Winter In the Arctic: The Action Is Underground.

Biological processes occurring during the Arctic winter play important roles in Arctic biogeochemical cycles. Winter soil respiration can determine whether the tundra is a net C sink or source, yet the processes regulating winter microbial dynamics remain perplexing. Microbes appear to shift into cold-season metabolism before soils freeze, shifting metabolism from plant detritus to stress-resistance metabolisms that rely proportionally more heavily on recycling microbial products than on plant detritus. Some organisms make the transition successfully enough that they are able to grow even when soils are frozen, assimilating C into cell membrane fatty acids and replicating DNA. The shift in metabolic patterns cause a major shift in N metabolic patterns: microbes may be intensely N limited during the summer, but C limited during the winter. This shift in resource use patterns appears at all levels of processing, from net mineralization, to shifts in how microbes allocate C- vs. N-rich substrates. I will synthesize our current understanding of how microbes function during the winter in the Arctic and how the physiological responses regulate large-scale biogeochemical functioning.