Land carbon sink function variation across bedrock types in Southwest China.

Terrestrial ecosystem carbon sinks are a natural deposit that absorbs carbon from the atmosphere. A stable land carbon sink facilitates more reliable predictions of carbon sequestration under changing climate conditions. In contrast, a highly variable land carbon sink will introduce significant uncertainty into model predictions. Karst regions have attracted increasing attention due to their significant contribution to global land carbon sequestration capacity. However, understanding the stability of land carbon sinks and its driving factors in karst areas remains limited. This study focused on the world's largest karst zone, located in Southwest China (SWC), to assess the stability of land carbon sinks. By analyzing inter-annual variation (IAV) in net ecosystem productivity (NEP), we aimed to elucidate the spatial distribution of the stability of land carbon sinks and the dominant climatic drivers. We compared the stability of land carbon sinks across bedrocks, which were classified by carbonate content: non-karst, Discontinuous Carbonate Rocks (DCR), and Continuous Carbonate Rocks (CCR). Our findings showed that while land carbon sinks in karst bedrocks exhibited higher increased NEP rates than those in non-karst areas. Notably, we observed an inverse relationship between the rate and stability-regions with rapid land carbon sink enhancement were often characterized by instability, particularly in karst areas. Moreover, the drivers of the stability of land carbon sinks varied significantly between bedrock types. In non-karst regions, water availability was the primary factor influencing stability, whereas temperature was more dominant in karst regions. DCR regions showed lower stability due to the high sensitivity of land carbon sinks to temperature, while CCR regions experienced reduced stability linked to greater temperature variability. Our results highlight the need to consider the combined effects of bedrock type and climate factors on stability, offering valuable insights for managing and enhancing carbon sequestration capacity in a changing environment.