Understanding soil organic carbon (SOC) distribution and its environmental controls in permafrost regions is essential for achieving carbon neutrality and mitigating climate change. This study examines the spatial pattern of SOC and its drivers in the Headwater Area of the Yellow River (HAYR), northeastern Qinghai-Xizang Plateau (QXP), a region highly susceptible to permafrost degradation. Field investigations at topsoils of 86 sites over three summers (2021-2023) provided data on SOC, vegetation structure, and soil properties. Moreover, the spatial distribution of key permafrost parameters was simulated: temperature at the top of permafrost (TTOP), active layer thickness (ALT), and maximum seasonal freezing depth (MSFD) using the TTOP model and Stefan Equation. Results reveal a distinct latitudinal SOC gradient (high south, low north), primarily mediated by vegetation structure, soil properties, and permafrost parameters. Vegetation coverage and above-ground biomass showed positive correlation with SOC, while soil bulk density (SBD) exhibited a negative correlation. Climate warming trends resulted in increased ALT and TTOP. Random Forest analysis identified SBD as the most important predictor of SOC variability, which explains 38.20% of the variance, followed by ALT and vegetation coverage. These findings likely enhance the understanding of carbon storage controls in vulnerable alpine permafrost ecosystems and provide insights to mitigate carbon release under climate change.

Evapotranspiration (ET) is a critical component of the soil-plant-atmosphere continuum, significantly influencing the water and energy balance of ecosystems. However, existing studies on ET have primarily focused on the growing season or specific years, with limited long-term analyses spanning decades. This study aims to analyse the components of ET within the alpine ecosystem of the Heihe River Basin, specifically investigating the dynamics of vegetation transpiration (T) and soil evaporation (Ev). Utilizing the SPAC model and integrating meteorological observations and eddy covariance data from 2013 to 2022, we investigate the impact of solar radiation and vegetation dynamics on ET and its partitioning (T/ET). The agreement between measured and simulated energy fluxes (net radiation and latent energy flux) and soil temperature underscores the validity of the model's performance. Additionally, a comparison employing the underlying water use efficiency method reveals consistent T/ET values during the growing season, further confirming the model's accuracy. Results indicate that the annual average T/ET during the 10-year study period is 0.41 +/- 0.03, close to the global average but lower than in warmer, humid regions. Seasonal analysis reveals a significant increase in T/ET during the growing season (April to October), particularly in May and June, coinciding with the thawing of permafrost and increased soil moisture. In addition, the study finds that the leaf area index and canopy stomatal conductance exhibit a logarithmic relationship with T/ET, whereas soil temperature and downward longwave radiation show an exponential relationship with T/ET. This study highlights the importance of understanding the stomatal conductance dynamics and their controls of transpiration process within alpine ecosystems. By providing key insights into the hydrological processes of these environments, it offers guidance for adapting to climate change impacts.

Alpine grasslands are vital in regulating carbon balance on the Qinghai-Tibetan Plateau (QTP) because of the large soil organic carbon (SOC) stocks, while persistent disturbance from the endemic small semifossorial herbivore, plateau pika (Ochotona curzoniae, hereafter pika), may break this balance. Pika affect the soil microclimate by creating a heterogeneous underlying surface, which is expected to alter soil microbial communities and eventually SOC stocks. However, our knowledge regarding the potential influence mechanism is still limited. Here, we investigated vegetation biomass, soil properties and soil microbes among 4 different surfaces (i.e., original vegetation, new pika pile, old pika pile and bare patch) of typical alpine grasslands to reveal soil microbial communities and the associated effect on SOC in response to pika bioturbation. Our results showed that pika bioturbation increased both bacterial and fungal diversity and their phyla abundance for SOC decomposition. Vegetation biomass, electrical conductivity and NH4+-N accounted for the variation in both bacterial and fungal community compositions and diversity. SOC stocks were 15-30% lower in pika piles and bare patches than in the original vegetation, which was mainly attributed to the reduced soil organic matter input from vegetation and the enhanced SOC consumption by soil microbial communities. Overall, we conclude that pika bioturbation altered the diversity and composition of soil microbial communities, which was associated with SOC loss and positive carbon feedback in alpine grasslands. Our findings provide insights into the role of small semifossorial herbivores in the carbon cycle of global grasslands.

Artificial pulling tests are the most practical method of assessing the maximum resistance of trees to lateral forces (e.g., from the wind), particularly in relation to their anchoring capacity in the ground. The traditional method is to pull the tree monotonically until failure. However, there are still many uncertainties regarding the possibility of mimicking wind gusts in such a tree pulling test. More specifically, it is supposed that a succession of wind gusts during a windstorm may cause fatigue to the root system, leading to a propagation of damage at the rootsoil interface which will eventually lead to the collapse of the tree. This work aims to provide initial insights into the biomechanical response of shallow-rooted Norway spruce (Picea abies (L.) Karst.) growing in mineral soils by repeatedly pulling to failure six trees with increasing load magnitude. The mechanical behaviour of the tested trees was first analysed using a classical equilibrium approach by calculating peak applied loads, stem base rotation, equivalent stiffness trend over subsequent cycles and residual rotations. Then, the biomechanics of the trees were analysed using an energetic approach, focusing on the energy absorbed and dissipated during either the single load cycle or the complete cyclic test, by applying consolidated procedures used in the field of mechanical engineering. Results show how small but measurable residual rotations were measured after each load repetition, indicating permanent damage even in seemingly undamaged trees. Additionally, loads producing base rotations about 0.3 - 0.4 times those corresponding to the peak resistance dissipate less than 1 % of the maximum dissipated energy calculated at the same peak point. Additionally, this peak energy is found to be strongly correlated to both the peak moment and a typical stem volume predictor such as diameter at breast height squared times height. All these outcomes are intended to provide a starting point for the development of a different characterisation of tree resistance as an alternative to the current methodologies, especially when it is important to consider the effects of repeated loading on trees.

The seasonal coupling of plant and soil microbial nutrient demands is crucial for efficient ecosystem nutrient cycling and plant production, especially in strongly seasonal alpine ecosystems. Yet, how these seasonal nutrient cycling processes are modified by climate change and what the consequences are for nutrient loss and retention in alpine ecosystems remain unclear. Here, we explored how two pervasive climate change factors, reduced snow cover and shrub expansion, interactively modify the seasonal coupling of plant and soil microbial nitrogen (N) cycling in alpine grasslands, which are warming at double the rate of the global average. We found that the combination of reduced snow cover and shrub expansion disrupted the seasonal coupling of plant and soil N-cycling, with pronounced effects in spring (shortly after snow melt) and autumn (at the onset of plant senescence). In combination, both climate change factors decreased plant organic N-uptake by 70% and 82%, soil microbial biomass N by 19% and 38% and increased soil denitrifier abundances by 253% and 136% in spring and autumn, respectively. Shrub expansion also individually modified the seasonality of soil microbial community composition and stoichiometry towards more N-limited conditions and slower nutrient cycling in spring and autumn. In winter, snow removal markedly reduced the fungal:bacterial biomass ratio, soil N pools and shifted bacterial community composition. Taken together, our findings suggest that interactions between climate change factors can disrupt the temporal coupling of plant and soil microbial N-cycling processes in alpine grasslands. This could diminish the capacity of these globally widespread alpine ecosystems to retain N and support plant productivity under future climate change. Seasonal transfers of nutrients between plants and soil microbes are crucial for nutrient retention in alpine ecosystems. Here, we show that two important climate change factors in alpine ecosystems, reduced snow cover and shifts in vegetation, interactively disrupt these seasonal transfers of nutrients. Future climate change could therefore diminish the capacity of globally widespread alpine ecosystems to retain nutrients, with far-reaching consequences for nutrient cycling and plant productivity.image

All ecosystems face ecological challenges in this century. Therefore, it is becoming increasingly important to understand the ecology and degree of local adaptation of functionally important Arctic-alpine biomes by looking at the most diverse taxon of metazoans: the Arthropoda. This is the first study to utilize metabarcoding in the Alpine tundra, providing insights into the effects of micro-environmental parameters on alpha- and beta-diversity of arthropods in such unique environments. To characterize arthropod diversity, pitfall traps were set at three middle-alpine sampling sites in the Scandinavian mountain range in Norway during the snow-free season in 2015. A metabarcoding approach was then used to determine the small-scale biodiversity patterns of arthropods in the Alpine tundra. All DNA was extracted directly from the preservative EtOH from 27 pitfall traps. In order to identify the controlling environmental conditions, all sampling locations were equipped with automatic data loggers for permanent measurement of the microenvironmental conditions. The variables measured were: air temperature [degrees C] at 15 cm height, soil temperature [degrees C] at 15 cm depth, and soil moisture [vol.%] at 15 cm depth. A total of 233 Arthropoda OTUs were identified. The number of unique OTUs found per sampling location (ridge, south-facing slope, and depression) was generally higher than the OTUs shared between the sampling locations, demonstrating that niche features greatly impact arthropod community structure. Our findings emphasize the fine-scale heterogeneity of arctic-alpine ecosystems and provide evidence for trait-based and niche-driven adaptation. The spatial and temporal differences in arthropod diversity were best explained by soil moisture and soil temperature at the respective locations. Furthermore, our results show that arthropod diversity is underestimated in alpine-tundra ecosystems using classical approaches and highlight the importance of integrating long-term functional environmental data and modern taxonomic techniques into biodiversity research to expand our ecological understanding of fine- and meso-scale biogeographical patterns. Our study examines the alpha- and beta-diversity of arthropods in the Arctic-alpine biomes of the Scandes using environmental DNA (eDNA)/metabarcoding. We found that micro-climatological parameters such as air/soil temperature and soil moisture significantly influence the arthropod community structure, highlighting the fine-scale heterogeneity of these ecosystems. Our study emphasizes the importance of integrating long-term functional environmental data and modern taxonomic techniques to accurately assess arthropod diversity and broaden our understanding of biogeographical patterns in alpine-tundra ecosystems.image

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg ‧ha  1 ‧a  1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Alpine vegetation plays an important role in the thermal stability of the permafrost under a warming climate, as it affects ground hydrothermal dynamics. The response of soil hydrothermal dynamics in the active layer to permafrost degradation under different alpine grassland types is unclear on the Qinghai-Tibet Plateau. In this study, long-term soil temperature and soil water content in the active layer were monitored in situ from October 2010 to December 2018 at five sites in the Kaixinling permafrost region on the interior Qinghai-Tibet Plateau along the Qinghai-Tibet Railway. The sites included an alpine steppe (AS), three alpine meadows (AM) with different degrees of degraded vegetation, and an alpine swamp meadow (ASM). Based on field-monitored data, the variations in soil temperature, soil water content, and freeze-thaw processes were examined in the active layer. The response characteristics of the soil hydrothermal processes to climate change were analysed under the different alpine grasslands. The results showed that the duration of the thawing and freezing stages of the active layer of the AMs was shorter than that of the ASM and the AS. The average mean annual soil temperature (MAST) in the active layer of the AM ((-1.25 & PLUSMN; 0.50) & DEG;C) was lower than those in the AS ((-0.71 & PLUSMN; 0.39) & DEG;C) and ASM ((-0.45 & PLUSMN; 0.57) & DEG;C), while the AM had the highest rate of soil temperature increase ((0.2 & PLUSMN; 0.06) & DEG;C per year). The annual amplitude of ground temperature in the active layer increased with the transition direction of the alpine vegetation type from ASM to AM to AS. The small surface offset (SO) and thermal offset (TO) (absolute values) indicated that the ground thermal state of the AM was more unstable, as it was more sensitive to the increase in air temperature than the ASM or the AS. Soil properties controlled the distribution of soil water content within the active layer, but vegetation improved the shallow soil structure by producing more belowground phytomass, thus, enhancing soil water content in the 0-30 cm layer. The average soil water content at depths of 0-30 cm was directly proportional ( p < 0.05) to the phytomass. Soil water contents at depths of 0-30 cm in the ASM ((37.7 & PLUSMN; 5.3)%) and the AM ((40.8 & PLUSMN; 5.9)%) were significantly higher than those in the AS ((22.7 & PLUSMN; 3.2)%). These results provide valuable insight into the hydrothermal interactions between the degradation of permafrost and alpine vegetation under a warming climate.

Alpine ecosystems play an important role in maintaining carbon sequestration, water balance, ecological security, biodiversity and human well-being. However, climate change and high-intensity human activities lead to the continuous degradation of vulnerable alpine ecosystems. Based on this, we reveal trends in ecosystem change in the Qilian Mountains of China on a 40-year scale and identify the primary driving factors of change in alpine ecosystems from the perspective of ecosystem service value (ESV) change, providing a more comprehensive picture of the interactions between human society and natural ecosystem. The results showed that more than 55 % of ecosystem types changed from 1980 to 2018, with forests, grasslands, glaciers and bare land being the most vulnerable ecosystems to disturbance, and forest and grassland ecosystems having significant ESV potential (43.99 % and 29.57 %, respectively). However, significant land use and land cover (LULC) changes over the last decade have led to a reduction in ESV stability in alpine ecosystems, where human activities have a more significant impact on ESV of sparse woodland, shrubland and grassland ecosystem at 2800-4000 m. The temperature rise had a more noticeable impact on the ESV of glaciers, alpine meadows and bare land ecosystems at 4000-5500 m. In the long terms, climate change and population growth will threaten the restoration and management of alpine ecosystems. Different ecological development strategies need to be adopted along the altitude, and the establishment of cross regional horizontal ecological compensation mechanism should be accelerated to promote the sustainable development of ecology and people's livelihood in mountainous areas. The results of this study will provide relevant theoretical basis and reference for decision makers, and provide a model for scientific management and sustainable development of alpine ecosystem resources worldwide.

Continuing permafrost degradation is increasing the risk of mercury (Hg) exposure in the permafrost regions on the Qinghai-Tibetan Plateau (QTP), but related studies are still limited, especially the ones on the detailed Hg migration processes in permafrost. The vertical distribution characteristics of soil Hg were investigated in three ecosystems in the Beiluhe area on the QTP, and its influencing factors and formation mechanism were investigated. The results indicate that the total soil mercury (THg) concentration in the Beiluhe area remains at an extremely low level (6.33 +/- 2.45 ng/g). In the vertical profile, the THg concentration of the shallow soil layer (0-50 cm) (5.96 +/- 2.22 ng/g) is significantly lower than that of the deep layer (50-400 cm) (7.44 +/- 2.71 ng/g) ( p < 0.05). Within the upper 50 cm, the THg concentration decreases with soil depth, and the peak THg concentration occurs at 100-300 cm on the entire profile. Although the THg concentration is slightly affected by the organic matter in the shallow soil layer, in general, the soil parent material is the dominant factor affecting the THg concentration. Intense weathering results in a low THg concentration in the shallow soil layer because the soil Hg is carried downward with the soil moisture. To a certain depth, the impermeable frozen soil layer intercepts the flow of the soil Hg, and it forms a Hg enrichment layer. This paper presents the distinctive pattern of the soil Hg distribution in the permafrost regions of the QTP. (c) 2021 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.