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 (C) dynamics under warming and elevated CO2 (eCO2) remain unclear. In a peatland experiment with five warming treatments each under ambient (aCO2) and eCO2 (+500 ppm), a two-month extreme drought in 2021 reduced net ecosystem productivity by 444.0 ± 65.8 and 736.6 ± 57.8 g C m-2 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 C inputs. Findings indicate that future climate will greatly amplify C loss during extreme drought, reinforcing positive C-climate feedbacks.