<i>Epichloë gansuensis</i> Enhances <i>Achnatherum inebrians</i> Seedlings Growth and Antioxidant Capacity Under UV-B Stress

Strong UV-B radiation is one of the main climatic characteristics of the Qinghai–Tibet Plateau. Plants grown on the Tibetan Plateau are exposed to high-intensity UV radiation and therefore require effective mechanisms to adapt to these stresses. However, little attention has been paid to the response of grass–endophytic fungi symbiosis to UV-B radiation in this area. In this study, we investigated the relationship between <i>Epichloë gansuensis</i> and the growth and antioxidant responses of <i>Achnatherum inebrians</i> seedlings exposed to different UV-B doses, aiming to evaluate the growth and antioxidant capacity of <i>A. inebrians</i> seedlings under UV-B stress. The plant height, tillers, biomass, electrical conductivity, soluble sugars, malondialdehyde (MDA), proline, hydrogen peroxide (H₂O₂), superoxide dismutase (SOD), polyphenol oxidase (POD), and catalase (CAT) of <i>A. inebrians</i> seedlings were determined under different intensities of UV-B radiation treatments. The results showed that, with the increase in UV-B radiation intensity, the plant height, tiller and biomass of <i>A. inebrians</i> seedlings showed a decreasing trend, the electrical conductivity increased, malondialdehyde content increased, soluble sugar and proline content decreased, SOD, POD, and CAT activities showed a decreasing trend, and the content of H₂O₂ increased, which means that the UV-B radiation was able to inhibit the morphogenesis and aggravate the membrane lipid peroxidation of <i>A. inebrians</i> seedlings. The tolerance of the <i>A. inebrians</i>–<i>E. gansuensis</i> symbiont to UV-B may enable it to have a high infection rate on the Qinghai–Tibet Plateau.