Boreal forest soil CO2 and CH4 fluxes following fire and their responses to experimental warming and drying

Highlights: • Post-fire boreal forest had higher soil CO₂ flux than the mature forest. • Fire changed the boreal forest soil from a weak source of CH₄ to a weak sink. • Warming, drying and their combination made the post-fire soil a stronger C flux. Boreal forests store large amounts of organic carbon and are susceptible to climate changes, particularly rising temperature, changed soil water and increased fire frequency. The young post-fire ecosystems might occupy larger proportions of the boreal forests region with the expected increases in fire frequency in the future and change the carbon (C) balance of this region. However, it is unclear how soil C fluxes in the post-fire boreal forest response to the climate changes. Therefore, a two-year field experiment was conducted in a boreal forest to investigate the effects of fire on the soil C (CO₂ and CH₄) fluxes and the responses of these fluxes to simulated warmer and drier climate conditions. The results showed that the boreal forest recovered form wildfire 7–8 years had higher soil CO₂ flux than the mature forest. Furthermore, the treatments of warming, drying and the combination of warming and drying increased growing season cumulative soil CO₂ flux in the post-fire forest by 15.8%, 20.4% and 34.2%, respectively. However, the boreal forest soil changed from a weak CH₄ source to a weak CH₄ sink after fire disturbance. Although CH₄ absorption increased by warming and drying treatments, the interaction of warming and drying led to a decrease in soil CH₄ uptake. The results indicated that the post-fire soil showed CO₂ and CH₄ fluxes with a greater global warming potential than before burning and that the global warming potential of the soil gas fluxes further increased by warming and drying. The predictive power of models of C cycle-climate feedbacks could be increased by incorporating the distinct ecosystem following fire with permafrost degradation and climate change across the boreal zone.