact with elevated CO2 and other components of global enviromental change.

2487^1^Gruters,U^1999^1^On the role of wheat stem reserves when source-sink balance is disturbed by elevated CO2^292^73^1-2^55-62^^^^^May^^^^^7733
130^2051^417^434^435^92^ces, and biomass and NPP in this simple model can be substantially but only transiently N limited. We then modify the model by adding: (1) losses of N in forms other than excess available N (e.g., dissolved orgaA^7732^Spring wheat (Triticum aestivum L. cv. Minaret) was exposed to 360 and 680 mu mol mol(-1) CO2 in open top chambers during the vegetation periods of 1994/1995. In 1994 fractionated harvests were carried out at weekly intervals from the onset of stem elongation,. At final harvest CO, enhanced aboveground biomass and yield by 49.7 and 43.2%, respectively. From all plant organs stem dry weights showed the largest increases under doubled CO2, whereas leaf-blade dry weights increased only slightly. Since stems are known as sites of intermediary carbohydrate-storage, carbohydrate composition was analysed in the internodes of the main stem. Carbohydrates were determined as fructans, sucrose and reducing sugars. CO2 stimulated the amounts per organ of all components, but fructans showed the largest increases. Fructan accumulation lasted about one week longer and remobilisation was faster under elevated CO2. The results are consistent with current knowledge, that temporary storage pools accomodate source photosynthate supply to sink demand and suggested a predominant role of the intermediary stem reserves, when source-sink relations are changed under elevated CO2. The contribution of the main stem reserves to the main stem yield was also enhanced by elevated CO2 (6.1-8.7% compared to 10.0-14.2%). In 1995 growth and yield increase due to elevated CO2 (50.6 and 53%) was comparable to 1994. A functional growth analysis of the stem dry weight was carried out in this year. There was only a slightly longer accumulation phase in response to elevated CO2. Combined stem reserves contributed 12-18% to the final grain yield thereby contradicting, the suggestions based on the results of the year 1994.

2488^2^Ambus,P^Robertson,G P^1999^1^Fluxes of CH4 and N2O in aspen stands grown under ambient and twice-ambient CO2^206^209^1^1-8^^^^^^^^^^7735
1030^1298^1599^3019^3327^3573^3574^374^376^398^n was faster under elevated CO2. The results are consistent with current knowledge, that temporary storage pools accomodate source photosA^7734^Elevated atmospheric CO2 has the potential to change below- ground nutrient cycling and thereby alter the soil-atmosphere exchange of biogenic trace gases. We measured fluxes of CH4 and N2O in trembling aspen (Populus tremuloides Michx.) stands grown in open-top chambers under ambient and twice-ambient CO2 concentrations crossed with `high' and low soil-N conditions. Flux measurements with small static chambers indicated net CH4 oxidation in the open-top chambers. Across dates, CH4 oxidation activity was significantly (P < 0.05) greater with ambient CO2 (8.7 mu g CH4-C m(-2) h(-1)) than with elevated CO2 (6.5 mu g CH4-C m(-2) h(-1)) in the low N soil. Likewise, across dates and soil N treatments CH4 was oxidized more rapidly (P < 0.05) in chambers with ambient CO2 (9.5 mu g CH4-C m(-2) h(-1)) than in chambers with elevated CO2 (8.8 mu g CH4-C m(-2) h(-1)). Methane oxidation in soils incubated in serum bottles did not show any response to the CO2 treatment. We suggest that the depressed CH4 oxidation under elevated CO2 in the field chambers is due to soil moisture which tended to be higher in the twice-ambient CO2 treatment than in the ambient CO2 treatment. Phase I denitrification (denitrification enzyme activity) was 12-26% greater under elevated CO2 than under ambient CO2 in the `high' N soil; one sampling, however, showed a 39% lower enzyme activity with elevated CO2. In both soil N treatments, denitrification potentials measured after 24 or 48 h were between 11% and 21% greater (P < 0.05) with twice- ambient CO2 than with ambient CO2. Fluxes of N2O in the open- top chambers and in separate 44 cm(2) cores +/-N fertilization were not affected by CO2 treatment and soil N status. Our data show that elevated atmospheric CO2 may have a negative effect on terrestrial CH4 oxidation. The data also indicated temporary greater denitrification with elevated CO2 than with ambient CO2. In contrast, we found no evidence for altered fluxes of N2O in response to increases in atmospheric CO2.
epressed CH4 oxidation u2489^6^Faria,T^Vaz,M^Schwanz,P^Polle,A^Pereira,J S^Chaves,M M^1999^1^Responses of photosynthetic and defence systems to high temperature stress in Quercus suber L-seedlings crown under elevated CO2^380^1^3^365-371^^^^^May^^^^^7737
1240^1633^1676^1998^312^3484^3487^360^417^493^ in the `high' N soil; one sampling, however, showed a 39% lower enzyme activity with elevated CO2. In both soil N treatments, denitrification potentials measured after 24 or 48 h were between 11% and 21% greater (P < 0.05) with twice- ambient CO2 than with ambient CO2. Fluxes of N2O in the open- top chambers and in separate 44 cm(2) cores +/-N fertilization were not affected by CO2 treatment and soil N status. Our data show that elevated atmospheric CO2 may have a negative effect on terrestrial CH4 oxidation. The data also indicated temporary greater denitrification with elevated CO2 than with ambient CO2. In contrast, we found no evidence for altered fluxes of N2O in response to increases in atmospheric CO2.
epressed CH4 oxidation uA^7736^Growth in elevated CO2 led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO2-grown plants. No down- regulation of photosynthesis was found after six months of growth under elevated CO2. Photosynthetic rates at 15 degrees C or 35 degrees C were also higher in elevated than in ambient CO2-grown plants, when measured at their respective CO2 growth condition. Stomata of elevated CO2-grown plants were less responsive to temperature as compared to ambient CO2 plants. The after effect of a heat-shock treatment (4 h at 45 degrees C in a chamber with 80% of relative humidity and 800-1000 mu mol m(-2) s(-1) photon flux density) on A(max) was less in elevated than in ambient CO2-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO2-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO2-grown plants, in comparison to ambient CO2 plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 degrees C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO2-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO2-grown plants immediately after 1 h at 45 degrees C. The observed increase in catalase after 1 h at 45 degrees C in both ambient and elevated CO2-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature.

2490^4^Telewski,F W^Swanson,R T^Strain,B R^Burns,J M^1999^1^Wood properties and ring width responses to long-term atmospheric CO2 enrichment in field-grown loblolly pine (Pinus taeda L.)^9^22^2^213-219^^^^^Feb^^^^^7739
1203^1655^227^243^312^3575^372^423^669^751^lightly more pronounced in ambient than in elevated CO2-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO2A^7738^Loblolly pine (Pinus taeda L.) were grown in the field, under non-limiting nutrient conditions, in open-top chambers for 4 years at ambient CO2 partial pressures (pCO(2)) and with a CO2- enriched atmosphere (+ 30 Pa pCO(2) compared to ambient concentration). A third replicate of trees were grown without chambers at ambient pCO(2). Wood anatomy, wood density and tree ring width were analysed using stem wood samples. No significant differences were observed in the cell wall to cell lumen ratio within the latewood of the third growth ring formed in 1994. No significant differences were observed in the density of resin canals or in the ratio of resin canal cross- sectional area to xylem area within the same growth ring. Ring widths were significantly wider in the CO2-enrichment treatment for 3 of 4 years compared to the ambient chamber control treatment. Latewood in the 1995 growth ring was significantly wider than that in the ambient control and represented a larger percentage of the total growth-ring width. Carbon dioxide enrichment also significantly increased the total wood specific gravity (determined by displacement). However, when determined as total sample wood density by X-ray densitometry, the density of enriched samples was not significantly higher than that of the ambient chamber controls. Only the 1993 growth ring of enriched trees had a significantly higher maximum latewood density than that of trees grown on non-chambered plots or ambient chambered controls. No significant differences were observed in the minimum earlywood density of individual growth rings between chambered treatments. These results show that the most significant effect of CO2 enrichment on wood production in loblolly pine is its influence on radial growth, measured as annual tree ring widths. This influence is most pronounced in the first year of growth and decreases with age.
wood in the 1995 growth ring was significantly wider than that in the ambient control and represented a larger percentage of the total growth-ring wi2491^3^Jiao,J^Goodwin,P^Grodzinski,B^1999^1^Inhibition of photosynthesis and export in geranium grown at two CO2 levels and infected with Xanthomonas campestris pv. Pelargonii^9^22^1^15-25^^^^^Jan^^^^^7741
245^2600^344^348^360^372^385^417^528^820^ntly higher than that of the ambient chamber controls. Only the 1993 growth ring of enriched trees had a significantly higher maximum latewood density than that of trees grown on non-chambered plots or ambient chambered controls. No significant differences were observed in the minimum earlywood density of individual growth rings between chambered treatments. These results show that the most significant effect of CO2 enrichment on wood production in loblolly pine is its influence on radial growth, measured as annual tree ring widths. This influence is most pronounced in the first year of growth and decreases with age.
wood in the 1995 growth ring was significantly wider than that in the ambient control and represented a larger percentage of the total growth-ring wiA^7740^The effects of CO2 enrichment on growth of Xanthomonas campestris pv. pelargonii and the impact of infection on the photosynthesis and export of attached, intact, 'source' leaves of geranium (Pelargonium x domesticum, 'Scarlet Orbit Improved') are reported. Two experiments were performed, one with plants without flower buds, and another with plants which were flowering. Measurements were made on healthy and diseased leaves at the CO2 levels (35 Pa or 90 Pa) at which the plants were grown. There were no losses of chlorophyll, or any signs of visible chlorosis or necrosis due to infection. Lower numbers of bacteria were found in leaves at high CO2, suggesting growth at elevated CO2 created a less favourable condition in the leaf for bacterial growth. Although high CO2 lowered the bacterial number in infected leaves, reductions in photosynthesis and export were greater than at ambient CO2. The capacity of infected source leaves to export photoassimilates at rates observed in the controls was reduced in both light and darkness. In summary, the severity of infection on source leaf function by the bacteria was increased, rather than reduced by CO2 enrichment, underscoring the need for further assessment of plant diseases and bacterial virulence in plants growing under varying CO2 levels.

2492^4^Lovelock,C E^Virgo,A^Popp,M^Winter,K^1999^1^Effects of elevated CO2 concentrations on photosynthesis, growth and reproduction of branches of the tropical canopy tree species, Luehea seemannii Tr. & Planch^9^22^1^49-59^^^^^Jan^^^^^7743
312^344^3576^374^376^384^385^407^508^669^or necrosis due to infection. Lower numbers of bacteria were found in leaves at high CO2, suggesting growth at elevated CO2 created a less favourable condition in the leaf for bacterial growth. Although high CO2 lowered the bacterial number in infected leaves, reductions in photosynthesis and export were greater than at ambient CO2. The capacity of infected source leaves to export photoassimilates at rates observed in the controls was reduced in bA^7742^Mature trees have already experienced substantial increases in CO2 concentrations during their lifetimes, and will experience continuing increases in the future. Small open-top chambers were used to enclose branchlets that were at a height of between 20 and 25 m in the canopy of the tree species Luehea seemannii Tr. & Planch. in a tropical forest in Panama. Elevated concentrations of CO2 increased the rate of photosynthetic carbon fixation and decreased stomatal conductance of leaves, but did not influence the growth of leaf area per chamber, the production of flower buds and fruit nor the concentration of nonstructural carbohydrates within leaves. The production of flower buds was highly correlated with the leaf area produced in the second flush of leaves, indicating that the branchlets of mature trees of Luehea seemannii are autonomous to a considerable extent. Elevated levels of CO2 did increase the concentration of nonstructural carbohydrates in woody stem tissue. Elevated CO2 concentration also they increased the ratio of leaf area to total biomass of branchlets, and tended to reduce individual fruit weight. These data suggest that the biomass allocation patterns of mature trees may change under future elevated levels of CO2. Although there were no effects on growth during the experiment, the possibility of increased growth in the season following CO2 enrichment due to increased carbohydrate concentrations in woody tissue cannot be excluded.

2493^3^Griffin,K L^Sims,D A^Seemann,J R^1999^1^Altered night-time CO2 concentration affects the growth, physiology and biochemistry of soybean^9^22^1^91-99^^^^^Jan^^^^^7745
243^2514^3577^367^389^417^430^448^733^749^uction of flower buds was highly correlated with the leaf area produced in the second flush of leaves, indicating that the branchlets of mature trees of Luehea seemannii are autonomous to a considerable extent. Elevated levels of CO2 did increase the concentration of nonstructural carbohydrates in woody stem tissue. Elevated CO2 concentration also tA^7744^Soybean plants (Glycine max (L.) Merr. c. v. Williams) were grown in CO2 controlled, natural-light growth chambers under one of four atmospheric CO2 concentrations ([CO2]): (1) 250 mu mol mol(-1) 24 h d(-1) [250/250]; (2) 1000 mu mol mol(-1) 24 h d(-1) [1000/1000]; (3) 250 mu mol mol(-1) during daylight hours and 1000 mmol mol(-1) during nighttime hours [250/1000] or (4) 1000 mu mol mol(-1) during daylight hours and 250 mmol mol(-1) during night-time hours [1000/250]. During the vegetative growth phase few physiological differences were observed between plants exposed to a constant 24 h [CO2] (250/250 and 1000/1000) and those that were switched to a higher or lower [CO2] at night (250/1000 and 1000/250), suggesting that the primary physiological responses of plants to growth in elevated [CO2] is apparently a response to daytime [CO2] only. However, by the end of the reproductive growth phase, major differences were observed. Plants grown in the 1000/250 regime, when compared with those in the 1000/1000 regime, had significantly more leaf area and leaf mass, 27% more total plant dry mass, but only 18% of the fruit mass. After 12 weeks of growth these plants also had 19% higher respiration rates and 32% lower photosynthetic rates than the 1000/1000 plants. As a result the ratio of carbon gain to carbon loss was reduced significantly in the plants exposed to the reduced night-time [CO2]. Plants grown in the opposite switching environment, 250/1000 versus 250/250, showed no major differences in biomass accumulation or allocation with the exception of a significant increase in the amount of leaf mass per unit area. Physiologically, those plants exposed to elevated night-time [CO2] had 21% lower respiration rates, 14% lower photosynthetic rates and a significant increase in the ratio of carbon gain to carbon loss, again when compared with the 250/250 plants. Biochemical differences also were found. Ribulose-1,5-bisphosphate carboxylase/ oxygenase concentrations decreased in the 250/1000 treatment compared with the 250/250 plants, and phosphoenolpyruvate carboxylase activity decreased in the 1000/250 compared with the 1000/1000 plants. Glucose, fructose and to a lesser extent sucrose concentrations also were reduced in the 1000/250 treatment compared with the 1000/1000 plants. These results indicate that experimental protocols that do not maintain elevated CO2 levels 24 h d(-1) can have significant effects on plant biomass, carbon allocation and physiology, at least for fast-growing annual crop plants. Furthermore, the results suggest some plant processes other than photosynthesis are sensitive to [CO2] and under ecologically relevant conditions, such as high night-time [CO2], whole plant carbon balance can be affected.

2494^5^Ito,J^Hasegawa,S^Fujita,K^Ogasawara,S^Fujiwara,T^1999^1^Effect of CO2 enrichment on fruit growth and quality in Japanese pear (Pyrus serotina reheder cv. Kosui)^316^45^2^385-393^^^^^Jun^^^^^7747
2082^2258^243^244^312^344^3578^360^417^857^ns decreased in the 250/1000 treatment compared withA^7746^Six year-old Japanese pear (Pyrus serotina Reheder cv. Kosui) trees grafted on P. serotina cv. Nihonyamanashi were grown in containers filled with Granite Regosol under glasshouse conditions. At different stages of fruit growth, pear trees were exposed to an elevated CO2 concentration (130 Pa CO2) along with a control (35 Pa CO2). For one group of plants, CO2 enrichment was applied for 79 d from 52 d after full bloom (DAB) to fruit maturity (long-term CO2 enrichment) and for another group the same treatment was applied for 35 d from 96 DAB to fruit maturity (short-term CO2 enrichment). The effects of the elevated CO2 concentration on vegetative growth, mineral contents, and fruit production and quality were examined. Long- term CO2 enrichment enhanced vegetative growth, without any significant effect on the mineral contents in either flower bud or fruit except for a remarkable increase in the K content. Long-term CO2 enrichment increased the fruit size and fresh weight, but had no significant effect on the fruit quality. On the other hand, the short-term CO2 enrichment did not induce any significant change in the fruit size but increased the fruit sugar concentration. Along with the reduction of the sorbitol concentration in fruit, the fructose and sucrose concentrations increased and these changes occurred earlier at elevated CO2 than at ambient CO2 concentrations. From these results, we concluded that the effect of CO2 enrichment on fruit growth varies depending upon the growth stages of fruit: during the initial and fruitlet stages when fruit expansion occurs, CO2 enrichment increases the fruit size, whereas, during maturation when fruit expansion has slowed down and sugar accumulation in fruit is active, it increases the fruit sugar concentration.

2495^4^Owensby,C E^Ham,J M^Knapp,A K^Auen,L M^1999^1^Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2^127^5^5^497-506^^^^^Jun^^^^^7749t, but had no significant effect o1044^312^3579^374^56^57^715^740^91^956^the short-term CO2 enrichment did not induce any significant change in the fruit size but increased the fruit sugar concentration. Along with the reduction of the sorbitol concentration in fruit, the fructose and sucrose concentrations increased and these changes occurred earlier at elevated CO2 than at ambient CO2 concentrations. From these results, we concluded that the effect of CO2 enrichment on fruit growth varies depending upon the growth stages of fruit: during the initial and fruitlet stages when fruit expansion occurs, CO2 enrichment increases the fruit size, whereas, during maturation when fruit expansion has slowed down and sugar accumulation in fruit is active, it increases the fruit sugar concentration.

2495^4^Owensby,C E^Ham,J M^Knapp,A K^Auen,L M^1999^1^Biomass production and species composition change in a tallgrass prairie ecosystem after long-term exposure to elevated atmospheric CO2^127^5^5^497-506^^^^^Jun^^^^^7749t, but had no significant effect oA^7748^To determine the long-term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice-ambient atmospheric CO2 levels over an 8-year period. Plots in open-top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Aboveground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0-100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak aboveground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above-ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late-season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm-season perennial grasses (C4) in the stand changed little during the 8-year period, but basal cover and relative amount of cool-season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4-dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.
ambient CO2 plots with or without chambers d2496^2^Catovsky,S^Bazzaz,F A^1999^1^Elevated CO2 influences the responses of two birch species to soil moisture: implications for forest community structure^127^5^5^507-518^^^^^Jun^^^^^7751
1291^312^342^344^345^3580^384^483^546^715^was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm-season perennial grasses (C4) in the stand changed little during the 8-year period, but basal cover and relative amount of cool-season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4-dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.
ambient CO2 plots with or without chambers dA^7750^Increased levels of atmospheric CO2 may alter the structure and composition of plant communities by affecting how species respond to their physical and biological environment. We investigated how elevated CO2 influenced the response of paper birch (Betula papyrifera Marsh.) and yellow birch (Betula alleghaniensis Britt.) seedlings to variation in soil moisture. Seedlings were grown for four months on a soil moisture gradient, individually and in mixed species stands, in controlled environment facilities at ambient (375 mu L L-1) and elevated (700 mu L L-1) atmospheric CO2. For both individually and competitively grown paper birch seedlings, there was a greater CO2 growth enhancement for seedlings watered less frequently than for well-watered seedlings. This differential change in CO2 responsiveness across the moisture gradient reduced the difference in seedling growth between high and low water levels and effectively broadened the regeneration niche of paper birch. In contrast, for yellow birch seedlings, elevated CO2 only produced a significant growth enhancement at the wet end of the soil moisture gradient, and increased the size difference between seedlings at the two ends of the gradient. Gas exchange measurements showed that paper birch seedlings were more sensitive than yellow birch seedlings to declines in soil moisture, and that elevated CO2 reduced this sensitivity. Additionally, elevated CO2 improved survival of yellow birch seedlings growing in competition with paper birch in dry stands. Thus, elevated CO2 may influence regeneration patterns of paper birch and yellow birch on sites of differing soil moisture. In the future, as atmospheric CO2 levels rise, growth of paper birch seedlings and survival of yellow birch seedlings may be enhanced on xeric sites, while yellow birch may show improved growth on mesic sites.
nt reduced the difference in seedling growth between high and low water levels and effectively broadened the regeneration niche of paper birch. In contrast, for yellow birch seedli2497^9^Wechsung,G^Wechsung,F^Wall,G W^Adamsen,F J^Kimball,B A^Pinter,P J^Lamorte,R L^Garcia,R L^Kartschall,T^1999^1^The effects of free-air CO2 enrichment and soil water availability on spatial and seasonal patterns of wheat root growth^127^5^5^519-529^^^^^Jun^^^^^7753
341^3466^374^442^507^56^57^58^733^738^clines in soil moisture, and that elevated CO2 reduced this sensitivity. Additionally, elevated CO2 improved survival of yellow birch seedlings growing in com