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Selected AbstractsRespiration of nitrous oxide in suboxic soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2009B. Vieten Summary Reduction of nitrous oxide (N2O) is an autonomous respiratory pathway. Nitrous oxide is an alternative electron acceptor to O2 when intensive biological activity and reduced diffusivity result in an O2 deficit. Hypoxic or anoxic micro sites may form even in well-aerated soils, and provide a sink for N2O diffusing through the gas-filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O2) flow-through incubation experiments with samples from a Stagnosol and from a Histosol. Apparent half-saturation constants (km) for N2O reduction were similar for both soils and were, on average, 3.8 ,mol mol,1 at 5°C, 5.1 ,mol mol,1 at 10°C, and 6.9 ,mol mol,1 at 20°C. Respiration of N2O was estimated to contribute a maximum proportion of 1.7% to total respiration in the Stagnosol (pH 7.0) and 0.9% in the Histosol (pH 2.9). [source] Engineering NADH metabolism in Saccharomyces cerevisiae: formate as an electron donor for glycerol production by anaerobic, glucose-limited chemostat culturesFEMS YEAST RESEARCH, Issue 8 2006Jan-Maarten A. Geertman Abstract Anaerobic Saccharomyces cerevisiae cultures reoxidize the excess NADH formed in biosynthesis via glycerol production. This study investigates whether cometabolism of formate, a well-known NADH-generating substrate in aerobic cultures, can increase glycerol production in anaerobic S. cerevisiae cultures. In anaerobic, glucose-limited chemostat sultures (D=0.10 h,1) with molar formate-to-glucose ratios of 0 to 0.5, only a small fraction of the formate added to the cultures was consumed. To investigate whether incomplete formate consumption was by the unfavourable kinetics of yeast formate dehydrogenase (high kM for formate at low intracellular NAD+ concentrations) strains were constructed in which the FDH1 and/or GPD2 genes, encoding formate dehydrogenase and glycerol-3-phosphate dehydrogenase, respectively, were overexpressed. The engineered strains consumed up to 70% of the formate added to the feed, thereby increasing glycerol yields to 0.3 mol mol,1 glucose at a formate-to-glucose ratio of 0.34. In all strains tested, the molar ratio between formate consumption and additional glycerol production relative to a reference culture equalled one. While demonstrating that that format can be use to enhance glycerol yields in anaerobic S. cerevisiae cultures, This study also reveals kinetic constraints of yeast formate dehydrogenase as an NADH-generating system in yeast mediated reduction processes. [source] Last-century changes of alpine grassland water-use efficiency: a reconstruction through carbon isotope analysis of a time-series of Capra ibex hornsGLOBAL CHANGE BIOLOGY, Issue 4 2010INÊS C. R. BARBOSA Abstract The ecophysiological response of an alpine grassland to recent climate change and increasing atmospheric CO2 concentration was investigated with a new strategy to go back in time: using a time-series of Capra ibex horns as archives of the alpine grasslands' carbon isotope discrimination (13,). From the collection of the Natural History Museum of Bern, horns of 24 males from the population of the Augstmatthorn,Brienzer Rothorn mountains, Switzerland, were sampled covering the period from 1938 to 2006. Samples were taken from the beginning of each year-ring of the horns, representing the beginning of the horn growth period, the spring. The horns' carbon 13C content (,13C) declined together with that of atmospheric CO2 over the 69-year period, but 13, increased slightly (+0.4,), though significantly (P<0.05), over the observation period. Estimated intercellular CO2 concentration increased (+56 ,mol mol,1) less than the atmospheric CO2 concentration (+81 ,mol mol,1), so that intrinsic water-use efficiency increased by 17.8% during the 69-year period. However, the atmospheric evaporative demand at the site increased by approximately 0.1 kPa between 1955 and 2006, thus counteracting the improvement of intrinsic water-use efficiency. As a result, instantaneous water-use efficiency did not change. The observed changes in intrinsic water-use efficiency were in the same range as those of trees (as reported by others), indicating that leaf-level control of water-use efficiency of grassland and forests followed the same principles. This is the first reconstruction of the water-use efficiency response of a natural grassland ecosystem to last century CO2 and climatic changes. The results indicate that the alpine grassland community has responded to climate change by improving the physiological control of carbon gain to water loss, following the increases in atmospheric CO2 and evaporative demand. But, effective leaf-level water-use efficiency has remained unchanged. [source] Plant nitrogen acquisition and interactions under elevated carbon dioxide: impact of endophytes and mycorrhizaeGLOBAL CHANGE BIOLOGY, Issue 6 2007XIN CHEN Abstract Both endophytic and mycorrhizal fungi interact with plants to form symbiosis in which the fungal partners rely on, and sometimes compete for, carbon (C) sources from their hosts. Changes in photosynthesis in host plants caused by atmospheric carbon dioxide (CO2) enrichment may, therefore, influence those mutualistic interactions, potentially modifying plant nutrient acquisition and interactions with other coexisting plant species. However, few studies have so far examined the interactive controls of endophytes and mycorrhizae over plant responses to atmospheric CO2 enrichment. Using Festuca arundinacea Schreb and Plantago lanceolata L. as model plants, we examined the effects of elevated CO2 on mycorrhizae and endophyte (Neotyphodium coenophialum) and plant nitrogen (N) acquisition in two microcosm experiments, and determined whether and how mycorrhizae and endophytes mediate interactions between their host plant species. Endophyte-free and endophyte-infected F. arundinacea varieties, P. lanceolata L., and their combination with or without mycorrhizal inocula were grown under ambient (400 ,mol mol,1) and elevated CO2 (ambient + 330 ,mol mol,1). A 15N isotope tracer was used to quantify the mycorrhiza-mediated plant acquisition of N from soil. Elevated CO2 stimulated the growth of P. lanceolata greater than F. arundinacea, increasing the shoot biomass ratio of P. lanceolata to F. arundinacea in all the mixtures. Elevated CO2 also increased mycorrhizal root colonization of P. lanceolata, but had no impact on that of F. arundinacea. Mycorrhizae increased the shoot biomass ratio of P. lanceolata to F. arundinacea under elevated CO2. In the absence of endophytes, both elevated CO2 and mycorrhizae enhanced 15N and total N uptake of P. lanceolata but had either no or even negative effects on N acquisition of F. arundinacea, altering N distribution between these two species in the mixture. The presence of endophytes in F. arundinacea, however, reduced the CO2 effect on N acquisition in P. lanceolata, although it did not affect growth responses of their host plants to elevated CO2. These results suggest that mycorrhizal fungi and endophytes might interactively affect the responses of their host plants and their coexisting species to elevated CO2. [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] Plant and microbial N acquisition under elevated atmospheric CO2 in two mesocosm experiments with annual grassesGLOBAL CHANGE BIOLOGY, Issue 2 2005Shuijin Hu Abstract The impact of elevated CO2 on terrestrial ecosystem C balance, both in sign or magnitude, is not clear because the resulting alterations in C input, plant nutrient demand and water use efficiency often have contrasting impacts on microbial decomposition processes. One major source of uncertainty stems from the impact of elevated CO2 on N availability to plants and microbes. We examined the effects of atmospheric CO2 enrichment (ambient+370 ,mol mol,1) on plant and microbial N acquisition in two different mesocosm experiments, using model plant species of annual grasses of Avena barbata and A. fatua, respectively. The A. barbata experiment was conducted in a N-poor sandy loam and the A. fatua experiment was on a N-rich clayey loam. Plant,microbial N partitioning was examined through determining the distribution of a 15N tracer. In the A. barbata experiment, 15N tracer was introduced to a field labeling experiment in the previous year so that 15N predominantly existed in nonextractable soil pools. In the A. fatua experiment, 15N was introduced in a mineral solution [(15NH4)2SO4 solution] during the growing season of A. fatua. Results of both N budget and 15N tracer analyses indicated that elevated CO2 increased plant N acquisition from the soil. In the A. barbata experiment, elevated CO2 increased plant biomass N by ca. 10% but there was no corresponding decrease in soil extractable N, suggesting that plants might have obtained N from the nonextractable organic N pool because of enhanced microbial activity. In the A. fatua experiment, however, the CO2 -led increase in plant biomass N was statistically equal to the reduction in soil extractable N. Although atmospheric CO2 enrichment enhanced microbial biomass C under A. barbata or microbial activity (respiration) under A. fatua, it had no significant effect on microbial biomass N in either experiment. Elevated CO2 increased the colonization of A. fatua roots by arbuscular mycorrhizal fungi, which coincided with the enhancement of plant competitiveness for soluble soil N. Together, these results suggest that elevated CO2 may tighten N cycling through facilitating plant N acquisition. However, it is unknown to what degree results from these short-term microcosm experiments can be extrapolated to field conditions. Long-term studies in less-disturbed soils are needed to determine whether CO2 -enhancement of plant N acquisition can significantly relieve N limitation over plant growth in an elevated CO2 environment. [source] Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres?GLOBAL CHANGE BIOLOGY, Issue 6 2004An analysis of diurnal courses of CO2 uptake under free-air concentration enrichment (FACE) Abstract The C4 grass Zea mays (maize or corn) is the third most important food crop globally in terms of production and demand is predicted to increase 45% from 1997 to 2020. However, the effects of rising [CO2] upon C4 plants, and Z. mays specifically, are not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment utilizing free-air concentration enrichment (FACE) technology in the primary area of global corn production (US Corn Belt) was undertaken to determine the effects of elevated [CO2] on corn. FACE technology allows experimental treatments to be imposed upon a complete soil,plant,atmosphere continuum with none of the effects of experimental enclosures on plant microclimate. Crop performance was compared at ambient [CO2] (354 , mol mol,1) and the elevated [CO2] (549 ,mol mol,1) predicted for 2050. Previous laboratory studies suggest that under favorable growing conditions C4 photosynthesis is not typically enhanced by elevated [CO2]. However, stomatal conductance and transpiration are decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and relatively high rainfall of the US Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO2]. The diurnal course of gas exchange of upper canopy leaves was measured in situ across the growing season of 2002. Contrary to the prediction, growth at elevated [CO2] significantly increased leaf photosynthetic CO2 uptake rate (A) by up to 41%, and 10% on average. Greater A was associated with greater intercellular [CO2], lower stomatal conductance and lower transpiration. Summer rainfall during 2002 was very close to the 50-year average for this site, indicating that the year was not atypical or a drought year. The results call for a reassessment of the established view that C4 photosynthesis is insensitive to elevated [CO2] under favorable growing conditions and that the production potential of corn in the US Corn Belt will not be affected by the global rise in [CO2]. [source] Effects of atmospheric CO2 concentration and defoliation on the growth of Themeda triandraGRASS & FORAGE SCIENCE, Issue 3 2004S. J. E. Wand Abstract The effects of elevated atmospheric carbon dioxide (CO2) concentration (700 ,mol mol,1) on defoliated (three clippings at 3-week intervals) and undefoliated plants were determined for the C4 grass Themeda triandra, Forsk. The elevated CO2 concentration significantly increased leaf regrowth following defoliation, and total leaf production was greatest in this treatment. Shoot biomass of undefoliated plants was also increased under the elevated CO2 concentration treatment. The primary effect of the elevated CO2 concentration in both defoliated and undefoliated plants was an increase in individual leaf length and mass of dry matter, linked to a higher leaf water content and increased photosynthetic rates at the canopy level. Photosynthetic down-regulation at the leaf level occurred, but this was compensated for by increased assimilation rates and greater canopy leaf area at the elevated CO2 concentration. Increases in leaf and sheath growth of defoliated plants in the elevated CO2 concentration treatment were lost following a final 3-week reversion to ambient CO2 concentration, but occurred in plants exposed to the elevated CO2 concentration for the final 3-week period only. In conclusion, elevated atmospheric CO2 concentration increases shoot growth via increased leaf extension, which is directly dependent on stimulation of concurrent photosynthesis. CO2 responsiveness is sustained following moderate defoliation but is reduced when plants experience reduced vigour as a result of maturation or high frequency of defoliation. [source] Optimization of the reaction parameters of epoxidation of rapeseed oil with peracetic acidJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2010Eugeniusz Milchert Abstract BACKGROUND: The epoxidation of vegetable oils has been a subject of interest for many years; epoxidized oils are frequently used as plasticizers and as renewable materials for the manufacture of alcohols, glycols and many other complex compounds with excellent antioxidant and antifriction properties. In this work the epoxidation process of rapeseed oil (RO) with peracetic acid generated in situ by the reaction of 30 wt% hydrogen peroxide and acetic acid has been studied. Optimization studies were performed by application of a statistical experimental design method utilizing a rotatable-uniform design. RESULTS: The significant parameters for the RO epoxidation process were established as temperature, molar ratio of hydrogen peroxide to rapeseed oil, molar ratio of acetic acid to rapeseed oil and reaction time. The process description was based on five response functions: iodine number, epoxy number, conversion, yield and selectivity. The highest values of all functions with the exception of selectivity were achieved for the same values of parameters: temperature 65 °C, molar ratio of hydrogen peroxide to RO 11.1:1 mol mol,1, molar ratio of acetic acid to RO 1.89:1 mol mol,1 and reaction time 6 h. CONCLUSION: In summary, these optimum parameters allow one to obtain epoxidized rapeseed oil with a yield of 66.2 mol% at an oil conversion of 91.0 mol% in mild and relatively safe conditions. The epoxy number of the product was 0.207 mol per 100 g, whereas the iodine number was 0.027 mol per 100 g. Copyright © 2010 Society of Chemical Industry [source] Strain isolation and optimization of process parameters for bioconversion of glycerol to lactic acidJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2009An-An Hong Abstract BACKGROUND: The crude glycerol from biodiesel production represents an abundant and inexpensive source which can be used as raw material for lactic acid production. The first aim of this investigation was to select a strain suitable for producing lactic acid from glycerol with a high concentration and productivity. The second aim was to obtain the optimum fermentation conditions, as a basis for large-scale lactate production in the future. RESULTS: Eight bacterial strains, which could aerobically convert glycerol to lactic acid, were screened from soil samples. One of the strains, AC-521, which synthesized lactic acid with a higher concentration, was identified based on its 16S rDNA sequences and physiological characteristics. These results indicated that this strain was a member of Escherichia coli. The optimal fermentation conditions for Escherichia coli AC-521 were 42 °C, pH 6.5, 0.85 min,1 (KLa). CONCLUSION:Escherichia coli AC-521 suitable for producing lactic acid from glycerol with high concentration and productivity was identified. After 88 h of fed-batch fermentation, both the lactic acid concentration and glycerol consumption reached maximum, giving 85.8 g L,1 of lactic acid with a productivity of 0.97 g L,1 h,1 and a yield of 0.9 mol mol,1 glycerol. Copyright © 2009 Society of Chemical Industry [source] Over-expression of glycerol dehydrogenase and 1,3-propanediol oxidoreductase in Klebsiella pneumoniae and their effects on conversion of glycerol into 1,3-propanediol in resting cell systemJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2009Li Zhao Abstract BACKGROUND: Glycerol dehydrogenase [EC.1.1.1.6] and 1,3-propanediol oxidoreductase [EC.1.1.1.202] were proved to be two of the key enzymes for glycerol conversion to 1,3-propanediol in Klebsiella pneumoniae under anaerobic conditions. For insight into their significance on 1,3-propanediol production under micro-aerobic conditions, these two enzymes were over-expressed in K. pneumoniae individually, and their effects on conversion of glycerol into 1,3-propanediol in a resting cell system under micro-aerobic conditions were investigated. RESULTS: In the resting cell system, over-expression of 1,3-propanediol oxidoreductase led to faster glycerol conversion and 1,3-propanediol production. After a 12 h conversion process, it improved the yield of 1,3-propanediol by 20.4% (222.1 mmol L,1 versus 184.4 mmol L,1) and enhanced the conversion ratio of glycerol into 1,3-propanediol from 50.8% to 59.8% (mol mol,1). Over-expression of glycerol dehydrogenase in K. pneumoniae had no significant influence both on 1,3-propanediol yield and on the conversion ratio of glycerol into 1,3-propanediol in the resting cell system. CONCLUSION: The results were important for an understanding of the significance of glycerol dehydrogenase and 1,3-propanediol oxidoreductase in 1,3-proanediol production under micro-aerobic conditions, and for developing better strategies to improve 1,3-propanediol yield. Copyright © 2008 Society of Chemical Industry [source] Storage of biodegradable polymers by an enriched microbial community in a sequencing batch reactor operated at high organic load rateJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2005Davide Dionisi Abstract The production of polyhydroxyalkanoates (PHAs) from organic acids by mixed bacterial cultures using a process based on aerobic enrichment of activated sludge, that selects for mixed microbial cultures able to store PHAs at high rates and yields, is described. Enrichment resulted from the selective pressure established by periodic feeding the carbon source in a sequencing batch reactor (SBR); a mixture of acetic, lactic and propionic acids was fed at high frequency (2 hourly), high dilution rate (1 d,1), and at high organic load rate (12.75 g chemical oxygen demand (COD) L,1 d,1). The performance of the SBR was assessed by microbial biomass and PHA production as well as the composition and polymer content of the biomass. A final batch stage was used to increase the polymer concentration of the excess sludge produced in the SBR and in which the behaviour of the biomass was investigated by determining PHA production rates and yields. The microbial biomass selected in the SBR produced PHAs at high rate [278 mg PHAs (as COD) g biomass (as COD),1 h,1, with a yield of 0.39 mg PHAs (as COD) mg removed substrates (as COD),1], reaching a polymer content higher than 50% (on a COD basis). The stored polymer was the copolymer poly(3-hydroxybutyrate/3-hydroxyvalerate) [P(HB/HV)], with an HV fraction of 18% mol mol,1. The microbial community selected in the SBR was analysed by DGGE (denaturing gradient gel electrophoresis). The operating conditions of the SBR were shown to select for a restricted microbial population which appeared quite different in terms of composition with respect to the initial microbial cenosis in the activated sludge used as inoculum. On the basis of the sequencing of the major bands in the DGGE profiles, four main genera were identified: a Methylobacteriaceae bacterium, Flavobacterium sp, Candidatus Meganema perideroedes, and Thauera sp. The effects of nitrogen depletion (ie absence of growth) and pH variation were also investigated in the batch stage and compared with the SBR operative mode. Absence of growth did not stimulate higher PHA production, so indicating that the periodic feed regime fully exploited the storage potential of the enriched culture. Polymer production rates remained high between pH 6.5 and 9.5, whereas the HV content in the stored polymer strongly increased as the pH value increased. This study shows that polymer composition in the final batch stage can readily be controlled independently from the feed composition in the SBR. Copyright © 2005 Society of Chemical Industry [source] Effects of phosphate supply and elevated CO2 on root acid phosphatase activity in Pinus densiflora seedlingsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006Mariko Norisada Abstract The exudation of root acid phosphatase (APase) is a plant response mechanism to phosphorus (P) deficiency. Under conditions of elevated CO2, P demand increases and possibly further enhances APase activity. We examined the activity of APase in 1-year-old ectomycorrhizal Pinus densiflora Sieb. et Zucc. seedlings grown in potted sand in the greenhouse under ambient (400 ,mol mol,1) and elevated (700 ,mol mol,1) CO2 with three modes of P supply: inorganic (NaH2PO4; Pin), organic (inositol hexaphosphate dodecasodium salt; Porg), and no phosphate (P0) for 78 d. Phosphorus limitations decreased P content in leaves and roots with lowest P content in P0 treatments, irrespective of CO2 conditions. However, P limitations decreased plant biomass at elevated CO2 levels, but not at ambient CO2 levels. The content in leaves of nutrients other than P was mostly unaffected by P supply, but decreased under elevated CO2. This observation was attributed to starch accumulation in leaves at elevated CO2, especially in the P0 treatment. The photosynthetic activity (expressed per unit of chlorophyll) was unaffected by P supply, but tended to be less at elevated CO2. There was no increase in root APase activity of Pinus densifolia in response to the P shortage caused by elevated CO2. [source] Gluconic acid production by Aspergillus terreusLETTERS IN APPLIED MICROBIOLOGY, Issue 3 2010C. Dowdells Abstract Aim:,Aspergillus terreus produces itaconic acid at low pH but lovastatin and other secondary metabolites at higher pH in the fermentation. The utilization of glucose as a carbon substrate was investigated for secondary metabolite production by A. terreus. Methods and Results:, With a starting pH of 6·5, glucose was rapidly metabolized to gluconic acid by the wild-type strain and by transformants harbouring Aspergillus niger genes encoding 6-phosphofructo-1-kinases with superior kinetic and regulatory properties for bioproduction of metabolites from glucose. On exhaustion of the glucose in batch fermentations, the accumulated gluconic acid was utilized as a carbon source. Conclusions:, A novel pathway of glucose catabolism was demonstrated in A. terreus, a species whose wild type is, without any strain development, capable of producing gluconic acid at high molar conversion efficiency (up to 0·7 mol mol,1 glucose consumed). Significance and Impact of the Study:,Aspergillus terreus is a potential novel producer organism for gluconic acid, a compound with many uses as a bulk chemical. With a new knowledge of glucose catabolism by A. terreus, fermentation strategies for secondary metabolite production can be devised with glucose feeding using feedback regulation by pH. [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] Carbon use efficiency depends on growth respiration, maintenance respiration, and relative growth rate.PLANT CELL & ENVIRONMENT, Issue 9 2003A case study with lettuce ABSTRACT Carbon use efficiency (CUE, the ratio between the amount of carbon incorporated into dry matter to the amount of carbon fixed in gross photosynthesis) is an important parameter in estimating growth rate from photosynthesis data or models. It previously has been found to be relatively constant among species and under different environmental conditions. Here it is shown that CUE can be expressed as a function of the relative growth rate (rGR) and the growth (gr) and maintenance respiration coefficients (mr): 1/CUE = 1 + gr + mr/rGR. Net daily carbon gain (Cdg), rGR, and CUE were estimated from whole-plant gas exchange measurements on lettuce (Lactuca sativa L.) ranging from 24 to 66 d old. Carbon use efficiency decreased from 0.6 to 0.2 with increasing dry mass, but there was no correlation between CUE and Cdg. The decrease in CUE with increasing dry mass was correlated with a simultaneous decrease in rGR. From the above equation, gr and mr were estimated to be 0.48 mol mol,1 and 0.039 g glucose g,1 dry matter d,1, respectively. Based on the gr estimate, the theoretical upper limit for CUE of these plants was 0.68. The importance of maintenance respiration in the carbon balance of the plants increased with increasing plant size. Maintenance accounted for 25% of total respiration in small plants and 90% in large plants. [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] Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high lightPLANT CELL & ENVIRONMENT, Issue 3 2000Hiroyuki Muraoka ABSTRACT Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non-diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1,A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 ,mol mol,1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ,peak' of diurnal assimilation was 70% greater than that obtained before the ,peak', but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (,F/Fm,) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ,peak'. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 ,mol m,2 s,1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ,peak', but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non-photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. [source] Acclimation of photosynthesis to elevated CO2 in onion (Allium cepa) grown at a range of temperaturesANNALS OF APPLIED BIOLOGY, Issue 1 2004T R WHEELER Summary Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5°C to +2.5°C from outside temperatures) maintained at either 374 or 532 ,mol mol,1 CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (Asat) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C1/C3 ratio) was 7.4% less for plants grown at elevated compared with normal CO2. Asat in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C1. Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops. [source] | |||||||||||||