Spatial Partitioning and Driving Factors of Soil Carbon and Nitrogen Contents in Subtropical Urban Forests—A Case of Shenzhen, China

Global change seriously affects human survival, and urban forests can improve human living environments and mitigate the negative impacts of global change. The spatial distribution of carbon and nitrogen is key to assessing the health of forest ecosystems. However, the mechanism underlying the spatial distribution of carbon and nitrogen in urban forests in subtropical regions remains unclear. To study the characteristics and factors influencing the carbon and nitrogen contents of forest soils in Shenzhen, 126 soil samples were collected. Multivariate statistics and spatial analysis methods revealed the spatial distribution patterns and influencing factors of SOC, TN, and C/N in Shenzhen forest soils. The results showed the following: (1) The mean values of SOC, TN, and C/N of the 0–10 cm soil were 18.32 g·kg−1, 1.29 g·kg−1 and 14.43, with coefficients of variation (CVs) of 38.21%, 37.98%, and 15.73%, respectively, and those of the 10–30 cm soil were 9.24 g·kg−1, 0.67 g·kg−1, and 13.75, with CVs of 45.24%, 41.79%, and 19.45%, respectively. (2) The kriging spatial interpolation showed that the high- and low-value areas of 0–10 cm SOC and TN were concentrated in the northwestern and central and northern parts of the study area, respectively. The high value areas of 10–30 cm SOC and TN expanded to the southeastern part of the study area, and the low-value areas of SOC were distributed in the northern part. (3) The edges of the study area were fragmented, and the low-value areas of TN were mainly distributed in the western region, the high-value areas of C/N were mainly distributed in the west, and the low-value areas were mainly distributed at the eastern edge. Soil bulk weight and conductivity were the key factors affecting SOC and TN, which were the key factors affecting C/N. We emphasized the inhomogeneity of the spatial distribution of C/N in the subtropical region and that soil C/N is co-regulated by multiple factors. The results may provide insights for the government’s urban green space construction.