Contrasting plant water-use responses to groundwater depth from seedlings to mature trees in the Gurbantunggut Desert

Abstract

• Stable hydrogen and oxygen isotope method was used to research size-dependent water use pattern of Haloxylon ammodendron woodland. • Both development stage and groundwater depth had significant effect on water use pattern of H. ammodendron . • H. ammodendron used water from increasingly deeper soil layers throughout its development. • Water absorption depth decreased for seedlings but increased for mature trees with increasing groundwater depth. Haloxylon ammodendron is one of the major dominant woody species in Central Asian desert, and the size-dependent water use pattern of this species significantly affects the functioning of the local ecosystem. Here, we investigated the water-use responses of H. ammodendron to groundwater depth from seedling to mature tree in the Gurbantunggut Desert, China. Three sites were selected along a groundwater depth gradient, with 4.6 m, 7.4 m, and 11.0 m, respectively. Based on basal stem diameter, H. ammodendron plants were grouped into three development stages, namely seedling, sapling, and mature tree. Hydrogen isotope ratios ( δ 2 H) and oxygen isotope ratios ( δ 18 O) were measured for xylem water at different basal stem diameter (BSD) values, soil water in different soil layers, and groundwater. The water sources used by the seedlings, saplings, and mature trees were determined by applying the IsoSource model. The relationship between δ 18 O value of xylem for H. ammodendron and basal stem diameter reflected changes in the water source from upper soil water to deeper soil water as H. ammodendron grows. With the decline in groundwater depth, seedlings decreased their water uptake depth, whereas saplings increased at mid depth but decreased at maximum depth. However, mature trees constantly increased their water absorption depth across sites. Tree height, crown width, and BSD presented a decreasing trend as the groundwater depth declined. The above study promotes the evaluation of the impact of groundwater retrogression on H. ammodendron population in its natural habitat.