Impacts of wildfire on greenhouse gas and soil microbial community dynamics in peatlands

Background/Question/Methods

Peatlands are an important component of the global carbon (C) cycle, they operate as long-term global sinks of atmospheric carbon dioxide (CO2) and sources of methane (CH4). Wildfire is the largest contemporary threat to North American peatlands. Loss of labile substrates and methanogenic community are often attributed as main drivers behind CO2 and CH4 emission reductions in peatlands post-wildfire. However, the role of wildfire fire-generated charcoal and its potential to impact soil CO2 and CH4 emissions in peatlands post-fire is not well understood. To address this knowledge gap, we measured in-situ CH4 and CO2 fluxes in burned and unburned peatlands approximately 2 months and 2 years post-fire. We also collected soil samples and conducted soil incubation experiments to measure and compare CH4 production potential and oxidation. An additional sub-group of samples were incubated where the wildfire-generated charcoal layer from the burned samples was removed and added to unburned samples to examine the impact of charcoal on microbial activity. Environmental variables such as water table depth, soil temperature and moisture were collected at each site. Microbial community composition was analyzed using 16rRNA S amplicon sequencing, targeting methanogens and methanotrophs. Soil samples were also analyzed for phenolic compounds, pH, and electric conductivity.

Results/Conclusions

In both the recently burned and 2-year post fire incubations a ‘charcoal effect’ was observed, where samples with wildfire-generated charcoal exhibited lower CH4 production potential and oxidation than those without. The microbial analysis revealed a diverse population of methanogens and methanotrophs present at the natural and burned sites, indicating that the burn did not result in a loss or reduction of the methanogenic community. In-situ field fluxes determined that both ecosystem respiration (ER) and net ecosystem CO2 exchange (NEE) were lower at the burned site compared to the natural site. Overall, this study enhances our understanding of the impacts of wildfire and therefore wildfire-generated charcoal on greenhouse gas dynamics and carbon storage in peatland ecosystems both immediately and 2-years post-burn.