Biochar alleviates apple replant disease by reducing the growth of Fusarium oxysporum and regulating microbial communities

Apple replant disease (ARD) negatively affects plant growth and reduces yields in replanted orchards. In this study, biochar was applied to apple replant soil with Fusarium oxysporum. Our aim was to investigate whether biochar could promote plant growth and alleviate apple replant disease by reducing the growth of harmful soil microorganisms, changing soil microbial community structure and improving the soil environment. This experiment included five treatments: apple replant soil (CK), methyl bromide fumigation apple replant soil (FM), replant soil with biochar addition (2%), replant soil with F. oxysporum spore solution (8 x 107 spores $ mL-1), and replant soil with biochar and F. oxysporum spore solution addition. Seedling biomass, the activity of antioxidant enzymes in the leaves and roots, and soil environmental variables were measured. Microbial community composition and community structure were analyzed using 16S rDNA and ITS2 gene sequencing. Biochar significantly reduced the abundance of F. oxysporum and increased soil microbial diversity and richness. Biochar also increased the soil enzyme activities (urease, invertase, neutral phosphatase, and catalase), the biomass (plant height, fresh weight, dry weight) and the activity of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase). The root indexes of apple seedlings was also increased in replant soil by biochar. In sum, biochar promoted the growth of plants, improved the replant soil environment, and alleviated apple replant disease.