Meiofaunal diversity in the Atlantic Forest soil: A quest for nematodes in a native reserve using eukaryotic metabarcoding analysis

The assessment of environmental communities may lead to the identification of the novel or not-yet-classified organisms. Few studies have focused on the meiofauna of poorly known habitats such as native soils in subtropical forests. We surveyed eukaryotic communities inhabiting soil in an unexplored area of a native Atlantic Forest in southern Brazil using high-throughput sequencing. We analyzed a total of 281,400 sequences using V4 and V9 hypervariable regions of 18S rRNA gene. Opisthokonta was the most abundant supergroup, with Fungi and Metazoa representing an average of 40.6% and 15.8% of the sequences, respectively. Among the metazoan, Nematoda was the second most abundant phylum (4.8%). Isolation and morphological assessment 1745 specimens of nematodes, classified by functional feeding groups as plant parasites (35%), bacterial feeders (30%), omnivores (7%) and predators (5%). Specimens belonged to the class Chromadorea (89.6%) and Enoplea (10.4%). Approximately 65% of them could be morphologically classified only to order level. Results identified a considerable number of newly or still uncharacterized nematodes in soil biota in Atlantic Forest soils. Furthermore, this is the first study in this subtropical area to show that both high throughput sequencing and morphology can give complementary indications of the diversity of nematodes in soil samples.