Effects of the endophyte Epichloë coenophiala on the root microbial community and growth performance of tall fescue in different saline-alkali soils

Soil salinization is detrimental to plant growth and yield in agroecosystems worldwide. Epichloë endophytes, a class of clavicipitaceous fungi, enhance the resistance of host plants to saline-alkali stress. This study explored the effects of the systemic fungal endophyte Epichloë coenophiala on the root microbial community and growth performance of tall fescue (Lolium arundinaceum) growing under different saline-alkali stress conditions. Structural equation modeling (SEM) was conducted to analyze the direct and indirect effects (mediated by root microbial community diversity and soil properties) of the endophyte on the growth of tall fescue under saline-alkali stress. The endophyte-infected plants produced higher shoot and root biomass compared to endophyte-free plants under saline-alkali stress (200 and 400 mM). Endophyte infection increased the fungal community diversity and altered its composition in the roots, decreasing the relative abundance of Ascomycota and increasing that of Glomeromycota. Furthermore, endophyte infection decreased the bacterial community diversity and the relative abundance of dominant Proteobacteria. SEM showed that endophyte infection increased the shoot and root biomass under saline-alkali stress (200 and 400 mM) by increasing the arbuscular mycorrhizal fungal diversity in the roots, and soil total nitrogen and phosphorus concentrations. Therefore, it is important to examine aboveground microbes as factors influencing plant growth in saline-alkali stress by affecting belowground microbes and soil chemical properties.