Epichloe endophytes alter the soil microbial communities and soil metabolite profile after their host decomposition under salt stress

Background and aim Decomposition plays a crucial role in regulating the structure and function of microbial ecosystems. However, the response of soil microorganisms to endophyte-mediated decomposition in salinized soils remains elusive. Methods The diversity and composition of microbial communities in soil samples with Epichloe gansuensis-infected (E+) or E. gansuensis-free (E-) Achnatherum inebrians litter, which underwent decomposition under 0, 100, and 200 mM NaCl concentrations, were evaluated by Illumina sequencing. Meanwhile, soil metabolome was determined by LC-MS. Results The diversity and richness of fungal community in E- soil samples were more sensitive to salinity than bacterial community, and E. gansuensis mitigated the adverse effects of NaCl on microbial community diversity. Salinity led to an increase in the relative abundance of Proteobacteria, Firmicutes, and Bacteroidota while decreasing the Acidobacteriota abundance. Additionally, E. gansuensis significantly enriched pathways involved in stress responses such as "replication and repair" and "folding, sorting and degradation" in soil bacterial community. E. gansuensis infection increased the activities of invertase and catalase while decreasing the activities of alkaline phosphatase and urease after its host litter decomposition under 100 mM NaCl concentration. Additionally, salinity increased the ectoine content and decreased the levels of choline sulfate and O-acetylserine following A. inebrians decomposition. The co-occurrence network analysis indicated that salinity enhanced the E. gansuensis-mediated association among the soil properties, differential metabolites, and microbial communities. Conclusions These findings could further enhance our understanding of the role played by Epichloe endophytes in grassland ecosystems and provide valuable insights for sustainable management of salinized soils.