Abstract: In order to explore the effects of different continuous cropping years on soil microbial flora in the tobacco rhizosphere,the effects of two,four and six years of continuous cropping on soil microbial quantity,community structure and diversity in the tobacco rhizosphere were analyzed by the sequencing of gene diversity.The results showed that the number of culturable bacteria and actinomycetes in rhizosphere soil decreased and the number of fungi increased with the increase of continuous cropping years of tobacco.The results of gene sequencing showed that the diversity of the microbial community decreased gradually with the increase of continuous cropping years,and the community structure changed.The structure of the bacterial community in rhizosphere soil differed greatly under vigorous and long-term no-cropping years,and the structure of the fungal community also differed before and during vigorous and long-term transplantation.The relative abundances of microbial species may be responsible for the differences in fungal community structure between different cropping years.The species of the dominant genus of the bacterial community in the rhizosphere soil of the tobacco field changed little during different continuous cropping years,while the species of the dominant genus of the fungal community changed greatly.The results showed the enrichment of pathogenic microorganisms and the decrease of beneficial microorganisms in rhizosphere soil with the increase of continuous cropping years.

Key words: Continuous cropping;Tobacco;Rhizosphere soil;Microbial diversity;Microbial community structure