Abstract
Carbon-fixation is a critical process in severely oligotrophic Antarctic Dry Valley (DV) soils and may represent the major source of carbon in these arid environments. However, rates of C-fixation in DVs are currently unknown and the microorganisms responsible for these activities unidentified. In this study, C-fixation rates measured in the bulk arid soils (<5% moisture) ranged from below detection limits to ∼12 nmol C/cc/h. Rates in ephemerally wet soils ranged from ∼20 to 750 nmol C/cc/h, equating to turnover rates of ∼7–140 days, with lower rates in stream-associated soils as compared to lake-associated soils. Sequencing of the large subunit of RuBisCO (cbbL) in these soils identified green-type sequences dominated by the 1B cyanobacterial phylotype in both arid and wet soils including the RNA fraction of the wet soil. Red-type cbbL genes were dominated by 1C actinobacterial phylotypes in arid soils, with wetted soils containing nearly equal proportions of 1C (actinobacterial and proteobacterial signatures) and 1D (algal) phylotypes. Complementary 16S rRNA and 18S rRNA gene sequencing also revealed distinct differences in community structure between biotopes. This study is the first of its kind to examine C-fixation rates in DV soils and the microorganisms potentially responsible for these activities.
Highlights
The McMurdo Dry Valleys (DV) of Antarctica represents one of the coldest, driest and most oligotrophic desert systems on Earth (Cary et al, 2010)
Soil organic carbon (SOC) concentrations in the bulk arid DV soils do not typically exceed 1.0 mg g−1, with concentrations being at least an order of magnitude higher in soils associated with ephemerally wetted lake and stream systems (Parsons et al, 2004; Barrett et al, 2006a; Elberling et al, 2006; Hopkins et al, 2006b, 2009; Ball et al, 2009; Cary et al, 2010; Feng et al, 2010)
This transect was chosen due to the noticeable differences in C-fixation rates between wetted and arid soils, and because the N2-fixing microorganisms and nitrogenase activities of the soils have previously been described (Niederberger et al, 2012). Both form I green- and red-type cbbL genes were detected in total DNA extracts from wet (ML1–2) and dry (ML1– 4) sites
Summary
The McMurdo Dry Valleys (DV) of Antarctica represents one of the coldest, driest and most oligotrophic desert systems on Earth (Cary et al, 2010). The wetted soils associated with these systems are well-documented hotspots of biogeochemical cycling and can contain dense microbial mat communities that bind the top 1–2 cm of soil together (Runkel et al, 1998; McKnight et al, 1999, 2004, 2007; Maurice et al, 2002; Gooseff et al, 2003) Mat communities in these ephemerally wet soils are typically cyanobacterial-, or mossdominated and exhibit extremely patchy distribution (McKnight et al, 2004; Adams et al, 2006; Takacs-Vesbach et al, 2010). These communities survive the winter months in a desiccated state and, in some cases, are re-activated through hydration by summer melt-waters and over multiple wetting events can form large concentrations of responsive biomass (Vincent and Howard-Williams, 1986; McKnight et al, 1999)
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