Alpine Desert Research Articles

Effects of Enclosure on Plant and Soil Nutrients in Different Types of Alpine Grassland

Enclosure is one of the most widely used management tools for degraded alpine grassland on the northern Tibetan Plateau, but the responses of different types of grassland to enclosure may vary, and research on these responses can provide a scientific basis for improving ecological conservation. This study took one site for each of three grassland types (alpine meadow, alpine steppe and alpine desert) on the northern Tibetan Plateau as examples, and explored the effects of enclosure on plant and soil nutrients by comparing differences in plant community biomass, leaf-soil nutrient content and their stoichiometry between samples from inside and outside the fence. The results showed that enclosure can significantly increase all aboveground biomass in these three grassland types, but it only increased the 10–20 cm underground biomass in the alpine desert. Enclosure also significantly increased the leaf nutrient content of the dominant plants and contents of total nitrogen (N), total potassium (K), and organic carbon (C) in 10–20 cm soil in alpine desert, thus changing the stoichiometry between C, N and P (phosphorus). However, enclosure significantly increased only the N content of dominant plant leaves in alpine steppe, while other nutrients and stoichiometries of both plant leaves and soil did not show significant differences in alpine meadow and alpine steppe. These results suggested that enclosure has differential effects on these three types of alpine grasslands on the northern Tibetan Plateau, and the alpine desert showed the most active ecological conservation in the responses of its soil and plant nutrients.

Airflow Field Around Hippophae rhamnoides in Alpine Semi-Arid Desert

The research on wind regimes and the wind protection mechanism of sand-fixing plants has mainly relied on wind tunnel experiments; few observations have been made in the field. At the same time, airflow around individual standing vegetation elements and communities is relatively lacking in alpine semi-arid deserts. Therefore, this paper selected 10-year-old Hippophae rhamnoides (sea buckthorn) on sandy land on the eastern shore of Qinghai Lake as the study object. Based on spatial and temporal changes of wind regime in the afforestation forest, a structural simulation of airflow near the plant and at different layers above the ground, and the annual changes in wind protection, we studied the wind protection mechanisms of H. rhamnoides as single elements or communities. The results were as follows: the effective protection length of the sublayer of H. rhamnoides was 1.0 to 1.8 m. The higher the layer, the smaller the decrease in wind velocity behind elements, and the smaller the effective protection length. Wind velocity downwind of H. rhamnoides increased, with height increasing where the airflow decreases rate (R) decreased in the sublayer, and increasing in the middle layer as plant height increased. Meanwhile, the airflow decreases rate (R) was negative in the upper layer because it decreased as the plant height increased. The airflow movement between elements had various directions because the upper layer was prone to fluctuations due to the swinging of the crown and branches, and turbulence was seen at the sublayers owing to the mechanical resistance of the elements. When the wind speed at the standard point was 8.5 m/s and the wind direction was east (E), the increase of airflow velocity at the side and center in the upper layer was more significant, and there was a strong wind zone in the azimuth of NW‒N‒NE‒E‒SE, while the S‒SW‒W azimuth zone was weaker. The sand-fixing shrub H. rhamnoides had a significant windproof function, and the 1.5 m square interval density of H. rhamnoides was suitable for alpine desert control projects.

Variable soil pH can drive changes in slope aspect preference of plants in alpine desert of the Central Great Caucasus (Kazbegi district, Georgia)

Alpine deserts are noteworthy habitats in temperate high mountain systems such as the Caucasus. Botanically this biome is well studied, yet little is known about its vegetation patterns in quantitative terms, whilst the role of soil pH in species distributions is particularly unexplored. Here we describe and quantitatively analyse vegetation patterns and soil pH in an alpine desert along elevation range (3000–4000 m a.s.l.) on two contrasting slope aspects (N versus S) of Mt. Kazbegi, the Central Greater Caucasus, Georgia. We sampled vegetation with standardized stratified-random design and collected soil samples for measuring pH; the collected data were analyzed using multivariate ordination methods. Overall, 63 species were recorded and, as expected, strong dependence of species distribution on elevation and between slopes was observed. However, we also found that soil pH increased monotonically and more steeply on N than on S slope, and many relatively abundant species changed their preference to slope aspect from N to S in parallel with the increasing difference in soil pH between N and S slopes. Our results suggest that the observed shift in slope preference from N to S, at least in part, can be explained by the differences in soil pH gradient between N and S slopes.

Elevational differences in the net primary productivity response to climate constraints in a dryland mountain ecosystem of northwestern China

AbstractDryland mountain ecosystems regulate global terrestrial carbon cycling and show high sensitivity to climate variability. The Qilian Mountains (QLMs) typify dryland mountain ranges in northern temperate belts and offer fundamental ecosystem services including forage production and water conservation. However, dominant controls on the interannual trend and variability of net primary productivity (NPP) in this region are unknown. Thus, we examined magnitude and direction of the NPP trend and quantified NPP sensitivity to temperature and precipitation under different biomes and altitudes using ground and remote sensing data. Our results showed that 12% of the QLMs had a reversed NPP trend from increasing to decreasing from 2000 to 2016, particularly in the western and southern parts, where NPP reductions were related to precipitation deficits. About 34% of the QLMs showed accelerated or persistent increasing NPP trends, mainly from the mid‐altitude between 3,100 and 4,300 m. The growth rate of NPP was higher in deserts and grasslands than in forests and increased in deserts but decreased in forests and grasslands with increasing elevation. Precipitation showed a stronger effect on the interannual variability in NPP than temperature did. The temperature sensitivity of NPP was similar along elevation gradients in forest steppes but decreased with increasing elevation in alpine deserts. The precipitation sensitivity of NPP reached highest in shrubby meadows when compared with coniferous forests and alpine deserts. This research provides new insights into climate controls of the NPP over the QLMs and to present drought as a growing threat to shrubby meadows and alpine deserts.

Differences in species diversity, biomass, and soil properties of five types of alpine grasslands in the Northern Tibetan Plateau.

Approximately 94% of the land area of the Northern Tibetan Plateau is covered by grasslands, which comprise one of five key livestock producing regions in China. In contrast to most other regions worldwide, these alpine grasslands are much more sensitive to global climate change, thus they are under intense study. The differences in species diversity, plant biomass, and soil properties of five representative's alpine grassland types in the Northern Tibetan Plateau were investigated in this research. The results revealed that 11 community types were identified according to the importance of dominant species and constructive species. There were significant differences in the Margalef index (H), Simpson diversity index (D), Shannon-wiener diversity index (H'), and Pielou evenness index (J) indices between these five alpine grasslands. Further, the above-ground biomass (AGB), below-ground biomass (BGB), total biomass (TB), root:shoot (R/S) ratio, and coverage showed significant differences in 5 alpine grasslands. There were also considerable variations in the pH, total nitrogen concentration (TN), total phosphorus concentration (TP), soil organic carbon (SOC) and C-to-N ratio (C:N) among the five alpine grasslands. The highest value of biomass and soil characteristics was always in the alpine steppe (AS), or AM, while the lowest of that was in the alpine desert steppe (ADS), or alpine desert (AD). Moreover, there were significant differences in the soil particle size fractions between the five alpine grasslands. In the AM and AS, the dominant soil particle was clay, while in the alpine meadow-steppe (AMS), ADS, and AD it was fine and medium sand. Substantial correlations were found between the biomass and species diversity indices H, D or H' and soil TN, TP, or SOC. Moreover, silt had a significantly positive correlation with soil C:N, BGB, TB, and R/S, while medium sand and coarse sand was significant negatively correlated. With regard to these grassland types, it is proposed that the AM or AS may be an actively changing grassland types in the Northern Tibetan Plateau.

Nitrogen economy of alpine plants on the north Tibetan Plateau: Nitrogen conservation by resorption rather than open sources through biological symbiotic fixation.

Nitrogen (N) is one of the most important factors limiting plant productivity, and N fixation by legume species is an important source of N input into ecosystems. Meanwhile, N resorption from senescent plant tissues conserves nutrients taken up in the current season, which may alleviate ecosystem N limitation. N fixation was assessed by the 15N dilution technique in four types of alpine grasslands along the precipitation and soil nutrient gradients. The N resorption efficiency (NRE) was also measured in these alpine grasslands. The aboveground biomass in the alpine meadow was 4–6 times higher than in the alpine meadow steppe, alpine steppe, and alpine desert steppe. However, the proportion of legume species to community biomass in the alpine steppe and the alpine desert steppe was significantly higher than the proportion in the alpine meadow. N fixation by the legume plants in the alpine meadow was 0.236 g N/m2, which was significantly higher than N fixation in other alpine grasslands (0.041 to 0.089 g N/m2). The NRE in the alpine meadows was lower than in the other three alpine grasslands. Both the aboveground biomass and N fixation of the legume plants showed decreasing trends with the decline of precipitation and soil N gradients from east to west, while the NRE of alpine plants showed increasing trends along the gradients, which indicates that alpine plants enhance the NRE to adapt to the increasing droughts and nutrient‐poor environments. The opposite trends of N fixation and NRE along the precipitation and soil nutrient gradients indicate that alpine plants adapt to precipitation and soil nutrient limitation by promoting NRE (conservative nutrient use by alpine plants) rather than biological N fixation (open sources by legume plants) on the north Tibetan Plateau.

Evaluation of Heavy Metal Level in Soil of Typical Alpine Grassland Communities

Objective: Through the investigation, determination and analysis of heavy metals in the soil of typical alpine grassland community, five kinds of alpine grasslands with different degeneration degree of Maduo County in Alpine area, two kinds of alpine grassland with high Maqu County, high Alpine desert along the coast of Qinghai Lake, alpine thickets in the yellow South region, Alpine wetlands, The condition of soil heavy metals in alpine meadow and other communities is analyzed, which provides scientific guidance for the ecological protection measures of typical alpine grassland communities, and provides a basis for the sustainable utilization of Alpine grassland. Methods: The content of various kinds of heavy metals in soil samples was determined by ICP-MS, and the pollution status of heavy metals was analyzed by means of single factor pollution index method, Nemero comprehensive pollution index method and potential ecological risk index method by using Excel. Results: (1) The content of Cd in Maduo, Maqu, Qinghai Lake and Huangnan was 1.74, 0.97, 1.84 and 1.06 times times the soil environment background respectively, and the content of Hg in Maqu was 1.36 times times that of soil environmental background value. The variation coefficient of Hg and Pb in Maqu and the coefficient of variation of Cd in Qinghai Lake are more than 100%, which is in the degree of high variation, which is greatly influenced by man. (2) The highest total pollution index in the 4 sample places was in the area of MA diversity, at 1.33. The second is the Huangnan sample, with an exponential value of 0.86. The Nemero comprehensive pollution Index of the Maqu sample is 0.77. The index value of Qinghai Lake sample is the lowest, at 0.61. (3) The highest potential ecological hazard index is the most diverse, in 0-10, 10-20, 20-30cm three soil layers are 96.96, 103.58, 102.46, Maqu in 0-10, 10-20cm soil, the potential ecological hazard index is 65.70, 71.01, the potential ecological hazard index of Huangnan in three soil layer is 78.23, 73.42 and 72.84 respectively, which refers to the smallest value of Qinghai Lake sample, three, 51.07 and 51.72 in 51.48 soil layer respectively. Conclusion: The Nemero comprehensive pollution Index of Qinghai Lake sample is less than 0.7, at the level of cleanliness, the exponential value of Huangnan and Maqu two samples is between 0.7~1, at the level of cordon, and the exponential value of ma variety is between 1~2, at the level of mild pollution. The comprehensive potential ecological hazard index of 80~160 has the potential ecological risk of strength, and the exponential value of the other three samples is between 40~80, which has medium potential ecological risk. Generally, the pollution degree of heavy metals is small in the whole alpine grassland area.

Alpine Vegetation on the Paekdu-San (Changbaishan) Summit of the North-east China

We aim to provide a syntaxonomical scheme for the alpine tundra vegetation of volcano Mount Paekdu (Changbaishan) bordering China and North Korea. From the field investigations in 1991, 2004, and 2009 a total of 89 phytosociological releves were sampled by the Braun-Blanquet method. Obtained data sets were analyzed by tabular hand-sorting technique. Syntaxonomic position and nomenclature of units were determined by comparison with mainly Japanese relevant communities. Ten rankless units in four physiognomic vegetation types were classified: alpine desert vegetation (Papaver radicatum var. pseudoradicatum community, Minuartia arctica community, Polytrichastrum alpinum-Minuartia macrocarpa var. koreana community), alpine windswept dwarf vegetation (Chrysanthemum zawadskii var. alpinum-Festuca ovina var. koreano-alpina community, Scirpus maximowiczii community, Oxytropis anertii-Salix rotundifolia community, Carex longirostrata-Dryas octopetala var. asiatica community), snow-bed vegetation (Phyllodoce caerulea-Tofieldia coccinea community, Viola biflora-Calamagrostis langsdorfii community), and colluvial drainage channel vegetation (Carex atrata-Sanguisorba stipulata var. riishiriensis community). The variation of the vegetation resulted from primarily the rock and soil particle size and soil mobility, and slope inclination. Some of the plant communities were regarded as local and endemic types. Yet we firmly believe that further researches are requested by much richer materials and syntaxonomical comprehensive evaluation in between elsewhere in the Pan-East Sea (Sea of Japan).

High Below-Ground Productivity Allocation of Alpine Grasslands on the Northern Tibet.

The allocation of net primary production (NPP) between above- and belowground components is a key step of ecosystem material cycling and energy flows, which determines many critical parameters, e.g., the fraction of below ground NPP (BNPP) to NPP (fBNPP) and root turnover rates (RTR), in vegetation models. However, direct NPP estimation and partition are scarcely based on field measurements of biomass dynamics in the alpine grasslands on the Northern Tibetan Plateau (NTP). Consequently, these parameters are unverifiable and controversial. Here, we measured above- and belowground biomass dynamics (monthly from May to September each year from 2013 to 2015) to estimate NPP dynamics and allocations in four typical alpine grassland ecosystems, i.e., an alpine meadow, alpine meadow steppe, alpine steppe and alpine desert steppe. We found that NPP and its components, above and below ground NPP (ANPP and BNPP), increased significantly from west to east on the NTP, and ANPP was mainly affected by temperature while BNPP and NPP were mainly affected by precipitation. The bulk of BNPP was generally concentrated in the top 10 cm soil layers in all four alpine grasslands (76.1% ± 9.1%, mean ± SD). Our results showed that fBNPP was significantly different among these four alpine grasslands, with its means in alpine meadow (0.93), alpine desert steppe (0.92) being larger than that in the alpine meadow steppe (0.76) and alpine steppe (0.77). Both temperature and precipitation had significant and positive effects on the fBNPP, while their interaction effects were significantly opposite. RTR decreased with increasing precipitation, but increased with increasing temperature across this ecoregion. Our study illustrated that alpine grasslands on the NTP, especially in the alpine meadow and alpine desert steppe, partitioned an unexpected and greater NPP to below ground than most historical reports across global grasslands, indicating a more critical role of the root carbon pool in carbon cycling in alpine grasslands on the NTP.

Thermal properties of active layer in permafrost regions with different vegetation types on the Qinghai-Tibetan Plateau

Active layer plays a key role in regulating the dynamics of hydrothermal processes and ecosystems that are sensitive to the changing climate in permafrost regions. However, little is known about the hydrothermal dynamics during freeze-thaw processes in permafrost regions with different vegetation types on the Qinghai-Tibetan Plateau (QTP). In the present study, the freezing and thawing processes at four sites (QT01, 03, 04, and 05) with different vegetation types on the QTP was analyzed. The results indicated that the impact on the soil water and heat during the summer thawing process was markedly greater than that during the autumn freezing process. Furthermore, the thermal-orbit regression slopes for all sites exhibited a homologous variation as the depth increased, with the slowest attenuation for the meadow sites (QT01 and QT03) and a slightly faster attenuation for the desert steppe site (QT05). The air and ground surface temperatures were similar in winter, but the ground surface temperature was significantly higher than the air temperature in summer in the radiation-rich environment at all sites on the QTP. The results also indicated that the n-factors were between 0.36 and 0.55 during the thawing season, and the annual mean temperature near the permafrost table was between − 1.26 and − 1.84 °C. In the alpine desert steppe region, the thermal conditions exhibited to show a warming trend, with a current permafrost table temperature of − 0.22 °C. The annual changing amplitude of the ground temperature at the permafrost table was different for different vegetation types.

Soil microbial communities in alpine grasslands on the Tibet Plateau and their influencing factors

As an indicator and regulator of climate and environmental change, the Tibet Plateau is an important barrier for ecological security. However, despite the importance of soil microbial communities in almost all soil biochemical processes and ecosystem functions, the biogeography of soil microbial communities on the Tibet Plateau is poorly understood, especially at large scales over different ecosystem types. In this study, we collected samples from 64 sampling sites representing different grassland ecosystem types and spanning 2121 km across on the Tibet Plateau. We then used next generation high-throughput sequencing to investigate the soil prokaryote community (i.e. bacteria and archaea) diversity and spatial patterns and to explore their relationship with biotic (e.g. plant functional group diversity and biomass) and abiotic (e.g. aridity index, soil carbon and nitrogen levels) factors. Among the four alpine grassland types (i.e. alpine meadow, alpine steppe, alpine shrub and alpine desert) sampled in this study, alpine meadow had the highest soil microbial biomass and alpine desert had the lowest soil microbial richness and Shannon diversity. The soil microbial diversity in the alpine grassland correlated with plant diversity and climate factors. Soil microbial diversity negatively correlated with the annual average air temperature, but was not correlated with the annual average precipitation, indicating that temperature, rather than precipitation, may be more important in controlling the soil microbial diversity in alpine grassland ecosystems at cold temperatures. Higher air temperature likely led to an intensified aridity under limited precipitation, and thus decreased microbial diversity. As a result, the aridity index combined with temperature and precipitation explained more of the variance in the soil microbial diversity than air temperature or precipitation did individually. Moreover, after separating plant species into four functional groups (grass, forb, legume and sedge), microbial diversity positively correlated with plant functional group diversity, explaining more of the variance in microbial diversity than plant species diversity did. Results of structural equation modeling revealed that the aridity index and annual air temperature affected soil microbial diversity, directly or indirectly, through influencing plant functional group diversity and aboveground biomass; while aboveground biomass changed the soil carbon to nitrogen ratio in the upper soil layers and thus impacted soil microbial diversity. However, in contrast to microbial diversity, soil microbial biomass carbon was not correlated with plant functional group diversity, plant species diversity, or the climate factors annual average air temperature, annual precipitation and aridity index, but were linked to soil nutrient status (e.g. soil dissolved organic carbon, ammonia, available phosphorus, and carbon to nitrogen ratio) and plant biomass of sedges and forbs, demonstrating that microbial biomass and diversity were likely controlled by different factors. In summary, this study investigated the spatial patterns of soil microbial communities across different alpine grassland ecosystem types on the Tibet Plateau and enhanced our understanding of biotic and abiotic factors controlling microbial biomass and diversity, which will be important in predicting microbial changes on the Tibet Plateau under future climate change. Under future warming and wetting scenarios on the Tibet Plateau, it is possible that the aridity index would decrease, leading to increased soil microbial diversity. Results of this study also suggest a focus on the aridity index and plant functional group diversity in future microbial biogeography studies in order to further determine their roles in controlling or mediating soil microbial biomass and diversity.

Vegetation dynamics dominate the energy flux partitioning across typical ecosystem in the Heihe River Basin: Observation with numerical modeling

Understanding the controls on seasonal variation of energy partitioning and separation between canopy and soil surface are important for qualifying the vegetation feedback to climate system. Using observed day-to-day variations of energy balance components including net radiation, sensible heat flux, latent heat flux ground heat flux, and meteorological variables combined with an energy-balanced two-source model, energy partitioning were investigated at six sites in Heihe River Basin from 2014 to 2016. Bowen ratio (β) among the six sites exhibited significant seasonal variations while showed smaller inter-annual fluctuations. All ecosystems exhibit a “U-shaped” pattern, characterized by smaller value of β in growing season, with a minimum value in July, and fluctuating day to day. During the growing season, average Bowen ratio was the highest for the alpine swamp meadow (0.60 ± 0.30), followed by the desert riparian forest Populus euphratica (0.47 ± 0.72), the alpine desert(0.46 ± 0.10), the Tamarix ramosissima desert riparian shrub ecosystem (0.33 ± 0.57), alpine meadow ecosystem (0.32 ± 0.17), and cropland ecosystem (0.27 ± 0.46). The agreement of Bowen ratio between simulated and observed values demonstrated that the two-source model is a promising tool for energy partitioning and separation between canopy and soil surface. The importance of biophysical control explains the convergence of seasonal and annual patterns of Bowen ratio for all ecosystems, and the changes in Bowen ratio showed divergence among varied ecosystems because of different physiological responses to energy flow pathways between canopy and soil surface.

Pollen in surface soil at the southern slope of western Tianshan, China.

We analyzed 52 pollen samples of surface soils from the southern slope of western Tian-shan, China, to understand the relationship between the surface pollen and modern vegetation, and the significance of the Artemisia/Chenopodiaceae (A/C). The results showed that there were five vegetation zones from the mountain top to the foot, i.e., alpine desert zone, alpine meadow zone, meadow and steppe zone, mountain desert zone, and typical desert zone. The typical taxa were Artemisia, Chenopodiaceae, Poaceae and Ephedra. The surface pollen assemblages greatly differed across different vegetation zones in this area. Surface pollen in the southern slope of the western Tianshan Mountains was affected by the northern slope, with the impacts increasing with the increases of altitude. The A/C increased with altitude, peaked in the alpine meadow zone, and then decreased, which could effectively indicate the vertical moisture change. Given the great fluctuation of A/C value, when using this ratio to reconstruct climate and environment, attention should be paid to the fact that high values caused by human activities and other factors may lead to misjudgments.

Evaluation of reanalysis air temperature products in permafrost regions on the Qinghai-Tibetan Plateau

Surface air temperature is important for climate change, hydrological, and ecosystems undergoing climate warming in the permafrost regions on the Qinghai-Tibetan Plateau (QTP). We monitored daily air temperatures at five sites (alpine desert, alpine desert steppe, alpine steppe, alpine meadow, and alpine wet meadow) from 2011 to 2015 in permafrost regions on the QTP. Using this data, we evaluated the performance of five different reanalysis air temperature products (CFSR, ERA-Interim, GLDAS-NOAH, MERRA, JRA-55, and CMFD). These results demonstrated that the ERA-Interim air temperature products exhibited the best performance at the majority of sites. However, the original ERA-Interim air temperature products were found to overestimate air temperature at most sites. The calibration models were established by the observed daily air temperatures measured from 2013 to 2015 for the ERA-Interim air temperature products, which validated with observational data from 2011 to 2012. Following calibration, ERA-Interim products were found to be closer to the observations made across all sites. In addition, this paper demonstrated a warming trend present in month, seasonal, and annual mean air temperature from the calibration results collected from 1980 to 2015. These results demonstrated that the largest warming trend was observed in February, while the smallest warming trend was observed in March. We demonstrated that all air temperatures warmed fastest in the summer and winter, more slowly in autumn, and the slowest in spring at the majority of sites tested. In addition, we found that the average annual air temperature warming trends were 0.0398, 0.0394, 0.0288, 0.0259, and 0.0254 °C/year in the alpine desert steppe, alpine desert, alpine steppe, alpine meadow, and alpine wet meadow in the permafrost regions on the QTP, respectively. These findings generate a useful tool for the recognizing of the variation in permafrost under climate change in permafrost regions on the QTP.

Plant and soil’s δ15N are regulated by climate, soil nutrients, and species diversity in alpine grasslands on the northern Tibetan Plateau

Nitrogen (N) cycling is a critical pathway by which producer, consumer, and decomposer interact with each other and with environmental circumstances simultaneously. The natural abundance composition of 15N/14N in plants and soils (termed as δ15Nplant and δ15Nsoil), as well as the difference between them (δ15Nsoil-to-plant = δ15Nplant −δ15Nsoil), is a useful tool for better understanding ecosystem N cycling. However, the drivers and mechanisms of ecosystem N cycling in alpine grasslands on the Tibetan Plateau are mostly unknown, especially across different grassland types at a regional scale. To fill this knowledge gap, we measured δ15Nplant (200 samples of top-dominant species) and δ15Nsoil (85 samples of top-layer soils, 0–20 cm) at nine sites that represent zonal communities of alpine deserts, steppes, and meadows in North Tibet, and calculated the corresponding δ15Nsoil-to-plant. Our results showed that δ15Nplant, δ15Nsoil, and δ15Nsoil-to-plant were significantly different among the three zonal grassland types (analysis of differences with non-parametric Kruskal Test, P < 0.05), with the lowest values in meadows and the highest values in deserts. Regression analyses showed that the δ15Nplant, δ15Nsoil, and δ15Nsoil-to-plant decreased with the increases of growing season precipitation (GSP) and habitat aridity index (Aridity), soil organic carbon (SOC) and soil total nitrogen (STN), plant species richness, Shannon diversity index, and plant community productivity, whereas increased with the increases of accumulated active temperature (AccT) and soil total phosphorus (STP) across alpine grassland types at the regional scale. Multiple linear models with analysis of covariance (ANCOVA) confirmed GSP to be the most critical driver, which alone explained most variances of δ15Nplant (56%), δ15Nsoil (62%), and δ15Nsoil-to-plant (35%). However, structural equation modeling performed better than multiple linear modeling in predicting δ15Nplant (76% vs. 66%) and worse in predicting δ15Nsoil (79% vs. 84%) and δ15Nsoil-to-plant (31% vs. 46%), likely due to the exclusion of collinear predictors and the removal of non-significant influencing paths. Overall, this study has highlighted the importance to uncover the complexity of climate, soil nutrients, and vegetation properties in networking to drive the different components of ecosystem N cycling in alpine grasslands on the Tibetan Plateau.

Time-Series InSAR Monitoring of Permafrost Freeze-Thaw Seasonal Displacement over Qinghai–Tibetan Plateau Using Sentinel-1 Data

Permafrost is widely distributed in the Tibetan Plateau. Seasonal freeze–thaw cycles of permafrost result in upward and downward surface displacement. Multitemporal interferometric synthetic aperture radar (MT-InSAR) observations provide an effective method for monitoring permafrost displacement under difficult terrain and climatic conditions. In this study, a seasonal sinusoidal model-based new small baselines subset (NSBAS) chain was adopted to obtain a deformation time series. An experimental study was carried out using 33 scenes of Sentinel-1 data (S-1) from 28 November 2017 to 29 December 2018 with frequent revisit (12 days) observations. The spatial and temporal characteristics of the surface displacements variation combined with different types of surface land cover, elevation and surface temperature factors were analyzed. The results revealed that the seasonal changes observed in the time series of ground movements, induced by freeze–thaw cycles were observed on flat surfaces of sedimentary basins and mountainous areas with gentle slopes. The estimated seasonal oscillations ranged from 2 mm to 30 mm, which were smaller in Alpine deserts than in Alpine meadows. In particular, there were significant systematic differences in seasonal surface deformation between areas near mountains and sedimentary basins. It was also found that the time series of deformation was consistent with the variation of surface temperature. Based on soil moisture active/passive (SMAP) L4 surface and root zone soil moisture data, the deformation analysis influenced by soil moisture factors was also carried out. The comprehensive analysis of deformation results and auxiliary data (elevation, soil moisture and surface temperature et al.) provides important insights for the monitoring of the seasonal freeze-thaw cycles in the Tibetan Plateau.

Comparison of Soil Organic Matter Transformation Processes in Different Alpine Ecosystems in the Qinghai‐Tibet Plateau

AbstractSoils in the Qinghai‐Tibet Plateau are young in terms of development and form a thin, skeletal soil layer because the gravel parent materials are glaciofluvial deposit, eluvium, and fluvial sediment, which are extremely sensitive to global climate change. The lack of understanding of soil organic matter (SOM) transformation processes in this region hinders the prediction of SOM stocks under future climate conditions. In this study, SOM transformation processes were investigated by density groupings and pyrolysis‐gas chromatography/tandem‐mass spectrometry (Py‐GC–MS/MS) in five alpine ecosystems: alpine desert, alpine grassland, alpine meadow, alpine wetland, and alpine forest. The roles of microbial community in different density fractions were elucidated. Soil samples were separated into three fractions with NaI solution: labile fraction (FL; ρ ≤ 1.6 g/cm3), moderate fraction (FM; 1.6 &lt; ρ &lt; 2.25 g/cm3), and recalcitrant fraction (FR; ρ ≥ 2.25 g/cm3). The following results were obtained. (1) The ratios of different fractions (FM/FL, FR/FM, and FR/FL) indicated the transformation processes of SOM, and ratios less than 1 represented degradation. The transformation processes were similar in alpine grassland and meadow and were similar in alpine desert, wetland, and forest but differed from each other. (2) Fungi preferred to degrade plant detritus, which mainly affected FL, whereas bacteria chiefly affected FM. (3) Precipitation altered vegetation type and soil pH, thus affecting communities and microorganism activities and resulting in the above differences. These findings highlight the importance of understanding the limited transformation processes of SOM in ecosystems to predict the impact of climate change on SOM preservation.

Spatiotemporal distribution changes in alpine desert belt in Qilian Mountains under climate changes in past 30 years

Spatiotemporal distribution changes in alpine desert belt in Qilian Mountains under climate changes in past 30 years

气候变化与放牧对西藏典型高寒荒漠草地植被指数变化的相对影响

气候变化与放牧对西藏典型高寒荒漠草地植被指数变化的相对影响

Aeolian Material Transport and Its Role in Landscape Connectivity in the McMurdo Dry Valleys, Antarctica

AbstractArid regions, particularly polar and alpine desert environments, have diminished landscape connectivity compared to temperate regions due to limited and/or seasonal hydrological processes. For these environments, aeolian processes play a particularly important role in landscape evolution and biotic community vitality through nutrient and solute additions. The McMurdo Dry Valleys (MDV) are the largest ice‐free area in Antarctica and are potentially a major source of aeolian material for the continent. From this region, samples were collected at five heights (~5, 10, 20, 50, and 100 cm) above the surface seasonally for 2013 through 2015 from Alatna Valley, Victoria Valley, Miers Valley, and Taylor Valley (Taylor Glacier, East Lake Bonney, F6 (Lake Fryxell), and Explorer's Cove). Despite significant geological separation and varying glacial histories, low‐elevation and coastal sites had similar major ion chemistries, as did high‐elevation and inland locations. This locational clustering of compositions was also evident in scanning electron microscopy images and principal component analyses, particularly for samples collected at ~100 cm above the surface. Compared to published soil literature, aeolian material in Taylor Valley demonstrates a primarily down‐valley transport of material toward the coast. Soluble N:P ratios in the aeolian material reflect relative nutrient enrichments seen in MDV soils and lakes, where younger, coastal soils are relatively N depleted, while older, up‐valley soils are relatively P depleted. The aeolian transport of materials, including water‐soluble nutrients, is an important vector of connectivity within the MDV and provides a mechanism to help “homogenize” the geochemistry of both soil and aquatic ecosystems.