Spatial heterogeneity of soil water content in the reversion process of desertification in arid areas

Abstract

Sandy soils in arid, rain-fed environments have low and limited water content, which is a principal factor limiting vegetation development, and a key constraint controlling the structure and functions of the ecological systems in arid areas. The spatial heterogeneity of soil water content is a major soil property, and a focus of soil science and hydrology. On the southern edge of the Tengger Desert, sample plots were selected from mobile sand dunes in desertified lands that had been enclosed for 5, 15 and 25 years, respectively. This study explored the dynamic and spatial heterogeneity of soil water content in these different layers of soil that were also in the reversion process of desertification. The results showed that the soil water content of the mobile sand dunes was highest when in the initial stages of the reversion process of desertification, while the soil water content in the 0-20 cm, 20-40 cm and 40-60 cm layers of soil was 1.769%, 3.011%, and 2.967% respectively, presenting a restoring tendency after 25 years of enclosure. There were significant differences, as a whole, in the soil water content among different restoration stages and different soil layers, respectively. Changes in soil water content, in different soil layers, at different restoration stages, exhibited exponential or spherical patterns. The spatial distribution of soil water content exhibited a mosaic patch pattern with obvious spatial heterogeneity. The ratio of the heterogeneity of spatial autocorrelation to gross spatial heterogeneity was greater than 50%. The gross spatial heterogeneity of the 0-20 cm layer of soil improved gradually, while those of the 20-40 cm and 40-60 cm layers improved initially, then weakened in the reversion process of desertification. This study revealed that restoration with sand-binding vegetation reduced soil water content, and increased its spatial heterogeneity in arid areas. However, after 25 years of vegetation-soil system restoration, the soil water content started to increase and its spatial heterogeneity started to weaken. These results will further benefit the understanding of the ecological mechanism between soil water and sand-binding vegetation.