Biochar and Bacillus subtilis boost cut chrysanthemum growth via intensified microbial interkingdom interactions

Abstract Soil continuous monocropping obstacles pose a significant challenge to the sustainable production of cut chrysanthemums. Yet, the effectiveness of integrating biochar and microbial antagonists in alleviating these obstacles in cut chrysanthemum production remains unclear. Here, we collected soils from a 12-year continuous cropping system with a high incidence of disease to establish a pot experiment comprising four treatments: control (CK), biochar (BC), Bacillus subtilis (BM), and their combined addition (BM_BC), investigating the effects of biochar and B. subtilis on the disease incidence, plant growth, pathogenic and antagonistic microbial populations, and the bacterial and fungal communities in diseased soil. The results showed that BM_BC treatment effectively controlled the disease and significantly increased ( P < 0.05) the plant biomass and root activity of cut chrysanthemum by 41.3% and 254%, respectively, compared to the CK. Notably, the BM_BC exhibited the lowest population of Fusarium oxysporum and the highest population of B. subtilis , along with the greatest alpha diversity (measured by Chao1 and Shannon indices) of both bacterial and fungal communities among the four treatments. The amendments of BC, BM, and BM_BC significantly altered the structure and composition of bacterial and fungal communities, with BM_BC primarily enriching beneficial bacteria and suppressing pathogen. Microbial co-occurrence network analysis revealed that BM_BC increased the abundance of module 2, co-dominated by bacterial and fungal species, and strengthened the interactions between them. The PLS-PM analysis demonstrated that bacteria-fungi interkingdom interactions played a crucial role in promoting the growth of cut chrysanthemums in diseased soil. Therefore, our findings underscore the synergistic effects of biochar and B. subtilis in suppressing Fusarium wilt disease and enhancing the growth of cut chrysanthemums by strengthening microbial interkingdom interactions. Graphical Abstract