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Under the background of China's "double carbon" goal, it is essential to better understand the carbon accounting and control factors in complex terrain areas. Guizhou Province, as one of the provinces with the most typical karst landform development in Southwest China, has been regarded as an important carbon pool. Nevertheless, it is not clear how the change in soil organic carbon density (SOCD) is influenced by the combined effects of natural factors and human activities at the provincial scale. This study used geostatistical methods to explore the spatial pattern of SOCD, and the factors affecting SOCD were analyzed using classical statistics, correlation analysis, random forest model, and structural equation model methods. Additionally, soil organic carbon (SOC) storage under typical land use types in Guizhou Province was also estimated. The results showed that the SOCD of two soil layers (0–10 cm and 10–20 cm) in Guizhou Province had medium-intensity variation. Spatially, SOCD displayed a distribution pattern of high values in the west and low values in the north and south. The SOC storage (0–20 cm) of woodland, arable land, garden land and grassland in Guizhou Province was 476.47 Tg C, 139.8 Tg C, 22.53 Tg C, and 7.66 Tg C, respectively. Altitude had the greatest indirect effect on SOCD at the two soil depths. Human disturbance and light intensity directly impacted SOCD at only 0–10 cm soil depth. Slope position, slope and mean annual precipitation indirectly affected SOCD through human disturbance. Our research provides a reliable reference value for the in-depth understanding of the regional carbon cycle and the formulation and implementation of regional carbon sink strategies. • Spatial pattern of SOCD in Guizhou Province was studied. • The total SOC storage of topsoil in Guizhou Province was estimated. • The relationship between SOCD and influencing factors was analyzed. • Controlling factors affecting the SOCD level were determined. • The influence paths of various factors on SOCD were analyzed. [ABSTRACT FROM AUTHOR]

• SOC has strong spatial variability due to complex topography and landscape. • Effects of environmental factors on SOC variations were explored. • Altitude, rocky desertification and land use are the key factors affecting SOC level. • Rocky desertification control is a major means to increase soil carbon sequestration. Global karst landforms account for about 15 % of the land area. The development of karst landforms in southwest China accounts for>1/3 of the country's land area, and is considered to be an important carbon storage with considerable carbon sequestration potential to alleviate global warming. Clarifying the response mechanism of soil organic carbon (SOC) to different controlling factors is of great significance to formulate and implement regional carbon sink strategies. Based on 517 soil samples in Guizhou Province, this study used geostatistical methods to analyze the spatial heterogeneity of SOC in Guizhou Province. The effects of altitude, land use, soil type, slope direction, slope position, slope gradient and rock exposure rate on the spatial variability of SOC in karst areas were quantitatively compared by statistical analysis methods. The results showed that the mean value of SOC content in Guizhou Province was 19.59 g/kg, and the coefficient of variation was 69.11 %, showing moderate-intensity variation. Spatially, the SOC content in Guizhou Province showed a declining trend from west to east, with the low-value areas predominantly distributed in the south and north areas. The semi-variogram model showed that the nugget coefficient C 0 /(C 0 + C) was < 25 %, and the SOC in the study area had a strong spatial autocorrelation. The artificial neural network analysis showed that the important coefficients of each independent variable on SOC level were as follows: altitude (0.355) > slope gradient (0.255) > rock exposure rate (0.166) > land use (0.08) > slope position (0.059) > slope direction (0.043) > soil type (0.041). This research suggests that the provincial government should pay attention to the control of rocky desertification and the development of modern low-carbon agriculture in the work of increasing soil carbon sequestration. [ABSTRACT FROM AUTHOR]