Spatiotemporal dynamics and controls of carbonate rock weathering carbon sink flux in the forest-covered karst area of the Karst Valley, Southwest China: The central role of soil water availability

Carbonate rock weathering (CRW) carbon sinks in forest-covered karst ecosystems are important components of the global carbon cycle, yet their spatiotemporal dynamics and controls remain unclear. Here, we improved a conventional thermodynamic dissolution model by integrating soil moisture (SM), vegetation activity, and soil physicochemical properties, and validated it against in situ limestone tablet measurements in forest-covered karst regions of the Karst Valley in Southwest China. The improved model substantially outperformed the conventional model, achieving calibration R 2 = 0.84, validation R 2 = 0.74, absolute percent bias (|PB|) < 3.7 %, and root mean square error (RMSE) < 3.8 t C km −2 yr −1 . Using the improved model, we quantified CRW carbon sink flux (CSF) dynamics during 2001–2024. Mean CSF was 28.97 t C km −2 yr −1 and exhibited a pronounced southwest-to-northeast decreasing gradient, while 87.75 % of the area showed significant increasing trends at an average rate of 0.44 t C km −2 yr −1 . SM emerged as the dominant control of CSF spatial variability and interacted synergistically with vegetation activity. Factorial attribution further showed that SM and vegetation activity accounted for 55.05 ± 9.94 % and 41.64 ± 9.73 % of temporal CSF variability, respectively. Long-term classification identified SM dominance across 56.23 % of the area, followed by SM-vegetation activity co-dominance (32.00 %) and vegetation activity dominance (11.77 %), with substantial interannual redistribution among these regimes. These findings identify soil water availability as a key constraint on CRW CSF in forest-covered karst regions and highlight the need to incorporate coupled SM-vegetation dynamics into regional carbon sink assessment and projection.