Effects of salinity on growth,membrane permeability and root hydraulic conductivity in three saltbush species

The species of the genus Atriplex have been introduced in West Asia and North Africa to determine their adaptability for use as fodder species. These halophytes are well adapted to extreme environmental conditions and may possess interesting properties for soil rehabilitation. The effect of NaCl stress on growth, water relation and mineral nutrition were investigated in three xero-halophyte species of Atriplex used for rehabilitation of arid steppe in Algeria. Atriplex halimus, Atriplex canescens and Atriplex nummularia, were cultivated in hydroponic conditions and treated with increasing doses of NaCl (0–300 mM). All species showed positive plant growth for low and moderate levels of salinity. A. halimus had higher dry weight production than A. nummularia and A. canescens in high salinity concentration. Increasing concentration of salinity induced decrease in chlorophyll content (Chl a and b) and root hydraulic conductivity (L₀) in all species, especially in A. canescens. All three species showed marked increase in electrolyte leakage across the salinity gradient. In addition all species were able to accumulate a large quantity of sodium (Na), chloride (Cl) and proline and to maintain higher relative water content, which was probably associated with a greater capacity for osmotic adjustment, whereas potassium (K) and calcium (Ca) decreased with increase salinity. The data suggest that salt tolerance strategies in all Atriplex species could involve a delicate balance among ion accumulation, osmotic adjustment, production of osmotica and maintenance of relative water content and growth.     

The role of cotyledons in the establishment of Suaeda physophora seedlings

The role of cotyledons in seedling establishment of the euhalophyte Suaeda physophora under non-saline and saline conditions (addition of 1 mM or 400 mM NaCl) was investigated. Survival and fresh and dry weights were greater for seedlings grown in the light (12-h light/12-h dark) than in the dark (24-h dark). The shading of cotyledons tended to decrease shoot height, shoot organic dry weight, number of leaves, and survival of seedlings regardless of NaCl treatment, but the effect of cotyledon shading was greater with 400 mM NaCl. Concentrations of Na⁺ were higher in cotyledons than in leaves, regardless of NaCl treatment. The K⁺/Na⁺ ratio was lower in cotyledons than in leaves for seedlings treated with 1 mM NaCl but not for seedlings treated with 400 mM NaCl. Addition of 400 mM NaCl decreased oxygen production in cotyledons but especially in leaves. These results are consistent with the hypothesis that, by generating oxygen via photosynthesis and by compartmentalizing Na⁺, cotyledons are crucial for the establishment of S. physophora seedlings in saline environments.     

Quantitative ion localization within Suaeda maritima leaf mesophyll cells

Grown under saline conditions, Suaeda maritima accumulates Na⁺ and Cl^- into its leaves, where individual mesophyll cells behave differently in their compartmentation of these ions. Measurements of ion concentrations within selected subcellular compartments show that freeze-substitution with dry sectioning is a valuable preparative technique for analytical electron microscopy of highly vacuolate plant material. Using this approach, absolute estimates were made of Na⁺, K⁺ and Cl^- concentrations in the cytoplasm, cell walls, chloroplasts and vacuoles of leaf mesophyll cells.Abbreviation TAEM transmission analytical electron microscopy     

Comparison of niche breadths and overlaps of halophytes on salt marshes of differing diversity

Comparisons were made of niche breadths and niche overlaps of halophytes growing in two emergent saltmarsh communities differing in the number of their constituent species and in diversity. Niche parameters were calculated along the major niche dimension of tidal inundation which was assessed using three related measurements, namely height on the marsh, number of submergences per year, and longest period of continuous exposure. This reduces the danger of measuring niches on one resource dimension along which species exhibit non-linear responses. Results obtained using these three measurements were very similar. Mean niche overlaps were significantly smaller, and most species had lower niche breadths, on the marsh with more diverse vegetation. These results agree with Pianka's (1974) niche overlap hypothesis; they indicate that competitive interactions between species are acting with different intensity on the two marshes, and that such interactions are important in determining the distribution limits of both low-and high-marsh species in the emergent salt-marsh community.Nomenclature follows Clapham, Tutin & Warburg (1962). Acknowledgements. The authors gratefully acknowledge a travel grant from the British Council enabling them to attend the conference. The work was conducted whilst P.J.R. was in receipt of a Natural Environment Research Council studentship.     

Biochemical indicators of salt stress in Plantago maritima: Implications for environmental stress assessment

Our study is focused on native spontaneous species of saline ecosystems Plantago maritima. Plants were cultivated at several salt concentrations (0, 50, 100, 200, 300, 400 and 500 mM NaCl) in a glass greenhouse under semi-controlled conditions. Growth parameters, water parameters and ionic status were determined and they were used as criteria to assess the response of P. maritima under a salinity gradient. Catalase, guaiacaol and ascobate peroxidase activities, total protein and proline were also determined. Our results show that P. maritima is a facultative halophyte capable of expressing its maximum growth potential at relatively low concentrations of salt (less than 3 g l⁻¹ NaCl). At high doses of salt (concentrations > 200 mM), the decrease in the growth of P. maritima is associated to a decrease in the uptake of K⁺. There is a disruption of the water intake of their organs and therefore results an invasion of the cytoplasm by Na⁺ toxic ion. However, stressed plants use K⁺ more sparingly. They invest especially in the production of biomass expressed by the dry weight of the shoots, and they use Na⁺ and proline for osmotic adjustment. The halophyte studied is able to accumulate high levels of proline in response to increasing salt concentration. The accumulation of the amino compound, mainly in roots, is interpreted as an indicator of salt tolerance. Additionally, a significant correlation between the tolerance of the plants to salinity and the activity of several antioxidant enzymes has been observed. Hence, we suggest the possibility of using these activities as a biochemical indicator for salt tolerance in P. maritima. Our study points out two types of biomarkers of salt exposure: enzymatic biomarkers in the leaves and proline content in the roots. Both did show very good correlation with salt exposure, and thus may be considered good biomarkers of exposure with a very good dose–response relationship.     

Assessing of tolerance to metallic and saline stresses in the halophyte Suaeda fruticosa: The indicator role of antioxidative enzymes

Many areas are simultaneously affected by high concentrations of salts and trace metal elements (TME), the latter constituting a serious threat to human health. In the present study, we determined the combined effect of high salinity and toxic levels of trace elements on physiological behavior of the halophytic species Suaeda fruticosa. Plants were cultivated for three months with an irrigation solution supplemented separately with different concentrations of Pb²⁺ and Zn²⁺ (0, 200, 400 and 600 μM) with and without 200 mM NaCl. Growth, total chlorophyll, water status and ion nutrition were quantified and antioxidant enzyme activities [ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and catalase (CAT)] were studied. Our results revealed that S. fruticosa has a strong ability to tolerate lead and zinc. This halophyte accumulated higher concentrations of TME in their roots. Growth parameters of S. fruticosa were not significantly affected by TME. An enhancement of Ca²⁺ concentration accompanied by a decrease of Mg²⁺ content was observed under Pb²⁺ or Zn²⁺ treatments whereas K⁺ content was not affected by TME. Of the antioxidant enzymes, the activity of CAT and APX was increased by metal stress. However, the activity of GPX was diminished by increasing TME concentrations. It was concluded that NaCl 200 mM had a positive impact on the response of S. fruticosa to Zn²⁺ toxicity, acting through a decrease in Zn absorption.     

A note on the vegetation on islands in Lake Manzala,Egypt

Lake Manzala is one of the Deltaic Mediterranean lakes in Egypt. It comprises over 1000 islands of various sizes, the vegetation of which is halophytic. Seven community types are described, dominated by: Phragmites australis, Juncus acutus, J. rigidus, Arthrocnemum macrostachyum, Atriplex portulacoides, Halocnemum strobilaceum and Zygophyllum aegyptium. Each of these communities has been analysed and its habitat described and discussed.     

盐生植物翅碱蓬的内生真菌多样性分析

【目的】对辽宁省盘锦市双台子河口国家自然保护区的盐生植物翅碱蓬(Suaedaheteroptera Kitag.)的内生真菌进行研究。【方法】利用传统分离方法对翅碱蓬的根、茎、叶组织进行分离和纯化,根据形态学和理化特征,并结合rDNA-ITS序列分析对菌种进行鉴定。【结果】共分离得到内生真菌49株,这些内生真菌分属于13个属,其中小丛壳菌属(Glomerella)、链格孢属(Alternaria)、毛盘孢属(Colletotrichum)和枝孢属(Cladosporium)为优势菌属。翅碱蓬的内生真菌分布具有一定的组织特异性,两种不同生境中的翅碱蓬内生真菌群落丰富度差异较小,相似度较高,但在某些种属上存在特异性。【结论】翅碱蓬体内含有丰富的内生真菌资源,其内生真菌具有很高的宿主特异性,而且其分布受生境影响。