Effects of nitrogen addition on litter decomposition and nutrient release in typical broadleaf-Korean pine mixed forest

A two-year field experiment was conducted in a typical broadleaf-Korean pine mixed forest in Xiaoxing'an Mountains, northeastern China, to explore the short-term effects of nitrogen (N) addition on litter decomposition and nutrient dynamics of Pinus koraiensis, Betula costata, Fraxinus mandshurica and the mixture of above species, using a litterbag method. Four levels of N addition were control (N0, 0 kg/(ha·a), low N (N1, 30 kg/(ha·a), medium N (N2, 60 kg/(ha·a) and high N (N3, 120 kg/(ha·a). N addition accelerated the decomposition rate of mixed leaf litter significantly (P0.05). The decomposition remaining rate of leaf litter had a significantly negative correlation with N concentration of substrate and a significantly positive correlation with C concentration and C/N ratio of the substrate. For all four leaf litter types, N addition increased the N concentration, and the interaction between time and N treatments influenced significantly phosphorus (P) concentration. N addition promoted N and P release of F. mandshurica leaf litter, but inhibited the release of the other three leaf litter types. N3 treatment inhibited carbon (C) release in P. koraiensis leaf litter and accelerated that in F. mandshurica leaf litter, while N1 treatment accelerated C release in F. mandshurica and mixed leaf litter. We suggest that N addition affects nutrient release patterns of leaf litter and has a significant influence in regulating carbon and nutrient cycling in forest ecosystem.