Effects of nitrogen and phosphorus addition on soil microbial community in a secondary tropical forest of China

Nutrient availability greatly regulates soil microbial processes and functions in tropical forests. However, few studies have explored the impacts of nitrogen (N) addition (100 kg P ha(-1) year(-1)), phosphorus (P) addition (100 kg N ha(-1) year(-1)), and N x P interaction on soil microbial biomass and microbial community composition in tropical forests. We established a field nutrient manipulation experiment in a secondary tropical forest of South China. Soil physicochemical properties and microbial community composition were measured. Analysis of phospholipid fatty acids (PLFAs) was used to determine soil microbial biomass and composition, and both were related to environmental factors by the redundancy analysis (RDA) and principal response curves (PRC). We demonstrated that N addition usually did not affect microbial biomass, which was increased by P addition over 3 years of fertilization. Nitrogen addition decreased soil bacterial biomass but did not affect soil fungal biomass after 3 years of fertilization. After P addition, soil fungal biomass increased faster than soil bacterial biomass, indicating a more sensitive response of soil fungi to P addition than bacteria. Phosphorus addition increased fungi/bacteria ratio (F/B) ratios after 3 years of fertilization. Both N and P additions had different effects on soil microbial community in this tropical forest and, thus, probably altered ecosystem functioning.