Abstract: In this paper plate isolation method,combined with 16S rDNA sequence analysis,were used to investigate the diversity and community structure of rhizosphere nitrogen-fixing bacteria isolated from Larix gmelinii in Arxan National Forest Park.A total of 28 isolates were obtained from L.gmelinii rhizosphere soil and their 16s rDNAs were sequenced and analyzed.The isolates were classified into 10 genera and 18 species.The genera isolated included Pseudomonas,Serratia,Burkholderia,Rhizobium,Phyllobacterium,Paenibacillus,Bacillus,Rhodococcus,Curtobacterium and Arthrobacter,with Pseu- domonas,Phyllobacterium,Arthrobacter are dominant groups.The results showed the community structure and diversity of nitrogen-fixing bacteria in the rhizosphere soil of L.gmelinii in Arxan National Forest Park.

Key words: Arxan;Larixgmelinii;Nitrogen-fixing bacteria;16S rDNA