Amid global climate change, freeze-thaw cycles in cold regions have intensified, reducing the stability of infrastructures and significantly increasing the demand for grouting reinforcement. However, the deterioration in the durability of existing grouting materials under the combined effects of freeze-thaw cycles and low temperatures has become a major technical bottleneck restricting their application in cold regions. This paper focuses on polyurethane (PU) grouting materials with foaming and lifting characteristics, systematically reviewing the research progress and technical challenges associated with their engineering applications in cold regions. First, in terms of material composition and preparation, the core components and modified additives are detailed to establish a theoretical foundation for performance regulation. Second, addressing the application requirements in cold regions, standardized testing methods and comprehensive evaluation systems are summarized based on key indicators such as heat release temperature, impermeability, diffusion properties, mechanical strength, and expansion properties. Combined with microstructural characteristics, the deformation behavior and failure mechanisms of PU grouting materials under freeze-thaw cycles and salt-freezing environments are revealed. At the engineering application level, the challenges faced by PU grouting materials in cold regions-such as inhibited low-temperature reactivity and insufficient long-term durability-are highlighted. Finally, considering current research gaps, including the unclear mechanisms of microscopic dynamic evolution and the lack of studies on the combined effects of complex environments, future research directions are proposed. This paper aims to provide theoretical support for the development and application of PU grouting materials in cold-region geotechnical engineering.

Glacier shrinkage, a notable consequence of climate change, is expected to intensify, particularly in high-elevation areas. While plant diversity and soil microbial communities have been studied, research on soil organic matter (SOM) and soil protein function dynamics in glacier forefields is limited. This limited understanding, especially regarding the link between microbial protein functions and biogeochemical functions, hampers our knowledge of soil-ecosystem processes along chronosequences. This study aims to elucidate the mechanistic relationships among soil bacterial protein functions, SOM decomposition, and environmental factors such as plant density and soil pH to advance understanding of the processes driving ecosystem succession in glacier forefields over time. Proteomic analysis showed that as ecosystems matured, the dominant protein functions transition from primarily managing cellular and physiological processes (biological controllers) to orchestrating broader ecological processes (ecosystem regulators) and increasingly include proteins involved in the degradation and utilization of OM. This shift was driven by plant density and pH, leading to increased ecosystem complexity and stability. Our confirmatory path analysis findings indicate that plant density is the main driver of soil process evolution, with plant colonization directly affecting pH, which in turn influenced nutrient metabolizing protein abundance, and SOM decomposition rate. Nutrient availability was primarily influenced by plant density, nutrient metabolizing proteins, and SOM decomposition, with SOM decomposition increasing with site age. These results underscore the critical role of plant colonization and pH in guiding soil ecosystem trajectories, revealing complex mechanisms and emphasizing the need for ongoing research to understand long-term ecosystem resilience and carbon sequestration.

Arctic ecosystems are highly vulnerable to ongoing and projected climate change. Rapid warming and growing anthropogenic pressure are driving a profound transformation of these regions, increasingly positioning the Arctic as a persistent, globally significant source of greenhouse gases. In the Russian Arctic-a critical zone for national economic growth and transport infrastructure-intensive development is replacing natural ecosystems with anthropogenically modified ones. In this context, Nature-based Solutions (NbS) represent a vital tool for climate change adaptation and mitigation. However, many NbS successfully applied globally have limited applicability in the Arctic due to its inaccessibility, short growing season, low temperatures, and permafrost. This review demonstrates the potential for adapting existing NbS and developing new ones tailored to the Arctic's environmental and socioeconomic conditions. We analyze five key NbS pathways: forest management, sustainable grazing, rewilding, wetland conservation, and ecosystem restoration. Our findings indicate that protective and restorative measures are the most promising; these can deliver measurable benefits for both climate, biodiversity and traditional land-use. Combining NbS with biodiversity offset mechanisms appears optimal for preserving ecosystems while enhancing carbon sequestration in biomass and soil organic matter and reducing soil emissions. The study identifies critical knowledge gaps and proposes priority research areas to advance Arctic-specific NbS, emphasizing the need for multidisciplinary carbon cycle studies, integrated field and remote sensing data, and predictive modeling under various land-use scenarios.

Substantial nitrous oxide (N2O) emissions from permafrost-affected regions could accelerate climate warming, given that N2O exhibits approximately 300 times greater radiative forcing potential than carbon dioxide. Pronounced differences exist in N2O emissions between freeze and thaw periods (FP and TP), but the mechanisms by which environmental factors regulate the production and emission of N2O during these two periods have not been thoroughly examined. We therefore combined static chamber gas chromatography, in-situ soil temperature (ST) and moisture (SM) monitoring, and 16S rRNA sequencing to investigate seasonal N2O variations in the Qinghai-Tibet Plateau (QTP) alpine meadow ecosystem, and assess the relative contributions of environmental and microbial drivers. Our findings indicate that N2O fluxes (-3.15 to 6.10 mu g m-2 h-1) fluctuated between weak sources and sinks, peaking during FP, particularly at its late stage with initial surface soil thawing. Soil properties affect N2O emissions by regulating denitrification processes and altering microbial community diversity. During the FP, ST fluctuations control N2O release by modifying mineral nutrient availability. During TP, soil texture modulates denitrification-driven N2O production through its effect on SM. Spring N2O pulses likely originate from microbial reactivation in thawed soil. N2O accumulated in frozen soil may gradually release during vertical profile thawing. On the QTP, a warmer and wetter climate scenario may alter N2O emissions by modifying the duration of the FP and TP and phase-specific hydrothermal allocation. This study provides mechanistic insights for predicting climate change impacts on N2O flux in fragile alpine meadow ecosystems.

This research explores the stabilization of clay soil through the application of geopolymer binder derived from silicomanganese slag (SiMnS) and activated by sodium hydroxide (NaOH). This research aims to evaluate the effects of key parameters, including the percentage of slag, the activator-to-stabilizer ratio, and curing conditions (time and temperature), on the mechanical properties of the stabilized soil. Unconfined compressive strength (UCS) tests were conducted to assess improvements in soil strength, while scanning electron microscopy (SEM) was employed to analyze the microstructural changes and stabilization mechanisms. The results demonstrated that clay soil stabilized with SiMnS-based geopolymers exhibited significant strength enhancement. Specifically, the sample stabilized with 20% SiMnS and an activator-to-slag ratio of 1.6, cured at room temperature for 90 days, achieved a UCS of 27.03 kg & frasl;cm2. The uniaxial strength was found to be positively correlated with the SiMnS content, activator ratio, curing time, and temperature. Additionally, the strain at failure remained below 1.5% for all samples, indicating a marked improvement in soil stiffness. SEM analysis revealed that geopolymerization led to the formation of a dense matrix, enhancing soil particle bonding and overall durability. These results emphasize the potential of SiMnS-based geopolymers as a sustainable and effective soil stabilizer for geotechnical applications.

Soil organic carbon (SOC) plays a critical role in global carbon cycling and climate regulation, particularly in high-altitude permafrost regions. However, the impact of altitudinal gradients of alpine shrubs on SOC fractions remains poorly understood. In this study, we evaluated the rhizosphere SOC fractions and microbial biomass of Potentilla parvifolia along an altitudinal gradient (3,204, 3,350, 3,550, and 3,650 m). Our findings revealed that P. parvifolia significantly increased gram-positive bacterial and fungal biomass at medium and low altitudes (3,204, 3,350, and 3,550 m), enhancing the contribution of mineral-associated organic carbon (MAOC) to total SOC compared to bare soil. Moreover, SOC accumulation was primarily driven by the buildup of microbial necromass carbon, particularly fungal necromass carbon, within the MAOC fraction. These results improve our understanding of how altitudinal gradients influence SOC dynamics and microbial mechanisms, providing a scientific basis for developing effective bioprotection strategies to conserve high-altitude ecosystems under global climate change.IMPORTANCEThis study addresses critical knowledge gaps in understanding how altitudinal variation of shrubs affects soil carbon dynamics in the Qilian Mountains' seasonal permafrost. Investigating the redistribution between particulate organic carbon and mineral-associated organic carbon, along with microbial necromass (fungal vs bacterial), is vital for predicting alpine carbon-climate feedbacks. Shrub encroachment into higher elevations may alter vegetation-derived carbon inputs and decomposition pathways, potentially destabilizing historically protected permafrost carbon stocks. The unique freeze-thaw cycles in seasonal permafrost likely modulate microbial processing of necromass into stable carbon pools, a mechanism poorly understood in cold biomes. By elucidating altitude-dependent shifts in carbon fractions and microbial legacy effects, this research provides mechanistic insights into vegetation-mediated carbon sequestration under climate change. Findings will inform models predicting permafrost carbon vulnerability and guide alpine ecosystem management strategies in this climate-sensitive headwater region critical for downstream water security.

Shallow cut-and-cover underground structures, such as subway stations, are traditionally designed as rigid boxes (moment-resisting connections between the main structural members), seeking internal hyperstaticity and high lateral (transverse) stiffness to achieve important seismic capacity. However, since seismic ground motions impose racking drifts, this proved rather prejudicial, with great structural damage and little resilience. Therefore, two previous papers proposed an opposite strategy seeking low lateral (transverse) stiffness by connecting the structural elements flexibly (hinging and sliding). Under severe seismic inputs, these structures would accommodate racking without significant damage; this behaviour is highly resilient. The seismic resilience of this solution was numerically demonstrated in the well-known Daikai station (Kobe, Japan) and a station located in Chengdu (China). This paper is a continuation of these studies; it aims to extend, deepen, and ground this conclusion by performing a numerical parametric study on these two stations in a wide and representative set of situations characterised by the soil type, overburden depth, engineering bedrock position, and high- and lowlateral-stiffness of the stations. The performance indices are the racking displacement and the structural damage (quantified through concrete damage variables). The findings of this study validate the previous remarks and provide new insights.

Expansive soil, characterized by significant swelling-shrinkage behavior, is prone to cracking under wet-dry cycles, severely compromising engineering stability. This study combines experimental and molecular dynamics (MD) simulation approaches to systematically investigate the improvement effects and micromechanisms of polyvinyl alcohol (PVA) on expansive soil. First, direct shear tests were conducted to analyze the effects of PVA content (0 %-4 %) and moisture content (30 %-50 %) on the shear strength, cohesive force, and internal friction angle of modified soil. Results show that PVA significantly enhances soil cohesive force, with optimal improvement achieved at 3 % PVA content. Second, wet-dry cycle experiments revealed that PVA effectively suppresses crack propagation by improving tensile strength and water retention. Finally, molecular dynamics simulations uncovered the distribution of PVA between montmorillonite (MMT) layers and its influence on interfacial friction behavior. The simulations demonstrated that PVA forms hydrogen bonding networks, enhancing interlayer interactions and frictional resistance. The improved mechanical performance of PVAmodified soil is attributed to both nanoscale bonding effects and macroscale structural reinforcement. This study provides theoretical insights and technical support for expansive soil stabilization.

Permafrost thaw and thermokarst development pose urgent challenges to Arctic communities, threatening infrastructure and essential services. This study examines the reciprocal impacts of permafrost degradation and infrastructure in Point Lay (Kali), Alaska, drawing on field data from similar to 60 boreholes, measured and modeled ground temperature records, remote sensing analysis, and community interviews. Field campaigns from 2022-2024 reveal widespread thermokarst development and ground subsidence driven by the thaw of ice-rich permafrost. Borehole analysis confirms excess-ice contents averaging similar to 40%, with syngenetic ice wedges extending over 12 m deep. Measured and modeled ground temperature data indicate a warming trend, with increasing mean annual ground temperatures and active layer thickness (ALT). Since 1949, modeled ALTs have generally deepened, with a marked shift toward consistently thicker ALTs in the 21st century. Remote sensing shows ice wedge thermokarst expanded from 60% in developed areas by 2019, with thaw rates increasing tenfold between 1974 and 2019. In contrast, adjacent, undisturbed tundra exhibited more consistent thermokarst expansion (similar to 0.2% yr(-1)), underscoring the amplifying role of infrastructure, surface disturbance, and climate change. Community interviews reveal the lived consequences of permafrost degradation, including structural damage to homes, failing utilities, and growing dependence on alternative water and wastewater strategies. Engineering recommendations include deeper pile foundations, targeted ice wedge stabilization, aboveground utilities, enhanced snow management strategies, and improved drainage to mitigate ongoing infrastructure issues. As climate change accelerates permafrost thaw across the Arctic, this study highlights the need for integrated, community-driven adaptation strategies that blend geocryological research, engineering solutions, and local and Indigenous knowledge.

Forests are increasingly impacted by climate change, affecting tree growth and carbon sequestration. Tree-ring width, closely related to tree growth, is a key climate proxy, yet models describing ring width or growth often lack comprehensive environmental data. This study assesses ERA5-Land data for tree-ring width prediction compared to automatic weather station observations, emphasizing the value of extended and global climate data. We analyzed 723 site-averaged and detrended tree-ring chronologies from two broadleaved and two gymnosperm species across Europe, integrating them with ERA5-Land climate data, CO2 concentration, and a drought index (SPEI12). A subset was compared with weather station data. For modelling interannual variations of tree-ring width we used linear models to assess parameter importance. ERA5-Land and weather-station-based models performed similarly, maintaining stable correlations and consistent errors. Models based on meteorological data from weather stations highlighted SPEI12, sunshine duration, and temperature extremes, while ERA5-Land models emphasized SPEI12, dew-point temperature (humidity), and total precipitation. CO2 positively influenced the growth of gymnosperm species. ERA5-Land facilitated broader spatial analysis and incorporated additional factors like evaporation, snow cover, and soil moisture. Monthly assessments revealed the importance of parameters for each species. Our findings confirm that ERA5-Land is a reliable alternative for modeling tree growth, offering new insights into climate-vegetation interactions. The ready availability of underutilized parameters, such as air humidity, soil moisture and temperature, and runoff, enables their inclusion in future growth models. Using ERA5-Land can therefore deepen our understanding of forest responses to diverse environmental drivers on a global scale.