水分是制约半干旱区沙地植物生长发育和生态建设的关键非生物因子。于2008—2010年和2018—2021年生长季（4—10月）对毛乌素沙地流动、半固定和固定沙地0~100 cm深土壤水分进行了连续观测，系统分析了不同固定程度沙地土壤水分动态变化规律及其对降雨的响应。结果表明：（1） 受降雨季节变化的影响，流动、半固定和固定沙地不同深度土壤水分季节变化一般呈∽型或双峰型，10 cm和30 cm深土壤水分含量波动较大，60 cm和100 cm深土壤水分含量波动较小。（2） 3种固定程度沙地生长季土壤水分动态差异明显，总体来看，流动沙地土壤水分状况最好，且土壤水分含量变化相对平缓，固定沙地土壤水分状况最差，且土壤水分含量变化最为剧烈，半固定沙地居于二者之间；固定沙地10~30 cm深土壤水分状况好于半固定沙地和流动沙地，30~100 cm深土壤水分状况则相反。（3） 降雨格局是形成土壤水分时空格局的主要原因，随降雨事件降雨量增加，降雨的入渗深度逐渐增加；但是固定沙地土壤水分的深层补充需较强的降雨和较长的时间。生长季降雨事件以小降雨事件为主，表层土壤水分波动更剧烈。生长季初期降雨较少且以小降雨事件为主，10 cm以下土壤水分补充困难，土壤水分状况较差。流动沙地和半固定沙地10~30 cm深土壤水分状况好于30~100 cm深土壤，而固定沙地土壤水分状况则相反。研究结果可为半干旱区沙化土地近自然植被恢复与固沙植被稳定性维持提供科学依据。

Soil moisture is a crucial abiotic factor that limits the growth and development of plants and the ecological construction of sandy areas in semi-arid regions. In this study, continuous observations were performed on soil moisture at depths of 0-100 cm in shifting, semifixed, and fixed sandy land in the Mu Us Sandy Land during the growing seasons from 2008 to 2010 and from 2018 to 2021 (April to October). The dynamic changes in soil moisture and its response to rainfall were systematically analyzed. The results are as follows: (1) Affected by seasonal changes in rainfall, the seasonal variation of soil moisture in shifting, semifixed, and fixed sandy land exhibited a generally “∽”-shaped or double-peaked pattern. The soil moisture in the 10- and 30-cm depth ranges exhibited greater fluctuations, whereas that in the 60- and 100-cm depth ranges showed smaller fluctuations. (2) The dynamic differences in soil moisture during the growing season were significant among the three degrees of fixation. Overall, the shifting sandy land had the best soil moisture status with smooth changes, whereas the fixed sandy land had the worst soil moisture status with the most drastic changes. The semifixed sandy land fell between the two. The soil moisture in the 10-30 cm depth range of the fixed sandy land was better than that of the semifixed and shifting sandy lands, whereas the situation was opposite at depths of 30-100 cm. (3) The pattern of rainfall was the main factor determining the spatiotemporal distribution of soil moisture. As rainfall events occur and the amount of rain increases, the depth of rainwater infiltration gradually increases. However, deep replenishment of soil moisture in fixed sandy land requires higher rainfall amounts and longer periods. During the growing season, small rainfall events were dominant, resulting in greater fluctuations in soil moisture in the surface layers. At the beginning of the growing season, soil moisture below 10 cm was not replenished because of low rainfall and small rainfall events, resulting in poor soil moisture conditions. The shifting and semifixed sandy lands had better soil moisture at depths of 10-30 cm than at depths of 30-100 cm, whereas the opposite was true for the fixed sandy land. These results provide a scientific basis for the restoration of near-natural vegetation and the stable maintenance of sand-fixing vegetation on sandy decertified land in semi-arid regions.