Permafrost thaw releases nutrients and metals from previously frozen soils and these nutrients may affect important biogeochemical processes including methane (CH₄) production and oxidation. Here we assessed how concentrations of nutrients, solutes, and metals varied across four plant communities undergoing permafrost thaw and if these geochemical characteristics affected rates of CH₄ production and oxidation. We tested nutrient limitation in CH₄ production and oxidation by experimentally adding nitrogen (N), phosphorus (P) and a permafrost leachate to peat across these four plant communities. The upper 20 cm of permafrost contained 715 ± 298 mg m⁻² of extractable inorganic N and 20 ± 6 mg m⁻² of resin-extractable phosphorus (Pᵣₑₛᵢₙ), for a N:P ratio of 36:1. These low amounts of Pᵣₑₛᵢₙ coincide with high acid-digestible aluminum (Al), iron (Fe), and P concentrations in the permafrost soil and suggest that P may accumulate via sorption and constrain easily available forms of P for plants and microbes. Permafrost leachate additions decreased potential CH₄ production rates up to 80% and decreased CH₄ oxidation rates by 66%, likely due to inhibitory effects of N in the permafrost. In contrast, organic and inorganic P additions increased CH₄ oxidation rates up to 36% in the tall graminoid fen, a community where phosphate availability was low and CH₄ production was high. Our results suggest that (1) inorganic N is available immediately from permafrost thaw, while (2) P availability is controlled by sorption properties, and (3) plant community, nutrient stoichiometry, and metal availability modulate how permafrost thaw affects CH₄ production and oxidation.
