Physiological mechanisms behind endophytic fungus Phomopsis liquidambari-mediated symbiosis enhancement of peanut in a monocropping system

Background and aims Fungal endophyte Phomopsis liquidambari B3 effectively increases nodule number and productivity of peanut when grown in a monoculturing system, but the underlying mechanisms are not well understood. Plant physiological status is the key mechanism that determines the legume-rhizobium interaction under stressful conditions. Therefore, this research aimed to study the physiological mechanisms behind the P. liquidambari-mediated monoculturing peanut nodulation enhancement. Methods Peanut-rhizobia symbiosis, plant defense enzyme activity in shoots and roots, photosynthetic activity and soluble sugar content in leaves, as well as the carbon metabolism-related enzyme activity and carbon metabolites content in nodules were measured after live P. liquidambari and P. liquidambari fragments treatment under continuous monoculturing condition. Results P. liquidambari instead of its fragments significantly enhanced nodule initiation, nodule development and nodule N2-fixation efficiency. Plants treated with live P. liquidambari showed higher leaf photosynthetic activity, soluble sugar accumulation, nodule carbohydrate catabolism activity and seed yield, whereas plant defense response was similar in endophyte and endophyte fragments treated plants. Conclusion Our results demonstrated that the improved efficiency of symbiosis in peanut continuous monoculturing system, induced by P. liquidambari, was likely linked to the improved plant aboveground nutritional status rather than to the induction of plant defense.