微地形对高寒固沙植物水分利用特征的影响

Water is the most important limiting factor for plant survival, and the study of plant water utilization in desert has become the key to ecological protection and vegetation restoration program. In the sandy land at east shore of the Qinghai Lake, we focuses on three typical sand-fixing plants (Pinus syivestris var.mongolica, Populus simonii and Hippophae rhamnoides) as the research object. The potential water source (different levels of soil water) and the main water sources of plants under the influence of micro-topography were analyzed by hydrogen and oxygen stable isotope technology (18O and D) and IsoSource isotope mixing model. The results show that: (1)the soil water content has micro-topography differences, manifested in the lower soil water content on the windward slope being higher than that on the top of the sand dunes and the middle of the windward slope, and the soil water content is at its highest value in September. (2)the 18O value of xylem water is different in tree species under different micro-topographic conditions. The 18O values of P. syivestris in the lowland of windward slope are the lowest, while those of H. rhamnoides and P. simonii are the lowest in the middle of windward slope. (3)there are significant seasonal differences in the main sources of water for different plants. In June, both P. syivestris and H. rhamnoides used deep soil water as the main source of water under different micro-topographic conditions, while P. simonii mainly used deep soil water at the top of sand dunes. Middle-layer soil water is more utilized in the middle and lowland of windward slope, but with the increase of precipitation, various tree species turned to mainly use shallow and middle soil water in September. In summary, the water use patterns of sand-fixing plants in alpine sandy land are influenced by micro-topographic conditions, and different species showed different degrees of response to precipitation.