Microbiomes of Virgin Soils of Southern Vietnam Tropical Forests

Abstract

Numbers of bacterial, archaeal, and fungal ribosomal gene copies and the taxonomic structure of prokaryotic communities in virgin tropical soils under weakly impacted monsoon forests at the CKat Tien National Park (Southern Vietnam) were determined, and their relation with the major physicochemical parameters of the studied soils were investigated. Samples were collected from genetic horizons of brown tropical (Cambisol) and dark-colored (Umbrisol) soils on volcanic deposits, red-yellow tropical soil (Regosol) on metamorphic slates, and alluvial sandy-loam soil (Fluvisol). The numbers of ribosomal gene copies in virgin soils of southern Vietnam tropical forests were up to 10¹¹–10¹² gene copies per 1 g, which was comparable to the richest soils of the temperate zone. The highest numbers of microbial genes were found in the upper horizons (4–10 cm). Higher abundance of microbial ribosomal genes was found in volcanic soils, compared to red-yellow tropical and alluvial ones. The dominant prokaryotic phyla were Proteobacteria and Acidobacteria (subgroup 1, Acidobacteriales; subgroup 2; and Solibacterales). The share of Acidobacteria in soils correlated with pH and was highest in the most acidic red-yellow tropical soil. The share of Verrucomicrobia was highest in the surface soil layers and decreased with depth. The share of Chloroflexi increased with depth. Members of the recently described bacterial phylum Rokubacteria were revealed. The differences in soil-forming rocks (volcanic deposits, meatmorphic slates, and alluvium) determined the differences in the chemical properties of soils and the taxonomic structure of their prokaryotic communities. Organic carbon content is probably the main factor determining both the abundance of microbial ribosomal genes and the taxonomic structure of prokaryotic communities from virgin forest tropical soils.