Effect of Forest Greening on Carbonate Rock Weathering Carbon Sink in the Subtropical Humid Zone

The karst inorganic carbon sink is crucial for carbon neutrality, but its trends and drivers in subtropical humid zones remain unclear. This study selected subtropical humid zones in China with significant forest greening, quantified the carbonate rock weathering carbon sink (CCS) using a thermodynamic dissolution model, and explored the effects of climate, vegetation, hydrology, and radiation energy on CCS through importance analysis. The results showed that from 1982 to 2020, the CCS flux was 12.40 t C km−2 yr−1, and the total carbon sink was 1188.54 × 104 t C yr−1. Normalized difference vegetation index, leaf area index, and CCS exhibited an increasing trend, with growth rates of 0.002, 0.01 m2 m−2, and 0.05 t C km−2 yr−1, respectively. Surface available water, precipitation, and evapotranspiration were the dominant factors affecting CCS. This study found that forest greening caused precipitation to increase faster than evapotranspiration, driving an increase in available surface water and ultimately promoting the karst carbon sink in subtropical humid zones. Our findings highlight forest greening as a vital strategy for carbon neutrality.