Effects of different nitrogen form ratios on the occurrence of tobacco bacterial wilt and soil bacterial community

【Objective】The purpose of the study was to explore the relationship between different nitrogen form ratios and the occurrence of tobacco bacterial wilt, the physical and chemical properties of tobacco rhizosphere soil and soil bacterial communities, and to screen out the key microorganisms and soil factors, so as to provide theoretical basis for the prevention and control of tobacco bacterial wilt and the rational application of nitrogen fertilizers.【Method】Using plots with severe occurrence of tobacco bacterial wilt in previous years as experimental plots, five different nitrogen form ratios and conventional control(CK) treatments were designed to investigate the occurrence of tobacco bacterial wilt in different treatments with different nitrate nitrogen and ammonium nitrogen ratios. The physical and chemical properties of the rhizosphere soil were determined by collecting the rhizosphere soil of tobacco plants treated with different nitrate nitrogen and ammonium nitrogen ratios.Using 16S rDNA sequencing technology, the differences in the occurrence of tobacco bacterial wilt and the bacterial community structure in rhizosphere soil under different nitrate nitrogen and ammonium nitrogen ratios were investigated.【Result】Compared with CK treatment, when nitrate nitrogen and ammonium nitrogen were applied in combination at a ratio of 1∶1, the morbidity and disease index of tobacco bacterial wilt were effectively reduced, and the SPAD value of tobacco leaf was increased. When nitrate nitrogen and ammonium nitrogen were applied in combination at a ratio of 7∶3, the abundance and evenness of soil bacterial community were increased. The results of PCoA analysis indicated that different nitrogen form ratios had significant effects on soil bacterial communities(P<0.05, the same below). At the phyla classification level, Proteobacteria and Acidobacteria were the most dominant soil bacteria phyla. At the genus classification level, Bacillus was the most dominant genus of soil bacteria, followed by Sphingomonas., Candidatus_ Udaeobacter, Bryobacter and Flavobacterium. The results of redundancy analysis(RDA) and Pearson analysis indicated that soil organic matter(SOM), available potassium(AK), and nitrate nitrogen(NO-N) were the main physical and chemical factors affecting the occurrence of changes in soil bacterial communities.【Conclusion】Different nitrogen form ratios can affect the occurrence of tobacco bacterial wilt, as well as the diversity and species composition of soil bacterial communities. The ratio of nitrate nitrogen to ammonium nitrogenat 1∶1 is the optimal treatment, which can effectively reduce the morbidity and disease index of tobacco bacterial wilt and increase the relative abundance of Bacillus and Flavobacterium in the soil. Properly increasing the proportion of nitrate nitrogen is beneficial for the construction of soil healthy microecology.