Contributions of the dark septate endophyte extracellular metabolites to plant growth, metabolism and root-associated microbial community structure

Inoculation with dark septate endophytes (DSE) has emerged as a highly effective practical approach for facilitating ecological restoration and promoting vegetation reconstruction. However, the emphasis on the utilization of microbial-based preparations has resulted in a significant neglect of metabolites generated by DSE.

In soils with varying phosphorus (P) concentrations (0, 20, 200 mg kg⁻¹ KH₂PO₄), we supplemented DSE extracellular metabolites and conducted non-targeted metabolomics analysis of leaves, stems, roots, rhizosphere soils, as well as diversity analysis of root-associated bacterial communities.

DSE extracellular metabolites significantly enhanced the biomass of alfalfa under low and medium P concentrations. The leaf, stem, root tissue, and rhizosphere soil contained a total of 572, 264, 329, and 63 different identified metabolites respectively. The differential metabolic pathways mainly focus on glucose metabolism, lipid metabolism and amino acid metabolism. There were significant differences in the metabolic functions of root-associated bacterial communities in different treatments. The abundance of Sphingomonas and Rhizobiales in the root-associated bacterial communities increased after the addition of DSE extracellular metabolites, which enhanced the phosphonate and phosphinate metabolism.

The regulation of alfalfa metabolism by DSE extracellular metabolites occurs through two crucial mechanisms: signal regulation within the plant and the facilitation of positive interactions between the plant and root-associated bacterial communities, leading to recruitment of beneficial microorganisms. This study offers significant insights into the mechanism by which DSE extracellular metabolites coordinate plant nutrient balance and regulate microbial community diversity.