Carbohydrate reserve partitioning and reproductive decline following defoliation induced carbon source limitation in mango ( Mangifera indica )

Abstract

Non-structural carbohydrate (NSC) reserves can support fruit development and buffer source–sink imbalances in fruit trees, yet their organ-specific contributions remain poorly understood in mango (Mangifera indica). This study investigated the impacts of severe carbon source limitation on fruit productivity and NSC reserve dynamics over two consecutive growing seasons. A near-complete defoliation, retaining only 40 leaves (<0.5% of estimated leaves per tree), was imposed during rapid fruit growth in the first season. Starch and soluble sugar concentrations were monitored in roots, trunks, branches, shoots, pedicels, and leaves, alongside fruit growth and yield. Fruit growth, number, and dry matter content declined, with whole-tree fruit NSC content reduced to one-third of controls by end of the first season. In the following season, fruit NSC concentrations recovered to control levels, but reproductive output remained impaired, with fewer fruiting trees and lower yields, highlighting lasting impacts of prior source limitation on reproductive processes. NSC reserve dynamics varied across organs. Trunks behaved as long-term starch storage tissues, exhibiting marked depletion under defoliation in the first season, followed by strong recovery in the second. Coarse roots, assessed only in the second season, also showed similar storage behaviour, with previously defoliated trees ending the season with higher reserve concentrations than controls. Branches and medium roots operated as more transient buffering tissues, with dynamics in medium roots driven more by phenology than tree carbon status. Shoots, leaves, and pedicels, dominated by soluble sugars, served as short-term buffers, rapidly depleted under canopy loss but recovering once fruit load was reduced. Mango trees responded to source limitation through widespread NSC reserve remobilisation, followed by synchronised reserve rebuilding across structural organs at the expense of reproduction. These findings emphasise the central role of foliar source capacity in sustaining productivity and clarify the hierarchical functions of NSC pools in buffering carbon limitation.