Interpreting the decrease in leaf photosynthesis during flowering in mango
Laurent Urban (1, 2), Loïc Jegouzo (3), Gaëlle Damour (3), Marc Vandame (4) and Christophe François (5)
1. INRA, Unité de Recherche GEQA, 20230 San Giuliano, France / 2. Corresponding author () / 3. CIRAD, PERSYST, Station de Bassin-Plat, BP 180, 97455 Saint-Pierre Cedex, France / 4. UMR PIAF INRA, Site de Crouël, 234 avenue du Brézet, 63039 Clermont-Ferrand Cedex 02, France / 5. CNRS, Ecologie, Systématique et Evolution, Département d’Ecophysiologie Végétale, Université Paris-Sud, Bâtiment 362, 91405
Orsay Cedex, France / Received June 7, 2007; accepted December 4, 2007; published online May 1, 2008
Summary
Little is known about the effect of flowering on leaf photosynthesis. To understand why net photosynthesis (Anet) is lower in Mangifera indica L. leaves close to inflorescences than in leaves on vegetative shoots, we measured nitrogen and carbohydrate concentrations,
chlorophyll a fluorescence and gas exchange in recently matured leaves on vegetative terminals and on floral terminals of
4-year-old trees. We used models to estimate photosynthetic electron fluxes and mesophyll conductance (gm). Lower Anet in leaves close to developing inflorescences was attributable to substantial decreases in stomatal conductance and gm, and also in photosynthetic capacity as indicated by the decrease in the light-saturated rate of photosynthetic electron
transport (Jmax). The decrease in Jmax was the result of decreases in the amount of foliar nitrogen per unit leaf area, and may have been triggered by a decrease
in sink activity as indicated by the increase in the hexose:sucrose ratio. Parameters measured on leaves close to panicles
bearing set fruits were generally intermediate between those measured on leaves on vegetative shoots and on leaves close to
inflorescences, suggesting that the changes in Anet associated with flowering are reversible.
