Host-Specific and Environment-Dependent Effects of Endophyte on Three Locoweed Species in China.

Plant-endophyte symbioses are widespread in grasslands. While symbiotic interactions often provide hosts with major fitness enhancements, the role of the endophyte , which produces swainsonine in locoweeds ( and spp.), remains enigmatic. We compared endophyte-infected (E+) and endophyte-free (E-) plants of three main Chinese locoweed species (, , and ) under controlled conditions, and analyzed environmental factors at locoweed poisoning hotspots for herbivores. The results demonstrated significant species-specific effects: E+ plants of and exhibited 26-39% reductions in biomass, net photosynthetic rate, and stomatal conductance, with elevated CO levels, while showed no measurable impacts. Swainsonine concentrations were 16-20 times higher in E+ plants (122.6-151.7 mg/kg) than in E- plants. Geospatial analysis revealed that poisoning hotspots for herbivores consistently occurred in regions with extreme winter conditions (minimum temperatures ≤ -17 °C and precipitation ≤ 1 mm during the driest month), suggesting context-dependent benefits under abiotic stress. These findings suggest that the ecological role of may vary depending on both host species and environmental context, highlighting a trade-off between growth costs and potential stress tolerance conferred by . The study underscores the need for field validation to elucidate the adaptive mechanisms maintaining this symbiosis in harsh environments.