Integrated microbiology and metabolomics analysis reveal patterns and mechanisms of improvement the Achnatherum inebrians adaptability to N addition by endophytic fungus Epichloë gansuensis

Frequent anthropogenic activities have led to a rapid increase in atmospheric reactive N inputs in terrestrial ecosystems, negatively affecting plant and microbial communities. Endophytic fungi are important symbiotic microbes that are beneficial for improving host environmental adaptability. However, it remains poorly understood how endophytic fungi affect bacterial communities and related root metabolites contribute to improved plant adaptability to elevated N inputs. Here, we used 16 S rRNA gene sequencing and GC-MS platform to investigate the effects of Epichloë gansuensis infection on Achnatherum inebrians response to N addition. The results showed E. gansuensis infected (E+) A. inebrians exhibited more biomass and less phosphorus (P) limitation than E. gansuensis uninfected (E-) A. inebrians under N enrichment conditions. Analysis of the bacterial community indicated that rhizosphere and endophyte bacterial community compositions and structures presented significant differences between E+ and E- plants. N addition enhanced the proportion of Proteobacteria, Firmicutes, Nitrospirae, and putative plant growth promoting rhizobacteria (PGPR) (e.g. Bacillus and Lysobacter) in the E+ plant, facilitating the uptake of rhizosphere nutrients. Network analysis showed that E. gansuensis-infection enhanced the complexity and intraspecific cooperation of bacterial community under N addition conditions. Moreover, metabolomics analysis indicated that the compositions of root exudates of E- plant were more susceptible to N addition than those of E+ plant. Correlation analysis showed that root microbiota were also closely related to the accumulation of root metabolites. Our findings provide a significant understanding of the symbiotic relationship between host and endophytic fungi in the N enrichment environment.