Effect of exogenous nitrogen and phosphorus inputs on the microbe-soil interaction in the secondary Castanopsis sclerophylla forest in east China

Soil microbes play a key role in the formation and decomposition of organic materials and in the improvement of the ecological environment. Despite continuous increases in nitrogen (N) and phosphorus (P) inputs due to the atmospheric deposition or fertilization, the response of soil to exogenous inorganic nutrients inputs remains elusive. By a manipulative experiment we simulated N and P depositions in a subtropical secondary Castanopsis sclerophylla forest in east China over the period 2011-2015, to evaluate the impact of inorganic nutrient addition on soil bacterial communities. Four treatments were administered (control and nutrient-enrichment: N, P, and N+P), with N added at a total of 100 kg N ha-1 yr-1 in the form of NH4NO3, and P at 50 kg P ha-1 yr-1 in Ca(H2PO4)2, sprayed near the soil surface at the end of each trimester. Quantitative PCR technique and Illumina platform-based sequencing analysis of the V3-V4 16S rRNA gene region were performed on total DNA extracted from soil samples to characterize the soil bacterial community abundance and diversity. As Proteobacteria, Acidobacteria and Actinobacteria were the predominant phyla in all conditions, treatments did not alter the distribution of bacterial phyla, while their relative abundances responded differently to N, P additions. A GLMM analysis showed that N input significantly (P < 0.05) reduced the relative abundance of Acidobacteria (13.11%), Bacteroidetes (0.6%), Elusimicrobia (0.21%), Nitrospirae (0.1%) and TM6 (0.04%). Relative abundance after P treatment significantly (P < 0.01) decreased for Nitrospirae (0.07%), and pronounced interactive effects of N and P additions (N:P) were observed on phylum Nitrospirae (P < 0.01) and TM6 (P < 0.05). Moreover, redundancy analysis revealed that soil pH was closely related to the bacterial community (r2 = 0.622, P = 0.015). Our findings suggest that exogenous N and P inputs affected the relative abundances and caused compositional shifts in the local bacterial community that closely associated with soil pH, thus providing the evidence that microbe-soil interactions are influenced by N and P availability in subtropical forest ecosystem of east China.