Abstract: Soil nutrient cycling is of great significance to the maintenance of forest ecosystem stability, selection and renewal of tree species, and forest sustainable management. Learning the sources and processes of nutrient inputs can facilitate the analysis of matter cycling and energy flow and the evaluation of ecosystem functions. Leaf litter, root turnover, and root exudates are the main sources of nutrients in forest soils and important components of soil nutrient cycling. In this paper, the three major nutrient input processes and their influencing factors were analyzed. The effects of litter composition and physicochemical properties, biotic factors, and environmental factors on litter decomposition and soil nutrient cycling were summarized. The effects of fine root substrate properties, tree species composition, soil biology, and environmental factor changes on fine root turnover and soil nutrient cycling were reviewed. The role of root exudates in the soil nutrient cycling process was explored. Finally, important directions that need urgent research in this filed are proposed to provide reference for related research and nutrient management of forest ecosystems.

Key words: Gap, Disturbance status, Southeast Tibet, Fir forest