Enhanced sequestration of plant-carbon (C) inputs to soil may alleviate rising atmospheric C02 concentrations and related climate change but how this sequestration will respond to anthropogenic nitrogen (N) and phosphorous (P) deposition is uncertain. We conducted a 2 year field manipulative experiment of N and P addition in two tropical mountain rainforests in China. The objectives of the study were to test the following hypotheses: (1) soil respiration would be stimulated by P treatment and N+P treatment due to P-poor tropical soil; (2) N and P additions would alter the temperature sensitivity of soil respiration, basal soil respiration and the contributions of different components to total soil respiration; (3) Primary forest and secondary forest would have different responses of soil respiration to N treatment. Our results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the wet season and the lowest rates in the dry season. Soil respiration rates showed a significant positive relationship with soil temperature, whereas soil moisture only affected soil respiration at dry season. In the control plots, annual accumulative soil respiration in primary forest (15.6-16.4 MgC ha-l yr-1) was significantly higher than that of secondary forest (14.1-15.0 Mg C ha-l yr-1). Annual mean soil respiration rate in the primary rainforest was 32-38% higher in N+P plots and 12-18% higher in P plots than in the control plots, and the differences between the control and N treatment did not differ significantly. In secondary rainforest, annual mean soil respiration rate was 28-32% higher in N+P plots, 14-15% higher in N plots and 7% higher in P plots than in the control plots. In the primary forest, N and P additions increased the attribution of autotrophic respiration to total soil respiration. and decreased the proportion of litter respiration to total soil respiration; however, N and P additions increased the attribution of heterotrophic respiration or litter respiration to total soil respiration in the secondary forest. N and P additions in both forests decreased the temperature sensitivity of soil respiration, and increased basal soil respiration. Our results suggest that N and P addition drove substantial soil C02 losses to the atmosphere in the tropical mountain rainforests, but the increasing trends may depend on the rate and duration of N deposition and P addition. Figure :Comparisons of mean soil respiration rate among N and P treatments in tropical mountain rainforests. Bars indicate±1SE. N=3.Different stars denote significant difference(P < 0.05) between control plots and fertilization treatments plots.