General Enhancement of Soil Water Repellency by Moss Crusts in Degraded Subtropical Karst Ecosystems

Soil water repellency, a crucial soil physical property, is widespread globally, affecting hydrology positively or negatively by impeding soil wetting. Nonetheless, research on soil and biocrust water repellency in degraded subtropical karst environments is lacking. This research examined how moss crusts affect soil water repellency in these environments using the Water Drop Penetration Time (WDPT) method. The research utilised moss crusts from degraded karst areas with varying levels of degradation, contrasting them with bare soils as controls. Results indicate that degraded subtropical karst soils (calcareous and yellow soils) exhibited no water repellency (WDPT < 5 s). Moss crusts notably enhanced water repellency consistently across various degradation stages, exhibiting slight water repellency (5 s ≤ WDPT < 60 s). Soil water repellency diminished following the removal of moss; however, it remained significantly elevated compared to bare soil. Factors such as soil water content, fine particle content, aggregate stability, organic carbon, total nitrogen, and total potassium were found to significantly influence water repellency. In bare soils, water repellency peaked at 10% water content, weakening thereafter, whereas moss crusts exhibited strongest repellency at 0% water content, diminishing as water content increased. Moreover, both moss crusts and bare soils showed heightened repellency with smaller particle sizes (< 0.05 mm). The hydrological impacts of biocrust-induced water repellency vary, presenting both positive and negative effects that necessitate further investigation. This research establishes a foundation for upcoming studies on the impact of biocrusts on hydrology within these environments, providing essential theoretical knowledge for addressing soil erosion and loss in the context of global changes.