Microbial life influences and controls both carbon storage and the vulnerability of soils. Understanding
microbial communities and functions and their shifting states in response to accelerated warming of the
global and northern realm crystalise increasingly as both one of the fastest effected sentinels as well as
amplifiers to environmental change. Yet, while soil ecology is well studied in agricultural systems,
permafrost microbiology in particular is still a relatively novel research area. As permafrost thaws,
immense ancient carbon stocks become available to an increasingly abundant community of fast-growing
taxa, readily decomposing organic matter into potent greenhouse gases, such as carbon dioxide (CO2),
methane (CH4), and nitrous oxide (N2O).
As a rare initial exploration and description of the freshly collapsed thermokarst gulley in Northeast (NE)
Greenland, Zackenberg, physicochemical analysis led to the discovery of up to 26’500-year-old material
at only 1 m depth, which contributed to a first publication (Paper S1). The main incentive of the first Ph.D.
publication (Paper I) was to apply amplicon sequencing to understand how the Bacteria, archaea, and
fungi abundances changed with depth over three consecutive years of abrupt thaw. We found increased
abundances of fast-growing taxa in freshly thawed permafrost, while the intact permafrost layers still
inhabited a unique community. Thaw state and age of layers were best explaining the community changes
with depth.
The following publication (Paper II) differentiated the putatively active from the total community within
these vulnerable depths by sequencing total RNA from samples of 2020. The results did not only confirm
trends from Paper I, but also indicated a microbial bloom, a high number of active organisms in the total
community, consisting of copiotrophic Betaproteobacteria and Bacteroidota. Furthermore, the
community across all kingdoms of life could be described for the first time in situ in eroding permafrost,
revealing significant predation patterns upon thaw. This novel insight on trophic relationships in such an
immediate response to thaw is unexpected and yet highlights the complexity of this eroding ecosystem.
The final publication (Paper III) described the use of quantifying methanogen abundances via qPCR in an
actively methane-emitting fen peatland, in an attempt to explore the use of quantitive molecular methods
as potential monitoring addition. Together with the age of soil cores, these genetic methods added to
understanding the shift from methane sink to source within this relatively young ecosystem. This
publication helped to highlight the importance of microbial understanding and genetic methods in the
analysis and interpretation of carbon fluxes