Spatial and temporal distribution characteristics of soil moisture in the non-freezing period under the bare land and vegetation cover in the Mu Us desert

In the sandy land ecosystem with water shortage, soil moisture is the main controlling factor for vegetation restoration and water resources management. Therefore, a correct understanding of the distribution characteristics and spatial-temporal variation of soil moisture in the sandy land is the basis for promoting the sustainable development of sandy land water resources. The Mu Us desert is taken as the study area, in-situ experimental observations, classical statistical analysis and hierarchical clustering analysis methods are used to reveal the spatial and temporal changes of soil profile moisture with or without vegetation cover, and the effect of plant growth on soil water distribution are discussed in this paper. The results show that in the non-freezing period of 2016, when the groundwater depth was relatively shallow, the average soil moisture content increased with the increasing soil depth under the bare land and vegetation coverage. The soil layer of 0−350 cm thick can be divided into the climate-influencing layer, transition layer and groundwater-influencing layer. The average moisture content of the bare soil profile is 23.59%, and the coefficient of variation is 4.25%, which belongs to weak variation. The profile moisture content increased significantly during the observation period, and the rate of increase reached the maximum when the heavy rainfall event occurred in mid-August. The average moisture content of the soil profile under the vegetation cover is 17.74%, and the coefficient of variation is 15.61%, which is a medium variation. The water content of the profile dropped significantly during the observation period, and it dropeds the fastest in August after the Salix matures. At the vertical depth, the influence of vegetation on the soil profile moisture content approximates a Gaussian curve, and has the greatest influence on the moisture content of the transition layer, accounting for more than 50% of the total influence. The impact on climate-influencing layer and groundwater-influencing layer is relatively small. As plants grow, the relative influence on the climate-influencing layer gradually weakens, and the relative influence on the groundwater-influencing layer gradually increases. The research results can provide references for the rational regulation of water resources in the semi-arid Mu Us Sandy Land and the stable development of the sandy land ecosystem.