Impacts of rock-soil interface on soil infiltration and spatio-temporal water distribution during ecosystem succession in karst areas

Karst areas feature unique geology and hydrology, where the rock-soil interface is vital for soil infiltration and ecosystem water cycling. In the study, we used dyeing tracer sprinkling test and irrigation test, combined with soil water content monitoring and soil physical property investigation, to systematically evaluate the preferential flow at rock-soil interface (PF-RSI) in grassland, shrubland and forestland. The results indicated that as the ecosystem succession progressed, the PF-RSI increased but the water transfer from overground rock to soil weakened, with a similar reduction in the rock-soil interface’s influence on soil infiltration. Furthermore, the spatial heterogeneity and temporal stability of soil water post-rain decreased, revealing differentiated ecohydrological functions of PF-RSI across ecosystems. In addition, it was found that soil properties like bulk density hindered soil infiltration but enhanced PF-RSI development, while macro-porosity and macro-aggregate content promoted soil infiltration but reduced PF-RSI. Our results emphasized the co-regulation of hydrological processes in karst areas by the complex system composed of vegetation, soil and rock-soil interface, and pointed out that karst ecosystem succession weakened the hydrological effect of rock-soil interface. This study deepens the understanding of soil water dynamics in karst areas and provides scientific basis for plant water utilization and ecological restoration. However, it should be pointed out that due to the research scope of specific geomorphic units, the universality of relevant conclusions in regions with significant differences in karst development needs to be further verified by multi-scale comparative studies.