Endophytic Fungus Drives Nodulation and N Fixation Attributable to Specific Root Exudates.

Endophytic fungi play important roles in the modification of ecosystem productivity; however, the underlying mechanisms are only partly understood. A 2-year field plot experiment verified that the endophytic fungus increased peanut ( L.) yields and significantly increased nodulation and N fixation regardless of whether N fertilizers were added. Root exudates collected from -colonized plants significantly improved nodulation and N fixation. Rhizosphere stimulation experiments further showed that colonized root exudates had significantly decreased soil nitrate (NO) concentrations, with decreased abundance and diversity of ammonia oxidizing archaea (AOA). In contrast, the abundance and diversity of diazotrophs significantly increased, and most diazotrophs identified were peanut nodulation-related strains ( sp.). symbiosis increased the expression of phenolic and flavonoid synthesis-related genes, and the derived phenolics and flavonoids could effectively increase the chemotaxis, biofilm formation, and gene expression (nodulation-related biological processes) of the strain. Metabolic pattern analysis showed that phenolics and flavonoids are more likely to accumulate to higher levels in the rhizosphere soil of peanuts colonized with Finally, a synthetic root exudate experiment further confirmed the underlying mechanisms for the -induced improvement in nodulation and N fixation, i.e., that the specific root exudates derived from colonization decrease nitrate concentration and increase the population and biological activities of peanut nodulation-related species, which beneficially enhance peanut- interactions. Therefore, this study is the first to provide new insight into a positive relationship between an exotic endophytic fungus, crop nodulation, and N fixation increase. Endophytic fungi play an important role in balancing the ecosystem and boosting host growth; however, the underpinning mechanisms remain poorly understood. Here, we found that endophytic fungal colonization with significantly increased the productivity, nodulation, and N fixation of peanuts through the secretion of specific root exudates. We provide a reasonable mechanism explaining how promotes peanut nodulation and N fixation, whereby the specific root exudates produced by colonization decrease rhizosphere soil nitrate (NO3) and increase the population and biological activities of peanut-nodulating-related strains, which is beneficial to enhancing the peanut- symbiotic interaction. Our study provides reliable empirical evidence to show the mechanism of how an exotic endophytic fungus drives an increase in nodulation and N fixation, which will be helpful in erecting a resource-efficient and sustainable agricultural system.