Taklimakan Research Articles

The Transport Path and Vertical Structure of Dust Storms in East Asia and the Impacts on Cities in Northern China

Dust storm disasters have emerged as a significant environmental challenge in East Asia. However, relying on a single monitoring method to track dust storms presents limitations and can be variable. Therefore, it is necessary to use a combination of ground and remote sensing monitoring methods to explore the source and impact range of dust storms in order to fully characterize them. To achieve this, we examined the sources and impact ranges of dust storms in East Asia from 1980 to 2020 using both ground station data and remote sensing data. In addition, we focused on three specific dust storm events in the region. Our results indicate that the central source areas of dust storms are located in southern Mongolia and the Taklamakan Desert in China. Dust storms are mainly transported and spread in the northwestern region, while they are relatively rare in the southeastern region. The HYSPLIT model simulations reveal that the primary source directions of dust storms in East Asia are northwest, west, and north, the region involved includes Kazakhstan, southern Mongolia, and the Taklimakan Desert in China. The vertical structure of the dust storm layer depends on the source of the dust storm and the intensity of the dust storm event. Dust grain stratification probably occurs due to differences in dust storm sources, grain size, and regularity. These findings demonstrate that a combination of ground-based and remote sensing monitoring methods is an effective approach to fully characterize dust storms and can provide more comprehensive information for dust storm studies.

Evaluation of CAMEL over the Taklimakan Desert Using Field Observations

Infrared (IR) land surface emissivity (LSE) plays an important role in numerical weather prediction (NWP) models through the satellite radiance assimilation. However, due to the large uncertainties in LSE over the desert, many land-surface sensitive channels of satellite IR sensors are not assimilated. This calls for further assessments of the quality of satellite-retrieved LSE in these desert regions. A set of LSE observations were made from field experiments conducted on 16–18 October 2013 along a south/north desert road in the Taklimakan Desert (TD), China. The observed LSEs (EOBS) are thus used in this study as the reference values to evaluate the quality of Combined ASTER MODIS Emissivity over Land (CAMEL) data. Analysis of these data shows four main results. First, the CAMEL datasets appear to sufficiently capture the spatial variations in LSE from the oasis to the hinterland of the TD (this is especially the case in the quartz reststrahlen band). From site 1 at the southern edge of the Taklimakan Desert to site 10 at the northern edge, the measured LSE and the corresponding CAMEL observation in the quartz reststrahlen band first decrease and reach their minimum around sites 4–6 in the hinterland of the Taklimakan Desert. Then, the LSE increases gradually and finally reaches its maximum at site 10, which has a clay ground surface, showing that the LSE is higher at the edges of the desert and lower in the center. Second, the CAMEL values at 11.3 μm have a zonal distribution characterized by a northeast–southwest strike, though such an artifact might have been introduced by ASTER LSE data during the merging process that created the CAMEL dataset. Third, the unrealistic variation of the original EOBS can be filtered out with useful signals, as identified by the first six principal components of the PCA conducted on the laboratory-measured hyperspectral emissivity spectra (ELAB). Fourth, the CAMEL results correlate well with the measured LSE at the 10 observation sites, with the observed LSE being slightly smaller than the CAMEL values in general.

On the dynamics and air-quality impact of the exceptional East Asian dust outbreak in mid-March 2021

In mid-March 2021, one of the strongest dust storms of the last decade hit East Asia with adverse impacts on socio-economic activities and loss of life. The aim of this study is to assess the atmospheric dynamics involved in the temporal evolution of the Mongolian extra-tropical cyclone driving the dust event in different dust source regions in East Asia and to quantify to what extent the event was unusual for the first time. To that end, we use observation and model data from different sources. We identify that dust aerosols of the event primarily originated in the Gobi Desert. The anomalously strong dust-emitting winds were here associated with the passage of a cold front and exceeded the 99th percentile of the near-surface wind climatology for March 1992–2021 by far. Over the Loess Plateau, the dust deposition mostly exceeded the regional dust emission, indicative of the region being a net sink for dust aerosols, even during a high-impact event like in mid-March 2021. The formed dust aerosol layer of thousands of kilometers in extent led to sharp decreases in the air quality across China with record-high urban particulate matter concentrations, poor air quality, and low atmospheric visibility. Our results highlight that also the Taklamakan Desert contributed to the dust outbreak in the Western part of China. The dust emissions in the Taklamakan Desert were associated with nocturnal low-level jets that were favored by the cold air intrusion. It provides the first evidence for a link between different dust-emission mechanisms across East Asian Deserts during synoptic-scale dust outbreaks.

Validation of FY-4A Temperature Profiles by Radiosonde Observations in Taklimakan Desert in China

The atmospheric temperature profiles (ATPs) retrieved through the geostationary Interferometric Infrared Sounder (GIIRS) onboard the FY-4A satellite (GIIRS/FY-4A) can effectively fill the gap of the scarce conventional sounding data in the Taklimakan Desert (TD), the second largest desert in the world, with an area of 330,000 square kilometers. In this study, we take the experimental radiosonde observations (RAOB) from one RAOB station in the hinterland of TD and seven conventional radiosondes in the oasis region around the desert as the true values and analyze the bias distribution characteristics of GIIRS/FY-4A ATPs with quality control (QC) flags 0 or 1 for this region. In addition, a bias comparison is made with GIIRS/FY-4A ATPs, and the fifth generation ECMWF atmospheric reanalysis of the global climate (ERA5) ATPs. The results show that (1) Missing measurements in GIIRS/FY-4A ATPs are the most frequent in the near-surface layer, accounting for more than 80% of all the retrieved grid points. The averaged total proportion of GIIRS/FY-4A ATPs with QC marks 0 or 1 is about 33.06%. (2) The root mean square error (RMSE) of GIIRS/FY-4A ATPs is less than 3 K, smaller than that of ERA5 ATPs. The RMSE of ERA5 ATPs can exceed 10 K in the desert hinterland. The absolute mean biases of GIIRS/FY-4A ATPs and ERA5 ATPs are, respectively, smaller than 3 K and 2 K, the former being slightly larger. The correlation coefficients of GIIRS/FY-4A ATPs with ERA5 ATPs and RAOB ATPs are higher than 0.98 and 0.99, respectively, and the correlation between GIIRS/FY-4A ATPs and RAOB ATPs is inferior to the latter. (3) The overall atmospheric temperature retrieved by GIIRS/FY-4A is 0.08 K higher than the temperature of RAOB, on average, while the overall temperature from ERA5 is 0.13 K lower than that of RAOB, indicating that the temperature profile obtained by integrating GIIRS/FY-4A ATPs and ERA5 ATPs may be much closer to RAOB ATPs. (4) The probability density of the GIIRS/FY-4A ATP biases in the TD region generally follows the Gaussian distribution so that it can be effectively assimilated in the 3-D variational assimilation modules. The probability density distribution characteristics of the GIIRS/FY-4A ATP biases in the desert hinterland and oasis are not much different. However, due to the fusion analysis of the relatively rich multi-source conventional observation data from the oasis stations, the probability density of ERA5 ATPs biases at the oasis stations is nearer to Gaussian distribution than that of the GIIRS/FY-4A ATPs. In the desert hinterland, where conventional observation is not enough, the probability density distributions of the ATPs biases from ERA5 and GIIRS/FY-4A are alike. Therefore, the GIIRS FY4A can contribute to a more accurate estimation of ERA5 ATPs in the TD region.

Summer Extreme Dust Activity in the Taklimakan Desert Regulated by the South Asian High

Summer dust aerosol in the Taklimakan Desert (TD) affects not only the albedo of the snow and ice sheets on the Tibetan Plateau (TP) but also air quality and precipitation in the downstream areas. In this study, the summer extreme dust activity in the TD was jointly investigated by using satellite observations and MERRA-2 reanalysis datasets and divided into two states: dust active period and dust inactive period. The horizontal and vertical distribution of summer dust during both the dust active and inactive periods, as derived from the MERRA-2 dataset, is consistent with satellite observations. By comparing the upper-level circulation and surface meteorological elements at two periods, we identify the South Asian High (SAH) as the dominant factor driving the extreme dust activity in the TD during summer. When the SAH is centered on the Iranian Plateau (IP), the dust aerosol in the TD exhibits increased activity and is lifted to higher altitudes due to significantly enhanced westerly winds, near-surface wind speed, and an ascending motion. Conversely, when the SAH is centered on the TP, the summer dust activity shows the opposite behavior. These new findings on the regulatory mechanism of the SAH on the summer dust activity in the TD are highly significant for understanding the occurrence and transport of summer Asian dust and its potential impact on heavy precipitation in the downstream areas.

Mongolia Contributed More than 42% of the Dust Concentrations in Northern China in March and April 2023

Dust storms are one of the most frequent meteorological disasters in China, endangering agricultural production, transportation, air quality, and the safety of people’s lives and property. Against the backdrop of climate change, Mongolia’s contribution to China’s dust cannot be ignored in recent years. In this study, we used the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), along with dynamic dust sources and the HYSPLIT model, to analyze the contributions of different dust sources to dust concentrations in northern China in March and April 2023. The results show that the frequency of dust storms in 2023 was the highest observed in the past decade. Mongolia and the Taklimakan Desert were identified as two main dust sources contributing to northern China. Specifically, Mongolia contributed more than 42% of dust, while the Taklimakan Desert accounted for 26%. A cold high-pressure center, a cold front, and a Mongolian cyclone resulted in the transport of dust aerosols from Mongolia and the Taklimakan Desert to northern China, where they affected most parts of the region. Moreover, two machine learning methods [the XGBoost algorithm and the Synthetic Minority Oversampling Technique (SMOTE)] were used to forecast the dust storms in March 2023, based on ground observations and WRF-Chem simulations over East Asia. XGBoost-SMOTE performed well in predicting hourly PM10 concentrations in China in March 2023, with a mean absolute error of 33.8 µg m−3 and RMSE of 54.2 µg m−3.

Georgenia halotolerans sp. nov., a halotolerant actinobacterium isolated from Taklamakan desert soil.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming and rod-shaped actinobacterium, designated strain 10Sc9-8T, was isolated from Taklamakan desert soil sampled in the Xinjiang Uygur Autonomous Region, China. Strain 10Sc9-8T grew at 8‒37 °C (optimum, 28‒30 °C), pH 6.0‒10.0 (optimum, pH 7.0-8.0) and in the presence of 0‒15 % (w/v) NaCl (optimum, 0-3 %). Phylogenetic analysis based on 16S rRNA gene sequence suggested that strain 10Sc9-8T was affiliated with members of the genus Georgenia and showed the highest 16S rRNA gene sequence similarity to Georgenia yuyongxinii Z443T (97.4 %). Phylogenomic analysis based on the whole genome sequences indicated that strain 10Sc9-8T should be assigned into the genus Georgenia. The average nucleotide identity and digital DNA-DNA hybridization values calculated from the whole genome sequences indicated that strain 10Sc9-8T was clearly separated from other closely related species of the genus Georgenia with values below the thresholds for species delineation. Chemotaxonomic analyses showed that the cell-wall peptidoglycan was in a variant of A4α type with an interpeptide bridge comprising l-Lys-l-Ala-Gly-l-Asp. The predominant menaquinone was MK-8(H4). The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, several unidentified phospholipids, glycolipids and one unidentified lipid. The major fatty acids were anteiso-C15 : 0, anteiso-C15 : 1 A and C16 : 0. The genomic DNA G+C content was 72.7 mol%. On the basis of phenotypic, phylogenetic and phylogenomic data, strain 10Sc9-8T represents a novel species of the genus Georgenia, for which the name Georgenia halotolerans sp. nov. is proposed. The type strain is 10Sc9-8T (=JCM 33946T=CPCC 206219T).

Predictions of Land Use/Land Cover Change and Landscape Pattern Analysis in the Lower Reaches of the Tarim River, China

Natural vegetation on both sides of the Tarim River Basin (TRB) is the only barrier—a critical ecological niche—between the economic belt in the artificial oasis and the Taklimakan Desert. To understand the impact of human activities on the TRB, we explored the spatial and temporal variations in land use/land cover change (LUCC) and landscape pattern evolution from 2000 to 2020. These variations were simulated for 2030 with the 20 years of data using the cellular automata–Markov model and geographical information system analyses. The results predicted substantial LUCCs in the lower reaches of the Tarim River (TRlr), with 3400 km2 (20.29%) of the total area (16,760.94 km2) undergoing changes. Wetland, artificial land, grassland, farmland, and forestland areas increased by 578.59, 43.90, 339.90, 201.62, and 536.11 km2, respectively, during the period from 2020 to 2030. The only decreases were in the Gobi/other deserts and bare soils (1700.13 km2). We also determined current and future changes in TRlr landscape pattern indices at the class and landscape levels. Combined with a field survey and hydrological data, theoretical support for effective land use management strategies is provided. The findings offer a scientific basis for future ecological civilization construction and sustainable development in the TRB.

Variations of PM2.5-bound elements and their associated effects during long-distance transport of dust storms: Insights from multi-sites observations

Dust storms are a significant concern because of their adverse effects on ambient air quality and human health. To investigate the evolution of dust storms during long-distance transport and its impacts on air quality and human health risks in cities along the transport pathway, we monitored the major fraction of dust (i.e., particle-bound elements) online in four cities in northern China during March 2021. Three dust events originating from the Gobi Desert of North China and Mongolia and the Taklimakan Desert of Northwest China were captured. We investigated the source regions of dust storms using daily multi-sensor absorbing aerosol index products, backward trajectories, and specific element ratios, identified and quantified sources of particle-bound elements using Positive Matrix Factorization model, and calculated the carcinogenic and non-carcinogenic risks of elements using a health risk assessment model. Our results indicated that under the influence of dust storms, mass concentrations of crustal elements increased up to dozens of times in cities near the dust source and up to ten times in cities farther from the source. In contrast, anthropogenic elements increased less or even decreased, depending on the relative contributions of the increase caused by accumulation of dust itself and entrainment along the transport path and the decrease caused by dilution of high wind speeds. Si/Fe ratio was found to be a valuable indicator for characterizing the attenuation of the amount of dust along its transport pathways, especially for the case originated from northern source regions. This study highlights the significant role of source regions, intensity and attenuation rates of dust storms, and wind speeds in determining the increased levels of element concentrations during dust storms and its associated impacts on downwind areas. Furthermore, non-carcinogenic risks of particle-bound elements increased at all sites during dust events, emphasizing the importance of personal exposure protection during dust storms.

Responses of arid plant species diversity and composition to environmental factors

An oasis is a unique natural landscape in arid and semi-arid areas, significant for regulating regional microclimates and hydrological processes in deserts. However, little is known regarding the response of natural oasis plants communities to various environmental factors. Nineteen sample plots (50 m × 50 m) were selected in the Daliyabuyi Oasis in the Taklimakan Desert hinterland based on the location of groundwater monitoring wells and 76 vegetation quadrats (25 m × 25 m) were established. A two-way indicator species analysis, Mantel test, detrended correspondence analysis, canonical correspondence analysis (CCA), and hierarchical partitioning were used to provide an in-depth analysis of community classification, species composition, and environmental interpretation of the oasis. A generalized linear model was used to verify the results which showed that the current oasis community could be divided into four types according to the dominant species, which is controlled by soil moisture. Measurement of species composition and distribution of communities showed significant differences between species diversity of individual community types. Variations in groundwater depth affects patterns of species diversity which is sensitive to richness, while the degree of surface water disturbance affects the pattern of species evenness. Moreover, the CCA ordination map showed that community distribution and diversity characteristics have their own preferences in habitat gradients. The study concluded that the species dominance of the community and the composition and distribution are not dominated by a single factor. There are differences in the scale and effect of different water resource types in maintaining community characteristics.

Long‐Term Variation of Dust Devils in East Asia During 1959–2021

AbstractDust devils play an important role in dust transport by carrying it from the surface into the atmosphere, especially in summer. However, information on how dust devils changed in the past decades and what caused these changes remains lacking. Based on thermodynamic criteria and ERA5 reanalysis data set, this study investigated the long‐term variation of favorable conditions for dust devil occurrence in East Asia over the past 63 years and defined it as potential dust devil and dusty plume (PDDP) occurrence in hours. Annual mean frequency of PDDP in East Asia was approximately 217.2 hr from 1959 to 2021. An overall downward trend in PDDP frequency has been found over 63 years in East Asia among which strong PDDPs drop significantly at the fastest rate while the weak ones dropped insignificantly. Moreover, PDDP frequency in the Gobi Desert increased but they decreased in the Taklimakan Desert. The monthly variation of PDDP shows a single‐peak structure with a tendency for the peak to move from June to July. For the diurnal changes, PDDP mainly occurred between 10:00 and 16:00 at local time (LT), with over 60% of them happening between 12:00 LT and 14:00 LT. We also found a negative correlation between precipitation and PDDP occurrence. This study provides a comprehensive understanding of favorable conditions for dust devil occurrence in East Asia over the past decades, which is of great importance to further evaluate its impact on climate, environment as well as ecosystem.

OSL chronology reveals Late Pleistocene floods and their impact on landform evolution in the lower reaches of the Keriya River in the Taklimakan Desert

OSL chronology reveals Late Pleistocene floods and their impact on landform evolution in the lower reaches of the Keriya River in the Taklimakan Desert

Effects of groundwater and seasonal streamflow on the symbiotic nitrogen fixation of deep-rooted legumes in a dryland floodplain

Biological nitrogen fixation of deep-rooted legumes is a major pathway of nitrogen (N) inputs to drylands. Water sources including groundwater and streamflow are vital to the growth of deep-rooted legumes in drylands, but it is unclear how their different availability and biochemical properties may influence plant N fixation. We established two sampling transects at the southern fringe of the Taklimakan Desert (Xinjiang province, north-west China) to study the effects of both the groundwater depth and distance to a seasonally active river on the N fixation rate of Alhagi sparsifolia, a dominant deep-rooted legume species. We quantified the N fixation rate of A. sparsifolia using the 15N natural abundance method, and related variation in N fixation to water source use and soil biochemical properties along the two transects. The N fixation rate of A. sparsifolia decreased with groundwater depth and increased with distance from the river channel. Instead of variation in the water source or nutrient concentrations, we found that the gradient in salinity formed by groundwater flow and streamflow was most responsible for the spatial pattern in N fixation of A. sparsifolia. In many dryland regions, water availability controls the spatial variability of symbiotic N fixation along hydrological gradients. Our study system provides a contrasting condition where salinity most strongly regulates N fixation. In addition to understanding the important role of variation in water source and nutrient availability, our study suggests that the impact of soil salinity in mediating N fixation in dryland ecosystems is deserving of attention.

Desert Abiotic Carbon Sequestration Weakening by Precipitation

Desert carbon sequestration plays an active role in promoting carbon neutralization. However, the current understanding of the effect of hydrothermal interactions and soil properties on desert carbon sequestration after precipitation remains unclear. Based on the experiment in the hinterland of the Taklimakan Desert, we found that the heavy precipitation will accelerate the weakening of abiotic carbon sequestration in deserts under the background of global warming and intensified water cycle. The high soil moisture can significantly stimulate sand to release CO2 at an incredible speed by rapidly increasing microbial activity and organic matter diffusion. At this time, the CO2 flux in the shifting sand was synergistically affected by soil temperature and soil moisture. As far as soil properties are concerned, with less organic carbon substrate and stronger soil alkalinity, the carbon sequestration of shifting sand is gradually highlighted and strengthened at low temperature. On the contrary, the carbon sequestration of shifting sand is gradually weakened. Our study provides a new way to assess the contribution of desert to the global carbon cycle and improve the accuracy and scope of application.

Population structure, genetic diversity and prolificacy in pishan red sheep under an extreme desert environment.

Extreme environmental conditions are a major challenge for livestock production. Changes in climate conditions, especially those that lead to extreme weather, can reduce livestock production. The screening of genes and molecular markers is of great significance to explore the genetic mechanism of sheep prolificacy traits in Taklimakan Desert environment. We selected healthy adult Pishan Red Sheep (PRS) and Qira Black Sheep (QR) which live in Taklimakan Desert environment, collected blood from jugular vein, extracted DNA, and prepared Illumina Ovine SNP50 chip. For PRS, linkage disequilibrium (LD) was calculated using the ovine SNP50 Beadchip and the effective population size (Ne) was estimated using SMC++. The genetic characteristics of PRS were analyzed by integrated haplotype score (iHS) and fixation index (F ST ). The result showed that r 2 of PRS was 0.233 ± 0.280 in the range of 0-10Kb and decreased with increasing distances. SMC++ tested that the Ne of PRS remained at 236.99 in recent generations. 184 genes were screened out under iHS 1% threshold, and 1148 genes were screened out with F ST under the 5% threshold, and 29 genes were obtained from the intersection of the two gene sets. In this study, the genetic characteristics of PRS and QR were compared by ovine genome chip, and the related excellent genes were searched, providing reference for the protection of sheep germplasm resources and molecular breeding in a desert environment.

Spatiotemporal Changes and Driving Force Analysis of Land Sensitivity to Desertification in Xinjiang Based on GEE

Land desertification profoundly affects economic and social development, thus necessitating a collective response. Regional land control planning needs to assess the land sensitivity to desertification across different regions. In this study, we selected 12 factors from soil, vegetation, climate, and terrain aspects to calculate and evaluate Xinjiang’s land sensitivity to desertification, from 2001 to 2020, and analyzed its trends and drivers. The results indicated that the region is highly (22.93%) to extremely sensitive (34.63%) to desertification. Of these, deserts, Gobi lands, oasis–desert transitional zones, and the downstream of rivers are highly and extremely sensitive areas. Mountainous areas, oases, and along rivers are non- and mildly sensitive areas. Over the past two decades, most areas have experienced stability (45.07%) and a slight improvement of desertification (26.18%), while the Junggar Basin and Central Taklamakan Desert have seen slight and severe intensification trends, respectively. Climate-related indicators, such as surface temperature and potential evapotranspiration (PET), were identified as the most important drivers of changes in land sensitivity to desertification. Having an integrated water resource allocation and establishing the long-term monitoring of land sensitivity to desertification would have positive implications for desertification control.

Soil salinization increases the stability of fungal not bacterial communities in the Taklamakan desert

Soil salinization increases the stability of fungal not bacterial communities in the Taklamakan desert

On the Association between Fine Dust Concentrations from Sand Dunes and Environmental Factors in the Taklimakan Desert

Dust in sand dunes is an effective and important source of dust emission. The Taklimakan Desert (TD) is one of the main sources of global dust: the sand dunes account for approximately 85% of the total area of the TD. However, the dust concentration, emission characteristics, and physical factors of different parts of the sand dunes in the TD during the day and night, as well as dust and non-dust days, remain unclear. In this study, dust observations were collected over a 3 month period in the TD to investigate the physical processes by which dust moves across a surface and generates PM10 and PM2.5 from the top and bottom of sand dunes. The results showed that the daily average maximum concentrations of particulate matter with diameters below 2.5 and 10 µm (PM2.5 and PM10) in the dune during the observation period reach ~90 and ~190 µg·m−3, respectively. Dust emission generated in the saltation process (maximum emission of PM10 was 3–5 mg·m−2·s−1) in the TD dunes was larger than that in other areas and had a good correlation with u* (friction velocity), where u* = 0.4 m·s−1 was the threshold of sand dune dust emission. The wind speed at the top of dunes was larger than that at the bottom, which was conducive to the accumulation of PM10 at the top of the dune. Furthermore, the MLH (mixed layer height) decreased after sunset and the turbulence weakens, which was conducive to the retention of dust in the air. Moreover, the dust made the solar radiation at the top of the dune −15 W·m−2 (average) lower than at the bottom. These results provided a new understanding of dune emissions in the TD and could be used for dust modeling in regional and global models.

Forty-year spatio-temporal dynamics of agricultural climate suitability in China reveal shifted major crop production areas

Studies measuring climate change effects on crop production and development usually focus on extreme temperature and heat indicators while ignoring water requirements and land suitability. In this study, spatially continuous differences in climate data from 1980 to 2017 using meteorological station data and elevation data as covariates were analysed with the ANUSPLIN software. The analysis integrated the effects of water and thermal resources on the agricultural production layout. Cover remote sensing of China’s multi-period land use showed that the centre of gravity of the suitable planting area of winter wheat, spring maize, and medium rice has changed according to climate conditions. It is anticipated that other arable land reserve resources, including unused lands, grasslands, and forest land, in sensitive areas such as the Taklamakan Desert, Loess Plateau, and Hexi Corridor could be rationally developed. This study provides valuable references for agricultural zoning adjustment and agricultural development policy formulation.

Contrasting responses of two C4 desert shrubs to drought but consistent decoupling of photosynthesis and stomatal conductance at high temperature

How desert shrubs respond to drought and heat remains poorly understood. We investigated how drought affected the morphology and physiology of two C4 species with different root architecture, Calligonum arborescens and Haloxylon ammodendron, in the Taklamakan Desert. We measured leaf traits, chlorophyll fluorescence and temperature responses of photosynthesis after ∼3 years of experimental drought and asked: (1) Do both species adjust similarly to drought? (2) Does transpirational cooling increase at high temperature, and if so, how is this affected by drought? Drought plants of H. ammodendron had shorter and thinner leaves than controls, and lower chlorophyll content, photochemical efficiency, and electron transport rate. In contrast, C. arborescens leaves became shorter and thicker. Drought reduced maximum photosynthesis by 63 % and 21 % in H. ammodendron and C. arborescens, respectively. The optimum temperature did not change significantly in H. ammodendron and decreased by ∼2 °C in C. arborescens. Surprisingly, above 40–45 °C, stomatal conductance (gsw) and transpiration increased—even under drought stomata partially reopened. This consistent uncoupling of photosynthesis and gsw suggests that widely-implemented stomatal optimization models may poorly reflect high-temperature behaviors in dryland ecosystems. Our study established the basis for predicting the eco-physiological responses of C4 species in hyper-arid ecosystems to climate change.