Aspergillus niger ZJ-17 enhances the yield and quality of Angelica dahurica var. formosana by modulating beneficial rhizobacteria: a sustainable strategy for plant production.

backgroundAngelica dahurica var. formosana is a medicinal and edible plant. Higher abundance of Proteobacteria is an excellent characteristic of its rhizosphere bacterial community. Aspergillus niger ZJ-17 (AN17) significantly improved plant yield and quality while reducing fertilizer input application in both pot and field experiments. However, the impact of inoculants on resident soil bacteria directly determines their field application. Therefore, to systematically analyze how AN17 remodels host rhizosphere bacterial communities, we inoculated AN17 into the roots of A. dahurica var. formosana. The rhizosphere bacterial communities and root exudates were investigated at the harvest stage. Rhizosphere bacteria were isolated for in vitro experiments to elucidate the reasons for the changes in the rhizosphere bacterial community.

resultsAN17 promoted nutrient utilization and absorption in rhizosphere soil and increased the accumulation of IAA and JA in plant roots. In the microbiome, the relative abundance of rhizosphere Proteobacteria increased after inoculation. A total of 832 bacterial strains were isolated from the rhizosphere of the host for in vitro experiments. In in vitro experiments, AN17 induced the enrichment of Proteobacteria through microbial interactions and the modulation of host root exudates. These root exudates promoted the proliferation of bacterial genera with higher abundance and diversity. In the metabolome, host root activity increased following AN17 inoculation. According to the KEGG analysis of root exudates, AN17 upregulated microbial metabolism in diverse environments, the biosynthesis of alkaloids derived from the shikimate pathway and tryptophan metabolism. Correlation analysis and in vitro tests revealed that AN17 regulated the secretion of phenolic acids (4-chlorophenol, 2-oxoadipic acid, pyrogallol, and vanillic acid) from roots, which serve as crucial components driving the enrichment of Proteobacteria. In both plate and pot experiments, these bacteria promoted the growth of A. dahurica var. formosana and activated nutrient availability.

conclusionsWe supplemented multiple growth-promoting strategies by which AN17 improves rhizosphere bacterial communities. Phenolic acids in root exudates were recognized during the stimulation of rhizosphere bacterial proliferation by AN17. The interaction relationships among plants, beneficial fungi and rhizobacteria were explored and revealed. This result provides a sustainable approach for rhizosphere bacterial optimization and chemical fertilizer reduction in agricultural production.