Network analysis uncovers associations in the turnover of C1 molecules in a winter lake

The generation and consumption of single carbon molecules (CO 2 and CH 4 ) by aquatic microbial communities is an essential aspect of the global carbon budget. Organic carbon flow (warm sunlit regimes) is depicted as beginning at the surface with autochthonous fixation followed by biomass settling to sediments, CO2 respiration to the atmosphere, and outflow. We sought to broaden understanding of C1 cycling and consortia by examining the microbial community of a below-ice lake water column in which both input and output are likely disrupted due to ice cover. By analysing the microbial community composition and co-occurrence network of an ice-covered lake timeseries, we were able to identify potential consortia involved in C1 cycling. The network confirmed known associations supporting the efficacy of such analyses but also pointed to previously unknown potential associations. Further and contrary to typical organic carbon flow under warm sunlit regimes, we found support for upward flow of recently fixed carbon in cold low-light conditions under-ice in winter.