Drought-induced peatland carbon loss exacerbated by elevated CO₂ and warming.

Extreme drought events are predicted to increase with climate change, yet their impacts on ecosystem carbon dynamics under warming and elevated carbon dioxide (eCO2) remain unclear. In a peatland experiment with five warming treatments each under ambient carbon dioxide (aCO2) and eCO2 (+500 parts per million), a 2-month extreme drought in 2021 reduced net ecosystem productivity by 444.0 ± 65.8 and 736.6 ± 57.8 grams of carbon per square meter at +9°C under aCO2 and eCO2, respectively—228.6 ± 56.8% and 381.9 ± 83.4% of the reduction at +0°C under aCO2. This exacerbation was driven by warming-induced water table decline, prolonged low water tables, and CO2-enhanced substrate availability through increased plant carbon inputs. Findings indicate that future climate will greatly amplify carbon loss during extreme drought, reinforcing positive carbon-climate feedbacks. Editor's summary: Droughts are increasing in frequency and severity with climate change, which can reduce ecosystems' primary productivity. However, more studies are needed to determine how drought combines with warming and elevated carbon dioxide to affect ecosystems. Quan et al. manipulated these factors in peatland, a system that stores large amounts of carbon due to inhibited decomposition, in northern Minnesota. Extreme drought conditions over 2 months combined with warming substantially reduced primary productivity under both ambient and elevated carbon dioxide. Lower water tables and increased substrate for decomposition from plants increased respiration. This study suggests that future droughts could undermine peatlands' carbon sequestration, creating a positive feedback for climate change. —Bianca Lopez [ABSTRACT FROM AUTHOR]