半干旱黄土高原苜蓿草地撂荒过程土壤水分变化特征

土壤水分是黄土高原植被恢复和生态建设的主要限制因子，明确土壤水分随植被演替的变化规律是阐明黄土高原植被与水分相互作用机制的重要基础。以半干旱黄土高原小流域苜蓿草地撂荒过程为研究对象，通过对2016-2018年生长季苜蓿群落、苜蓿+赖草群落、赖草群落和长芒草群落四种草地群落0-1.8 m土壤水分进行动态监测以及0-5 m深度土壤水分测定，分析不同演替阶段苜蓿草地土壤水分的动态特征，探讨土壤水分对苜蓿草地撂荒过程的响应。结果表明：（1）在苜蓿草地撂荒演替过程中，土壤水分随群落恢复时间的延长呈先增加后降低的变化，降水的年际动态显著影响不同演替群落的土壤水分响应；（2）0-0.4 m土壤水分主要受降水影响，使得各草地群落在这一层次没有显著差异（P>0.05），而1 m以下的土壤水分含量则主要受植被类型的影响，各草地群落之间存在显著差异（P<0.05）；（3）0-5 m深层土壤水分随群落的演替，1 m以下各土层土壤水分含量逐渐增加，表明撂荒过程中使土壤水分得到了一定程度的恢复。研究结果揭示了苜蓿草地撂荒过程土壤水分的变化规律，可为黄土高原生态恢复提供理论依据。

Characteristics of soil moisture variation during the abandonment process of Medicago sative grassland in the semi-arid the Loess Plateau

Soil moisture is the main limiting factor for vegetation restoration and ecological construction in semi-arid loess hilly region. It is clear that the change of soil moisture with vegetation succession is an important basis for elucidating the interaction mechanism between vegetation and water in semi-arid ecosystem. This paper takes the Medicago sativa grassland abandonment process in the small watershed of the semi-arid loess plateau as the research object, through the dynamic monitoring of 0-1.8 m soil moisture in the four grassland communities of Medicago sativa community, Medicago sativa+Leymus chinensis community, Leymus chinensis community and Stipa bungeana community during the growing season of 2016-2018 and the measurement of soil moisture at a depth of 0-5 m were carried out to analyze the dynamic characteristics of soil moisture in different succession stages, and to explore the response of soil moisture to the process of Medicago sativa grassland reclamation. The results showed that: (1) In the process of Medicago sativa grassland succession, the soil moisture increased first and then decreased with the extension of community recovery time. The interannual dynamics of the second precipitation significantly affected the soil moisture response of different succession communities; (2) 0-0.4 m soil moisture is mainly affected by precipitation, so that there is no significant difference in the grassland communities at this level (P>0.05), while soil moisture content below 1 m is mainly affected by vegetation type, with significant difference among grassland communities (P<0.05); (3) with the succession of community, the soil moisture in the deep layer of 0-5 m increased gradually with the soil moisture content below 1 m, indicating that the soil moisture was recovered to a certain extent during the process of abandonment. The results reveal the change rule of soil moisture in the process of Medicago sativa grass fattening, which can provide theoretical basis for vegetation restoration and ecological construction on the loess plateau.