Modelling diurnal courses of photosynthesis and transpiration of leaves onthe basis of stomatal and non-stomatal responses, includingphotoinhibition

摘要

A mathematical model for photoinhibition of leaf photosynthesis was developed by formalising the assumptions that (1) the rate of photoinhibition is proportional to irradiance; and (2) the rate of recovery, derived from the formulae for a pseudo first-order process, is proportional to the extent of inhibition. The photoinhibition model to calculate initial photo yield is integrated into a photosynthesis-stomatal conductance (g(s)) model that combines net photosynthetic rate (P-N), transpiration rate (E), and g(s), and also the leaf energy balance. The model was run to simulate the diurnal courses of P-N, E, g(s), photochemical efficiency, i.e., ratio of intercellular CO2 concentration and CO2 concentration over leaf surface (C-i/C-s), and leaf temperature (T-1) under different irradiances, air temperature, and humidity separately with fixed time courses of others. When midday depression occurred under high temperature, g(s) decreased the most and E the least. The duration of midday depression of g(s) was the longest and that in E the shortest. E increased with increasing vapour pressure deficit (VPD) initially, but when VPD exceeded a certain value, it decreased with increasing VPD; this was caused by a rapid decrease in g(s). When air temperature exceeded a certain value, an increase in solar irradiance raised T-1 and the degree of midday depression. High solar radiation caused large decrease in initial photon efficiency (alpha)- P-N, E, and g(s) showed reasonable decreases under conditions causing photoinhibtion compared with non-photoinhibition condition under high irradiance. The T-1 under photoinhibition was higher than that under non-photoinhibition conditions, which was evident under high solar irradiance around noon. The decrease in C-1/C-s at midday implies that stomatal closure is a factor causing midday depression of photosynthesis.