Spatial distribution of vegetation and its strategy in using water in the lower reaches of the Tarim River, western China

Spatial distribution of vegetation and their influencing factors in the lower reaches of the Tarim River of western China were studied by the method of situ observations and sampling. 67 sampling points in 16 transects were selected, and two stands, the Tamarisk spp. stand and the Populus euphratica stand, were selected for situ observations. With the increase of the distance to the river channel, the groundwater level logarithmically declined, and vegetation cover exponentially decreased, respectively. Soil textures had significant impacts on soil water retention. The field capacity of silty loam (0.32 g/g) was more than 3 folds of that of sandy soil (0.10 g/g), and the effective water content of the former was 1.6 folds of the latter. The vegetation cover was controlled by the groundwater level and soil water content together. Populus euphratica and Tamarix spp. had the ability to adapt to hyper-dry environment, but the water use strategies of them were different. Roots of Populus euphratica directly took up groundwater and soil water, and had the obvious hydraulic lift during the growing season. However, Tamarisk spp. roots mainly absorbed groundwater and the saturated soil water in the layer near the groundwater level.