Effects of combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers on tobacco bacterial wilt and soil microbial community

【Objective】This study aimed to investigate effects of combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers on tobacco bacterial wilt and soil microbial community， and to provide a theoretical basis for tobacco bacterial wilt control and appropriate fertilizer application.【Method】Field plots with record of tobacco bacterial wilt was selected to conduct organic fertilization experiment of combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers. Treatments included a conventional fertilization control （ZN0） and three combined applications of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers： 20% nitrogen reduction （ZN1）， 25% nitrogen reduction （ZN2）， and 30% nitrogen reduction （ZN3）. Rhizosphere soil physiochemical properties and enzyme activities were determined， and soil microbial community structures were analyzed based on 16S rDNA and ITS sequencing. In addition， the incidence and disease index of tobacco bacterial wilt were investigated， and key microbial genera associated with disease occurrence were identified.【Result】Combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers could improve soil nutrient supply and soil microbial community structures， thereby decreasing disease severity. The ZN3 treatment showed the best effects： compared with the control， the disease index of tobacco bacterial wilt decreased by 5.29%； contents of organic matter and available nitrogen in tobacco rhizosphere soil significantly increased by 8.57% and 19.37% （P<0.05， the same below）； activities of soil urease and acid phosphatase increased significantly by 7.57% and 68.54%， respectively； and catalase activity significantly decreased by 36.25%； relative abundances of Acidobacteriota， Basidiomycota， Mucoromycota， Mortierellomycota， Sphingomonas， Bryobacter， and Mortierella were increased. Furthermore， soil pH and organic matter were identified as the main driving factors shaping the soil microbial community after treatments of combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers， and they also reduced the enrichment of Bacillus and Fusarium.【Conclusion】The combined application of nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers mitigates tobacco bacterial wilt by improving rhizosphere soil nutrient status， regulating the soil microenvironment， and reshaping the soil microbial community structure. A combined application of 30% nitrogen-reduced chemical fertilizers and biochar-based organic fertilizers could reduce the incidence and severity of tobacco bacterial wilt.