The transcription factor ThDOF8 binds to a novel cis-element and mediates molecular responses to salt stress in Tamarix hispida.

Salt stress is a common abiotic factor that restricts plant growth and development. As a halophyte, Tamarix hispida is a good model plant for exploring salt-tolerance genes and regulatory mechanisms. DNA-binding with one finger (DOF) is an important transcription factor (TF) that influences and controls various signaling substances involved in diverse biological processes related to plant growth and development, but the regulatory mechanisms of DOF TFs in response to salt stress are largely unknown in T. hispida. In the present study, a newly identified Dof gene, ThDOF8, was cloned from T. hispida, and its expression was found to be induced by salt stress. Transient overexpression of ThDOF8 enhanced T. hispida salt tolerance by enhancing proline levels, and increasing the activities of the antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD). These results were also verified in stably transformed Arabidopsis. Results from TF-centered yeast one-hybrid (Y1H) assays and EMSAs showed that ThDOF8 binds to a newly identified cis-element (TGCG). Expression profiling by gene chip analysis identified four potential direct targets of ThDOF8, namely the cysteine-rich receptor-like kinases genes, CRK10 and CRK26, and two glutamate decarboxylase genes, GAD41, and GAD42, and these were further verified by ChIP-quantitative-PCR, EMSAs, Y1H assays, and ß-glucuronidase enzyme activity assays. ThDOF8 can bind to the TGCG element in the promoter regions of its target genes, and transient overexpression of ThCRK10 also enhanced T. hispida salt tolerance. On the basis of our results, we propose a new regulatory mechanism model, in which ThDOF8 binds to the TGCG cis-element in the promoter of the target gene CRK10 to regulate its expression and improve salt tolerance in T. hispida. This study provides a basis for furthering our understanding the role of DOF TFs and identifying other downstream candidate genes that have the potential for improving plant salt tolerance via molecular breeding.

The salt secretion of leaves promotes the competitiveness of Reaumuria soongarica in a desert grassland.

BACKGROUND: For better understanding the mechanism of Reaumuria soongarica community formation in a salt stressed grassland ecosystem, we designed a field experiment to test how leaves salt secretion changes the competitive relationship between species in this plant communities. RESULTS: Among the three species (R. soongarica, Stipa glareosa and Allium polyrhizum) of the salt stressed grassland ecosystem, the conductivity of R. soongarica rhizosphere soil was the highest in five soil layers (0-55 cm depth). The high soil conductivity can increase the daily salt secretion rate of plant leaves of R. soongarica. In addition, we found the canopy size of R. soongarica was positively related to the distance from S. glareosa or A. polyrhizum. The salt-tolerance of R. soongarica was significantly higher than the other two herbs (S. glareosa and A. polyrhizum). Moreover, there was a threshold (600 µS/cm) for interspecific competition of plants mediated by soil conductivity. When the soil conductivity was lower than 600 µS/cm, the relative biomass of R. soongarica increased with the soil conductivity increase. CONCLUSIONS: The efficient salt secretion ability of leaves increases soil conductivity under the canopy. This leads the formation of a "saline island" of R. soongarica. Meanwhile R. soongarica have stronger salt tolerance than S. glareosa and A. polyrhizum. These promote the competitiveness of R. soongarica and inhibit interspecies competition advantage of the other two herbs (S. glareosa and A. polyrhizum) in the plant community. It is beneficial for R. soongarica to establish dominant communities in saline regions of desert grassland.

Overexpression of ThMYB8 mediates salt stress tolerance by directly activating stress-responsive gene expression.

MYB transcription factors are important in abiotic stress responses; however, the detailed mechanisms are unclear. Tamarix hispida contains multiple MYB genes. The present study characterized T. hispida MYB8 (ThMYB8) during salt stress using transgenic T. hispida and Arabidopsis assays. ThMYB8 overexpression and ThMYB8 RNAi analysis demonstrated that ThMYB8 enhanced the salt stress tolerance. Transgenic Arabidopsis ectopic expression of ThMYB8 significantly increased root growth, fresh weight, and seed germination rate compared with that of the wild-type under salt stress. Physiological parameters analysis in T. hispida and Arabidopsis showed that ThMYB8 overexpressing plants had the lowest levels of O2, H2O2, cell death, malondialdehyde, and electrolyte leakage. Overexpression of ThMYB8 regulated Na+ and K+ concentrations in plant tissues while maintaining K+/Na+ homeostasis. Analysis using qRT-PCR and ChIP-PCR identified possible downstream ThMYB8-regulated genes. ThMYB8 regulated the expression of ThCYP450-2 (cytochrome p450-2), Thltk (leucine-rich repeat transmembrane protein kinase), and ThTIP (aquaporin TIP) by binding to the MBSI motif ('CAACTG') in their promoters. The results indicated that ThMYB8 enhanced salt stress tolerance in T. hispida by regulating gene expression related to the activation of stress-associated physiological changes, such as enhanced reactive oxygen species scavenging capability, maintaining K+/Na+ homeostasis, and decreasing the malondialdehyde content and lipid peroxidation cell membranes.

Vacuolar membrane H+-ATPase c`` subunit gene (ThVHAc``1) from Tamarix hispida Willd improves salt stress tolerance.

The plant vacuolar H+-ATPase (V-ATPase) is a multisubunit complex. In addition to performing basic housekeeping functions, this complex is also involved in abiotic stress resistance in plants. In this study, a V-ATPase c`` subunit gene (ThVHAc``1) from Tamarix hispida Willd was cloned with a 534-bp ORF. Sequence analysis showed that the ThVHAc``1 protein contains four transmembrane helices and lacks a signal peptide. qRT-PCR results showed that ThVHAc``1 was primarily induced by treatments of NaCl, NaHCO3, PEG6000, CdCl2 or ABA in roots, stems and leaves of T. hispida. The expression pattern of ThVHAc``1 was significantly different from that of ThVHAc1 (a V-ATPase c subunit in T. hispida). Furthermore, the cell survival rates and density (OD600) results showed that the transgenic yeast overexpressing ThVHAc``1 exhibited increased tolerance to the above-mentioned abiotic stresses. In addition, the overexpression of ThVHAc``1 confers salt tolerance to transgenic Arabidopsis plants by improving the ROS content and decreasing the accumulation of O2- and H2O2. Similarly, the homologous transformation of the ThVHAc``1 gene into T. hispida also improved salt tolerance. Our results suggest that the ThVHAc``1 gene plays an important role in plant stress tolerance.

A 2-Cys peroxiredoxin gene from Tamarix hispida improved salt stress tolerance in plants.

BACKGROUND: Peroxiredoxins (Prxs) are a large family of antioxidant enzymes that respond to biotic and abiotic stress by decomposing reactive oxygen species (ROS). In this study, the stress tolerance function of the Th2CysPrx gene was further analysed. It lays a foundation for further studies on the salt tolerance molecular mechanism of T. hispida and improved salt tolerance via transgenic plants. RESULTS: In this study, the stress tolerance function of the Th2CysPrx gene was further analysed. The results of transgenic tobacco showed higher seed germination rates, root lengths, and fresh weight under salt stress than wild-type tobacco. Simultaneously, physiological indicators of transgenic tobacco and T. hispida showed that Th2CysPrx improved the activities of antioxidant enzymes and enhanced ROS removal ability to decrease cellular damage under salt stress. Moreover, Th2CysPrx improved the expression levels of four antioxidant genes (ThGSTZ1, ThGPX, ThSOD and ThPOD). CONCLUSIONS: Overall, these results suggested that Th2CysPrx enhanced the salt tolerance of the transgenic plants. These findings lay a foundation for further studies on the salt tolerance molecular mechanism of T. hispida and improved salt tolerance via transgenic plants.

Reaumuria trigyna transcription factor RtWRKY23 enhances salt stress tolerance and delays flowering in plants.

Reaumuria trigyna (Reaumuria Linn genus, family Tamaricaceae), an endangered dicotyledonous shrub with the features of a recretohalophyte, is endemic to the Eastern Alxa-Western Ordos area of China. Based on R. trigyna transcriptome data and expression pattern analysis of RtWRKYs, RtWRKY23, a Group II WRKY transcription factor, was isolated from R. trigyna cDNA. RtWRKY23 was mainly expressed in the stem and was induced by salt, drought, cold, ultraviolet radiation, and ABA treatments, but suppressed by heat treatment. Overexpression of RtWRKY23 in Arabidopsis increased chlorophyll content, root length, and fresh weight of the transgenic lines under salt stress. Real-time quantitative PCR (qPCR) analysis and yeast one-hybrid analysis demonstrated that RtWRKY23 protein directly or indirectly modulated the expression levels of downstream genes, including stress-related genes AtPOD, AtPOD22, AtPOD23, AtP5CS1, AtP5CS2, and AtPRODH2, and reproductive development-related genes AtMAF5, AtHAT1, and AtANT. RtWRKY23 transgenic Arabidopsis had higher proline content, peroxidase activity, and superoxide anion clearance rate, and lower H2O2 and malondialdehyde content than WT plants under salt stress conditions. Moreover, RtWRKY23 transgenic Arabidopsis exhibited later flowering and shorter pods, but little change in seed yield, compared with WT plants under salt stress. Our study demonstrated that RtWRKY23 not only enhanced salt stress tolerance through maintaining the ROS and osmotic balances in plants, but also participated in the regulation of flowering under salt stress.

Ecological effect of the riparian ecosystem in the lower reaches of the Tarim River in northwest China.

The riparian vegetation in the lower reaches of the Tarim River is an irreplaceable natural resource for its ecosystem, and also a guarantee for the transportation safety in this area. Here, we analyzed different plant influences on soil erosion and evaluate the main ecosystem service functions served by the riparian vegetation to study area. Results showed that the total amount of sand-fixation in the study area was 4.14×1013 t and that Tamarix chinensis had a greater influence on wind speed and sediment transport than Populus euphratica, and the Tamarix chinensis can be used as suitable vegetation for wind erosion measures and provide scientific basis for the optimization of vegetation matching and reasonable allocation scheme for ecological construction in arid areas. The total ecosystem service value was calculated to be $11.03×1011. Of the main ecosystem service functions, riparian vegetation primarily served as sand fixation. Results show that, this research was identical, and the construction of shelterbelt plays an important role in the promotion of wind and sand control measures. Finally, our findings highlights the need for further research on how vegetation function as windbreak and sand fixation.

Functional Analysis of Ion Transport Properties and Salt Tolerance Mechanisms of RtHKT1 from the Recretohalophyte Reaumuria trigyna.

Reaumuria trigyna is an endangered recretohalophyte and a small archaic feral shrub that is endemic to arid and semi-arid plateau regions of Inner Mongolia, China. Based on transcriptomic data, we isolated a high-affinity potassium transporter gene (RtHKT1) from R. trigyna, which encoded a plasma membrane-localized protein. RtHKT1 was rapidly up-regulated by high Na+ or low K+ and exhibited different tissue-specific expression patterns before and after stress treatment. Transgenic yeast showed tolerance to high Na+ or low K+, while transgenic Arabidopsis exhibited tolerance to high Na+ and sensitivity to high K+, or high Na+-low K+, confirming that Na+ tolerance in transgenic Arabidopsis depends on a sufficient external K+ concentration. Under external high Na+, high K+ and low K+ conditions, transgenic yeast accumulated more Na+-K+, Na+ and K+, while transgenic Arabidopsis accumulated less Na+-more K+, more Na+ and more Na+-K+, respectively, indicating that the ion transport properties of RtHKT1 depend on the external Na+-K+ environment. Salt stress induced up-regulation of some ion transporter genes (AtSOS1/AtHAK5/AtKUP5-6), as well as down-regulation of some genes (AtNHX1/AtAVP1/AtKUP9-12), revealing that multi-ion-transporter synergism maintains Na+/K+ homeostasis under salt stress in transgenic Arabidopsis. Overexpression of RtHKT1 enhanced K+ accumulation and prevented Na+ transport from roots to shoots, improved biomass accumulation and Chl content in salt-stressed transgenic Arabidopsis. The proline content and relative water content increased significantly, and some proline biosynthesis genes (AtP5CS1 and AtP5CS2) were also up-regulated in salt-stressed transgenic plants. These results suggest that RtHKT1 confers salt tolerance on transgenic Arabidopsis by maintaining Na+/K+ homeostasis and osmotic homeostasis.

Characterization and comparison of nitrate fluxes in Tamarix ramosissima and cotton roots under simulated drought conditions.

Tamarix ramosissima Ledeb., a major host plant for the parasitic angiosperm Cistanche tubulosa, and known for its unique drought tolerance, has significant ecological and economic benefits. However, the mechanisms of nitrogen acquisition by the T. ramosissima root system under drought have remained uncharacterized. Here, uptake of nitrate (NO3-) in various regions of the root system was measured in T. ramosissima using Non-invasive Micro-test Technology at the cellular level, and using a 15NO3--enrichment technique at the whole-root level. These results were compared with responses in the model system cotton (Gossypium hirsutum L.). Tamarix ramosissima had lower net NO3- influx and a significantly lower Km (the apparent Michalis-Menten constant; 8.5 µM) for NO3- uptake than cotton under normal conditions. Upon simulated drought conditions, using polyethylene glycol (PEG), NO3- flux in cotton switched from net influx to net efflux, with a substantive peak in the white zone (WZ) of the root. There were no significant NO3- influx signals observed in the WZ of T. ramosissima under control conditions, whereas PEG treatment significantly enhanced NO3- influx in the WZ of T. ramosissima. The effect of PEG application on NO3- fluxes was highly localized, and the increase in net NO3- influx in response to PEG stimulation was also found in C. tubulosa-inoculated T. ramosissima. Consistently, root nitrogen (N) content and root biomass were higher in T. ramosissima than in cotton under PEG treatment. Our study provides insights into NO3- uptake and the influence of C. tubulosa inoculation in T. ramosissima roots during acclimation to PEG-induced drought stress and provides guidelines for silvicultural practice and for breeding of T. ramosissima under coupled conditions of soil drought and N deficiency.

Responses of soil respiration to rainfall addition in a desert ecosystem: Linking physiological activities and rainfall pattern.

The tight linkage between photosynthesis (An) and soil respiration (Rs) has been verified in many terrestrial ecosystems. However, it remains unclear whether this linkage occurs in desert ecosystems, where water is considered an important trigger of carbon cycling. A field experiment was performed under seven simulated rainfall amounts (0, 3, 5, 10, 15, 25, and 40 mm) with two co-existing desert plants (Reaumuria soongorica and Nitraria sphaerocarpa) in June (early growing season, EGS) and August (middle growing season, MGS) in 2016. An, Rs, predawn water potential (Ψpd), soil temperature (Ts) and soil moisture (Swc) were measured for each treatment or control plot for 3 weeks. Our objective was to examine the effects of rainfall pattern on Rs and physiological responses of the two plants and the relationships between Rs and biotic and abiotic factors. No obvious variations in Ψpd or An were found under small rainfall events. However, when the rainfall amount exceeded 10 mm, both plants responded strongly, and the response patterns of Rs showed trends similar to those of An, which varied between species and seasons. Moreover, rain additions of 3-40 mm significantly increased Rs, and the relative changes in Rs (ΔRs) of both species were much larger in the EGS than in the MGS. Importantly, abiotic factors may have controlled the variations in Rs under small rain events while An played a more important role in regulating the variations in Rs when the rainfall amount exceeded 10 mm for both species, suggest that the rainfall pattern-driven changes in Rs composition interact with physiological activity and abiotic factors to regulate the response of Rs to rainfall variability in desert ecosystems. Thus, climate change in the coming decades may lead to carbon sequestration by desert plants, which may cause desert ecosystems to act as carbon sinks.

An ERF transcription factor from Tamarix hispida, ThCRF1, can adjust osmotic potential and reactive oxygen species scavenging capability to improve salt tolerance.

Ethylene-Responsive Factors (ERFs) are plant-specific transcription factors (TFs) involved in multiple biological processes, especially in abiotic stress tolerance. However, the ERFs from woody halophytes that are involved in salt stress have been little studied. In the present investigation, we characterized a subfamily member of ERF TFs from Tamarix hispida, ThCRF1, which responds to salt stress. ThCRF1 is a nuclear protein that binds to the motifs including TTG, DRE and GCC-box. Transient transformation was performed to generate T. hispida overexpressing ThCRF1 and RNA interference (RNAi)-silenced ThCRF1 to analyze its function using gain- and loss-of-function methods. Overexpression of ThCRF1 in T. hispida significantly improved tolerance to salt-shock-induced stress; by contrast, RNAi-silence of ThCRF1 significantly decreased tolerance to salt-shock-induced stress. Further experiments showed that ThCRF1 induces the expression of genes including those encoding pyrroline-5-carboxylate synthetase (P5CS), trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), superoxide dismutase (SOD) and peroxidase (POD), which lead to enhanced proline and trehalose levels and increased SOD and POD activities. These results were further confirmed by studying transgenic Arabidopsis plants overexpressing ThCRF1. Therefore, the results suggested that ThCRF1 improves tolerance to salt-shock-induced stress by enhancing trehalose and proline biosynthesis to adjust the osmotic potential, and by improving SOD and POD activities to increase reactive oxygen species scavenging capability.

Expression of a Na+/H+ antiporter RtNHX1 from a recretohalophyte Reaumuria trigyna improved salt tolerance of transgenic Arabidopsis thaliana.

Reaumuria trigyna is an endangered recretohalophyte and a small xeric shrub that is endemic to the eastern Alxa and western Ordos areas of Inner Mongolia, China. Using transcriptome data, we identified a 1662-bp open reading frame encoding a 553-amino-acid protein corresponding to a Na+/H+ antiporter (RtNHX1) from R. trigyna. RtNHX1 was rapidly up-regulated by NaCl and exogenous abscisic acid treatment and had different tissue-specific expression patterns before and after salt-stress treatment. Overexpression of RtNHX1 enhanced seed germination, biomass accumulation, chlorophyll content, and root elongation in transgenic Arabidopsis plants under salt stress and rescued the salt-sensitive deficiencies of the nhx1 mutant. POD and CAT enzyme activities, proline content, and RWC all increased significantly in salt-stressed transgenic Arabidopsis plants, whereas MDA content did not. Additionally, there was a corresponding upregulation of some antioxidant-enzyme, proline biosynthesis and other stress responsive genes (AtPOD1, AtCAT1, AtP5CS1, AtP5CS2, AtRD29A, AtRD29B, AtKIN1, and AtABI2). The transgenic Arabidopsis plants accumulated more K+ and less Na+ in their leaves and had lower Na+/K+ ratios than WT plants. This was reflected in the upregulation of some ion transport-related genes (AtAVP1, AtSOS1, AtKUP6, and AtKUP8). When RtNHX1 was expressed in the AXT3 yeast strain, the accumulation of Na+ and K+ in the vacuole increased and the Na+/K+ ratio decreased. These results reveal that R. trigyna RtNHX1 is a functional antiporter that sequesters Na+ and K+ in the vacuole and could confer salt tolerance on transgenic Arabidopsis plants by maintaining Na+/K+ homeostasis and enhancing osmotic and antioxidant regulatory capacity. These results suggest that RtNHX1 may be a good target for improving salt tolerance in plants.

Transcription factor ThWRKY4 binds to a novel WLS motif and a RAV1A element in addition to the W-box to regulate gene expression.

WRKY transcription factors play important roles in many biological processes, and mainly bind to the W-box element to regulate gene expression. Previously, we characterized a WRKY gene from Tamarix hispida, ThWRKY4, in response to abiotic stress, and showed that it bound to the W-box motif. However, whether ThWRKY4 could bind to other motifs remains unknown. In this study, we employed a Transcription Factor-Centered Yeast one Hybrid (TF-Centered Y1H) screen to study the motifs recognized by ThWRKY4. In addition to the W-box core cis-element (termed W-box), we identified that ThWRKY4 could bind to two other motifs: the RAV1A element (CAACA) and a novel motif with sequence of GTCTA (W-box like sequence, WLS). The distributions of these motifs were screened in the promoter regions of genes regulated by some WRKYs. The results showed that the W-box, RAV1A, and WLS motifs were all present in high numbers, suggesting that they play key roles in gene expression mediated by WRKYs. Furthermore, five WRKY proteins from different WRKY subfamilies in Arabidopsis thaliana were selected and confirmed to bind to the RAV1A and WLS motifs, indicating that they are recognized commonly by WRKYs. These findings will help to further reveal the functions of WRKY proteins.

Experimental study on water transport observations of desert riparian forests in the lower reaches of the Tarim River in China.

Studying the water use processes of desert riparian vegetation in arid regions and analyzing the response and adaptation strategies of plants to drought stress are of great significance for developing ecological restoration measures. Based on field monitoring and test analyses of physiological ecological indicators of dominant species (Populus euphratica and Tamarix chinensis) in the desert riparian forest in the lower reaches of the Tarim River, the water relations of P. euphratica and T. chinensis under drought stress are discussed and some water use strategies put forward. The results show that (1) concerning plant water uptake, desert riparian forests depend mainly on groundwater to survive under long-term water stress. (2) Concerning plant water distribution, the survival of P. euphratica and nearby shallow root plants is mainly due to the hydraulic lift and water redistribution of P. euphratica under drought stress. (3) Concerning plant water transport, P. euphratica sustains the survival of competitive and advantageous branches by improving their ability to acquire water while restraining the growth of inferior branches. (4) Concerning plant transpiration, the sap flow curves of daily variations of P. euphratica and T. chinensis were wide-peak sin and narrower-peak respectively. T. chinensis has better environmental adaptability.

The effects of groundwater depth on water uptake of Populus euphratica and Tamarix ramosissima in the hyperarid region of Northwestern China.

Knowledge of the water sources used by desert trees and shrubs is critical for understanding how they function and respond to groundwater decline and predicting the influence of water table changes on riparian plants. In this paper, we test whether increased depth to groundwater changed the water uptake pattern of desert riparian species and whether competition for water resources between trees and shrubs became more intense with a groundwater depth gradient. The water sources used by plants were calculated using the IsoSource model, and the results suggested differences in water uptake patterns with varying groundwater depths. At the river bank (groundwater depth = 1.8 m), Populus euphratica and Tamarix ramosissima both used a mixture of river water, groundwater, and deeper soil water (>75 cm). When groundwater depth was 3.8 m, trees and shrubs both depended predominantly on soil water stored at 150-375 cm depth. When the groundwater depth was 7.2 m, plant species switched to predominantly use both groundwater and deeper soil water (>375 cm). However, differences in water acquisition patterns between species were not found. The proportional similarity index (PSI) of proportional contribution to water uptake of different water resources between P. euphratica and T. ramosissima was calculated, and results showed that there was intense water resource competition between P. euphratica and T. ramosissima when grown at shallow groundwater depth (not more than 3.8 m), and the competition weakened when the groundwater depth increased to 7.2 m.

[Early selection of drought-resistant superior families of Reaumuria soongorica based on the analysis of osmoregulation substances and chlorophyll].

By using 77 families of 3 year-old Reaumuria soongorica seedlings that grew well without injection of any pests and diseases as experimental material, the contents of soluble protein (SP), soluble sugar (SS), proline (Pro) and chlorophyll (Chl) were measured, and their drought resistance was evaluated with principal component analysis and subordinate function method. The results showed that there were great differences in leaf osmolytes and chlorophyll among the 77 families. The soluble protein content varied from 2.14 to 8.60 mg · g⁻¹ FM, the soluble sugar content was from 6.82 to 21.86 mg · g⁻¹ FM, the proline content was from 118.73 to 1494.30 µg · g⁻¹ FM, the chlorophyll a content was from 321.88 to 897.37 µg · g⁻¹ FM, the chlorophyll b content was from 53.65 to 249.04 µg · g⁻¹ FM, chlorophyll (a+b) was from 387.39 to 1146.40 µg · g⁻¹ FM, and the chlorophyll a/b was from 3.46 to 6.42. All drought-resistant indices had significant difference among R. soongorica families, among which the proline content varied most, followed by the soluble sugar content. Evaluated by using the synthesized multi-index, it was found that 12 families showed good drought resistance, with Zhazigou 1-2 and Zhazigou 1-1 performing the best.

Tamarix arborea var. arborea and Tamarix parviflora: Two species valued for their adaptability to stress conditions.

The choice of stress resistant and highly adaptable species is a fundamental step for landscaping and ornamental purposes in arid and coastal environments such as those in the Mediterranean basin. The genus Tamarix L. includes about 90 species with a high endurance of adversity. We investigated the water relations and photosynthetic response of Tamarix arborea (Sieb. ex Ehrenb.) Bge. var. arborea and T. parviflora DC. growing in an urban environment. Both species showed no evidence of drought or salt stress in summer, and appeared to follow two strategies with T. arborea var. arborea investing in high carbon gain at the beginning of the summer, and then reducing photosynthetic activity at the end of the season, and T. parviflora showing lower but constant levels of photosynthetic activity throughout the vegetative season. For landscaping and ornamental purposes, we suggest T. arborea var. arborea when a fast-growing, high-cover species is necessary, and T. parviflora when less-invasive species are required.

Diversity of endophytic fungi of Myricaria laxiflora grown under pre- and post-flooding conditions.

Myricaria laxiflora is distributed along the riverbanks of the Yangtze River valley. The Three Gorges Dam has dramatically changed the habitat of M. laxiflora, which has evolved to develop increased resistance to flooding stress. In order to elucidate the relationship between plant endophytic fungi and flooding stress, we isolated and taxonomically characterized the endophytic fungi of M. laxiflora. One hundred and sixty-three fungi were isolated from healthy stems, leaves and roots of M. laxiflora grown under pre- and post-flooding conditions. Culture and isolation were carried out under aerobic and anaerobic conditions. Based on internal transcribed spacer sequence analysis and morphological characteristics, the isolates exhibited abundant biodiversity; they were classified into 5 subphyla, 7 classes, 12 orders, 17 families, and 26 genera. Dominant endophytes varied between pre- and post-flooding plants, among different plant tissues, and between aerobic and anaerobic culture conditions. Aspergillus and Alternaria accounted for more than 55% of all isolates. Although the number of isolates from post-flooding plants was greater, endophytes from pre-flooding plants were more diverse and abundant. Endophytes were distributed preferentially in particular tissues; this affinity was constrained by both the host habitat and the oxygen availability of the host.

Growth, chlorophyll fluorescence and mineral nutrition in the halophyte Tamarix gallica cultivated in combined stress conditions: Arsenic and NaCl.

Trace metal elements can cause various environmental and health issues due to their accumulation and integration in the food chain. In the present study, we determined the major toxic effects of arsenic on physiological behaviour of plants. For this propose, several combinations of high salinity and arsenic (As) concentrations were applied to the halophytic shrub, Tamarix gallica, by growing for three months with an irrigation solution supplemented with different concentrations of As (0, 200, 500 and 800M) with and without 200mM NaCl. The effect of the combined stress conditions on growth, physiological patterns and biochemical parameters were also assessed. The results demonstrated that T. gallica is a tolerant plant regarding arsenic. The photosynthesis apparatus Fo, Fm and Fv fluorescence, as well as Fv/Fm were not affected by As nor by As combined with salt. Likewise, pigment and nutrient (K(+), Ca(2+) and Mg(2+)) contents were not affected either. However, the study results revealed that As adversely and significantly influenced the growth with increasing the concentration of As. Despite shoots growth reduction, the present research demonstrates that T. gallica is able to cope with high external concentrations of As (under 500µM) alone or in combination with NaCl.

European Tamaricaceae in bioengineering on dry soils.

We tested the bioengineering capabilities and resistance to drought of cuttings of two typical riparian species of Mediterranean and Alpine streams scarcely used in soil bioengineering: Myricaria germanica (L.) Desv. and Tamarix gallica L. We conducted two experiments, one ex situ and one in situ, with different drought treatments on cuttings of these two species in comparison with Salix purpurea L., a willow very commonly used in bioengineering. The biological traits considered were resprouting/survival rate, quantity of structural roots, above- and belowground biomass, shoot-to-root ratio, and ratio of the biomass increase between the first and second season. T. gallica and M. Germanica showed generally good capabilities for soil bioengineering use. T. gallica showed especially good resprouting rates in drought conditions with a survival rate of 97% in dry modality of the in situ experiment. M. germanica cuttings presented a much lower survival rate than the other two species in in situ experiments with harsh drought conditions from the beginning. T. gallica had a lower shoot-to-root ratio than S. purpurea for all drought treatments. M. germanica and T. gallica showed a very significant increase in belowground biomass during the second vegetative period, demonstrating that these species can quickly achieve strong anchoring. These observations confirmed the interest of these species in bioengineering.