Haloxylon Ammodendron Research Articles

Allelopathic potential of Haloxylon ammodendron against Syntrichia caninervis and comparative analysis of soil microbial differences between inside and outside of the bare patches under its canopies

In the Gurbantunggut Desert, Haloxylon ammodendron and Syntrichia caninervis are often found at the base of the dunes. In these areas, bare patches usually form under H. ammodendron canopy, but not under other shrub canopies. We compared the soil chemical properties under H. ammodendron canopy inside the bare patches (UC11In this paper, the bare patch under H. ammodendron canopy is also referred to as “inside the bare patch” or UC.) and of soil under moss crust outside of H. ammodendron canopy bare patches (UM22The area under the moss crust around H. ammodendron is also referred to as “outside the bare patch” or UM.), and used untargeted metabolomics to analyze soil metabolites and metagenomic sequencing to characterize the soil microbial structure. The results showed that a total of 951 metabolites were identified in the soil samples, and 518 differential metabolites were observed. The content of amide compounds, such as oleamide, in UC soil was significantly higher than that in UM soil, suggesting that the amide compounds may be the main allelochemicals inhibiting S. caninervis. Soil chemical properties and soil metabolites were quite different between inside and outside of the bare patches, and these differences affected soil microorganisms, resulting in significantly lower species richness in UC than in UM, but there were no significant differences in microbial community function. Fungi were minimally affected by the environment, archaea were significantly affected by NO3−-N (P < 0.01), bacteria were significantly affected by TN (P < 0.01), and none of the three communities correlated significantly with the major differential metabolites. Therefore, it can be concluded that the amide compounds secreted by H. ammodendron roots create a concentration gradient under its canopy, with high concentrations inhibiting S. caninervis, causing changes in soil chemical factors inside and outside of the bare patches and inhibiting microbial richness inside the bare patches. The results provide important theoretical references for the further study of desert communities in terms of interspecific relationships and species distribution patterns, and are of great significance in promoting comprehensive desertification management and building desert ecological security systems.

Genetic Diversity and Population Structure of Haloxylon Aphyllum in Iran by ISSR Markers

Haloxylon aphyllum is a significant species adapted to salinity conditions and plays an important role in stabilising soil, providing forage, and serving as a source of firewood for residents. In this study, the genetic diversity of four populations of H. aphyllum in Iran was examined using four primers to assess genetic diversity, which produced a total of 41 bands. The AMOVA test showed that the studied populations differed in their genetic content. Specifically, 46% of genetic variability occurred within populations, while 54% arose between populations, indicating a high degree of genetic variation among H. aphyllum populations. The Mantel test presented a significant correlation between genetic distance and geographic distance. Additionally, the STRUCTURE analysis presented comprehensive information on the genetic structure of the studied H. aphyllum populations. The presence of genetic diversity and heterozygosity among H. aphyllum populations suggests local adaptation among populations, which may be due to the heterogeneity of environmental factors such as soil moisture and nutrients that create genetic heterogeneity.

Identification and transcriptome analysis of the R2R3-MYB gene family in Haloxylon ammodendron

The MYB transcription factor family is widespread in plants and plays an important role in plant growth and development as well as in plant responses to stress. The MYB transcription factor family has been identified in a variety of organisms; however, it has not been identified and analysed in the desert plant Haloxylon ammodendron. In this study, R2R3-MYB genes were identified and analysed using a bioinformatic approach. A total of 78 R2R3-MYB genes were identified and named according to their position on the chromosome. The R2R3-MYB genes were unevenly distributed on nine chromosomes. Phylogenetic analysis showed that the HaMYB genes were all divided into 31 subfamilies. Covariance analysis revealed the presence of three pairs of fragmentary duplicated genes in H. ammodendron (HaMYB54 and HaMYB17, HaMYB44 and HaMYB36, HaMYB42 and HaMYB27). Gene structure and conserved structural domain analysis revealed different subgroups with different orders of magnitude of variation in gene structures and conserved structural domains. Analysis of cis-elements showed that the cis-acting elements of HaMYBs were mainly associated with hormone and abiotic stress responses. Real-time quantitative PCR was used to detect the expression levels of HaR2R3-MYB genes, and six HaR2R3-MYB genes were found to respond to salt stress and six HaR2R3-MYB genes to drought stress, with HaMYB22 and HaMYB27 showing upregulated expression under both stresses. Transcriptome analysis showed that HaMYB63 was significantly differentially expressed in the assimilated branches of H. ammodendron, and the subcellular localization of this protein showed that it was located in the nucleus and had transcriptional self-activating activity. These results provide a theoretical basis for further studies on the functions of the R2R3-MYB gene family and the molecular mechanisms of resistance in H. ammodendron.

Soil Bacterial Community Structure and Physicochemical Influencing Factors of Artificial Haloxylon ammodendron Forest in the Sand Blocking and Fixing Belt of Minqin, China

Microbial activity plays a crucial role in upholding the functional stability of vegetation–soil ecosystems. Nevertheless, there exists a paucity of studies concerning the impact of sand-fixing vegetation (Haloxylon ammodendron) on the structure and functional attributes of soil microbial communities. We employed Illumina high-throughput sequencing and PICRUSt2 functional prediction technology to investigate the characteristics of soil bacterial community structure, diversity, and metabolic functions in an artificial H. ammodendron forest, and RDA analysis and the Mantel test were used to reveal the main environmental factors affecting the structure and ecological functions of soil bacterial communities. The findings revealed a significant increase in the principal nutrient contents (organic matter, total nitrogen, total phosphorus) in the H. ammodendron forest soil compared to the mobile dune soil, while a reduction of 17.17% in the surface soil water content was observed. The H. ammodendron forest exhibited a significant enhancement in the diversity and richness index of soil bacteria. Specifically, Actinobacteria (24.94% ± 11.85%), Proteobacteria (29.99% ± 11.56%), and Chloroflexi (11.14% ± 4.55%) emerged as the dominant bacterial phyla, with Actinobacteria displaying significantly higher abundance compared to the mobile dune soil. PICRUSt2 analyses revealed that the predominant secondary metabolic functions of soil bacteria were carbohydrate metabolism, amino acid metabolism, and the metabolism of cofactors and vitamins. Additionally, the tertiary metabolic pathways exhibited greater activity in relation to enzyme function, nucleotide metabolism, energy metabolism, and antibiotics. The RDA results demonstrated that SOM, AK, and pH collectively accounted for 82.4% of the cumulative contribution, significantly influencing the bacterial community. Moreover, the Mantel test revealed that the metabolic function of soil bacteria primarily relied on five environmental factors, namely SOM, TN, AK, pH, and EC. This study significantly advances our understanding of the structural and functional changes in soil bacterial communities during the reclamation of sandy land through the establishment of artificial H. ammodendron forests.

Simulation of the soil water-carrying capacity of Haloxylon ammodendron plantations in the Alxa Desert, China: Implications for afforestation

In recent years, China has achieved remarkable results in curbing desertification through afforestation. However, the dry soil layer resulting from the long-term water consumption of overloaded perennial plants seriously threatens the sustainability of afforestation, and quantifying the maximum vegetation carrying capacity under certain soil moisture conditions is crucial to the sustainability of afforestation in arid areas. Therefore, we aimed to simulate soil water in Haloxylon ammodendron plantations at different growth stages using the simultaneous heat and water transfer (SHAW) model to determine the vegetation carrying capacity threshold. Field-measured soil and vegetation data for 2021 were used to calibrate the SHAW model. Good consistency in soil water content (SWC) was observed between measurements and simulations in the calibration and validation phases of the model, with considerable linear correlation and low prediction error values. Therefore, the soil water dynamics of H. ammodendron plantations in the study area could be accurately predicted using the SHAW model. The simulation results show that, with increasing forest age, the SWC at 0–400 cm gradually decreases and a dry soil layer starts to form when the forest age reaches 11 years. The dry layer thickness reaches 120 cm by 22 years, thus the optimal growth age of artificial H. ammodendron plantations in the study area should not exceed 22 years, and the maximum biomass soil water carrying capacity of vegetation is 1,650 kg/hm2. A vegetation carrying capacity threshold can be determined in this study for the sustainable management of future afforestation activities.

Evaluating the Stand Structure, Carbon Sequestration, Oxygen Release Function, and Carbon Sink Value of Three Artificial Shrubs alongside the Tarim Desert Highway

Currently, the ecological problems caused by the greenhouse effect are growing more serious, and implementing carbon sequestration methods is an effective way to address them. Arid and semi-arid desert areas have tremendous potential as carbon sinks, and artificial forests in these areas play an important role in absorbing and sequestering carbon dioxide. This study selected three main species of artificial protective trees along the Tarim Desert Highway—Haloxylon ammodendron (C.A.Mey.) Bunge, Calligonum mongolicum Turcz. and Tamarix chinensis Lour.—and evaluated them for their carbon sequestration, oxygen release capacity, and economic benefits using Pn (net photosynthetic rate) and biomass methods. The results showed that the average daily Pn value and carbon sequestration and oxygen release per unit leaf area of T. chinensis were significantly higher than those of H. ammodendron and C. mongolicum (p &lt; 0.05). The total carbon storage of the three shelterbelts was 15.41 × 104 t, and the carbon storage of H. ammodendron was significantly higher than that of C. mongolicum and T. chinensis (p &lt; 0.05). According to the net photosynthetic rate method, the annual carbon sequestration and oxygen release of the shelter forest is 6.13 × 104 t a−1, and the transaction price is CNY 13.73 million a−1. The total amount of carbon sequestration and oxygen release of the shelter forest obtained via the biomass method is 97.61 × 104 t, and the transaction price is CNY 218.77 million. This study conducted research on the carbon sequestration capacity of protective forests along the Tarim Desert Highway located in an extremely arid region. It highlights the significant contribution of these protective forests in terms of carbon storage, playing a crucial role in promoting ecological restoration and sustainable development in arid areas. Additionally, this study provides a scientific basis for estimating carbon storage and promoting the sustainable management of artificial forests in arid desert regions.

Different Physiological Responses to Continuous Drought between Seedlings and Younger Individuals of Haloxylon ammodendron.

Drought is an important environmental factor that influences physiological processes in plants; however, few studies have examined the physiological mechanisms underlying plants' responses to continuous drought. In this study, the seedlings and younger individuals of Haloxylon ammodendron were experimentally planted in the southern part of the Gurbantunggut Desert. We measured their photosynthetic traits, functional traits and non-structural carbohydrate contents (NSCs) in order to assess the effects of continuous drought (at 15-day and 30-day drought points) on the plants' physiological responses. The results showed that at the 15-day (15 d) drought point, the leaf light-saturated net photosynthetic rate (An) values of both the seedlings and the younger individuals were decreased (by -68.9% and -45.2%, respectively). The intrinsic water use efficiency (iWUE) of the seedlings was significantly lower than that of the control group (-52.2%), but there was no diffenrence of iWUE observed in younger individuals. At the 30-day (30 d) drought point, a decrease in the An (-129.8%) of the seedlings was induced via biochemical inhibition, with a lower potential maximum photochemical rate (Fv/Fm, 0.42) compared with the control group, while a decrease in the An (-52.3%) of the younger individuals was induced due to lower stomatal conductance (gs, -50.5%). Our results indicated that prolonged drought induced a greater risk of seedling mortality as the relatively limited ability of stomatal regulation may increase the possibility of massive embolism, resulting in hydraulic failure.

Survival of experimentally buried large, winged seeds from open sandy habitats defies the established theory of relatedness between seed size, shape, and longevity

Accumulated evidence indicates that species with small, rounded seeds predominantly maintain a persistent soil seed bank, while those having larger and less isodiametric seeds have a transient seed bank. We assumed that species in certain special habitats may be exceptions to this rule. In habitats with sandy soil and open vegetation, the seeds do not necessarily have to penetrate the deeper soil layers through cracks in the soil. Instead, the seeds can become buried by a windblown layer of sand, thus seed morphology does not really affect the burial process. To test our hypothesis, we selected five semi-desert shrubs and one perennial herb of open sandy grasslands, all of which had large and flattened seeds. For each species, 12 repetitions of 50 seeds were buried in the soil. Seeds were recovered after 3, 20 and 26 months of burial and subjected to germination tests. Seeds of each species germinated in all test occasions, with final germination as follows: Atriplex canescens 89.0%, Haloxylon ammodendron 11.5%, H. persicum 11.5%, Pteropyrum aucheri 43.5%, Xylosalsola richteri 12.0% and Asclepias syriaca 26.0%. The results confirm the hypothesis that each of the six species is capable of forming a persistent soil seed bank. The results also show that in habitats where seed burial can take place passively through windblown soil, plant species might bypass the tradeoff between seed size/shape and seed longevity.

Sap flow of two typical woody halophyte species responding to the meteorological and irrigation water conditions in Taklimakan Desert

Understanding plant water consumption is crucial for artificial afforestation under drought environments and water stress in desert regions. However, the water consumption characteristics of desert species responding to the irrigation regimes are often neglected. By conducting a field test in the Taklimakan Desert Highway shelterbelt, this study examines the sap flow traits of two typical woody halophyte species (Calligonum mongolicum and Haloxylon ammodendron) and how they react to weather conditions and watering practices. Under the same irrigation treatment, the stem flux of C. mongolicum on sunny days was 1.5–5.3 times that on dusty days, while the stem flux of H. ammodendron on sunny days was 3.5–5.5 times that on dusty days. Both species demonstrated some sap flow during the night, representing 14.3%–24.9% and 7.3%–10.4% of the total sap flow for C. mongolicum and H. ammodendron, respectively. H. ammodendron maintained a higher stem flow during daytime and was more drought resistant than C. mongolicum. The daily sap flow patterns of these two species varied, showing both ‘single’ and ‘double peak’ curves depending on the watering conditions. A delay was also observed between the sap flow of these two species and the environmental factors. The factors influencing plant sap flow were found to be in the order of solar radiation, temperature, relative humidity, and saturated water vapor pressure difference. A BP-neural network proved highly effective for accurately simulating the sap flow of these two species. This research provides insights into how two common desert tree species adapt their water use in response to drought conditions, which is vital for artificial forest creation in desert areas.

Estimating rainfall interception loss of three dominant shrub species in an oasis–desert ecotone using in situ measurements and the revised Gash analytical model

Canopy interception loss affects the local water budget by removing a non-negligible proportion of rainfall from the terrestrial surface. Thus, quantifying interception loss is essential for thoroughly understanding the role of vegetation in the local hydrological cycle, especially in dryland ecosystems. However, sparse shrubs in dryland ecosystems have not been sufficiently studied, owing to time- and labor-intensive field experiments and challenging model parameterization. In this work, 4-year growing season field experiments on rainfall partitioning were conducted for three dominant shrub species (Haloxylon ammodendron, Nitraria sphaerocarpa, and Calligonum mongolicum) in an oasis–desert ecotone in northwestern China. The revised Gash analytical model was well parameterized, which reliably simulated the cumulative interception loss for sparse shrubs, and the validated model performed better for H. ammodendron, followed by C. mongolicum and N. sphaerocarpa, with relative errors of 8.4%, 15.4%, and 23.9%, respectively. The mean individual interception loss percentage for H. ammodendron (28.4%) was significantly higher than that for C. mongolicum (11.0%) and N. sphaerocarpa (10.9%) (p < 0.05), which could be ascribed to the higher canopy storage capacity and wet-canopy evaporation rate of H. ammodendron. For all shrub species, the majority proportion of interception loss occurred during canopy saturation and drying-out periods, accounting for approximately 79–85% of the cumulative interception loss. Overall, the mean local interception loss of three dominant shrub species in the ecotone removed nearly 17% of the corresponding cumulative rainfall during the growing season. These results not only provide methodological references for estimating the interception loss of sparse vegetation in dryland ecosystems, but also provide scientific insights for water resource management and ecosystem restoration in water-limited regions similar to the experimental site.

Stem and leaf photosynthesis of seven desert woody species and its influencing factors

Stem photosynthesis widely presents in desert plants, which increases carbon uptake capacity. In this study, we measured the photosynthetic characteristics of leaves and stems in seven desert woody plants (Populus euphratica, Populus alba var. pyramidalis, Populus pruinose, Haloxylon ammodendron, Calligonum rubicundum, Calligonum caput-medusae, Ammopiptanthus mongolicus) in the same habitat, using a portable Li-6400XT photosynthesis system combined with P-Chamber. We analyzed stem photosynthetic rate and its relationship with leaf photosynthetic rate. We measured the stem functional traits, including water content, stem dry matter content, chlorophyll content, water potential, non-structure carbohydrate (NSC), etc., to find out the main affecting factors of stem photosynthesis. The results showed that stem photosynthetic rate of seven species ranged from 0.72 to 1.71 μmol·m-2·s-1, with the largest of P. pruinose and the smallest of H. ammodendron. Stem photosynthetic rate could offset CO2 of stem respiration by 57%-83%. Leaf photosynthetic rate of the seven sepceis ranged from 12.80 to 22.54 μmol·m-2·s-1, with H. ammodendron and A. mongolicus being lower than those of the other five species. There was a significant positive correlation between leaf photosynthetic rate and stem photosynthetic rate. Stem water use efficiency was 2.2-7.7 times of the leaf. Chlorophyll content, NSC, stem respiration rate, and leaf photosynthetic rate were the main factors affecting stem photosynthesis.

Effects of Water Control and Nitrogen Addition on Functional Traits and Rhizosphere Microbial Community Diversity of Haloxylon ammodendron Seedlings

Water and nitrogen sources have always been the primary limiting factors for vegetation growth in arid and semi-arid regions and play an important role in the physiological ecology of vegetation. In this work, we studied the effects of water deficit and nitrogen addition on the physiological traits and rhizosphere bacterial microbial community of Haloxylon ammodendron seedlings in sterilized and non-sterilized soil habitats. A pot experiment was conducted to control the water and nitrogen sources of H. ammodendron seedlings. The water deficit treatment was divided into two groups based on gradient: a normal water group (CK, 70% field water holding capacity) and water deficit group (D, 30% field water holding capacity). The nitrogen addition treatment was divided into a no addition group (CK, 2.8 mg·kg−1) and addition group (N, 22.4 mg·kg−1). At the end of the growing season, the biochemical indexes of H. ammodendron seedlings were measured, and the rhizosphere soil was subjected to 16S rDNA-high-throughput sequencing to determine the rhizosphere bacterial community composition of H. ammodendron seedlings under different treatments. The results showed that the root-to-crown ratio of H. ammodendron seedlings increased significantly (p &lt; 0.05) under the water deficit treatment compared to the control and nitrogen addition treatments, indicating that H. ammodendron seedlings preferred to allocate biological carbon to the lower part of the ground. In contrast, plant height and root length were significantly lower (p &lt; 0.05) under water deficit treatment compared to the control, and no significant change was observed under water deficit and nitrogen addition compared to the control, indicating that water deficit inhibited the growth of H. ammodendron seedlings and nitrogen addition mitigated the effect of water deficit on the growth of H. ammodendron seedlings. Under sterilized soil conditions, both water deficit and nitrogen addition significantly increased the abundance and diversity of bacterial communities in H. ammodendron seedlings (p &lt; 0.05). Conversely, under non-sterilized conditions, both inhibited the diversity of microbial bacterial communities, and the microbial characteristic species under different controls were different. Therefore, in the short-term experiment, H. ammodendron seedlings were affected by water deficit and allocated greater quantities of biomass to the underground part, especially in the non-sterile microbial environment; different initial soil conditions resulted in divergent responses of rhizosphere bacterial communities to water deficit and nitrogen addition. Under different initial soil conditions, the same water deficit and nitrogen addition treatment will lead to the development of distinct differences in rhizosphere bacterial community composition.

Quantifying the effects of precipitation exclusion and groundwater drawdown on functional traits of Haloxylon ammodendron — How does this xeric shrub survive the drought?

The increasing frequency of drought and decline in groundwater levels are causing ecophysiological changes in woody plants, particularly in desert ecosystems in arid regions. However, the combined effects of meteorological and hydrological droughts on perennial desert plants, especially phreatophytes, remain poorly understood. To address this knowledge gap, we conducted a 5-year precipitation exclusion experiment at two sites with contrasting groundwater depths in the Gurbantunggut Desert located in northwest China. Our study aimed to investigate the impacts of precipitation exclusion and groundwater depth decline on multiple traits of H. ammodendron. We found that long-term precipitation exclusion enhanced midday leaf water potential, stomatal conductance, chlorophyll content, root nonstructural carbohydrates concentration, leaf starch concentration, but decreased water use efficiency. Groundwater drawdown decreased predawn and midday leaf water potentials, maximum net photosynthetic rate, stomatal conductance, Huber value, stem water δ18O, but enhanced water use efficiency and branch nonstructural carbohydrates concentration. A combination of precipitation exclusion and groundwater depth decline reduced Huber value, but did not show exacerbated effects. The findings demonstrate that hydrological drought induced by groundwater depth decline poses a greater threat to the survival of H. ammodendron than future changes in precipitation.

Effects of groundwater depth on ecological stoichiometric characteristics of assimilated branches and soil of two desert plants.

Groundwater plays a crucial role in regulating plant growth in arid regions and has significant effects on plant physiological mechanisms. However, research on the influence of groundwater change on plant ecological stoichiometry is still limited. Therefore, this study was carried out to obtain the variations in assimilated branches and soil ecological stoichiometry of two dominant species in the Gurbantunggut Desert (Haloxylon ammodendron and Haloxylon persicum) at different groundwater depths to reveal the responses of desert plants to groundwater depth changes. The results showed that (1) H. persicum branches' stress tolerance indicators (C:N, C:P) are higher, while nutritional indicators (N:P) are lower. The soil nutrient of H. ammodendron is richer. (2) The ecological stoichiometry varied significantly along the groundwater gradient. With the deepening of groundwater, the branches C, N and P increased, and the variation in element ratio was inconsistent. Most of the soil properties was inversely proportional to the depth of groundwater. (3) Groundwater depth was a vital environmental factor affecting the assimilated branches ecological stoichiometry. Soil properties also had a significant influence on element accumulation in assimilated branches. (4) Regulating the allocation of branches ecological stoichiometry is an adaptation of two Haloxylon species to cope with local hydrological conditions changes. These findings provide novel insights into desert plant responses to different groundwater conditions within fragile desert ecosystems and may have implications for the implementation of effective measures related to the stability and sustainability of desert ecosystems.

The effects of N-addition on litter mixture effects depend on decomposition time: A case from mixed-litter decomposition in the Gurbantunggut Desert.

Changes in nitrogen (N) deposition and litter mixtures have been shown to influence ecosystem processes such as litter decomposition. However, the interactive effects of litter mixing and N-deposition on decomposition process in desert regions remain poorly identified. We assessed the simultaneous effects of both N addition and litter mixture on mass loss in a litterbag decomposition experiment using six native plants in single-species samples with diverse quality and 14-species combinations in the Gurbantunggut Desert under two N addition treatments (control and N addition). The N addition had no significant effect on decomposition rate of single-species litter (expect Haloxylon ammodendron), whereas litter mass loss and decomposition rate differed significantly among species, with variations positively correlated with initial phosphorus concentration and negatively correlated with initial lignin concentration. After 18 months, the average mass loss across litter mixtures did not overall differ from those predicted from single species either in control or N addition treatments, that is, mixing of different species had no non-additive effects on decomposition. The N addition, however, did modify the direction of mixture effects and interacted with incubation time. Added N transformed synergistic effects of litter mixtures to antagonistic effects on mass loss after 1 month of decomposition, while transforming neutral effects of litter mixture to synergistic effects after 6 months of decomposition. Our results demonstrated that initial chemical properties played an important role in litter decomposition, while no effects of litter mixture on decomposition process in this desert region. The N addition altered the litter mixture effects on mass loss with incubation time, implying that increased N deposition in the future may have profound effects on carbon turnover to a greater extent than previously thought in desert ecosystems.

Seasonal use of pastures of Karakalpak Ustyurt (Uzbekistan)

The electronic-digital “Map of the pastures of the Karakalpak Ustyurt” and the legend to it have been compiled. The map shows 43 pasture differences consisting of 5 pasture types common on the Ustyurt plateau. The article presents the seasonal use of pastures of the Karakalpak Ustyurt. According to seasonal use, three groups of pastures are allocated: year-round, summer-autumn-winter, autumn-winter. Autumn-winter pastures make up 58 % of the total pasture differences of the Karakalpak Ustyurt. Autumn and winter-spring precipitation play the main role in the fodder yield of pastures. A brief description is given of the main and permanent species of plant communities on the plateau, such as Artemisia terrae-albae, Caroxylon orientale and Anabasis salsa. Halophytic plants have versatile economic values. Many of them play an important role in the forage fund of desert animal husbandry. In particular, Caroxylon orientale, Salsola arbusculiformis, Haloxylon aphyllum significantly increases the productivity of pastures, and they are eaten by camels and small cattle all year round. The productivity of the aboveground mass of the studied pasture differences is determined, the yield of pastures depends on favorable climatic conditions of the year.

Rhizobacteria isolated from xerophyte Haloxylon ammodendron manipulate root system architecture and enhance drought and salt tolerance in Arabidopsis thaliana.

The objective of this study was to identify bacteria from the rhizosphere of the black saxaul (Haloxylon ammodendron) and test the possibility of using the bacteria for enhancement of drought and/or salt tolerance in the model plant, Arabidopsis thaliana. We collected rhizosphere and bulk soil samples from a natural habitat of H. ammodendron in Iran and identified 58 morphotypes of bacteria that were enriched in the rhizosphere. From this collection, we focused our further experiments on eight isolates. Microbiological analyses showed that these isolates have different levels of tolerance to heat, salt, and drought stresses, and showed different capabilities of auxin production and phosphorous solubilization. We first tested the effects of these bacteria on the salt tolerance of Arabidopsis on agar plate assays. The bacteria substantially influenced the root system architecture, but they were not effective in increasing salt tolerance significantly. Pot assays were then conducted to evaluate the effects of the bacteria on salt or drought tolerance of Arabidopsis on peat moss. Results showed that three of these bacteria (Pseudomonas spp. and Peribacillus sp.) effectively enhanced drought tolerance in Arabidopsis, so that while none of the mock-inoculated plants survived after 19days of water withholding, the survival rate was 50-100% for the plants that were inoculated with these bacteria. The positive effects of the rhizobacteria on a phylogenetically-distant plant species imply that the desert rhizobacteria may be used to enhance abiotic stress in crops.

In vitro regeneration of Haloxylon ammodendron

Haloxylon ammodendron (C.A.Mey) Bunge is one of the important species of arid desert vegetation in China, and it is also an ideal material for studying plant stress resistance, which plays an extremely important role in protecting desert ecosystems and preventing land desertification. However, there are relatively few studies on the regeneration of the fusiform, and the genetic transformation system has not been successfully reported, which restricts the in-depth study of the molecular mechanism of shuttle propagation and stress resistance. In the present study, the seeds, hypocotyls, cotyledons, cotyledon nodes, terminal buds and fixed buds were used as explants, and a set of tissue culture and plant regeneration system was established by inducing adventitious buds, adventitious bud rooting and transplanting. The results showed that amongst different H. ammodendron explants, i.e., seeds, hypocotyls, cotyledons and cotyledon nodes, the last induced budding effect was better. The optimal medium for inducing clandine buds by cotyledon segment differentiation is 0.5 mg·L-1 NAA+0.5 mg·L-1 6-BA induced budding rate was high, reaching 61.90%, rooting medium was 1/2 MS+1 mg·L-1 NAA +1 mg·L-1 IBA + 1 mg·L-1 IAA with a rooting rate of 50%. The results of this study will provide a theoretical basis for the genetic transformation of H. ammodendron.

Soil calcium prompts organic carbon accumulation after decadal saline-water irrigation in the Taklamakan desert

Soil organic carbon (SOC), as a crucial measure of soil quality, is typically low in arid regions due to salinization, which is a global issue. How soil organic carbon changes with salinization is not a simple concept, as high salinity simultaneously affects plant inputs and microbial decomposition, which exert opposite effects on SOC accumulation. Meanwhile, salinization could affect SOC by altering soil Ca2+ (a salt component), which stabilizes organic matter via cation bridging, but this process is often overlooked. Here, we aimed to explore i) how soil organic carbon changes with salinization induced by saline-water irrigation and ii) which process drives soil organic carbon content with salinization, plant inputs, microbial decomposition, or soil Ca2+ level. To this end, we assessed SOC content, plant inputs represented by aboveground biomass, microbial decomposition revealed by extracellular enzyme activity, and soil Ca2+ along a salinity gradient (0.60–31.09 g kg−1) in the Taklamakan Desert. We found that, in contrast to our prediction, SOC in the topsoil (0–20 cm) increased with soil salinity, but it did not change with the aboveground biomass of the dominant species (Haloxylon ammodendron) or the activity of three carbon-cycling relevant enzymes (β-glucosidase, cellulosidase, and N-acetyl-beta-glucosaminidase) along the salinity gradient. Instead, SOC changed positively with soil exchangeable Ca2+, which increased linearly with salinity. These results suggest that soil organic carbon accumulation could be driven by increases in soil exchangeable Ca2+ under salinization in salt-adapted ecosystems. Our study provides empirical evidence for the beneficial impact of soil Ca2+ on organic carbon accumulation in the field under salinization, which is apparent and should not be disregarded. In addition, the management of soil carbon sequestration in salt-affected areas should be taken into account by adjusting the soil exchangeable Ca2+ level.

Ectopic over-expression of HaFT-1, a 14-3-3 protein from Haloxylon ammodendron, enhances acquired thermotolerance in transgenic Arabidopsis.

Haloxylon ammodendron, an important shrub utilized for afforestation in desert areas, can withstand harsh ecological conditions such as drought, high salt and extreme heat. A better understanding of the stress adaptation mechanisms of H. ammodendron is vital for ecological improvement in desert areas. In this study, the role of the H. ammodendron 14-3-3 protein HaFT-1 in thermotolerance was investigated. qRT-PCR analysis showed that heat stress (HS) priming (the first HS) enhanced the expression of HaFT-1 during the second HS and subsequent recovery phase. The subcellular localization of YFP-HaFT-1 fusion protein was mainly detected in cytoplasm. HaFT-1 overexpression increased the germination rate of transgenic Arabidopsis seeds, and the survival rate of HaFT-1 overexpression seedlings was higher than that of wild-type (WT) Arabidopsis after priming-and-triggering and non-primed control treatments. Cell death staining showed that HaFT-1 overexpression lines exhibited significantly reduced cell death during HS compared to WT. Transcriptome analysis showed that genes associated with energy generation, protein metabolism, proline metabolism, autophagy, chlorophyll metabolism and reactive oxygen species (ROS) scavenging were important to the thermotolerance of HS-primed HaFT-1 transgenic plants. Growth physiology analysis indicated that priming-and-triggering treatment of Arabidopsis seedlings overexpressing HaFT-1 increased proline content and strengthened ROS scavenging activity. These results demonstrated that overexpression of HaFT-1 increased not only HS priming but also tolerance to the second HS of transgenic Arabidopsis, suggesting that HaFT-1 is a positive regulator in acquired thermotolerance.