An eco-evolutionary optimality model explains the acclimated temperature response of photosynthesis

The optimal temperature of photosynthesis (T_opt) generally increases with plant growth temperature. Changes in T_opt are associated with changes in the maximum carboxylation capacity at 25°C (V_cmax25) and the maximum electron transport rate at 25°C (J_max25). The ratio between J_max25 and V_cmax25 declines with warming. Accurate representation of leaf-level photosynthetic responses to temperature is essential for realistic projections of the terrestrial carbon cycle and its response to ongoing climate changes. However, many land surface models incorporate thermal acclimation through empirical approaches and through assigning distinct but static parameter values to plant functional types (PFTs). Eco-evolutionary optimality (EEO) approaches provide a simpler way of modelling photosynthesis without recourse to PFTs. Here, we use the subdaily P model, an EEO-based model of photosynthesis that explicitly separates the instantaneous and acclimated responses of photosynthetic parameters to temperature to investigate how optimal temperature changes with growth temperature, as represented by leaf or air temperature. We show that the simulated responses are consistent with observations from both controlled experiments and eddy covariance flux tower data. We show that changes in T_opt, and in the assimilation rate at T_opt, are caused by changes in carboxylation capacity and electron transport rate that follow directly from the hypotheses underlying the model.