The Science

Climate warming causes permafrost thaw predicted to increase methane (CH₄), carbon dioxide (CO₂), and toxic methylmercury (MeHg) formation, as well as nitrous oxide (N₂O), another potent greenhouse gas formed during degradation of nitrogen-containing soil organic matter in the Arctic.

A microcosm incubation study with Arctic tundra soil over 145 days demonstrated that N₂O at concentrations as low as 0.1 mM markedly inhibited microbial MeHg formation, methanogenesis, and sulfate reduction while slightly promoting CO₂ production. Microbial community analyses indicate that N₂O decreased the relative abundances of methanogenic archaea and microbial clades implicated in sulfate reduction and MeHg formation. Following depletion of N₂O, both MeHg formation and sulfate reduction rapidly resumed, whereas CH₄ production remained low, suggesting that N₂O affected susceptible microbial guilds differently.

MeHg formation strongly coincided with sulfate reduction, supporting prior reports linking sulfate-reducing bacteria (SRB) to MeHg formation in the Arctic soil. Our results suggest that microbial production of CH₄, CO₂, and MeHg is more complicated than previously thought. This research demonstrates complex biogeochemical interactions governing CH₄ and MeHg formation and thus lays the foundation for future mechanistic studies for improved predictive understanding of MeHg and greenhouse gas fluxes from thawing permafrost ecosystems.

The Impact

We observe that N₂O strongly inhibits MeHg and CH₄ production in Arctic permafrost, which is considered a critical-zone environment for MeHg formation and greenhouse gas (e.g., CH₄, CO₂, N₂O) emissions under climate warming scenarios. The observed inhibitory effects of N₂O have important implications for predicting the formation of neurotoxic MeHg and greenhouse gas emissions in Arctic ecosystems.

Summary

Climate warming causes permafrost thaw and soil organic matter degradation, resulting in the formation and release of CH₄, CO₂, N₂O, and toxic MeHg in the Arctic. We found that N₂O strongly inhibits CH₄ and MeHg formation, suggesting that microbial production of CH₄, CO₂, and MeHg is more complicated than previously thought. The complex interplay of microbial processes ultimately may determine how climate change will influence greenhouse gas formation and mercury transformation in the anoxic Arctic tundra.

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