Every major carbon-cycle model predicts that warming will release carbon from boreal soils. The prediction is intuitive: higher temperatures accelerate decomposition, decomposition releases stored carbon, and boreal peatlands store roughly 500 gigatonnes of it — a third of all terrestrial soil carbon. Published in Nature Ecology & Evolution, Feng Xiaojuan and colleagues from the Chinese Academy of Sciences and the University of Helsinki found the opposite in boreal Sphagnum peatlands. Warming enhances carbon accumulation, not release.
Three mechanisms produce this counterintuitive result, and all three are driven by the same warming signal. First, warming stimulates Sphagnum growth and ecosystem productivity when moisture is sufficient — more biomass enters the soil faster than it decomposes. Second, warming increases Sphagnum synthesis of antimicrobial secondary metabolites, which suppress the soil microbial communities that perform decomposition. The moss responds to warmth by producing more chemical defense, and that defense cascades into reduced decay rates. Third, warming promotes the accumulation of reactive iron hydroxides in the peat, which physically protect organic carbon by binding it to mineral surfaces.
The structural insight is about the failure of sign prediction in complex systems. The intuitive model — warming accelerates decomposition — is correct for boreal forests and tundra. It is incorrect for Sphagnum peatlands because Sphagnum is not a passive carbon reservoir. It is an organism that responds to its environment, and its response happens to counteract the thermodynamic prediction. The sign of the effect depends on whether the dominant player is the chemistry (decomposition rates) or the biology (Sphagnum's metabolic response). In peatlands, the biology wins. The warming that should release carbon instead triggers a biological defense that locks more carbon away.