Soil Moisture Characteristics Of Different Plant Communities In The Hilly Region Of Loess Plateau In Northwest Shanxi

Soil moisture is one of the main limiting factors for vegetation growth on the Loess Plateau. In this study, six types of plant communities (abandoned land, Salix matsudana, Caragana Korshinskii Kom, Populus cathayana, Populus simonii Carr and Pinus tabulaefor mis) in loess hilly region of northwest Shanxi are taken as the study objects. Measuring the soil moisture of each plant communities in the 0-600cm soil layer, we analyzed the spatial and temporal variation of soil moisture and the degree of variability of different plant communities and evaluated soil desiccation of various plant communities in different layers. The results are as follows:(1)The soil moisture content of six plant communities in terms of time: according to the seasonal variation of soil moisture, it can be divided into three periods:strong depletion period of soil moisture in spring (April-May), recovery accumulation period of soil moisture in summer(June to August) and resolution period of soil moisture in autumn (September to October). Affected by rainfall, the soil moisture of the same plant communities varies in different time, and it also varies among different plant communities in the same month.(2)The soil moisture content of six plant communities in terms of space: the average soil moisture content of the same plant communities is different due to different soil profiles. The soil moisture content goes basically in this trend:it decreases first and then rises as the soil depth increases. The average soil moisture content in the same soil profile is significantly different due to different plant communities.(3)Variation degrees of the six plant communities:the variation degrees in temporal order are abandoned land<Populus simonii Carr<Salix matsudana<Pinus tabulaefor mis<Populus cathayana<Caragana Korshinskii Kom; the variation degrees in different soil profiles of 0-600cm soil layers are in sequence of Populus simonii Carr<Caragana Korshinskii Kom<abandoned land<Populus cathayana Salix matsudana<Pinus tabulaefor mis.(4)Soil desiccation degrees of six plant communities:these three kinds of plant communities (abandoned land, Caragana Korshinskii Kom and Populus cathayana) all become dry in the depth of 200-300cm soil layer; Salix matsudana and Populus simonii Carr become dry in the depth of 100～200cm soil layer and Pinus tabulaefor mis’s dry layer is in the depth of 100～300cm.(5)Vertical variation of soil moisture and desiccation index:soil desiccation varies in the same soil profile:in 0～100cm soil layers, soil moisture content is the highest in spring and lowest in summer; in 100-300cm soil layers, it is the highest in spring and lowest in autumn; however, in 400-600cm soil layers, it fails to show a unique season and soil desiccation characteristic. Based on the spacial changing rules of soil moisture and desiccation, soil profiles can be divided into three parts: variable layers (0～100cm), regulating layers (100～300cm) and relatively stable layers (300～600cm) of soil moisture.