Effects of a dark septate endophyte and extracellular metabolites on alfalfa root exudates: a non‐targeted metabolomics analysis

Abstract Dark septate endophytes (DSE) are widespread colonizers of plant roots and have important ecological functions such as the regulation of plant growth and nutrient uptake. The mechanisms by which DSE mycelium and its extracellular metabolites promote plant growth have not yet been determined. Here, the growth‐promoting effects of DSE mycelium (H) and extracellular metabolites (M) on alfalfa ( Medicago sativa L.) were investigated. Treatments H, M and HM increased the total biomass of alfalfa by 23.9%, 47.2% and 47.1%, respectively. H and M modified root structure by increasing root volume and reducing root tissue density, and promoting nutrient uptake. Metabolomic analysis indicates that alfalfa root exudates contained 204 metabolites of different types, mainly lipids and lipid‐like molecules, organic acids and derivatives, benzenoids. There were more organoheterocyclic compounds and fewer organic acids and derivatives in root exudates in treatment H than in treatment M. Pathway analysis shows that DSE and its extracellular metabolites had greater effects on glycerophospholipid metabolism and N‐glycan biosynthesis pathway. The results provide information on the mechanisms involved in the metabolic regulation of plant growth promotion by DSE.