The biogeochemical variability of Arctic thermokarst ponds is reflected by stochastic and niche-driven microbial community assembly processes.

Alizée Le Moigne,Jakob Pernthaler,Samuel Abiven,Gabriela Schaepman‐Strub,Maciej Bartosiewicz

doi:10.1111/1462-2920.15260

Alizée Le Moigne, Jakob Pernthaler + Show 3 more

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https://doi.org/10.1111/1462-2920.15260

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Abstract

SummaryShallow thermokarst ponds are a conspicuous landscape element of the Arctic Siberian tundra with high biogeochemical variability. Little is known about how microbes from the regional species pool assemble into local pond communities and how the resulting patterns affect functional properties such as dissolved organic carbon (DOC) remineralization and greenhouse gas (GHG) turnover. We analysed the pelagic microbiomes of 20 ponds in north‐eastern Siberia in the context of their physico‐chemical properties. Ponds were categorized as polygonal or trough according to their geomorphological origin. The diversity of bacteria and eukaryotic microbes was assessed by ribosomal gene tag sequencing. Null model analysis revealed an important role of stochastic assembly processes within ponds of identical origin, in particular for genotypes only occurring in few systems. Nevertheless, the two pond types clearly represented distinct niches for both the bacterial and eukaryotic microbial communities. Carbon dioxide concentration, indicative of heterotrophic microbial processes, varied greatly, especially in the trough ponds. Methane concentrations were lower in polygonal ponds and were correlated with the estimated abundance of methanotrophs. Thus, the overall functional variability of Arctic ponds reflects the stochastic assembly of their microbial communities. Distinct functional subcommunities can, nevertheless, be related to GHG concentrations.

Highlights

Lakes and ponds are common landscape elements of the arctic permafrost lowlands
Little is known about how microbes from the regional species pool assemble into local pond communities and how the resulting patterns affect functional properties such as dissolved organic carbon (DOC) remineralization and greenhouse gas (GHG) turnover
We investigated the bacterial and eukaryotic pelagic microbial communities in the context of physico-chemical variability in two distinct types of shallow Arctic ponds with the following objectives: assess (i) if the microbial community structure in these ponds was primarily shaped by neutral assembly processes or determined by differences in habitat structure and/or pond origin and (ii) if the microbial assembly processes and resulting structure were reflected in the biogeochemistry of these shallow ponds in the context of GHG saturation and potential emissions

Summary

Introduction

Lakes and ponds are common landscape elements of the arctic permafrost lowlands. The most prevalent water bodies of the northern tundra are small shallow ponds with a surface area under 1 km and a depth lower than 2 m (Verpoorter et al, 2014; Muster et al, 2017). The hydrology of these ponds seems to follow natural cycles of formation, expansion and drainage (van Huissteden et al, 2011), climate warming is likely to trigger an acceleration of these cycles in the Arctic regions (Vincent et al, 2013). Given their shallowness and small size, arctic ponds are characterized by a large interface between the water and the sediments, the surrounding terrestrial ecosystems and the atmosphere. Periodically acting as CO2 sinks (Laurion et al, 2010), thermokarst ponds are often

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