Reindeer Rangifer tarandus, a large circumpolar herbivore, can influence whether nitrogen (N) or phosphorus (P) is the primary limiting nutrient in tundra plant communities. Specifically, findings from a site in northern Scandinavia suggest that under conditions where reindeer grazing stimulates inorganic N availability, grazing may drive ecosystems towards P limitation. However, the mechanisms driving such effects on tundra soil P biogeochemistry remain poorly understood. We conducted a study, where heavily grazed areas locate close to long-term lightly grazed areas in both meadows and heaths in northern Norway, to assess how reindeer grazing moderates soil inorganic N and P concentrations, and particularly the relationship between P availability and soil P sorption capacity. We measured water extractable inorganic N (NH4-N and NO3-N) and water extractable P (PO4-P) concentrations, P sorption index, and the P-sorbing elements aluminium (Al) and iron (Fe). Our results demonstrate that high reindeer grazing pressure was related to higher extractable inorganic N concentrations in the organic soil layer in meadows, and a higher extractable inorganic N:P ratio in both vegetation types. Also, the higher reindeer grazing pressure significantly increased the soil P sorption index, which was positively related to soil Al + Fe concentrations and decreased extractable PO4-P in the organic layer in the heath. In the meadow, extractable PO4-P concentrations remained unchanged while the extractable N:P ratio increased from 21 to 30, thus decreasing the amount of extractable PO4-P per unit of inorganic N. We conclude that herbivores shift both habitats in our study area in the direction of P limitation, but the mechanism seems to vary from increased P sorption in the heath to increased N availability in the meadow. This shift in mechanism could be important for understanding how herbivores can influence the relative importance of N and P limitation in ecosystems across the Arctic.

Permafrost degradation, driven by rising temperatures in high-latitude regions, destabilizes previously sequestered soil organic carbon (OC), increasing greenhouse gas emissions and amplifying global warming. In these ecosystems, interactions with mineral surfaces and metal oxides, particularly iron (Fe), stabilize up to 80% of soil OC. This study investigates the mechanisms of Fe solubilization and OC release across a permafrost thaw gradient in Stordalen, Abisko, Sweden, including palsa, intermediate, and highly degraded permafrost stages. By integrating geophysical measurements-including relative elevation, thaw depth, soil water content, and soil temperature with redox potential and soil pore water chemistry, we identify the environmental conditions driving iron and organic carbon release into soil pore waters with permafrost degradation. Our results show that combining relative elevation, thaw depth, soil water content, soil pore water pH, and soil pore water conductivity with shifts in vegetation species enables very-high-resolution detection of permafrost degradation at submeter scales, distinguishing intact from degraded permafrost soils. We show that small-scale changes in thaw depth and water content alter soil pH and redox conditions, driving the release of Fe and dissolved organic carbon (DOC) and promoting the formation of Fe-DOC complexes in soil pore water. The amount of exported Fe-DOC complexes from thawed soils varies with the stage of permafrost degradation, and the fate of Fe-DOC complexes is likely to evolve along the soil-stream continuum. This study highlights how environmental conditions upon thaw control the type of Fe-DOC association in soil pore waters, a parameter to consider when quantifying what DOC is available for microbial and photo-degradation in aquatic systems which are significant sources of greenhouse gas emissions across Arctic landscapes.

Organic phosphorus (P) plays a crucial role in maintaining the health and productivity of soils. Understanding the composition of organic phosphorus in soils is thus relevant to a range of disciplines, spanning from agricultural sciences to ecology. Over the past few decades, efforts have been directed towards characterizing and quantifying various soil organic P compounds and determining their turnover rates. Despite these efforts, the precise nature of soil organic P remains unclear, particularly that of orthophosphate monoesters, which dominate 31P NMR spectra of NaOH-EDTA extracts globally.Typically, the monoester region of 1D 31P NMR spectra appears as a series of sharp signals "sitting" on a broad background where the broad background can account for a substantial part of the monoester region. This is prompting questions about how to integrate and identify these signals and to what extent this fraction may be ecologically important. To investigate this monoester background, we employed 1D 31P NMR and 2D 1H-31P NMR1, along with 31P transverse relaxation (T2)2 measurements to calculate intrinsic linewidths. We related this linewidth to molecular weight to unveil the nature of the observed background. Analysing seven soils from different ecosystems, we observed linewidths ranging from 0.5 to 3 Hz for both resolved monoester signals and the background. This suggests that the background comprises numerous, possibly exceeding 100, sharp signals associated with small (

Differences in catchment properties may be major drivers in mercury (Hg) cycling. However, the complex interplay of these environmental drivers with Hg speciation, transport, and bioavailability is still not fully understood. To relate Hg speciation to different catchment types (tundra, birch, boreal) and their inherent differences in stream and lake chemistry, we studied Hg speciation and concentrations along a climate and vegetation gradient in sub‐arctic northern Sweden (including 18 streams and 8 lakes). We find differences in Hg concentrations aligning with differences in water chemistry between the studied catchment types. All observed differences between catchments align with the gradient in aquatic and terrestrial biological productivity (tundra < birch < boreal). Moreover, we find higher methylmercury (MeHg) concentrations in lakes compared to streams. Overall, our data suggests that dissolved organic matter (DOM) components play a crucial role in (a) the concentrations of total Hg and MeHg in the studied waters (especially allochthonous DOM) and (b) Hg methylation (especially autochthonous DOM).

The consequences of permafrost thaw for organic carbon release are mainly studied in summer, considering the frozen soil is inert in winter. Here, we show that biogeochemical processes also occur during early winter. We combine Si isotopes and Ge/Si with Fe and dissolved organic carbon (DOC) concentrations in soil porewater along a natural gradient of permafrost degradation (palsa, intermediate and degraded palsa sites) and in river water (Stordalen, Sweden) collected during late autumn and early winter. The data support: (i) the occurrence of early winter snowmelt water infiltration in soils diluting more extensively the soil porewater in dry well-drained palsa soils; (ii) the decrease of the redox potential (by 30 %) induced by snowmelt water infiltration and water table rise at the intermediate site, favouring Fe-oxides dissolution and the release of the associated DOC in soil porewater; (iii) the contribution of snowmelt water infiltration to the Fe and DOC lateral export from permafrost degrading soils to rivers.

In situ field studies in thawing permafrost regions have shown that C emissions resulting from organic carbon (OC) decomposition depend among others on the variability in soil water content, which can be directly related to microtopography. A more precise assessment of the evolution of permafrost C emissions as a function of thermokarst development requires high-resolution quantification of thermokarst-affected areas, as lowland thermokarst development induces fine-scale spatial variability (~ 50 – 100 cm). Here, we investigate a gradient of lowland thermokarst development at Stordalen mire, Abisko, Sweden, from well-drained undisturbed palsas to inundated fens, which have undergone ground subsidence. We produced orthomosaics and digital elevation models from very-high resolution (10 cm) UAV photogrammetry as well as a spatially continuous map of soil electrical conductivity (EC) based on Electromagnetic Induction (EMI) measurements performed in September 2021. In conjunction, we measured in situ the soil water content from the different stages of thermokarst development at the same period. The soil EC values are contrasted along the gradient in line with contrasts observed in the landscape classification derived from the orthomosaics and digital elevation models: palsas are flat areas with low soil EC (drier), whereas fens are subsided areas with higher EC (water-saturated). Areas in the course of degradation (transition zones) are well identified based on their higher slope, and broad range of EC. Importantly, these transition zones are only detected using a very fine spatial scale (i.e., 10 cm) coupled to information on the microtopography. Compared to a set of previously collected orthomosaics and digital elevation models, our results show an acceleration of thermokarst development in this area with a rate of palsa decline 4 to 10 times greater in 2019-2021 than in 2000-2014.

Understanding the composition of organic phosphorus (P) in soils is relevant to various disciplines, from agricultural sciences to ecology. Despite past efforts, the precise nature of soil organic P remains an enigma, especially that of the orthophosphate monoesters, which dominate 31P NMR spectra of NaOH-EDTA extracts of soils worldwide. The monoester region often exhibits an unidentified, broad background believed to represent high molecular weight (MW) P. We investigated this monoester background using 1D 31P NMR and 2D 1H31P NMR, as well as 31P transverse relaxation (T2) measurements to calculate its intrinsic linewidth and relate it to MW. Analyzing seven soils from different ecosystems, we observed linewidths of 0.5 to 3 Hz for resolved monoester signals and the background, indicating that it consists of many, possibly >100, sharp signals associated with small (<1.5 kDa) organic P molecules. This result was further supported by 2D 1H31P NMR spectra revealing signals not resolved in the 1D spectra. Our findings align with 31P NMR studies detecting background signals in soil-free samples and modern evidence that alkali-soluble soil organic matter consists of self-assemblies of small organic compounds mimicking large molecules.

Phosphorus (P) is an essential element for all life on Earth. Understanding P cycling is in the context of global change crucial both for modelling of global biogeochemical cycles and for agricultural productivity. Recently, concerns about the future of P fertilizer supply have prompted much research on soil P and method development. 31P Nuclear Magnetic Resonance (NMR) Spectroscopy has been used to analyse speciation of inorganic and of organic P species (Po), using in alkaline soil extracts1. The region containing signals from phosphomonoesters is particularly important because these compounds are considered biologically active, but there are still significant problems to be resolved particularly for this region of P NMR spectra, including: 1. Poor signal resolution often makes quantification of Po species in this region very challenging. 2. It is unclear if observed signals are due to free P species, or originate from P compounds bound to high-molecular weight soil matter. 3. The question needs to be addressed how signals observed in alkaline extracts relate to P species that were originally present in the soil. Here we present two approaches to address these problems:In a study of a 5000-year soil chronosequence in Northern Sweden2, we found that humus P composition barely changed, although time since fire varied up to 5000 years. We will present a new method to back-calculate original Po speciation from the observed composition. Results of this method indicate absence of “recalcitrant” Po species, and instead indicate that most Po was originally present as biologically active P metabolites, probably present in live soil organisms. We will discuss implication of these findings for P biogeochemistry.Second, we studied a diverse group of soils to address how the poorly resolved phosphomonoester region should best be analysed. Deconvolution techniques are required to handle the overlap, but a better understanding of the nature of the signals is required for reliable quantification. Based on combined analysis of 1D 31P NMR, 2D 1H-31P NMR and 31P linewidth measurements, we present a strategy for quantification of phosphomonoester species, as next step in linking observed Po speciation to P bioavailability. (1) Cade-Menun BJ, Preston CM (1996) A comparison of soil extraction procedures for 31P NMR spectroscopy. Soil Sci 161:770–785(2) Andrea G. Vincent, Jürgen Schleucher, Reiner Giesler, David A. Wardle (2022) Soil phosphorus forms show only minor changes across a 5000‑year‑old boreal wildfire chronosequence. Biogeochemistry (2022) 159:15–32 https://doi.org/10.1007/s10533-022-00910-2(3) Vestergren J, Vincent AG, Jansson M et al (2012) High-resolution characterization of organic phosphorus in soil extracts using 2D 1H–31P NMR correlation spectroscopy. Environ Sci Technol 46:3950–3956. https:// doi. org/ 10. 1021/ es204016h

Vegetation holds the key to many properties that make natural mires unique, such as surface microtopography, high biodiversity values, effective carbon sequestration and regulation of water and nutrient fluxes across the landscape. Despite this, landscape controls behind mire vegetation patterns have previously been poorly described at large spatial scales, which limits the understanding of basic drivers underpinning mire ecosystem services. We studied catchment controls on mire nutrient regimes and vegetation patterns using a geographically constrained natural mire chronosequence along the isostatically rising coastline in Northern Sweden. By comparing mires of different ages, we can partition vegetation patterns caused by long-term mire succession (<5000 years) and present-day vegetation responses to catchment eco-hydrological settings. We used the remote sensing based normalized difference vegetation index (NDVI) to describe mire vegetation and combined peat physicochemical measures with catchment properties to identify the most important factors that determine mire NDVI. We found strong evidence that mire NDVI depends on nutrient inputs from the catchment area or underlying mineral soil, especially concerning phosphorus and potassium concentrations. Steep mire and catchment slopes, dry conditions and large catchment areas relative to mire areas were associated with higher NDVI. We also found long-term successional patterns, with lower NDVI in older mires. Importantly, the NDVI should be used to describe mire vegetation patterns in open mires if the focus is on surface vegetation, since the canopy cover in tree-covered mires completely dominated the NDVI signal. With our study approach, we can quantitatively describe the connection between landscape properties and mire nutrient regime. Our results confirm that mire vegetation responds to the upslope catchment area, but importantly, also suggest that mire and catchment aging can override the role of catchment influence. This effect was clear across mires of all ages, but was strongest in younger mires.

Microbial sulfate reduction (MSR), which transforms sulfate into sulfide through the consumption of organic matter, is an integral part of sulfur and carbon cycling. Yet, the knowledge on MSR magnitudes is limited and mostly restricted to snap-shot conditions in specific surface water bodies. Potential impacts of MSR have consequently been unaccounted for, e.g., in regional or global weathering budgets. Here, we synthesize results from previous studies on sulfur isotope dynamics in stream water samples and apply a sulfur isotopic fractionation and mixing scheme combined with Monte Carlo simulations to derive MSR in entire hydrological catchments. This allowed comparison of magnitudes both within and between five study areas located between southern Sweden and the Kola Peninsula, Russia. Our results showed that the freshwater MSR ranged from 0 to 79 % (interquartile range of 19 percentage units) locally within the catchments, with average values from 2 to 28 % between the catchments, displaying a non-negligible catchment-average value of 13 %. The combined abundance or deficiency of several landscape elements (e.g., the areal percentage of forest and lakes/wetlands) were found to indicate relatively well whether or not catchmentscale MSR would be high. A regression analysis showed specifically that average slope was the individual element that best reflected the MSR magnitude, both at sub-catchment scale and between the different study areas. However, the regression results of individual parameters were generally weak. The MSR-values additionally showed differences between seasons, in particular in wetland/lake dominated catchments. Here MSR was high during the spring flood, which is consistent with the mobilization of water that under low-flow winter periods have developed the needed anoxic conditions for sulfate-reducing microorganisms. This study presents for the first time compelling evidence from multiple catchments of wide-spread MSR at levels slightly above 10 %, implying that the terrestrial pyrite oxidation may be underestimated in global weathering budgets.

Wildfire is the main disturbance in most boreal forests. In the prolonged absence of wildfire, ecosystem retrogression occurs, which is characterized by reduced productivity, plant biomass and belowground process rates. Previous evidence suggests that phosphorus (P) decreases during retrogression, but the mechanisms involved remain poorly understood. Here we use 1-D 31P and 2-D, 1H-31P NMR to characterize changes in humus P composition across a 5000 year post-fire chronosequence in northern Sweden, to understand why P availability declines during long term fire absence. Against expectations, humus P composition varied only modestly with increasing time since fire. Using a method to back-calculate the in situ soil organic P speciation, we found that it was dominated by biologically active compounds such as RNA (41%), phospholipids (28%) and DNA (22%). The concentration of DNA and pyrophosphate was 19% and 29% lower, respectively, on infrequently burnt than recently burnt islands, and the concentration of DNA, phospholipids and nucleotides was positively correlated with net primary productivity (NPP). Given the lack of evidence for the accumulation of “recalcitrant” P or a geochemical P sink, reductions in P availability during retrogression may be associated with impaired P cycling through slower decomposition rates, and increasing humus depth separating surface humus from P-rich mineral soil. Our findings align with observed negative relationships between NPP and organic P concentration across other chronosequences. They also suggest that changing fire regimes in the boreal zone could indirectly affect the P cycle through changes in NPP and soil microflora rather than through changes in humus P composition.

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

Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity. We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3-) uptake biweekly using short-term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements. Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3- concentrations (average: 46 mu g N/L) and rates of GPP (0.2 g O-2 m(-2) day(-1)). By comparison, the birch forest stream was more NO3- rich (88 mu g N/L) and productive (GPP: 1.7 g O-2 m(-2) day(-1)). These differences corresponded to greater areal NO3- uptake rate and increased NO3- use efficiency (as uptake velocity) in the birch forest stream (max 192 mu g N m(-2) min(-1) and 96 mm/hr) compared to its tundra counterpart (max 52 mu g N m(-2) min(-1) and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3- concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream. Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand. Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use.

Global warming is enhancing the mobilization of organic carbon (C) from Arctic soils into streams, where it can be mineralized to CO(2)and released to the atmosphere. Abiotic photo-oxidation might drive C mineralization, but this process has not been quantitatively integrated with biological processes that also influence CO(2)dynamics in aquatic ecosystems. We measured CO(2)concentrations and the isotopic composition of dissolved inorganic C (delta C-13(DIC)) at diel resolution in two Arctic streams, and coupled this with whole-system metabolism estimates to assess the effect of biotic and abiotic processes on stream C dynamics. CO(2)concentrations consistently decreased from night to day, a pattern counter to the hypothesis that photo-oxidation is the dominant source of CO2. Instead, the observed decrease in CO(2)during daytime was explained by photosynthetic rates, which were strongly correlated with diurnal changes in delta(13)C(DIC)values. However, on days when modeled photosynthetic rates were near zero, there was still a significant diel change in delta(13)C(DIC)values, suggesting that metabolic estimates are partly masked by O(2)consumption from photo-oxidation. Our results suggest that 6-12 mmol CO2-C m(-2)d(-1)may be generated from photo-oxidation, a range that corresponds well to previous laboratory measurements. Moreover, ecosystem respiration rates were 10 times greater than published photo-oxidation rates for these Arctic streams, and accounted for 33-80% of total CO(2)evasion. Our results suggest that metabolic activity is the dominant process for CO(2)production in Arctic streams. Thus, future aquatic CO(2)emissions may depend on how biotic processes respond to the ongoing environmental change.

Ecosystem responses of carbon and nitrogen (N) biogeochemistry to N deposition have a high variation across sites. Phosphorus (P), which can interact strongly with N, can be the cause of some of this variation. We quantified plant N and P concentrations and estimated P stocks in aboveground foliage, and soil O-horizon P concentrations and stocks after 18 years in a long-term stand-scale (0.1 ha) N addition experiment [12.5 kg (N1) and 50 kg (N2) N ha−1 year−1] in a c. 100-years-old boreal spruce [Picea abies (L.) Karst] forest. Basal area growth had increased by 65% in the N2 treatment compared to control, along with a higher leaf area index, and lower litter decomposition rates. The higher tree growth occurred during the initial c. 10-years period thereafter resuming to control rates. We hypothesized that increased plant demand for P together with decreased recycling of organic matter in this initially N limited system may have decreased plant-available P, with possible consequences for longer-term biogeochemistry and ecosystem production. However, resin-extractable P did not differ between the three treatments (0.32 kg P ha−1), and plant NP ratios and P concentrations and O-horizon P characteristics were similar in the N1 and control treatments. The N2 treatment doubled total P in the O-horizon (100 vs. 54 kg P ha−1), explained by an increase in organic P. The N concentration, NP ratio, and spruce needle biomass were higher in N2, while the P stock in current year needles was similar as in the control due to a lower P concentration. In addition to P dilution, increased light competition and/or premature aging may have caused the reduction of N-stimulated growth of the trees. For the dominant understory shrub [Vaccinium myrtillus (L.)] no changes in growth was apparent in N2 despite a significantly higher NP ratio compared to control (15 vs. 9, respectively). We therefore conclude that increased NP ratio of vegetation cannot be used as a sole indicator of P limitation. The vegetation and O-horizon changes in N2 were still large enough to merit further studies addressing whether such high N loads may alter ecosystem biogeochemistry toward P limitation. For the lower N addition rate, relevant from an anthropogenic N deposition perspective, we suggest it had no such effect.

Permafrost peatlands are a significant source of methane (CH4) emissions to the atmosphere and could emit more CH4 with continued permafrost thaw. Aerobic methane-oxidizing bacteria may attenuate a substantial fraction of CH4 emissions in thawing permafrost peatlands; however, the impact of permafrost thaw on CH4 oxidation is uncertain. We measured potential CH4 oxidation rates (hereafter, CH4 oxidation) and their predictors using laboratory incubations and in situ porewater redox chemistry across a permafrost thaw gradient of eight thaw stages at Stordalen Mire, a permafrost peatland complex in northernmost Sweden. Methane oxidation rates increased across a gradient of permafrost thaw and differed in transitional thaw stages relative to end-member stages. Oxidation was consistently higher in submerged fens than in bogs or palsas across a range of CH4 concentrations. We also observed that CH4 oxidation increased with decreasing in situ redox potential and was highest in sites with lower redox potential (Eh < 10 mV) and high water table. Our results suggest that redox potential can be used as an important predictor of CH4 oxidation, especially in thawed permafrost peatlands. Our results also highlight the importance of considering transitional thaw stages when characterizing landscape-scale CH4 dynamics, because these transitional areas have different rates and controls of CH4 oxidation relative to intact or completely thawed permafrost areas. As permafrost thaw increases the total area of semiwet and wet thaw stages in permafrost peatlands, CH4 oxidation represents an important control on CH4 emissions to the atmosphere.

Arctic and subarctic ecosystems are experiencing substantial changes in hydrology, vegetation, permafrost conditions, and carbon cycling, in response to climatic change and other anthropogenic drivers, and these changes are likely to continue over this century. The total magnitude of these changes results from multiple interactions among these drivers. Field measurements can address the overall responses to different changing drivers, but are less capable of quantifying the interactions among them. Currently, a comprehensive assessment of the drivers of ecosystem changes, and the magnitude of their direct and indirect impacts on subarctic ecosystems, is missing. The Torneträsk area, in the Swedish subarctic, has an unrivalled history of environmental observation over 100 years, and is one of the most studied sites in the Arctic. In this study, we summarize and rank the drivers of ecosystem change in the Torneträsk area, and propose research priorities identified, by expert assessment, to improve predictions of ecosystem changes. The research priorities identified include understanding impacts on ecosystems brought on by altered frequency and intensity of winter warming events, evapotranspiration rates, rainfall, duration of snow cover and lake-ice, changed soil moisture, and droughts. This case study can help us understand the ongoing ecosystem changes occurring in the Torneträsk area, and contribute to improve predictions of future ecosystem changes at a larger scale. This understanding will provide the basis for the future mitigation and adaptation plans needed in a changing climate.

The biological conversion of frozen carbon-rich soil (permafrost) into greenhouse gases such as carbon dioxide could cause a positive feedback to climate change. Another significant consequence of permafrost thaw is the collapse of soil structure and subsequent higher water table that can shift vegetation toward water-adapted plant communities that emit high concentrations of methane (CH4). Plants and microbes respond rapidly to labile carbon (C) and nitrogen (N) released from permafrost thaw, however, the microbial response to phosphorus (P) is unknown. Here we investigated how the nutrient status of permafrost and peat affect microbial activities in four minerotrophic communities in a peatland undergoing permafrost thaw. We experimentally fertilized soils in vitro with a permafrost soil slurry, inorganic P, organic N, or organic N and P. This method isolated the effect of permafrost thaw on microbial processes by removing the confounding effect of plant-soil interactions. The four peatland communities include 1. palsas (intact permafrost mounds rising above the surrounding peatlands), 2. pockets of collapsed palsas dominated by Sphagnum fuscum, 3. adjacent eutrophic Sphagnum-dominated lawns with thawing permafrost and 4. inundated, sedge-dominated minerotrophic fens with no permafrost remaining. Permafrost had high extractable inorganic N concentrations, averaging 30 µg N g-1 soil dry weight (dw), whereas extractable P concentrations were low, averaging 1.4 µg P g-1 soil dw. While N concentrations in the permafrost were over four times the concentration in adjacent peatland communities, extractable P concentrations were relatively lower. Sphagnum lawns positioned at the base of palsas, had nine times the extractable P concentrations averaging 12.6 µg P g-1 soil dw compared to the permafrost, suggesting that P availability increases as permafrost thaws. However, in the fen where no permafrost remains, extractable P concentrations were again low, 2.4 µg P g-1 soil dw, despite high total P. These fen communities are also marked by higher iron concentrations, likely resulting in P immobilization by higher concentrations of metals. The addition of inorganic P and the combination of organic N and P in these fen sites strongly enhanced CH4 oxidation rates while organic N did not, indicating the importance of P for these energy intensive transformations. Nutrient amendments did not have a significant effect on CH4 production rates, however, permafrost slurries significantly decreased CH4 production in Sphagnum lawn communities, suggesting an unknown inhibitory effect of permafrost chemistry on CH4 production. The results of our study highlight the effects of permafrost degradation on nutrient release and provide new insight into how nutrients unlocked from permafrost affects greenhouse gases.