Seasonal effects of intercropping on tree water use strategies in semiarid plantations: Evidence from natural and labelling stable isotopes

Abstract

Intercropping in plantations can improve ecosystem services, but its potential effects on trees’ water use and production are concerns due to increases in water scarcity related to climate change. The aim of this study was to address these concerns by exploring water uptake responses of jujube (Ziziphus jujuba Mill.) trees to intercropping and extremely dry periods on the semi-arid Loess Plateau of China. Natural stable isotopes (2H and 18O) were analysed to characterize water use patterns of jujube trees and intercrops in the main tree and crop root overlap layer (ROL, 0–120 cm). 10% stable deuterated water was injected at three targeted depths (2, 3 and 4 m) to characterize the water uptake of jujube trees below the main root overlap layers (BOL). In ROL, intercropped jujube trees obtained higher proportions of water in shallower and deeper layers than monocultured jujube trees during wet and dry periods, respectively. Proportional contributions of soil layers to the trees’ water uptake were positively correlated with the layers’ water amount ratios (relative to the entire profile) in intercropped orchards but not in monoculture. In some extremely dry periods, intercropping resulted in jujube trees absorbing deeper water (up to 3 m) in BOL. At the early stage of land-use change from plantation to agroforestry, intercrops induce jujube trees to absorb higher proportions of water from soil layers with high proportions of total water contents in ROL. The soil water in BOL is an important buffer for maintaining water supplies for tree growth in agroforestry systems in case of extreme drought.