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  • 1
    Electronic Resource
    Electronic Resource
    Photosynthesis, respiration, and net primary production of sunflower stands in ambient and elevated atmospheric CO2 concentrations: an invariant NPP:GPP ratio? (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The effect of elevated CO2 on photosynthesis, respiration, and growth efficiency of sunflower plants at the whole-stand level was investigated using a whole-system gas exchange facility (the EcoCELLs at the Desert Research Institute) and a 13C natural tracer method. Total daily photosynthesis (GPP), net primary production (NPP), and respiration under the elevated CO2 treatment were consistently higher than under the ambient CO2 treatment. The overall level of enhancement due to elevated CO2 was consistent with published results for a typical C3 plant species. The patterns of daily GPP and NPP through time approximated logistic curves under both CO2 treatments. Regression analysis indicated that both the rate of increase (the parameter ‘r’) and the maximum value (the parameter ‘k’) of daily GPP and NPP under the elevated CO2 treatment were significantly higher than under the ambient CO2 treatment. The percentage increase in daily GPP due to elevated CO2 varied systematically through time according to the logistic equations used for the two treatments. The GPP increase due to elevated CO2 ranged from approximately 10% initially to 73% at the peak, while declining to about 33%, as predicted by the ratio of the two maximum values. Different values of percentage increase in GPP and NPP were obtained at different sampling times. This result demonstrated that one-time measurements of percentage increases due to elevated CO2 could be misleading, thereby making interpretation difficult. Although rhizosphere respiration was substantially enhanced by elevated CO2, no effect of elevated CO2 on R:P (respiration:photosynthesis) was found, suggesting an invariant NPP:GPP ratio during the entire experiment. Further validation of the notion of an invariant NPP:GPP ratio may significantly simplify the process of quantifying terrestrial carbon sequestration by directly relating total photosynthesis to net primary production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00367.x
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  • 2
    Electronic Resource
    Electronic Resource
    The photosynthesis – leaf nitrogen relationship at ambient and elevated atmospheric carbon dioxide: a meta-analysis (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Estimation of leaf photosynthetic rate (A) from leaf nitrogen content (N) is both conceptually and numerically important in models of plant, ecosystem, and biosphere responses to global change. The relationship between A and N has been studied extensively at ambient CO2 but much less at elevated CO2. This study was designed to (i) assess whether the A–N relationship was more similar for species within than between community and vegetation types, and (ii) examine how growth at elevated CO2 affects the A–N relationship. Data were obtained for 39 C3 species grown at ambient CO2 and 10 C3 species grown at ambient and elevated CO2. A regression model was applied to each species as well as to species pooled within different community and vegetation types. Cluster analysis of the regression coefficients indicated that species measured at ambient CO2 did not separate into distinct groups matching community or vegetation type. Instead, most community and vegetation types shared the same general parameter space for regression coefficients. Growth at elevated CO2 increased photosynthetic nitrogen use efficiency for pines and deciduous trees. When species were pooled by vegetation type, the A–N relationship for deciduous trees expressed on a leaf-mass basis was not altered by elevated CO2, while the intercept increased for pines. When regression coefficients were averaged to give mean responses for different vegetation types, elevated CO2 increased the intercept and the slope for deciduous trees but increased only the intercept for pines. There were no statistical differences between the pines and deciduous trees for the effect of CO2. Generalizations about the effect of elevated CO2 on the A–N relationship, and differences between pines and deciduous trees will be enhanced as more data become available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00234.x
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  • 3
    Electronic Resource
    Electronic Resource
    A search for predictive understanding of plant responses to elevated [CO2] (1999)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 5 (1999), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This paper reviews two decades of effort by the scientific community in a search for predictive understanding of plant responses to elevated [CO2]. To evaluate the progress of research in leaf photosynthesis, plant respiration, root nutrient uptake, and carbon partitioning, we divided scientific activities into four phases: (I) initial assessments derived from our existing knowledge base to provide frameworks for experimental studies; (II) experimental tests of the initial assessments; (III) in cases where assessments were invalidated, synthesis of experimental results to stimulate alternative hypotheses and further experimentation; and (IV) formation of new knowledge. This paper suggests that photosynthetic research may have gone through all four phases, considering that (a) variable responses of photosynthesis to [CO2] are generally explainable, (b) extrapolation of leaf-level studies to the global scale has been examined, and (c) molecular studies are under way. Investigation of plant respiratory responses to [CO2] has reached the third phase: experimental results have been accumulated, and mechanistic approaches are being developed to examine alternative hypotheses in search for new concepts and/or new quantitative frameworks to understand respiratory responses to elevated [CO2]. The study of nutrient uptake kinetics is still in the second phase: experimental evidence has contradicted some of the initial assessments, and more experimental studies need to be designed before generalizations can be made. It is quite unfortunate that we have not made much progress in understanding mechanisms of carbon partitioning during the past two decades. This is due in part to the fact that some of the holistic theories, such as functional balance and optimality, have not evolved into testable hypotheses to guide experimental studies. This paper urges modelers to play an increasing role in plant–CO2 research by disassembling these existing theories into hypotheses and urges experimentalists to design experiments to examine these holistic concepts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1999.00215.x
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  • 4
    Electronic Resource
    Electronic Resource
    Integration of photosynthetic acclimation to CO2 at the whole-plant level (1998)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 4 (1998), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Primary events in photosynthetic (PS) acclimation to elevated CO2 concentration ([CO2]) occur at the molecular level in leaf mesophyll cells, but final growth response to [CO2] involves acclimation responses associated with photosynthate partitioning among plant organs in relation to resources limiting growth. Source–sink interactions, particularly with regard to carbon (C) and nitrogen (N), are key determinants of PS acclimation to elevated [CO2] at the whole-plant level. In the long term, PS and growth response to [CO2] are dependent on genotypic and environmental factors affecting the plant's ability to develop new sinks for C, and acquire adequate N and other resources to support an enhanced growth potential. Growth at elevated [CO2] usually increases N use efficiency because PS rates can be maintained at levels comparable to those observed at ambient [CO2] with less N investment in PS enzymes. A frequent acclimation response, particularly under N-limited conditions, is for the accumulation of leaf carbohydrates at elevated [CO2] to lead to repression of genes associated with the production of PS enzymes. The hypothesis that this is an adaptive response, leading to a diversion of N to plant organs where it is of greatest benefit in terms of competitive ability and reproductive fitness, needs to be more rigorously tested. The biological control mechanisms which plants have evolved to acclimate to shifts in source–sink balance caused by elevated [CO2] are complex, and will only be fully elucidated by probing at all scales along the hierarchy from molecular to ecosystem. Use of environmental manipulations and genotypic comparisons will facilitate the testing of specific hypotheses. Improving our ability to predict PS acclimation to [CO2] will require the integration of results from laboratory studies using simple model systems with results from whole-plant studies that include measurements of processes operating at several scales. Abbreviations: CAM, crassulacean acid metabolism; FACE, Free-Air CO2 Enrichment; Pi, inorganic phosphate; LAR, leaf area ratio (m2 g-1); LWR, leaf weight ratio (g g-1); NAR, net assimilation rate (g m-2 d- 1); PS, photosynthetic; RGR, relative growth rate (g g-1 d-1); R:S, root/shoot ratio; rubisco, ribulose bisphosphate carboxylase/oxygenase; RuBP, ribulose bisphosphate; SLA, specific leaf area (m2 g-1); SPS, sucrose phosphate synthase; WUE, water use efficiency (g biomass g H2O-1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1998.00183.x
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinearity of photosynthetic responses to growth in rising atmospheric CO2: an experimental and modelling study (1998)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 4 (1998), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Nonlinear responses of photosynthesis to the CO2 concentration at which plants were grown (Cg) have been often reported in the literature. This study was designed to develop mechanistic understanding of the nonlinear responses with both experimental and modelling approaches. Soybean (Glycine max) was grown in five levels of Cg (280, 350, 525, 700, 1000 ppm) with either a high or low rate of nitrogen fertilization. When the rate of nitrogen fertilization was high, the photosynthetic rate measured at Cg was highest in plants from the 700 ppm CO2 treatment. When the rate of nitrogen fertilization was low, little variation was observed in the photosynthetic rates of plants from the different treatments measured at their respective Cg. Measurements of CO2-induced changes in mass-based leaf nitrogen concentration (nm, an index of changes in biochemical processes) and leaf mass per unit area (h, an index of morphological properties) were used in a model and indicate that the nonlinearity of photosynthetic responses to Cg is largely determined by relative changes in photosynthetic sensitivity, biochemical downregulation, and morphological upregulation. In order to further understand the nonlinear responses, we compiled data from the literature on CO2-induced changes in nm and h. These compiled data indicate that h generally increases and nm usually decreases with increasing Cg, but that the trajectories and magnitudes of the changes in h and nm vary with species and growth environments. Integration of these variables (nm and h) into a biochemically based model of photosynthesis enabled us to predict diverse responses of photosynthesis to Cg. Thus a general mechanism is suggested for the highly variable, nonlinear responses of photosynthesis to Cg reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.1998.00116.x
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  • 6
    Electronic Resource
    Electronic Resource
    Plant nitrogen concentration, use efficiency, and contents in a tallgrass prairie ecosystem under experimental warming (2005)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 11 (2005), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Plant nitrogen (N) relationship has the potential to regulate plant and ecosystem responses strongly to global warming but has not been carefully examined under warmed environments. This study was conducted to examine responses of plant N relationship (i.e. leaf N concentration, N use efficiency, and plant N content in this study) to a 4-year experimental warming in a tallgrass prairie in the central Great Plains in USA. We measured mass-based N and carbon (C) concentrations of stem, green, and senescent leaves, and calculated N resorption efficiency, N use efficiency, plant N content, and C : N ratios of five dominant species (two C4 grasses, one C3 grass, and two C3 forbs). The results showed that warming decreased N concentration of both green and senescent leaves, and N resorption efficiency for all species. N use efficiencies and C : N ratios were accordingly higher under warming than control. Total plant N content increased under warming because of warming-induced increases in biomass production that are larger than the warming-induced decreases in tissue N concentration. The increases in N contents in both green and senescent plant tissues suggest that warming enhanced both plant N uptake and return through litterfall in the tallgrass ecosystem. Our results also suggest that the increased N use efficiency in C4 grasses is a primary mechanism leading to increased biomass production under warming in the grassland ecosystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2005.01030.x
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  • 7
    Electronic Resource
    Electronic Resource
    Net ecosystem carbon exchange in two experimental grassland ecosystems (2004)
    Oxford, UK : Blackwell Publishing
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Increases in net primary production (NPP) may not necessarily result in increased C sequestration since an increase in uptake can be negated by concurrent increases in ecosystem C losses via respiratory processes. Continuous measurements of net ecosystem C exchange between the atmosphere and two experimental cheatgrass (Bromus tectorum L.) ecosystems in large dynamic flux chambers (EcoCELLs) showed net ecosystem C losses to the atmosphere in excess of 300 g C m−2 over two growing cycles. Even a doubling of net ecosystem production (NEP) after N fertilization in the second growing season did not compensate for soil C losses incurred during the fallow period. Fertilization not only increased C uptake in biomass but also enhanced C losses through soil respiration from 287 to 469 g C m−2, mainly through an increase in rhizosphere respiration. Fertilization decreased dissolved inorganic C losses through leaching of from 45 to 10 g C m−2.Unfertilized cheatgrass added 215 g C m−2 as root-derived organic matter but the contribution of these inputs to long-term C sequestration was limited as these deposits rapidly decomposed. Fertilization increased NEP but did not increase belowground C inputs most likely due to a concurrent increase in the production and decomposition of rhizodeposits. Decomposition of soil organic matter (SOM) was reduced by fertilizer additions. The results from our study show that, although annual grassland ecosystems can add considerable amounts of C to soils during the growing season, it is unlikely that they sequester large amounts of C because of high respiratory losses during dormancy periods. Although fertilization could increase NEP, fertilization might reduce soil C inputs as heterotrophic organisms favor root-derived organic matter over native SOM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00744.x
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  • 8
    Electronic Resource
    Electronic Resource
    Canopy radiation- and water-use efficiencies as affected by elevated [CO2] (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This study used an environmentally controlled plant growth facility, EcoCELLs, to measure canopy gas exchanges directly and to examine the effects of elevated [CO2] on canopy radiation- and water-use efficiencies. Sunflowers (Helianthus annus var. Mammoth) were grown at ambient (399 μmol mol−1) and elevated [CO2] (746 μmol mol−1) for 53 days in EcoCELLs. Whole canopy carbon- and water-fluxes were measured continuously during the period of the experiment. The results indicated that elevated [CO2] enhanced daily total canopy carbon- and water-fluxes by 53% and 11%, respectively, on a ground-area basis, resulting in a 54% increase in radiation-use efficiency (RUE) based on intercepted photosynthetic active radiation and a 26% increase in water-use efficiency (WUE) by the end of the experiment. Canopy carbon- and water-fluxes at both CO2 treatments varied with canopy development. They were small at 22 days after planting (DAP) and gradually increased to the maxima at 46 DAP. When canopy carbon- and water-fluxes were expressed on a leaf-area basis, no effect of CO2 was found for canopy water-flux while elevated [CO2] still enhanced canopy carbon-flux by 29%, on average. Night-time canopy carbon-flux was 32% higher at elevated than at ambient [CO2]. In addition, RUE and WUE displayed strong diurnal variations, high at noon and low in the morning or afternoon for WUE but opposite for RUE. This study provided direct evidence that plant canopy may consume more, instead of less, water but utilize both water and radiation more efficiently at elevated than at ambient [CO2], at least during the exponential growth period as illustrated in this experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2001.00391.x
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  • 9
    Electronic Resource
    Electronic Resource
    Uncertainties in interpretation of isotope signals for estimation of fine root longevity: theoretical considerations (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This paper examines uncertainties in the interpretation of isotope signals when estimating fine root longevity, particularly in forests. The isotope signals are depleted δ13C values from elevated CO2 experiments and enriched Δ14C values from bomb 14C in atmospheric CO2. For the CO2 experiments, I explored the effects of six root mortality patterns (on–off, proportional, constant, normal, left skew, and right skew distributions), five levels of nonstructural carbohydrate (NSC) reserves, and increased root growth on root δ13C values after CO2 fumigation. My analysis indicates that fitting a linear equation to δ13C data provides unbiased estimates of longevity only if root mortality follows an on–off model, without dilution of isotope signals by pretreatment NSC reserves, and under a steady state between growth and death. If root mortality follows the other patterns, the linear extrapolation considerably overestimates root longevity. In contrast, fitting an exponential equation to δ13C data underestimates longevity with all the mortality patterns except the proportional one. With either linear or exponential extrapolation, dilution of isotope signals by pretreatment NSC reserves could result in overestimation of root longevity by several-fold. Root longevity is underestimated if elevated CO2 stimulates fine root growth. For the bomb 14C approach, I examined the effects of four mortality patterns (on–off, proportional, constant, and normal distribution) on root Δ14C values. For a given Δ14C value, the proportional pattern usually provides a shorter estimate of root longevity than the other patterns. Overall, we have to improve our understanding of root growth and mortality patterns and to measure NSC reserves in order to reduce uncertainties in estimated fine root longevity from isotope data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00642.x
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  • 10
    Electronic Resource
    Electronic Resource
    Carbon budgeting in plant–soil mesocosms under elevated CO2: locally missing carbon? (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Studies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO2 than could subsequently be found in plant biomass and soils –- the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open-flow, mass-balance systems at the mesocosm scale. Naturally occurring 13C tracers were also used to separately measure plant-derived carbon and soil-derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO2 and the other under elevated CO2 (ambient plus 350 μL L− 1). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux-based net primary production (NPPf) was similar to pool-based primary production (NPPp) under ambient CO2, and the discrepancy between the two carbon budgets (12 g C m− 2, or 4% of NPPf) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO2 was accounted for at the end of the experiment. Under elevated CO2, however, the amount of NPPf was much higher than NPPp, resulting in missing carbon of approximately 80 g C m− 2 or 19% of NPPf which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO2 remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00284.x
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