Abstract: [Objective] To investigate the characteristics of soil bacterial community structures in Inner Mongolia grasslands and identify key environmental drivers, providing a microbiological basis for grassland ecosystem conservation. [Methods] Along a west-to-east gradient of Inner Mongolia grasslands （desert steppe, meadow steppe, natural meadow, and artificial grassland）, eight representative sampling sites were selected: Urad Grassland in Bayannur City （BM）, Urad Grassland in Baotou City （BT）, Gegentala Grassland in Ulanqab City （WH）, Huitengxile Grassland in Ulanqab City （HT）, Ulanqab Grassland in Ulanqab City （WL）, Hulun Buir Grassland in Hulun Buir City （HM）, Horqin Grassland in Tongliao City （TL）, and the core forage planting area in Ar Horqin Banner, Chifeng City （CF）. Soil samples from these eight sites were collected from the 0-20 cm soil layer. Soil physicochemical properties were measured and soil bacterial community compositions were characterized using high-throughput sequencing. Distance based redundancy analysis （dbRDA） and FAPROTAX functional prediction were employed to examine the structure, functional characteristics, and relationships with environmental factors of soil bacterial communities across different grasslands. [Results] ①Soils in Inner Mongolia grasslands were generally alkaline （pH 7.65-10.13）; ②Proteobacteria, Bacteroidota, and Firmicutes were the three most abundant bacterial phyla, while Bacteroides, Rubrobacter, and Bacillus were the top three most abundant genera; ③dbRDA revealed that available phosphorus, organic matter, available potassium, pH, bulk density, total nitrogen, and total water-soluble salts were drivers of differences in bacterial community characteristics （cumulative explanation power：79.20%）; ④Ulanqab Grassland （WL） exhibited highest Shannon （10.41） and Chao1 （6 184.13） indices compared to other sites, with enrichment of Actinobacteria and Proteobacteria and higher predatory or ectoparasitic functional activity. The bacterial community composition of Urad Grassland （BM） was highly similar to that of WL （ANOVA, P>0.05）; ⑤ FAPROTAX functional predictions indicated significant chemoheterotrophic activity in Hulun Buir Grassland （HM）, the strongest aerobic chemoheterotrophic activity in Horqin Grassland （TL）, robust nitrogen cycling activity in the core forage planting area in Ar Horqin Banner （CF）, and the highest aerobic ammonia oxidation and nitrification activity in Gegentala Grassland （WH）. [Conclusion] The soil bacterial community structure and functions in Inner Mongolia grasslands exhibit significant spatial heterogeneity, with Ulanqab Grassland （WL） displaying the highest microbial diversity and functional complexity. Soil physicochemical factors, including available phosphorus, organic matter, available potassium, pH, bulk density, total nitrogen, and total water-soluble salts, are crucial in shaping bacterial community structure. These findings provide valuable data for understanding the ecological mechanisms of soil bacteria and supporting sustainable management of Inner Mongolia grasslands.

Key words: Inner Mongolia grasslands, microbial diversity, bacterial community structure, environmental driving factors, functional prediction