Abstract
Microbial eukaryotes are increasingly being recognised for their role in global biogeochemical cycles, yet very few studies have focussed on their distribution in high-latitude stream sediments, an important habitat which influences stream water nutrient chemistry. In this study, we present the first comparison of microbial eukaryotes from two different polar habitats by determining the abundance and taxonomic affiliation of 18S rRNA gene fragments recovered from four sediment samples in Svalbard: two from a glaciated catchment and two from an unglaciated permafrost-dominated catchment. Whilst there was no difference between the two catchments in terms of Rao’s phylogenetic diversity (0.18±0.04, 1SD), the glaciated catchment samples had slightly higher richness (138–139) than the unglaciated catchment samples (67–106). At the phylum level, Ciliophora had the highest relative abundance in the samples from the glaciated catchment (32–63%), but only comprised 0–17% of the unglaciated catchment samples. Bacillariophyta was the most abundant phylum in one of the samples from the unglaciated catchment (43%) but phototrophic microbial eukaryotes only formed a minor component of the glaciated catchment samples (<2%), suggesting that in these environments the microbial eukaryotes are predominantly heterotrophic (chemotrophic). This is in contrast to previously published data from Robertson Glacier, Canada where the relative abundance of chlorophyta (phototrophs) in three samples was 48–57%. The contrast may be due to differences in glacial hydrology and/or geology, highlighting the variation in microbial eukaryote communities between nominally similar environments.
Highlights
Northern latitude Polar environments have been shown to contain active and diverse microbial communities (e.g. Anesio and Laybourn-Parry 2012; Hamilton et al 2013; Jansson and Taş 2014) whose compositions and associated activities are susceptible to external physical and chemical change, for example, permafrost thaw (e.g. Mackelprang et al 2011; Liebner et al 2015)
Whether Arctic streams are net sources or sinks of carbon dioxide depends on the balance between autotrophic and heterotrophic organisms which directly impacts on stream dissolved organic carbon (DOC) dynamics (e.g. Battin et al 2008)
The eukaryal 18S rRNA gene alignment block was subjected to evolutionary model prediction via jModeltest (Darriba et al 2012), Maximum-Likelihood phylogenetic reconstruction via PhyML (Guindon and Gascuel 2003) specifying the general time reversible model and gamma distributed rate variation with a proportion of invariable sites, and rate smoothing using the multidimensional version of Rambaut’s parameterisation as implemented in PAUP (Swofford 2001) as previously described (Meuser et al 2013)
Summary
Northern latitude Polar environments have been shown to contain active and diverse microbial communities (e.g. Anesio and Laybourn-Parry 2012; Hamilton et al 2013; Jansson and Taş 2014) whose compositions and associated activities are susceptible to external physical and chemical change, for example, permafrost thaw (e.g. Mackelprang et al 2011; Liebner et al 2015). Anesio and Laybourn-Parry 2012; Hamilton et al 2013; Jansson and Taş 2014) whose compositions and associated activities are susceptible to external physical and chemical change, for example, permafrost thaw (e.g. Mackelprang et al 2011; Liebner et al 2015) These microbial communities have been shown to play key roles in biogeochemical cycles, in particular the carbon cycle (McCalley et al 2014). The number of studies that use gene or transcript sequencing to characterise microbial communities and their role in biogeochemical cycling in high-latitude systems has grown tremendously over the past decade (Anesio and Laybourn-Parry 2012; Boetius et al 2015) These studies have shown the presence of diverse bacterial and archaeal communities that directly impact the extent. In addition to recycling organic matter, Ciliophora, and heterotrophic eukarya in general, are themselves dependent on organic carbon and were found to comprise a significant fraction of active eukaryotes in a subglacial sediment sample (Hamilton et al 2013), further indicating their potential role in carbon cycling
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