The Impacts Of Green Manure-Tobacco Crop Rotation On Diversity Of Soil Bacteria And Disease Occurrence Of Tobacco Bacterial Wilt

Tobacco is one of the main cash crop in China, and XiangXi was the main produced-area of Hunan Tobacco industry. Currently, Continuous cropping obstacles has gradually become a heated issue in tobacco farmlands of XiangXi. Green manure could improve soil nutrients and crop production, playing a significant role in sustainable agriculture. However, the impacts of green manure on crop health and the roles soil bacterial communities play in the process haven't been clarified clearly yet. In this study, we investigated soil bacterial community composition and structure in four tobacco farmlands, which were treated with different green manure(control, ryegrass, pea and rape), using 16S rRNA gene amplicons sequencing. Results showed that green manure had significant impacts on soil properties, bacterial communities and tobacco health.First, soil total C and N content increased significantly in groups treated with green manure than control, the improve of total nitrogen content was most noticeable in ryegrass group, while the improve of total carbon content was most noticeable in pea group. Meanwhile, geochemical properties of soil such as Fe, Zn and Co content shows no difference in four groups, but the content of Ca increased significantly in groups treated with green manure especially in ryegrass group. All soil samples were acidic with pH and higher in Rape and lower in Control and Ryegrass. Water content (17%)was significantly (p< 0.05) higher in Control.Second, to evaluate the difference of these bacterial communities in structure generally, we conducted dissimilarity test and DCA. Dissimilarity test showed that bacterial communities were significantly (p< 0.01) different among four groups. Similar results can also be seen from DCA graph. Fertilization of green manure had significant impacts on soil bacterial community composition and structure. At the phylum level, Proteobacteria, Actinobacteria were more abundant in Control; Crenarchaeota was more abundant in Rape; Acidobacteria was more abundant in Pea and had the fewest reads in Control; And soil community diversity was significantly higher in groups treated with green manure.Third, green manure especially ryegrass, decreased tobacco disease (bacterial wilt) rate dramatically, and the process might be mediated by soil bacterial communities. On the one hand, several bacterial populations were found to be potentially disease inducible or suppressive. For example, the abundances of Dokdonella and Rhodanobacter were positively correlated to tobacco disease rate, while Acidobacteira_Gp4 and Gp6 had negative correlations with tobacco disease. On the other hand, soil bacterial communities were shaped by soil properties (e.g., pH, C and N content).