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Volume 13, issue 1 | Copyright

Special issue: Freshwater ecosystems in changing permafrost landscapes

Biogeosciences, 13, 13-26, 2016
https://doi.org/10.5194/bg-13-13-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Jan 2016

Research article | 14 Jan 2016

Phototrophic pigment diversity and picophytoplankton in permafrost thaw lakes

A. Przytulska1,2, J. Comte1,2,3, S. Crevecoeur1,2,3, C. Lovejoy1,2,3, I. Laurion4, and W. F. Vincent1,2 A. Przytulska et al.
  • 1Centre d'études nordiques (CEN) and Département de biologie, Université Laval, Québec City, QC G1V 0A6, Canada
  • 2Takuvik Joint International Laboratory, Centre National de la Recherche Scientifique (France, CNRS UMI 3376) and Département de Biologie, Université Laval, Québec City, QC G1V 0A6, Canada
  • 3Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec City, QC G1V 0A6, Canada
  • 4Centre d'études nordiques (CEN) and Centre Eau Terre Environnement, Institut National de la Recherche Scientifique (INRS-ETE), Québec City, QC G1K 9A9, Canada

Abstract. Permafrost thaw lakes (thermokarst lakes) are widely distributed across the northern landscape, and are known to be biogeochemically active sites that emit large amounts of carbon to the atmosphere as CH4 and CO2. However, the abundance and composition of the photosynthetic communities that fix CO2 have been little explored in this ecosystem type. In order to identify the major groups of phototrophic organisms and their controlling variables, we sampled 12 permafrost thaw lakes along a permafrost degradation gradient in northern Québec, Canada. Additional samples were taken from five rock-basin reference lakes in the region to determine if the thaw lakes differed in limnological properties and phototrophs. Phytoplankton community structure was determined by high-performance liquid chromatography analysis of their photoprotective and photosynthetic pigments, and autotrophic picoplankton concentrations were assessed by flow cytometry. One of the black-colored lakes located in a landscape of rapidly degrading palsas (permafrost mounds) was selected for high-throughput 18S rRNA sequencing to complement conclusions based on the pigment and cytometry analyses. The results showed that the limnological properties of the thaw lakes differed significantly from the reference lakes, and were more highly stratified. However, both waterbody types contained similarly diverse phytoplankton groups, with dominance of the pigment assemblages by fucoxanthin-containing taxa, as well as chlorophytes, cryptophytes and cyanobacteria. Chlorophyll a concentrations (Chl a) were correlated with total phosphorus (TP), and both were significantly higher in the thaw lakes (overall means of 3.3µgChl a L−1 and 34µgTPL−1) relative to the reference lakes (2.0µgChl aL−1 and 8.2µgTPL−1). Stepwise multiple regression of Chl a against the other algal pigments showed that it was largely a function of alloxanthin, fucoxanthin and Chl b (R2 = 0.85). The bottom waters of two of the thaw lakes also contained high concentrations of bacteriochlorophyll d, showing the presence of green photosynthetic sulphur bacteria. The molecular analyses indicated a relatively minor contribution of diatoms, while chrysophytes, dinoflagellates and chlorophytes were well represented; the heterotrophic eukaryote fraction was dominated by numerous ciliate taxa, and also included Heliozoa, Rhizaria, chytrids and flagellates. Autotrophic picoplankton occurred in biovolume concentrations up to 3.1 × 105µm3picocyanobacteria mL−1 and 1.9 × 106µm3picoeukaryotesmL−1, with large variations among lakes. Both groups of picophytoplankton were positively correlated with total phytoplankton abundance, as measured by Chl a; picocyanobacteria were inversely correlated with dissolved organic carbon, while picoeukaryotes were inversely correlated with conductivity. Despite their net heterotrophic character, subarctic thaw lakes are rich habitats for diverse phototrophic communities.

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Permafrost thaw lakes are a subject of increasing research interest given their abundance across the northern landscape. Our aim in the present study was to characterize the photosynthetic communities in a range of subarctic thaw lakes using a combination of HPLC analysis of algal and bacterial pigments, flow cytometry and molecular analysis. Our results showed that the thaw lakes contain diverse phototrophic communities and are a previously unrecognized habitat for abundant picophotoautotrophs.
Permafrost thaw lakes are a subject of increasing research interest given their abundance across...
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