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Net CO2 Assimilation Rate (net + co2_assimilation_rate)
Selected AbstractsIncreased 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] Interactions between the effects of atmospheric CO2 content and P nutrition on photosynthesis in white lupin (Lupinus albus L.)PLANT CELL & ENVIRONMENT, Issue 5 2006CATHERINE D. CAMPBELL ABSTRACT Phosphorus (P) is a major factor limiting the response of carbon acquisition of plants and ecosystems to increasing atmospheric CO2 content. An important consideration, however, is the effect of P deficiency at the low atmospheric CO2 content common in recent geological history, because plants adapted to these conditions may also be limited in their ability to respond to further increases in CO2 content. To ascertain the effects of low P on various components of photosynthesis, white lupin (Lupinus albus L.) was grown hydroponically at 200, 400 and 750 µmol mol,1 CO2, under sufficient and deficient P supply (250 and 0.69 µm P, respectively). Increasing growth CO2 content increased photosynthesis only under sufficient growth P. Ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) content and activation state were not reduced to the same degree as the net CO2 assimilation rate (A), and the in vivo rate of electron transport was sufficient to support photosynthesis in all cases. The rate of triose phosphate use did not appear limiting either, because all the treatments continued to respond positively to a drop in oxygen levels. We conclude that, at ambient and elevated CO2 content, photosynthesis in low-P plants appears limited by the rate of ribulose biphosphate (RuBP) regeneration, probably through inhibition of the Calvin cycle. This failure of P-deficient plants to respond to rising CO2 content above 200 µmol mol,1 indicates that P status already imposes a widespread restriction in plant responses to increases in CO2 content from the pre-industrial level to current values. [source] On the need to incorporate sensitivity to CO2 transfer conductance into the Farquhar,von Caemmerer,Berry leaf photosynthesis modelPLANT CELL & ENVIRONMENT, Issue 2 2004G. J. ETHIER ABSTRACT Virtually all current estimates of the maximum carboxylation rate (Vcmax) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the maximum electron transport rate (Jmax) for C3 species implicitly assume an infinite CO2 transfer conductance (gi). And yet, most measurements in perennial plant species or in ageing or stressed leaves show that gi imposes a significant limitation on photosynthesis. Herein, we demonstrate that many current parameterizations of the photosynthesis model of Farquhar, von Caemmerer & Berry (Planta 149, 78,90, 1980) based on the leaf intercellular CO2 concentration (Ci) are incorrect for leaves where gi limits photosynthesis. We show how conventional A,Ci curve (net CO2 assimilation rate of a leaf ,An, as a function of Ci) fitting methods which rely on a rectangular hyperbola model under the assumption of infinite gi can significantly underestimate Vcmax for such leaves. Alternative parameterizations of the conventional method based on a single, apparent Michaelis,Menten constant for CO2 evaluated at Ci[Km(CO2)i] used for all C3 plants are also not acceptable since the relationship between Vcmax and gi is not conserved among species. We present an alternative A,Ci curve fitting method that accounts for gi through a non-rectangular hyperbola version of the model of Farquhar et al. (1980). Simulated and real examples are used to demonstrate how this new approach eliminates the errors of the conventional A,Ci curve fitting method and provides Vcmax estimates that are virtually insensitive to gi. Finally, we show how the new A,Ci curve fitting method can be used to estimate the value of the kinetic constants of Rubisco in vivo is presented [source] Energy Dissipation and Photoinhibition in Douglas-Fir Needles with a Fungal-Mediated Reduction in Photosynthetic RatesJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2002Daniel K. Manter Abstract The dissipation of absorbed light and potential for photooxidative damage was explored in Douglas-fir (Pseudotsuga menziesii ) seedlings with and without Phaeocryptopus gaeumannii infection. The presence of P. gaeumannii significantly reduced net CO2 assimilation rates from ca. 6 ,mol/m2/s to 1.5 ,mol/m2/s, without any significant impact on chloroplast pigments. The partitioning of absorbed light-energy to photochemistry or thermal dissipation was determined from chlorophyll fluorescence measurements. Maximum thermal dissipation for both control and infected needles was ca. 80%, consistent with the similar xanthophyll pool sizes in the two treatments. At high photosynthetic photon flux density (PPFD), when thermal dissipation was maximized, the lower photochemical utilization in infected needles resulted in greater amounts of excess absorbed light (ca. 20 and 10% for the infected and control needles, respectively). A second experiment, monitoring changes in photosystem II (PSII) efficiency (Fv/Fm) in response to a 1 h high light treatment (PPFD=2000 ,mol/m2/s) also suggests that infected needles absorb greater amounts of excess light. In this experiment, declines in Fv/Fm were 1.5 times greater in infected needles, despite the similar xanthophyll pool sizes. Furthermore, increases in minimum fluorescence (178 and 122% of initial values for the infected and control needles, respectively) suggest that the reduction in PSII efficiency is largely attributable to photooxidative damage. Finally, reductions in PSII efficiency under high light conditions provide a plausible explanation for the greater pathogenicity (e.g. premature needle abscission) of P. gaeumannii in sun-exposed foliage. [source] | ||||||||||