Climate warming restructures food webs and carbon flow in high-latitude ecosystems

Rapid warming of high-latitude ecosystems is increasing microbial activity and accelerating the decomposition of permafrost soils. This proliferation of microbial energy could restructure high-latitude food webs and alter carbon cycling between above-ground and below-ground habitats. We used stable isotope analysis (δ13C) of amino acids to trace carbon flow through food webs exposed to warming and quantified changes in the assimilation of microbial carbon by Arctic tundra and boreal forest consumers. From 1990 to 2021, small mammals in boreal forests exhibited a significant reduction in the use of plant-based ‘green’ food webs and an increased use of microbially mediated ‘brown’ food webs, punctuated by a >30% rise in fungal carbon assimilation. Similarly, fungal carbon assimilation rose 27% in wolf spiders under experimental warming in Arctic tundra. These findings reveal a climate-mediated ‘browning’ of high-latitude food webs and point to an understudied pathway by which animals can impact carbon cycling under climate warming.