Difference in soil bacterial community composition depends on forest type rather than nitrogen and phosphorus additions in tropical montane rainforests

Rapid increase of nitrogen (N) deposition could alter nutrient availability, leading to changes in soil microbial processes and ecosystem carbon and nutrient cycling. However, the effects of N deposition on soil microbes remain elusive in the tropical rainforests in Asia. Here, we conducted a 3-year N addition experiment with four treatments (0, 20, 50, and 100 kg N ha−1 year−1) in a primary and secondary tropical montane forest in Hainan Island, China, to explore the effects of elevated N availability on soil microbial community composition. We also conducted a phosphorus (P) treatment (50 kg P ha−1 year−1) and a N + P treatment (50 kg N ha−1 year−1 + 50 kg P ha−1 year−1) to examine potential P limitation driven by N deposition in highly weathered tropical soils, using a bar-coded pyrosequencing technique. The composition of soil bacterial communities differed dramatically between the primary and secondary forests, but not significant dissimilarity among the fertilization treatments. The community composition, phylogenetic diversity and phylotype richness were significantly correlated with soil pH, total organic C (TOC), and total N (TN), respectively. There were significant differences between the primary and secondary forest in pH, TOC, and TN, but not among the fertilization treatments. These results suggest that differences in soil nutrient status between the primary and secondary forests due to different successional stages rather than chronic N fertilization may be the major factor affecting soil bacterial composition in the tropical montane rainforests.