Page 247 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

for climate policies, although controlling and reducing its fluxes requires an in-depth understanding of source and sink dynamics (Government of Alberta 2016; van Dingenen et al. 2018).
Although CO2 and CH4 are the most important biologically produced and human activity- affected GHGs, one should not forget the contribution of other trace gasses like nitrous oxide (N2O) (Etminan et al. 2016). Due to time and resource constraints, we did not include N2O fluxes in our experimental studies on permafrost soils and thermokarst lakes. To stress its potential relevance in a warming world, N2O has an even higher global warming potential than CO2 and CH4 (Myhre et al. 2013). Recent evidence suggests that there is a strong potential for N2O emissions from permafrost soils, ponds, lakes, and subarctic tundra (Abnizova et al. 2012; Voigt et al. 2017a, 2020). For example, recent measurements of N2O emissions in vegetated permafrost soils have shown that, despite their limited nitrogen availability through nitrogen fixation and mineralization, they are small but clear sources of N2O during the growing season (~30 μg N2O–N m−2 day−1) (Yergeau et al. 2010; Chen et al. 2018; Voigt et al. 2020). This question becomes increasingly relevant on the short term for peatlands and organic-rich sediments that experience increased nitrogen loads, such as reflected in Chapter 3. To better approximate impacts of climate change, integrating N2O fluxes in GHG flux measurements in both field set-ups and laboratory-based studies is urgently needed.
We need both top-down and bottom-up approaches in climate research
Top-down approaches include in situ GHG measurements, macro-, meso- and microcosms, enrichments, -omics approaches, and isolation strategies. We have to realize that especially meso- and microcosm studies are relatively easy, fast, and manipulatable. They may, however, not always fully reflect the processes occurring in a natural ecosystem. Nevertheless, these experiments are the best we currently have, and they provide a crucial link between natural ecosystems and laboratory-based cultures. Here, we used top-down approaches to study the microbial diversity and metabolic potential of permafrost ecosystems, peat sediments, and coal deposits. These studies (Chapter 4, 5, 7, 8 and 9) provided valuable insights in ecosystem functioning and potential.
Bottom-up approaches provide us with valuable first insights into the factors that control microbial activity. We investigated the possibilities for co-cultivation of CH4 cycling
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