Bidirectional Gradient Effect of CO<sub>2</sub> Concentration in Soil Profile of Karst Peak–cluster Depressions and Its Influencing Factors

<p indent="0mm"> Soil CO₂ in karst regions is a crucial driver of karst processes. Investigating the stratification effects of soil profile CO₂ concentration and its response to environmental factors could provide essential insights into karst carbon sinks and carbon cycling. This study examines five land use types (shrubland, forest, orchard, grassland, and farmland) in a typical peak-cluster depression in Guancun, Guangxi. Soil CO₂ concentrations at different depths, environmental factors, and standard dissolution test pieces were analyzed using correlation and principal component analysis. The results show that soil CO₂ concentrations exhibit seasonal variations, being higher in the rainy season and lower in the dry season. Soil temperature correlated positively with soil CO₂ concentration overall (<italic>R</italic>² = 0.53, <italic>P</italic> &lt; 0.05). Temperature is the key factor influencing soil CO₂ at depths of 5 and <sc>20 cm.</sc> At <sc>50 cm</sc> depth, CO₂ concentration is primarily affected by karst processes. A bidirectional gradient effect was observed in soil CO₂ concentration, with lower levels at 5 and <sc>50 cm</sc> and a peak at <sc>20 cm</sc> depth, which is attributed to karst processes and serves as strong evidence of karst carbon sinks. However, whether soil CO₂ concentration can directly indicate the intensity of subsurface karst processes and how it reflects carbon cycling in karst systems require further research.