Complexity of nutrient enrichment on subarctic peatland soil CO2 and CH4 production under increasing wildfire and permafrost thaw

Abstract. The adverse impacts of excessive soil nutrients on water quality and carbon sequestration have been recognized in tropical and temperate regions, with already widespread industrial farming and urbanization, but rarely in subarctic regions. However, recent studies have shown significant increases in porewater nitrogen (N) and phosphorus (P) concentrations in burned subarctic peatlands and downstream waters, which is a growing concern as climate change leads to increasing wildfires, permafrost thaws, and waterlogged peatlands. In this study, we present the results of a short-term incubation experiment conducted on soils from subarctic bogs and fens, aimed at evaluating the effects of high levels of nutrients on carbon gas production rates. We divided aliquots of the peatland soil samples into separate containers and added artificial porewater to each, enriching them with dissolved inorganic nitrogen (N), phosphorus (P), both, or none for controls. Overall, the fen samples showed higher carbon dioxide (CO₂) and methane (CH₄) production rates at 1, 5, 15, and 25 °C compared to the bog samples, which we attributed to differences in soil properties and initial microbial biomass. The bog sample with added N produced more CO₂ compared to its control, while the fen sample with added P produced more CO₂ compared to its control. It was unexpected that the addition of both N and P reduced CO₂ but increased CH₄ production in both soils compared to their controls. After a month, the pore water C, N, and P stochiometric ratios approached the initial soil microbial biomass ratios, suggesting microbial nutrient recycling in an inherently nutrient-poor soil environment. These preliminary results imply a complex response of carbon turnover in peatland soils to nutrient enrichment.