To better understand the response mechanisms of seasonal changes in high-altitude areas to ecological and environmental factors amid global climate change, it is crucial to study the indicators of seasonal early or late and length grade duration classification in Xizang. In this study, we analyzed daily temperature data from 38 meteorological stations in Xizang (1981-2023) using temperature thresholds of 6 ℃, 17 ℃, 17 ℃ and 6 ℃ for four seasons, to explore the classification indices and evolution laws of seasonal early or late and length grade. The results revealed the following: (1) The average start dates for spring, summer, autumn, and winter at the 38 stations were April 21, June 17, July 17, and October 17, with average lengths of 56 d, 29 d, 92 d, and 188 d, respectively. (2) The start and end times, as well as the lengths of the climatic seasons, exhibit characteristics of minimum standard deviation in winter and maximum standard deviation in summer. (3) The start dates, end dates, and length of the climatic seasons, as well as the start and end times and length of the four seasons, showed the following patterns: Normal>slightly early (late) and early (late)>significantly early (late) and abnormally early (late). A indicator is more in line with the threshold of the classification indicators of early or late and length grade. (4) In Xizang, the onset of spring and summer trends was earlier, while autumn and winter had late trends. (5) The start date of spring, the end date of winter, and the length of summer across the 38 stations were primarily classified as normal, whereas the start dates of summer, autumn, and winter, along with the end dates of spring and autumn, were mainly categorized as early. Conversely, the lengths of spring and autumn were mainly classified as short, while winter was predominantly classified as long, and the end date of summer was primarily considered late. These findings provide valuable insights into climate resource management, ecological protection, and the overall impact on human production and life.

In this study, we analyzed meteorological observation data from the Kaidu-Kongque River basin in Xinjiang between 1961 and 2021 to investigate trends of vapor pressure deficit (VPD), as well as saturated (es) and actual (ea) water vapor pressure. We explored VPD changes across mountainous, oasis, and desert environments along with the factors influencing these changes. The results revealed the following: (1) Annual and seasonal VPD showed an upward trend from 1961 to 2021, characterized by distinct phases in which a sudden change occurred in 1997, shifting from a downward trend from 1961 to 1996 to an upward trend from 1997 to 2021, highlighting an intensification of atmospheric drought post 1997, particularly in spring. (2) VPD trends align with those of temperature and ea, showing the most significant increase in desert environments, followed by oasis and mountainous environments. (3) VPD changes are primarily affected by ea and es, positively correlated with temperature changes and negatively correlated with Relative Humidity changes. The rapid rise in temperature and decline in RH since 1997 are the primary causes of accelerated VPD, with the growth rate of ea being lower than that of es. These findings enhance our understanding of atmospheric drought and its response to climate change.

In this study, we aimed to accurately quantify evapotranspiration (ET) and its components while exploring the factors that control it, which will facilitate the practical evaluation, planning, and management of regional water resources. Utilizing continuous long-term observation data and field tests conducted from 2016 to 2020 in the Nanxiaohegou watershed—a typical small watershed for water and soil conservation on the Loess Plateau—this study simulated the dynamic changes of ET and its components in typical plantation land using the improved Shuttleworth-Wallace (S-W) model. Additionally, we analyzed the coupling relationships between plant transpiration (T), soil evaporation (E), and control factors using a structural equation model. The results revealed the following: (1) The modified S-W model was effective for evaluating ET and its components in Nanxiaohe Valley. The threshold value of soil surface resistance ( r_s^s) was 50-2500 s·m^-1, exhibiting an exponential relationship with the empirical function of soil surface water content (θ); moreover, higher sand content in the soil particles correlated with a steeper linear slope. (2) ET ranged from 276.76 mm to 402.86 mm in typical plantation land, with annual averages of T and E accounting for 51.6% and 48.4% of ET, respectively. While monthly ET, T, and E patterns were not pronounced, daily fluctuations were significant. The fluctuation trends of T and E largely reflected annual precipitation patterns but lagged behind rainfall. (3) Structural equation modeling analysis revealed that net radiation (R_n), temperature (T_a), and θ exerted the most significant effects on ET, with R_n having the largest impact on T (total impact of 0.614) and T_a having the most significant impact on E (total impact of 0.426). T was positively correlated with E, with a contribution coefficient of 0.503. Evaluating ET and its components using an improved S-W model establishes a foundation for a deeper understanding of ecological and hydrological processes in arid and semiarid regions.

Studying the degree and mechanism of landscape pattern’s influence on inland river water quality is of great significance for the water environment protection of inland river basins in arid areas. This study was based on the Liyuan River in Linze County. We studied landscape pattern data and measured water quality, using redundancy and correlation analyses to investigate the relationship between landscape patterns and water quality in different buffer zones. The water bodies in the study area generally met the Class II water quality standard, except for the average value of the chemical oxygen demand (COD_Cr) concentration, which fell into Class III. Additionally, the average dissolved oxygen (DO), total phosphorus (TP), permanganate index (COD_Mn), and ammonia nitrogen (NH₃-N) concentration values met the Class II water quality standard. The buffer zone’s landscape composition was dominated by arable land, and construction land was the second largest type. Analyzing the landscape index revealed that the strength of human activities was not evenly distributed in the buffer zone, and the degree of human interference was the greatest in the 100 m buffer zone. The human interference degree in the 100 m buffer zone was the greatest. The proportion of cultivated land was significantly and positively correlated with DO, TP, electrical conductivity (EC), dissolved solids (TDS), and salinity, while constructed land was significantly and positively correlated with TP and NH₃-N. The largest patch index (LPI) and contagion index (CONTAG) were positively correlated with the water quality indicators, whereas patch density (PD), edge density (ED), landscape shape index (LSI), and Shannon’s diversity index (SHDI) were negatively correlated. Redundancy analysis indicated that the explanatory rate of the changes in the water quality indicators by the composition of the landscape and landscape indices was the highest in the 300 m buffer zone. The analysis indicated that the explanatory rate of landscape composition and index on water quality index changes were the highest in the 300 m buffer zone, and the 300 m buffer zone was determined to be the optimal buffer scale for landscape pattern’s influence on the water quality index. Therefore, optimizing the landscape structure within the 300 m buffer zone to enhance the retention and adsorption capacity of pollutants can improve the water quality of the Liyuan River.

The lower reaches of the Shiyang River are the most serious resource-based water shortage areas, and water resources have a significant restraining effect on local social and economic development. Based on the runoff sequence data of the Caiqi hydrological station in Shiyanghe from 1956 to 2020, the sliding t-method, cumulative anomaly method, and M-K mutation test method were used to analyze the trend and abrupt year of runoff at the Caiqi hydrological station. The periodic change of runoff was analyzed using the Morlet wavelet method, and the factors influencing runoff change were analyzed by the double cumulative curve and correlation analysis methods. The results indicated that from 1956 to 2020, the annual runoff of the Caiqi hydrological station decreased and then increased; the runoff in spring, summer, and autumn decreased first and then increased, while winter displayed a decreasing trend. The runoff of the Caiqi hydrological station was studied for 46 years as the main period, which existed during the whole study period, and the fluctuation of abundance and drought changed significantly. The runoff of the Caiqi hydrological station occurred in two apparent mutations in 1972 and 2010, and it decreased significantly after the first mutation and increased considerably after the second mutation. Under the background of regional climate change, human activities, such as land use change, cross-basin water diversion, adjustment of industrial and planting structures, and water conservation in irrigation areas, are the principal reasons for the runoff change at the Caiqi hydrological station. The results can provide a scientific basis for the river basin management department to formulate a rational water resource allocation and transfer plan.

In this study, 63 samples comprising atmospheric precipitation, river water, groundwater, lake surface brine, and intercrystaline bittern were collected from the Nalenggele River. These samples were analyzed to assess the distribution characteristics and influencing factors of hydrogen and oxygen isotope, as well as deuterium surplus. The key findings are as follows: (1) The δD and δ¹⁸O values of atmospheric precipitation in the study area are higher than the average values across China. Due to the combined effect of evaporation and water vapor recirculation, the slope of the meteoric water line in the study area is lower than the global meteoric water line but higher than that of other drainage basins in the northwest arid zone. The East Asian monsoon, which transports water vapor over long distances, is the primary factor contributing to the low deuterium surplus in the atmospheric precipitation of the study area in August. (2) The river water line slope in the study area is smaller than that of the global meteoric water line. The deuterium surplus in river water is negatively correlated with δ¹⁸O and TDS (Total dissolved solids), which is attributed to isotopic fractionation caused by evaporation. The river is primarily recharged by atmospheric precipitation from southern mountainous areas. Variations in isotopic elevation effects result in differences in δD and δ¹⁸O values across different sections of the Nalenggele River. (3) Groundwater-surface water interactions, along with the groundwater recharge from multiple sources in the southern mountainous areas, cause the slope and intercept of the groundwater lines to be larger than those of both the global and local meteoric water lines. (4) The hydrogen and oxygen isotopes of surface brine and intercrystaline brine show an “oxygen drift” phenomenon, with deuterium surplus values falling below zero. This is attributed to excessive fractionation induced by evaporation. The deuterium surplus value in intercrystaline is lower than that of surface brine, likely due to the dissolution and filtration of salt minerals.

Soil quality is essential for vegetation cover and ecological recovery in Gobi zones. In this study, we analyzed 56 typical soil samples from the Hami Gobi to evaluate soil texture, salinity, and nutrient characteristics using eight indices, including soil moisture content, soil bulk density, pH, total salt content, organic matter, total nitrogen, total phosphorus, and total potassium. Based on these indices, we constructed a soil quality index (SQI) for a comprehensive soil quality assessment. The results revealed that soil quality in the Hami Gobi region was generally low, characterized by high gravel cover, low moisture content, severe salinization, and nutrient deficiency. The average soil quality in the Yiwu and Barkol regions was slightly higher than in the Yizhou zone, with better soil quality observed in areas where Gobi transitions into other land types. Overall, the SQI ranged from 0.4 to 0.5 across the Hami Gobi region and its subregions, showing a decreasing trend from north to south. This study highlights the urgent need for enhanced environmental protection and sustainable development strategies to copy with the impact of increasing human activities on the ecosystem.

Caragana microphylla, a shrub species commonly used to promote vegetation recovery in grasslands affected by desertification, plays a significant role in the ecological restoration and sustainable development of sandy lands. Understanding its impact on understory vegetation and soil physicochemical characteristics during different stages of desertified grassland recovery is crucial. This study focuses on C. microphylla shrublands in three typical stages of desertified grassland vegetation recovery in the Hulun Buir sandy land: semi-fixed, fixed, and sandy grasslands. This study used ANOVA, Pearson’s correlation analysis, and redundancy analysis methods to explore the changes in understory plant communities and soil physicochemical characteristics in C. microphylla shrublands during different stages of desertified grassland vegetation recovery and their interrelationships. The results indicate that, as the degree of vegetation recovery in desertified grasslands increases, the species richness of the understory vegetation, Shannon-Wiener index, community height, and biomass also increase. The community height and biomass within the shrublands are higher than outside, with species richness within the shrublands being higher than outside during the semi-fixed and fixed sandland stages. In the 0-10 cm and 10-20 cm soil layers, SWC displays an increasing trend, peaking in the sandy grassland stage (1.2%), and is higher within the shrublands than outside. The SWC at 10-20 cm is higher at 0-10 cm. In both layers, clay and silt content gradually increases with the degree of vegetation recovery in the sandy land and is higher within the shrublands than outside, while the opposite is true for sand content. In both soil layers, SOC gradually increases with the degree of vegetation recovery, peaking in the sandy grassland stage (4.12 g·kg^-1) and is higher within the shrublands than outside. TN increases from the semi-fixed to the fixed sand land stage, with higher levels within the shrublands than outside at all stages. Soil pH within the shrublands decreases as the degree of vegetation recovery increases. No significant change in TP is observed. Additionally, soil physicochemical characteristics account for 59.6% and 46.9% of the vegetation changes in both soil layers within and outside the shrublands, respectively, with the main influencing factors being soil particle size, TN, SWC, and SOC. This study demonstrates that during vegetation recovery in desertified grasslands, C. microphylla shrublands promote vegetation growth and development by improving the soil physicochemical characteristics under the shrublands, including soil particle size, SWC, SOC, and TN.

Vegetation-based sand fixation is a key measure to control wind and sand disasters in the arid and semi-arid regions of northern China. Reaumuria soongorica, a semi-shrub widely distributed in desert areas, holds a significant application value in this context. This study used Fluent software to perform numerical simulations of the airflow fields around R. soongorica during various growth seasons, analyzing wind speed characteristics and sand deposition patterns. The research yielded the following conclusions: (1) At an initial wind speed of 10 m·s^-1, vortices form in front of and behind the plant, with their height and intensity varying with the distance from the plant, generally below 0.25 m. (2) The numerical simulation results indicate that changes in horizontal airflow speed often exhibit N- and W-shaped curves, while vertical airflow speed changes follow a V-shaped curve. (3) At lower wind speeds, the wind-blocking effect of R. Soongorica in the non-growing season is better than that in the growing season, with a protection distance of 4 m behind the plant; when the wind speed is greater than 6 m·s^-1, the wind speed reduction behind double rows of R. Soongorica growing season can be greater than 94.45%. (4) R. soongorica has excellent sand-blocking effects. At an initial wind speed of 6 m·s^-1, most sand particles accumulate at the plant base, in front and behind it. When the wind speed increases to 10 m·s^-1, R. soongorica during the vigorous season effectively blocks sand, with sand particles primarily depositing between 1.5-3 H behind the plant, with a height lower than 0.1 m. At an initial wind speed of 15 m·s^-1, sand deposition behind the vigorous season R. soongorica is mainly distributed between height 2-3.5 H. In contrast, for the withering season, sand accumulation ranges from height 1-10 H behind the plant. Regardless of the growth season, R. soongorica effectively reduces airflow speed within the wind field and promotes the settling of sand particles carried by the airflow, playing a crucial role in vegetation-based sand control projects.

In this study, the typical desert plants, Haloxylon ammodendron and Nitraria tangutorum in the sand-blocking and sand-fixing belt of the Hexi Corridor were studied, Through the combination of field survey, sample collection, indoor analysis and statistics, To explore the adaptation strategies of desert plants to arid environment. Select Minqin oasis the sand-blocking and sand-fixing belt and Gaotai oasis the sand-blocking and sand-fixing belt. The natural vegetation sealing protection zone from the upper direction and the downwind tree irrigation shelterbelt, and the sand resistance and sand fixation belt with consistent spatial structure characteristics, Set three 10 m×10 m H. ammodendron quadrats and three 10 m×10 m N. tangutorum quadrats. The spatial distribution characteristics of the main leaf parameters and the environmental factors were analyzed. It aims to provide data support for the evaluation of leaf functional traits in two desert plants. Results showed that, Typical desert plants can adapt leaf functional traits to soil and climatic conditions under specific habitat conditions: (1) Leaf dry material content (LDMC) and specific leaf area (SLA) were significantly different (P<0.05), Leaf organic carbon (LOC), leaf nitrogen (LN) and leaf phosphorus (LP) showed significant differences in the two habitats (P<0.001). (2) Principal component analysis as indicated, The top three index factors affecting the leaf traits of Minqin plants are LN, C:N and C:P; The top three index factors affecting the leaf traits of Gaotai plants are LP, C:N and N:P. (3) Redundancy analysis showed that, soil water content (SWC), soil organic carbon (SOC), and air dryness (AD) are the main limiting environmental factors affecting the functional traits of the two desert plants.

The Three River Source Region is a crucial source and catchment area, and its ecological security is vital. Investigating the spatial and temporal variations of landscape ecological risks and their drivers in this region is essential for promoting ecological security and the sustainable development of water resources in Southeast Asia. In this study, we focused on the Three River Source Region and constructed an evaluation model using land use data from the fifth phase to analyze the spatial and temporal characteristics and trends of landscape ecological risk. We employed a parametric optimal geodetector to compare and analyze the driving factors behind the spatial variation of landscape ecological risk at both global and local scales. The results revealed the following: (1) From 2000 to 2020, the study area exhibited a significant positive correlation with landscape ecological risk, particularly within the medium-and medium-low-risk areas, with areas classified as high-risk. (2) From 2000 to 2020, the landscape ecological risk in the study area improved, with high-and low-risk areas transitioning into predominantly medium-low, medium-and medium-high-risk areas. The Lancang River source exhibited a slightly higher risk level than the Yangtze and Yellow River sources. (3) The area and fragmentation degree of landscape types were identified as key determinants of landscape ecological risk variations in the region, with spatial differentiation resulting from the combined influence of multiple driving factors. Among these, Normalized Difference Vegetation Index (NDVI), elevation, and slope were identified as the primary driving factors, with their impacts varying significantly across terrain. To ensure ecological integrity and sustain ecological functions, the government should prioritize the protection and monitoring of snow-capped glaciers, implement measures to curb grassland desertification, and prevent the resurgence of ecological risks.

In this study, we aimed to examine the vegetation damage and reclamation status of mining pits and waste dumps in open-pit mines and provide an ecological basis for diagnosing vegetation damage in mining areas and assessing natural and artificial vegetation restoration. Using Sentinel-2 data, we calculated non-red edge vegetation indices (Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index) and red edge vegetation indices (Red Edge Normalized Difference Vegetation Index (RENDVI), Modified Red Edge Simple Ratio, Chlorophyll Index red edge, and Transformed Chlorophyll Absorption in Reflectance Index) as indicators for evaluating ecological restoration. We employed regression analysis, trend analysis, and correlation analysis to assess the impacts of mining activities and climate change on the ecological environment of five open-pit mines (Wulanhada, Jingwei, Wujiata, Langwoqu, and Hongshengyuan) from 2018 to 2021. This approach enabled us to identify the spatial and temporal patterns of change in vegetation across mining pits, waste dumps, and buffer zones. The results revealed the following: (1) The Hongshengyuan open-pit mine had the most severe vegetation damage (k=-0.2996) but had the most effective manual restoration on its waste dump (k=0.1364). (2) A comparison of the 5 km buffer zones around the five open-pit mines indicated that the pixel-by-pixel RENDVI trends predominantly showed degradation, with over 50% of the areas exhibiting signs of decline. (3) In the desertified grassland area, temperature had a more significant impact on vegetation NDVI than temperature. Open-pit mining exacerbates the ecological degradation of desertified grassland vegetation, while artificial restoration of waste dumps is highly effective in improving the ecological conditions of regional vegetation

This study aimed to explore the impact of land use change on the space of arable land and provide a reference to optimize the land use pattern and strengthen arable land protection. Based on five periods of land use data from 2000 to 2020, the framework of land use change intensity analysis, PLUS model, and spatial autocorrelation analysis method were introduced to explore the impacts of future land use changes on the space of arable land in Changji City. The study found that land use types in Changji City were dominated by grassland, arable land, and unused land; arable and construction lands displayed a changing trend of continuous growth, and the conversion of forest and grassland to arable and construction lands and of arable land to construction land was the main feature of land use change in Changji City. Regarding conversion intensity, apparent differences were observed in the conversion intensity of each type of arable land, and the intensity of transferring in and out of the conversion intensity between arable and construction land was higher than the average. Regarding the conversion intensity, evident differences were observed in the conversion intensity between each category and arable land, and the conversion intensity between arable and construction lands was higher than the average conversion intensity; the conversion of its land use will have a more significant impact on the regional land use cover structure. The simulation results of the PLUS model indicated that the area of arable land in the natural development, arable land protection, and sustainable development scenarios decreased by 36.21 km², increased by 28.19 km², and decreased by 25.66 km², respectively; the sustainable development scenario was more able to consider the dual demands of economic development and arable land protection. Changes in the pattern of arable land have prominent spatial agglomeration characteristics; they are dominated by high-high agglomeration, mainly distributed in Yushugou Town, Erliugong Town, Daxiqiu Town in the central part of the city and Sanguo Town in the southwestern part of the major city. The spatial distributions of high-high agglomeration are basically similar in different scenarios, but differences exist in the number of types. Finally, relevant suggestions were made to coordinate the protection of arable land with economic development and optimize the spatial layout of land use. The results can provide a reference for balancing the relationship between financial development and arable land protection in oasis cities in arid zones.

Finding ways to scientifically identify the priority areas of ecological protection and restoration and implement adapted strategies in different regions is a challenge faced by current ecological protection and restoration work. This study was based on the Yellow River Basin in Inner Mongolia, and the ecological security evaluation was conducted using spatial principal component analysis (SPCA) and morphological spatial pattern analysis (MSPA). The ecological protection and restoration areas were identified by combining the matching degree of landscape elements. The results indicated that (1) the study area was dominated by areas with moderate ecological security, accounting for 40.58% of the total area. (2) 14 ecological sources (accounting for 20.92% of the study area), 42 ecological corridors, and 78 ecological nodes were identified by MSPA and minimum cumulative resistance model (MCR). (3) among the 62 sub-watersheds in the study area, 8 had a high matching level of landscape elements, accounting for 23.34% of the total area, and 38 watersheds had a low matching level, accounting for 43.20% of the total area. and (4) the priority areas of the third- and first-level ecological restoration accounted for 35.53% (the largest) and 18.63%, respectively. Based on the identification results of priority areas of ecological protection and restoration, the restoration strategies of different regions were discussed. Our results can provide a basis for ecological protection and high-quality development of the Yellow River Basin in Inner Mongolia.

In this study, we aimed to investigate the chemical characteristics of groundwater in farmland within Hetao Irrigation District, focusing on deep water conservation and the relationship between water and salt migration among various types of farmland. Typical irrigated farmland in Hetao Irrigation District was selected as the study area, and an analysis was conducted on shallow groundwater ions and changes in groundwater levels using classical statistics, principal component analysis, and the principle of solute dynamics. The main factors affecting groundwater quality were identified, and the changes in soil ions before and after crop cultivation were examined. Furthermore, the contribution of groundwater to salt accumulation across different types of farmland was quantified, and a water-salt equilibrium model was developed using the locational flux method. The results revealed the following: (1) Shallow groundwater cations were dominated by Na⁺+K⁺, constituting 53.22% of total cations, while anions were dominated by SO₄^2-, making up 41.04% of total anions; thus, the principal chemical type of groundwater was classified as HCO₃·SO₄-Na, with key factors affecting groundwater quality identified as Total Dissolved Solids (TDS), Na⁺+K⁺, HCO₃^-, and SO₄^2- through principal component analysis. (2) Salt accumulation before and after crop cultivation was mainly comprised of NaCl and Na₂SO₄. (3) Evapotranspiration (ET) varied across different types of fields, with measurements of 422.6 mm for wasteland, 475.6 mm for sunflower fields, and 625.8 mm for maize fields. (4) Maize, sunflower, and wasteland soils exhibited salt accumulation, with horizontal infiltration contributing 1924 kg·hm^-2 of salt to wasteland, accounting for 22.00% of total salt accumulation. (5) There is a salt transition zone between wasteland and arable land, indicating the planting of salt-tolerant cash crops, such as sunflower, near wasteland to mitigate crop yield reductions due to high salinity levels. This study offers valuable insights into the efficient use of local water resources, soil salinity management, and sustainable agricultural development.

Climate change has increased the frequency of long-term droughts and heavy rainfall events, impacting ecosystems’ carbon cycle. Therefore, understanding how soil enzyme activity in different dry/wet conditions affects organic carbon mineralization can help deepen our understanding of the carbon cycle mechanism and advance the goal of global carbon neutrality. This study was based on the unique terraces built to control erosion in the Loess Plateau, and three treatments of flooding stress, drought stress, and wet/dry cycles were designed to monitor soil enzyme activity and organic carbon mineralization. The results indicate that the wet/dry cycle has a transient stimulating effect on organic carbon mineralization, and the cumulative mineralized organic carbon occurs between the drought and flooding stress. At the same time, the wet/dry cycle will increase the activity of carbon and nitrogen cycle-related enzymes; however, the enzyme activity will gradually decrease and stabilize as the number of cycles increases. The enzyme activity in all three water treatment conditions was limited by carbon and phosphorus, and the carbon limitation was more substantial with increasing wet/dry cycles. After the fourth alternating wet/dry cycle, the phosphorus limitation exceeded the flooding and drought stress treatments. When the soil was under drought stress, flooding stress, or wet/dry cycles, the enzyme activity factors that limit organic carbon mineralization were different. The direct effect of the phosphatase factor under drought stress was 99%, the direct impact of EAA_C/N (carbon cycle- /nitrogen cycle-related enzyme) and xyloglucosidase factor under flooding stress was 87%, and the direct effect of the interaction between factors under drought and flooding stress was only 1% and 13%. Under wet/dry cycle conditions, the direct impact of phosphatase and N-acetyl-beta-glucosaminidase factor was 75%, the direct effect of interaction between factors was 25%, and the wet/dry cycle significantly increased the interaction between factors. This study provides theoretical support for clarifying the role of Loess Terrace.