Abstract: In this paper traditional bacterial isolation and culture techniques, combined with 16S rDNA sequence analysis, were used to investigate diversity of community structure and seasonal dynamics of endophytic bacteria in cortex tissues of Populus tomentosa and P. ×euramericana cv. Robusta 94. A total of 532 isolates were obtained from the two poplars and their 16S rDNAs were sequenced and analyzed. Results showed that the isolates were classified into 26 genera and 47 species. There was difference in the isolate composition between two poplars. The number of bacteria genera and species isolated from P. tomentosa and P. × euramericana cv. Robusta 94 was much different. There were 18 genera and 30 species isolated from P. tomentosa, and Rhizobium and Bacillus were the most predominant, while there were 16 genera and 22 species from P. × euramericana cv. Robusta 94, Rhizobium and Microbacterium were the most widely distributed and predominant. The results indicated that the community structure of plant endophytic bacteria was diverse in the poplars. The seasonal variation in the number of bacterial isolates from the two poplars exhibited that endophytic bacteria isolated in summer and autumn were more than in winter and spring. The dominant species of the bacterial communities changed significantly with the seasonal fluctuation.

Key words: poplar, endophytic bacteria, seasonal fluctuation, diversity, 16S rDNA, phylogenetic diversity