Extreme Arid Environments Research Articles

Natural History of the Genus Elasmoderus Saussure, 1888 (Orthoptera: Tristiridae), an Endemic and Eremic Element of the Transitional Coastal Desert of Chile.

The genus Elasmoderus belongs to the family Tristiridae, an orthopteran group that is distributed across the transitional region of South America and represented in the Andean areas of Peru, Argentina, and Chile. The species of Elasmoderus have morphological adaptations that make them especially suited for surviving in extreme arid environments and are an endemic and eremic group of the north-central region of Chile. On the basis of field samplings, direct observations, and a comprehensive literature review, we collected information about the genus Elasmoderus. The objectives of this research were: (i) to provide updated information on the geographical distribution range of the species of the genus Elasmoderus, and (ii) to collect and synthesize the most relevant information on the natural history and ecology of this orthopteran group as a basis for future long-term studies of its populations. Although this genus is underrepresented compared to other orthopteran families, it has developed interesting adaptations to extreme arid environments that remain unstudied to this date. E. lutescens is known to be one of the species with a wider latitudinal distribution, mostly on the coast and longitudinal valley of Atacama. E. minutus has a more restricted distribution, whereas E. wagenknechti is concentrated in coastal and interior environments of the Coquimbo region, an area where it reaches high population densities, thus affecting crops and natural vegetation and polluting water sources. Our findings underscore the importance of conducting comprehensive research on native insect groups that are poorly known but crucial for arid and semiarid ecosystems. These data will serve as a starting point for conducting long-term studies on this orthopteran group to gain a better understanding of the importance and role of these species in the semiarid ecosystems of northern Chile.

The effects of climate and soil depth on living and dead bacterial communities along a longitudinal gradient in Chile

Soil bacterial communities play a critical role in shaping soil stability and formation, exhibiting a dynamic interaction with local climate and soil depth. We employed an innovative DNA separation method to characterize microbial assemblages in low-biomass environments such as deserts and distinguish between intracellular DNA (iDNA) and extracellular DNA (eDNA) in soils. This approach, combined with analyses of physicochemical properties and co-occurrence networks, investigated soil bacterial communities across four sites representing diverse climatic gradients (i.e., arid, semi-arid, Mediterranean, and humid) along the Chilean Coastal Cordillera. The separation method yielded a distinctive unimodal pattern in the iDNA pool alpha diversity, increasing from arid to semi-arid climates and decreasing in humid environments, highlighting the rapid feedback of the iDNA community to increasing soil moisture. In the arid region, harsh surface conditions restrict bacterial growth, leading to peak iDNA abundance and diversity occurring in slightly deeper layers than the other sites. Our findings confirmed the association between specialist bacteria and ecosystem-functional traits. We observed transitions from Halomonas and Delftia, resistant to extreme arid environments, to Class AD3 and the genus Bradyrhizobium, associated with plants and organic matter in humid environments. The distance-based redundancy analysis (dbRDA) analysis revealed that soil pH and moisture were the key parameters that influenced bacterial community variation. The eDNA community correlated slightly better with the environment than the iDNA community. Soil depth was found to influence the iDNA community significantly but not the eDNA community, which might be related to depth-related metabolic activity. Our investigation into iDNA communities uncovered deterministic community assembly and distinct co-occurrence modules correlated with unique bacterial taxa, thereby showing connections with sites and key environmental factors. The study additionally revealed the effects of climatic gradients and soil depth on living and dead bacterial communities, emphasizing the need to distinguish between iDNA and eDNA pools.

Studies on the Correlation between δ13C and Nutrient Elements in Two Desert Plants

Stable carbon isotopes (δ13C) and elemental stoichiometry characteristics are important ways to research the water and nutrient use strategies of plants. Investigating the variation patterns inof δ13C and the major nutrient elements in different organs of plants and the correlation among them can reveal the ecological strategies of desert plants in extreme arid environments. In this study, two typical desert plants, Alhagi sparsifolia and Karelinia caspia, were studied in the Tarim Basin. By analyzing the changes in δ13C, carbon (C), nitrogen (N), and phosphorus (P) and the ecological stoichiometry of their roots, stems, and leaves, the distribution patterns among different organs and their correlation with soil environmental factors were revealed. The results showed the following: (1) The δ13C of the two plants differed significantly among different organs (p < 0.01). The root and stem of Alhagi sparsifolia had significantly greater δ13C than the leave, while the δ13C of Karelinia caspia showed a root > stem > leaf gradient; (2) the C content in the leaves of the two plants was significantly lower than that of the root (p < 0.01), whereas the N content showed the opposite trend (p < 0.01); (3) the average N:P of Alhagi sparsifolia was >16.00, indicating it was mainly limited by P elements, while the average N:P of Karelinia caspia was <14.00, suggesting it was mainly limited by N elements; (4) in the root, stem and leave of Alhagi sparsifolia and Karelinia caspia, the N content and C:N and the P content and C:P showed a significantly negative correlation (p < 0.01), and δ13C was negatively correlated with C:P; (5) soil total phosphorus (TP) is an important soil environmental factor affecting δ13C and the nutrient elements in Alhagi sparsifolia and Karelinia caspia. This study demonstrates that Alhagi sparsifolia and Karelinia caspia are able to effectively coordinate and regulate their water, N, and P use strategies in response to environmental stress. These results can provide scientific reference for the evaluation of plant physiological and ecological adaptations for ecological conservation in arid areas.

Gregarines from darkling beetles of the Atacama Desert, Atacamagregarina paposa gen. et sp. nov. from Scotobius and Xiphocephalus ovatus sp. nov. from Psectrascelis (Coleoptera, Tenebrionidae)

Gregarine apicomplexans, a group of single celled organisms, inhabit the extracellular spaces of most invertebrate species. The nature of the gregarine-host interactions is not yet fully resolved, mutualistic, commensal and parasitic life forms have been recorded. In the extreme arid environment of the Atacama Desert, only a few groups of invertebrates hosting gregarines such as darkling beetles (Tenebrionidae) were able to adapt, providing an unparalleled opportunity to study co-evolutionary diversification. Here, we describe one novel gregarine genus comprising one species, Atacamagregarina paposa gen. et sp. nov., and a new species, Xiphocephalus ovatus sp. nov. (Apicomplexa: Eugregarinoridea, Stylocephalidae), found in the tenebrionid beetle genera Scotobius (Tenebrioninae, Scotobiini) and Psectrascelis intricaticollis ovata (Pimeliinae, Nycteliini), respectively. In the phylogenetic analysis based on SSU rDNA, Atacamgregarina paposa representing the new genus is basal, forming a separate clade with terrestrial gregarines specific for North American darkling beetles.

极端干旱区多枝柽柳叶片功能性状及其与土壤理化因子的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 极端干旱区多枝柽柳叶片功能性状及其与土壤理化因子的关系 DOI: 10.5846/stxb202204070904 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 新疆维吾尔自治区自然科学基金(2020D01C053);国家自然科学基金(32001145);新疆维吾尔自治区教育厅"天池博士计划"(TCBS202054) Leaf functional traits of Tamarix ramosissima in extremely arid region and their relationship with soil physicochemical factors Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:叶片是植物获取资源的重要器官,研究其功能性状与环境因子的关系,有助于更好地了解植物对环境要素变化的生态适应性。以塔里木盆地北缘不同生境下(绿洲、过渡带、荒漠)典型荒漠植物多枝柽柳(Tamarix ramosissima)为研究对象,分析其叶片结构和生理性状在不同生境间的差异,建立叶片性状与土壤理化因子的相关关系,解析荒漠植物的生态适应性并揭示影响荒漠植物叶片功能性状的关键环境因子。结果表明:(1)多枝柽柳叶片功能性状具有不同程度的变异,其中叶片面积变异幅度最大(40%),比叶面积、可溶性蛋白含量等变异幅度最小(均为15%)。(2)多枝柽柳叶片厚度和叶片面积等结构性状以及叶片可溶性蛋白、脯氨酸、淀粉含量等生理性状在不同生境中均具有显著差异(P<0.05),其中可溶性蛋白、脯氨酸含量均在荒漠生境中达到最高。(3)多枝柽柳叶片部分功能性状之间存在显著的相关关系,其中叶片厚度、淀粉含量等与叶组织密度呈显著负相关关系(P<0.05),而叶片厚度与淀粉含量之间、可溶性糖含量与非结构性碳水化合物含量之间均呈极显著正相关关系(P<0.01)。(4)通过RDA排序分析发现,土壤速效磷含量、土壤含水量、pH、容重等土壤环境因子影响较大,对多枝柽柳叶片功能性状有较好的解释。研究表明多枝柽柳通过叶片功能性状变化以及性状之间协同-权衡的生态对策来适应极端干旱环境,土壤水分和速效磷含量是影响其叶片功能性状最关键的土壤环境因子,研究可为极端干旱区荒漠植被的科学管理、保护和恢复提供理论依据。 Abstract:Leaf is an important organ for plants to obtain resources. Studying the relationships between its functional traits and environmental factors helps to better understand the ecological adaptability of plants to environmental changes. In this study, with the aim of determining the ecological adaptations of desert plants and revealing the environmental factors that influencing the functional traits of them, we investigated a typical desert plant, Tamarix ramosissima, in different habitats (oasis, transition zone and desert) at the northern edge of the Tarim Basin, analyzed the differences in its leaf structure and physiological traits, and established the correlation between them with soil physicochemical factors. The results showed that: (1) the functional traits of Tamarix ramosissima leaves exhibited different degrees of variation, with the greatest variation in leaf area (40%) and the least variation in specific leaf area and soluble protein content (both 15%). (2) The structural traits including leaf thickness and leaf area, as well as physiological traits including leaf soluble protein, proline, and starch contents of Tamarix ramosissima were significantly different among the three habitats (P<0.05), with soluble protein and proline contents reaching the highest levels in desert habitats. (3) There were significant correlations between several functional traits of Tamarix ramosissima leaves. Leaf thickness and starch content were significantly negatively correlated with leaf tissue density (P<0.05), while the correlations between leaf thickness and starch content, soluble sugar content and non-structural carbohydrate content were significantly positive (P<0.01). (4) The RDA analysis revealed that soil environmental factors including soil available phosphorus content, soil water content, pH and bulk density had the greatest influence, and could explain the leaf functional trait variations of Tamarix ramosissima better. This study indicates that Tamarix ramosissima adapts to extreme arid environment by developing ecological responses that varying in leaf functional traits and forming synergistic trade-offs between them. Soil available phosphorus content and soil water content are the most critical soil environmental factors affecting leaf functional traits of Tamarix ramosissima. The findings of this study provide a theoretical basis for the scientific management, conservation, and restoration of desert vegetation in extreme arid region. 参考文献 相似文献 引证文献

Differences and allometric relationships among assimilative branch traits of four shrubs in Central Asia.

Shrubs play a major role in maintaining ecosystem stability in the arid deserts of Central Asia. During the long-term adaptation to extreme arid environments, shrubs have developed special assimilative branches that replace leaves for photosynthesis. In this study, four dominant shrubs with assimilative branches, namely Haloxylon ammodendron, Haloxylon persicum, Calligonum mongolicum, and Ephedra przewalskii, were selected as the research objects, and the dry mass, total length, node number, and basal diameter of their assimilative branches and the average length of the first three nodes were carefully measured, and the allometric relationships among five traits of four species were systematically compared. The results indicated that: (1) Four desert shrubs have different assimilative branches traits. Compared with H. persicum and H. ammodendron, C. mongolicum and E. przewalskii have longer internodes and fewer nodes. The dry mass of H. ammodendron and the basal diameter of H. persicum were the smallest; (2) Significant allometric scaling relationships were found between dry mass, total length, basal diameter, and each trait of assimilative branches, all of which were significantly less than 1; (3) The scaling exponents of the allometric relationship between four traits and the dry mass of assimilative branches of H. persicum were greater or significantly greater than those of H. ammodendron. The scaling exponents of the relationships between the basal diameter, dry mass, and total length of E. przewalskii were higher than those of the other three shrubs. Therefore, although different species have adapted to drought and high temperatures by convergence, there was great variability in morphological characteristics of assimilative branches, as well as in the scaling exponents of relationships among traits. The results of this study will provide valuable insights into the ecological functions of assimilative branches and survival strategies of these shrubs to cope with aridity and drought in desert environments.

Macroevolutionary trends and diversification dynamics in Atripliceae (Amaranthaceae s.l., Chenopodioideae): a first approach.

Atripliceae evolved and diversified by dispersals and radiations across continents in both hemispheres, colonizing similar semi-arid, saline-alkaline environments throughout the world. Meanwhile, its species developed different life forms, photosynthetic pathways, mono- or dioecy, and different morphological features in flowers, fruiting bracteoles and seeds. In this study, we introduce a first approach to the macroevolutionary patterns and diversification dynamics of the Atripliceae to understand how time, traits, speciation, extinction and new habitats influenced the evolution of this lineage. We performed molecular phylogenetic analyses and clade age estimation of Atripliceae to apply time-, trait- and geographic-dependent diversification analyses and ancestral state reconstructions to explore diversification patterns within the tribe. Opposite diversification dynamics within the two major clades of Atripliceae, the Archiatriplex and Atriplex clades, could explain the unbalanced species richness between them; we found low mean speciation rates in the Archiatriplex clade and one shift to higher speciation rates placed in the branch of the Atriplex core. This acceleration in diversification seems to have started before the transition between C3 and C4 metabolism and before the arrival of Atriplex in the Americas, and matches the Mid-Miocene Climatic Optimum. Besides, the American species of Atriplex exhibit slightly higher net diversification rates than the Australian and Eurasian ones. While time seems not to be associated with diversification, traits such as life form, photosynthetic pathway and plant sex may have played roles as diversification drivers. Traits more than time played a key role in Atripliceae diversification, and we could speculate that climate changes could have triggered speciation. The extreme arid or saline environments where Atripliceae species prevail may explain its particular evolutionary trends and trait correlations compared with other angiosperms and highlight the importance of conservation efforts needed to preserve them as genetic resources to deal with climatic changes.

Arnebia euchroma, a Plant Species of Cold Desert in the Himalayas, Harbors Beneficial Cultivable Endophytes in Roots and Leaves

The endophytic mutualism of plants with microorganisms often leads to several benefits to its host including plant health and survival under extreme environments. Arnebia euchroma is an endangered medicinal plant that grows naturally in extreme cold and arid environments in the Himalayas. The present study was conducted to decipher the cultivable endophytic diversity associated with the leaf and root tissues of A. euchroma. A total of 60 bacteria and 33 fungi including nine yeasts were isolated and characterized at the molecular level. Among these, Proteobacteria was the most abundant bacterial phylum with the abundance of Gammaproteobacteria (76.67%) and genus Pseudomonas. Ascomycota was the most abundant phylum (72.73%) dominated by class Eurotiales (42.42%) and genus Penicillium among isolated fungal endophytes. Leaf tissues showed a higher richness (Schao1) of both bacterial and fungal communities as compared to root tissues. The abilities of endophytes to display plant growth promotion (PGP) through phosphorus (P) and potassium (K) solubilization and production of ACC deaminase (ACCD), indole acetic acid (IAA), and siderophores were also investigated under in vitro conditions. Of all the endophytes, 21.51% produced ACCD, 89.25% solubilized P, 43.01% solubilized K, 68.82% produced IAA, and 76.34% produced siderophores. Six bacteria and one fungal endophyte displayed all the five PGP traits. The study demonstrated that A. euchroma is a promising source of beneficial endophytes with multiple growth-promoting traits. These endophytes can be used for improving stress tolerance in plants under nutrient-deficient and cold/arid conditions.

Bounding linear rainfall-runoff models with fractional derivatives applied to a barren catchment of the Jordan Rift Valley

A new concept is developed to mathematically understand the dynamics of the rainfall-runoff events in a barren catchment of the Jordan Rift Valley. Time series data of rainfall and runoff have been acquired at an observation point in the catchment. Due to the extreme arid environment, water current as the runoff from the catchment is ephemeral, and the rainfall-runoff events are clearly distinguishable from each other. Firstly, a pair of linear autoregressive models with exogenous input (ARX models) is identified to tightly bound each runoff time series using the simplex method of linear programming. The exogenous input part is compatible with the conventional unit hydrograph method, while the autoregressive part is regarded as a discretized differential operator of fractional orders. Then, a linear fractional differential equation is determined to approximate each linear ARX model, which restricts the perturbation of the actual causal relationship between rainfall intensity and runoff discharge. The resulting lower and upper bounding rainfall-runoff models with fractional derivatives are examined in the system-theoretic framework. Finally, a nominal model from which actual nonlinear and stochastic phenomena perturb is arranged to envelope the all upper bounding rainfall-runoff models in the frequency domain, leading to the formulation of a challenging fractional optimal control problem involving stochastic processes.

Water Use Efficiency of Acacia seyal (Del.) in extreme arid environment prevails in South-Western Desert, Egypt

The present investigation involves the studies of water use efficiency of Acacia seyal (Del.) seedlings under extreme arid conditions. Experiments were performed in a hyper arid environment to study the effects of drought stress using different water regimes at 12%, 9%, 6%, 4% and 2%. Calculated instantaneous water use efficiency was measured under full Photosynthetic Active Radiation range (0-2500μmols-1m-2). Acacia seyal showed maximum photosynthesis rate at 9% soil moisture content, and at high Photosynthetic Active Radiation levels. Maximum transpiration rate recorded at 9% soil moisture content at highest Photosynthetic Active Radiation. The maximum instantaneous water use efficiency was noticed at 4% soil moisture content at high Photosynthetic Active Radiation level. Acacia seyal maximized photosynthesis rate and minimized transpiration rate, giving maximum instantaneous water use efficiency at the high Photosynthetic Active Radiation and low soil moisture content levels.

Water Resource Evaluation and Identifying Groundwater Potential Zones in Arid area using Remote Sensing and Geographic Information System

Groundwater resource is the main conventional source of fresh water all over the world. However, recent revelations indicated that the shortage of water resources remains the main challenge for the arid areas. In this regard, identifying groundwater potential zones or areas can help to improve the availability of fresh water and effective management of groundwater in arid areas. This work finds the water resources and identify the groundwater potential zones of arid areas using remote sensing and GIS techniques. The study uses Kingdom of Saudi Arabia (KSA) as one of the most arid area and divides entire KSA into five regions namely northern, central, western, southern and eastern to evaluate and indicate the groundwater prospective zones effectively and clearly. The northern region (Al Jouf, Tabuk, Hail and Al-Qassim), Saq and overlying aquifers play an important role in water supply in Saudi Arabia. About 17.90% of the total area of this region identified as a groundwater potential zone. Based on geomorphological factors, the Wadi catchment areas act as the best appropriate regions for groundwater recharge in the northern area. Regarding the central region (Al-Riyad province), about 1.47% and 4.15% may be categorized as excellent and very good while 12.59%, 74.82% and 6.97% are considered as good, poor and very poor groundwater potential zone. In the western area (Wadi Yalanlan basin), the lower part of the Wadi Yalamlam basin is the most promising zone for groundwater availability containing both high and moderate potential areas. Also, high groundwater potential zones can be found on the northern side of the central dyke region surrounding Abu Helal’s farm. 50.5% and 31% of the southern area (Jazan region) contain excellent and good groundwater potential areas while 16% and 2.5% of the regions showed average low groundwater potential zones. The eastern region had characteristics of extreme arid and desert environments. Based on the features, the area did not contain any groundwater potential zone. The current evaluation of groundwater potential areas in Saudi Arabia can serve as a significant tool for efficient groundwater resource management.

Using pastoral ideology to understand human–wildlife coexistence in arid agricultural landscapes

AbstractIntegrating social and ecological knowledge is requisite for solutions to global conservation problems, including human–wildlife conflict, but gathering sufficient data to facilitate integration has proved difficult. Social–ecological systems models have also traditionally overlooked individual human thought and behavior that can affect the success of management interventions. In response to these challenges, we drew upon psychological theory and long‐term ecological data on wildlife populations and conflict occurrence to inform qualitative research on pastoralists' values toward wildlife in the northern Namib Desert. We explored how values and ecological conditions shaped individuals': (a) interactions with and tolerance of species; and (b) perceptions of challenges and potential solutions to living with wildlife. Semi‐structured interview data revealed a prevailing domination value orientation toward wildlife, reflected in concerns for human and livestock wellbeing. Despite these concerns and high rates of reported conflicts, pastoralists were generally tolerant of wildlife, including predators, and indicated this in their proposed management solutions. In addition to its practical implications for informing human–wildlife coexistence strategies in the Namibian context, our approach advances knowledge about wildlife values globally, offers insights on the utility of qualitative assessments for cross‐cultural social–ecological systems research, and furthers understanding of conservation challenges and opportunities in extreme arid environments.

In situ real-time quantification of microbial communities: Applications to cold and dry volcanic habitats

We report field tests of an instrument using multi-wavelength excitation and detection of fluorescence capable of detection and discrimination of viable cells, non-viable cells (not metabolically active but not decomposed), and spores in extreme arid environments where low microbial abundances are expected. These new results are presented for cold and dry volcanic habitats worldwide, e.g., the arid core of the Atacama Desert, Mt. Kilimanjaro glacier and Kibo area, Pali Aike caldera, and the western US volcanic and desert soils in Utah, Idaho, Nevada, and California. Our results are comparable to previous studies reported in the literature for the same environments. We find these extreme environments there have a base level of ∼103 - 104 cells/g. This is the lower limit of detectable life on terrestrial soils, as we did not observe any quantities less than this, even though the described instrumentation is capable of such measurements. Samples from more conventional environments show much higher microbial cell densities, ca. 108 cells/g or higher, with this same instrument. This base level of microbial life is nearly equal in all the measurements from the extreme environments both hot and cold, and is likely controlled primarily by the sparse nutrients rather than temperature.

Sap Flow Measurements in a Socotra Dragon’s Blood Tree (Dracaena cinnabari) in its Area of Origin

For the first time, in situ field measurements of sap flow were conducted in adult Dracaena cinnabari plant native to the arid tropical climate of Socotra Island. The heat field deformation (HFD) method was applied using both single and multi-point sensors to study azimuthal and radial sap flow variability in stem, roots and first-order branches over two weeks during a winter monsoon. The main aim of this work was to monitor sap flow in adult D. cinnabari in-situ to better understand its physiological adaptation to extreme arid environments. The second aim was to compare our results with earlier sap flow measurements in adult D. draco uing the same HFD method. The last question we wanted to answer was comparison of sap flow measurements in both, young and adult Dracaena species. We found that sap flow magnitude is low and of a similar range in all observed D. species. High sap flow variability was recorded in different parts of adult D. cinnabari plant which changed throughout the day responding to interplay between intrinsic and extrinsic water potential gradients induced by sunlight. Maximum sap flow levels had variable pattern around stem in response to sun exposure, similarly as it was observed in adult D. draco plant. Sensors installed tangentially in stem xylem showed that water transport in adult D. cinnabari may move in lateral direction. This work also presents several methodological aspects detected from earlier observations of dicots which proved to be more pronounced in adult D. species. These methodologies relate to interpreting negative sap flow rates in conjunction with established axial flow reversal during hydraulic redistribution usually occurring under low evaporative demands and dry soil. Conversely, flow reversal during the day under high evaporative demands and wet soil may designate lateral water movement induced by internal water redistribution.

Draft Genome Sequence of Streptomyces sp. Strain DH-12, a Soilborne Isolate from the Thar Desert with Broad-Spectrum Antibacterial Activity.

ABSTRACTStrain DH-12 exhibits broad-spectrum antibacterial activity toward Gram-positive and Gram-negative pathogens. The 7.6-Mb draft genome sequence gives insight into the complete secondary metabolite production capacity and reveals genes putatively responsible for its antibacterial activity, as well as genes which enable the survival of the organism in an extreme arid environment.

Extreme drought stress shifts net facilitation to neutral interactions between shrubs and sub‐canopy plants in an arid desert

The stress gradient hypothesis (SGH) predicts that the importance or intensity of competition and facilitation will change inversely along abiotic stress gradients. It was originally postulated that increasing environmental stress can induce a monotonic increase in facilitation. However, more recent models predicted that the relationship between severity and interaction exhibits a hump‐shaped pattern, in which positive interactions prevail under moderate stress but decline at the extreme ends of stress gradients. In the present study, we conducted a field experiment along a temporal rainfall gradient for five consecutive years, in order to investigate interactions in a shrub‐herbaceous plant community at the southern edge of the Badain Jaran Desert, and, more specifically, investigated the effects of Calligonum mongolicum, a dominant shrub species, on both abiotic environmental variables and the performance of sub‐canopy plant species. We found that shrubs can improve sub‐canopy water regimes, soil properties, plant biomass, density, cover, and richness and, more importantly, that the positive effect of shrubs on sub‐canopy soil moisture during the summer diminishes as rainfall decreases, a pattern that partly explains the collapse of the positive interaction between shrubs and their understory plants. These results provide empirical evidence that the positive effect of shrubs on understory plant communities in extreme arid environments may decline and become neutral with increasing drought stress.

Analysis of urban heat in a corridor environment – The case of Doha, Qatar

Doha, Qatar is one of the arid coastal cities of the Gulf Cooperation Council (GCC) countries. Like similar cities, temperatures can vary widely throughout, with rapid and extensive development that has contributed to micro-climate changes. While numerous studies since the 1950s have assessed urban micro-climates, few have offered insights into urban corridor environments. This research is one of few projects to examine temperature records along two major roadways and identify factors that explain variation. The research uses vehicle-based air temperature traverses during late spring and summer 2016 using a Type T fine gauge thermocouple mounted in a white plastic tube and supported above the vehicle on the passenger-side window. The data were assessed in terms of four factors that may impact temperature along the corridors, including: distance from the coast, traffic volume, vegetation density, and building volume density from 50m up to 400m (in 50m intervals) from the centerline of the traverse. Results indicated that the two most critical variables that predict air temperature patterns along the corridors are the distance to the coast and the traffic volume. This knowledge can be incorporated into urban planning and design practice for extreme arid environments to maintain temperatures that reduce heat-related stress.

Standardization of DNA extraction and genetic diversity analysis of Haloxylon salicornicum: An underutilized species of extreme arid environment

Extraction of pure DNA is a prerequisite for DNA based molecular marker analysis. In present investigation we standardized DNA extraction protocol amenable to PCR. 5M NaCl was found to be effective for removal of polysaccharides which otherwise may hinder precipitation of pure DNA in Haloxylon salicornicum. DNA based markers RAPD and ISJ were used for population genetic analysis of Haloxylon salicornicum in present investigation. H. salicornicum is an under shrub, perennial plant of extreme arid environment and belongs to family Chenopodiaceae. It is a key stone and promising species of sandy soil and is a source of fuel, food additives and feed for livestocks in arid regions. Six geographical areas of Indian Thar Desert such as Bhadariya, Chandan, Jaisalmer, Sam, Hameer Nada and Nachana of Jaisalmer district were selected in present study. A total of 67 amplified products (32 RAPD and 35 ISJ) scored, exhibited 98.5% polymorphism. AMOVA revealed 79% variation within population and 21% variation among population. Similar pattern of distribution were observed in NJ tree construct and PCoA. The population genetics of H. salicornicum will be further useful for understanding breeding patterns, population history and effect of environmental factors on growth and development for prospects.

Do species' strategies and type of stress predict net positive effects in an arid ecosystem?

A proposed refinement to the stress-gradient hypothesis requires consideration of the strategies of the interacting species and the characteristics of the stress factors. While the strength and direction of these interactions can be predicted for different ecosystems, this idea remains largely untested in the field. We performed a manipulative field experiment complemented with a descriptive study to test the predictions in a natural setting that represents the extreme end of a precipitation gradient. There, wind driven desiccation and water availability are the main stressors (non-resource and resource-based stresses, respectively). We evaluated the interaction between the shrub and grasses that are dominant in the Patagonian steppe. The species had differences in morpho-functional traits and drought tolerance that fit into the C-S axis of Grime's strategies. We experimentally separated root zones to limit direct competition for soil moisture and reduce the resource-based stress on grasses. We also manipulated the distance to shrubs to evaluate non-resource stress amelioration by canopies (e.g., sun and wind) on grasses. Finally, we evaluated the distribution of naturally established C and S grasses in the neighborhood of C and S shrubs to infer process-pattern relationships. Our growth data coincide to a large degree to the predictions. We found positive effects on the growth of beneficiaries when stress was non-resource based and when strategies differed (i.e., Cshrub -Sgrass and Sshrub -Cgrass ). We also found strong negative effects when the abiotic stress was driven by water, particularly on C grasses. Additionally, shrubs only increased the survival of grasses when strategies differed (i.e., Cshrub -Sgrass and Sshrub -Cgrass ). Our manipulative and descriptive study supported previous results that showed that stress-tolerant species are important for the persistence of competitive species at high stress. While the applicability and generality of these predictions remains to be tested with more field experiments, some ecological factors, such as stress types and species traits, can explain much of the variation in how dominant shrubs and grasses interact in this extreme arid environment. Moreover, this framework could be extended to specifically test the importance of facilitation under different levels of stress.

Middle Pleistocene subsistence in the Azraq Oasis, Jordan: Protein residue and other proxies

Excavations at Shishan Marsh, a former desert oasis in Azraq, northeast Jordan, reveal a unique ecosystem and provide direct family-specific protein residue evidence of hominin adaptations in an increasingly arid environment approximately 250,000 years ago. Based on lithic, faunal, paleoenvironmental and protein residue data, we conclude that Late Pleistocene hominins were able to subsist in extreme arid environments through a reliance on surprisingly human-like adaptations including a broadened subsistence base, modified tool kit and strategies for predator avoidance and carcass protection.