Differential response of soil respiration to nitrogen and phosphorus addition in a highly phosphorus-limited subtropical forest, China

Understanding feedback between terrestrial carbon (C) cycle and climate change is linked to the effects of nitrogen (N) and phosphorus (P) on soil respiration (Rs). However, the individual and interactive effects of N and P additions on soil respiration and its components (autotrophic [Ra] and heterotrophic respiration [Rh]) are not fully understood, especially in highly P limited subtropical forests. In this study, both field experiment and laboratory incubation (at 15 °C and 25 °C temperatures) were undertaken to examine the effects of N, P and N + P additions on Rs and Rh. Our results showed that N addition significantly increased Rs by 21.09%, but P and N + P additions exhibited no effects on Rs under field conditions. Under laboratory condition, N addition significantly suppressed Rh whereas P and N + P additions increased Rh compared with control. Meanwhile, N and P additions exhibited an antagonistic interaction on Rs, but N and P additions synergistically affected Rh under laboratory incubations at both incubation temperatures of 15 °C and 25 °C. Cumulative Rh was negatively correlated with fine root biomass, but was positively correlated with microbial biomass carbon regardless of incubation temperatures. Our findings indicated that both individual and interactive effects of N and P additions on Rs and Rh were required to be considered to improve prediction of N and P effects on forest C dynamics in the highly P limited subtropical forests.