Greenlandic Microbiomes and Greenhouse Gas Emissions

Thursday, 18 December 2014
Carsten Suhr Jacobsen1, Morten Schostag Nielsen1,2, Anders Prieme2, William E Holben1,3, Marek Stibal1, Sergio Morales3, Jacob Bælum1, Bo Elberling2, Peter Kuhry4 and Gustav Hugelius4, (1)Geological Survey of Denmark and Greenland, Copenhagen, Denmark, (2)University of Copenhagen, Copenhagen, Denmark, (3)University of Montana, Missoula, MT, United States, (4)Stockholm University, Stockholm, Sweden
Thawing permafrost and the resulting mineralization of previously frozen organic carbon (C) and nitrogen (N) are considered important future feedbacks from terrestrial ecosystems to the atmosphere. We characterized two contrasting permafrost cores as well as 21 top permafrost cores from Zackenberg in High-Arctic Greenland which is a site characterized by progressive permafrost thawing of more than 1 cm y-1 since 1996. Samples have been analyzed for total C and N content, dissolved C and N as well as the potential production of carbon dioxide, methane and nitrous oxide in an incubation experiment.

10 days after the thawing was initiated, rRNA from selected samples were extracted, transformed into cDNA and cloned to obtain an overview of the most abundant active bacterial populations in the incubation experiment. A total of 697 clones were successfully sequenced, yielding 21 unique OTUs. Despite the relatively high coverage values the diversity of bacteria in the samples was low (with a maximum Shannon-Wiener diversity index of 2.1).

Firmicutes (6 OTUs, 45-77% of clones) and Gammaproteobacteria (5 OTUs, 19-47% of clones) were the dominant groups in the samples, with Betaproteobacteria (4 OTUs), Actinobacteria (4 OTUs), Alphaproteobacteria (1 OTU) and Bacteroidetes (1 OTU) being less dominant. These characterizations revealed that those bacteria that are able to quickly colonize the thawing permafrost are mainly related to three groups of bacterial clones: Lysinibacillus; Pseudomonas and Clostridium.

Quantification of functional genes related to soil nitrogen transformation were performed both on the DNA and on the mRNA level using primers specific for genes involved in production of nitrous oxide (nirS, nirK) and consumption of nitrous oxide (nosZ). This showed that the genes were found in most soils, but that they only were expressed at a low level. We further measured the rates of nitrous oxide release from the soils and found that these were not clearly related to the potential (DNA) and activity (mRNA) found in the soils.

However, distinct differences were found in the active microbiomes of the thawed soils, and this is discussed in relation to the emission of N2O, CH4 and CO2.