Nutrient addition affects the rate of cumulative CO2 emission,qCO2,SOM mineralization, and microbial biomass. Low nutrient input levels increased the decomposition rate, and cumulative C respired by respiration in paddy soil caused a positive PE owing to nutrient limitation that promoted microbial activity and qCO2. Conversely, because of decreasing microbial biomass and increased CUE (confirmed by the decreased qCO2), a negative PE was observed for high nutrient inputs.