Abstract: As one of the important processes of carbon(C) cycling in forest ecosystems, fine root litter decomposition is potentially affected by elevated atmospheric nitrogen(N) deposition. Since 2009, a five-year fine root decomposition experiment was conducted in long-term N addition plots using a litter bag method. The decomposition rates of fine roots were higher at the early stage and slower at the later stage of decomposition. Mass loss of fine roots was up to 30% 50% in the 516th day of decomposition, and the variation in the remaining mass was relatively stable in the later stage. In general, the asymptotic decomposition models provided the best prediction for fine root decomposition of the five species. Nitrogen addition had a stage-specific effect on fine root decomposition, which was promotion for the early stage while inhibition for the later. At the later stage, N addition slowed down decomposition rate of fine roots, which was partly due to the direct effect of increasing proportion of recalcitrant compounds, such as lignin, and the indirect effect of alteration in microbial activity was affected by N addition.

Key words: nitrogen deposition, temperate forest, fine root, litter decomposition