Abstract
Amazonia is an environmentally heterogeneous and biologically megadiverse region, and its biodiversity varies considerably over space. However, existing knowledge on Amazonian biodiversity and its environmental determinants stems almost exclusively from studies of macroscopic above‐ground organisms, notably vertebrates and trees. In contrast, diversity patterns of most other organisms remain elusive, although some of them, for instance microorganisms, constitute the overwhelming majority of taxa in any given location, both in terms of diversity and abundance. Here, we use DNA metabarcoding to estimate prokaryote and eukaryote diversity in environmental soil and litter samples from 39 survey plots in a longitudinal transect across Brazilian Amazonia using 16S and 18S gene sequences, respectively. We characterize richness and community composition based on operational taxonomic units (OTUs) and test their correlation with longitude and habitat. We find that prokaryote and eukaryote OTU richness and community composition differ significantly among localities and habitats, and that prokaryotes are more strongly structured by locality and habitat type than eukaryotes. Our results 1) provide a first large‐scale mapping of Amazonian soil biodiversity, suggesting that OTU richness patterns might follow substantially different patterns from those observed for macro‐organisms; and 2) indicate that locality and habitat factors interact in determining OTU richness patterns and community composition. This study shows the potential of DNA metabarcoding in unveiling Amazonia's outstanding diversity, despite the lack of complete reference sequence databases for the organisms sequenced.
Highlights
The Amazon drainage basin (Amazonia) has the highest biodiversity of all tropical rainforests and is a global biodiversity hotspot (Hansen et al 2013)
The weak correlation found between prokaryotes (16S) and eukaryotes (18S) OTUs indicates that richness patterns may be different between the two groups
In south-eastern Brazilian Amazonia, vast areas have been converted for agricultural use, and those areas are notably poor in animal and plant diversity
Summary
The Amazon drainage basin (Amazonia) has the highest biodiversity of all tropical rainforests and is a global biodiversity hotspot (Hansen et al 2013). A west-to-east diversity gradient from highly diverse areas on the Andean slopes in western Amazonia towards relatively less diverse areas on the Guiana shield and the eastern Amazonian lowlands has been observed in many animal and plant groups (ter Steege et al 2003, Bass et al 2010, Hoorn et al 2010, Zizka et al 2018) The drivers for this gradient remain elusive, but have been attributed to bedrock geology (Tuomisto et al 2017), historical processes including mountain and basin formation (Hoorn et al 2010), marine incursions (Bates 2001, Lovejoy et al 2006, Antonelli et al 2009), and soil fertility (Moran et al 2000). These four habitat types support distinct communities of plants and animals and are often associated with differences in species richness and community composition
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