Revealing regional-scale differences in microbial community structure and metabolic strategies across different land use types and soil types and how these differences relate to soil carbon (C) cycling function is crucial for understanding the mechanisms of soil organic carbon (SOC) sequestration in agroecosystems. However, our understanding of these knowledge still remains unclear. Here, we employed metagenomic methods to explore differences in microbial community structure, functional potential, and ecological strategies in calcareous soil and red soil, as well as the relationships among these factors and SOC stocks. The results showed that the bacterial absolute abundance and diversity were higher and the fungal absolute abundance and diversity were lower in calcareous soil than in red soil. This may be attributed to stochastic processes dominated the assembly of bacterial and fungal communities in calcareous soil and red soil, respectively. This in turn was closely related to soil pH and Ca2 + content. Linear discriminant analysis showed that genes related to microbial growth and reproduction (e.g., amino acid biosynthesis, central carbon metabolism, and membrane transport) were enriched in calcareous soil. While genes related to stress tolerance (e.g., bacterial chemotaxis, DNA damage repair, biofilm formation) were enriched in red soil. The great difference in soil properties between calcareous soil and red soil may be the cause of this result. Compared with red soil, the higher soil pH, SOC, and calcium and magnesium content in calcareous soil increased the bacterial absolute abundance and diversity, thus increasing the SOC sequestration potential of microorganisms, but also increased the decomposition of organic carbon by fungi, thus increasing the SOC loss potential. However, the bacterial absolute abundance and diversity were much higher than that of fungi. Therefore, soil carbon sequestration potential was still greater than its loss potential in karst agroecosystems. Agricultural disturbance intensity may be the main factor affecting these relationships. Overall, these findings advance our understanding of how soil microbial metabolic processes are related to SOC sequestration.

Soil freeze-thaw state influences multiple terrestrial ecosystem processes, such as soil hydrology and carbon cycling. However, knowledge of historical long-term changes in the timing, duration, and temperature of freeze-thaw processes remains insufficient, and studies exploring the combined or individual contributions of climatic factors-such as air temperature, precipitation, snow depth, and wind speed-are rare, particularly in current thermokarst landscapes induced by abrupt permafrost thawing. Based on ERA5-Land reanalysis, MODIS observations, and integrated thermokarst landform maps, we found that: 1) Hourly soil temperature from the reanalysis effectively captured the temporal variations of in-situ observations, with Pearson' r of 0.66-0.91. 2) Despite an insignificant decrease in daily freeze-thaw cycles in 1981-2022, other indicators in the Qinghai-Tibet Plateau (QTP) changed significantly, including delayed freezing onset (0.113 d yr- 1), advanced thawing onset (-0.22 d yr- 1), reduced frozen days (-0.365 d yr- 1), increased frozen temperature (0.014 degrees C yr- 1), and decreased daily freeze-thaw temperature range (-0.015 degrees C yr- 1). 3) Total contributions indicated air temperature was the dominant climatic driver of these changes, while indicators characterizing daily freeze-thaw cycles were influenced mainly by the combined effects of increased precipitation and air temperature, with remarkable spatial heterogeneity. 4) When regionally averaged, completely thawed days increased faster in the thermokarstaffected areas than in their primarily distributed grasslands-alpine steppe (47.69%) and alpine meadow (22.64%)-likely because of their stronger warming effect of precipitation. Locally, paired comparison within 3 x 3 pixel windows from MODIS data revealed consistent results, which were pronounced when the thermokarst-affected area exceeded about 38% per 1 km2. Conclusively, the warming and wetting climate has significantly altered soil freeze-thaw processes on the QTP, with the frozen soil environment in thermokarstaffected areas, dominated by thermokarst lakes, undergoing more rapid degradation. These insights are crucial for predicting freeze-thaw dynamics and assessing their ecological impacts on alpine grasslands.

In urban regions with karst developments, grouting is commonly utilized to fill cavities. However, the extent and control standards of grouting reinforcement are primarily determined through experience and field testing, which poses challenges in ensuring its effectiveness. Based on the instability mechanism of surrounding rocks in underwater karst shield tunnels, this study develops a mechanical model for analyzing the grouting reinforcement extent of such tunnels using strength theory. The reinforcement range for karst formations at various tunnel locations is clarified, and corresponding grouting reinforcement control standards are proposed based on cusp catastrophe theory. The findings indicate the following: the primary cause of surrounding rock instability in underwater karst shield tunnels is that the reduction in surrounding rock thickness during shield tunneling modifies the original constraints and boundary conditions and disrupts the initial equilibrium state. These changes influence the water content of the surrounding rocks and disturb the surrounding rock and soil mass, leading to surrounding rock instability. When grouting causes damage to the surrounding rocks between the karst and tunnel, the system is simplified into cantilever beam and plate models for analysis. It is determined that the grouting reinforcement extent is primarily influenced by factors such as karst size, properties of the karst filling material, and tunnel span. The total potential energy of the rock mass between the karst and tunnel is calculated, leading to the development of an instability and catastrophe model for the surrounding rocks. The proposed grouting reinforcement control standards are mainly dependent on factors such as the distance of the karst, characteristics of the reinforced surrounding rocks, shield machine support force, material properties post-reinforcement, and karst size.

Permafrost roughly affects half of the boreal region in Alaska and varies greatly in its thermo-physical properties and genesis. In boreal ecosystems, permafrost formation and degradation respond to complex interactions among climate, topography, hydrology, soils, vegetation, and disturbance. We synthesized data on soil thermal conditions and permafrost characteristics to assess current permafrost conditions in central Alaska, and classified and mapped soil landscapes vulnerable to future thaw and thermokarst development. Permafrost soil properties at 160 sites ranged from rocky soils in hillslope colluvium and glacial till, to silty loess, to thick peats on abandoned floodplains and bogs, across 64 geomorphic units. Ground-ice contents (% moisture) varied greatly across geomorphic units. Mean annual ground temperatures at similar to 1 m depth varied 12.5 degrees C across 77 sites with most permafrost near thawing or actively thawing. To assess the vulnerability of permafrost to climate variability and disturbance, we differentiated permafrost responses in terms of rate of thaw, potential thaw settlement, and thermokarst development. Using a rule-based model that uses geomorphic units for spatial extrapolation at the landscape scale, we mapped 10 vulnerability classes across three areas in central Alaska ranging from high potential settlement/low thaw rate in extremely ice-rich loess to low potential settlement/high thaw rate in rocky hillslope colluvium. Permafrost degradation is expected to result in 10 thermokarst landform types. Vulnerability classes corresponded to thermokarst features that developed in response to past climates. Differing patterns in permafrost vulnerability have large implications for ecosystem trajectories, land use, and infrastructure damage from permafrost thaw.

The Sanjiangyuan region, known as the Chinese Water Tower, serves as a crucial ecological zone that is highly sensitive to climate change. In recent years, rising temperatures and increased precipitation have led to permafrost melt and frequent occurrences of thermokarst landslides, exacerbating soil erosion issues. Although studies have explored the impact of freeze-thaw action (FTA) on soil properties, research on this phenomenon within the unique geomorphological unit of thermokarst landslides, formed from degrading permafrost, remains sparse. This study, set against the backdrop of temperature-induced soil landslides, combines field investigations and controlled laboratory experiments on typical thermokarst landslide bodies within the permafrost region of Sanjiangyuan to systematically investigate the effects of FTA on the properties of soils within thermokarst landslides. Furthermore, this study employs the EPIC model to establish an empirical formula for the soil erodibility (SE) factor before and after freeze-thaw cycles (FTCs). The results indicate that: (1) FTCs significantly alter soil particle composition, reducing the content of clay particles in the surface soil while increasing the content of sand particles and the median particle size, thus compromising soil structure and enhancing erodibility. (2) FTA initially significantly increases soil organic matter content (OMC); however, as the number of FTCs increases, the magnitude of these changes diminishes. The initial moisture content of the soil significantly influences the effects of FTA, with more pronounced changes in particle composition and OMC in soils with higher moisture content. (3) With an increasing number of FTCs, the SE K-value first significantly increases and then tends to stabilize, showing significant differences across the cycles (1 to 15) (p < 0.05). This study reveals that FTCs, by altering the physicochemical properties of the soil, significantly increase SE, providing a scientific basis for soil erosion control and ecological environmental protection in the Sanjiangyuan area.

In the context of global warming, landscapes with ice-rich permafrost, such as the Qinghai-Tibet Plateau (QTP), are highly vulnerable. The expansion of thermokarst lakes erodes the surrounding land, leading to collapses of various scales and posing a threat to nearby infrastructure and the environment. Assessing the susceptibility of thermokarst lakes in remote, data-scarce areas remains a challenging task. In this study, Landsat imagery and human-computer interaction were employed to improve the accuracy of thermokarst lake classification. The study also identified the key factors influencing the occurrence of thermokarst lakes, including the lake density, soil moisture (SM), slope, vegetation, snow cover, ground temperature, precipitation, and permafrost stability (PS). The results indicate that the most susceptible areas cover 19.02% of the QTP's permafrost region, primarily located in southwestern Qinghai, northeastern Tibet, and the Hoh Xil region. This study provides a framework for mapping the spatial distribution of thermokarst lakes and contributes to understanding the impact of climate change on the QTP.

Revegetation following human-induced damage to vegetation is now a common phenomenon in many ecologically fragile areas around the globe. However, more attention has been paid to climate and ecological engineering factors as influences on the effectiveness of vegetation restoration, while the extent to which socioeconomic factors influence vegetation restoration remains a question that has not been clearly answered. In this study, socio-economic data were obtained through field and household surveys, and then the extent to which socio-economic factors influence the effects of vegetation restoration and their mechanisms of action were assessed using a generalized linear mixed effects model, a partial least squares variable projection significant indicator approach, and a partial least squares path modeling approach. It was found that among the socioeconomic factors, variables such as percentage of cars, conservation awareness, and agricultural practices significantly influenced vegetation restoration (the R2 values are 0.21, 0.15 and 0.15). In terms of importance analysis, economic factors ranked first in terms of importance, followed by psychological factors, agricultural system factors, cultural factors, and natural factors in that order. From the comprehensive impact analysis, economic factors, cultural factors, and agricultural system factors positively affect vegetation recovery (the path coefficients are 0.26, 0.06 and 0.08), and psychological factors negatively affect vegetation recovery (the path coefficient is -0.31). To summarize, in addition to ecological engineering, the remaining socio-economic factors are also important and cannot be ignored for their influence on the effectiveness of vegetation restoration.

Karst ground collapse, a geological disaster in karst areas characterized by the sudden subsidence of surface rock and soil, poses significant risks to human life and property owing to its abrupt and frequent occurrence. Karst ground collapses can be classified into soil-cave-type and hourglass-type, based on the viscosity of the overlying layer. Among these, the hourglass-type presents a higher collapse risk owing to the lack of cohesive forces in the overlying layer. This study focused on hourglass-type karst ground collapse, utilizing physical model tests and the discrete element numerical simulations to develop and validate a collapse model. The physical model tests reproduced the collapse process and provided insights into its underlying mechanism. Numerical simulations were employed to evaluate the effects of karst channel conditions and drilling-induced vibrations on hourglass-type collapses. The results indicated that although the length of the karst channel had minimal impact on collapse speed and pattern, a wider karst channel resulted in a faster collapse and a larger final collapse pit. Moreover, vibration loads increased the collapse speed, shifted the collapse pit towards the vibration source, and expanded the scale of the collapse, thereby amplifying the overall damage extent.

The complexity of modelling in karst environments necessitates substantial adjustments to existing hydrogeological models, with particular emphasis on accurately representing surface and deep processes. This study proposes an advanced methodology for modelling regional coastal karst aquifers using an integrated SWAT-MODFLOW approach. The focus is on the regional coastal karst aquifer of Salento (Italy), which is characterised by significant heterogeneity, anisotropy and data scarcity, such as limited discharge measurements and water levels over time. The integrated SWAT - MODFLOW approach allows an accurate description of both surface and subsurface hydrological processes specific to karst environments and demonstrates the adaptability of the models to karstspecific features such as sinkholes, dolines and fault permeability. The study successfully addresses the challenges posed by the distinctive characteristics of karst systems through the integration of SWAT-MODFLOW. Additionally, incorporating of satellite data enhances the precision and dependability of the model by augmenting the traditional datasets. The entire simulation period, which included both the calibration and validation phases, extended from 2008 to 2018. The calibration phase occurred between 2008 and 2011, followed by the validation phase between 2015 and 2018. The temporal choices were exclusively based on the availability of meteorological and hydrogeological data. During calibration, satellite data, previous study results, and groundwater level measurements were used to optimize the SWAT and MODFLOW models. Validation subsequently confirmed model accuracy by comparing simulated groundwater levels with observed data, demonstrating a satisfactory root mean square error (RMSE) of 0.22 m. Modelling results indicate that evapotranspiration is the predominant hydrological process, and excessive withdrawals could lead to a water deficit. Simulated piezometric maps provide crucial information on recharge areas and hydraulic compartments delineated by faults. The study not only advances the understanding of the hydrogeology of the specific case study but also provides a valuable reference for future modelling of karst aquifers. Additionally, it highlights the crucial need for ongoing enhancement in the management and monitoring of coastal karst aquifers.

Karst collapse as a unique environmental geological hazard in karst areas, easily causes changes in surrounding water and soil environments. Train-induced vibration is a significant inducement for shallow karst ground collapse. Previous studies on the dynamic properties of surrounding soil under train vibration loads often neglected the impact of time intermittent effects. Taking the red soil covering a typical potential karst collapse area along a high-speed railway in China as the research object, field monitoring of the vibration characteristics of the surrounding environment was conducted. A series of continuous loading and continuous-stop-continuous dynamic triaxial tests and scanning electron microscopy (SEM) tests were designed considering factors such as loading frequency, intermittent duration, and dynamic stress amplitude. The effects of loading intermittence on the dynamic response and microstructure of red soil were compared and analyzed. The experimental results show that the drainage and unloading of red soil samples during the intermittent phase dissipate the accumulated excess pore water pressure and adjust the internal particle and structure of the soil, reducing the accumulation of plastic deformation during subsequent loading stages. The residual strain under vibration loading conditions considering the time intermittent effect is significantly reduced, and the residual strain decreases significantly with the increase of time intervals. The weakening effects of both macro and micro characteristics of red soil in karst-prone areas are significantly enhanced with the increase of intermittent time. The research results are of great significance for the prevention and control of karst ground collapse in karst areas.