Changes in soil water retention and content during shrub encroachment process in Inner Mongolia, northern China

Abstract

Soil water retention is the link between hydrologic processes and ecological patterns, and is one of the vital hydrological properties of soils. However, the influence of shrub encroachment on soil water retention and content remains unclear, and the factors influencing soil water retention and content are also not well understood. Therefore, this study aims to investigate the changes in soil water retention and content during the shrub encroachment process and to reveal their influencing factors. In this study, three states of shrub encroachment were identified according to the percentage of shrub cover. Soil samples of the shrub patches and adjacent interspace grass patches were collected in each state of shrub encroachment. The soil water retention curves of the samples were generated, and the soil water contents of the samples were measured. The results showed that the field capacity (FC) and plant-available water capacity (PAWC) of both shrub patches and interspace grass patches increased during shrub encroachment, which suggests that shrub encroachment has positive effects on soil water retention. The FC and PAWC of the shrub patches were 14.7% and 14.5% higher than those of the interspace grass patches, respectively. The shrub patches were also characterized by higher soil water content and storage than the interspace grass patches. Shrub roots, soil organic matter, and clay content were the three most crucial factors positively affecting soil water retention and content during shrub encroachment process. This study can further our understanding of the ecohydrological effects of shrub encroachment in arid and semiarid grasslands and facilitate related modeling studies.