Ecophysiological responses to drought stress of Populus euphratica in Alashan Desert Eco-hydrology Experimental Research Station were investigated. Results show that under mild and moderate drought stress, stomatal length, aperture, area and density is likely to decrease in the early days, but afterwards this is likely to recovery with treatment over the passage of treatment time. Under severe drought stress, these properties appear to decline continuously. However, after 45 days of drought-stress treatment, the decline is not as noticeable as before, indicating that Populus euphratica could possibly reduce water evaporation by shutting down the stoma, leading to an improvement in its water use efficiency with better survival under drought stress conditions. The leaf area first decreases, and then increases under mild and moderate drought stress conditions, with the average values under different degree of stress found to be approximately 129.52, 120.08, 116.63 and 107.28 cm², respectively. Under moderate stress conditions, the leaf water potential appears to show a continuous decline where the average values under different degree of stress are found to be -1.27, -1.85, -4.29 and -4.80 MPa, respectively. In terms of proline content, the results demonstrate that this factor appears to increase significantly under moderate and severe drought stress conditions. Especially under severe drought stress condition, the content is found to be more than 700 μg/g. Ranging over average values of 14.64 and 15.90 nmol/g under moderate and severe drought stress, respectively, Malondialdehyde content is found to increase quite rapidly under moderate and severe drought stress conditions at first, which then appears to decrease gradually with the treatment over time.

Black Carbon (BC), as a driver of environmental change, could significantly impact the snow by accelerating melting and decreasing albedo. Systematic documentation of BC studies is crucial for a better understanding of its spatial and temporal trends. This study reviewed the BC studies in the ice core and remote lake sediments and their sources in the northern hemisphere. The literature surveyed points to around 2.9 to 3.7 times increase of BC in the European Alps and up to a three-fold increase of BC in the Himalayan-Tibetan Plateau (HTP) after the onset of industrialization in Europe and Asia, respectively. BC concentration from Greenland ice core showed seven times increase with an interrupted trend after 1950's. South Asian emissions were dominant in the HTP along with a contribution from the Middle East, whereas Western European and local emissions were responsible for the change in BC concentration in the European Alps. In the Arctic, contributions from North America, Europe and Asia persisted. Similarly, a historical reconstruction of lake sediments records demonstrates the effects of emissions from long-range transport, sediment focusing, local anthropogenic activities, precipitation and total input of flux on the BC concentration.

Holocene δ¹⁸O records from various archives (ice cores, cave stalagmites, and peat sediments) from the Xinjiang region of northwestern China, in arid central Asia (ACA), are all derived ultimately from local precipitation δ¹⁸O (δ¹⁸O_p). Nevertheless, they have been proposed as indicators of different climatic parameters, such as wetness and temperature changes. This article summarizes previously reported records of moisture sources for the Xinjiang region and the results of modern observations conducted at an ice core site and a peat site in the Altai Mountains. The findings are used to propose that the overall positive trends in Holocene δ¹⁸O records from the various archives from the Xinjiang region primarily reflect the Holocene's long-term warming trend. It is concluded that more site-specific modern observations are needed to further elucidate the environmental significance of Holocene δ¹⁸O records from this region, especially for the separation of different seasonal temperature signals present within δ¹⁸O records.

Studying the climatic and environmental changes on different time scales in inland arid regions of Asia can greatly improve our understanding of climatic influences for the Qinghai-Tibet Plateau in the context of global change. Pollen, as a remnant of seed plants, is sensitive to environmental factors including precipitation, temperature and altitude, and is a classic proxy in environmental reconstruction. In the last two decades, great progress in the application of palynology to inland areas of Asia has highlighted the role of palynology in paleoclimatic and paleoenvironmental research. The main progress is as follows. (1) On the tectonic time scale of the late Cenozoic, the palaeoclimatological sequence has been established on the basis of pollen percentage, concentration and taxon. Pollen data have revealed a continuous enhancement of drought in the inland arid region of Asia, in contrast to evidence acquired based on other proxies. (2) In the late Quaternary, an increase in herbaceous plants further supports the intensification of drought associated with global cooling. In more detail, the palynological record shows a glacial-interglacial pattern consistent with changes in global ice volume. (3) The Holocene pollen record has been established at a high resolution and across a wide range of inland areas. In general, it presents an arid grassland environment in the early Holocene, followed by the development of woody plants in the mid- to late-Holocene climate optimum. This pattern is related to moisture changes in areas dominated by the westerlies. There are also significant regional differences in the pattern and amplitude of vegetation response to the Holocene environment. (4) Modern pollen studies based on vegetation surveys, meteorological data and statistics show that topsoil palynology can better reflect regional vegetation types (e.g., grassland, meadow, desert). Drier climates yield higher pollen contents of drought-tolerant plants such as Chenopodioideae, Ephedra, and Nitriaria, while contents of Artemisia and Poaceae are greater under humid climates. Besides these achievements, problems remain in palynological research: for example, pollen extraction, identification, interpretation, and quantitative reconstruction. In the future, we encourage strengthened interdisciplinary cooperation to improve experimental methods and innovation. Firstly, we should strengthen palynological classification and improve the skill of identification; secondly, laboratory experiments are needed to better constrain pollen transport dynamics in water and air; thirdly, more rigorous mathematical principles will improve the reliability of reconstructions and deepen the knowledge of plant geography; and finally, new areas and methods in palynology should be explored, for example DNA, UV-B and isotopic analysis. It is expected that palynology will continue to develop, and we hope it will continue to play an important role in the study of past climatic and environmental changes.

Land surface actual evapotranspiration is an important process that influences the Earth's energy and water cycles and determines the water and heat transfer in the soil-vegetation-atmosphere system. Meanwhile, the cryosphere's hydrological process is receiving extensive attention, and its water problem needs to be understood from multiple perspectives. As the main part of the Chinese cryosphere, the Tibetan Plateau faces significant climate and environmental change. There are active interaction and pronounced feedback between the environment and ET_a in the cryosphere. This article mainly focuses on the research progress of ET_a in the Tibetan Plateau. It first reviews the ET_a process, characteristics, and impact factors of typical underlying surfaces in the Tibetan Plateau (alpine meadows, alpine steppes, alpine wetlands, alpine forests, lakes). Then it compares the temporal and spatial variations of ET_a at different scales. In addition, considering the current greening of cryosphere vegetation due to climate change, it discusses the relationship between vegetation greening and transpiration to help clarify how vegetation activities are related to the regional water cycle and surface energy budget.

Light-absorbing impurities on glaciers are important factors that influence glacial surface albedo and accelerate glacier melt. In this study, the quantity of light-absorbing impurities on Keqikaer Glacier in western Tien Shan, Central Asia, was measured. We found that the average concentrations of black carbon was 2,180 ng/g, with a range from 250 ng/g to more than 10,000 ng/g. The average concentrations of organic carbon and mineral dust were 1,738 ng/g and 194 μg/g, respectively. Based on simulations performed with the Snow Ice Aerosol Radiative model simulations, black carbon and dust are responsible for approximately 64% and 9%, respectively, of the albedo reduction, and are associated with instantaneous radiative forcing of 323.18 W/m² (ranging from 142.16 to 619.25 W/m²) and 24.05 W/m² (ranging from 0.15 to 69.77 W/m²), respectively. For different scenarios, the albedo and radiative forcing effect of black carbon is considerably greater than that of dust. The estimated radiative forcing at Keqikaer Glacier is higher than most similar values estimated by previous studies on the Tibetan Plateau, perhaps as a result of black carbon enrichment by melt scavenging. Light-absorbing impurities deposited on Keqikaer Glacier appear to mainly originate from central Asia, Siberia, western China (including the Taklimakan Desert) and parts of South Asia in summer, and from the Middle East and Central Asia in winter. A footprint analysis indicates that a large fraction (>60%) of the black carbon contributions on Keqikaer Glacier comes from anthropogenic sources. These results provide a scientific basis for regional mitigation efforts to reduce black carbon.

Fossil Taiwania was discovered from the Lower Cretaceous Yixian Formation of Lingyuan City, western Liaoning Province, Northeast China. It is identified as a new species, Taiwania lingyuanensis sp. nov.. The present specimen is preserved as impressions with well defined leaf shoots system and reproductive structures. Leaves are dimorphic, spirally and imbricately arranged. They are scale-like on the main and cone-bearing branchlets, and subulate to falcate-subulate on the juvenile or sterile shoots. The seed cones are singly elliptic, ovate or elongate-ovate and terminally borne on ultimate shoots, bearing 22–24 scale-bracts complexes imbricately and helically arranged around the cone axis, the bracts are broad-ovate, rhomboidal or hexagonal with entire margins. Both the leafy shoots morphology and reproductive structures are similar to extant Taiwania. Furthermore, geological distribution and molecular biological evidences support that Taiwania is probably originated from the eastern Asia at least in the Early Cretaceous and widely distributed in the North Hemisphere thereafter.

As a linkage between plants and soil, litter decomposition and its effect on nutrient recirculation have an important ecological significance as they contribute to soil structure improvement and the restoration of degraded ecosystems. Fragile ecosystems in arid regions (both hot and cold) are depleted in soil organic matter, and as a result of various factors their circulation of material and energy is slower. Here we discuss how litter decomposition is necessary to maintain the stability of fragile ecosystems. We reviewed research on litter decomposition carried out in arid regions. Our objective in this review is to outline how litter decomposition, and the subsequent buildup of organic matter in soil, is a key process determining the stability of fragile ecosystems. Our review shows that existing studies have focused on the influence of single ecological factors on litter decomposition and nutrient cycling, and highlights how the exploration of interactions among factors determining litter decomposition is still lacking. This interaction is a key aspect, since in the real world, decomposition and nutrient return to soil of litter products is affected by multiple factors. We propose a network setup on a cross-regional scale using standardized methods (e.g., the tea bag method) to understand litter decomposition and nutrient return in fragile ecosystems. Such a unique network could contribute to establish predictive models suitable for litter decomposition and nutrient return in these areas, and thus could provide theoretical and practical support for regional ecological protection and high-quality development.

Ice documentation and response to prominent warming, especially after the 1990s, is further investigated because it is concerned whether ice records have absence. A δ¹⁸O series of a Laohugou (LHG) shallow ice core (20.12 m) in the northeastern Tibetan Plateau was reconstructed covering the period of 1960-2006. The ice core δ¹⁸O record had significant positive correlations with the warm season (May-September) air temperatures at adjacent meteorological stations and the 500 hPa temperatures in boreal China, indicating that the δ¹⁸O record could be considered a credible proxy of regional temperature. A clear, cold temperature event in 1967 and rapid warming after the 1990s were captured in the LHG δ¹⁸O series, revealing that it could record extreme air-temperature events on both regional and global scales. The LHG δ¹⁸O variations had evident positive correlations with both the summer surface outgoing longwave radiation (OLR) in the Mongolia region and the summer meridional wind at 500 hPa in the LHG region during 1960-2006, suggesting that the increased OLR in the Mongolia region might have intensified the Mongolia Low and expanded the pressure gradient to the LHG region (the Shulehe High), which would have pushed the westerlies further north and suppressed southward incursions of cold air into the LHG region, and thus augmented the temperature rise. The regional atmospheric circulation difference (1985-2006 minus 1960-1984) suggested that the anticyclone in the Mongolia region might have developed the easterly wind, which transported warmer air from the east toward the LHG region and weakened the cold penetration of the westerlies, resulting in the temperature rise since the middle 1980s.

In cold regions, the widened subgrade could produce uneven frost heave that is detrimental to the pavement. This study investigates the differential frost heave characteristics in a widened subgrade. The field monitoring system mainly consists of temperature, moisture, and displacement sensors and distributed optical fiber cables for strain measurement. The monitoring results show that the cooling period in the subgrade is longer than the warming period. Water content in the subgrade changes significantly within 0-2 m below the subgrade surface but stabilizes within 2-5 m. The maximum frost heave occurs from February to March. In comparison, the existing subgrade has a longer freezing period and larger heave value, caused by the higher density and water content inside. Water in the existing subgrade migrates into the new one after widening, leading to frost heave reduction in the existing subgrade. Simultaneously, the traffic loads result in the consolidation of the new subgrade, thus reducing the heave value in the second year. In the third year, the water supply from the existing subgrade facilitates the frost heave in the new subgrade. The tensile strain distributions obtained by the distributed optical fiber cables show that the maximum differential frost heave occurs at the joint between the existing and new subgrades. The differential frost heave gradually stabilizes after three years. Finally, an improved frost heave prediction model is developed based on the segregation potential concept and monitoring results.

The Elkon Horst is a geological structure that consists of heterogeneous strata with highly variable geocryological and temperature conditions. Gaining accurate knowledge of permafrost distribution patterns within this structure is of both scientific and practical importance. In mountainous terrain, the ground thermal regime is controlled by both surface and subsurface conditions. Surface conditions include snow cover characteristics, the presence or absence of vegetation, vegetation density, etc.. In contrast, subsurface conditions involve rock lithology or petrography, density, quantity and depth of fissures, groundwater, etc.. This article examines ground thermal regimes in various geomorphological settings based on temperature measurement data from geotechnical boreholes. The occurrence and extent of permafrost were evaluated for the entire horst area using direct and indirect methods. The maximum permafrost thickness measured in the Elkon Horst is 330 m, and the estimated maximum is 450 m at higher elevations. Thermophysical properties were determined for the major rock types, and the geothermal heat flux was estimated for the study area. The thermal conductivities were found to vary from 1.47 to 4.20 W/(m·K), and the dry bulk densities to range between 2,236 kg/m³ and 3,235 kg/m³. The average geothermal heat flux was estimated to be 44 mW/m².

Ganzhou District is an oasis city in the Zhangye Municipality of Gansu Province, China. Based on multi-temporal TM and ETM satellite remote sensing data in 1985, 1996, 2000, and 2012, and by using corrected figures of land use status over the same periods, the spatial area of Ganzhou District since 1985 was extracted with statistical methods, and urban spatial expansion was measured by quantitative research methods. The characteristics of spatial expansion of Ganzhou District were analyzed by urban expansion rate, expansion intensity index, compactness, fractal dimension, and the city center shift method. The results showed that the built-up area of Ganzhou District increased by 3.46 times during 1985-2012. The expansion in 1985-1996 was slow, during 1996-2000 it was rapid, and during 2000-2012 it was at a high speed. This city mainly expanded to the northeast and northwest. Government decision making had a decisive influence on urban expansion. Initially the expansion was uniform, but later the local transportation, economy, resources, population, and national policies factors had an obvious influence on urban expansion.

The original landform along the China-Russia Crude Oil Pipeline (CRCOP, line 2) was disturbed during installation of pavement for the pipeline. Forest and vegetation coverage is dense, and runoff develops along the pipe. Since the operation of the CRCOP (line 2) began in 2018, ponding has appeared on both sides of the pipeline. If there is no drainage, ponding can hardly dissipate, due to the low permeability of the permafrost layer. With the supply of surface flow and the transportation of oil at positive temperatures, ponding promotes an increase in temperature and changes the boundary thermal conditions of the pipeline. Meanwhile, when the ponding freezes and thaws, frost heave threatens operational safety of the pipeline. Furthermore, the ponding can affect the thermal condition of line 1. In this paper, the distribution of ponding along the CRCOP was obtained by field investigation. The type and cause of ponding were summarized, and the catchment and stream order were extracted by the Digital Elevation Model (DEM). According to the statistical results in attributes for topographic factors, it is known that ponding along the pipeline is relative to elevation, slope, aspect, and the Topographic Wetness Index (TWI). Water easily accumulates at altitudes of 300-450 m, slopes within 3°-5°, aspect in the northeast or south, TWI within 13-16, flow direction in north-east-south, and flow length within 90-150 km. This paper proposes a theoretical basis for the cause and characteristics of ponding along the pipeline.

Reeds are widely distributed in drought and high salt conditions of northwestern China.Leaf epidermal micromorphology,anatomy,chloroplast ultrastructure and physio-chemical characteristics due to long-term adaptation in the natural habitats of common reed (Phragmites communis Trin.) contrasted considerably among three different ecotypes:dune reed (DR),Gobi salt reed (GSR) and swamp reed (SR).The main objective of the present study is to determine the adapting characteristics of morphology,anatomy and physiological responses of thin roots in DR,GSR and SR.The results show that root length density was higher in SR and few root hairs were observed in DR.Cross-section anatomical features show that each ecotype has an endodermis and exodermis,while cortex thickness and proportion of root cortical aerenchyma and stele in root structure varied among the three ecotypes.The stele and xylem share a larger area in DR compared to GSR and SR.GSR has a large proportion of the cortex with radialized distribution of aerenchyma cells spacing,and the cortex has a peripheral,mechanically stiff ring in the exodermis.SEM and TEM microscope images show that GSR has a sclerenchyma ring with high lignification in the exodermis.The physio-chemical parameters show that GSR had a higher level of stress tolerance than DR.These findings indicate that developed water-absorbing tissues were largely distributed in the root structure of DR,and a main framework with supporting function spacing with aerenchyma was dominant in GSR in the long term adaptation to their natural habitats,respectively.

Transport structures built throughout the period from 1960 to 1980 in permafrost regions based on the principle of permafrost preservation are subject to deformations. In many cases, the reason is a gradual change in temperature and their subgrade condition within the active zone due to the structures' technogenic impact. Design solutions for the fifty-year-old structures fail to ensure in all cases their reliable operation at the present time. The greatest danger to the reliable operation of railway lines in cold regions is uneven deformations of bridges, which are barrier places. Therefore, the solution to this problem is urgent especially due to the necessity of increase carrying capacity. The purpose of this study is to increase reliability of bridge operation in cold regions through strengthening the subgrade by reinforcement with injection of solidifying solutions. The problem of uneven deformations due to permafrost degradation is considered using the example of a railway bridge located in the northern line of the Krasnoyarsk railway. Deformations of the bridge abutments began immediately after the construction was completed and the bridge was open for traffic-since 1977. Permafrost degradation was developing more actively straight under the abutments due to higher thermal conductivity of the piles concrete. Notably, thawing intensity of frozen soils under the bridge abutments is uneven due to its orientation to the cardinal points. The analysis of archive materials and results of the geodetic survey made it possible to systematize the features of augmenting deformations of each abutment over time. The engineering-geological survey with drilling wells near the abutments ensured determination of soil characteristics, both in the frozen and thawed states. Thermometric wells were arranged to measure temperatures. The analysis and systematization of the data obtained allowed us to develop geotechnical models for each abutment of the bridge. The peculiarity of these models is allowance for changes in the strength and deformation characteristics of the soil calculated layers depending on changes in temperature and the soil condition. Thus, different calculated geological elements with the corresponding strength and deformation characteristics were identified in the soil layers of the same origin. The analysis of the systematized geodetic data allowed us to confirm adequacy of the developed geotechnical models. Studies carried out using geotechnical models made it possible to predict improvement of physical and mechanical characteristics of the subgrade to prevent further growth deformations of the bridge abutments. The method of reinforcement by injection is proposed. Injecting a solution under pressure leads to strengthening of weakened thawed soils and improving their physical and mechanical properties. This research theoretically substantiates and develops the geotechnical models of the reinforced pier footing of bridge abutments by injection of solidifying solutions. The models take into account the reinforcement parameters and elements for the case in question. The influence of reinforcement on the change in physical and mechanical properties of the soil mass is determined.

Determining an optimal sample size is a key step in designing field surveys, and is particularly important for detecting the spatial pattern of highly variable properties such as soil organic carbon (SOC). Based on 550 soil sampling points in the near-surface layer (0 to 20 cm) in a representative region of northern China’s agro-pastoral ecotone, we studied effects of four interpolation methods such as ordinary kriging (OK), universal kriging (UK), inverse distance weighting (IDW) and radial basis function (RBF) and random subsampling (50, 100, 200, 300, 400, and 500) on the prediction accuracy of SOC estimation. When the Shannon's Diversity Index (SHDI) and Shannon's Evenness Index (SHEI) was 2.01 and 0.67, the OK method appeared to be a superior method, which had the smallest root mean square error (RMSE) and the mean error (ME) nearest to zero. On the contrary, the UK method performed poorly for the interpolation of SOC in the present study. The sample size of 200 had the most accurate prediction; 50 sampling points produced the worst prediction accuracy. Thus, we used 200 samples to estimate the study area's soil organic carbon density (SOCD) by the OK method. The total SOC storage to a depth of 20 cm in the study area was 117.94 Mt, and its mean SOCD was 2.40 kg/m². The SOCD kg/(C?m²) of different land use types were in the following order: woodland (3.29) > grassland (2.35) > cropland (2.19) > sandy land (1.55).

The glaciers of the Hengduan Mountains play an important role in the hydrology processes of this region.In this study,the HBV Light model,which relies on a degree-day model to simulate glacier melting,was employed to simulate both glacier runoff and total runoff.The daily temperature and precipitation at the Hailuo Creek No.1 Glacier from 1952 to 2009 were obtained from daily meteorological observed data at the glacier and from six national meteorological stations near the Hailuo Creek Basin.The daily air temperature,precipitation,runoff depth,and monthly potential evaporation in 1995,1996,and 2002 were used to obtain a set of optimal parameters,and the annual total runoff and glacier runoff of the Hailuo Creek Glacier (1952-2009) were calculated using the HBV Light model.Results showed the average annual runoff in the Hailuo Creek Basin was 2,114 mm from 1952 to 2009,of which glacial melting accounted for about 1,078 mm.The river runoff in the Hailuo Creek catchment increased as a result of increased glacier runoff.Glacier runoff accounted for 51.1% of the Hailuo Creek stream flow in 1994 and increased to 72.6% in 2006.About 95% of the increased stream flow derived from the increased glacier runoff.

The Tibetan Plateau (TP) has powerful dynamics and thermal effects, which makes the interaction between its land and atmosphere significantly affect climate and environment in the regional or global area. By retrospecting the latest research progress in the simulation of land-surface processes (LSPs) over the past 20 years, this study discusses both the simulation ability of land-surface models (LSMs) and the modification of parameterization schemes from two perspectives, the models' applicability and improved parameterization schemes. Our review suggests that different LSMs can well capture the spatiotemporal variations of the physical quantities of LSPs; but none of them can be fully applied to the plateau, meaning that all need to be revised according to the characteristics specific to the TP. Avoiding the unstable iterative computation and determining the freeze?thaw critical temperature according to the thermodynamic equilibrium equation, the unreasonable freeze?thaw parameterization scheme can be improved. Due to the complex underlying surface of the TP, no parameterization scheme of roughness length can well simulate the various characteristics of the turbulent flux over the TP at different temporal scales. The uniform soil thermodynamic and hydraulic parameterization scheme is unreasonable when it is applied to the plateau, as a result of the strong soil heterogeneity. There is little research on the snow-cover process so far, and the improved scheme has no advantage over the original one due to the lack of some related physical processes. The constant interaction among subprocesses of LSPs makes the improvement of a multiparameterization scheme yield better simulation results. According to the review of existing research, adding high-quality observation stations, developing a parameterization scheme suitable for the special LSPs of the TP, and adjusting the model structures can be helpful to the simulation of LSPs on the TP.

The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions (i.e., power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils (i.e., sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.

The Cretaceous (ca. 145 Ma~65 Ma) was characterized by remarkable greenhouse conditions which was more server than present greenhouse gas emissions. However, this special climate condition is mainly documented from marine records. The information derived from continental sediments including terrestrial vegetation is relatively scarce. Here, we report on a palynological study of 17 samples from the Lower Cretaceous Liupanshan Group of the Sikouzi Section (spanning 116 Ma~103 Ma), Liupanshan Basin and analyzed for paleoclimate implications. The palynoflora is diverse, dominated by Classopollis (Cheirolepidiaceae), with abundant ferns and rare angiosperms. The dominant ferns are from Lygodiaceae and Schizaeaceae. The palynological data shows that the Early Cretaceous floras are derived from various settings, i.e., the Coniferales on high elevation mountains, Cheirolepidiaceae along low hills near lakes, ferns in marsh wetlands, and algae in fresh water lakes. The palynoflora indicates that the climate in the Liupanshan area is hot and dry, and the palaeogeography is characterized by complex and various outlook during the Early Cretaceous, furthermore, climate evolution revealed by the vegetation can be divided into two stages during this period. From 116 Ma to 112 Ma, the concentration of thermophilic and xerophilous species such as Cheirolepidiaceae and Schizaeaceae were relatively low, conifers increased significantly, and fern concentration remained steady. This ecosystem suggests a humid and cold climate during this period. From 112 Ma to 103 Ma, the concentration of Cheirolepidiaceae and Schizaeaceae was relatively high, and conifers decreased significantly. Compared to the upper stage, the total percentage of Lygodiaceae spores were relatively low. Vegetation change during this period may indicate an increased trend of a dry and hot environment in this region. The trend of climate change recorded by the pollen assemblages during this period coincide with global sea surface temperature fluctuation. Thus, climate change recorded by the palynological assemblage in the Sikouzi section correlates well with global climate change during the Early Cretaceous.

The moisture content of a road subgrade in cold regions will increase after freeze-thaw cycles, resulting in subgrade strength and stiffness losses. Electroosmosis is widely used in treating saturated soft soils to decrease the moisture content. The induced moisture migration during electroosmosis in unsaturated soil is much more complex than that of saturated soil because of a series of nonlinear changes in soil properties. This study first uses an exponential function to characterize the relationship between electroosmotic permeability and saturation degree. Then, a one-dimensional model is developed to simulate the electroosmosis-induced moisture migration in unsaturated soil. Simulation results show that electroosmosis reduces the saturation degree of the unsaturated soil, indicating that it can be applied to subgrade dewatering. Key parameters such as soil pore size distribution coefficient, air entry value, and effective voltage significantly affect moisture migration. Electroosmotic properties of unsaturated soils are extremely important to the efficiency of electroosmosis.

After the construction of Qinghai-Tibet Highway and Railway, the Qinghai-Tibet Power Transmission (QTPT) line is another major permafrost engineering project with new types of engineering structures. The changing process and trend of ground temperature around tower foundations are crucial for the stability of QTPT. We analyzed the change characteristics and tendencies of the ground temperature based on field monitoring data from 2010 to 2014. The results reveal that soil around the tower foundations froze and connected with the artificial permafrost induced during the construction of footings after the first freezing period, and the soil below the original permafrost table kept freezing in subsequent thawing periods. The ground temperature lowered to that of natural fields, fast or slowly for tower foundations with thermosyphons, while for tower foundations without thermosyphons, the increase in ground temperature resulted in higher temperature than that of natural fields. Also, the permafrost temperature and ice content are significant factors that influence the ground temperature around tower foundations. Specifically, the ground temperature around tower foundations in warm and ice-rich permafrost regions decreased slowly, while that in cold and ice poor permafrost regions cooled faster. Moreover, foundations types impacted the ground temperature, which consisted of different technical processes during construction and variant of tower footing structures. The revealed changing process and trend of the ground temperature is beneficial for evaluating the thermal regime evolution around tower foundations in the context of climate change.

Groundwater is a key factor controlling the growth of vegetation in desert riparian systems. It is important to recognise how groundwater changes affect the riparian forest ecosystem. This information will not only help us to understand the ecological and hydrological process of the riparian forest but also provide support for ecological recovery of riparian forests and water-resources management of arid inland river basins. This study aims to estimate the suitability of the Water Vegetation Energy and Solute Modelling (WAVES) model to simulate the Ejina Desert riparian forest ecosystem changes, China, to assess effects of groundwater-depth change on the canopy leaf area index (LAI) and water budgets, and to ascertain the suitable groundwater depth for preserving the stability and structure of desert riparian forest. Results demonstrated that the WAVES model can simulate changes to ecological and hydrological processes. The annual mean water consumption of a Tamarix chinensis riparian forest was less than that of a Populus euphratica riparian forest, and the canopy LAI of the desert riparian forest should increase as groundwater depth decreases. Groundwater changes could significantly influence water budgets for T. chinensis and P. euphratica riparian forests and show the positive and negative effects on vegetation growth and water budgets of riparian forests. Maintaining the annual mean groundwater depth at around 1.7?2.7 m is critical for healthy riparian forest growth. This study highlights the importance of considering groundwater-change impacts on desert riparian vegetation and water-balance applications in ecological restoration and efficient water-resource management in the Heihe River Basin.

Based on salt-frost heave tests of sulfate saline soil under repeated freeze-thaw cycles, this paper discusses the mechanism of the salt-frost heave under long-term freeze-thaw cycles. The results show that the salt-frost heave can be restricted considerably by loads, and there is a critical load for the salt-frost heave cumulative effect. Under this load, peak values of salt-frost heave approach a constant, and the residual values become 0. There is no longer structure heave or cumulative effect of saline soil exposed to freeze-thaw cycles under the critical load. Taking cumulative effect into account in calculations of salt-frost heave, a salt-frost heave model under freeze-thaw cycles is developed.

Based on the engineering background of the contact channel between Shangyang and Gushan of Fuzhou Metro Line 2 undercrossing the existing tunnel line, the freezing temperature field of the contact channel, the displacement field of the existing tunnel line and the contact channel with different net distances and horizontal angles are analyzed by ANSYS finite element software and field measurement method. The obtained results indicate that during the freezing period, the temperature drops at different measuring holes are almost the same. The temperature near the bottom freezing tube drops faster than that far from the tube. It is found that the bilateral freezing technique improves the formation of the freezing wall in the intersection area. In this case, the intersection time of the cross-section is 7 days faster than that of the adjacent ordinary section. The change curve of the displacement of the surface uplift in different freezing periods with the distance from the center of the channel is "M" shaped. The maximum uplift displacement at 12 m from channel center is 25 mm. The vertical displacement of the measuring point located above the central axis of the connecting channel is large. The farther the point from the central axis, the smaller the corresponding vertical displacement. When the horizontal angle between the existing tunnel and the connecting channel is less than 60°, the existing vertical displacement of the tunnel changes rapidly with the horizontal angle, reaching 0.17 mm/°. Meanwhile, when the net distance is less than 6.1 m, the change rate of the vertical displacement of the tunnel is up to 2.4 mm/m.

The active-layer soils overlying the permafrost are the most thermodynamically active zone of rock or soil and play important roles in the earth-atmosphere energy system. The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variation in mean annual temperatures and the formation of ground ice in permafrost regions. Using soil-temperature and -moisture data obtained from the active layer between September 2011 and October 2014 in the permafrost region of the Nanweng'he River in the Da Xing'anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Based on analysis of ground-temperature variation and hydrothermal transport characteristics, the thawing and freezing processes of the active layer were divided into three stages: (1) autumn-winter freezing, (2) winter freeze-up, and (3) spring-summer thawing. Variations in the soil temperature and moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freeze-thaw are discussed in this paper. The study's results show that thawing in the active layer was unidirectional, while the ground freezing was bidirectional (upward from the bottom of the active layer and downward from the ground surface). During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during a freezing-thawing cycle, the soil-water molecules migrate downward, i.e., soil moisture transports from the entire active layer to the upper limit of the permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil-moisture content and vegetation.

In recent years, the desertification of alpine meadows has become a serious ecological problem and has gradually become a threat to regional economic activities in Maqu County. To reveal the mechanism for sandy desertification of alpine meadows, we conducted wind tunnel experiments on aeolian processes over sandy alpine meadows. Results show that the sand-flux profile of mix-sized sediment decays exponentially with increasing height. However, the profile pattern of a group of uniform-sized particles depends on the experimental wind speeds. The profile pattern of all the groups studied can be expressed by exponential decay functions when the wind speed is less than or equal to 16 m/s. while that for all the groups studied can be expressed by a Gaussian distribution function when the wind speed is above 16 m/s. The average saltation heights of mixed sands at wind speeds of 12 m/s, 16 m/s, 20 m/s, and 24 m/s were 2.74, 4.19, 5.28, and 6.12 cm, respectively. The mean grain size basically first decreases and then increases with increasing height under different wind speeds. The sorting improves with increasing wind speed, while the kurtosis and skewness show relationships with only the characteristics of the parent soil.

Spatial heterogeneity is an inherent characteristic of natural forest landscapes, therefore estimation of structural variability, including the collection and analyzing of field measurements, is a growing challenge for monitoring wildlife habitat diversity and ecosystem sustainability. In this study, we investigated the combined influence of plot shape and size on the accuracy of assessment of conventional and rare structural features in two young-growth spruce-dominated forests in northwestern China. We used a series of inventory schemes and analytical approaches. Our data showed that options for sampling protocols, especially the selection of plot size considered in structural attributes measurement, dramatically affect the minimum number of plots required to meet a certain accuracy criteria. The degree of influence of plot shape is related to survey objectives; thus, effects of plot shape differ for evaluations of the "mean" or "representative" stand structural conditions from that for the range of habitat (in extreme values). Results of Monte Carlo simulations suggested that plot sizes <0.1 ha could be the most efficient way to sample for conventional characteristics (features with relative constancy within a site, such as stem density). Also, 0.25 ha or even larger plots may have a greater likelihood of capturing rare structural attributes (features possessing high randomness and spatial heterogeneity, such as volume of coarse woody debris) in our forest type. These findings have important implications for advisable sampling protocol (plot size and shape) to adequately capture information on forest habitat structure and diversity; such efforts must be based on a clear definition of which types are structural attributes to measure.

Finiteelement simulations are increasingly providing a versatile environment for this topic. In this study, a two-dimensional finite element analysis is conducted to predict the deformation of highembankment in Bazhun heavy-haul railway, China. A recently developed nonlinear softening-type constitutive model is utilized to model the behavior of subgrade filling materials subjected to freeze-thaw cycles. For the convenience of practical application, the dynamic loading induced by a vehicle is treated as a quasi-static axle load. The deformation of this embankmentwith different moisture content under freeze-thaw cycles is compared. The results show that when subjected to the first freeze-thaw cycle, the embankmentexperienced significant deformation variations. Maximum deformation was usually achieved after the embankment with optimum moisture content experienced six freeze-thaw cycles, however, the embankment with moisture content of 8.0% and 9.5% deforms continuously even after experiencing almost ten freeze-thaw cycles. Overall, this study provides a simple nonlinear finite element approach for calculating the deformation of the embankmentinchanging climate conditions.

The meso-structure of sandstone has a significant effect on its mechanical properties under external loads. In this paper, by taking two types of sandstone with different grain sizes as the study objects, the effects of grain size and freeze-thaw cycles on tensile strength and damage mode of sandstone are analyzed using a combination of laboratory tests, theoretical analysis, and numerical calculation. The Brazilian splitting tests are carried out on sandstone samples subjected to freeze-thaw cycles. The results show that: (1) The Brazilian splitting mode of the fine-grained sandstone is dominated by the central fracture, whereas that of the coarse-grained sandstone is controlled by a noncentral fracture. (2) The freeze-thaw cycles aggravate the initial damage of sandstone, and the cumulative freeze-thaw damage has a greater impact on the Brazilian splitting damage mode of the coarse-grained sandstone than on the fine-grained sandstone. (3) The numerical analysis software RFPA^2D system can simulate the Brazilian splitting failure process of the two types of sandstone with varying grain sizes under different freeze-thaw cycles. It is shown to be an effective method to reveal the tensile failure process and deterioration mechanism of sandstone under freeze-thaw cycling. (4) The formation mechanisms of the two splitting modes are analyzed according to the energy principle. The energy release of coarse-grained sandstone forms a noncentral splitting mode along the rock sample internal weak structural plane, whereas the fine-grained sandstone sample's energy accumulates in the rock sample center and releases it instantaneously at its center, showing the failure mode of central splitting. In addition, based on damage mechanics theory, the damage evolution equation of sandstone subjected to freeze-thaw cycles under tension is established, and the influence of energy release and dissipation on the sandstone's tensile properties is quantitatively analyzed.

High temperature rutting is a typical highway damage in Xinjiang, China, and its trigger process usually has a close relationship with characteristics of road temperature distribution. A numerical model of earth-atmosphere coupling heat transfer on a typical section of the Beijing-Xinjiang Expressway (G7) from Wutong Daquan to Yiwu was established in this work. Spatiotemporal characteristics of pavement structure layer temperature distribution, frequency and duration times of road surface high temperature from May 1 to September 30 are statistically studied. The effects of wind speed, weather and air temperature on asphalt layer and pavement temperature are analyzed. The results show that: (1) Spatial and temporal temperature distribution characteristics of pavement structural layers are greatly affected by the coupled earth-atmosphere heat transfer process. Surface temperature increases along the airflow direction and daily temperature variation of the pavement structure layer decreases with an increase of depth. (2) G7 expressway will face the challenge of high rutting damage. The proportion of temperature higher than 50 °C for pavement surface and asphalt upper layer both exceeds 50% and high temperature of road lasts for more than six hours in numerous days. (3) High temperatures of asphalt pavement are usually associated with low ambient wind speeds, while the wind flow has little cooling effect when the road surface temperature is relative high. Weather conditions have a significant impact on temperature of the road surface. The probability of high temperature in sunny days is obviously higher than other weather conditions. (4) Pavement temperature rises as air temperature rises. When air temperature is higher than 30 °C, the proportion of pavement daily maximum temperature over softening point reaches up to 78%.

Water is the most important limiting factor in arid areas, and thus water resource management is critical for the health of dryland ecosystems. However, global climate change and anthropogenic activity make water resource management more difficult, and this situation may be particularly crucial for dryland restoration, because of variation in water uptake patterns associated with artificial revegetation of different ages and vegetation type. However, there is lacking long-term restorations that are suitable for studying this issue. In Shapotou area, Northwest China, artificial revegetation areas were planted several times beginning in 1956, and now form a chronosequence of sand-binding landscapes that are ideal for studying variability in water uptake source by plants over succession. The stable isotopes δ¹⁸O and δ²H were employed to investigate the water uptake patterns of the typical revegetation shrubs Artemisia ordosica and Caragana korshinskii,which were planted in different years. We compared the stable isotope ratios of shrub stem water to groundwater, precipitation, and soil water pools at five layers (5-10, 10-40, 40-80, 80-150, and 150-300 cm). The results indicate that Artemisia ordosica derived the majority of their water from the 20-150 cm soil layer, whereas Caragana korshinskii obtained water from the 40-150 cm soil layer. The main water sources of Artemisia ordosica and C. korshinskii plants changed over time, from deeper about 150 cm depth to shallow 20 cm soil layer. This study can provide insights into water uptake patterns of major desert vegetation and thus water management of artificial ecosystems, at least in Northwest China.

Calling upon all nongovernmental sectors of the society is important to cope with the ecological crisis brought about by rapid development. Enterprises are the active agent of socialist market economic activities and possess a prominent position in the ecological civilization construction of the new age. Making use of the active agent role of enterprises and stimulating the green development of enterprises are essential to realizing the dream of a beautiful China. This paper discusses the development and management experiences of a typical ecological industrialization model, that of the Elion Resources Group in Inner Mongolia. Existing problems are disclosed, and feasible suggestions are given: (1) accelerate the registration of lands to protect legitimate rights and interests, (2) perfect the land-use administration system and make it cover all national land space, (3) perfect the natural resources management system, and (4) compile balance sheets of natural resources and strengthen accountabilities.

Distribution of rainfall event sizes and interval lengths between events are important characteristics of arid and semi-arid climates. Understanding their importance will contribute to our ability to understand ecosystem dynamics in these regions. Rainfall event timing and magnitude are important drivers of ecosystem processes and are instrumental in creating landscape heterogeneity in arid and semi-arid regions. Rainfall event characteristics were analyzed using an automatic tipping-bucket rain-gauge record across the entire summer monsoon season from 2008 to 2015 at the arid desert area of Shapotou in the Tengger Desert, China. Changing the minimum inter-event time (MIT) from 30 min to 24 h alters the number of rainfall events from 64 to 25 for the event depth larger than 0.1 mm. The mean rainfall intensity declined from 0.95 mm/h to 0.53 mm/h, and the geometric mean event duration rose from 0.55 h to 4.4 h. The number of rainfall events, mean rainfall intensity, and geometric mean event duration differed under different criteria of individual rainfall depths, except that for an individual rainfall depth of 0.5, 1.0, and 5.0 mm. The aforementioned features differed only at the lowest range of the mean rainfall intensity and depth for MIT=3 and 6 h. These findings suggest that identification of event-based rainfall in this specific arid region can be better achieved by setting the MIT at six hours. The wide variation in rainfall event properties indicate the need for paying more attention to the proper selection and reporting of event criteria in studies that adopt event-based data analysis. This is especially true in quantifying effective rainfall for soil water replenishment in terms of rainfall depth and intensity with infrequent rainfall events.

Understanding the effect of biodiversity on ecosystem function is critical to promoting the sustainability of ecosystems and species conservation in natural ecosystems. We observed species composition, species richness and aboveground biomass, and simulated the competitive assemblages in a natural grassland ecosystem of China, aiming to test some assumptions and predictions about biodiversity–stability relationships. Our results show that aboveground productivity and temporal stability increased significantly with increasing species richness, and via a combination of overyielding, species asynchrony, and portfolio effects. Species interactions resulted in overyielding caused by trait-independent complementarity, and were not offset by a negative dominance effect and trait-dependent complementarity effect. Therefore, the mechanisms underlying the biodiversity effect shifted from the selection effect to the complementarity effect as diversity increased, and both effects were coexisted but the complementarity effect represent a mechanism that facilitates long term species coexistence in a natural grassland ecosystem of China.

The colonization and development of biological soil crusts (BSCs) are rarely discussed when investigating vegetation restoration with difference arrangement and structure of anthropogenically damaged areas in semi-arid regions. The present study analyzes the relationships among coverage, height and density of woody vegetation and coverage and thickness of BSCs on the surface mine dumpsite in Heidaigou, China. Results showed that PR (Prunus sibirica L.), PT (Pinus tabulaeformis Carr.) and PPr (P. tabulaeformis Carr., P. sibirica L.) types had the highest coverage of total BSCs, which were 76.8%, 75.9% and 78.9%, respectively and PR showed the thickest BSCs of 4.41 mm. There was a significant correlation between coverage and thickness of BSCs and coverage and height of woody vegetation as a unimodal curve. Our findings suggest that a single woody plant species and low level coverage and height (no more than 30% and 300 cm, respectively) of woody plants may be able to create suitable conditions for facilitating BSCs restoration on the surface of mine dumpsites. The effects of vegetation arrangement and structure on BSCs colonization and development should be considered in reconstructing and managing woody vegetation in disturbed environments, such as surface mine dumpsites in semi-arid areas.

Desert plants take on unique physiologically adaptive mechanisms in response to an adverse environment. In this study, we determined the concentrations of leaf nitrogen (N), phosphorus (P), and calcium (Ca) fraction for dominant species of Artemisia ordosica, A. frigida, Calligonum mongolicum, and Oxytropis aciphylla in the Alxa Desert and discussed seasonal changes of their leaf N:P ratio and Ca fraction. The results showed that, from May to September, the N:P ratios of A. ordosica and C. mongolicum gradually and significantly increased, while those of A. frigida, and O. aciphylla had an increase trend that was not significant; the physiologically active Ca of A. ordosica and A. frigida increased significantly, while that of C. mongolicum and O. aciphylla decreased significantly. The physiologically inert calcium of C. mongolicum increased extremely significantly, while that of others was not significant. There was a significantly positive correlation between the N:P ratio and physiologically active Ca for A. ordosica, and the N:P ratio was significantly and negatively correlated with physiologically active Ca for O. aciphylla. These findings revealed that the physiological regulation mechanism was different for the plants either in earlier stage or later stage of plant-community succession.

This paper studied the basic properties of saline soil at different depths of a sampling site in Da'an, China, through field reconnaissance and laboratory analysis. A series of experiments which comprised the analyses of grain size distribution, mineral composition, soil physical properties, soluble salt concent, pH, organic content and cation exchange capacity were conducted. Through these experiments, the distribution rule of each property and their causes are discussed. These results could provide a fundamental base for the study of moisture migration.

A series of saline soil-related problems, including salt expansion and collapse, frost heave and thaw settlement, threaten the safety of the road traffic and the built infrastructure in cold regions. This article presents a comprehensive review of the physical and mechanical properties, salt migration mechanisms of saline soil in cold environment, and the countermeasures in practice. It is organized as follows: (1) The basic physical characteristics; (2) The strength criteria and constitutive models; (3) Water and salt migration characteristics and mechanisms; and (4) Countermeasures of frost heave and salt expansion. The review provides a holistic perspective for recent progress in the strength characteristics, mechanisms of frost heave and salt expansion, engineering countermeasures of saline soil in cold regions. Future research is proposed on issues such as the effects of salt erosion on concrete and salt corrosion of metal under the joint action of evaporation and freeze-thaw cycles.