Low-intensity fire-derived pyrogenic carbon decouples methane and carbon dioxide production in aerobic and hypoxic layers of permafrost peatlands

Wildfire frequency is increasing in high-latitude permafrost peatlands, leading to the input of pyrogenic carbon (PyC) into the active layer. The effect of PyC on the critical greenhouse gases CH 4 and CO 2 production in the active layer (aerobic and hypoxic) is poorly constrained. We conducted a laboratory incubation experiment using bulk peat soil from the active layer of the Great Khingan Mountains to investigate the effects of PyC addition (5 % and 10 %) on CH 4 and CO 2 production under aerobic and hypoxic conditions. Our results show that PyC addition suppressed CH 4 production under both conditions (by up to 57.6 %), but stimulated CO 2 production. Consequently, the net global warming potential (GWP) was reduced under hypoxic conditions, as the decrease in CH 4 -derived GWP offset the increase from CO 2 . PyC input increased the DIC/DOC ratio in the aerobic layer, reflecting a shift toward enhanced dissolved organic matter mineralization and CO 2 production. In the hypoxic layer, PyC input increased the dissolved electron shuttling capacity (D‑ESC), reflecting a greater abundance of redox‑active organic electron shuttles, thereby suppressing CH 4 production in peat. This study provides the first mechanistic explanation linking electron transfer processes and enzyme activity to the decoupled production of CH 4 and CO 2 in peatlands. Our findings demonstrate that PyC from low-severity fires can decouple the typically synergistic production of CH 4 and CO 2 , and its net effect on the greenhouse gas balance is governed by the redox conditions within the peat active layer.