Study on the Variation Characteristics of Grassland Vegetation Soil Water Potential in Xishui Forest Area of Qilian Mountains, Gansu

This study taking the grassland in the western water forest area of Qilian Mountains as the research object, the soil water potential of different soil layers was monitored in the field by using the soil water potential meter, and the temporal and spatial variation rule of the soil water potential and its response to atmospheric precipitation in April–October were statistically analyzed. The results show that due to the increase of precipitation and the thaw of seasonal permafrost, the fluctuation of soil water potential of grassland in different soil layers increased from April to July; due to the decrease of precipitation and the enhancement of soil evaporation and plant transpiration, the 10 cm soil layer reached the lowest value in August, while the other soil layers reached the lowest value in September; as the temperature drops, evaporation decreases, vegetation growth ends, and soil water potential of different soil layers rises again in October. The water potential inflection point in the grassland soil profile appeared at the depth of 30 cm, which showed an increase at the depth of 0–30 cm, an increase of 53.43 kPa, and a decrease at the depth of 30–60 cm, the water potential value decreased by 32.73 kPa. The evapotranspiration of grassland soil water occurred in the soil layer below 30 cm. Atmospheric precipitation significantly affects the soil water potential value of grassland. When the precipitation event is light rain, the soil water potential fluctuates around 0 kPa. Subsequently, with the increase of precipitation, the soil water potential also shows an increasing trend. The results can provide reference for understanding the characteristics of soil water potential change and protecting the ecological environment of grassland vegetation in Qilian Mountains.