Study on Soil Moisture Characteristics in Southern China Karst Plant Community Structure Types

An understanding of soil moisture variation patterns under different plant community structures is crucial for the restoration of vegetation in southern China karst regions. Therefore, four plant community structure types: arbor + herb (AH), shrub + herb (SH), arbor + shrub + herb (ASH), and herb (H), were selected as the research objects. A soil moisture sensor was used to monitor the soil moisture content in the 0–70 cm soil layer, to analyze the variation characteristics of soil moisture content and to explore the differences under different plant community structure types. The results indicate that: (1) A total of 31 plant species in 31 genera and 18 families were recorded, among which herbs were the most abundant. There were significant differences in diversity indexes for ASH and H. The differences between Shannon–Wiener index and Simpson index of AH and H were significant, and between AH and SH in Pielou index and Simpson index were statistically significant. The Pielou index between SH and H was significantly different. (2) There were significant differences in soil water content among the four plant community types, showing SH > AH > H > ASH. The variation of soil moisture was consistent with the trend of rainfall, with the surface soil moisture more sensitive to rainfall events, and the deeper soil moisture had a lag. The Shannon–Wiener index was significantly and positively correlated with the Simpson index and the Margalef index. There was a highly significant positive correlation between Margalef index and Simpson index. The 20–30 cm soil layer was highly negatively correlated with the Margalef index and significantly and negatively correlated with the Shannon–Wiener index and the Simpson index. (3) The response of soil moisture of plant community structure types to light rain event was not obvious. The growth rates of soil water content in the 30–50 and 50–70 cm layers of the SH were higher in moderate rain event than that in heavy rain event, and H, AH, and ASH had larger growth rates in heavy rain events. The results provide a reference for the effective utilization of soil and water resources and the restoration of vegetation, as well as for plant community structure configuration decisions in the southern China karst region.