Impact of leaf physiological characteristics on seasonal variation in CO2, latent and sensible heat exchanges over a tree plantation

This study investigated the impact of leaf physiological characteristics on CO2, sensible heat, and latent heat exchanges over a plant community. Measurements were carried out over plantation trees using an eddy correlation system, under well-watered soil conditions for several days spanning the year, and under soil drought conditions during autumn only. The following leaf physiological characteristics were investigated: the maximum rate of carboxylation (VcMAX25: [Planta 149 (1980) 78–90]), the relationship between stomatal conductance (gs) and net assimilation rate (An) adjusted by relative humidity (hs), and CO2 concentration at the leaf surface (cs) [An analysis of stomatal conductance. Ph.D. Thesis. Stanford University, CA, 89 pp.]. As the leaf physiological parameters, VcMAX and the relationship between stomatal conductance (gs) and Anhs/cs of four evergreen trees were estimated from gas exchange measurements at the single leaf scale. Numerical simulations were carried out using a multi-layer model consisting of a second-order closure model for atmospheric diffusion coupled with a radiation transfer model, a Farquhar type photosynthesis model, and Ball’s stomatal conductance model. The results suggest that the value of VcMAX25 changes every day, and that appropriate values should be used in simulations. The relationship between stomatal conductance (gs) and Ahs/cs changed under soil drought conditions, and this change should also be allowed for in simulations. These results show that changes in leaf physiological characteristics contribute considerably to seasonal variation in CO2, latent heat, and sensible heat exchanges over plantation trees.