Long-term phosphorus addition downregulates microbial investments on enzyme productions in a mature tropical forest

Purpose Phosphorus (P) addition could largely alter soil microbial activity. However, effects of long-term P addition on soil extracellular enzyme activity are not well understood in tropical forests. Materials and methods To address this question, we measured absolute activities (activity per unit of dry soil) and specific activities (activity per unit of microbial biomass carbon) of enzymes involved in carbon (C), nitrogen (N), and P cycling in a 10-year P addition experimental site in a tropical forest. Results and discussion Phosphorus addition decreased acid phosphatase absolute and specific activity by 37% and 47%, respectively. As to N-acquisition enzymes, P addition increased leucine amino peptidase absolute activity but decreased beta-1,4-N-acetylglucosaminidase absolute activity by 33%. Meanwhile, P addition had no effects on leucine amino peptidase specific activity but decreased beta-1,4-N-acetylglucosaminidase specific activity by 43%. Among C-acquisition enzymes, cellobiohydrolase, alpha-glucosidase, and beta-glycosidase absolute and specific activities showed no significant responses to P addition, while P addition decreased beta-xylosidase absolute and specific activity by 15% and 27% respectively. Phosphorus addition also decreased phenol oxidase absolute activity by 30% and peroxidase absolute activity by 29%. Conclusions These results suggest a strong P shortage for microorganisms and that P addition could decline microbial productions of enzymes in phosphorus-poor tropical forests. Results from this study emphasize again the important role of available P in tropical forests.