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