Effects of endophytic fungi on the growth and nitrogen metabolism of Achnatherum inebrians under different nitrogen concentrations

The endophytic fungi Epichloë gansuensis can influence the growth and nitrogen metabolism of the host plant Achnatherum inebrians through symbiotic association, with these effects being closely related to environmental nitrogen concentrations. Current research remains insufficient regarding the symbiotic interactions between E. gansuensis and A. inebrians under elevated nitrogen conditions. To investigate the impact of endophyte infection on A. inebrians growth and nitrogen metabolism under high nitrogen concentrations, we conducted a pot experiment comparing endophyte-infected (E+) and endophyte-free (E−) plants under 15 and 30 mmol·L⁻¹ nitrogen applications. Post-cultivation measurements included dry biomass, inorganic nitrogen accumulation, total nitrogen content, key nitrogen metabolism enzyme activities, and chlorophyll levels. Results demonstrated that at 15 mmol·L⁻¹ nitrogen, E+ plants exhibited 78.99% significantly higher dry weight than E− plants (P < 0.01), with leaf ammonium nitrogen content being significantly lower at 12.27%. Under 30 mmol·L⁻¹ nitrogen, root nitrate and ammonium nitrogen contents in E+ plants were 15.56% and 18.78%, respectively, significantly lower than their E− counterparts. E. gansuensis enhanced photosynthetic capacity and nitrogen utilization efficiency in E+ plants under high nitrogen conditions, optimized nitrogen allocation patterns, and significantly reduced inorganic nitrogen accumulation (P < 0.05), collectively improving host adaptation to nitrogen-rich environments. This study provides theoretical insights into the ecological functions of E. gansuensis-A. inebrians symbiosis and potential agricultural applications of grass-endophyte systems in high-nitrogen habitats.