Rock fragment content mediates the plant effect on soil water content in the arid valley of southwest China

As a crucial aspect of terrestrial ecosystems, water plays a key role in soil hydrological cycling and ecological management. However, limited knowledge exists on how soil water varies along rock fragment content (RFC) beneath plants. In this study, we investigated soil water content (SWC) and relative soil water deficit (DSWC) with four RFC levels ranging from 0 to 75 % (V/V) under four native species, including A. vestita, B. brachycarpa, C. szechuanensis, and S. davidii, and their relationships with soil physical properties and plant functional traits. Results showed that an increase in RFC significantly decreased SWC (except A. vestita) at soil depth of 10-50 cm and altered its vertical trend from unimodal to increasing under each plant. Notable differences in SWC between the wet and dry seasons in 75 % RFC disappeared under A. vestita and B. brachycarpa, suggesting that the RFC changed the spatiotemporal patterns of the SWC. DSWC generally decreased as soil depths deepened under A. vestita with shallow roots, in contrast to increasing under other deep-rooted species (B. brachycarpa, C. szechuanensis, and S. davidii). The seasonal variance of DSWC basically decreased with soil depth. This indicated that the plants generally deceased SWC, particularly in the wet season, and the effect depended on interspecific traits. SWC and DSWC had closely relationships with soil physical properties and plant performing. We suggest that varying RFC indirectly impacted soil water not only via altering soil structure and temperature, but also by shaping plant characteristics (especially root distribution and architecture), mediating plant effect on the spatiotemporal dynamics of SWC.