A COUPLED PHOTOSYNTHESIS AND STOMATAL CONDUCTANCE MODEL FOR MANGO LEAVES

The first step of the modelling approach consisted in designing a model of leaf diffusive conductance (g_s) adapted from Ball, Woodrow and Berry (1987), expressing g_s mainly as a function of A_net. The widely accepted biochemical model of C₃ leaf photosynthesis of Farquhar, von Caemmerer and Berry (1980) was parameterized for well-lit, young, mature mango leaves using response curves of net photosynthesis to intercellular CO₂ concentration (A-C_i curves). To obtain an analytical solution for leaf photosynthesis, we used the following additional conductance relation : C_i = C_a – A_net / g_b – A_net / g_s, where C_a stands for the ambient CO₂ concentration and g_b for the conductance across the laminar boundary layer. The resulting model of leaf photosynthesis was tested against three sets of data from gas exchange measurements obtained with a portable infrared gas analyser on leaves of 12 year old mango trees, cv. Lirfa, at two periods of the year : August, just before flowering, and from November to December, during the fruiting stage. The need to take into account the influence of light availability, leaf age and sink activity on photosynthetic capacity to upgrade the model is discussed.