Abstract: This research evaluated the responses of the soil bacterial community structure and diversity to different nitrogen (N) addition levels in Stipa baicalensis steppe. High-throughput sequencing technology was used to study the changes in soil under different N treatments (0, 15, 30, 50, 100, 150, 200, 300 kg N·ha^-1·yr^-1). Soil samples were collected from the 0-10 cm soil layer of the eight different N treatments. The Alpha diversity index of the bacterial community was highest in the mid-range of tested N treatments and lower at low and high N rates. There was no significant difference in Alpha diversity index between the seven N treatments and the control. The dominant bacterial phyla were Acidobacteria (19.01%-38.31%), Proteobacteria (6.64%-17.11%), Actinobacteria (5.07%-16.06%), Verrucomicrobia (3.57%-7.40%), Chloroflexi (3.38%-8.42%), Gemmatimonadetes (0.87%-1.81%). The relative abundance of the dominant bacteria and the structure of the soil bacterial community were both affected by the N addition level. The effect of high N addition on the soil bacterial community structure was greater than that of low N addition. A correlation analysis showed that the bacterial community structure was mainly influenced by the pH, nitrate nitrogen, ammonium nitrogen and total phosphorus levels, with pH being the factor most influencing community structure.

Key words: nitrogen addition, Stipa baicalensis steppe, bacterial community, diversity, high-throughput sequencing technology