Abstract: Soil carbon pool is an important component of forest ecosystem carbon pool, which plays an important role in regulating carbon cycling of terrestrial ecosystems and atmospheric CO₂ concentration. Previous studies mainly investigated the relationships between forest soil carbon and various factors (such as topography, vegetation, soil physical and chemical properties). However, key factors in the multiple factors and their interaction mechanisms are still unclear. Based on the observed data of 50 plots of Pinus tabuliformis aerial seeding plantation in Danfeng County, Shangluo City, Shaanxi Province, we used structural equation model to explore the influencing factors of soil organic carbon density. A total of 23 indices including stand structure, species diversity, biomass and soil physicochemical properties were selected as observation variables, and four latent variables including tree characteristics, shrub, herb and litter characteristics, other soil physicochemical properties, and soil organic carbon density were formed. A partial least square structural equation model was constructed. The results showed that: (1) 12 observation variables were included in the final structural equation model. Three observation variables were screened out from other soil physicochemical properties, namely, soil total nitrogen, soil total phosphorus, and soil water content. Five observation variables were selected from the latent variables of shrub, herb and litter characteristics, including shrub Simpson index, herb Simpson index, herb Margalef index, herb biomass, and litter layer thickness. Three observation variables were screened out from the latent variables of tree characteristics, including tree Simpson index, neighborhood comparison and number of tree species. (2) Other soil physicochemical properties were the direct influencing factors of the latent variable of soil organic carbon density (path coefficient of 0.877, P<0.01). Shrub, herb, and litter characteristics and tree characteristics were considered as the indirect influencing factors of the latent variable of soil organic carbon density (path coefficient of 0.552 and -0.299 respectively, both P<0.01). (3) The characteristics of shrub, herb, and litter affected the latent variable of soil organic carbon density by directly affecting other soil physicochemical properties (path coefficient of 0.630, P<0.01), and tree characteristics affected the latent variable of soil organic carbon density by directly affecting shrub, herb, and litter characteristics (path coefficient of -0.541, P<0.01). In conclusion, this study provides new insights into the relationship between different driving factors and has important implications for understanding soil organic carbon regulation in aerial seeding plantations.

Key words: soil organic carbon density, Pinus tabuliformis , aerial seeding plantation, structural equation model, multifactorial interaction