Vegetation vulnerability in karst desertification areas is related to land–atmosphere feedback induced by lithology

Although vegetation productivity in the karst desertification region is much lower than in other lithological areas at the same latitude, the exact mechanisms through which lithology constrains vegetation productivity via hydrological processes still need to be discovered. Two types of lithological zones (non-soluble and soluble rocks) were selected for this study, which can be categorized into three types of study units: non-karst unit (NKU), karst non-desertification unit (KNDU), and karst desertification unit (KDU). NKU and KNDU were used as comparisons to explore the effects of terrestrial and atmospheric water on vegetation productivity in KDU from 2001 to 2018. The results exhibited that although the climatic conditions were similar, there were differences in regolith thickness and hydrological processes in the different lithological zones. The shallow regolith in KDU increased the regolith moisture loss rate (RMLR) by 70.78% and 68.51% but decreased regolith moisture (RM) by 8.34% and 8.01% compared to the deep regolith of NKU and KNDU, indicating that a thinner regolith with a high RMLR exacerbates the loss of RM. Further analysis showed that low RM also increased the change rate of vapor pressure deficit by reducing evapotranspiration, revealing that low RM attenuates the water circulation from the surface to the atmosphere and creates atmospheric drying. Both approaches that contain surficial and atmospheric drying can constrain vegetation productivity. Overall, we found that RMLR in different lithological zones not only directly controls RM to affect vegetation growth but can also influence land–atmosphere feedback. The karst desertification region with shallow regolith is constrained by land–atmosphere feedback caused by high RMLR, so the vegetation system exhibits vulnerability.