Climate change is driving permafrost thaw, releasing previously frozen resources, such as nitrogen, to the soil active layer. In low-nitrogen systems, like boreal peatlands, this novel nitrogen source may benefit plant productivity. However, other resource limitations (for example, light) may limit plant access to thaw-front nitrogen. We used a stable isotope experiment to explore variations in understory boreal plant species' ability to take up different forms of newly released nitrogen from permafrost thaw under different canopy covers. This experiment occurred in a peatland in the sporadic discontinuous permafrost zone of the Northwest Territories, Canada. We added N-15 labelled ammonium, nitrate, and the amino acid glycine at the thaw front (40 cm depth) at two sites differentiated by high and low canopy cover and determined uptake of N-15 in leaves of several common and abundant boreal plant species. We found that the probability of plant uptake of thaw-front nitrogen was significantly greater at low canopy cover sites; however, nitrogen form, plant species, and foliar N-mass had no effect. We further found that Rubus chamaemorus had the highest foliar N-mass followed by Rhododendron groenlandicum, Chamaedaphne calyculata, and Vaccinium vitis-idaea. Our results demonstrate that access to nitrogen released from permafrost thaw by boreal plants may be mediated by light availability. Understanding the variation in site response to permafrost thaw contributes to our understanding of how boreal peatlands will change with ongoing climate change.

This study highlights the results of a palaeoecological analysis conducted on five permafrost peatlands in the northern tundra subzone along the Barents Sea coast in the European Arctic zone. The depth of the peat cores that were sampled was approximately 2 m. The analysis combined data on the main physical and chemical soil properties, radiocarbon dating, botanical composition, and mass fraction of polycyclic aromatic hydrocarbons (PAHs). The concentrations of 16 PAHs in peat organic layers ranged from 140 to 254 ng/g, with an average of 182 ng/g. The peatlands studied were dominated by PAHs with a low molecular weight: naphthalene, phenanthrene, fluoranthene, pyrene, chrysene. The vertical distribution patterns of PAHs along the peat profile in the active layer and permafrost were determined. PAHs migrating down the active layer profile encounter the permafrost barrier and accumulate at the boundary between active layer and permafrost layer. The deep permafrost layers accumulate large amounts of PAHs and PAH derivatives, which are products of lignin conversion during the decomposition of grassy and woody vegetation during the Holocene climate optima. The total toxic equivalency concentration (TEQ) was calculated. Peatlands from the Barents Sea coast have low toxicity for carcinogenic PAHs throughout the profile. TEQ ranged from a minimum of 0.1 ng/g to a maximum of 13.5 ng/g in all peatlands investigated. For further potential use in Arctic/sub-Arctic environmental studies, PAH indicator ratios were estimated. In all investigated sections and peatland horizons, the most characteristic ratios indicate the petrogenic (natural) origin of PAHs.

Simple Summary The enzymic latch and iron gate theories represent two prevailing and contrasting mechanisms governing ecosystem carbon stability: the former via a phenolics accumulation mediated biochemical cascade that suppresses hydrolytic enzyme activity, and the latter via an abiotic pathway where ferrous iron oxidation suppresses phenol oxidase activity and promotes iron-bound soil organic carbon formation. Therefore, deciphering the stabilization mechanisms for the vast carbon stocks in permafrost peatlands represents a central challenge for climate change projections. In this study, we assessed the spatial distribution and interrelationships of peatland soil extracellular enzyme activities, iron phases, and iron-bound soil organic carbon across three permafrost zones in the Great Hing'an Mountains. Contrary to the enzymic latch mechanism, our data revealed that hydrolytic enzyme activities (beta-glucosidase, cellobiohydrolase, and beta-N-acetylglucosaminidase) were neither negatively correlated with phenolics nor positively correlated with phenol oxidase activity. Instead, iron emerged as the central regulator, with a positive correlation between ferrous iron and phenol oxidase activity and with ferric iron stabilizing soil organic carbon through co-precipitation. Our results highlighted that permafrost degradation could poses a threat to the dominant iron gate carbon sequestration mechanism in peatlands, potentially triggering a positive climate feedback.Abstract Distinct paradigms, such as the enzymic latch and iron gate theories, have been proposed to elucidate SOC loss or accumulation, but their relative significance and whether they are mutually exclusive in permafrost peatlands remain unclear. To address this, we evaluated their relative importance and identified the dominant factors controlling SOC stability. Therefore, we employed a space-for-time substitution approach across a permafrost gradient (continuous, discontinuous, and isolated) by systematically quantifying extracellular enzyme activities, iron (Fe) phases, and iron-bound soil organic carbon (Fe-SOC) at various depths (0-10, 10-30, and 30-50 cm) in peatlands. Our results did not support the enzymic latch theory, with hydrolytic enzyme activities (beta-glucosidase (BG), cellobiohydrolase (CBH), and beta-N-acetylglucosaminidase (NAG)) showing positive correlations with phenolics but negative correlations with phenol oxidase (PHO) activity. However, ferrous iron (Fe(II)) was significantly positively correlated with PHO activity, and ferric iron (Fe(III)) stabilized SOC through co-precipitation with it to form Fe-SOC, supporting the iron gate theory. Moreover, Fe-SOC decreased from the continuous to the isolated permafrost zone, and with soil depth from 0-10 cm to 30-50 cm. Partial least squares path modeling (PLS-PM) analysis indicated that Fe(III) directly and indirectly (via Fe-SOC and phenolics) affected SOC. Our study demonstrated the primacy of the iron gate mechanism in controlling carbon stability in the Great Hing'an Mountains permafrost peatlands, providing new insights for projecting carbon-climate feedback.

A comprehensive series of tests, including dynamic triaxial, monotonic triaxial and unconfined compressive strength (UCS) tests, were carried out on reconstituted landfill waste material buried for over twenty years in a closed landfill site in Sydney, Australia. Waste materials collected from the landfill site were treated with varying percentages of cement, and both treated and untreated specimens were investigated to evaluate the influence of cement treatment. The study examined the dynamic properties of cement-treated landfill waste, including cumulative plastic deformation, resilient modulus, and damping ratio, and also analysed the impact of cyclic loading on post-cyclic shear strength in comparison to pre-cyclic shear strength. The UCS tests and monotonic triaxial tests demonstrated that untreated specimens subjected to monotonic loading exhibited a progressive increase in strength with rising axial strain, whereas cement-treated specimens reached a peak strength before experiencing a decline. During cyclic loading, with the inclusion of cement, a significant reduction in cumulative plastic deformation and damping ratio was observed, and this reduction was further enhanced with increasing cement content. Conversely, the resilient modulus showed substantial improvement with the addition of cement, and this enhancement was further amplified with increasing cement content. The formation of cementation bonds between particles curtails particle movement within the landfill waste material matrix and prevents interparticle sliding during cyclic loading, leading to lower plastic strains and damping ratio while increasing resilient modulus. Post-cyclic monotonic testing revealed that cyclic loading caused the partial breakage of the cementation bonds, resulting in reduced shear strength. This reduction was higher on samples treated with lower cement content. Overall, the findings of the research offer crucial insights into the possibility of cement-treated landfill waste as a railway subgrade, laying the groundwork for informed design decisions in developing transport infrastructure over closed landfill sites while using landfill waste materials available on site.

Permafrost peatlands store substantial amounts of carbon, though persistence of this soil carbon is unknown in a rapidly warming Arctic. To investigate potential carbon production from soils at different stages of permafrost degradation, we incubated soils from a palsa mire in northern Fennoscandia. Three soil horizons from four thaw stages were included within the transect, beginning with intact permafrost and ending in an established post-thaw wetland. Samples were incubated anaerobically for a year at different temperatures (4 degrees C, 20 degrees C) with the aim of investigating drivers of carbon degradation rates. Additional subsamples from the intact palsa were incubated under aerobic conditions, or inoculated with thermokarst pond water to further explore thaw processes on soil. Total CO2 and CH4 produced ranged from 9,910 +/- 626 (from the surface peat of the established post-thaw wetland, at 20 degrees C) to 1,921 +/- 126 mu g C g-1 DW (from the intermediate thaw stage of the palsa permafrost, incubated at 20 degrees C). The CH4 temperature sensitivity was markedly higher in permafrost soils, with Q 10 s more than four times larger than that of the active layer (active layer average: 1.7 +/- 1.6, permafrost average: 8.4 +/- 5). Methanogenesis generally increased with thaw, but the largest increase of cumulative methane production was between the wetland thaw stages (from 633 to 2,880 mu g CH4-C g-1 DW), where graminoids colonized the post-thaw environment. This uptick in CH4 production 30+ years after post-thaw wetland establishment implies that increases in CH4 production are largely due to vegetation inputs rather than thawed permafrost carbon contributions.

Peat soil is a significant global carbon storage pool, accounting for one-third of the global soil carbon pool. Its greenhouse gas emissions have a significant impact on climate change. Seasonal freeze-thaw cycles are common natural phenomena in high-latitude and high-altitude regions. They significantly affect the mineralization of soil organic carbon and greenhouse gas emissions by altering the physical structure, moisture conditions, and microbial communities of the soil. In this study, through the construction of an indoor simulation experiment of the typical freeze-thaw cycle models in spring and autumn in the Greater Xing'an Range region of China and the Jinchuan peatland of Jilin Longwan National Nature Reserve, the physicochemical properties, greenhouse gas emission fluxes, microbial community structure characteristics, and key metabolic pathways of peat soils in permafrost and seasonally frozen ground areas were determined. The characteristics of greenhouse gas emissions and their influencing mechanisms for peat soil in northern regions under different freeze-thaw conditions were explored. The research found that the freeze-thaw cycle significantly changed the chemical properties of peat soil and significantly affected the emission rates of CO2, CH4, and N2O. It also clarified the interaction relationship between soil's physicochemical properties (such as dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium nitrogen (NH4+), soil organic carbon (SOC), etc.) and the structure and metabolic function of microbial communities. It is of great significance for accurately assessing the role of peatlands in the global carbon cycle and formulating effective ecological protection and management strategies.

Permafrost thaw represents one of Earth's largest climate feedback risks, potentially releasing vast carbon (C) stores as greenhouse gases (GHG). However, our ability to predict emissions remains limited by poor understanding of how changing organic matter (OM) composition affects microbial carbon processing. We test a metabolism-centered redox framework, which views microbial processes as coupled oxidative-reductive reactions, to mechanistically explain how organic matter metabolite quality controls greenhouse gas production in permafrost-affected peatland ecosystems. Rather than relying solely on geochemical redox measurements, our approach examines how microbes balance electron flow through metabolic pathways. Using active layer peat (9-19 cm) from contrasting environments (bog and fen), we employed multi-omics approaches, including metabolomics, metagenomics, and metatranscriptomics, to link OM chemistry to microbial function. Our results reveal distinct dissolved organic matter metabolite composition, with fen systems enriched in compounds with higher substrate quality (low molecular weight (MW) sugars with high H:C ratios and low aromaticity) and bog systems dominated by compounds with lower substrate quality (high MW phenols with lower H:C ratios and higher aromaticity). In fen samples, these sugar-like compounds correlated with higher oxidative metabolism and methanogenesis, supported by increased glycolysis gene expression. Initially, electrons from increased oxidative metabolism were balanced through nitrate and sulfate reduction, but as these electron acceptors were depleted, methanogenesis increased to maintain redox balance. Fen samples showed rapid degradation of both high- and low-substrate-quality compounds, suggesting sufficient energy for efficient C cycling. Conversely, bog samples exhibited more polyphenolic compounds, lower glycolysis activity, and higher stress-related gene expression, suggesting energy was diverted towards cell maintenance under acidic conditions rather than C processing. This approach suggests that predicting greenhouse gas emissions requires an understanding of how organic matter quality shapes microbial energy allocation strategies, providing a mechanistic framework for improving emission predictions from permafrost-affected peatlands and similar ecosystems.

Mastering the mechanical properties of frozen soil under complex stress states in cold regions and establishing accurate constitutive models to predict the nonlinear stress-strain relationship of the soil under multi-factor coupling are key to ensuring the stability and safety of engineering projects. In this study, true triaxial tests were conducted on roadbed peat soil in seasonally frozen regions under different temperatures, confining pressures, and b-values. Based on analysis of the deviatoric stress-major principal strain curve, the variation patterns of the intermediate principal stress, volumetric strain and minor principal strain deformation characteristics, and anisotropy of deformation, as well as verification of the failure point strength criterion, an intelligent constitutive model that describes the soil's stress-strain behavior was established using the Transformer network, integrated with prior information, and the robustness and generalization ability of the model were evaluated. The results indicate that the deviatoric stress is positively correlated with the confining pressure and the b-value, and it is negatively correlated with the freezing temperature. The variation in the intermediate principal stress exhibits a significant nonlinear growth characteristic. The soil exhibits expansion deformation in the direction of the minor principal stress, and the volumetric strain exhibits shear shrinkage. The anisotropy of the specimen induced by stress is negatively correlated with temperature and positively correlated with the bvalue. Three strength criteria were used to validate the failure point of the sample, and it was found that the spatially mobilized plane strength criterion is the most suitable for describing the failure behavior of frozen peat soil. A path-dependent physics-informed Transformer model that considers the physical constraints and stress paths was established. This model can effectively predict the stress-strain characteristics of soil under different working conditions. The prediction correlation of the model under the Markov chain Monte Carlo strategy was used as an evaluation metric for the original model's robustness, and the analysis results demonstrate that the improved model has good robustness. The validation dataset was input to the trained model, and it was found that the model still exhibits a good prediction accuracy, demonstrating its strong generalization ability. The research results provide a deeper understanding of the mechanical properties of frozen peat soil under true triaxial stress states, and the established intelligent constitutive model provides theoretical support for preventing engineering disasters and for early disaster warning.

Widespread changes to near-surface permafrost in northern ecosystems are occurring through gradual top-down thaw and more abrupt localized thermokarst development. Both thaw types are associated with a loss of ecosystem services, including soil hydrothermal and mechanical stability and long-term carbon storage. Here, we analyzed relationships between the vascular understory, basal moss layer, active layer thickness (ALT), and greenhouse gas fluxes along a thaw gradient from permafrost peat plateau to thaw bog in Interior Alaska. We used ALT to define four distinct stages of thaw: Stable, Early, Intermediate, and Advanced, and we identified key plant taxa that serve as reliable indicators of each stage. Advanced thaw, with a thicker active layer and more developed thermokarst features, was associated with increased abundance of graminoids and Sphagnum mosses but decreased plant species richness and ericoid abundance, as well as a substantial increase in methane emissions. Early thaw, characterized by active layer thickening without thermokarst development, coincided with decreased ericoid cover and plant species richness and an increase in CH4 emissions. Our findings suggest that early stages of thaw, prior to the formation of thermokarst features, are associated with distinct vegetation and soil moisture changes that lead to abrupt increases in methane emissions, which then are perpetuated through ground surface subsidence and collapse scar bog formation. Current modeling of permafrost peatlands will underestimate carbon emissions from thawing permafrost unless these linkages between plant community, nonlinear active layer dynamics, and carbon fluxes of emerging thaw features are integrated into modeling frameworks.

Sodium hydroxide (NaOH)-sodium silicate-GGBS (ground granulated blast furnace slag) effectively stabilises sulfate-bearing soils by controlling swelling and enhancing strength. However, its dynamic behaviour under cyclic loading remains poorly understood. This study employed GGBS activated by sodium silicate and sodium hydroxide to stabilise sulfate-bearing soils. The dynamic mechanical properties, mineralogy, and microstructure were investigated. The results showed that the permanent strain (epsilon(p)) of sodium hydroxide-sodium silicate-GGBS-stabilised soil, with a ratio of sodium silicate to GGBS ranging from 1:9 to 3:7 after soaking (0.74%-1.3%), was lower than that of soil stabilised with cement after soaking (2.06%). The resilient modulus (E-d) and energy dissipation (W) of sodium hydroxide-sodium silicate-GGBS-stabilised soil did not change as the ratio of sodium silicate to GGBS increased. Compared to cement (E-d = 2.58 MPa, W = 19.96 kJ/m(3)), sulfate-bearing soil stabilised with sodium hydroxide-sodium silicate-GGBS exhibited better E-d (4.84 MPa) and lower W (15.93 kJ/m(3)) at a ratio of sodium silicate to GGBS of 2:8. Ettringite was absent in sodium hydroxide-sodium silicate-GGBS-stabilised soils but dominated pore spaces in cement-stabilised soil after soaking. Microscopic defects caused by soil swelling were observed through microscopic analysis, which had a significant negative impact on the dynamic mechanical properties of sulfate-bearing soils. This affected the application of sulfate-bearing soil in geotechnical engineering.