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

Summary 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.