Characterization of Dark Septate Endophytes Under Drought and Rehydration and Their Compensatory Mechanisms in Astragalus membranaceus

Drought is the most significant abiotic stress that impedes agroforestry development. In nature, drought tolerance also depends on the ability to compensate after water restoration. Dark septate endophytes (DSEs) are believed to enhance plant tolerance in drought environments. However, the compensatory mechanisms of DSEs for rehydration after drought stress have not been reported. To assess the drought tolerance and compensatory capacity of DSEs, the following DSEs were investigated in this study using solid-liquid screening and potting tests under different drought gradients, rehydration conditions, and field water-holding capacities: Stagonosporopsis lupini, Microsphaeropsis cytisi, Macrophomina pseudophaseolina, Paraphoma radicina, Alternaria alstroemeriae, Alternaria tellustris, and Papulaspora equi. The results showed that M. pseudophaseolina reached the maximum diameter for plate growth in only 4 d. In a liquid shaker, the biomass of S. lupini peaked after rehydration. The Mantel heatmap indicated that lipid metabolites were significantly expressed in M. pseudophaseolina and S. lupini under drought stress. Correlations between drought tolerance indexes and amino acid metabolites increased dramatically in both DSEs after rehydration. Moreover, in rehydration after drought, the treatments inoculated with M. pseudophaseolina and S. lupini showed significant increases in root weight of 20.36% and 23.82%, respectively, compared with the uninoculated treatment.