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Previously, the application of the fungal endophyte Phomopsis liquidambari B3 exhibited notable effect in alleviating soil obstacles caused by continuous cropping of peanut. It was supposed that P. liquidambari B3 could enhance the efficiency of nodulation and nitrogen fixation by enriching the diversity of nodular endophytic bacteria under continous monocropping system. To verify this hypothesis, a pot experiment was conducted under natural conditions. Four treatments were set as follow: discontinuous cropping soil (NS), continuous cropping soil (CK), continuous cropping soil inoculate with actived P. liquidambari B3 (CSB3), and continuous cropping soil inoculate with sterilized P. liquidambari B3 (CSIB3). As a result, a total of 120 isolates were obtained. Our study clearly declared that the addition of fungal endophyte effectively enriched the genetic diversity and the community composition in CSB3. In contrast, a low genetic diversity level and simplex community structure were exhibited in CK and CSIB3. Meanwhile, the positive percentage rate and corresponding community composition of the plant growth-promoting isolates in NS and CSB3 were larger and more abundant than the other. This is the first time to describe the effects of fungal endophytes on the diversity of the nodular culturable endophytic bacteria associated with continuous cropping of peanut. [ABSTRACT FROM AUTHOR]

• Peanuts cultivated in the sterilized soil with AM fungi-inoculated history exhibit enhanced drought performance. • Potassium-sequestering glomalin directly contributes to the enhanced peanut drought performance. • Peanut root exudates prime the dissociation of glomalin-bound potassium. In agroecosystems, drought stress severely threatens crops development. Although potassium (K) is required in amounts by crops under drought stress, the mobilization and availablity of K are limited by the soil water status. Arbuscular mycorrhizal (AM) fungi can form mutualistic associations with most crops and play direct or indirect roles in the host drought resistance. Considering that the glomalin generated by living AM fungal hyphae can sequester multiple minerals, however, the function of mineral-sequestering glomalin in the crop drought resistance remains unclear. In this study, peanuts cultivated in the sterilized soil with a history of AM fungi inoculation showed significantly enhanced leaf K accumulation, drought resistance and pod yield under drought stress. Through the collection of different types of mineral-sequestering glomalin from living AM fungal hyphae, the peanut drought resistance was improved only when K-sequestering glomalin was added. Moreover, we found that peanut root exudates could prime the dissociation of glomalin-bound K and further satisfy the K requirement of crops. Our study is the first report that K-sequestering glomalin could improve drought performance and peanut pod yield, and it helps us to understand the ecological importance of improving AM symbiosis to face agricultural challenges. [ABSTRACT FROM AUTHOR]

The growth and yield of crops are severely threatened by drought stress. As the symbiotic partners of plants, the function of the symbiotic interaction between arbuscular mycorrhizal fungi (AM fungi) and endophytic fungi on host drought resistance is still unclear. Through high-throughput sequencing of peanuts cultivated in a natural soil environment with different soil water conditions, our study showed that the inoculation of an endophytic fungus not only reassembled the root-dwelling AM fungal community by driving the colonization of Gigaspora, but also enhanced peanut drought resistance under drought stress. Co-inoculation experiments revealed that the synergetic interaction between the endophytic fungus and the AM fungi promoted the ecological service of the extraradical hyphae of Gigaspora margarita. In addition, both endophytic fungal exudates and root exudates failed to differentially affect the pre-symbiotic growth of different AM fungi. Overall, our study enabled us to better understand the ecological importance of the tripartite symbiosis between endophytic fungi , AM fungi and the host. • Endophytic fungus enhances host drought resistance and changes AM fungal community. • Interaction between endophytic fungus and Gigaspora enhances host drought resistance. • The ecological role of Gigaspora depends on its extraradical hyphal traits. [ABSTRACT FROM AUTHOR]

Root exudates play a crucial role in the symbiosis between leguminous plants and rhizobia. Our previous studies have shown that a fungal endophyte Phomopsis liquidambaris promotes peanut-rhizobia nodulation and nitrogen fixation, but the underlying mechanism are largely unknown. Here, we explore the role of peanut root exudates in Ph. liquidambaris -mediated nodulation enhancement. We first collected root exudates from Ph. liquidambaris -inoculated and un-inoculated peanuts and determined their effects on rhizobial growth, biofilm formation, chemotaxis, nodC gene expression, and peanut nodulation. Our results found a positive effect of Ph. liquidambaris -inoculated root exudates on these characteristics of rhizobia. Next, we compared the root exudates profile of Ph. liquidambaris- inoculated and un-inoculated plants and found that Ph. liquidambaris altered the concentrations of phenolic acids, flavonoids, organic acids and amino acids in root exudates. Furthermore, the rhizobial chemotaxis, growth and biofilm formation in response to the changed compounds at different concentrations showed that all of the test compounds induced rhizobial chemotactic behavior, and organic acids (citric acid and oxalic acid) and amino acid (glutamate, glycine and glutamine) at higher concentrations increased rhizobial growth and biofilm formation. Collectively, our results suggest that root exudates alterations contribute to Ph. liquidambaris -mediated peanut-rhizobia nodulation enhancement. [ABSTRACT FROM AUTHOR]