Epichloë  endophyte enhances intraspecific competition of Achnatherum inebrians  under nitrogen stress

Abstract Background and aims Drunken horse grass (DHG, Achnatherum inebrians) is a perennial grass widely distributed in the grasslands of northwestern China, forming a symbiosis with the Epichloë endophyte, and has a strong growth advantage in the community. However, the mechanism of its competitive success remains unclear. Methods Endophyte-infected (EI) and endophyte-free (EF) DHG were employed in greenhouse experiments. EI plants served as competitive species, while EF plants were the target species. Aggressivity was employed to quantify the competitiveness between EI and EF plants. The effects of endophyte, plant density, and three different nitrogen levels in pot on the competitiveness of DHG plants were investigated. Results The presence of Epichloë endophytes significantly improved growth performance, photosynthetic capacity, and nitrogen uptake efficiency of the host grasses, especially under low nitrogen conditions. the competitive abilities of DHG. Importantly, the gain effect of the endophyte on the competitiveness of DHG gradually weakened with the decrease in the number of EI plants. ConclusionThe Epichloë endophyte enhances DHG competitiveness under nitrogen limitation but diminishes as soil nitrogen content increases. These results provide insights into the strong competitive advantage of EI DHG and the high infection rate of DHG in natural grasslands with harsh habitats.