Shifts in methanogenic community composition and methane fluxes along the degradation of discontinuous permafrost.

Susanne Liebner,Dirk Wagner,Mette M Svenning,Sizhong Yang,Andrea Kiss,Lars Ganzert

doi:10.3389/fmicb.2015.00356

Abstract

The response of methanogens to thawing permafrost is an important factor for the global greenhouse gas budget. We tracked methanogenic community structure, activity, and abundance along the degradation of sub-Arctic palsa peatland permafrost. We observed the development of pronounced methane production, release, and abundance of functional (mcrA) methanogenic gene numbers following the transitions from permafrost (palsa) to thaw pond structures. This was associated with the establishment of a methanogenic community consisting both of hydrogenotrophic (Methanobacterium, Methanocellales), and potential acetoclastic (Methanosarcina) members and their activity. While peat bog development was not reflected in significant changes of mcrA copy numbers, potential methane production, and rates of methane release decreased. This was primarily linked to a decline of potential acetoclastic in favor of hydrogenotrophic methanogens. Although palsa peatland succession offers similarities with typical transitions from fen to bog ecosystems, the observed dynamics in methane fluxes and methanogenic communities are primarily attributed to changes within the dominant Bryophyta and Cyperaceae taxa rather than to changes in peat moss and sedge coverage, pH and nutrient regime. Overall, the palsa peatland methanogenic community was characterized by a few dominant operational taxonomic units (OTUs). These OTUs seem to be indicative for methanogenic species that thrive in terrestrial organic rich environments. In summary, our study shows that after an initial stage of high methane emissions following permafrost thaw, methane fluxes, and methanogenic communities establish that are typical for northern peat bogs.

Highlights

The sub-Arctic belongs to the regions where global climate change occurs stronger and earlier than in most other regions of the world (Serreze et al, 2000; Serreze and Francis, 2006)
There, a single methanogenic species of potentially hydrogenotrophic metabolism was identified as key driver for the formation of methane in a peat bog characterized by permafrost thaw (McCalley et al, 2014; Mondav et al, 2014)
Complete permafrost thaw and further peat bog succession led to the formation of the collapsed palsa (CP) site, a stable stage within the succession of palsa peatlands

Summary

Introduction

The sub-Arctic belongs to the regions where global climate change occurs stronger and earlier than in most other regions of the world (Serreze et al, 2000; Serreze and Francis, 2006). The. Methanogenic community in thawing permafrost carbon released to the atmosphere as greenhouse gases (GHG) is thereby an important variable for the global climate (IPCC, 2007). There, a single methanogenic species of potentially hydrogenotrophic metabolism was identified as key driver for the formation of methane in a peat bog characterized by permafrost thaw (McCalley et al, 2014; Mondav et al, 2014). While these studies considered methane dynamics until palsa collapse, we aim at extending the knowledge on the methanogenic response to degrading permafrost tracking the methane cycle of an initial permafrost structure (palsa) along complete thaw until late peat bog succession. Assuming that the methanogenic response to permafrost thaw is reflected in alterations of community activity, abundance, and structure we determine these parameters in the light of detailed environmental analyses

Methods

Results

Conclusion