Abstract Changing winter conditions in the Northern Hemisphere can alter metabolic processes and disrupt the activity of primary producers that provide the major source of autochthonous carbon to aquatic food webs. Photosynthetic primary producers and those that conserve energy from chemical reactions (chemoautotrophs) fix inorganic carbon into biomass and contribute fresh dissolved organic carbon via extracellular release or lysis. Because these guilds rely on different metabolic strategies to fix inorganic carbon, they may respond differently to changing winter conditions. Despite this, few studies have assessed both processes together. Here, we measured rates of photosynthetic primary production (PPP) and dark carbon fixation (DCF) in a Lake Superior connected waterbody throughout two winters and intervening seasons. We coupled these activity measurements with inhibitor incubations and molecular and microscopic assessments to examine guild‐level differences in responses to winter conditions. Our results revealed a diverse community of primary producers, including a late‐autumn cyanobacterial bloom, and showed that photosynthetic phytoplankton and chemolithoautotrophic microorganisms differentially contribute to the particulate and dissolved pools of autochthonous primary production, with chemolithoautotrophy contributing between 0.5% and 22.5% of net primary production. These findings provide insight into the relative importance of PPP and DCF to aquatic carbon production and responses to changing environmental conditions.
Tellez et al. (Sun,) studied this question.