It is unclear the mechanisms of nitrogen deposition to carbon sequestration and depletion in terrestrial ecosystem where restricted by nitrogen,especially lack of understanding on processes of soil organic carbon input,transformation and output.In this paper,newly research advances on the influence of extrinsic nitrogen(such as nitrogen deposition and adding nitrogen) on decomposition of litter and turnover of soil organic matter fractions are discussed.In addition,the different responses of soil respiration components(such as root respiration,microbial respiration of rhizodeposits and SOM decomposition) on nitrogen increase are also concerned.Furthermore,uncertainties and countermeasures and potential directions are pointed out in above three research fields.