Communities of arbuscular mycorrhizal fungi in forest ecosystems in Japan's temperate region may be primarily constituted by limited fungal taxa.

We investigated arbuscular mycorrhizal (AM) fungal communities in secondary forests and/or Chamaecyparis obtusa plantations at eight study sites in Japan's temperate region. In the secondary forests, AM plants of the families Lauraceae, Sapindaceae, Rutaceae, Araliaceae, Rosaceae, Magnoliaceae, Cornaceae, Piperaceae, and Anacardiaceae were found. The AM fungal communities were evaluated based on compositions of the AM fungal operational taxonomic units (OTUs), which were clustered at a 97% similarity threshold of the sequences of a partial small subunit of a nuclear ribosomal RNA gene obtained from the plant roots. The compositions of AM fungal OTUs were significantly correlated with the plant family compositions and were significantly differentiated among the study sites and between the study forests. Interestingly, only 19 OTUs remained after selecting for those that had more than 1.0% of the total reads, and these 19 OTUs accounted for 86.3% of the total rarefied reads that were classified into 121 OTUs. Furthermore, three dominant OTUs constituted 48.0% of the total reads, and the most dominant OTU was found at all study sites, except at one. These results indicate that AM fungal communities are primarily constituted by limited AM fungal taxa in the forest ecosystems with diverse plant taxa in Japan's temperate region. The results of basic local algorithm search tool (BLAST) searches against MaarjAM, a database of AM fungal sequences, also revealed that the AM fungi which were the three dominant OTUs are distributed in forest ecosystems on a worldwide scale.