Abstract: Litter decomposition in urban forests may be influenced by the elevated nitrogen (N) deposition and phosphorus (P) enrichment during rapid urbanization. In this paper, nylon litter bag method was used to simulated  the effects of  N deposition (10 g N·m^-2·a^-1, ［N］), P enrichment (2.5 g P·m^-2·a^-1, ［P］), and their combination (10 g N·m^-2·a^-1+2.5 g P·m^-2·a^-1, ［N+P］) on the decomposition rate, nutrient contents, and nutrient stoichiometric ratios of the litters in a Pinus elliottii Engelm. plantation in the suburb of Nanchang City, China. Compared with CK (without N and P addition), treatments ［N］, ［P］, and ［N+P］ increased the decomposition rate of the litters at early stage (0-180 d), but decreased it at the middle (180-360 d) and late (360-540 d) stages. By the end of the experiment (540 d), the decomposition rate in treatments ［N］, ［P］, and CK had no significant difference, but was higher than that in treatment ［N+P］ (P<0.05). Treatment ［N］ increased the litter N content, with the N immobilized at early stage but released later. Treatment ［P］ increased the litter P content, resulting in an increasing enrichment of P. Treatment［N+P］ increased the litter N and P contents, which were immobilized at early stage but released later. In all treatments, the litter C content showed a releasing trend. The relationships between the decomposition rate and the stoichiometric ratios of C, N, and P depended on decomposition stage. Our results suggested that the additive effect of elevated N deposition and P enrichment induced by urbanization could limit litter decomposition in urban forests.

Key words: River continuum concept, Ecosystem services, Ecosystem health, Ecosystem management, Watershed ecology