Soil moisture variations in response to precipitation properties and plant communities on steep gully slope on the Loess Plateau

The response of soil moisture to precipitation is likely greatly affected by precipitation properties and plant communities via influencing hydrological processes linking atmosphere-vegetation-soil continuum. Nevertheless, few studies have been carried out to investigate these responds after revegetation on steep gully slope in arid and semi-arid regions. This study was conducted to quantify the response of soil moisture to precipitation properties on steep gully slopes covered by different plant communities on the Loess Plateau. Soil moisture was measured consecutively at 20-min intervals from May 2019 to October 2020 for one bare land (as control), and two shrub and four grass communities. The results demonstrated that the response of soil moisture to precipitation at event scale varied greatly with rainfall types and occurred months. The dominant factors were precipitation amount, intensity, and soil initial water content for the changes in soil moisture of 10 cm and 30 cm soil layers and the lag time of 10 cm soil layer, whereas for the lag time of 30 cm soil layer they were slope gradient and precipitation duration. At monthly scale, soil moisture varied greatly within 0-100 cm soil layers, following a trend of decreasing (January to June), increasing (July to September), and decreasing (October to December). However, soil moisture was almost stable for soil depth deeper than 100 cm and only fluctuated under either extreme rainstorms or series of consecutive precipitations. At annual scale, soil water storage was similar between the year of 2019 and 2020, but varied greatly between different plant communities, attributed to the differences in above-ground biomass, field capacity, and land surface roughness. Their relative contributions were 71.6%, 22.1%, and 5.8%. These results are helpful to understand the temporal changes in soil hydrological processes and to choose vegetation restoration model on steep gully slopes in arid and semi-arid regions.