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Abstract. Growth of the pioneer grass Miscanthus condensatus, one of the first vegetation to be established on volcanic deposits, is promoted by root-associated fungi, particularly dark septate endophytes (DSE). Fungal taxa within DSE colonize the root of Miscanthus condensatus in oligotrophic Andosol, and their function in plant growth promotion remains largely unknown. We, therefore, comprehensively assessed the composition of the DSE community associated with Miscanthus condensatus root in volcanic ecosystems using the approaches of both metabarcoding (next-generation sequencing) and isolation (culturing). Also, their promotion effects of DSE on plant growth (rice as a proxy) were evaluated by inoculation of core isolates to rice roots. Here, we found: i) 70 % of culturable fungi that colonized Miscanthus condensatus phylogenetically belonged to DSE, ii) 7 orders were identified by both sequencing and culturing methods, and iii) inoculation of DSE isolates (Phialocephala fortinii, P. helvetica, and Phialocephala sp.) validated their effects on rice growth, particularly under an extremely low pH condition (compared to control without inoculation, rice biomass enhanced by 7.6 times after inoculation of P. fortinii). This study helps improve our understanding of the community of Miscanthus condensatus-associated DSE fungi and their functions in promoting plant growth.

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