Inhibitory effect of flowering and early fruit growth on leaf photosynthesis in mango

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Tree Physiology, 24:387–399

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Inhibitory effect of flowering and early fruit growth on leaf photosynthesis in mango

L. Urban (1, 2), P. Lu (3) and R. Thibaud (1)

1. INRA/CIRAD-Flhor, Station de Bassin-Martin, BP 180, 97455 Saint-Pierre, La Réunion, France / 2. Corresponding author (urban@cirad.fr) / 3. CSIRO Plant Industry, Darwin Laboratory, PMB 44, Winnellie, NT 0822, Australia / Received April 9, 2003; accepted July 6, 2003; published online February 2, 2004

Summary

Carbohydrate and nitrogen contents, chlorophyll fluorescence and gas exchange were measured in leaves from both vegetative and reproductive terminal shoots of 12-year-old flowering mango trees. Reproductive shoot leaves were close to swelling floral buds, inflorescences or panicles bearing set fruits. Leaves close to inflorescences had lower rates of mitochondrial respiration (R_d) and net photosynthesis (A_net), and lower stomatal conductance (g_s) and quantum efficiency of photosystem II under actinic light than vegetative shoot leaves. Leaf nitrogen concentration, which decreased from the beginning until the end of flowering, was lower in leaves close to inflorescences than in vegetative shoot leaves. However, these differences and changes were counterbalanced by an increase in leaf mass-to-area ratio so that leaf nitrogen per unit leaf area (N_a) remained nearly constant during the whole flowering period, except in leaves close to panicles bearing set fruits. Net CO₂ assimilation rate simulated by a biochemical model of leaf photosynthesis (Urban et al. 2003) was much higher than A_net measured at an ambient CO₂ partial pressure (C_a) of either 36 or 70 Pa. The overestimation of A_net was more pronounced in leaves close to inflorescences, to panicles bearing set fruits and to reversing inflorescences (characterized by the appearance of leaves in terminal positions on inflorescences) than in vegetative shoot leaves. It is concluded that low A_net in leaves close to inflorescences was probably due neither to changes in N_a nor to a decrease in Rubisco activity induced by low g_s, but rather to a decrease in electron flow in photosystem II. This decrease was not directly associated with higher starch or soluble sugar contents.

Keywords: leaf nitrogen, Mangifera indica, nonstructural carbohydrates, quantum efficiency of radiation use of photosystem II, starch, stomatal conductance.