Light intercepted and carbon gain in nonbearing branches of pistachio positioned in different parts of the canopy

Abstract

The strong resource involvement in the alternate bearing phenomenon in pistachio (Pistacia vera L.) is evidenced by the different levels of carbohydrates observed in nonbearing versus bearing branches. Several authors have demonstrated that a high fruit load induces premature leaf abscission, resulting in a 26% reduction in carbon (C) assimilation during the season. This reduction serves as the primary constraining factor in the seasonal photosynthetic performance of the bearing shoots. In Italy, the prevailing training system uses a free-vase canopy, characterized by low vegetative canopy density. Farmers commonly remove non-bearing branches to avoid mutual shading. However, considering the traits of the species, reducing the leaf area could compromise carbohydrate accumulation and trigger an increase of bud abscission, thereby affecting the following year’s yield. Understanding how much a nonbearing branch can contribute to the carbon gain on the economy of a bearing tree could be a useful tool for efficient canopy shaping. During the summer season, the amount of light intercepted by the leaves of nonbearing shoots with different light exposure (inner and outer part of the canopy) was measured by small light sensors. The data were implemented in the carbon balance model described by Marino et al. (2022) to check whether shoots represented sources or sinks in the system. The daily light intercepted by each leaf showed no significant differences between the two positions (inner and outer). The model simulations confirmed that internal nonbearing branches constitute a positive resource of C for the entire plant. Therefore, pruning techniques and the appropriate planting configuration can serve as pivotal techniques for overcoming the alternate bearing in pistachio.