Abstract:

Haloxylon ammodendron is the most widely distributed vegetation type in the desert areas of Central Asia，and has long been used as an excellent tree species for windbreak and sand fixation. In desert areas where precipitation is severely scarce， the depth of groundwater level plays a key role in the normal growth of H. ammodendron. In this study， the artificial H. ammodendron forest at the edge of the Linze Oasis in the middle reaches of the Heihe River was selected as the research area， and H. ammodendron of the same age growing in the sand dunes and inter-dune lowland was selected as the research object. The hydrogen and oxygen isotope values of H. ammodendron plant stem water and other potential water sources （precipitation， soil water， groundwater） were measured， and the ratio of water sources of H. ammodendron under different micro-topography conditions in the sand dunes and inter-dune lowland was calculated based on the IsoSource model. The results showed that there were significant differences in the δ¹⁸O values of the xylem water of H. ammodendron stalks distributed on the top of the sand dunes and inter-dune lowland， and the impact of precipitation changes on the sand dunes is more significant. The difference in groundwater depth between sand dunes and inter-dune lowland has a significant impact on the main water source of H. ammodendron and its response to water changes. The percentage of groundwater used by H. ammodendron distributed on the top of sand dunes was 60.6%； while the utilization ratio of groundwater by H. ammodendron was 86.4%. Therefore， the water use strategy of H. ammodendron distributed in sand dunes and inter-dune lowland has changed. H. ammodendron can respond in time when precipitation events occur， while H. ammodendron in the inter-dune lowland makes no significant use of precipitation. The severe drought stress in summer increased the utilization of groundwater by H. ammodendron on sand dunes and inter-dune lowland ，indicating that H. ammodendron has a strong dependence on groundwater， but it can adjust its own water use mode according to environmental conditions to adapt to the desert environment.

Key words: desert habitat, sand dunes and inter-dune lowland, stable oxygen isotopes, plant water source, Haloxylon ammodendron