Season effects on leaf nitrogen partitioning photosynthetic water use efficiency in mango

International audienceThe key parameters of photosynthetic capacity (maximum carboxylation rate (V-max), electron transport capacity (J(max)) and dark respiration rate (R-d)) and the slope (m) of the stomatal conductance model of Ball et at. [Progress in photosynthetic research, Martinus Nijhoff, Dordrecht, 1987] were measured for a whole growing season in fully expanded leaves of 12-year-old mango trees cv. Cogshall. in La Reunion island. Leaf nitrogen partitioning into carboxylation (P-c) and bioenergetic (P-b) pools were computed according to the model of Niinemets and Tenhunen [Plant Cell Environ 1997;20: 845-66]. V-cmax, J(max), R-d, P-c and P-b remained relatively stable over the whole study period, with the exception of the period of Linear fruit growth when J(max), R-d and P-b were slightly lower, and leaf non-structural carbohydrate content higher. During the pre-floral and floral periods, m decreased by more than 50%, indicating an increase in photosynthetic water use efficiency and m increased again during the period of Linear fruit growth. Our results show that, in tropical orchard conditions characterized by mild seasonal climatic changes and non-limiting water supply, leaf nitrogen partitioning is rather stable. Our results also advocate for more studies on the effect of phenology on m and photosynthetic water use efficiency, which is of paramount importance for building coupled biochemical models of photosynthetic carbon assimilation