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Title: Uncertainty in measurements of the photorespiratory CO2 compensation point and its impact on models of leaf photosynthesis

item WALKER, BERKLEY - Former ARS Employee
item ORR, DOUGLAS - Lancaster University
item CARMO-SILVA, ELIZABETE - Lancaster University
item PARRY, MARTIN A J - Lancaster University
item Bernacchi, Carl
item Ort, Donald

Submitted to: Photosynthesis Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2017
Publication Date: 2/27/2017
Citation: Walker, B.J., Orr, D.J., Carmo-Silva, E., Parry, M., Bernacchi, C.J., Ort, D.R. 2017. Uncertainty in measurements of the photorespiratory CO2 compensation point and its impact on models of leaf photosynthesis. Photosynthesis Research. 132(3):245-255.

Interpretive Summary: Biochemical models of leaf photosynthesis are increasingly important as we develop more sophisticated simulations of plant carbon budgets and search for new strategies to improve crop productivity. The widely-adopted biochemical model of leaf photosynthesis has proven invaluable since its development over 35 years ago and continues to be employed to represent photosynthesis from the cell to global scale. This model is characterized by its elegant combination of Rubisco kinetics with the physiology of photosynthesis and photorespiration to simulate net CO2 assimilation in response to CO2 partial pressures, making it useful both for predicting rates of carbon uptake as well as probing plant physiology and metabolism. Recently there has been a growing interest in parameterizing the model with species-specific temperature responses of to better represent photosynthesis and identify optimal kinetics for given environments which was the goal of this work.

Technical Abstract: Rates of carbon dioxide assimilation through photosynthesis are readily modeled through the Farquhar, von Caemmerer and Berry (FvCB) model based on the biochemistry of the initial Rubisco-catalyzed reaction of net C3 carbon assimilation. As models of CO2 assimilation are used more broadly for simulating photosynthesis among species and across scales, it is increasingly important that their temperature dependencies are accurately parameterized. A vital component of the FvCB model, the photorespiratory CO2 compensation point (G*), combines the biochemistry of Rubisco with the stoichiometry of photorespiratory release of CO2. This report details a comparison of the temperature response of G* measured using different techniques in three important model and crop species (Nicotiana tabacum, Triticum aestivum and Glycine max). We determined that the different G* determination methods produce different temperature responses in the same species that are large enough to impact higher-scale leaf models of CO2 assimilation. These differences are largest in Nicotiana tabacum, and could be the result of temperature-dependent increases in the amount of CO2 lost from photorespiration per Rubisco oxygenation reaction.