Fungal endophyte comprehensively orchestrates nodulation and nitrogen utilization of legume crop (Arachis hypogaea L.)

Abstract Aims This research aimed to explore the underlying mechanisms of endophytic fungus Phomopsis liquidambaris promoting nodulation and rhizosphere nitrogen (N) availability of continuous cropping peanuts during the whole growth stage under field conditions. Methods A consecutive 2-year field plot experiment was performed. The abundance and diversity of rhizosphere N transformation-related microorganisms and rhizosphere available N level were detected. The nodulation related physiological activities of peanuts and Bradyrhizobium sp. were analyzed. Low N fertilizer experiment was performed to verify the mechanisms of P. liquidambaris improving overall N utilization throughout growth period of peanuts. Results The colonization of fungal endophyte P. liquidambaris inhibited the growth of peanut rhizosphere ammonia oxidizing archaea and bacteria, resulting in reduction of rhizosphere nitrate (NO3−-N), but increase of ammonium (NH4+-N) at the seedling stage, which stimulated nodulation-related physiological responses of host peanuts. Simultaneously, peanut-specific Bradyrhizobium sp. in rhizosphere was enriched, and their nodulation-related biological activities were enhanced by the specific root exudates derived from P. liquidambaris colonization. Along with host development, P. liquidambaris further reshaped the communities of rhizosphere N transformation related microflora and then increase rhizosphere N availability at the crucial mid-late growth stage. Using low N fertilizer experiment, we confirmed that P. liquidambaris acted as a promising inoculant to maintain yield stabilization by stimulating nodulation in the early-stage and increasing rhizosphere N availability in the mid-late stage of long-term monocropped peanuts. Conclusions The underlying mechanisms of P. liquidambaris promoting nodulation and rhizosphere N availability were elucidated and contributed to reduce N fertilizer inputs.