Spatial pattern and controlling factors of soil organic carbon density in a typical karst province, China

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.