Modelling the effects of flowering, drought and fruit load on mango leaf photosynthesis

Our general objective is to design carbon-based models of flowering and fruit quality. The first step of our procedure consisted in modelling carbon gains in mango, cv. Cogshall, using the biochemical model of C3 leaf photosynthesis of Farquhar et al. (1980). Data are presented about the temperature-response of the key parameters of photosynthetic capacity which was assessed in 17-month old mango plants. The temperature-corrected photosynthesis model was then coupled to the model of leaf diffusive conductance (gs) of Ball et al. (1987). Simulation results obtained over one year on recently matured leaves from 13 to 13-year old trees show that our model is apparently robust for leaves from vegetative shoots, in orchard conditions characterized by mild seasonal changes in temperature and non-limiting water supply. However, our model failed to simulate Anet accurately during the flowering period and periods of drought, as well as when the source-sink balance is modified as, for instance, in girdled branches at different fruit loads. Using results obtained over the 5 last years about the effects of flowering, fruiting and waterstress on photosynthesis in mango, we tested three modifications of our model: 1) the fixed parameters of the model of gs were replaced by adapted values for leaves from water-stressed trees and leaves close to inflorescences; 2) the total light-driven photosynthetic electron flux (JT) was corrected to account for the existence of electron fluxes towards alternative sinks in leaves close to inflorescences; and 3) JT was corrected to account for the inhibiting effect of starch accumulation in leaves from girdled branches. Simulation results are presented and discussed in the perspective of our modelling approach.