Contrasting Responses of Protistan Plant Parasites and Phagotrophs to Ecosystems, Land Management and Soil Properties.

Anna Maria Fiore-Donno,Tim Richter-Heitmann,Michael Bonkowski

doi:10.3389/fmicb.2020.01823

Abstract

Functional traits are increasingly used in ecology to link the structure of microbial communities to ecosystem processes. We investigated two important protistan lineages, Cercozoa and Endomyxa (Rhizaria) in soil using Illumina sequencing and analyzed their diversity and functional traits along with their responses to environmental factors in grassland and forest across Germany. From 600 soil samples, we obtained 2,101 Operational Taxonomic Units representing ∼18 million Illumina reads (region V4, 18S rRNA gene). All major taxonomic and functional groups were present, dominated by small bacterivorous flagellates (Glissomonadida). Endomyxan plant parasites were absent from forests. In grassland, Cercozoa and Endomyxa were promoted by more intensive land use management. Grassland and forest strikingly differed in community composition. Relative abundances of bacterivores and eukaryvores were inversely influenced by environmental factors. These patterns provide new insights into the functional organization of soil biota and indications for a more sustainable land-use management.

Highlights

A major aim in terrestrial ecology is to understand the drivers affecting the composition and functioning of the soil food web, and how its components contribute to ecosystem functions and services
Our aims were : (i) the assessment of the diversity of Cercozoa and Endomyxa, classified into trophic guilds, in grassland and forest along regional and land use intensification gradients; (ii) the identification of environmental factors driving the distribution of the cercozoan and endomyxan communities, with a special focus on plant pathogens
Our primers were highly specific: the proportion of non-targeted Operational Taxonomic Units (OTUs) only accounted for 8%

Summary

Introduction

A major aim in terrestrial ecology is to understand the drivers affecting the composition and functioning of the soil food web, and how its components contribute to ecosystem functions and services. A main obstacle in food web models is the traditional, simplistic, but erroneous assumption that soil protists act only as bacterivores – protists occupy all trophic levels, including, autotrophs, mixotrophs, saprotrophs, eukaryvores, omnivores, as well as parasites of animals and plants and their hyperparasites (Geisen et al, 2016; Bonkowski et al, 2019). Disentangling the multiple roles of protists will increase the trophic resolution of the soil food web and will have a major influence on network properties, such as topology and connectivity (Henriksen et al, 2019) It is essential, to conduct large-scale molecular environmental sampling studies in soil, and to attribute ecologically meaningful traits to the identified sequences. This is facilitated by publicly available databases of protistan functional traits, including trophic guilds (Bjorbækmo et al, 2019; Dumack et al, 2019), and by community efforts to improve the reference databases for taxonomic annotation (del Campo et al, 2018)

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Conclusion