Endogonales fungi associated with understory herbaceous plants in Japanese temperate forests

Sporocarps of Endogonales fungi, collected from Japanese forest environments, have been described in previous studies; however, their root colonization has not been fully revealed. To investigate Endogonales diversity in the roots of understory herbaceous plants, we examined fungal partial nuclear small subunit ribosomal DNA amplicons obtained from 13 plant species in five forests. In total, 20 operational taxonomic units (OTU) clustered at 97% sequence similarity were identified and classified into two families, Endogonaceae and Densosporaceae, with most OTUs belonging to the latter. Most OTUs were not closely related to known species; however, some were closely related to plant mycobiont, as reported in previous studies. Although most OTUs were detected in only a few plant species and study sites, one OTU was found in most examined plant individuals. This widespread OTU fungus may play an ecologically important role, but its actual function and morphology remain unknown, requiring further studies.