Limitations to photosynthesis of leaves of apple (Malus domestica) trees across the growing season prior to and after harvest

Abstract

Photosynthetic responses to CO2 were followed on leaves of Malus domestica cv. Cox's Orange trees growing in orchard conditions, before and after harvest. Rates of photosynthesis, at ambient and CO2 saturated concentrations, were stable across the growing season, except for minor decreases at harvest although rates recovered and remained high thereafter. Stomatal conductance increased over the growing season but declined transiently just before harvest and recovered for most of the season. Rates of ribulose-1,5-bisphosphate (RuBP) carboxylation declined before harvest, however, rates of RuBP regeneration mirrored assimilation. After harvest, rates of RuBP regeneration increased whereas rates of carboxylation increased but remained low, limiting photosynthesis. Lack of change in photosynthesis after harvest was at odds with the literature where photosynthesis of high crop load trees declined soon after, suggesting crop load was not as demanding on the Cox's Orange trees as in other studies.