Effects of Nitrogen Addition on Rhizosphere Soil Microbial Community and Yield of Wheat in Loess Plateau

The soil microbial community diversity of wheat rhizosphere was affected by the amount of nitrogen fertilizer. In addition to bacterial community, ammonia-oxidizing archaea, nitrogen-fixing bacteria and denitrifying bacteria also play important roles in nitrogen cycle. At present, the microecological mechanism of its response to nitrogen application is still unclear. In this study, the rhizosphere soil microorganisms of winter wheat were used as the research object. The changes of soil bacteria, ammonia-oxidizing archaea, nitrogen-fixing bacteria and denitrifying bacteria communities under five nitrogen rates of 0—N(0), 90—N(6), 180—N(12), 240—N(16), 300—N(20) kg N ha –2 were studied by high-throughput sequencing technology. Under N(12) treatment, the Alpha diversity index of bacteria, AOA and nifH nitrogen-fixing bacteria and the Shannon and Simpson indices of nirK denitrifying bacteria were significantly increased. N(12) treatment significantly increased the relative abundance of Proteobacteria, but no significant difference was found at the nifH and nirK bacterial phyla levels. Under the high nitrogen treatment of N(16) and N(20), the dominant bacteria of nirK -type denitrifying bacteria increased significantly compared with N(12) treatment, there was no significant difference in microbial community distribution between N(20) and the control group. Therefore, the nitrogen addition under N(12) treatment was most conducive to the absorption and utilization of nitrogen fertilizer by soil microorganisms. The effect of nitrogen addition on microbial community was weaker than that of soil properties and wheat yield, and nitrogen addition was significantly correlated with yield, reaching the highest yield at 300 kg ha –2 .