Effects Of Continuous Cropping On Bacterial Community And Diversity In Tobacco Rhizospheric Soil

Tobacco(Nicotina Tabacum l.)is not only one of most important economic crops around the world,but also as a laboratory model plant play an important role in life science community,modern molecular biology arears and genetic breeding areas.Along with the decrease of tobacco planting area,it has become a common planting mode for tobacco.Tobacco is the crops avoiding continuous cropping,and long-term continuous cropping will result in deterioration of tobacco quality,decline in yield and aggravation of disease.The existing researches always focus on the relationship between abiotic factors such as soil PH,organic matter content,NPK content and continuous cropping.Few research study the variation of microbial community structure and diversity under the condition of continuous cropping tobacco soil.In this study,plot of tobacco for one year and the plot of tobacco for more than 10 years were studied.Illumina Miseq platform were used to study the change of the microorganism of the two groups of soil.The indexes of Shannon,Chao1,Ace and Simpson were used to evaluate the alpha diversity of soil microorganism.And the beta diversity were assessed by principal component analysis.By blasting with the Greengens database,the bacterial communities were classified form phylum level to specie level.We also used the PICRUSt software to predict the gene functions.The result as follows:After quality controlling,478,192 high quality reads were obtained from the 8 soil samples.Sequences with a similarity of more than 97 percent are defined as an operational taxonomic unit,namely OTU.Finally,46,522 OTUs were obtained.By blasting with the database,OTUs could be classified into seven categories: phylum,class,order,family,genus and species,the number and proportions are 30035(100%),29797(99.21%),25105(83.59%),11427(38.05%),2563(8.53%),342(1.14%),respectively..The bacterial community were classified from phylum level to genus level.The dominant bacterial communities in the phylum level were Acidobacteria,Proteobacteria,Chloroflexi,Firmicutes and Bacteroidetes.And the dominant bacterial communities in the genus level were Lactococcus,Corynebacterium,Neisseria,Rhodoplanes and Streptococcus.Analyzing the low abundance of genus showed that the relative abundance of pathogenic bacterium such as Fusarium and Mycetes increased,meanwhile the relative abundance of beneficial microbial communities such as Arthrobacter and Lysobacter reduced.Compared with the plot with no continuous cropping,the alpha diversity of the continuous cropping plot reduced.Within the four alpha diversity indexes,Shannon index reduced more significantly than others which indicated that Shannon can be an indicator for alpha diversity.PICRUSt was used to predict the gene function,the results showed that tobacco continuous cropping could change the function of soil microbial community and develop the pathogenic direction.The main difference of orthologous genes were glutathione Stransferase gene,beta-galactosidase and homoserine kinase,and the main KEGG pathway were amino sugar and nucleotide sugar metabolism pathway,membrane and intracellular structural molecules pathway and replication,recombination and repair proteins pathway.The enrichment of replication,recombination and repair proteins pathway may involve in the aggravation of tobacco target spot disease.And the increased glutathione metabolic pathway may be associated with increased of tobacco mosaic.