Search

The Tibetan Plateau holds the world's largest alpine permafrost and is undergoing an acceleration of warming. Phenological shifts over alpine permafrost in a warmer world have been little studied and are greatly underrepresented in current syntheses.Here, we conducted seasonal and gradient temperature‐controlled experiments in a permafrost‐affected meadow to evaluate how warming drives shifts in spring and autumn phenology, and associated growing‐season length at both community and species levels.We found that there is no sign of slowdown in spring advance with warming under a higher year‐around warming treatment, aligning with a future medium warming scenario. Although spring advance led to an advance in autumn senescence according to spring‐only warming experiments, the advance could not offset the delay due to concurrent warming. As a result, year‐around warming significantly delayed autumn senescence, although there was a deceleration in delay with warming under high temperature treatment than under the low one.This finding can be attributed to the possibility that winter warming is insufficient to reduce chilling accumulation, which would not delay spring phenology and then lead to a non‐slowdown in spring phenological advancement. Taken together, there is no slowdown in an extension of growing season length with warming under a higher year‐around warming treatment, with an increase of length by 9 and 21 days at the end of this century under a CO2 stabilization and medium warming scenarios, respectively.Synthesis. Our results suggest that a continued growing season extension at least under the medium warming scenario would help permafrost‐affected meadow ecosystems to mitigate permafrost carbon release on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Permafrost, characterized by its frozen soil, serves as a unique habitat for diverse microorganisms. Understanding these microbial communities is crucial for predicting the response of permafrost ecosystems to climate change. However, large-scale evidence regarding stratigraphic variations in microbial profiles remains limited. Here, we analyze microbial community structure and functional potential based on 16S rRNA gene amplicon sequencing and metagenomic data obtained from an ∼1000 km permafrost transect on the Tibetan Plateau. We find that microbial alpha diversity declines but beta diversity increases down the soil profile. Microbial assemblages are primarily governed by dispersal limitation and drift, with the importance of drift decreasing but that of dispersal limitation increasing with soil depth. Moreover, genes related to reduction reactions (e.g., ferric iron reduction, dissimilatory nitrate reduction, and denitrification) are enriched in the subsurface and permafrost layers. In addition, microbial groups involved in alternative electron accepting processes are more diverse and contribute highly to community-level metabolic profiles in the subsurface and permafrost layers, likely reflecting the lower redox potential and more complicated trophic strategies for microorganisms in deeper soils. Overall, these findings provide comprehensive insights into large-scale stratigraphic profiles of microbial community structure and functional potentials in permafrost regions. Research on permafrost microbial communities is crucial for predicting the response of permafrost ecosystems to climate change. Here, Kang et al. provide insights into the structure and functional potential of permafrost microbial communities by analyzing 16S rRNA gene sequence data and metagenomic data obtained from an ∼1000 km transect on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Phosphorous (P) is essential for mediating plant and microbial growth and thus could impact carbon (C) cycle in permafrost ecosystem. However, little is known about soil P availability and its biological acquisition strategies in permafrost environment. Based on a large‐scale survey along a ~1000 km transect, combining with shotgun metagenomics, we provided the first attempt to explore soil microbial P acquisition strategies across the Tibetan alpine permafrost region. Our results showed the widespread existence of microbial functional genes associated with inorganic P solubilization, organic P mineralization and transportation, reflecting divergent microbial P acquisition strategies in permafrost regions. Moreover, the higher gene abundance related to solubilization and mineralization as well as an increased ration of metagenomic assembled genomes (MAGs) carrying these genes were detected in the active layer, while the greater abundance of low‐affinity transporter gene (pit) and proportions of MAGs harbouring pit gene were observed in permafrost deposits, illustrating a stronger potential for P activation in active layer but an enhanced P transportation potential in permafrost deposits. Our results highlight multiple P‐related acquisition strategies and their differences among various soil layers should be considered simultaneously to improve model prediction for the responses of biogeochemical cycles in permafrost ecosystems to climate change. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (n). Here, we analyzed n values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in n for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on n over the past 27 y. Soil moisture was found to modulate the sensitivity of n to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback. [ABSTRACT FROM AUTHOR]

Summary: Knowledge about changes in plant functional traits is valuable for the mechanistic understanding of warming effects on ecosystem functions. However, observations have tended to focus on aboveground plant traits, and there is little information about changes in belowground plant traits or the coordination of above‐ and belowground traits under climate warming, particularly in permafrost ecosystems.Based on a 7‐yr field warming experiment, we measured 26 above‐ and belowground plant traits of four dominant species, and explored community functional composition and trait networks in response to experimental warming in a permafrost ecosystem on the Tibetan Plateau.Experimental warming shifted community‐level functional traits toward more acquisitive values, with earlier green‐up, greater plant height, larger leaves, higher photosynthetic resource‐use efficiency, thinner roots, and greater specific root length and root nutrient concentrations. However, warming had a negligible effect in terms of functional diversity. In addition, warming shifted hub traits which have the highest centrality in the network from specific root area to leaf area.These results demonstrate that above‐ and belowground traits exhibit consistent adaptive strategies, with more acquisitive traits in warmer environments. Such changes could provide an adaptive advantage for plants in response to environmental change. See also the Commentary on this article by Spitzer & Blume-Werry, 240: 1712–1713. [ABSTRACT FROM AUTHOR]

Aim: The formation of thermokarst lakes could make a large amount of carbon accessible to microbial degradation, potentially intensifying the permafrost carbon‐climate feedback via carbon dioxide/methane emissions. Because of their diverse functional roles, prokaryotes could strongly mediate biogeochemical cycles in thermokarst lakes. However, little is known about the large‐scale patterns and drivers of these communities. Location: Permafrost regions in the Northern Hemisphere. Time period: Present day. Major taxa studied: Prokaryotes. Methods: Based on a combination of large‐scale measurements on the Tibetan Plateau and data syntheses in pan‐Arctic regions, we constructed a comprehensive dataset of 16S rRNA sequences from 258 thermokarst lakes across Northern Hemisphere permafrost regions. We also used the local contributions to beta diversity (LCBD) to characterize the variance of prokaryotic species composition and screened underlying drivers by conducting a random forest modelling analysis. Results: Prokaryotes in thermokarst lake water were dominated by the orders Burkholderiales, Micrococcales, Flavobacteriales and Frankiales. The relative abundance of dominant taxa was positively associated with dissolved organic matter (DOM) properties, especially for the chromophoric/aromatic compounds. Microbial structure differed between high‐altitude and high‐latitude thermokarst lakes, with the dominance of Flavobacterium in high‐altitude lakes, and the enrichment of Polynucleobacter in high‐latitude lakes. More importantly, climatic variables were among the main drivers shaping the large‐scale variation of prokaryotic communities. Specifically, mean annual precipitation was the best predictor for prokaryotic beta diversity across the Northern Hemisphere, as well as in the high‐altitude permafrost regions, while mean annual air temperature played a key role in the high‐latitude thermokarst lakes. Main conclusions: Our findings demonstrate significant associations between dominant taxa and DOM properties, as well as the important role of climatic factors in affecting prokaryotic communities. These findings suggest that climatic change may alter DOM conditions and induce dynamics in prokaryotic communities of thermokarst lake water in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Large amounts of carbon sequestered in permafrost on the Tibetan Plateau (TP) are becoming vulnerable to microbial decomposition in a warming world. However, knowledge about how the responsible microbial community responds to warming-induced permafrost thaw on the TP is still limited. This study aimed to conduct a comprehensive comparison of the microbial communities and their functional potential in the active layer of thawing permafrost on the TP. We found that the microbial communities were diverse and varied across soil profiles. The microbial diversity declined and the relative abundance of Chloroflexi, Bacteroidetes, Euryarchaeota , and Bathyarchaeota significantly increased with permafrost thawing. Moreover, warming reduced the similarity and stability of active layer microbial communities. The high-throughput qPCR results showed that the abundance of functional genes involved in liable carbon degradation and methanogenesis increased with permafrost thawing. Notably, the significantly increased mcrA gene abundance and the higher methanogens to methanotrophs ratio implied enhanced methanogenic activities during permafrost thawing. Overall, the composition and functional potentials of the active layer microbial community in the Tibetan permafrost region are susceptible to warming. These changes in the responsible microbial community may accelerate carbon degradation, particularly in the methane releases from alpine permafrost ecosystems on the TP. [ABSTRACT FROM AUTHOR]

Copyright of Methods in Ecology & Evolution is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the major uncertainties for projecting permafrost carbon (C)‐climate feedback is a poor representation of the non‐growing season carbon dioxide (CO2) emissions under a changing climate. Here, combining in situ field observations, regional synthesis and a random forest model, we assessed contemporary and future soil respired CO2 (i.e., soil respiration, Rs) across the Tibetan alpine permafrost region, which has received much less attention compared with the Arctic permafrost domain. We estimated the regional mean Rs of 229.8, 72.9 and 302.7 g C m−2 year−1 during growing season, non‐growing season and the entire year, respectively; corresponding to the contemporary losses of 296.9, 94.3 and 391.2 Tg C year−1 from this high‐altitude permafrost‐affected area. The non‐growing season Rs accounted for a quarter of the annual soil CO2 efflux. Different from the prevailing view that temperature is the most limiting factor for cold‐period CO2 release in Arctic permafrost ecosystems, precipitation determined the spatial pattern of non‐growing season Rs on the Tibetan Plateau. Using the key predictors, model extrapolation demonstrated additional losses of 38.8 and 74.5 Tg C from the non‐growing season for a moderate mitigation scenario and a business‐as‐usual emissions scenario, respectively. These results provide a baseline for non‐growing season CO2 emissions from high‐altitude permafrost areas and help for accurate projection of permafrost C‐climate feedback. [ABSTRACT FROM AUTHOR]

Background: Alpine ecosystem underlain by permafrost is considered as one of the most vulnerable ecosystems to disturbance, especially the alpine grassland on the Tibetan plateau with an altitude above 4000 m. Plateau pika (Ochotona curzoniae) burrowing can create distinctive bare grounds and cause micro-topographical heterogeneity in alpine grasslands. The burrowing-induced changes in microtopography may directly alter plant and soil interactions as well as ecosystem carbon cycle, which have rarely been studied in Tibetan alpine grasslands. Methods: To test the responses of ecosystem respiration (Re) to pika burrowing-induced changes in microtopography, we investigated plant characteristics, soil properties and Re from the bare grounds and vegetated grounds in the alpine meadow and steppe on the Tibetan Plateau. Results: Our study showed that vegetation cover, species richness, plant biomass, soil moisture (SM), soil organic carbon (SOC), total nitrogen (STN), soil microbial biomass carbon (MBC) and nitrogen (MBN) in the bare grounds were significantly lower than in the vegetated grounds in both alpine meadow and alpine steppe (P < 0.05). However, soil temperature and inorganic nitrogen tended to increase in the bare grounds. The growing season Re was significantly lower in the bare grounds than that in the vegetated grounds (P < 0.01). Pika burrowing had negative effects on Re and its temperature sensitivity in both alpine vegetations (P < 0.05). The relative changes in Re due to burrowing-induced changes in microtopography were positively correlated with the burrowing caused changes of AGB, BGB, SOC and MBC (P < 0.05). Pika burrowing-induced changes in soil temperature, soil moisture, plant biomass and microbial biomass are the major factors for the decrease of Re in the bare grounds. Conclusion: In view of the large number of pika burrows in the alpine grasslands and the loss of soil organic carbon due to pika bioturbation, the impacts of pika burrowing-induced changes in microtopography on Re must be considered in predicting the carbon cycle in alpine grasslands. [ABSTRACT FROM AUTHOR]

Recognizing the status of permafrost thawing and providing information for permafrost treatment in the Tibetan Plateau is a key problem. In this paper, a GPR experiment is designed to explore effective geophysical attributes for characterizing and evaluating the impact of key factors on permafrost thawing. A new algorithm for the assessment of rapid relative water content is also presented. After processing the GPR data, the weighted average frequency attribute, sweetness attribute and relative wave impedance attribute, which better characterize the effect of different factors on permafrost thawing, are selected. The weighted average frequency attribute can distinguish the thawing front and evaluate the extent of thawing in addition to the completely thawed fringe; the sweetness attribute can help to characterize thawing in water ice mixed with permafrost and evaluate the impact of free water on permafrost below the thawing front. The relative wave impedance attribute highlights the completely thawed fringe and other smaller internal stratifications in the permafrost thawing zone. Using the rapid relative water content assessment algorithm, it is easy to evaluate the extent of thawing using only GPR data. In addition, a thermokarst lake strengthens the degree of permafrost thawing. Permafrost thawing accelerates on sunny slopes. This study shows that roadbeds inhibit permafrost thawing and that a thermosyphon significantly inhibits permafrost thawing. [ABSTRACT FROM AUTHOR]

An R package was developed for computing permafrost indices (PIC v1.3) that integrates meteorological observations, gridded meteorological datasets, soil databases, and field measurements to compute the factors or indices of permafrost and seasonal frozen soil. At present, 16 temperature- and depth-related indices are integrated into the PIC v1.3 R package to estimate the possible trends of frozen soil in the Qinghai-Tibet Plateau (QTP). These indices include the mean annual air temperature (MAAT), mean annual ground surface temperature (MAGST), mean annual ground temperature (MAGT), seasonal thawing-freezing n factor (nt=nf), thawing-freezing degree-days for air and the ground surface (DDTa=DDTs=DDFa=DDFs), temperature at the top of the permafrost (TTOP), active layer thickness (ALT), and maximum seasonal freeze depth. PIC v1.3 supports two computational modes, namely the stations and regional calculations that enable statistical analysis and intuitive visualization of the time series and spatial simulations. Datasets of 52 weather stations and a central region of the QTP were prepared and simulated to evaluate the temporal-spatial trends of permafrost with the climate. More than 10 statistical methods and a sequential Mann-Kendall trend test were adopted to evaluate these indices in stations, and spatial methods were adopted to assess the spatial trends. Multiple visual methods were used to display the temporal and spatial variability of the stations and region. Simulation results show extensive permafrost degradation in the QTP, and the temporal-spatial trends of the permafrost conditions in the QTP are close to those of previous studies. The transparency and repeatability of the PIC v1.3 package and its data can be used and extended to assess the impact of climate change on permafrost. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibetan Plateau (QTP) accounts for approximately 70 % of global alpine permafrost and is an area sensitive to climate change. The thawing and mobilization of ice and organic carbon-rich permafrost impact hydrologic conditions and biogeochemical processes on the QTP. Despite numerous studies of Arctic permafrost, there are no reports to date for the molecular-level in-stream processing of permafrost-derived dissolved organic matter (DOM) on the QTP. In this study, we examine temporal and spatial changes of chemical composition of DOM and 14C age of dissolved organic carbon (DOC) along an alpine stream (3850–3207 m above sea level) by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), accelerator mass spectrometry (AMS) and UV-visible spectroscopy. Compared to downstream sites, the DOM at the headstream exhibited older radiocarbon (14C-DOC) age, higher mean molecular weight, higher aromaticity and fewer polyunsaturated components. At the molecular level, 6409 and 1345 formulas were identified as unique to the active layer (AL) leachate and permafrost layer (PL) leachate, respectively. Comparing permafrost leachates to the downstream site, 59 % of AL-specific formulas and 90 % of PL-specific formulas were degraded, likely a result of rapid instream degradation of permafrost-derived DOM. From peak discharge in the summer to low flow in late autumn, the DOC concentration at the headstream site decreased from 13.9 to 10.2 mg/L, while the 14C-DOC age increased from 745 to 1560 years before present (BP), reflecting an increase in relative contribution of deep permafrost carbon due to the effect of changing hydrological conditions over the course of the summer on DOM source (AL vs. PL). Our study thus demonstrates that hydrological conditions impact the mobilization of permafrost carbon in an alpine fluvial network, the signature of which is quickly lost through in-stream metabolism. [ABSTRACT FROM AUTHOR]

Due to the vulnerability of permafrost environment to climate changes, permafrost in the Qinghai-Tibet Plateau (QTP) is experiencing thickening of the active layer and warming ground temperatures that together have a significant influence on the ground motion characteristics. A series of in situ wave velocity tests were carried out in permafrost regions along the Qinghai-Tibet Railway (QTR) and the characteristics of shear wave velocity of frozen soil were summarized. Then, the ground motion responses in permafrost regions were simulated, and the impact of permafrost change on the seismic site response was discussed. Moreover, the dynamic response of the traditional embankment at the Beiluhe site in permafrost regions was studied. The changes of ground motion parameters were significantly impacted and showed reproducible changes with different active layer thicknesses and permafrost thicknesses. The ground motion amplification coefficients increased with the increase of active layer thickness, and the amplification coefficients were greater in a warm season than that in a cold season. Furthermore, the active layer thickness had little influence on the characteristic site period, and the variation of the characteristic site period with the permafrost thickness showed the logarithmic variation characteristic. Compared with the soil profile away from the center of the railway subgrade, the acceleration under the embankment showed a significant increase due to the overlying subgrade embankment. The increase in amplitude was about 29%, which illustrated that the deformation of the soil under the embankment became greater and may be more prone to damage during the seismic loading. [ABSTRACT FROM AUTHOR]

An R package permafrost indices computing (PIC) was developed, which integrates meteorological observations, remote sensing data, and field measurements to compute the factors or indices of permafrost and seasonal frozen soil. At present, 16 temperature/depth-related indices are integrated into the R package PIC to estimate the possible change trends of frozen soil in the Qinghai-Tibet Plateau (QTP). These indices include the mean annual air temperature, mean annual ground surface temperature, mean annual ground temperature, seasonal thawing/freezing n factor (nt/nf), thawing/freezing degree-days of air and ground surface (DDTa/DDTs/DDFa/DDFs), temperature at the top of the permafrost, active layer thickness, and maximum seasonal freeze depth. The PIC package supports two computational modes, namely, the stations and region calculation that enables statistical analysis and intuitive visualization on the time series and spatial simulations. Over 10 statistical methods were adopted to evaluate these indices in stations, and a sequential Mann-Kendall trend test and spatial trend method were adopted. Multiple visual manners display the temporal and spatial variabilities on the stations and region. The data sets of 52 weather stations and a central region of QTP were prepared and simulated to evaluate the temporal-spatial change trends of permafrost with the climate. Simulation results show extensive permafrost degradation in QTP, and the temporal-spatial trends of the permafrost conditions in QTP were consistent with those of previous studies. The PIC package will serve engineering applications and can be used to assess the impact of climate change on permafrost. [ABSTRACT FROM AUTHOR]

Information regarding the response of ecosystem respiration (ER) to various warming levels, especially in different grassland types and seasons, is scarce at the field scale in the permafrost region of the Tibetan Plateau (TP). In this study, we examined how different warming levels during different seasons affected ER in Tibetan alpine meadow and swamp meadow after 6 years experimental warming. The interpolated annual ER of swamp meadow (387.0 gC m −2 ) was higher than that of alpine meadow (284.5 gC m −2 ) in natural conditions. A moderate warming of 2.4 °C increased ER by 62.2% and 36.6%, and a high warming of 5.3 °C increased ER by 101.3% and 52.0% in alpine meadow and swamp meadow, respectively. The warming effects on ER were greater in the non-growing season compared with the growing season; this significantly increased the contribution of non-growing season emissions to annual ER from 25% in natural conditions to 31% in high warming treatments. ER was significantly affected by soil temperature, aboveground biomass and the duration of thaw days. The temperature sensitivity of ER ( Q 10 ) was higher in the non-growing season (3.02–5.02) than in the growing season (2.11–2.75) and decreased with increasing temperature. Our results indicated that the magnitude of warming-induced increases in ER differed by grassland type and season, and there was strong potential for the non-growing season to serve as a positive feedback to annual carbon balance. [ABSTRACT FROM AUTHOR]

The soil moisture movement is an important carrier of material cycle and energy flow among the various geo-spheres in the cold regions. Thus, this research takes the north slope of Bayan Har Mountains in Qinghai-Tibet Plateau as a case study. The present study firstly investigates the change of permafrost moisture in different slope positions and depths. Based on this investigation, this article attempts to investigate the spatial variability of permafrost moisture and identifies the key influence factors in different terrain conditions. The method of classification and regression tree (CART) is adopted to identify the main controlling factors influencing the soil moisture movement. The relationships between soil moisture and environmental factors are revealed by the use of the method of canonical correspondence analysis (CCA). The results show that: 1) Due to the terrain slope and the freezing-thawing process, the horizontal flow weakens in the freezing period. The vertical migration of the soil moisture movement strengthens. It will lead to that the soil-moisture content in the up-slope is higher than that in the down-slope. The conclusion is contrary during the melting period. 2) Elevation, soil texture, soil temperature and vegetation coverage are the main environmental factors which affect the slope-permafrost soil-moisture. 3) Slope, elevation and vegetation coverage are the main factors that affect the slope-permafrost soil-moisture at the shallow depth of 0-20 cm. It is complex at the middle and lower depth. [ABSTRACT FROM AUTHOR]

Beiluhe basin is underlain by warm and ice-rich permafrost, and covered by vegetation and soils characteristic of the Qinghai-Tibet Plateau. A field monitoring network was established to investigate permafrost conditions and to assess potential impacts of local factors and climate change. This paper describes the spatial variations in permafrost conditions from instrumented boreholes, controlling environmental factors, and recent thermal evolution of permafrost in the basin. The study area was divided into 10 ecotypes using satellite imagery based classification. The field investigations and cluster analysis of ground temperatures indicated that permafrost underlies most of the ground in swamp meadow, undisturbed alpine meadow, degrading alpine meadow, and desert alpine grassland, but is absent in other cover types. Permafrost-ecotope relations examined over a 2-year (2014–2016) period indicated that: (i) ground surface temperatures varied largely among ecotopes; (ii) annual mean ground temperatures ranged from − 1.5 to 0 °C in permafrost, indicating sensitive permafrost conditions; (iii) active-layer thicknesses ranged from 1.4 m to 3.4 m; (iv) ground ice content at the top of permafrost is high, but the active-layer soil is relatively dry. Long-term climate warming has driven thermal changes to permafrost, but ground surface characteristics and soil moisture content strongly influence the ground thermal state. These factors control local-scale spatial variations in permafrost conditions. The warm permafrost in the basin is commonly in thermal disequilibrium, and is sensitive to future climate change. Active-layer thicknesses have increased by at least 42 cm and the mean annual ground temperatures have increased by up to 0.2 °C in the past 10 years over the basin. A permafrost distribution map was produced based on ecotypes, suggesting that permafrost underlies 64% of the study region. [ABSTRACT FROM AUTHOR]

Thermokarst is a term associated with the thaw of ice-rich permafrost and the resulting formation of irregular depressions in the landscape from thaw settlement. Thermokarst lakes may subsequently develop from ponds formed in depressions. These lakes commonly have collapsing shorelines, and the development of thermokarst terrain and associated thermal erosion may significantly influence the stability of infrastructure and the hydrothermal conditions of the surrounding permafrost. In this study, we examined interannual variations in the hydrothermal regime of a thermokarst lake in Beiluhe Basin based on field data measured in 2006–2013. The timing and nature of lake ice growth and melt were recorded. We observed considerable seasonal differences in lake water level (~ 0.5 m) and differences in water level between the lake and the water table in the surrounding ground (over 1.0 m). The nearly-saturated ground at the lakeshore (~ 35% in maximum volumetric water content) highlights the seepage effect from the lake to the surrounding ground. The vertical temperature profile from + 2 m (air) to − 2 m (lake bottom) and to 60 m depth in the ground was measured. The annual mean air temperature, lake-surface temperature, and annual mean lake-bottom temperature in 2010–2011 were approximately − 3.6, 0.4, and > 5 °C, respectively. The thermal offsets between the air and the lake surface and between the lake surface and lake bottom were 3 and 7 °C, respectively. The annual mean lake-bottom temperatures ranged from 2.3 to 6.9 °C at water depths from 1.2 to 2.1 m. The asymmetry of the bathymetry has resulted in distinct thermal regimes beneath the lake bottom in different locations. A through-talik was present at the deepest side of the lake, but some permafrost extended laterally beneath the lake bottom at the shallower side, forming an hourglass shape in cross section at one end. Lateral thermal erosion along the lakeshore was linked to the lake-bottom temperature and lake depth. Variation in permafrost table depth from the lake center to the lakeshore was greater on the east side near deeper water (≥ 2 m) than at the west side where water was shallower (≤ 70 cm). The results from this study have highlighted the hydrothermal relations between thermokarst lake development and permafrost conditions. [ABSTRACT FROM AUTHOR]

• Thermokarst lakes are an important ecosystem component in permafrost terrains. • We quantified changes in thermokarst lakes using aerial and satellite images. • Overall significant increase in lake number and surface area was observed • We predict likely future continued expansion of thermokarst lakes on the central Tibetan Plateau. Thermokarst lakes are an important ecosystem component in permafrost terrains; therefore, quantifying changes in these lakes is important for evaluating the water balance and carbon budget on the Qinghai-Tibet Plateau (QTP). In this study, we utilized high spatial resolution aerial and satellite images from 1969, 2010, and 2019 to quantify changes in thermokarst lakes > 0.1 ha across four regions on the central QTP. The results indicated an overall significant increase in the lake number (+158%) and surface area (+123%) for all study regions over the last five decades, despite variations in change in these trends among the different landform types. Changes in individual lake processes indicated that the above lake changes were mainly characterized by a significant increase in the number of small lakes and area enlargements of large lakes, whereas thermokarst lake drainage only occurred in some gentle slope areas. By analyzing the potential factors that drive changes in thermokarst lakes in the study region, we found that persistent climate warming and the increasing of precipitation were the most likely explanations for the observed results. With continued climate warming and permafrost degradation, we expect a persistent increase in the number and surface area of thermokarst lakes; however, the probability of lake drainage may also increase with lake expansion. [ABSTRACT FROM AUTHOR]

Stability of the embankment is largely concerned with the height and pavement type in permafrost area. Climate is another key factor. The heat transfer model with phase change and finite element method are used to simulate the thermal regime of permafrost beneath embankment of Qinghai-Tibet Highway, considering the changing of pavement type, height of embankment and climate warming since the building of the road was started in 1954. In-situ observation of ground temperature was performed. Simulated results indicate that increasing embankment height can decrease the depth of permafrost table temporarily, and then the permafrost table goes deeper soon. Heat absorbing of black pavement is a key factor that causes permafrost degradation beneath the embankment. Both the simulated and the measured results indicate a continuous trend of permafrost degradation beneath both the embankment and the natural ground under the scenario of climate warming, which implies that only increase the embankment height is not enough to keep it stable. [ABSTRACT FROM AUTHOR]

Understanding the processes that influence the structure of biotic communities is one of the major ecological topics, and both stochastic and deterministic processes are expected to be at work simultaneously in most communities. Here, we investigated the vertical distribution patterns of bacterial communities in a 10-m-long soil core taken within permafrost of the Qinghai-Tibet Plateau. To get a better understanding of the forces that govern these patterns, we examined the diversity and structure of bacterial communities, and the change in community composition along the vertical distance (spatial turnover) from both taxonomic and phylogenetic perspectives. Measures of taxonomic and phylogenetic beta diversity revealed that bacterial community composition changed continuously along the soil core, and showed a vertical distance-decay relationship. Multiple stepwise regression analysis suggested that bacterial alpha diversity and phylogenetic structure were strongly correlated with soil conductivity and pH but weakly correlated with depth. There was evidence that deterministic and stochastic processes collectively drived bacterial vertically-structured pattern. Bacterial communities in five soil horizons (two originated from the active layer and three from permafrost) of the permafrost core were phylogenetically random, indicator of stochastic processes. However, we found a stronger effect of deterministic processes related to soil pH, conductivity, and organic carbon content that were structuring the bacterial communities. We therefore conclude that the vertical distribution of bacterial communities was governed primarily by deterministic ecological selection, although stochastic processes were also at work. Furthermore, the strong impact of environmental conditions (for example, soil physicochemical parameters and seasonal freeze-thaw cycles) on these communities underlines the sensitivity of permafrost microorganisms to climate change and potentially subsequent permafrost thaw. [ABSTRACT FROM AUTHOR]

The permafrost in Qinghai-Tibet Plateau (QTP) has long been the focus of many researchers. In this study, we first use the method that integrates synthetic aperture radar (SAR) intensity and phase information to monitor permafrost environment in the Beiluhe Region, using time series advanced SAR images. The backscattering coefficients (σ0) and deformation were extracted for the main features, and the influences of meteorological conditions to them were also quantified. The results show that both the change inσ0and surface deformation are closely related to the active layer, and the deformation is also affected by the permafrost table. First, over meadow and sparse vegetation regions,σ0rose about 6.9 and 4 dB from the freezing to thawing period, respectively, which can be mainly attributed to the thaw of the active layer and increased precipitation. Second, seasonal deformation, derived from the freeze-thaw cycle of the active layer, was characteristic of frost heave and thaw settlement and exhibited a negative correlation with air temperature. Its magnitude was larger than 1 cm in a seasonal cycle. Last, significant secular settlement was observed, with rates ranging from –16 to 2 mm/a, and it was primarily due to the thaw of the permafrost table caused by climate warming. [ABSTRACT FROM AUTHOR]

As a key attribute of soil quality, soil organic matter (SOM) and its different fractions play an important role in regulating soil nutrient cycling and soil properties. This study evaluated the soil carbon (C) and nitrogen (N) concentrations in different SOM fractions (light- and heavy fractions, microbial biomass) under different vegetation types and analyzed their influencing factors in continuous permafrost regions along the Qinghai-Tibet Highway in the North of Kunlun Mountains, China. Soil samples were collected in pits under four vegetation types - Alpine swamp meadow (ASM), Alpine meadow (AM), Alpine steppe (AS) and Alpine desert (AD) - at the depth of 0-50 cm. The vegetation coverage was the highest at ASM and AM, followed by AS and AD. The results indicated that the concentrations of light fraction carbon (LFC) and nitrogen (LFN), and microbial biomass carbon (MBC) and nitrogen (MBN) decreased as follows: ASM >AM >AS >AD, with the relatively stronger decrease of LFC, whereas the heavy fraction carbon (HFC) and nitrogen (HFN) concentrations were lower in AS soils than in the AD soils. The relatively higher proportions of LFC/SOC and MBC/SOC in the 0-10 cm depth under the ASM soils are mainly resulted from its higher substrate input and soil moisture content. Correlation analysis demonstrated that aboveground biomass, soil moisture content, soil organic carbon (SOC) and total nitrogen (TN) positively correlated to LFC, LFN, HFC, HFN, MBC and MBN, while pH negatively correlated to LFC, LFN, HFC, HFN, MBC and MBN. There was no relationship between active layer thickness and SOM fractions, except for the LFC. Results suggested that vegetation cover, soil moisture content, and SOC and TN concentrations were significantly correlated with the amount and availability of SOM fractions, while permafrost had less impact on SOM fractions in permafrost regions of the central Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

Commonly, permafrost conditions are characterised by one or two temperature profiles within each unit of a study area. Intra-unit variation is therefore unknown, and the extent to which the data represent unit conditions cannot be estimated. We have collected ground temperatures from 55 boreholes to 5 m depth drilled in four 200 m2 plots next to the Qinghai-Tibet Railway near the town of Wudaoliang. The sites are in a dry area of active aeolian erosion and straddle an alpine meadow ecotone between well- and sparsely vegetated ground cover. The annual mean air temperature at Wudaoliang is currently about -4°C. There is pronounced asymmetry in the seasonal distribution of precipitation, with very little falling between October and April, so that there is almost no snow cover in winter. At every site, air and ground surface temperatures were similar in winter, but the ground surface was considerably warmer than the air in summer in the radiation-rich environment of the Qinghai-Tibet Plateau. Thawing season n-factors were between 2 and 3 as a result. Ground conditions in the well-vegetated meadows were in thermal equilibrium with surface conditions, with the annual mean temperature near the permafrost table (Tps) between -1.2 and -1.9°C. Within plot spatial variability for Tps, estimated from the standard error of the replicate measurements, was ∼ 0.05°C at each site. Thermal conditions in the eroded, sparsely vegetated area appeared to be transient and warming, with current Tps of -0.5°C. The driest site showed a reversed thermal offset in the uppermost active layer. We hypothesise that the reversed offset may occur due to extremely dry conditions in winter, so that at the ground surface, the thermal conductivity is lower in winter than under the moist conditions of summer. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Soil–landscape models serve as a basis for understanding the relationships between soils and landscape, and such models also allow us to study soil distribution, and classification. To understand the distribution of soils and landform relationships in permafrost regions, we developed a soil–landscape model by using See5.0 decision tree software in the Wenquan region of Xinghai County, in the eastern part of permafrost regions of Qinghai–Xizang (Tibetan) Plateau (QTP). The model was based on soil pedon data from 2009. Nine environmental factors closely related to permafrost-affected-soil formation were selected as variables for the model: land surface temperature for warm season and cool season, elevation, slope gradient, slope aspect, planform and profile curvatures, wetness index and NDVI. A 5-fold cross-validation method was applied to verify the effectiveness of the soil–landscape model. The model results were consistent with field observations, and the slope was the most strongly correlated factor with soil type of the nine environmental variables. The soils in the modeled area are mainly Ustic Cambosols and Ustic Isohumisols, which cover about 60.0% and 25.6% of the total area, respectively. Gelic cambosols occur mainly in permafrost region, while Ustic isohumosols occur in the transition region between permafrost and seasonally frozen ground. Further studies are required to utilize the soil–landscape model to predict the spatial distribution of soil types over the QTP. [ABSTRACT FROM AUTHOR]

The warming of permafrost soils and the resulting change in soil respiration (Rs) is one of the most uncertainties in research on global change. To better understand the effect of warming on permafrost soils and the feedback of Rs to climatic warming, a manipulative warming experiment was conducted with two warming levels (low- and high-level warming; increases of 1.88 °C (W1) and 3.19 °C (W2) in soil surface temperature, respectively) from year 2010 to 2011 using infrared heaters in inland area of the Qinghai-Tibet Plateau (QTP). Warming significantly decreased the soil moisture at depths of 0-10 and 10-20 cm, but increased it at depths of 40-60 and 60-100 cm, most likely because of the permafrost melting. Both warming treatments delayed the onset of freezing and advanced the onset of thawing in the active layer of permafrost with a stronger effect observed in W2. Annual soil C release increased by 77.1 and 125.8 g C year in the W1 and W2 treatments, respectively, which equated to an increase of 18 and 29 % compared with the control (C). The increase in Rs was higher in the thawing period than in the freezing period. The decrease in soil water content in the upper soil layer did not significantly inhibit Rs because warming extended the thawing period and increased the soil labile C. Our results indicate that permafrost soils will release more C to the atmosphere, even though surface soil moisture decreases in a warming climate in the dry alpine meadow in the QTP. [ABSTRACT FROM AUTHOR]

Abstract: In the Tibetan permafrost region, vegetation types and soil properties have been affected by permafrost degradation, but little is known about the corresponding patterns of their soil microbial communities. Thus, we analyzed the effects of vegetation types and their covariant soil properties on bacterial and fungal community structure and membership and bacterial community-level physiological patterns. Pyrosequencing and Biolog EcoPlates were used to analyze 19 permafrost-affected soil samples from four principal vegetation types: swamp meadow (SM), meadow (M), steppe (S) and desert steppe (DS). Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria dominated bacterial communities and the main fungal phyla were Ascomycota, Basidiomycota and Mucoromycotina. The ratios of Proteobacteria/Acidobacteria decreased in the order: SM>M>S>DS, whereas the Ascomycota/Basidiomycota ratios increased. The distributions of carbon and nitrogen cycling bacterial genera detected were related to soil properties. The bacterial communities in SM/M soils degraded amines/amino acids very rapidly, while polymers were degraded rapidly by S/DS communities. UniFrac analysis of bacterial communities detected differences among vegetation types. The fungal UniFrac community patterns of SM differed from the others. Redundancy analysis showed that the carbon/nitrogen ratio had the main effect on bacteria community structures and their diversity in alkaline soil, whereas soil moisture was mainly responsible for structuring fungal communities. Thus, microbial communities and their functioning are probably affected by soil environmental change in response to permafrost degradation. [Copyright &y& Elsevier]

lpine ecosystems in permafrost region are extremely sensitive to climate change. The headwater regions of Yangtze River and Yellow River of the Qinghai-Tibet plateau permafrost area were selected. Spatial-temporal shifts in the extent and distribution of tundra ecosystems were investigated for the period 1967-2000 by landscape ecological method and aerial photographs for 1967, and satellite remote sensing data (the Landsat's TM) for 1986 and 2000. The relationships were analyzed between climate change and the distribution area variation of tundra ecosystems and between the permafrost change and tundra ecosystems. The responding model of tundra ecosystem to the combined effects of climate and permafrost changes was established by using statistic regression method, and the contribution of climate changes and permafrost variation to the degradation of tundra ecosystems was estimated. The regional climate exhibited a tendency towards significant warming and desiccation with the air temperature increased by 0.4-0.67°C/10a and relative stable precipitation over the last 45 years. Owing to the climate continuous warming, the intensity of surface heat source ( HI) increased at the average of 0.45 W/m per year, the difference of surface soil temperature and air temperature (DT) increased at the range of 4.1°C-4.5°C, and the 20-cm depth soil temperature within the active layer increased at the range of 1.1°C-1.4°C. The alpine meadow and alpine swamp meadow were more sensitive to permafrost changes than alpine steppe. The area of alpine swamp meadow decreased by 13.6-28.9%, while the alpine meadow area decreased by 13.5-21.3% from 1967 to 2000. The contributions of climate change to the degradation of the alpine meadow and alpine swamp was 58-68% and 59-65% between 1967 and 2000. The synergic effects of climate change and permafrost variation were the major drivers for the observed degradation in tundra ecosystems of the Qinghai-Tibet plateau. [ABSTRACT FROM AUTHOR]

Abstract: The 1076-km-long Golmud–Lhasa oil product pipeline is located closely parallel to the highway constructed 20years earlier within the relatively narrow north–south engineering corridor crossing the treeless central area of the Qinghai–Tibet Plateau. Much of the corridor is at elevations exceeding 4500m and high-elevation, generally warm permafrost is encountered in more than one-half of the length. The pipeline, transporting mostly diesel, motor and aviation fuels at ambient temperatures, is 159mm in diameter, has a wall thickness of 6mm and was buried in a trench at a nominal depth of between 1.2 and 1.4m. The soils encountered, mostly periglacial sands, silts and gravels, often have elevated saline contents and are subject to severe wind erosion and occasional monsoon flash flooding conditions. During its first quarter century of operation, the pipeline suffered at least 30 significant leaks and four pipeline ruptures. About 337km of the pipeline was extensively rehabilitated, including relocations or replacements in major problem areas and, where feasible for an existing pipeline, improvements in pipeline protection during 2001–2004. It was supposed to safely operate for another 30years with proper checks and needed repairs. This paper provides a review on the history of the permafrost and cold regions environmental problems of the pipeline, and their major rehabilitation, repairs and problems in the future, which might have useful implications for similar oil product pipeline at high elevations or permafrost regions. [Copyright &y& Elsevier]