The role of leaf water potential in the temperature response of mesophyll conductance.

Variation in temperature (T) is usually accompanied by changes in leaf water potential (Ψleaf ), which may influence mesophyll conductance (gm ). However, the effects of Ψleaf on gm have not yet been considered in models of the gm response to temperature. Temperature responses of gm and Ψleaf and the response of gm to Ψleaf were studied in rice (Oryza sativa) and wheat (Triticum aestivum), and then an empirical model of Ψleaf was incorporated into an existing gm -T model. In wheat, Ψleaf was dramatically decreased with increasing T, whereas in rice Ψleaf was less sensitive or insensitive to T. Without taking Ψleaf into account, gm for wheat showed no response to T. However, at a given Ψleaf , gm was significantly higher at high temperature compared with low. After incorporating the function of Ψleaf into the gm -T model, we suggest that the gm -T relationship can be influenced by the activation and deactivation energy for membrane permeability, Ψleaf gradient between temperatures, and the sensitivity of gm to Ψleaf , below a threshold (Ψleaf,0 ). The data presented here suggest that Ψleaf plays an important role in the gm -T relationship and should be considered in future studies related to the temperature response of gm and photosynthesis.