Soil Bacterial Community Response to Short-Term Manipulation of the Nitrogen Deposition Form and Dose in a Chinese Fir Plantation in Southern China

The changes of soil bacterial biomass and community composition were monitored in a simulated nitrogen (N) deposition experiment during 4 years of Cunninghamia lanceolata growth in a plantation site in southern China. The experimental design included two N forms (NH4Cl and KNO3) and five levels of N deposition (0, 20, 40, 60, 80 kg N ha(-1)) for 2 years. Research into the bacterial population was conducted using plate count, phospholipid fatty acid (PLFA) composition, and 16Sr DNA gene-based high-throughput pyrosequencing methods. The results of plate count and PLFA analysis indicated that ammonium (NH4+) addition increased bacterial number and biomass, whereas nitrate (NO3-) addition decreased these values. The high-throughput sequencing showed that N deposition of the two N forms inhibited the growth of bacteria compared with control plots, and the changing trend was related to the NH4+-N/NO3--N ratio of soil. When the N deposition dose exceeded 20 kg N ha(-1), there was a significant effect on cultured bacteria counts and bacterial biomass. When examining the bacterial community, we observed 22 bacterial phyla of which Proteobacteria, Acidobacteria, and Actinobacteria were dominant. Acidobacteria abundance was higher in NH4+ treatments than NO3- treatments. When the rates of NH4+ deposition increased, Acidobacteria abundance decreased; however, it showed a positive correlation in NO3- treatments. The bacterial cluster structures were significantly different between different N addition rates in the NO3--treated plots. This research will provide data support to addressing the negative influences of nitrogen deposition and provide reference for soil management.