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CO2 Treatment (co2 + treatment)
Kinds of CO2 Treatment Selected AbstractsSpecies-level effects more important than functional group-level responses to elevated CO2: evidence from simulated turvesFUNCTIONAL ECOLOGY, Issue 3 2004M. E. HANLEY Summary 1Using mixtures of 14 calcareous grassland plant species drawn from three functional groups, we looked at the effects of elevated atmospheric CO2 on contrasting levels of ecosystem performance (species, functional group and community). Experimental communities were subjected to ambient (,350 µmol mol,1) or elevated CO2 (,600 µmol mol,1) in controlled environments, with grazing simulated by clipping at monthly intervals for 546 days. 2We assessed the effect of elevated CO2 on plant performance by quantifying the productivity (biomass) and cover of component species. We also examined the effect of elevated CO2 on the vertical structure of the plant canopy. Elevated CO2 resulted in a significant increase in total community biomass only following nutrient addition. Within functional groups, non-leguminous forb species had significantly greater biomass and cover in elevated CO2 both before and after nutrient addition, although the effect was mainly due to the influence of one species (Centaurea nigra). Grasses, in contrast, responded negatively to elevated CO2, although again significant reductions in biomass and cover could mainly be ascribed to a single species (Brachypodium pinnatum). Legumes exhibited increased biomass and cover in elevated CO2 (the effects being particularly marked for Anthyllis vulneraria and Lotus corniculatus), but this response disappeared following nutrient addition. Vertical structure was little affected by CO2 treatment. 3We conclude that due to the idiosyncratic responses of individual species, the categorization of plants into broad functional groups is of limited use in guiding our understanding of the impacts of elevated atmospheric CO2 on plant communities. [source] Indirect effects of soil moisture reverse soil C sequestration responses of a spring wheat agroecosystem to elevated CO2GLOBAL CHANGE BIOLOGY, Issue 1 2010SVEN MARHAN Abstract Increased plant productivity under elevated atmospheric CO2 concentrations might increase soil carbon (C) inputs and storage, which would constitute an important negative feedback on the ongoing atmospheric CO2 rise. However, elevated CO2 often also leads to increased soil moisture, which could accelerate the decomposition of soil organic matter, thus counteracting the positive effects via C cycling. We investigated soil C sequestration responses to 5 years of elevated CO2 treatment in a temperate spring wheat agroecosystem. The application of 13C-depleted CO2 to the elevated CO2 plots enabled us to partition soil C into recently fixed C (Cnew) and pre-experimental C (Cold) by 13C/12C mass balance. Gross C inputs to soils associated with Cnew accumulation and the decomposition of Cold were then simulated using the Rothamsted C model ,RothC.' We also ran simulations with a modified RothC version that was driven directly by measured soil moisture and temperature data instead of the original water balance equation that required potential evaporation and precipitation as input. The model accurately reproduced the measured Cnew in bulk soil and microbial biomass C. Assuming equal soil moisture in both ambient and elevated CO2, simulation results indicated that elevated CO2 soils accumulated an extra ,40,50 g C m,2 relative to ambient CO2 soils over the 5 year treatment period. However, when accounting for the increased soil moisture under elevated CO2 that we observed, a faster decomposition of Cold resulted; this extra C loss under elevated CO2 resulted in a negative net effect on total soil C of ,30 g C m,2 relative to ambient conditions. The present study therefore demonstrates that positive effects of elevated CO2 on soil C due to extra soil C inputs can be more than compensated by negative effects of elevated CO2 via the hydrological cycle. [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] Where temperate meets tropical: multi-factorial effects of elevated CO2, nitrogen enrichment, and competition on a mangrove-salt marsh communityGLOBAL CHANGE BIOLOGY, Issue 5 2008KAREN L. McKEE Abstract Our understanding of how elevated CO2 and interactions with other factors will affect coastal plant communities is limited. Such information is particularly needed for transitional communities where major vegetation types converge. Tropical mangroves (Avicennia germinans) intergrade with temperate salt marshes (Spartina alterniflora) in the northern Gulf of Mexico, and this transitional community represents an important experimental system to test hypotheses about global change impacts on critical ecosystems. We examined the responses of A. germinans (C3) and S. alterniflora (C4), grown in monoculture and mixture in mesocosms for 18 months, to interactive effects of atmospheric CO2 and pore water nitrogen (N) concentrations typical of these marshes. A. germinans, grown without competition from S. alterniflora, increased final biomass (35%) under elevated CO2 treatment and higher N availability. Growth of A. germinans was severely curtailed, however, when grown in mixture with S. alterniflora, and enrichment with CO2 and N could not reverse this growth suppression. A field experiment using mangrove seedlings produced by CO2 - and N-enriched trees confirmed that competition from S. alterniflora suppressed growth under natural conditions and further showed that herbivory greatly reduced survival of all seedlings. Thus, mangroves will not supplant marsh vegetation due to elevated CO2 alone, but instead will require changes in climate, environmental stress, or disturbance to alter the competitive balance between these species. However, where competition and herbivory are low, elevated CO2 may accelerate mangrove transition from the seedling to sapling stage and also increase above- and belowground production of existing mangrove stands, particularly in combination with higher soil N. [source] Increasing CO2 from subambient to elevated concentrations increases grassland respiration per unit of net carbon fixationGLOBAL CHANGE BIOLOGY, Issue 8 2006H. WAYNE POLLEY Abstract Respiration (carbon efflux) by terrestrial ecosystems is a major component of the global carbon (C) cycle, but the response of C efflux to atmospheric CO2 enrichment remains uncertain. Respiration may respond directly to an increase in the availability of C substrates at high CO2, but also may be affected indirectly by a CO2 -mediated alteration in the amount by which respiration changes per unit of change in temperature or C uptake (sensitivity of respiration to temperature or C uptake). We measured CO2 fluxes continuously during the final 2 years of a 4-year experiment on C3/C4 grassland that was exposed to a 200,560 ,mol mol,1 CO2 gradient. Flux measurements were used to determine whether CO2 treatment affected nighttime respiration rates and the response of ecosystem respiration to seasonal changes in net C uptake and air temperature. Increasing CO2 from subambient to elevated concentrations stimulated grassland respiration at night by increasing the net amount of C fixed during daylight and by increasing either the sensitivity of C efflux to daily changes in C fixation or the respiration rate in the absence of C uptake (basal ecosystem respiration rate). These latter two changes contributed to a 30,47% increase in the ratio of nighttime respiration to daytime net C influx as CO2 increased from subamient to elevated concentrations. Daily changes in net C uptake were highly correlated with variation in temperature, meaning that the shared contribution of C uptake and temperature in explaining variance in respiration rates was large. Statistically controlling for collinearity between temperature and C uptake reduced the effect of a given change in C influx on respiration. Conversely, CO2 treatment did not affect the response of grassland respiration to seasonal variation in temperature. Elevating CO2 concentration increased grassland respiration rates by increasing both net C input and respiration per unit of C input. A better understanding of how C efflux varies with substrate supply thus may be required to accurately assess the C balance of terrestrial ecosystems. [source] The effect of elevated CO2 on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoidesGLOBAL CHANGE BIOLOGY, Issue 8 2005Achim Walter Abstract Image sequence processing methods were applied to study the effect of elevated CO2 on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO2 for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO2. Increased final leaf area at elevated CO2 was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30,40% day,1 was increased by a factor of two in the elevated CO2 treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO2 as the growing season progressed. During this minimum, leaves grown under elevated CO2 decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO2, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO2. Net CO2 exchange and starch concentration of growing leaves was higher in elevated CO2. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO2 is discussed. [source] The microfood web of grassland soils responds to a moderate increase in atmospheric CO2GLOBAL CHANGE BIOLOGY, Issue 7 2005Ilja Sonnemann Abstract The response of the soil microfood web (microflora, nematodes) to a moderate increase in atmospheric CO2 (+20%) was investigated by means of a free air CO2 enrichment experiment. The study was carried out in a seminatural temperate grassland for a period of 4 consecutive years (1 year before fumigation commenced and 3 years with fumigation). Several soil biological parameters showed no change (microbial biomass, bacterial biomass) or decline (microbial respiration) in the first year of elevated CO2 treatment as compared with controls. Each of these parameters were higher than controls, however, after 3 years of treatment. The relative abundance of predaceous nematodes also decreased in year 1 of the experiment, increased in year 2, but decreased again in year 3. In contrast, the relative abundance of root hair feeding nematodes, at first, increased under elevated CO2 and then returned to the initial level again. Increased microbial biomass indicates enhanced C storage in the labile carbon pool of the active microfood web in subsequent years. According to measurements on the amounts of soil extractable C, changes in resource availability seem to be key to the response of the soil microfood web. We found a strong response of bacteria to elevated CO2, while the fungal biomass remained largely unchanged. This contrasts to findings reported in the literature. We hypothesize that this may be because of contrasting effects of different levels of CO2 enrichment on the microbial community (i.e. stimulation of bacteria at moderate levels and stimulation of fungi at high levels of CO2 enrichment). However, various CO2 effects observed in our study are similar in magnitude to those observed in other studies for a much higher level of atmospheric carbon. These include the particular sensitivity of predaceous nematodes and the long-term increase of microbial respiration. Our findings confirm that the potential of terrestrial ecosystems to accumulate additional carbon might be lower than previously thought. Furthermore, CO2 -induced changes of temperate grassland ecosystems might emerge much earlier than expected. [source] Genetic variation in Sanguisorba minor after 6 years in situ selection under elevated CO2GLOBAL CHANGE BIOLOGY, Issue 8 2004Silvia Wieneke Abstract Genetic variation within plant species in their response to elevated CO2 could be important for long-term changes in plant community composition because it allows for selection of responsive genotypes. Six years of in situ CO2 enrichment in a temperate grassland offered a unique opportunity to investigate such microevolutionary changes in a common herb of that plant community, Sanguisorba minor. Plants were grown from seeds collected at the end of a 6-year treatment in either ambient or elevated CO2. The resulting seedlings were grown under ambient or elevated CO2 and with or without interspecific competition by Bromus erectus in the greenhouse for two seasons. The effect of competition was included because we expected selection under elevated CO2 to favour increased competitive ability. Elevated CO2 in the greenhouse and competition both caused a significant reduction of the total dry mass in S. minor, by 12% and 40%, respectively, with no interaction between CO2 and competition. Genetic variation in all traits was substantial. Seed families responded differently to competition, but the family × greenhouse CO2 interaction was rather weak. There was no main effect of the field CO2 treatment on any parameter analysed in the greenhouse. However, the field CO2 treatment did significantly interact with the greenhouse CO2 treatment for the cumulative number of leaves, suggesting microevolutionary change in this plant trait. Families from ambient field CO2 produced fewer leaves under elevated greenhouse CO2, whereas families from elevated field CO2 retained constant number of leaves in either greenhouse CO2 treatment. Since this resulted in increased litter production of the families from elevated field CO2 under elevated greenhouse CO2, the microevolutionary response should, in turn, affect ecosystem functions through dry matter recycling. [source] Root production and demography in a california annual grassland under elevated atmospheric carbon dioxideGLOBAL CHANGE BIOLOGY, Issue 9 2002Paul A. T. Higgins Abstract This study examined root production and turnover in a California grassland during the third year of a long-term experiment with ambient (LO) and twice-ambient atmospheric CO2 (HI), using harvests, ingrowth cores, and minirhizotrons. Based on one-time harvest data, root biomass was 32% greater in the HI treatment, comparable to the stimulation of aboveground production during the study year. However, the 30,70% increase in photosynthesis under elevated CO2 for the dominant species in our system is considerably larger than the combined increase in above and belowground biomass. One possible explanation is, increased root turnover, which could be a sink for the additional fixed carbon. Cumulative root production in ingrowth cores from both treatments harvested at four dates was 2,3 times that in the single harvested cores, suggesting substantial root turnover within the growing season. Minirhizotron data confirmed this result, demonstrating that production and mortality occurred simultaneously through much of the season. As a result, cumulative root production was 54%, 47% and 44% greater than peak standing root length for the no chamber (X), LO, and HI plots, respectively. Elevated CO2, however, had little effect on rates of turnover (i.e. rates of turnover were equal in the LO and HI plots throughout most of the year) and cumulative root production was unaffected by treatment. Elevated CO2 increased monthly production of new root length (59%) only at the end of the season (April,June) when root growth had largely ceased in the LO plots but continued in the HI plots. This end-of-season increase in production coincided with an 18% greater soil moisture content in the HI plots previously described. Total standing root length was not affected by CO2 treatment. Root mortality was unaffected by elevated CO2 in all months except April, in which plants grown in the HI plots had higher mortality rates. Together, these results demonstrate that root turnover is considerable in the grassland community and easily missed by destructive soil coring. However, increased fine root turnover under elevated CO2 is apparently not a major sink for extra photosynthate in this system. [source] Leaf respiratory CO2 is 13C-enriched relative to leaf organic components in five species of C3 plantsNEW PHYTOLOGIST, Issue 3 2004Cheng-yuan Xu Summary ,,Here, we compared the carbon isotope ratios of leaf respiratory CO2 (,13CR) and leaf organic components (soluble sugar, water soluble fraction, starch, protein and bulk organic matter) in five C3 plants grown in a glasshouse and inside Biosphere 2. One species, Populus deltoides, was grown under three different CO2 concentrations. ,,The Keeling plot approach was applied to the leaf scale to measure leaf ,13CR and these results were compared with the ,13C of leaf organic components. ,,In all cases, leaf respiratory CO2 was more 13C-enriched than leaf organic components. The amount of 13C enrichment displayed a significant species-specific pattern, but the effect of CO2 treatment was not significant on P. deltoides. ,,In C3 plant leaves, 13C-enriched respiratory CO2 appears widespread. Among currently hypothesized mechanisms contributing to this phenomenon, non-statistical carbon isotope distribution within the sugar substrates seems most likely. However, caution should be taken when attempting to predict the ,13C of leaf respiratory CO2 at the ecosystem scale by upscaling the relationship between leaf ,13CR and ,13C of leaf organic components. [source] Effects of arbuscular mycorrhizae on biomass and nutrients in the aquatic plant Littorella unifloraFRESHWATER BIOLOGY, Issue 9 2006FREDE Ø. ANDERSEN Summary 1. It has been hypothesised that the symbiosis with arbuscular mycorrhizal fungi (AMF) leads to a higher uptake of phosphorus (P) and nitrogen (N) in aquatic plants, but it has never been shown experimentally without the use of fungicides. In particular, the symbiosis may be important for nutrient uptake by isoetids in oligotrophic lakes, where low concentrations of inorganic N and P both in the water and in the sediment limit the growth of plants and where symbiosis facilitates the uptake of nutrients from the sediment. 2. Plants of the isoetid Littorella uniflora were propagated under the sterile conditions without an AMF infection. The plants were then grown for 60 days with and without re-infection by AMF, and with either high (150 ,m) or low (ambient concentration approximately 15 ,m) CO2 concentration. 3. The study proved that the symbiosis between AMF and L. uniflora had a positive impact on the retention of N and P in the plants at very low nutrient concentrations in the water and on biomass development. Shoot biomass and standing stocks of both P and N were significantly higher in re-infected plants. 4. Raised CO2 concentration resulted in a fivefold increase in hyphal infection, but had no impact on the number of arbuscules and vesicles in the cross sections. There were significantly higher biomass and lower tissue P and N concentrations in the plants from high CO2 treatments. This resulted in similar standing stocks of P and N in plants from low and high CO2 treatments. 5. The results from this study showed that the symbiosis between AMF and L. uniflora is an important adaptation enabling isoetids to grow on nutrient-poor sediments in oligotrophic lakes. [source] Respiratory carbon loss of calcareous grasslands in winter shows no effects of 4 years' CO2 enrichmentFUNCTIONAL ECOLOGY, Issue 2 2002M. Volk Summary 1CO2 exchange measurements in long-term CO2 -enrichment experiments suggest large net carbon gains by ecosystems during the growing season that are not accounted for by above-ground plant biomass. Considerable amounts of C might therefore be allocated below ground. 2Winter ecosystem respiration from temperate grasslands under elevated CO2 may account for the loss of a significant part of the extra C gained during the growing season. To test this hypothesis, dark respiration was assessed throughout the winter of the fourth year of CO2 enrichment in a calcareous grassland. 3Using these data, a model was parameterized to estimate whole-winter respiratory CO2 losses. From November to February, 154 9 g C m,2 were respired under elevated CO2 and 144 5 g C m,2 under ambient [CO2], with no significant difference between the CO2 treatments. 4We conclude that (i) wintertime respiration does not constitute a larger C loss from the ecosystem at elevated CO2; and (ii) the absence of respiratory responses implies no extra growing-season C inputs with month-to-year turnover times at elevated CO2. [source] The effects of elevated CO2 on root respiration rates of two Mojave Desert shrubsGLOBAL CHANGE BIOLOGY, Issue 5 2010NAOMI M. CLARK Abstract Although desert ecosystems are predicted to be the most responsive to elevated CO2, low nutrient availability may limit increases in productivity and cause plants in deserts to allocate more resources to root biomass or activity for increased nutrient acquisition. We measured root respiration of two Mojave Desert shrubs, Ambrosia dumosa and Larrea tridentata, grown under ambient (,375 ppm) and elevated (,517 ppm) CO2 concentrations at the Nevada Desert FACE Facility (NDFF) over five growing seasons. In addition, we grew L. tridentata seedlings in a greenhouse with similar CO2 treatments to determine responses of primary and lateral roots to an increase in CO2. In both field and greenhouse studies, root respiration was not significantly affected by elevated CO2. However, respiration of A. dumosa roots <1 month old was significantly greater than respiration of A. dumosa roots between 1 and 4 months old. For both shrub species, respiration rates of very fine (<1.0 mm diameter) roots were significantly greater than those of fine (1,2 mm diameter) roots, and root respiration decreased as soil water decreased. Because specific root length was not significantly affected by CO2 and because field minirhizotron measurements of root production were not significantly different, we infer that root growth at the NDFF has not increased with elevated CO2. Furthermore, other studies at the NDFF have shown increased nutrient availability under elevated CO2, which reduces the need for roots to increase scavenging for nutrients. Thus, we conclude that A. dumosa and L. tridentata root systems have not increased in size or activity, and increased shoot production observed under elevated CO2 for these species does not appear to be constrained by the plant's root growth or activity. [source] Increased leaf area dominates carbon flux response to elevated CO2 in stands of Populus deltoides (Bartr.)GLOBAL CHANGE BIOLOGY, Issue 5 2005Ramesh Murthy Abstract We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf- and stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6,14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25,39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf- and stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand=3.2,3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8,1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. [source] Above- and below-ground responses of C3,C4 species mixtures to elevated CO2 and soil water availabilityGLOBAL CHANGE BIOLOGY, Issue 3 2003JUSTIN D. DERNER Abstract We evaluated the influences of CO2[Control, , 370 µmol mol,1; 200 µmol mol,1 above ambient applied by free-air CO2 enrichment (FACE)] and soil water (Wet, Dry) on above- and below-ground responses of C3 (cotton, Gossypium hirsutum) and C4 (sorghum, Sorghum bicolor) plants in monocultures and two density mixtures. In monocultures, CO2 enrichment increased height, leaf area, above-ground biomass and reproductive output of cotton, but not sorghum, and was independent of soil water treatment. In mixtures, cotton, but not sorghum, above-ground biomass and height were generally reduced compared to monocultures, across both CO2 and soil water treatments. Density did not affect individual plant responses of either cotton or sorghum across the other treatments. Total (cotton + sorghum) leaf area and above-ground biomass in low-density mixtures were similar between CO2 treatments, but increased by 17,21% with FACE in high-density mixtures, due to a 121% enhancement of cotton leaf area and a 276% increase in biomass under the FACE treatment. Total root biomass in the upper 1.2 m of the soil was not influenced by CO2 or by soil water in monoculture or mixtures; however, under dry conditions we observed significantly more roots at lower soil depths (> 45 cm). Sorghum roots comprised 81,85% of the total roots in the low-density mixture and 58,73% in the high-density mixture. CO2 -enrichment partly offset negative effects of interspecific competition on cotton in both low- and high-density mixtures by increasing above-ground biomass, with a greater relative increase in the high-density mixture. As a consequence, CO2 -enrichment increased total above-ground yield of the mixture at high density. Individual plant responses to CO2 enrichment in global change models that evaluate mixed plant communities should be adjusted to incorporate feedbacks for interspecific competition. Future field studies in natural ecosystems should address the role that a CO2 -mediated increase in C3 growth may have on subsequent vegetation change. [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] Antimicrobial activity of glucose oxidase-immobilized plasma-activated polypropylene filmsPACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2005Jari Vartiainen Abstract Antimicrobial enzyme, glucose oxidase (GOX), was covalently immobilized onto amino- and carboxyl-plasma-activated biorientated polypropylene films (BOPP) via glutaraldehyde and carbodiimide chemistries. N2 -plasma + NH3 and N2 -plasma + CO2 treatments were utilized to create amino (1.1,nmol/cm2) and carboxyl (0.9,nmol/cm2) groups densities onto the surface of BOPP films. GOX-immobilized onto amino-activated BOPP films using 2.5% glutaraldehyde produced higher enzymatic activities than GOX-immobilized by 0.4% carbodiimide. Further immobilizations were carried out with glutaraldehyde as the coupling agent at temperatures of 4,75°C at pH 5.6 and 7.2. 10,s treatment was sufficient to immobilize GOX at high temperatures in both pH conditions, producing enzymatically active films which remained active over 30 days of storage. GOX covalently immobilized onto BOPP films completely inhibited the growth of Escherichia coli and substantially inhibited the growth of Bacillus subtilis; thus, they may have great potential to be exploited in various antimicrobial packaging film applications. Copyright © 2005 John Wiley & Sons, Ltd. [source] Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedlingPLANT CELL & ENVIRONMENT, Issue 12 2002A. D. B. LEAKEY Abstract The survivorship of dipterocarp seedlings in the deeply shaded understorey of South-east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO2 upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO2. Equal total daily photon flux density (PFD) (,7·7 mol m,2 d,1) was supplied as either uniform irradiance (,170 µmol m,2 s,1) or shade/fleck sequences (,30 µmol m,2 s,1/,525 µmol m,2 s,1). Photosynthesis and growth were enhanced by elevated CO2 treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO2 but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO2 were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post-irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO2 under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition. [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. 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