Fine root decomposition is the main source of soil organic matter and soil nutrients in grasslands. Fine root decomposition dynamics under the background of global nitrogen deposition plays an important role in carbon and nutrient cycling of terrestrial ecosystem. In this study

buried bag experiment was used to investigate fine root decomposition rate and nutrient release characteristics of three dominant grass species on the Loess Plateau

and their response to nitrogen deposition (10 g N /m2/a). The results showed that the decomposition process of fine roots could be divided into rapid (0~60 d) and slow (60~719 d) decomposition stages. The root mass residual rates of Stipa grandis

Stipa przewalskyi and Artemisia sacrorum were 86.3%

86.2% and 90.7% on the 60th day

respectively

and they were 58.1%

64.7% and 70.5% on the 719th day

respectively

indicating that the fine roots decomposition of S. grandis was the fastest and it of A. sacrorum was the lowest. Correlation analyses showed that the decomposition constant of fine roots was positively related with nitrogen content and N/P ratio

and negatively correlated with the carbon content and C /N ratio. During the fine root decomposition

the carbon transfer models of the three species were all direct releasing

and the nitrogen transfer models were enriching

and phosphorus exhibited enriching-releasing model

and all of them tended to decrease generally. Simulated nitrogen deposition suppressed the fine root decomposition rates of S. grandis

S. przewalskyi and A. sacrorum

with the decomposition constants decreased by 21.3%

26.8% and 47.4%

respectively. While

it increased the carbon remaining rates of S. grandis

S. przewalskyi and A. sacrorum by 26.8%

20.7% and 16.6%

respectively

and increased nitrogen remaining rates by 18.2%

17.0% and 13.4% at the end of our study period. However

phosphorus remaining rates of fine roots in all three species were not significantly influenced by simulated nitrogen deposition. Nitrogen deposition in the future will inhibit the fine roots decomposition rates of the three dominant species in fenced grassland on the Loess Plateau

and slow down the process of inputting carbon and nitrogen from plant into soil.