Temperature responses of photosynthesis and stomatal conductance in rice and wheat plants

The mechanisms for the different temperature (T) responses of leaf photosynthetic rate (A) and stomatal conductance (gs) have not been thoroughly elucidated, and the uncertainties and limitations facing the optimal-stomata models have not been systematically investigated. In the present study, the temperature responses of A, gs, and mesophyll conductance (gm) were studied in the selected rice and wheat genotypes, and the C3 photosynthesis model and three widely used optimal-stomata models were introduced to investigate these two questions. The photosynthetic limiting process varied significantly between rice and wheat plants. The photosynthetic limitation and gm had strong impacts on the temperature response of λ, the key parameter for the optimal-stomata models. λ was increased with T when photosynthesis was limited by the RuBP carboxylation, while it was decreased with T when it was limited by the RuBP regeneration. Because of the negative correlation between λ and gs, the differing λ-T relationships may explain the different gs-T relationships between the selected genotypes. This is the first study using the optimal-stomata models to interpret the differential gs-T relationships and highlights the importance of estimating gm and the photosynthetic limitations before applying the optimal-stomata models.