Abstract: The aim of this study was to clarify soil bacterial diversity and community structure in cold temperate forest ecosystem and their response to soil physicochemical properties. The root associatedbacterial community structure and diversity in the rhizosphere of Betula platyphylla, Pinus sylvestrisvar.mongolica, Larix gmelinii and Pinus pumilain Genhe were investigated with Illumina highthroughput sequencing technology. The key environmental factors affecting the bacterial community structure were analyzed. The results showed that bacteria in the rootassociated soil of four tree species from 20 phyla, 63 classes, 127 orders, 225 families, and 371 genera were detected. There were 10 bacterial phyla with relative abundance greater than 1.0%. Proteobacteria, Acidobacteria and Actinobacteria were the predominant bacteria, with a total relative abundance of more than 75.0%. The richness and evenness of rootassociated bacteria of P. sylvestris var.mongolica were  the highest. Results of Pearson correlation analysis showed that bacterial diversity and abundance were significantly affected by soil physicochemical properties. RDA was used to analyze the contribution rates of soil physicochemical factors to the formation of bacterial community structure. All the factors explained 94.0% of bacterial community variation. Among them, pH had an extremely significant effect on the distribution of bacteria, with an explanation degree of 70.1% (P<0.01), followed by nitrate concentration, with an explanation degree of 6.9% (P<0.05). Our results provide a basis for understanding the structure and function of soil microorganisms in the cold temperate forest.

Key words: bacteria, community structure, soil physicochemical properties, high-throughput sequencing.