Modeling seasonal branch carbon dynamics in pistachio as a function of crop load

Abstract

A simplified model for the prediction of carbon balance was developed to elucidate the seasonal trend of sink-source relationships in bearing and non-bearing pistachio (Pistacia vera L.) branches. Seasonal changes in growth rate of vegetative (leaf and shoot) and reproductive (infructescence) organs were monitored in branches of mature rainfed pistachio trees during the entire growing season (April–September). Simulations from the model were used to gain understanding of the implications of crop load on branch carbon (C) depletion and alternate bearing. Results showed that the pistachio branch was energetically able to sustain up to two infructescences (∼28 fruits) having a slightly positive carbon budget (2.6 g of C) at the end of the season. A branch with 4 infructescences (∼56 fruits) ended the season with a very negative carbon budget (-14.1 g of C) suggesting the implication of resource mobilization during heavy crop load. The simulations with the model allowed the identification of two energetically critical periods for pistachio, both characterized by a decreasing trend of the carbon budget. The first is at the beginning of the season, from leaf out until 35/40 days after full bloom (DAFB), when leaves are still not source of carbon, and the branch energetic need is largely satisfied by the remobilization of carbon from the reserves accumulated the previous year and stored through the winter. The second critical period is at the end of the season for bearing branches, at ∼100 DAFB, when a strong reduction in leaf area due to early leaf senescence and drop coincides with high carbon request for kernel growth. Overall, results demonstrate that the branch carbon budget model is a valid tool to study bearing dynamics in tree species and can help to develop physiologically-based management strategies for achieving increased and more constant productions in pistachio orchard systems.