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Ambient CO2 (ambient + co2)
Terms modified by Ambient CO2 Selected AbstractsTropospheric O3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE projectFUNCTIONAL ECOLOGY, Issue 3 2003D. F. Karnosky Summary 1The impacts of elevated atmospheric CO2 and/or O3 have been examined over 4 years using an open-air exposure system in an aggrading northern temperate forest containing two different functional groups (the indeterminate, pioneer, O3 -sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late successional, O3 -tolerant species Sugar Maple, Acer saccharum). 2The responses to these interacting greenhouse gases have been remarkably consistent in pure Aspen stands and in mixed Aspen/Birch and Aspen/Maple stands, from leaf to ecosystem level, for O3 -tolerant as well as O3 -sensitive genotypes and across various trophic levels. These two gases act in opposing ways, and even at low concentrations (1·5 × ambient, with ambient averaging 34,36 nL L,1 during the summer daylight hours), O3 offsets or moderates the responses induced by elevated CO2. 3After 3 years of exposure to 560 µmol mol,1 CO2, the above-ground volume of Aspen stands was 40% above those grown at ambient CO2, and there was no indication of a diminishing growth trend. In contrast, O3 at 1·5 × ambient completely offset the growth enhancement by CO2, both for O3 -sensitive and O3 -tolerant clones. Implications of this finding for carbon sequestration, plantations to reduce excess CO2, and global models of forest productivity and climate change are presented. [source] Enhanced litter input rather than changes in litter chemistry drive soil carbon and nitrogen cycles under elevated CO2: a microcosm studyGLOBAL CHANGE BIOLOGY, Issue 2 2009LINGLI LIU Abstract Elevated CO2 has been shown to stimulate plant productivity and change litter chemistry. These changes in substrate availability may then alter soil microbial processes and possibly lead to feedback effects on N availability. However, the strength of this feedback, and even its direction, remains unknown. Further, uncertainty remains whether sustained increases in net primary productivity will lead to increased long-term C storage in soil. To examine how changes in litter chemistry and productivity under elevated CO2 influence microbial activity and soil C formation, we conducted a 230-day microcosm incubation with five levels of litter addition rate that represented 0, 0.5, 1.0, 1.4 and 1.8 × litterfall rates observed in the field for aspen stand growing under control treatments at the Aspen FACE experiment in Rhinelander, WI, USA. Litter and soil samples were collected from the corresponding field control and elevated CO2 treatment after trees were exposed to elevated CO2 (560 ppm) for 7 years. We found that small decreases in litter [N] under elevated CO2 had minor effects on microbial biomass carbon, microbial biomass nitrogen and dissolved inorganic nitrogen. Increasing litter addition rates resulted in linear increase in total C and new C (C from added litter) that accumulated in whole soil as well as in the high density soil fraction (HDF), despite higher cumulative C loss by respiration. Total N retained in whole soil and in HDF also increased with litter addition rate as did accumulation of new C per unit of accumulated N. Based on our microcosm comparisons and regression models, we expected that enhanced C inputs rather than changes in litter chemistry would be the dominant factor controlling soil C levels and turnover at the current level of litter production rate (230 g C m,2 yr,1 under ambient CO2). However, our analysis also suggests that the effects of changes in biochemistry caused by elevated CO2 could become significant at a higher level of litter production rate, with a trend of decreasing total C in HDF, new C in whole soil, as well as total N in whole soil and HDF. [source] Host-specific aphid population responses to elevated CO2 and increased N availabilityGLOBAL CHANGE BIOLOGY, Issue 11 2005Erika A. Sudderth Abstract Sap-feeding insects such as aphids are the only insect herbivores that show positive responses to elevated CO2. Recent models predict that increased nitrogen will increase aphid population size under elevated CO2, but few experiments have tested this idea empirically. To determine whether soil nitrogen (N) availability modifies aphid responses to elevated CO2, we tested the performance of Macrosiphum euphorbiae feeding on two host plants; a C3 plant (Solanum dulcamara), and a C4 plant (Amaranthus viridis). We expected aphid population size to increase on plants in elevated CO2, with the degree of increase depending on the N availability. We found a significant CO2× N interaction for the response of population size for M. euphorbiae feeding on S. dulcamara: aphids feeding on plants grown in ambient CO2, low N conditions increased in response to either high N availability or elevated CO2. No population size responses were observed for aphids infesting A. viridis. Elevated CO2 increased plant biomass, specific leaf weight, and C : N ratios of the C3 plant, S. dulcamara but did not affect the C4 plant, A. viridis. Increased N fertilization significantly increased plant biomass, leaf area, and the weight : height ratio in both experiments. Elevated CO2 decreased leaf N in S. dulcamara and had no effect on A. viridis, while higher N availability increased leaf N in A. viridis and had no effect in S. dulcamara. Aphid infestation only affected the weight : height ratio of S. dulcamara. We only observed an increase in aphid population size in response to elevated CO2 or increased N availability for aphids feeding on S. dulcamara grown under low N conditions. There appears to be a maximum population growth rate that M. euphorbiae aphids can attain, and we suggest that this response is because of intrinsic limits on development time and fecundity. [source] Interactive effects of elevated CO2, N deposition and climate change on extracellular enzyme activity and soil density fractionation in a California annual grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2005Hugh A. L. Henry Abstract Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively. [source] Effects of elevated CO2 on the size structure in even-aged monospecific stands of Chenopodium albumGLOBAL CHANGE BIOLOGY, Issue 4 2003HISAE NAGASHIMA Abstract To investigate the effect of elevated CO2 on the size inequality and size structure, even-aged monospecific stands of an annual, Chenopodium album, were established at ambient and doubled CO2 with high and low nutrient availabilities in open top chambers. The growth of individual plants was monitored non-destructively every week until flowering. Elevated CO2 significantly enhanced plant growth at high nutrients, but did not at low nutrients. The size inequality expressed as the coefficient of variation tended to increase at elevated CO2. Size structure of the stands was analyzed by the cumulative frequency distribution of plant size. At early stages of plant growth, CO2 elevation benefited all individuals and shifted the whole size distribution of the stand to large size classes. At later stages, dominant individuals were still larger at elevated than at ambient CO2, but the difference in small subordinate individuals between two CO2 levels became smaller. Although these tendencies were found at both nutrient availabilities, difference in size distribution between CO2 levels was larger at high nutrients. The CO2 elevation did not significantly enhance the growth rate as a function of plant size except for the high nutrient stand at the earliest stage, indicating that the higher biomass at elevated CO2 at later stages in the high nutrient stand was caused by the larger size of individuals at the earliest stage. Thus the effect of elevated CO2 on stand structure and size inequality strongly depended on the growth stage and nutrient availabilities. [source] Effects of climate change on labile and structural carbon in Douglas-fir needles as estimated by ,13C and Carea measurementsGLOBAL CHANGE BIOLOGY, Issue 11 2002ERIC A. HOBBIE Abstract Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2 but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar Carea (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (,13C) caused by inputs of 13C-depleted CO2 to estimate labile and structural C in needles of different ages in a four-year, closed-chamber mesocosm experiment in which Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO2 (ambient + 179 ppm). Declines in ,13C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The ,13C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second- and third-year needles, respectively, with higher proportions of new C in elevated than ambient CO2 chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second-year needles). Relative to ambient CO2, elevated CO2 increased labile C in both first- and second-year needles. Relative to ambient temperature, elevated temperature diminished labile C in second-year needles but not in first-year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant-soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations suggested that labile C was primarily determined by carbohydrates. Labile C was negatively correlated with concentrations of cellulose and protein. Elevated temperature increased foliar %C, possibly due to a shift of labile constituents from low %C carbohydrates to relatively high %C protein. Decreased sugar concentrations and increased nitrogen concentrations with elevated temperature were consistent with this explanation. Because foliar constituents that vary in isotopic signature also vary in concentrations with leaf age or environmental conditions, inferences of ci/ca values from ,13C of bulk leaf tissue should be done cautiously. Tracing of 13C through foliar carbon pools may provide new insight into foliar C constituents and turnover. [source] Response of Photosynthesis and Water Relations of Rice (Oryza sativa) to Elevated Atmospheric Carbon Dioxide in the Subhumid Zone of Sri LankaJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2003W. A. J. M. De Costa Abstract The objective of the present paper is to determine the response of the physiological parameters related to biomass production and plant water relations in a standard Sri Lankan rice (Oryza sativa) variety (BG-300) to elevated CO2 (i.e. 570 µmol/mol). During two seasons, rice crops were grown under three different experimental treatments; namely, at 570 µmol/mol (i.e. ,elevated') and 370 µmol/mol (,ambient') CO2 within open top chambers, and at ambient CO2 under open field conditions. Leaf net photosynthetic rate in the elevated treatment increased by 22,75 % in comparison to the ambient. However, the ratio between intercellular and ambient CO2 concentrations remained constant across different CO2 treatments and seasons. CO2 enrichment decreased individual leaf stomatal conductance and transpiration rate per unit leaf area, and increased both leaf and canopy temperatures. However, the overall canopy stomatal conductance and daily total canopy transpiration rate of the elevated treatment were approximately the same as those achieved under ambient conditions. This was because of the significantly greater leaf area index and greater leaf,air vapour pressure deficit under CO2 enrichment. The leaf chlorophyll content increased significantly under elevated CO2; however, the efficiency (i.e. photochemical yield) of light energy capture by Photosystem II (i.e. Fv/Fm) in chlorophyll a did not show a significant and consistent variation with CO2 enrichment. [source] Response of beech (Fagus sylvatica) to elevated CO2 and N: Influence on larval performance of the gypsy moth Lymantria dispar (Lep., Lymantriidae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2001M. W. Henn Two-year-old beech seedlings were kept from germination to bioassays with Lymantriadispar under the following conditions: ambient CO2/low N, elevated CO2/low N, ambient CO2/elevated N, and elevated CO2/elevated N. The effect of these growing conditions of the trees on the performance of the defoliator L. dispar was studied 2 years after initiating the tree cultivation. The developmental success of third-instar larvae of L. dispar was characterized by the weight gained, percentage of weight gain, relative growth rate (RGR), relative consumption rate (RCR), and efficiency of conversion of ingested food into body substance (ECI). Contrary to our expectations, additional N-fertilization did not increase and elevated CO2 did not delay larval growth rate. However, the environmental treatments of the beech seedlings were found to affect the larval performance. Larvae consumed significantly higher amounts of foliage (RCR) on beech trees under controlled conditions (ambient CO2 and low N) compared to those under elevated CO2 and enhanced N. The opposite was true for ECI. The lowest efficacy to convert consumed food to body substance was observed under control conditions and the highest when the larvae were kept on beech trees grown under elevated CO2 and additional N-fertilization. These opposite effects resulted in the weight gain-based parameters (absolute growth, percentage of growth, and RGR) of the gypsy moth larvae remaining unaffected. The results indicate that the gypsy moth larvae are able to change their ECI and RCR to obtain a specific growth rate. This is discussed as an adaptation to specific food qualities. [source] Effects of Elevated Carbon Dioxide on the Growth and Foliar Chemistry of Transgenic Bt CottonJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2007Gang Wu Abstract A field study was carried out to quantify plant growth and the foliar chemistry of transgenic Bacillus thuringiensis (Bt) cotton (cv. GK-12) exposed to ambient CO2 and elevated (double-ambient) CO2 for different lengths of time (1, 2 and 3 months) in 2004 and 2005. The results indicated that CO2 levels significantly affected plant height, leaf area per plant and leaf chemistry of transgenic Bt cotton. Significantly, higher plant height and leaf area per plant were observed after cotton plants that were grown in elevated CO2 were compared with plants grown in ambient CO2 for 1, 2 and 3 months in the investigation. Simultaneously, significant interaction between CO2 level × investigating year was observed in leaf area per plant.Moreover, foliar total amino acids were increased by 14%, 13%, 11% and 12%, 14%, 10% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 in 2004 and 2005, respectively. Condensed tannin occurrence increased by 17%, 11%, 9% in 2004 and 12%, 11%, 9% in 2005 in transgenic Bt cotton after being exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for the same time. However, Bt toxin decreased by 3.0%, 2.9%, 3.1% and 2.4%, 2.5%, 2.9% in transgenic Bt cotton after exposed to elevated CO2 for 1, 2 or 3 months compared with ambient CO2 for same time in 2004 and 2005, respectively. Furthermore, there was prominent interaction on the foliar total amino acids between the CO2 level and the time of cotton plant being exposed to elevated CO2. It is presumed that elevated CO2 can alter the plant growth and hence ultimately the phenotype allocation to foliar chemistical components of transgenic Bt cotton, which may in turn, affect the plant-herbivore interactions. [source] How will plant pathogens adapt to host plant resistance at elevated CO2 under a changing climate?NEW PHYTOLOGIST, Issue 3 2003Sukumar Chakraborty Summary , , To better understand evolution we have studied aggressiveness of the anthracnose pathogen, Colletotrichum gloeosporioides, collected from Stylosanthes scabra pastures between 1978 and 2000 and by inoculating two isolates onto two cultivars over 25 sequential infection cycles at ambient (350 ppm) and twice-ambient atmospheric CO2 in controlled environments. , , Regression analysis of the field population showed that aggressiveness increased towards a resistant cultivar, but not towards a susceptible cultivar, that is no longer grown commercially. , , Here we report for the first time that aggressiveness increased on both cultivars after a few initial infection cycles at twice-ambient CO2 as isolates adapted to combat enhanced host resistance, while at ambient CO2 this increased steadily for most cycles as both cultivars selected for increased aggressiveness. Genetic fingerprint and karyotype of isolates changed for some CO2 -cultivar combinations, but these were not related to changed aggressiveness. , , At 700 ppm fecundity increased for both isolates, and this increased population size, in combination with a conducive microclimate for anthracnose from an enlarged plant canopy under elevated CO2, could accelerate pathogen evolution. [source] How can we predict the effects of elevated CO2 on the balance between perennial C3 grass species competing for light?NEW PHYTOLOGIST, Issue 1 2002F. Teyssonneyre Summary ,,Changes in the balance between mixed plant species have been reported under elevated [CO2] compared with ambient atmospheric [CO2]. We hypothesized that species response to elevated CO2 in mixture can be explained by taking into account resource partitioning between mixed species. ,,This hypothesis was tested experimentally on three perennial C3 grass species (Lolium perenne, Festuca arundinacea and Holcus lanatus) grown in monocultures and in binary mixtures (Lolium,Festuca and Lolium,Holcus) under mild (frequent cuts) or severe (infrequent cuts) competition for light and at a high N supply (40 g N m,2). ,,Under mild competition for light, the dry matter yield response to elevated CO2 of the mixed grass species was similar to that observed in monocultures. By contrast, under severe light competition, the grass species that absorbed more light per unit leaf area (Holcus and Festuca), also had a greater response to elevated CO2 in mixture compared with monoculture. ,,Under our experimental conditions, we have shown that the dry matter yield response to CO2 in mixture can be predicted from both the species response in monoculture, and the light capture per unit leaf area in ambient CO2 of the mixed compared with the pure grasses. [source] Effects of elevated CO2, drought and temperature on the water relations and gas exchange of groundnut (Arachis hypogaea) stands grown in controlled environment glasshousesPHYSIOLOGIA PLANTARUM, Issue 1 2000Sean C. Clifford Stands of groundnut (Arachis hypogaea L. cv. Kadiri-3) were grown in controlled environment glasshouses at mean atmospheric CO2 concentrations of 375 or 700 ,mol mol,1 and daily mean air temperatures of 28 or 32°C on irrigated or drying soil profiles. Leaf water (,l) and solute potential (,s), relative water content (RWC), stomatal conductance (gl) and net photosynthesis (Pn) were measured at midday for the youngest mature leaf throughout the growing season. Elevated CO2 and temperature had no detectable effect on the water relations of irrigated plants, but higher values of RWC, ,l and ,s were maintained for longer under elevated CO2 during progressive drought. Turgor potential (,p) reached zero when ,l declined to ,1.6 to ,1.8 MPa in all treatments; turgor was lost sooner when droughted plants were grown under ambient CO2. A 4°C increase in mean air temperature had no effect on ,s in droughted plants, but elicited a small increase in ,l; midday gl values were lower under elevated than under ambient CO2, and ,l and gl declined below ,1.5 MPa and 0.25 cm s,1, respectively, as the soil dried. Despite the low gl values recorded for droughted plants late in the season, Pn was maintained under elevated CO2, but declined to zero 3 weeks before final harvest under ambient CO2. Concurrent reductions in gl and increases in water use efficiency under elevated CO2 prolonged photosynthetic activity during drought and increased pod yields relative to plants grown under ambient CO2. The implications of future increases in atmospheric CO2 for the productivity of indeterminate C3 crops grown in rainfed subsistence agricultural systems in the semi-arid tropics are discussed. [source] Differential gene expression in senescing leaves of two silver birch genotypes in response to elevated CO2 and tropospheric ozonePLANT CELL & ENVIRONMENT, Issue 6 2010SARI KONTUNEN-SOPPELA ABSTRACT Long-term effects of elevated CO2 and O3 concentrations on gene expression in silver birch (Betula pendula Roth) leaves were studied during the end of the growing season. Two birch genotypes, clones 4 and 80, with different ozone growth responses, were exposed to 2× ambient CO2 and/or O3 in open-top chambers (OTCs). Microarray analyses were performed after 2 years of exposure, and the transcriptional profiles were compared to key physiological characteristics during leaf senescence. There were genotypic differences in the responses to CO2 and O3. Clone 80 exhibited greater transcriptional response and capacity to alter metabolism, resulting in better stress tolerance. The gene expression patterns of birch leaves indicated contrasting responses of senescence-related genes to elevated CO2 and O3. Elevated CO2 delayed leaf senescence and reduced associated transcriptional changes, whereas elevated O3 advanced leaf senescence because of increased oxidative stress. The combined treatment demonstrated that elevated CO2 only temporarily alleviated the negative effects of O3. Gene expression data alone were insufficient to explain the O3 response in birch, and additional physiological and biochemical data were required to understand the true O3 sensitivity of these clones. [source] The temperature response of photosynthesis in tobacco with reduced amounts of RubiscoPLANT CELL & ENVIRONMENT, Issue 4 2008DAVID S. KUBIEN ABSTRACT The reasons for the decline in net CO2 assimilation (A) above its thermal optimum are controversial. We tested the hypothesis that increasing the ratio of Rubisco activase to Rubisco catalytic site concentration would increase the activation state of Rubisco at high temperatures. We measured photosynthetic gas exchange, in vivo electron transport (J) and the activation state of Rubisco between 15 and 45 °C, at 38 and 76 Pa ambient CO2, in wild-type (WT) and anti- rbcS tobacco. The Rubisco content of the anti- rbcS lines was 30% (S7-1) or 6% (S7-2) of WT, but activase levels were the same in the three genotypes. Anti- rbcS plants had lower A than WT at all temperatures, but had a similar thermal optimum for photosynthesis as WT at both CO2 levels. In WT plants, Rubisco was fully activated at 32 °C, but the activation state declined to 64% at 42 °C. By contrast, the activation state of Rubisco was above 90% in the S7-1 line, between 15 and 42 °C. Both A and J declined about 20% from Topt to the highest measurement temperatures in WT and the S7-1 line, but this was fully reversed after a 20 min recovery at 35 °C. At 76 Pa CO2, predicted rates of RuBP regeneration-limited photosynthesis corresponded with measured A in WT tobacco at all temperatures, and in S7-1 tobacco above 40 °C. Our observations are consistent with the hypothesis that the high temperature decline in A in the WT is because of an RuBP regeneration limitation, rather than the capacity of Rubisco activase to maintain high Rubisco activation state. [source] Oxygen dynamics during submergence in the halophytic stem succulent Halosarcia pergranulataPLANT CELL & ENVIRONMENT, Issue 7 2006O. PEDERSEN ABSTRACT This study elucidated O2 dynamics in shoots and roots of submerged Halosarcia pergranulata (Salicornioideae), a perennial halophytic stem succulent that grows on flood-prone mudflats of salt lakes. Oxygen within shoots and roots was measured using microelectrodes, for plants when waterlogged or completely submerged, with shoots in light or in darkness, in a controlled environment. Net photosynthesis (PN) when underwater, at a range of dissolved CO2 concentrations, was measured by monitoring O2 production rates by excised stems. The bulky nature and apparently low volume of gas-filled spaces of the succulent stems resulted in relatively high radial resistance to gas diffusion. At ambient CO2, quasi-steady state rates of PN by excised succulent stems were estimated to be close to zero; nevertheless, in intact plants, underwater photosynthesis provided O2 to tissues and led to radial O2 loss (ROL) from the roots, at least during the first several hours (the time period measured) after submergence or when light periods followed darkness. The influence of light on tissue O2 dynamics was confirmed in an experiment on a submerged plant in a salt lake in south-western Australia. In the late afternoon, partial pressure of O2 (pO2) in the succulent stem was 23.2 kPa (i.e. ,10% above that in the air), while in the roots, it was 6.2,9.8 kPa. Upon sunset, the pO2 in the succulent stems declined within 1 h to below detection, but then showed some fluctuations with the pO2 increasing to at most 2.5 kPa during the night. At night, pO2 in the roots remained higher than in the succulent stems, especially for a root with the basal portion in the floodwater. At sunrise, the pO2 increased in the succulent stems within minutes. In the roots, changes in the pO2 lagged behind those in the succulent stems. In summary, photosynthesis in stems of submerged plants increased the pO2 in the shoots and roots so that tissues experience diurnal changes in the pO2, but O2 from the H2O column also entered submerged plants. [source] Near-term impacts of elevated CO2, nitrogen and fungal endophyte-infection on Lolium perenne L. growth, chemical composition and alkaloid productionPLANT CELL & ENVIRONMENT, Issue 11 2005MATHEW G. HUNT ABSTRACT Carbon dioxide has been rapidly accumulating in the atmosphere and is expected to continue to do so. This accumulation is presumed to have important direct effects on plant growth. The interacting affects of a small increase in CO2 concentration (466 p.p.m., approximately 30% increase from current ambient conditions), nitrogen fertilization and fungal endophyte (Neotyphodium lolii) infection on the growth and chemical composition of perennial ryegrass (Lolium perenne) were investigated. It was found that dry mass production was approximately 50% greater under elevated CO2 than under ambient CO2, but only in conditions of high soil N. High molecular weight carbohydrates and total carbohydrates (LMW + HMW CHO) depended on an interaction between CO2 and endophyte infection. Infected plants contained significantly more carbohydrate than endophyte-free plants, and the difference was greatest in ambient CO2 conditions. Protein concentrations were also influenced by the interaction between CO2 and endophyte-infection. Endophyte-free plants had 40% lower concentrations of soluble protein under elevated CO2 than under ambient CO2, but this CO2 effect on soluble protein was largely absent in endophyte-infected plants. CO2, endophyte-infection and nitrogen interacted to influence the total chlorophyll concentration of the grass such that chlorophyll concentration was always lower in elevated CO2 but this decline was much greater in endophyte-free plants, particularly in conditions of high soil N. In the endophyte-infected plants, the concentrations of the pyrrolopyrazine alkaloid peramine depended on the interaction between CO2 and N fertilization such that peramine concentrations declined with increasing N at ambient CO2 but remained roughly constant across N levels at elevated CO2. A similar pattern was seen for the ergot alkaloid ergovaline. The biochemical responses of perennial ryegrass to elevated CO2 are clearly modified by the presence of endophytic fungi. [source] Impact of rising CO2 on emissions of volatile organic compounds: isoprene emission from Phragmites australis growing at elevated CO2 in a natural carbon dioxide spring,PLANT CELL & ENVIRONMENT, Issue 4 2004P. A. SCHOLEFIELD ABSTRACT Isoprene basal emission (the emission of isoprene from leaves exposed to a light intensity of 1000 µmol m,2 s,1 and maintained at a temperature of 30 °C) was measured in Phragmites australis plants growing under elevated CO2 in the Bossoleto CO2 spring at Rapolano Terme, Italy, and under ambient CO2 at a nearby control site. Gas exchange and biochemical measurements were concurrently taken. Isoprene emission was lower in the plants growing at elevated CO2 than in those growing at ambient CO2. Isoprene emission and isoprene synthase activity (IsoS) were very low in plants growing at the bottom of the spring under very rich CO2 and increased at increasing distance from the spring (and decreasing CO2 concentration). Distance from the spring did not significantly affect photosynthesis making it therefore unlikely that there is carbon limitation to isoprene formation. The isoprene emission rate was very quickly reduced after rapid switches from elevated to ambient CO2 in the gas-exchange cuvette, whereas it increased when switching from ambient to elevated CO2. The rapidity of the response may be consistent with post-translational modifications of enzymes in the biosynthetic pathway of isoprene formation. Reduction of IsoS activity is interpreted as a long-term response. Basal emission of isoprene was not constant over the day but showed a diurnal course opposite to photosynthesis, with a peak during the hottest hours of the day, independent of stomatal conductance and probably dependent on external air temperature or temporary reduction of CO2 concentration. The present experiments show that basal emission rate of isoprene is likely to be reduced under future elevated CO2 levels and allow improvement in the modelling of future isoprene emission rates. [source] Variable photosynthetic acclimation in consecutive cohorts of Scots pine needles during 3 years of growth at elevated CO2 and elevated temperaturePLANT CELL & ENVIRONMENT, Issue 5 2003E.-M. LUOMALA ABSTRACT In this experiment, the photosynthetic acclimation of successive needle cohorts of Scots pine were studied during 3 years of growth at elevated CO2 and temperature. Naturally regenerated Scots pine (Pinus sylvestris L.) trees were subjected to elevated CO2 concentration (+CO2, 700 p.p.m), elevated temperature (+T, ambient +2 to +6 °C) and to a combination of elevated CO2 and temperature (+CO2 + T) in closed-top chambers, starting in August 1996. Trees growing in chambers with ambient CO2 and ambient temperature served as controls (AmbC). Elevated CO2 influenced the dark reactions more than the light reactions of photosynthesis, as in the 1996 and 1997 cohorts the carboxylation capacity of Rubisco was reduced in the first and second year of exposure, but there was no consistent change in chlorophyll fluorescence. Net photosynthesis measured at growth concentration of CO2 was higher at +CO2 than at AmbC on only one measuring occasion, was generally lower at +T and was not changed at +CO2 + T. However, trees grown at +T tended to invest more nitrogen (N) in Rubisco, as Rubisco/chlorophyll and the proportion of the total needle N bound to Rubisco occasionally increased. The interaction of +CO2 and +T on Rubisco was mostly negative; consequently, in the second and third year of the experiment the carboxylation capacity decreased at +CO2 + T. In the 1996, 1997 and 1998 cohorts, the structural N concentration of needles was lower at +CO2 than at AmbC. Elevated CO2 and elevated temperature generally had a positive interaction on N concentration; consequently, N concentration in needles decreased less at +CO2 + T than at +CO2. At +CO2 + T, the acclimation response of needles varied between years and was more pronounced in the 1-year-old needles of the 1997 cohort than in those of the 1998 cohort. Thus, acclimation was not always greater in 1-year-old needles than in current-year needles. In the +CO2 + T treatment, elevated temperature had a greater effect on acclimation of needles than elevated CO2. [source] How does photorespiration modulate leaf amino acid contents?PLANT CELL & ENVIRONMENT, Issue 7 2002A dual approach through modelling, metabolite analysis Abstract The aim of this work was to establish the quantitative impact of photorespiration on leaf amino acid contents. Attached leaves of wheat and potato were incubated for 30,40 min under defined conditions in which net CO2 uptake (A) was manipulated by irradiance, ambient CO2 or ambient O2. The incubated portion of the leaf was sampled by a rapid-quench method and photorespiratory flux (vo) was modelled from the measured rate of net CO2 uptake. In both wheat and potato, the ratio between glycine and serine showed a strong positive correlation with vo. Aspartate and alanine correlated negatively with vo but glutamate and glutamine showed less clear relationships. In potato, glutamate and glutamine did not correlate clearly with either A or vo. In wheat, glutamine showed a general increase with A but no relationship with vo, whereas 2-oxoglutarate contents correlated positively with vo and negatively with A. As a result, glutamine : glutamate and glutamine : 2-oxoglutarate increased with net CO2 uptake in wheat, observations that are attributed primarily to imperfect and variable coupling between the supply of NH3 in primary nitrogen assimilation and the associated delivery of 2-oxoglutarate to the chloroplast. A simple theoretical analysis is used to illustrate the potentially marked impact of primary nitrogen assimilation on leaf glutamine, even against a background of high rates of photorespiratory ammonia recycling. [source] Growth in elevated CO2 protects photosynthesis against high-temperature damagePLANT CELL & ENVIRONMENT, Issue 6 2000Daniel R. Taub ABSTRACT We present evidence that plant growth at elevated atmospheric CO2 increases the high-temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 ,mol mol,1) and elevated CO2 (550,1000 ,mol mol,1) in three separate growth facilities, including the Nevada Desert Free-Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2 -grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient-grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2 -grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2 -grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2 -grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2 -grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high-temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2 -induced increase in plant high-temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century. [source] | ||||||||||