Key drivers and ecological insights into soil organic carbon variability in tobacco-growing region, China

• 180 soil samples collected from typical tobacco-growing region fields was conducted in this experiment. • Soil organic carbon and microbial diversity exhibit significant variations across different ecoregions in China. • Precipitation, soil texture, TN, and C/N ratio govern microbial composition and SOC across ecoregions. • Increased precipitation and soil sand content critically shape microbial abundance in Southwest China. Recently published information on spatial variability of soil organic carbon (SOC) in cultivated areas and the relative controlling factors that drive the variations across different ecological regions have rarely been reported in China. To address this gap, 180 soil samples were collected from typical tobacco-growing fields across the Huanghuai, Northeast, and Southwest regions of China to determine the spatial variability of SOC, climate factors, soil carbon fractions, soil texture, soil nutrients, and microbial communities. Results showed that organic SOC and microbial diversity display significant variations across different ecoregions in China. In the Huang-Huai and Northeast regions, increased microbial diversity facilitated the accumulation of organic carbon. Conversely, in the Southwest region, variations in precipitation and soil texture serve as critical determinants of microbial community abundance. In the Huang-Huai region, the C/N ratio play a pivotal role in influencing microbial dynamics. Notably, an increase in soil nitrogen significantly enhanced microbial diversity, thereby promoting SOC accumulation in the Northeast region. Collectively, these findings underscore that precipitation, soil texture, total nitrogen, and C/N ratio were key driver of microbial community composition and SOC across diverse ecological regions. These results suggest that recognizing the role of environmental conditions and soil characteristics can improve soil management and enhance carbon sequestration in various ecological contexts.