Fine-scale Effect of Karst Rock Outcrops on Adjacent Soil and Plant Communities in Southwest China

Rock outcrops (ROCs) are common structures in terrestrial ecosystems, particularly in regions characterised by karst-type landscapes. However, their effects on adjacent soil and plant communities have rarely been studied. In this study, soil physical and chemical parameters and plant biomass along distances adjacent to ROCs were investigated and compared to evaluate their effects on the surrounding environment. Thirty isolated ROCs were randomly selected from semi-humid karst grasslands in Southwest China. Rainfall and ROC runoff were collected for chemical analyses. The soil physical and chemical parameters as well as the aboveground and belowground biomass (AGB and BGB, respectively) of plants were determined at 0-30, 31-60, 61-90, 91-190, and 191-290 cm intervals, adjacent to the ROC rock-soil interface. The pH and total organic carbon and Ca contents were higher but P and K contents were lower in ROC runoff than in rainwater. A few of the soil physical and chemical parameters were significantly high in samples at 0-30 cm and corresponded with the contents in runoff. The AGB and BGB in the 0-30 cm and 31-60 cm plots were significantly higher than those located at a greater distance and correlated to the size parameters of ROCs. The maximum effective distance of ROCs was approximately 75 cm. Plant biomass increased sharply in the 0-30 cm and 31-60 cm plots, with an increase in coverage in the range of 0.7 and 1.3 m2. Our findings suggest that karst ROCs affect the physical and chemical parameters of soil and adjacent plant biomass significantly on fine scales, and these effects are correlated with the size parameters associated with ROCs, such as coverage area.