High intensity fire accelerates accumulation of a stable carbon pool in permafrost peatlands under climate warming

Peatland carbon pools store one-third of global soil carbon, but are increasingly threatened by wildfires, particularly high intensity wildfires, as a consequence of climate warming. However, with only a limited understanding of fire history reconstruction available, the long-term impacts of fire intensity on the stability of the peatland carbon pool remains poorly understood. Here, based on Fourier transform infrared spectroscopy and chemical analysis of PyC and organic matter in Hongtu (HT) peat core in the northern Great Khingan Mountains (China), historical fire intensity and fuel sources during the last 700 years were reconstructed and their effects on carbon stability evaluated. Our results showed that the major stable carbon pool (i.e. aromatics) and the retained labile carbon pool (i.e. iron-bound organic carbon, Fe-OC) in HT peatland are 278.1 ± 6.2 mg·g−1 and 6.78 ± 3.85 mg·g−1, respectively. High-intensity herb fires in peatlands occurred more easily under wet conditions and caused more PyC accumulation than shrub fires. Both climate warming and high-intensity fire promoted more aromatics and Fe-OC accumulation, increasing the overall stability of peatland carbon pool. High-intensity fire under warm climate conditions resulted in Fe-OC accumulation rates threefold higher (ca. 0.02 mg·cm−2 yr−1 to ca. 0.06 mg·cm−2 yr−1) but had no marked effects on the aromatic and PyC accumulation rates. Overall, our results suggest that high-intensity fires can accelerate stable carbon pool accumulation in peatlands during climate warming.