Examination of Soil Microbial Communities After Permafrost Thaw Subsequent to an Active Layer Detachment in the High Arctic

Cara N Inglese,Casper T Christiansen,Daniel Lamhonwah,Kristy Moniz,Scott N Montross,Scott Lamoureux,Melissa Lafrenière,Paul Grogan,Virginia K Walker

doi:10.1657/aaar0016-066

Abstract

ABSTRACTActive layer detachments (ALDs) are permafrost disturbances associated with climate change and increased seasonal warming. Such perturbations result from thawing of the upper permafrost and downslope movement of the overlying thawed material, including the active layer. ALDs have the potential to impact soil microbial community composition and function in arctic soil ecosystems. Here we report an initial investigation of an ALD located at Cape Bounty on Melville Island in the Canadian High Arctic. We examined soil nutrient content as well as microbial community structure using denaturing gradient gel electrophoresis and sequencing. Soil from the disturbed site showed changes in microbial communities with strikingly different fungal community composition compared to soils from an adjacent undisturbed site. These community changes were correlated with enhanced levels of dissolved organic carbon, microbial carbon, total dissolved nitrogen, and microbial nitrogen. The Nitrososphaerales—an order of ammonia-oxidizing Archaea—were more abundant in the disturbed soil and may have been responsible for the altered nitrogen cycling that resulted in higher levels of total dissolved nitrogen there. The fungal communities at both sites were dominated by orders within the Ascomycota, a phylum of mainly hyphal fungi. Intriguingly however, they were more numerous in the undisturbed soil compared to the disturbed soil, suggesting that certain Ascomycota could not reestablish within six years of the ALD, and more generally that fungal hyphal networks may help to stabilize tundra surface soils against erosional losses.

Highlights

Some areas of the Canadian High Arctic are already on track to follow predictions that there will be a 4–8 °C increase in average air temperature within this century (IPCC, 2007).it is not surprising to learn that the permafrost, which comprises a significant proportion of the terrestrial landscape, is warming and thawing, resulting in disturbances and changing soil conditions (Lamoureux and Lafrenière, 2009; Yergeau et al, 2010; Pautler et al, 2010)
Environmental and geochemical characteristics of core samples taken from an undisturbed (UN) and a disturbed (D) active layer detachment at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, in the Canadian High Arctic
Solute amounts are measured in ppm with neg. indicating that the negligible concentrations were beneath the detection limits of ~0.03 for each solute. bThe top of each core corresponded to 1 cm for the disturbed and 13 cm for the undisturbed core

Summary

Introduction

Some areas of the Canadian High Arctic are already on track to follow predictions that there will be a 4–8 °C increase in average air temperature within this century (IPCC, 2007).it is not surprising to learn that the permafrost, which comprises a significant proportion of the terrestrial landscape, is warming and thawing, resulting in disturbances and changing soil conditions (Lamoureux and Lafrenière, 2009; Yergeau et al, 2010; Pautler et al, 2010) This thawing can result in ecosystem- and landscape-scale disturbances such as thermokarst (including collapsed pingos and sinkholes), as well as disturbances including active layer detachments (ALDs) and larger retrogressive thaw slumps (Jones et al, 2013). Arctic fungal communities differ with soil pH, C:N ratio, and available phosphorus as well as in association with frost heave and long-term experimental warming (Fujimura and Egger, 2012; Timling et al, 2014; Geml et al, 2015).Together, these various bacteria, Archaea, and fungi perform key functions in global biogeochemical cycling, including nitrogen cycling.any changes in microbial assemblages following ALDs could have important consequences for soil function and nutrient availability to plants, and yet these effects have been largely unexplored

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Conclusion