Effects of Biocontrol Agents Application on Soil Bacterial Community and the Quality of Tobacco.

In this study, to evaluate the effect of different biocontrol agents (BCAs) on the soil bacterial community, we investigated the effects of Bacillus amyloliquefaciens, synthetic bacterial community (Aspergillus niger:Bacillus subtilis:Bacillus licheniformis:Streptomyces microflavus = 3:3:3:1, SynCom), and BCAs combined with lime-nitrogen on soil bacterial community by utilizing 16S rRNA sequencing technology. The sequencing shows that BCAs application can improve the value of Shannon and Sobs index of bacterial community during tobacco rosette and vigorous growing period. With the growth of tobacco, the effect of BCAs on the composition and difference of soil bacterial community structure becomes more and more obvious. In terms of average relative richness, the top six phyla of soil bacterial community are Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, and Bacteroidetes. Bacillus amyloliquefaciens application can increase the relative richness of Proteobacteria and Bacteroidetes. And the combination between BCAs and lime-nitrogen can increase the relative richness of Gemmatimonadetes and Bacteroidetes. The SynCom also can increase the relative richness of Bacteroidetes, whereas it decreases the relative richness of Acidobacteria. Proteobacteria, Acidobacteria, Gemmatimonadetes, and Bacteroidetes showing an extremely significant correlation with pH and exchangeable magnesium (EMg). BCAs application can improve the tobacco yield, effective leaves, and reducing sugar content that also has extremely significant positive correlation with pH and EMg. In conclusion, the results of our field experiments clearly show that BCAs application can significantly affect the soil pH and EMg by changing most of the dominant soil bacterial species. The richness of Bacteroidetes can serve as an indicator of the changes in soil pH and EMg caused by BCAs application.