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Title: The influence of photosynthetic acclimation to rising CO2 and warmer temperatures on leaf and canopy photosynthesis models

item BAGLEY, JUSTIN - Lawrence Berkeley National Laboratory
item ROSENTHAL, DAVID - Ohio University
item RUIZ-VERA, URSULA - University Of Illinois
item SIEBERS, MATHEW - University Of Illinois
item KUMAR, PRAVEEN - University Of Illinois
item Ort, Donald
item Bernacchi, Carl

Submitted to: Global Biogeochemical Cycles
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2015
Publication Date: 2/25/2015
Citation: Bagley, J.E., Rosenthal, D.M., Ruiz-Vera, U.M., Siebers, M., Kumar, P., Ort, D.R., Bernacchi, C.J. 2015. The influence of photosynthetic acclimation to rising CO2 and warmer temperatures on leaf and canopy photosynthesis models. Global Biogeochemical Cycles. 29:194-206.

Interpretive Summary: Ecosystem modeling is a useful tool, and the only means to assess how ecosystems respond to future environmental conditions. Many of the models that are used are assessed based on the ability to prdict past or present ecosystem function and text the model against measured conditions. Plant responses to the environment, however, are likely to change many of the underlying processes that drive photosynthesis – something not often accounted for in models. The goal of this paper is to test the importance of adjustments to underlying photosynthesis on predicting plant carbon uptake for plants grown under present-day conditions, elevated temperature, elevated CO2, and combined increases in CO2 and temperature. The conditions were chosen to represent future environmental conditions. The results of the study show that accounting for photosynthetic adjustments to elevated CO2 have little effect on ecosystem modeling. owever, neglecting the adjustment of photosynthesis to elevated temperature can overestimate productivity of major crops under future conditions. The outcome from this study suggests that assessment of crop production under global warming conditions needs to account for acclimation of photosynthesis.

Technical Abstract: There is an increasing necessity to understand how climate change factors, particularly increasing atmospheric concentrations of CO2 ([CO2]) and rising temperature, will influence photosynthetic carbon assimilation (A). Based on theory, an increased [CO2] concomitant with a rise in temperature will increase A in C3 plants beyond that of an increase in [CO2] alone. However, this theory does not consider the uncertainty surrounding the acclimation response of key photosynthetic parameters to these changes. In this work, the acclimation responses of C3 photosynthesis for soybean measured at the SoyFACE Temperature by Free Air CO2 Enrichment (T-FACE) experiment is incorporated in a leaf biochemical and canopy photosynthesis model. The two key parameters needed for modeling A, the maximum velocity for carboxylation (Vc,max) and maximum rate of electron transport (Jmax), were measured in a full factorial [CO2] by temperature experiment over two growing seasons and applied in leaf- and canopy-scale models to (1) reassess the theory of combined increases in [CO2] and temperature on A, (2) determine the role of photosynthetic acclimation in leaf and canopy predictions of A for these treatments, and (3) assess the diurnal and seasonal differences in leaf- and canopy-scale A associated with the imposed treatments. The results demonstrate that the theory behind combined increases in [CO2] and temperature are sound, however, incorporating more recent parameterizations into the photosynthesis model predicts greater increases in A when [CO2] and temperature are increased together. Photosynthetic acclimation is shown to decrease leaf-level A for all treatments, however, in elevated [CO2] the impact of acclimation does not result in any appreciable loss in photosynthetic potential at the canopy scale. Neglecting photosynthetic acclimation in heated treatments, with or without concomitant rise in [CO2], could over estimate predicted carbon gain for soybean.