The application of biochar and plant‐growth‐promoting bacteria (PGPBs) in biocontrol soil‐borne pathogens has garnered worldwide interest recently. However, how agricultural replanting disease is alleviated by a combination of biochar and PGPBs treatment (SYBB) remains largely unexplored. In this study, we investigated the beneficial effects of single biochar addition and the combination of biochar and PGPBs on alleviating replanting disease by altering the rhizosphere microbiome and metabolites. Our field experiment showed that the SYBB treatment had a better alleviating effect on replanting disease than the single biochar addition. The study indicated the dominant effect of deterministic processes on the bacterial community and of stochastic processes on the fungal community under biochar and PGPBs treatment. The combination of biochar and PGPBs tended to convert the stochastic processes of fungal community assembly into deterministic processes. We found SYBB treatment increased the abundance of potentially beneficial Pseudomonas, Lysobacter, Gemmatimonadetes and Nitrospira, and decreasing the abundance of potentially pathogenic Fusarium, Talaromyces and Fusarium oxysporum. Moreover, the SYBB treatment increased the abundances of carbohydrates, fatty acids and plant hormones, and decreased the abundances of amino acids in the rhizosphere soil. Co‐occurrence network analysis indicated that SYBB treatment increased the connections within the microbial communities and drove the alteration of co‐occurrence network among the microbial communities and metabolites, which increased positive correlations in bacteria‐metabolite networks and decreased positive correlations in fungi‐metabolite networks. Spearman correlation analysis showed the abundances of beneficial Streptomyces, Pseudomonas and Lysobacter were significantly and positively correlated to the metabolites most increased under SYBB treatment. The combination of biochar and PGPBs alleviated replanting disease by mediating the change of rhizosphere soil metabolites, and stimulating the proliferation of indigenous and beneficial soil microbes. The research results are intended to provide the basis for new strategies for green and sustainable remediation of soil‐borne pathogens.

Synthetic microbial communities (SynCom) contribute to mitigating soil-borne crop diseases while enhancing both crop quality and yield. However, relatively little research has been done on the intricate regulatory mechanisms of SynCom on the suppression of soil-borne diseases. We aimed to elucidate the dynamic regulatory mechanisms and legacy effects of a SynCom on the composition of soil functional microorganisms, soil multifunctionality and crucial functions, and the suppression of soil-borne diseases. We conducted an extensive series of experiments to assess the effect of a SynCom on the changes in the rhizosphere functional microorganisms and soil functions (e.g., multifunctionality, functionality of C, N, and P cycling) across six successive generations of strawberry in consecutive monoculture soils by employing amplicon metagenomics and transcriptome sequencing. Our results showed that the SynCom increased the aboveground fresh biomass of strawberry by 31-70.3% and the fruit biomass by 171.39-280.71%, and decreased the Fusarium oxysporum abundance by 17.91-49.51% compared to the consecutive monoculture. The SynCom significantly enhanced the soil C cycling and P cycling function, and soil multifunctionality (SMF). SynCom treatment significantly increased the Shannon diversity index and relative abundances of potentially beneficial bacteria and consumer protistan communities, while exerted a significant inhibitory effect on the Shannon diversity index and relative abundances of fungal pathogen. SEM result showed that SynCom significantly affected SMF by influencing soil nutrients, the abundance and diversity of functional microbial community. Our result also showed that the SynCom established the positive legacy effects on the abundance of rhizosphere soil beneficial bacteria, strawberry biomass and plant disease resistance-associated pathways (phenylpropanoid biosynthesis pathway, alpha-linolenic acid metabolism pathway), and negative effect on the abundance of pathogenic F. oxysporum under the 7th generation of strawberry cropping. Collectively, our study demonstrated the effectiveness of employing SynCom in mitigating soil-borne Fusarium oxysporum diseases by enhancing soil functional microbial abundance and soil multifunctionality.