In artificial ecosystems, mixed planting of gramineous and leguminous plants can have obvious advantages and is very common. Due to their improved growth performances and stress tolerance, endophyte-infected grasses are considered to be ideal plant species for grasslands. However, endophytic fungi can inhibit the growth of neighboring nonhost leguminous plants. In this study, we chose endophyte-infected and endophyte-free tall fescue (Lolium arundinaceum Darbyshire ex. Schreb.) and clover (Trifolium repens) as the experimental materials to explore whether arbuscular mycorrhizal fungi and rhizobium can alleviate the inhibitory effect of endophyte infection on clover. The results showed that endophytic fungi significantly reduced clover biomass. Arbuscular mycorrhizal fungi inoculation significantly increased the biomass of clover in both endophyte-infected tall fescue/clover and endophyte-free tall fescue/clover systems but the beneficial contribution of arbuscular mycorrhizal fungi was more obvious in the endophyte-infected tall fescue/clover system. Rhizobia inoculation could alleviate the detrimental effect of tall fescue on the growth of clover but did not alleviate the detrimental effect of endophyte infection on the growth of clover.

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Purpose: Grass-endophyte and legume-rhizobium symbionts coexist in grasslands. However, the effects of endophyte infection on legume-rhizobium symbionts remain poorly understood, especially in natural grasslands. Methods: In this study, Achnatherum sibiricum - Epichloë endophytes and Medicago ruthenica -rhizobia were selected as materials to investigate whether and how endophyte infection affected the growth of legume-rhizobia symbionts. It was hypothesized that endophytes can facilitate the coexistence of grass-legume systems. Results: The results demonstrated that endophyte infection affected the growth of both rhizobia and M. ruthenica -rhizobia symbionts, and the results depended on rhizobial identity. Endophyte infection inhibited the growth of Mesorhizobium ciceri , which significantly promoted the growth of M. ruthenica , and promoted Sinorhizobium meliloti , which had no significant effect on the growth of M. ruthenica . Endophyte infection also changed the interaction between A. sibiricum and M. ruthenica . When inoculated with M. ciceri , endophyte infection weakened the promoting effect of A. sibiricum on M. ruthenica , while when inoculated with S. meliloti , endophyte infection enhanced the promoting effect. Endophyte infection affected the growth of M. ruthenica -rhizobia symbionts by affecting rhizobia abundance in roots and nitrogen content in plant leaves. Conclusion: In conclusion, endophyte infection was beneficial to biomass accumulation and species coexistence in grass-legume mixed planting systems. In this study, it was proposed that endophyte infection may change the growth of legume-rhizobia symbionts by affecting the growth and nitrogen fixation of rhizobia.