Environmental selection of planktonic methanogens in permafrost thaw ponds.

Sophie Crevecoeur,Connie Lovejoy,Warwick F Vincent

doi:10.1038/srep31312

Sophie Crevecoeur, Connie Lovejoy + Show 1 more

Open Access

https://doi.org/10.1038/srep31312

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Abstract

The warming and thermal erosion of ice-containing permafrost results in thaw ponds that are strong emitters of methane to the atmosphere. Here we examined methanogens and other Archaea, in two types of thaw ponds that are formed by the collapse of either permafrost peat mounds (palsas) or mineral soil mounds (lithalsas) in subarctic Quebec, Canada. Using high-throughput sequencing of a hypervariable region of 16S rRNA, we determined the taxonomic structure and diversity of archaeal communities in near-bottom water samples, and analyzed the mcrA gene transcripts from two sites. The ponds at all sites were well stratified, with hypoxic or anoxic bottom waters. Their archaeal communities were dominated by Euryarchaeota, specifically taxa in the methanogenic orders Methanomicrobiales and Methanosarcinales, indicating a potentially active community of planktonic methanogens. The order Methanomicrobiales accounted for most of the mcrA transcripts in the two ponds. The Archaeal communities differed significantly between the lithalsa and palsa ponds, with higher alpha diversity in the organic-rich palsa ponds, and pronounced differences in community structure. These results indicate the widespread occurrence of planktonic, methane-producing Archaea in thaw ponds, with environmental selection of taxa according to permafrost landscape type.

Highlights

In the Hudson Bay region of subarctic Québec, thermokarst lakes and ponds have been increasing in size and number over the last three decades in response to rapid warming[17]
We evaluated the following hypotheses: (1) the bottom waters of these ponds provide a suitable habitat for methanogenic Archaea; (2) permafrost landscape type and the extent of permafrost degradation affect archaeal community structure; and (3), the carbon enriched conditions of the peatland palsa catchment favour greater archaeal diversity compared to mineral lithalsa dominated catchments
The bottom waters of all of the thaw ponds sampled in the present study harbored Archaea, with a major fraction of the 16S rRNA reads assigned to methanogenic taxa

Summary

Introduction

In the Hudson Bay region of subarctic Québec, thermokarst lakes and ponds have been increasing in size and number over the last three decades in response to rapid warming[17]. We evaluated the following hypotheses: (1) the bottom waters of these ponds provide a suitable habitat for methanogenic Archaea; (2) permafrost landscape type (peatland palsa versus mineral lithalsa) and the extent of permafrost degradation affect archaeal community structure; and (3), the carbon enriched conditions of the peatland palsa catchment favour greater archaeal diversity compared to mineral lithalsa dominated catchments. We tested these hypotheses using microbial plankton samples taken from ponds in three different permafrost valleys in subarctic Quebec, and the communities were identified using high-throughput sequencing (Illumina MiSeq) of the V6–V8 hypervariable region of archaeal 16S rRNA. Given that many of these thaw ponds contain high concentrations of suspended sediments[18], we tested for differences in archaeal taxonomic structure between particle-attached and free-living communities

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