Bedrock regulated climatic controls on the interannual variation of land sink in South-West China karst through soil water availability

South-West China (SWC) is a pivotal region for global greening, recognized as having great carbon sink potential. Multiple evidence underscores the expanding contribution of SWC's carbon sink to the global carbon sink enhancement. However, our understanding of carbon sink dynamics and the response to climate across bedrock remains limited. In this study, we investigated the divergence in trends in carbon sink across bedrocks, evaluating their respective contributions of bedrocks to the overall carbon sink in SWC. Additionally, we assessed the dominant climatic factors and examined how bedrocks shape the response of carbon sink to climate change. Our results revealed a notable increase in the regional carbon sink, with an average rate of 3.58 TgC/yr from 1981 to 2019. Continuous Carbonate Rocks (CCR) exhibited the highest increased rate of total carbon sequestration (1.57 TgC/yr), surpassing Discontinuous Carbonate Rocks (DCR) by threefold. Non-karst areas contributed the most to both the mean and interannual variations of the overall carbon sink, with CCR exerting the most contribution to the trends. Over time, the contribution of CCR to the overall carbon sink escalated, while the contributions of DCR and non-karst declined. All bedrocks displayed negative correlations between NEP and temperature, with DCR showing higher susceptibility. Non-karst areas experienced adverse impacts from vapor pressure deficit, while CCR benefited from positive soil moisture effects. Our findings implied that bedrock indeed played a critical role in the variations in NEP and the response of NEP to climate change. Bedrock regulated climatic controls on carbon sink through soil water availability as soil water availability is affected by the lithology of basement carbonate. This novel understanding emphasizes the necessity for tailored ecological restoration initiatives that consider the distinctive lithological features of the karst ecosystem, and holds significance for implementing ecologically sound projects in karst regions.