Responses of Soil Acid Phosphomonoesterase Activity to Simulated Nitrogen Deposition in Three Forests of Subtropical China

Soil acid phosphomonoesterase activity (APA) plays a vital role in controlling phosphorus (P) cycling and reflecting the current degree of P limitation. Responses of soil APA to elevating nitrogen (N) deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems. A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China. The three forests include a Masson pine (Pinus massoniana) forest (MPF)-pioneer community, a coniferous and broad-leaved mixed forest (MF)-transition community and a monsoon evergreen broad-leaved forest (MEBF)-climax community. Four N treatments were designed for MEBF: control (without N added), low-N (50 kg N ha-1 year-1), and medium-N (100 kg N ha-1 year-1) and high-N (150 kg N ha-1 year-1), and only three N treatments (i.e., control, low-N, medium-N) were established for MPF and MF. Results showed that soil APA was highest in MEBF, followed by MPF and MF. Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments. However, soil APA in MEBF exhibited negative responses to high N additions, indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem. Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.