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

Rates of carbon dioxide assimilation through photosynthesis are readily modeled using the Farquhar, von Caemmerer, and Berry (FvCB) model based on the biochemistry of the initial Rubisco-catalyzed reaction of net C₃ photosynthesis. As models of CO₂ assimilation rate 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 (Γ_*), combines the biochemistry of Rubisco with the stoichiometry of photorespiratory release of CO₂. This report details a comparison of the temperature response of Γ_* measured using different techniques in three important model and crop species (Nicotiana tabacum, Triticum aestivum, and Glycine max). We determined that the different Γ_* determination methods produce different temperature responses in the same species that are large enough to impact higher-scale leaf models of CO₂ assimilation rate. These differences are largest in N. tabacum and could be the result of temperature-dependent increases in the amount of CO₂ lost from photorespiration per Rubisco oxygenation reaction.