Co-occurrence analysis of root-associated fungi in roots of oak species reveals the positive association among ectomycorrhizal and non-ectomycorrhizal fungi and the levels of associations among root-associated fungi are different between host species.. rhizosphere metagenome

Root-associated fungi have various ecological functions and can affect the aboveground ecosystem through alterations in nutrient cycling. Research has shown direct evidence for interspecific interactions among mycorrhizal fungi in structuring mycorrhizal communities both under the laboratory condition and at the field. However, the mycorrhizal communities may be affected by the non-mycorrhizal fungi (e.g. endophytes) through fungal interactions among mycorrhizal and non-mycorrhizal fungi. Here we present the evidence for species interactions among ectomycorrhizal and endophytic Ascomycota within the roots of co-occurring two oak species, deciduous Quercus serrata and evergreen Q. glauca. To reveal comprehensive root-associated fungi, PCR-amplified fungal internal transcribe spacer (ITS) regions from 472 oak seedlings were sequenced using 454 pyrosequencing technique. A total of 65,150 sequencing reads were yielded and they represented 314 molecular operational taxonomic units (MOTUs) under the clustering analysis of 97% cut???off sequence similarity. Co-occurrence analyses indicated a striking pattern of spatial aggregation between ectomycorrhizal fungi and endophytic Ascomycota. It was also indicated that segregated spatial distribution between ecologically similar fungal species (between ectomycorrhizal fungi and between endophytic fungi). Moreover, many fungal pairs occurring in both Q. serrata and Q. glauca exhibited a different level of segregation or aggregation between the two host plant species. Those results would suggest that the ectomycorrhizal community assembly is affected by existence of endophytic fungi and that species interactions among fungi are different between host plants.