Abstract: The distribution of soil microbial diversity and its influencing factors have attracted much attention. Many studies at large spatial scales including global, continental, or national levels, have found that climate and soil properties are the main influencing factors. However, the distribution characteristics and influencing factors of soil bacterial diversity at medium and small spatial scales such as the county scale still need to be further clarified. To address this issue, 98 soil samples were collected from Youyi County, located in the Sanjiang Plain, Heilongjiang Province, China, and high-throughput sequencing and bioinformatics were performed to quantify bacterial diversity. Results showed that soil physicochemical properties and bacterial community composition differed significantly between paddy field and dryland, with soil bacterial α diversity being significantly higher in paddy field than in dryland. Soil pH, organic matter, total nitrogen, and total potassium were the main factors influencing soil bacterial α diversity and the relative abundance of dominant phyla in cultivated land. Soil bacterial community structures were also significantly different between paddy filed and dryland. Results of the Mantel test showed that soil bacterial community structure was primarily affected by soil pH and fertility factors, and as well as by geographic distance. When paddy field or dryland was considered separately, soil total phosphorus did not affect bacterial community structure in paddy field, and soil total phosphorus and geographic distance had no significant effects in dryland either. Empirical Bayesian kriging interpolation results showed that soil bacterial α diversity was higher in the northeast than in the southwest of the study area. In summary, land use and soil properties are the main factors affecting soil bacterial diversity and community structure at county level. The overall distribution trend of bacterial diversity in the study area is high in the northeast and low in the southwest. Our results would provide reference for soil health assessment of cultivated land at the county scale.

Key words: medium and small spatial scales, soil bacterial diversity, land use, distribution characteristics, influencing factor