Low-severity fire promote carbon emissions in permafrost peatlands of the Great Khingan Mountains, Northeast China

Abstract

Permafrost peatlands are critical carbon sinks in terrestrial ecosystems, but the use of prescribed fire in Northeast China threatens the stability of their carbon (C) stocks. The mechanism of low-severity fire (including plant loss and pyrogenic carbon/PyC input) affect soil CO₂ emissions from permafrost peatlands is still unknown. Thus, we selected permafrost peatlands in the Great Khingan Mountains (Northeast China) for three years of consecutive fire (fire plots: F plots; fire plots remove PyC: F-B plots) and simulated fire experiments. We found that fire increased CO₂ emissions by 2.25-fold. Total soil carbon decreased after fire, while light fraction carbon and the aromatic content of all four fractions increased due to PyC inputs. The labile C (DOC and light fraction C) increased after fire, and the average C distribution of light fraction increased significantly compared to the unburned plots. Soil CO₂ emissions was hastened by the rise in post-fire labile C substrate. Further structural equation model (SEM) analysis showed that the labile C substrate predominated under burned conditions, while enzyme activity predominated under unburned conditions for soil CO₂ emissions. Labile C substrates in peatland soils are more sensitive to fire and should be considered in carbon cycling studies after fires. In addition, the F-B plots promoted CO₂ emissions, while the simulated fire plots did not significantly alter CO₂ emissions, so considering only the effect of the PyC produced after the fire on CO₂ emissions is incomplete in peatlands. Overall, soil CO₂ emissions from permafrost peatlands is determined by changes in soil C fractions after fire, specifically the quantity of labile C, which is regulated by both plant residue and PyC after fire.