Microbial mitigation of greenhouse gas emissions from boreal lakes

Sammanfattning: The climate change crisis has drawn the attention of both the public and scientific community to the carbon cycle and particularly to the importance of greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4). CO2 has been a key component of Earth´s climate regulation throughout its geological history and is now the main driver of the current change in climate. CH4 has been responsible for a quarter of the cumulative radiative forcing observed so far. Recent studies suggest that lakes could be a major source of both CO2 and CH4. Boreal lakes are of special interest as they represent 27% of the global lake area, and their production of CO2 and CH4 are expected to increase in the future. This project aimed to investigate microbial processes with the potential to limit the emissions of GHGs from boreal lakes. For that purpose, the impact of an increase in phosphorus (P) concentration in the water on CH4 oxidation under the ice was investigated as well as the community composition of the methanotrophic guild. We also looked at the potential importance of chemolithoautotrophic microorganisms in fixing CO2 in the water column. Using a combination of geochemical analysis, genomic studies, and in vivo assays, we showed that P amendment has the potential to increase methane oxidation, possibly limiting the expected increase in CH4 emissions due to anthropogenic fertilization of boreal lakes. We also showed that methanotrophic community structure in boreal lakes is driven by CH4 concentration and that alphaproteobacterial methanotrophs might play an important role in removing CH4 from surface waters. Finally, we showed that dark carbon fixation is a common trait in boreal lakes and that it seems related to the iron cycle.