Deficit irrigation and warming during the late winter and spring affect vegetative growth and reproductive development in young olive trees

Abstract

To better understand the implications of climate change, the combined responses of olive trees to irrigation amount and warming need to be examined. Thus, the objective was to evaluate the effects of moderate deficit irrigation and warming during late winter and spring on vegetative growth and biomass, full bloom timing and intensity, and yield components in young olive trees. Two three month-long experiments were conducted using open top chambers with four treatment combinations: 100% irrigation with a control temperature; 100% irrigation with 4 °C warming; 50% irrigation with a control temperature; and 50% irrigation with 4 °C warming. The trees were potted two-year-old, cv. Arbequina trees in the 2018 experiment and three-year-old, cv. Coratina trees in the 2019 experiment. Flowering was low in the young cv. Arbequina trees in 2018, but it was much greater in the older cv. Coratina trees in 2019. Overall, lower flowering intensity and fruit set or more parthenocarpic fruit contributed to less viable fruit number with warming. These reproductive variables were less affected by deficit irrigation. In contrast, shoot growth and vegetative biomass were decreased by deficit irrigation in cv. Arbequina (2018) when fruit number was low in all trees with less response due to warming. In cv. Coratina (2019), the lower fruit number in warmed compared to control trees contributed to greater individual fruit weight at the end of the experimental period, and few significant effects of either deficit irrigation or warming on shoot growth were observed. Fruit yield was greater in the well-irrigated, temperature control than in the other treatment combinations in cv. Arbequina, while warming reduced fruit yield in cv. Coratina. From a production perspective, it does not appear that many early reproductive responses to warming can be easily counteracted by adjusting irrigation. Further studies with more mature trees and cultivars over several growing seasons are recommended.