Desert Shrub Species Research Articles

A whole-plant perspective of hydraulic strategy in temperate desert shrub species.

Desert shrubs play a crucial role in controlling desertification and promoting revegetation, but drought often hinders their growth. Investigating the hydraulic strategies of desert shrubs is important in order to understand their drought adaptation and predict future dynamics under climate change. In this study, we measured the hydraulic-related characteristics of roots, stems and leaves in 19 desert shrub species from northern China. We aimed to explore the hydraulic coordination and segmentation between different plant organs. The results were as follows: (i) specific root length was positively correlated with the water potential inducing a 50% loss in stem hydraulic conductivity (P50stem) and negatively correlated with stem hydraulic safety margin. This suggested that water uptake efficiency of the fine roots was traded off with stem embolism resistance and hydraulic safety. (ii) The water potential inducing a 50% loss in leaf hydraulic conductance was significantly less negative than P50stem, and fine root turgor loss point was significantly less negative than P50stem, indicating a hydraulic segmentation between the main stem and terminal organs. (iii) The most negative leaf turgor loss point indicated that leaf wilting occurred after substantial leaf and stem embolism. The high desiccation resistance of the leaves may serve as an important physiological mechanism to increase carbon gain in a relatively brief growth period. In summary, this study elucidated the hydraulic strategies employed by desert shrubs from a whole-plant perspective.

Characteristics, Relationships, and Anatomical Basis of Leaf Hydraulic Traits and Economic Traits in Temperate Desert Shrub Species.

Shrubs are a key component of desert ecosystems, playing a crucial role in controlling desertification and promoting revegetation, yet their growth is often impeded by drought. Leaf hydraulic traits and economic traits are both involved in the process of water exchange for carbon dioxide. Exploring the characteristics, relationships, and anatomical basis of these two suites of traits is crucial to understanding the mechanism of desert shrubs adapting to the desert arid environment. However, the relationship between these two sets of traits currently remains ambiguous. This study explored the leaf hydraulic, economic, and anatomical traits of 19 desert shrub species. The key findings include the following: Relatively larger LT values and smaller SLA values were observed in desert shrubs, aligning with the "slow strategy" in the leaf economics spectrum. The relatively high P50leaf, low HSMleaf, negative TLPleaf, and positive HSMtlp values indicated that severe embolism occurs in the leaves during the dry season, while most species were able to maintain normal leaf expansion. This implies a "tolerance" leaf hydraulic strategy in response to arid stress. No significant relationship was observed between P50leaf and Kmax, indicating the absence of a trade-off between hydraulic efficiency and embolism resistance. Certain coupling relationships were observed between leaf hydraulic traits and economic traits, both of which were closely tied to anatomical structures. Out of all of the leaf traits, LT was the central trait of the leaf traits network. The positive correlation between C content and WPleaf and HSMleaf, as well as the positive correlation between N content and HSMtlp, suggested that the cost of leaf construction was synergistic with hydraulic safety. The negative correlation between SLA, P content, GCL, and SAI suggested a functional synergistic relationship between water use efficiency and gas exchange rate. In summary, this research revealed that the coupling relationship between leaf hydraulic traits and economic traits was one of the important physiological and ecological mechanisms of desert shrubs for adapting to desert habitats.

Rapid recovery of desert shrubs is attributed to imbalance of water supply to demand after disturbance in Northwest China

BackgroundDisturbance is a key driver of changes in terrestrial ecosystems, especially in water limited regions. In the desert ecosystem of Northwest China, shrubs are often foraged by camels and this causes the shrubs lost their aboveground tissues. Although the aboveground tissue could recover after the disturbance, the mechanisms of resprouts’ recovery after the disturbance are still poorly understood. We investigated the morphological and physiological characteristics and root water uptake sources of resprouts and non-disturbed seedlings of four desert shrub species that were often foraged by camels.ResultsThe results showed that the resprouts grew rapidly after the removal of aboveground tissue. The height and aboveground biomass of resprouts reached the level of 5-year-old seedlings following a growing season. Compared to un-disturbed seedlings, higher leaf water potential, leaf hydraulic conductance and photosynthesis rate were observed in resprouts, indicating that resprouts grew rapidly after disturbance. Furthermore, we found that the root water uptake source did not change after disturbance. This indicated that the roots of resprouts kept intact water uptake capacity after disturbance, which could keep supplying sufficient water to the aboveground tissue. Due to the removal of aboveground tissue of the resprouts, the water demand of aboveground tissue decreased, which induced an imbalance of water supply from roots to demand of aboveground tissues of resprouts. This explained the improved physiological performance and rapid recovery of resprouts after disturbance.ConclusionsThe imbalance of water supply to demand contributes to the rapid recovery of desert shrubs after disturbance. The findings provide insight into the eco-physiological mechanism for the maintenance of desert ecosystems that are facing disturbance.

Ephedra shrubs facilitate local arthropod communities in the Andean Puna: Implications for conservation and habitat restoration

In high-altitude deserts, the vegetation is spatially structured as a mosaic of patches with vegetation and interpatches of bare soil. Shrub patches create microhabitats that facilitate the persistence of other organisms by ameliorating climate extremes and increasing soil nutrients and moisture. Although this facilitative effect has been studied mainly on shrub understorey plants, the positive influence of desert shrubs may extend to the local arthropod community. In this study, we examined the hypothesis that plant facilitation by the desert shrub species Ephedra multiflora and E. breana positively influences the epigeal arthropod communities of the Andean Puna. We found that arthropod abundance, richness and diversity were all higher on Ephedra shrub microsites relative to paired open microsites. The harsh environmental conditions prevailing in the Puna ecosystems and the protection and resources provided by plants could jointly explain the positive influence of Ephedra shrubs over the arthropod community. The growth of tourism and the boom for lithium, as well as the increasing drought expected for the region under climate change scenarios, strengthens the importance of conserving shrub cover in these ecosystems to sustain biodiversity and ecosystem functioning. Our results are also relevant for restoration projects that consider the whole biological community, where using Ephedra as foundation shrubs to support desert endemics could be a strategy for land restoration.

Tensile properties of six desert shrub species in Hobq Desert, China

Abstract Desert shrubs are often planted to control wind erosion, land desertification, and desert expansion. Their motions of bending and vibration can absorb and disperse kinetic energy of wind, so as to protect the erodible surfaces close-by. According to continuum mechanics, the quantification of mechanical properties of shrubs is critical to understand their dynamic behaviors. In this study, the conventional tensile tests of six dominant desert shrub species’ stems mainly sampled in the Hobq Desert of China are performed. It is found that the tensile strength of Tamarix ramosissima and Hedysarum scoparium are larger than others, whereas Caragana korshinskii and Hippophae rhamnoides are more flexible. And then, it is theoretically and experimentally proved that the tensile strength and Young’s modulus of these desert shrubs both decrease with the increase of diameter.

The Phylogeny ofErrazurizia(Fabaceae: Amorpheae) and Description of the New Monotypic GenusPictarena

Abstract—Errazurizia(Fabaceae) is a genus comprised of four species of New World desert shrubs with an ambiguous evolutionary history. Prior studies determined the North American species ofErrazuriziawere polyphyletic and the relationship ofE. rotundatawith other genera in the tribe Amorpheae remained undetermined. The sole South American species, which is also the type species, has never been included in a molecular study. We inferred the phylogenetic relationships ofErrazuriziaand six closely related genera using data from the cpDNA genome and nrDNA cistron from reference guided assemblies. Maximum likelihood and Bayesian analyses found two of the North American and the South American species were a monophyletic group, but thatE. rotundatawas sister to the monotypic genusParryella. Gland and pollen surface characters confirm the close relationship betweenP. filifoliaandE. rotundata. Cytonuclear discordance yielded partially incongruent tree topologies, and while the cpDNA phylogeny indicated a monophyleticAmorphawas sister to theE. rotundataandP. filifoliaclade, the nrDNA cistron phylogeny recovered a paraphyleticAmorpha, withA. californicasister to theE. rotundataandP. filifoliaclade. Molecular and morphological evidence support the elevation ofE. rotundatato its own monotypic genus,Pictarena. The new genusPictarenais defined by subsessile, suborbicular leaflets, mammiform leaflet glands, spicate inflorescences, and flowers with either all petals absent or rarely with a banner petal. ElevatingE. rotundatatoPictarenaresolves the confusing classification of the species, an imperiled endemic known only from four localities in northern Arizona and lends support for continued conservation.

Temporal heterogeneity in photosystem II photochemistry in Artemisia ordosica under a fluctuating desert environment.

Acclimation strategies in xerophytic plants to stressed environmental conditions vary with temporal scales. Our understanding of environmentally-induced variation in photosystem II (PSII) processes as a function of temporal scales is limited, as most studies have thus far been based on short-term, laboratory-controlled experiments. In a study of PSII processes, we acquired near-continuous, field-based measurements of PSII-energy partitioning in a dominant desert-shrub species, namely Artemisia ordosica, over a six-year period from 2012-2017. Continuous-wavelet transformation (CWT) and wavelet coherence analyses (WTC) were employed to examine the role of environmental variables in controlling the variation in the three main PSII-energy allocation pathways, i.e., photochemical efficiency and regulated and non-regulated thermal dissipation, i.e., Φ PSII, Φ NPQ, and Φ NO, respectively, across a time-frequency domain from hours to years. Convergent cross mapping (CCM) was subsequently used to isolate cause-and-effect interactions in PSII-energy partitioning response. The CWT method revealed that the three PSII-energy allocation pathways all had distinct daily periodicities, oscillating abruptly at intermediate timescales from days to weeks. On a diurnal scale, WTC revealed that all three pathways were influenced by photosynthetically active radiation (PAR), air temperature (T a), and vapor pressure deficit (VPD). By comparing associated time lags for the three forms of energy partitioning at diurnal scales, revealed that the sensitivity of response was more acutely influenced by PAR, declining thereafter with the other environmental variables, such that the order of influence was greatest for T a, followed by VPD, and then soil water content (SWC). PSII-energy partitioning on a seasonal scale, in contrast, displayed greater variability among the different environmental variables, e.g., Φ PSII and Φ NO being more predisposed to changes in T a, and Φ NPQ to changes in VPD. CCM confirmed the causal relationship between pairings of PSII-energy allocation pathways, according to shrub phenology. A. ordosica is shown to have an innate ability to (i) repair damaged PSII-photochemical apparatus (maximum quantum yield of PSII photochemistry, with F v/F m > 0.78), and (ii) acclimatize to excessive PAR, dry-air conditions, and prolonged drought. A. ordosica is relatively sensitive to extreme temperature and exhibits photoinhibition.

Hydraulic trade-off and coordination strategies mediated by leaf functional traits of desert shrubs.

Desert shrubs play important roles in desertification control and vegetation restoration, which are particularly affected by droughts caused by climate change. However, the hydraulic strategies associated with hydraulic functional traits of desert shrubs remain unclear. Here, eight desert shrub species with different life forms and morphologies were selected for a common garden experiment at the southeast edge of the Tengger Desert in northern China to study the hydraulic strategies mediated by leaf hydraulic functional traits. Diurnal leaf water potential change, leaf hydraulic efficiency and safety, hydraulic safety margin, hydraulic capacitance, and water potential and relative water content at the turgor loss point were observed to significantly differ among species, suggesting that leaf hydraulic functional traits were strongly associated with species even when living in the same environment. Additionally, shrubs with greater leaf hydraulic efficiency had lower midday leaf water potential and leaf hydraulic safety, suggesting that leaf hydraulic efficiency had a strong trade-off with hydraulic safety and minimum leaf water potential, whereas there was also a coordination between leaf hydraulic safety and the leaf minimal water potential. Moreover, shrubs with higher leaf hydraulic capacitance had greater hydraulic safety margins, indicating coordination between leaf hydraulic capacitance and hydraulic safety margin. Overall, this study indicated that minimal daily leaf water potential, as an easily measured parameter, may be used preliminarily to predict leaf hydraulic conductivity and the resistance to embolism of desert shrubs, providing critical insights into hydraulic trade-off and coordination strategies for native shrubs as priority species in desert vegetation restoration and reconstruction.

Elevated physiological plasticity in xerophytic-deciduous shrubs as demonstrated in their variable maximum carboxylation rate

A plant’s photosynthetic capacity is typically reflected by its maximum carboxylation rate (Vcmax), which varies with time and plant functional type. In what way Vcmax in a xerophytic-shrub species changes in response to variation in its desert habitat remains poorly understood. In this study, Vcmax was continuously monitored in a common desert-shrub species, Artemisia ordosica, with a portable photosynthetic system over seven growing seasons from 2013 to 2019. Vcmax’s annual and interannual variations were subsequently assessed in conjunction with a meta-analysis carried out as a separate study. Vcmax in the species did not show a distinct seasonal pattern over the seven growing seasons. It rather displayed extensive year-to-year variations in the seasonal peak and its associated timing, exhibiting greater plasticity as compared with other plant functional types. Seasonal variation in Vcmax was primarily controlled by leaf nitrogen content per area (Narea) in a positive, linear manner, with the relationship’s sensitivity varying as a function of soil volumetric water content (VWC). Interannual variation in Vcmax was regulated by annual mean VWC, also in a positive, linear manner. The effect of Narea on Vcmax was amplified during the leaf-expanding stage of the shrub. Given severe drought anticipated under continued climate change, xerophytic shrubs are believed sufficiently malleable to acclimatize to ongoing environmental change in deserts.

Fragmented cambia in roots of Coleogyne ramosissima

Axis splits are common for desert shrub species. Coleogyne ramosissima, a regionally important shrub species, grows along a transect from the cooler high deserts of Utah and Colorado to the warmer Mojave Desert, between 1200 and 1700 m elevation. The purpose of this study is to document tissue anomalies from transition zones to individual roots of C. ramosissima. Plants were obtained from La Verkin and Ivins, Utah. During secondary growth, axis splits, lobes and fragmented cambia occurred in roots larger than 12 mm in diameter. Lobes occurred in all root samples. The presence of lobes indicates that cambia in roots of in C. ramosissima were fragile. Axis splits and lobes are created fragmented cambia that separated from the original vascular cambium. These fragmented cambia produced growth centers that gave rise to new xylem cells, lead to further lobes and the origination independent roots. The current study hypothesizes that the production of the large number of roots derived from fragmented cambia. The large number of roots provided near the transition zone may provide for hydraulic reductancy to guard against plant death due to cavitations to individual roots caused by moisture deprivations. Overall, roots of C. ramosissima have many secondary xylem irregularities. The overall impact of these root irregularities are unknown, despite the fact that individual plants can live for many decades. To our knowledge, this is first study to document the process for the development of fragmented cambia in tandem with axis splitting and eccentric growth of roots in a shrub species.

Water Supply Increases N Acquisition and N Resorption from Old Branches in the Leafless Shrub Calligonum caput-medusae at the Taklimakan Desert Margin

Irrigation is the main strategy deployed to improve vegetation establishment, but the effects of increasing water availability on N use strategies in desert shrub species have received little attention. Pot experiments with drought-tolerant shrub Calligonum caput-medusae supplied with water at five field capacities in the range of 30–85% were conducted using local soil at the southern margin of the Taklimakan Desert. We examined the changes in plant biomass, soil N status, and plant N traits, and addressed the relationships between them in four- and seven-month-old saplings and mature shrubs after 28 months. Results showed that the growth of C. caput-medusae was highly responsive to increased soil moisture supply, and strongly depleted the soil available inorganic N pools from 16.7 mg kg−1 to an average of 1.9 mg kg−1, although the total soil N pool increased in all treatments. Enhancement of biomass production by increasing water supply was closely linked to increasing total plant N pool, N use efficiency (NUE), N resorption efficiency (NRE), and proficiency (NRP) in four-month saplings, but that to total plant N pool, NRE, and NRP after 28 months. The well-watered plants had lower N concentrations in senesced branches compared to their counterparts experiencing the two lowest water inputs. The mature shrubs had higher NRE and NRP than saplings and the world mean levels, suggesting a higher N conservation. Structural equation models showed that NRE was largely controlled by senesced branch N concentrations, and indirectly affected by water supply, whereas NRP was mainly determined by water supply. Our results indicated that increasing water availability increased the total N uptake and N resorption from old branches to satisfy the N requirement of C. caput-medusae. The findings lay important groundwork for vegetation establishment in desert ecosystems.

Grassification and Fast-Evolving Fire Connectivity and Risk in the Sonoran Desert, United States

In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km2and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro (Carnegia gigantea), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.

Antioxidant, antibacterial, and anticancer properties of Haloxylon salicornicum extracted by microwave-assisted extraction

Background The wild plant Haloxylon salicornicum is a desert shrub species that is present in North America and some Middle Eastern countries and is used as a source of vegetation. The reports demonstrated the significance of its bioactive compounds by extracting them with different solvents, such as hexane, methanol, and water fractions using standard extraction methods and evaluating their biological functions as antioxidants, antibacterial, and anti-inflammatory. Objective To analyze the chemical compositions of H. salicornicum extracted by microwave-assisted extraction (MAE) using the antioxidant, antibacterial, and anticancer activities. Materials and methods In this research, ethanol solvent and simple MAE with gas chromatography–mass spectrometry analysis were used to classify the chemical compositions, and the ethanol extract was evaluated for antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl process, antibacterial activity, anticancer activity using liver cancer cells (HCAM) through apoptosis (AO/EB staining), and flow cytometry analysis for apoptosis and cell cycle arrest ratios. Results and conclusion The gas chromatography–mass spectrometry study revealed ∼33 compounds. H. salicornicum antioxidant activity was IC50=4.120 μg/ml as compared with vitamin C IC50=4.898 μg/ml as a positive regulation. Antibacterial activity of H. salicornicum extract showed a significant inhibition toward Staphylococcus aureus and Escherichia coli. H. salicornicum cytotoxicity against liver cancer cells (HCAM) at 1000 μg/ml showed a significant inhibition ratio (42.35%). The AO/EB staining revealed DNA damage and apoptosis in the morphology of the cells. Early and late apoptosis were established, and the cell cycle was stopped in G1 phase. Our findings indicate that H. salicornicum is a valuable medicinal plant with biological applications. As a result, future research will focus on isolating the responsible natural molecules using MAE and mechanic studies.

Effects of grazing disturbance of spatial distribution pattern and interspecies relationship of two desert shrubs

Grazing significantly affects the distribution, growth, and productivity of shrubs. In this study, we evaluated the effects of grazing disturbance on the spatial distribution patterns and interspecific relationships of two desert shrubs, Ammopiptanthus mongolicus and Sarcozygium xanthoxylon. Three types of grazing conditions were considered, including enclosed area (EA), seasonal rotational grazing area (SRGA), and grazing area (GA) (100 m × 100 m), in the West Ordos Nature Reserve of Inner Mongolia, China. The results showed that A. mongolicus and S. xanthoxylon populations were uniformly distributed at a small scale, and the distribution in EA and SRGA became gradually random. In GA, A. mongolicus population showed aggregated distribution but S. xanthoxylon population showed random distribution at a small scale. Moreover, both A. mongolicus and S. xanthoxylon populations at the 5–7 m scale showed random distribution. At the small and intermediate scales, the two species showed positive interspecific relationships of GA. However, no interspecific relationship was noted between the two species in EA and SRGA. A significant positive relationship (P < 0.01) was noted between the two species at 2–9 m and a negative relationship (P < 0.01) at 13–17 m scales in GA. Positive relationship (P < 0.01) was noted between the two species at 6–13 m scales and a significant negative relationship (P < 0.01) at 14–24 m scales in SRGA. The two species of desert shrubs showed positive interspecific relationships at the small scale, and they showed negative relationships as the interspecific competition intensified in the presence of grazing disturbance. When the grazing intensity exceeds a certain threshold, the interspecific relationships become weak. Therefore, moderate grazing would facilitate interspecific competition and species succession, whereas excessive grazing would disrupt natural competition causing desertification ultimately.

Interannual variation in sap flow response in three xeric shrub species to periodic drought

Extreme seasonal droughts frequently occur in semiarid and arid areas of the world. They can exert a profound influence on the physiological state of desert plants. Short-term rainfall and long-term water shortages in the Mu Us Desert have differentiated the role of individual species with their distinct ability to resist and recover from drought. This study explores how the scale of rainfall events affects interannual variation in sap flow in three dominant desert-shrub species [i.e., Salix psammophila (SP), Artemisia ordosica (AO), and Hedysarum mongolicum (HM)], and whether the associated changes in soil-water dynamics helped to modify sap flow. As a result, interannual variation in sap flow (Js) was mostly driven by precipitation (PPT), Volumetric soil water content (VWC), and leaf area index (LAI), with their individual influences varying as a function of plant phenophases. The species acclimated to long-term summer drought (> 30 days, i.e., no rain over a 30-day period or longer) by reducing stomatal conductance in the three species by 66.5, 59.5, and 43.5%, respectively, suggesting a physiological adjustment in water conservation in response to drought. Average summer drought (June–July) reduced Js in the three species by 55.5 (in SP), 42 (AO), and 28.5% (HM), more than spring drought (May–June) at 28% in SP and 9.5% in AO. Among those species, HM exhibited the least sensitivity and the highest overall resistance and resilience to drought. The relationship between Js and VWC was modulated by the effect of PPT. Our findings provide compelling evidence that HM is seen to be better suited to future climatic warming, as the species may be capable of accessing deep groundwater reserves replenished by large PPT pulses (5–10 mm), in sustaining its physiological activity over longer periods. These results could help formulate a selection process in determining which shrub species to plant in the sustainable management of desert ecosystems.

Dynamics of chlorophyll fluorescence parameters under drought condition for three desert shrub species

Dynamics of chlorophyll fluorescence parameters under drought condition for three desert shrub species

HaASR1 gene cloned from a desert shrub, Haloxylon ammodendron, confers drought tolerance in transgenic Arabidopsis thaliana

Abiotic stresses pose adverse impact on plant growth and development and exploring the stress tolerance genes from dominant species is still urgent. The desert shrub, Haloxylon ammodendron, a C4 and succulent xero-halophyte species, has great drought and salt tolerance. Here, we reported the isolation and functions analysis of HaASR1 (abscisic acid, stress, and ripening) from H. ammodendron. HaASR1 interacts with HaPrxQ and HaBADH and may function in preventing PrxQ and BADH from denaturation in plants under drought stress. Overexpression of HaASR1 reduces the sensitivity of Arabidopsis plants to exogenous ABA and decreases the endogenous ABA level through down-regulating ABA biosynthesis genes under drought stress, which making the plants display less inhibition of shoot growth and enhanced drought tolerance. Overexpression of HaASR1 significantly enhances photosynthetic capacity of Arabidopsis plants under drought stress by reducing H2O2 accumulation through up-regulating AtCAT2, AtAPX1 and AtPrxQ and maintaining relatively integrity of chloroplasts. Overexpression of HaASR1 also significantly improves water-retaining ability. Taken together, we propose that HaASR1 plays critical roles in plant drought stress adaptation by making the plants partially defective in ABA signaling and participating in drought tolerance regulation through nonstomatal pathways, enhancing ROS-scavenging ability and water-retaining ability, which is different from the functions of previously reported ASR genes from other plant species. This research also reveals that HaASR1 gene from the desert shrub, Haloxylon ammodendron, has potential application values in improving abiotic stresses of other plant species by genetic engineering.

A multiple-temporal scale analysis of biophysical control of sap flow in Salix psammophila growing in a semiarid shrubland ecosystem of northwest China

With increased usage of plantations in the control of desertification and water shortages in the Mu Us Desert, water use by desert-dwelling shrubs, such as Salix psammophila has become a serious topic in the management of ecologically-important plants. However, our understanding of the unevenness in water consumption across multiple timescales is still limited for many desert shrub species. Interannual variation in water consumption and its environmental controls are scarcely documented. To attend to this deficit, sap-flow measurements were continuously collected in a region of the Mu Us Desert from 2012 to 2017 to investigate the biophysical controls on sap-flow and water-consumption dynamics in S. psammophila. Diurnally, sap flow per leaf area (Js) was shown to be controlled by shortwave radiation (Rs), peaking in summer about two hours ahead of Rs, and about three to five hours ahead of air temperature (Ta) and vapor pressure deficit (VPD), respectively. Seasonal patterns in Js varied with precipitation and subsequent changes in soil volumetric water content (VWC). Soil volumetric water content was observed to modify the influence of the other environmental variables on Js (i.e., Ta, Rs, and VPD), with Js being more responsive to the site variables, when VWC > 0.09 m3 m−3, and less responsive, when <0.09 m3 m−3. Furthermore, Ta and VPD were responsible for most of the variation observed in Js during the leaf-expansion stage. Meanwhile, VWC and leaf area index (LAI) became more important during the leaf-expanded stage, and Rs during the leaf-defoliation stage. Interannually, LAI and meteoric water input to soils was responsible for most of the variation observed in Js. Reduction in Js sensitivity to biophysical factors under water-stressed conditions across temporal scales and the hysteresis effect point to species acclimatization to dry soil conditions. This study has the potential to help: (i) clarify the temporal dynamics in Js for S. psammophila across multiple timescales; and (ii) contribute to the sustainable management and control of desertification in the region under future climate change and projected increases in severe drought.

N, P and K stoichiometry and resorption efficiency of nine dominant shrub species in the deserts of Xinjiang, China

AbstractPlant nutrient stoichiometry and resorption efficiency are important functional traits related to plant nutrient status and biogeochemical cycling. Such traits are not well documented for desert shrubs. We studied how the stoichiometry and resorption efficiency of nitrogen (N), phosphorus (P) and potassium (K) varied among nine dominant desert shrub species through systematically investigating their concentrations in green and senesced leaves (or assimilation branches) of desert plants at 24 sites across Xinjiang, China. We hypothesized that desert shrubs should have low leaf N and P but high leaf K concentrations; and have high leaf N and P but low K resorption efficiency, given the low N and P but high K availability in this arid region. These shrubs had a mean leaf N concentration of 18.9 mg g−1, and lower leaf P but higher leaf K concentration (1.2 and 17.0 mg g−1, respectively) than desert plants at national and global levels. The mean (± SE) resorption efficiencies of leaf N, P and K in the desert shrubs were 51.0 ± 2.4%, 54.9 ± 2.0% and 46.3 ± 3.5%, respectively, lower than in the woody plants globally. The higher green‐leaf N:P (17.2 ± 0.8) and K:P (15.3 ± 1.0) relative to the corresponding critical ratios, and the higher P resorption efficiency (54.9%) relative to N (51.0%) and K (46.3%) resorption efficiency, suggested that the dominant desert shrubs in Xinjiang generally suffer from P (or both P and N) deficiency. Additionally, our results showed little evidence of higher resorption relative to their counterparts in most other ecosystems.

Effects of sand burial disturbance on establishment of three desert shrub species in the margin of oasis in northwestern China

AbstractSand burial is an important environmental disturbance which determines seed germination, plant establishment, and plant fitness in sand dune ecosystems. But the critical importance of sand burial for seedling establishment of desert shrubs is rarely explored. We investigated the effects of sand burial at different regimes (0, 1, 2, 3, 4 and 5 cm, the main depths of soil seed bank) on the seedling emergence, growth and survival rate of three dominant desert shrubs (Calligonum mongolicum, Nitraria sphaerocarpa and Haloxylon ammodendron) for ecosystem restoration in sand dunes of northwestern China. The results indicated that shallow burial improved the seedling emergence and the subsequent seedling survival rate for the initial establishment period. The optimal burial depths were 2, 4 and 5 cm for H. ammodendron, N. sphaerocarpa and C. mongolicum, respectively; this difference in optimal burial depth may account for observed decreased regeneration of H. ammodendron as compared to the other two species. Beyond the optimal depths, we found that sand burial prevented seedling emergence for H. ammodendron and N. sphaerocarpa. Only a small proportion of seedlings can emerged from deep burial depth by increasing seedling biomass allocation to blow‐ground stem. However, after emergence deep sand burial stimulated growth rate of emerged seedlings, increased the seedling vigor and promoted the seedling establishment. We suggest that sand burial could affect plant regeneration and potentially leaded to shift in species composition. Choice of suitable species for ecosystem restoration needs to account for its ability in term of seed germination and plant establishment/regeneration to adapt to disturbance of sand burial.