The functional potential of methane producing and consuming microorganisms in a changing world : Den funktionella potentialen hos mikroorganismer som producerar och förbrukar metan i en föränderlig värld

Sammanfattning: It’s clear that human activities have heated our climate via the release of anthropogenic greenhouse gases. Recent changes within the earth climate are rapid, intensifying, and unprecedented. With each additional increment of warming, climate change is impacting ecosystems through changes in average conditions, climate variability, coupled with other associated changes such as biodiversity loss and changes in elemental cycles.One ecosystem of particular importance are peatlands. Despite covering only ~3% of the terrestrial environment, northern peatlands are estimated to store 415 ± 150 Pg carbon, while permafrost peatlands are estimated to store 185 ± 66 Pg of soil organic carbon soil, thus acting as a large carbon sink. The highly concentrated carbon is maintained by the waterlogged anaerobic conditions that limit oxygen and bacterial decomposition. However, these anaerobic conditions favour methanogenesis, i.e. the formation of the strong greenhouse gas methane. During the thesis, one laboratory and three in-situ field studies were conducted. In paper I, we studied variation in methane fluxes with the structure and function of methane producing and consuming communities. In paper II, we performed an in-situ drought experiment across two years where we identified the effects of drought on the functional potential of methane producing and consuming communities. While working on paper II, we conducted a temporal experiment (paper IV) to intemperate the variation in methane emission rates and their δ13C-CH4 values. Finally, paper III addresses how sub-arctic peatland microbial communities respond to permafrost thaw at different degradation rates and whether this change is reflected in greenhouse gas emissions.We found that the structure and composition of the whole methane producing, and consuming community has minor effect on predicting the magnitude methane fluxes (paper I), however, during drought the structure and functional composition significantly changed in favor of more methane oxidation despite the lower methane emissions (paper II). In the sub arctic, paper III concluded that peatlands with fast permafrost degradation yielded the most differences in functional potential between thaw categories, indicating that the microbial community may be responding to newly available substrate previously inaccessible to microbial degradation. Finally, paper IV suggested that the substrate availability for methanogenesis is a major factor in explaining the spatial variation, but not the temporal variation in methane fluxes. Combined, these results suggest that the methane producing, and consuming community hold a high functional potential and can produce and consume methane in many ways despite disturbances such as drought and permafrost loss. This highlights a resilient community with the functional ability to adapt to future climate conditions.