Page 14 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Summary
In Chapter 6 we reviewed the current state of knowledge on thermokarst lakes. These lakes, which form upon the thaw of ice-rich Yedoma deposits, are net greenhouse gas sources as century-old carbon deposits become bioavailable and are mineralized to the GHGs CO2, nitrous oxide (N2O), and CH4. Methane emissions are the net result of CH4 production by methanogenesis and CH4 oxidation by aerobic bacteria or anaerobic prokaryotes, with high levels of heterogeneity and intricate interactions that are not yet well understood. It is expected that future climate change will have disproportionate effects on the Arctic, which implies potentially strong consequences for future GHG fluxes and thaw progression.
Subsequently, we focused on the microbial controls of climate change in cold ecosystems (Chapter 7 and 8). We wanted to better understand how microbes affect climate change and how they will, in turn, be affected by altering conditions. Upon increasing the substrate availability and temperature of Alaskan thermokarst lake sediment, we observed a rapid response of both CH4 production and consumption (Chapter 7). On the long term, the community was largely controlled by substrate availability rather than temperature. Upon closer metagenomic investigation of the methanogenic communities, we observed methanogen species-specific responses that were initially not detected with a 16S rRNA gene-based approach (Chapter 8).
In Chapter 9 we studied the diversity and functional potential of the microbial communities in permafrost soils exposed to a 4°C warming scenario for over five years. The largest community shifts were observed in the transition layer and the permafrost, which are prone to warming and are therefore important future climate contributors in a warming world. Warming resulted in a decrease in metabolic genes and an increase in carbohydrate-active enzymes. Furthermore, the community shifted its potential towards less labile organic matter degradation upon warming. We concluded that GHG production in permafrost soils can be modulated through taxonomic and functional shifts.
The bottom-up approach of studying the interaction of methanogenic archaea (Methanosarcina barkeri) and aerobic methanotrophic bacteria (Methylocystis sp.) revealed a tight interaction of both groups (Chapter 10). Methanogens formed a tight cluster in the centre, methanotrophs
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