The response of tree growth to nitrogen and phosphorus additions in a tropical montane rainforest.

Rapid increase of global nitrogen (N) deposition has greatly altered carbon cycles and functioning of forest ecosystems. Previous studies have focused on changes in carbon dynamics of temperate and subtropical forests through N enrichment experiments; however, the effects of N deposition on tree growth remain inconsistent, especially in tropical forests. Here, we conducted a five-year N addition experiment (0 and 50kgNhayr) in a tropical montane rain forest in Hainan Island, China, to explore the effects of enhanced N deposition on growth of trees. We also set phosphorus (P) treatment (50kgPhayr) and N+P treatment (50kgNhayr+50kgPhayr) to examine potential P limitation driven by N deposition. Our results showed that N addition has not significantly influenced tree growth, while P addition significantly increased the relative growth rate of small (diameter at breast height, DBH≤10cm) and medium (10