Fungal, Bacterial, and Archaeal Diversity in Soils Beneath Native and Introduced Plants in Fiji, South Pacific

The Fiji Islands is an archipelago of more than 330 islands located in the tropics of the South Pacific Ocean. Microbial diversity and biogeography in this region is still not understood. Here, we present the first molecular characterization of fungal, bacterial, and archaeal communities in soils from different habitats within the largest Fijian island, Viti Levu. Soil samples were collected from under native vegetation in maritime-, forest-, stream-, grassland-, and casuarina-dominated habitats, as well as from under the introduced agricultural crops sugarcane, cassava, pine, and mahogany. Soil microbial diversity was analyzed through MiSeq amplicon sequencing of 16S (for prokaryotes), ITS, LSU ribosomal DNA (for fungi). Prokaryotic communities were dominated by Proteobacteria (~ 25%), Acidobacteria (~ 19%), and Actinobacteria (~ 17%), and there were no indicator species associated with particular habitats. ITS and LSU were congruent in β-diversity patterns of fungi, and fungal communities were dominated by Ascomycota (~ 57–64%), followed by Basidiomycota (~ 20–23%) and Mucoromycota (~ 10%) according to ITS, or Chytridiomycota (~ 9%) according to LSU. Indicator species analysis of fungi found statistical associations of Cenococcum, Wilcoxina, and Rhizopogon to Pinus caribaea. We hypothesize these obligate biotrophic fungi were co-introduced with their host plant. Entoloma was statistically associated with grassland soils, and Fusarium and Lecythophora with soils under cassava. Observed richness varied from 65 (casuarina) to 404 OTUs (cassava) for fungi according to ITS region, and from 1268 (pine) to 2931 OTUs (cassava) for bacteria and archaea. A major finding of this research is that nearly 25% of the fungal OTUs are poorly classified, indicative of novel biodiversity in this region. This preliminary survey provides important baseline data on fungal, bacterial, and archaeal diversity and biogeography in the Fiji Islands.