Nitrogen and phosphorus co-addition stimulates soil respiration in a subtropical evergreen broad-leaved forest

Background and aims Nutrient availability is a key regulator of soil respiration. Anthropogenic activities have dramatically accelerated the inputs of reactive nitrogen (N) and phosphorous (P) and increased the availability of N and P in soils. However, many previous studies of soil respiration have focused more on the effects of N, and less on the effects of P and its interaction with N. Therefore, the objective here was to examine the roles of N availability, P availability and their interaction in determining soil respiration. Methods A manipulative N addition (100 kg N ha(-1) year(-1)), P addition (50 kg P ha(-1) year(-1)) and NP co-addition (100 kg N ha(-1) year(-1) + 50 kg P ha(-1) year(-1)) experiment was conducted in a subtropical forest in Southwest China. N and P inputs were added monthly beginning in October 2017. The soil respiration rate was measured monthly from March 2018 to February 2019, and soil properties, microbial biomass carbon (MBC), and fine root biomass were measured in July 2018 and January 2019. Results The soil respiration rate in the control (without fertilizer added) treatment was 13.5% higher than that in the N treatment but 1.6% and 34.7% lower than those in the P treatment and NP treatment, respectively. Soil respiration was closely associated with soil temperature and soil moisture, and soil temperature played a more important role in regulating soil respiration than did soil moisture. The temperature sensitivity of respiration (Q10 values) in the CT, N, P and NP treatments did not differ significantly. Path analysis showed that nutrient additions changed soil respiration by regulating the MBC and fine root biomass. Conclusions Our results highlight the divergent effects of N addition and NP co-addition on soil respiration. Ongoing N and P inputs may increase soil respiration by stimulating soil microbial and plant root activities in the subtropical evergreen broad-leaved forests of Southwest China.