Microbial Functional Potential and Community Composition in Permafrost-Affected Soils of the NW Canadian Arctic

Abstract

Permafrost-affected soils are among the most obvious ecosystems in which current microbial controls on organic matter decomposition are changing as a result of global warming. Warmer conditions in polygonal tundra will lead to a deepening of the seasonal active layer, provoking changes in microbial processes and possibly resulting in exacerbated carbon degradation under increasing anoxic conditions. To identify current microbial assemblages in carbon rich, water saturated permafrost environments, four polygonal tundra sites were investigated on Herschel Island and the Yukon Coast, Western Canadian Arctic. Ion Torrent sequencing of bacterial and archaeal 16S rRNA amplicons revealed the presence of all major microbial soil groups and indicated a local, vertical heterogeneity of the polygonal tundra soil community with increasing depth. Microbial diversity was found to be highest in the surface layers, decreasing towards the permafrost table. Quantitative PCR analysis of functional genes involved in carbon and nitrogen-cycling revealed a high functional potential in the surface layers, decreasing with increasing active layer depth. We observed that soil properties driving microbial diversity and functional potential varied in each study site. These results highlight the small-scale heterogeneity of geomorphologically comparable sites, greatly restricting generalizations about the fate of permafrost-affected environments in a warming Arctic.

Impacts of temperature and soil characteristics on methane production and oxidation in Arctic polygonal tundra

“…Therefore, near-surface layers of soil and the rhizosphere would be expected to have the highest CH 4 oxidation activity (Shukla et al, 2013;Gulledge et al, 1997). The 5 relative abundance of the pmoA marker gene for CH 4 oxidation decreased with soil depth in HCP trough soils (Yang et al, 2017) and in permafrost-affected soils from the Canadian Arctic (Frank-Fahle et al, 2014), consistent with that conceptual model. Thus, we would expect that the active layers of FCP and HCP in the BEO tundra have the highest rates of CH 4 oxidation.…”

Permafrost soils and carbon cycling

“…The zero-curtain zone of the active layer provides favorable conditions for heterotrophic soil respiration during the late fall to early winter. Thus, appreciable gas fluxes have been measured on the snow surface during winter (Zimov et al, 1993(Zimov et al, , 1996Fahnestock et al, 1999). It is likely that frost cracks provide passages for gases to reach the atmosphere as there is often a strong pulse of gases during early spring thaw.…”

“…Although most of the studies on cryostructure are focused on its physical aspects, cryostructure also has a role in soil biogeochemical processes. As the unfrozen water in ice lenses or ice layers in the cryostructure engage in heat and mass transfer in the winter (Romanovsky and Osterkamp, 2000), unfrozen water can serve as a channel for biological activity and thereby affect carbon cycling during winter months (Fahnestock et al, 1999).…”

Ecology and biogeochemistry of cyanobacteria in soils, permafrost, aquatic and cryptic polar habitats

“…Estimates suggest that 25 % of the northern hemisphere is underlain by permafrost (soil that has remained frozen for at least two consecutive years; reviewed in Jansson and Tas 2014) and may comprise up to 50 % of subsurface organic carbon stocks (Frank-Fahle et al 2014). The extent of permafrost distribution has decreased over the last century and it is predicted that near-surface permafrost thawing will be a continuous feature in the coming years as a feature of global warming (Steven et al 2008).…”

“…The microbial response to this permafrost thawing is still unresolved, including the contributions of particular microbial groups to CO 2 and CH 4 fluxes. Interestingly, cyanobacteria have been absent from numerous phylogenetic surveys using Arctic permafrost samples, with actinobacteria and proteobacteria predominating (Steven et al 2008;Frank-Fahle et al 2014). A metagenomic study also reported no cyanobacteria signature in a 2-m deep permafrost sample (Yergeau et al 2010), although the possible detection of nitrogenase (nifH) belonging to cyanobacteria was proposed.…”