Abstract: Under constant anthropogenic disturbance, it is critical to understand the response of wetlands to nitrogen (N) and phosphorus (P) addition for protecting and maintaining wetland ecosystem functions. To evaluate the effects of N and P addition on soil nutrients and plant biomass in wetlands, a field experiment was conducted in a typical Carex wetland from the Poyang Lake Nanji National Nature Reserve. There were seven treatments: control, three levels of N addition (5, 10 and 30 g N·m^-2·a^-1), and three levels of P addition (0.6, 1.2 and 3.0 g P·m^-2·a^-1). The results showed that N and P addition significantly increased soil total and available N and P concentrations. Both the above and below ground biomass of Carex community significantly increased with increasing N and P addition levels. The effects of N and P addition on the root/shoot ratios ofCarex community were different, in that N addition reduced but P addition increased the root/shoot ratios. Both total and available contents of the corresponding added elements in soils were closely related to plant biomass. Overall, soils and plants in the Poyang Lake wetlands were relatively sensitive to N and P inputs.

Key words: nitrogen addition, phosphorus addition, soil nutrient, biomass, Poyang Lake.