Spatiotemporal changes and driving mechanism of ecosystem carbon sink in karst peak cluster depression basin in Southwest Guangxi based on the interaction of “water-rock-soil-air-biology”

Research on ecosystem carbon sinks is vital for developing policies to reduce emissions and enhance carbon sequestration. Analyzing the temporal and spatial trends of carbon sinks and their driving mechanisms is crucial for guiding policy and measures. Traditional methods for estimating carbon sinks in karst regions focus primarily on vegetation-soil carbon sinks, mainly comprising net primary productivity (NPP) and soil heterotrophic respiration (Rh). However, these methods overlook the unique karst carbon sink (KCS), leading to significant uncertainties in carbon sink evaluations. This study focuses on the karst peak cluster depression basin in southwest Guangxi and proposes a Karst Ecosystem Carbon Sink Assessment System (KECAS) based on the “water-rock-soil-air-biology” coupling framework, considering lithological characteristics. Theil-Sen trend analysis and restricted cubic spline (RCS) regression were used to explore the temporal and spatial variations and driving mechanisms of carbon sinks in the area from 2000 to 2022. The results show the following: (1) The total carbon sink flux (TCSF) in the study area has shown an upward trend over time, with a 23-year average ranging from 538 to 929 g CO₂ m⁻² a⁻¹ and a growth rate of 3.1039a⁻¹. This means TCSF increases by 6.78 g CO₂ m⁻² a⁻¹ each year. (2) Spatially, areas with increasing carbon sinks cover 34.17 % of the study area, mainly in Chongzuo, Nanning, and Wenshan Prefecture. Areas with decreasing carbon sinks cover 11.79 % of the total area, mainly in Chongzuo, with smaller areas in Nanning and Baise. The mean TCSF distribution is higher in the northwest and lower in the southeast. (3) The critical thresholds for influencing factors were identified using RCS regression: precipitation (1430 mm), temperature (17.9 °C), evapotranspiration (855 mm), NDVI (0.63), DEM (637 m), slope (16.3°), nighttime light index (6.21), and population density (421 people/km²). (4) Areas with high carbon sink supply potential, based on natural and human thresholds, account for 25.09 % and 92.97 % of the southwestern Guangxi study area, respectively. When considering both natural and human conditions, high potential areas account for approximately 22.31 % of the total study area. These findings provide a scientific basis for carbon sink protection and management and offer valuable references for government decision-making.