From Forest Soil to the Canopy: Increased Habitat Diversity Does Not Increase Species Richness of Cercozoa and Oomycota in Tree Canopies.

Robin-Tobias Jauss,Susanne Walden,Stefan Schaffer,Kenneth Dumack,Michael Bonkowski,Martin Schlegel,Ronny Wolf,Anna Maria Fiore-Donno

doi:10.3389/fmicb.2020.592189

Abstract

Tree canopies provide habitats for diverse and until now, still poorly characterized communities of microbial eukaryotes. One of the most general patterns in community ecology is the increase in species richness with increasing habitat diversity. Thus, environmental heterogeneity of tree canopies should be an important factor governing community structure and diversity in this subsystem of forest ecosystems. Nevertheless, it is unknown if similar patterns are reflected at the microbial scale within unicellular eukaryotes (protists). In this study, high-throughput sequencing of two prominent protistan taxa, Cercozoa (Rhizaria) and Oomycota (Stramenopiles), was performed. Group specific primers were used to comprehensively analyze their diversity in various microhabitats of a floodplain forest from the forest floor to the canopy region. Beta diversity indicated highly dissimilar protistan communities in the investigated microhabitats. However, the majority of operational taxonomic units (OTUs) was present in all samples, and therefore differences in beta diversity were mainly related to species performance (i.e., relative abundance). Accordingly, habitat diversity strongly favored distinct protistan taxa in terms of abundance, but due to their almost ubiquitous distribution the effect of species richness on community composition was negligible.

Highlights

Forest ecosystems harbor 80% of terrestrial biodiversity, influence climate through biogeochemical cycles, and provide ecosystem services to society (Bonan, 2008; Aerts and Honnay, 2011)
Application of taxon-specific primers ensured an exhaustive coverage of the investigated protistan taxa, which has two major consequences: First, operational taxonomic units (OTUs) richness of both Cercozoa and Oomycota in our study is at least an order of magnitude higher than in studies using general eukaryotic primers (Lentendu et al, 2014; Geisen et al, 2015; Mahé et al, 2017)
The majority of all OTUs were detected in all microhabitats, a crucial precondition to avoid an erroneous classification of species as absent or rare by undersampling (Supplementary Figure 2)

Summary

Introduction

Forest ecosystems harbor 80% of terrestrial biodiversity, influence climate through biogeochemical cycles, and provide ecosystem services to society (Bonan, 2008; Aerts and Honnay, 2011). There are more than 3 trillion trees on Earth, of which 43% can be found in tropical and subtropical regions and 22% in temperate biomes (Crowther et al, 2015). Their tree canopies form the functional interface between 90% of Earth’s terrestrial biomass and the atmosphere (Ozanne et al, 2003; Ellwood and Foster, 2004) and contain a variety of heterogeneous. A recent study on protistan diversity of tropical forest soils hypothesized that some protists may have originated from tree canopy communities from where they were washed down by rain (Mahé et al, 2017). A comprehensive comparative assessment of protistan communities of tree canopies across different tree microhabitats and a comparison to forest soil communities is still lacking

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