Seasonal variation in the groundwater dependency of two dominant woody species in a desert region of Central Asia

Abstract

Groundwater is an important water source for plants in desert regions and greatly affects the performance and survival of desert plants. Moreover, the effects of groundwater variations on desert plants are not completely understood. This study aims to investigate the groundwater dependency of two dominant woody species (Haloxylon ammodendron and H. persicum) in the Gurbantunggut Desert of Central Asia, and evaluate their water use and physiological responses under a decline in groundwater depth. Oxygen stable isotopes of soil water, groundwater and xylem water as well as the IsoSource model were used to determine seasonal variations in the water sources of the two studied species along a groundwater depth gradient. In addition, the plant water potential and stomatal conductance were measured to determine the physiological performance. (1) Although both species extracted groundwater, H. ammodendron was much more groundwater dependent; (2) the two species exhibited significant seasonal variations in their degree of groundwater dependency, which was relatively lower in the wet season, and higher during the dry period; and (3) when the groundwater availability declined, both species reduced their groundwater use, although only H. ammodendron exhibited a significantly negative physiological response. This study demonstrated that plants with different water sources respond differently to the decline of groundwater depth and the effects of groundwater drawdowns are determined by the groundwater dependency of desert plants. A better understanding of desert plant responses to water availability variations is crucial for modeling, predicting and managing desert ecosystems in the context of global change.