Trajectories of freshwater microbial genomics and greenhouse gas saturation upon glacial retreat

Abstract Due to climate warming, ice sheets around the world are losing mass, contributing to changes in runoff, loads of nutrients and organic carbon to recipient lakes and rivers, and on a longer time span to greening of terrestrial landscapes. These changes are expected to affect microbial communities and the release of greenhouse gases from these systems, and thus repercuss to climate. However, these repercussions are poorly constrained mostly due to limited knowledge on microbial responses to deglaciation. Using genomic and chemical data from freshwater chronosequences in Arctic Svalbard and Alpine Norway, we reveal the genomic succession from chemolithotrophic to photo- and heterotrophic microbial taxa upon glacial retreat and nutrient fertilization by birds. The highly resolved trait patterns were related to greenhouse gas concentrations including methane and carbon dioxide supersaturation. Although methanotrophs were present and increased along the chronosequence, methane consumption rates were low even in supersaturated systems. Nitrous oxide oversaturation and genomic information suggest active nitrogen cycling across the entire deglaciated landscape, and in the high Arctic, birds served as major modulators at many sites. Our findings show diverse microbial succession patterns, and trajectories in carbon and nitrogen cycle processes representing a positive feedback loop of deglaciation on climate warming.