Forest vegetation is affected by climate change, forest management activities, and diseases and pests, which can lead to changes in photosynthetic carbon supply, root input of forest land, composition of soil microbial community, and soil greenhouse gases emission. These changes and their underlying mechanisms are the basis for modelling change of forest ecological functions and for managing forest scientifically. Here, we studied level of root input of 2-year-old potted seedlings of Pinus massoniana under two densities, single-plant/pot and 3-plants/pot, and under two disturbance treatments, ring-barking and stem-severing to stop carbon transport to the root system. We aimed to simulate the effects of changes in root input and photosynthetic carbon supply on soil physical and chemical properties, microbial community structure and greenhouse gas emission under various conditions. Our results showed that the total nonstructural carbohydrate (TNC) and nitrogen in seedling roots were lower in 3-plants/pot treatment than in single-plant/pot treatment. The content of soil available nitrogen in 3-plants/basins was lower than that in single-plant/pot. In contrast, richness of soil Gram-positive bacteria, anaerobic bacteria, actinomycetes and arbuscular mycorrhizal fungi were higher in 3-plants/pot treatment than in single-plant/pot treatment. Further, the emission rate of soil carbon dioxide (CO₂) was higher in 3-plants/pot treatment than in single-plant/pot treatment. Planting density had no significant effects on emission rate of soil nitrous oxide (N₂O). Both the ring-barking and stem-severing treatments decreased the root biomass, root length, root surface and root TNC content in both single-plant/pot and 3-plants/pot treatments. Both the ring-barking and stem-severing treatments increased the content of nitrogen in soil and roots, the content of soil microbial biomass nitrogen (SMBN), and emission rate of soil N₂O, but decreased the content of soil microbial biomass carbon (SMBC), the richness of soil microbial and the emission rate of soil CO₂. Root biomass input and photosynthetic carbon supply have significant effect on soil bacterial and fungal contents. Soil bacterial contents were positively correlated with root biomass, SMBC and SMBN. Soil fungal content was negatively correlated with soil temperature, positively correlated with root biomass, SMBC and SMBN. Correlation analysis showed that soil CO₂ emission flux was positively correlated with soil temperature, soil humidity and root biomass, while negatively correlated with soil nitrate nitrogen; soil N₂O emission flux was positively correlated with soil temperature and soil humidity. The results suggest that root input and photosynthetic carbon supply work together to change soil physical and chemical properties and microbial environment, thus contribute to changes in the emissions rate of soil greenhouse gases.