Use Of Halophytes Research Articles

The Sustainable Use of Halophytes in Salt-Affected Land: State-of-the-Art and Next Steps in a Saltier World.

Salinization is a major cause of soil degradation that affects several million hectares of agricultural land, threatening food security and the sustainability of agricultural systems worldwide. Nevertheless, despite the negative impact of salinity, salt-affected land also provides several important ecosystem services, from providing habitats and nurseries for numerous species to sustainable food production. This opinion paper, written in the framework of the EU COST Action CA22144 SUSTAIN on the sustainable use of salt-affected land, therefore, focuses on the potential of halophytes and saline agriculture to transform and restore key functions of these salt-affected and marginal lands. As the current knowledge on sustainable saline agriculture upscaling is fragmented, we highlight (i) the research gaps in halophyte and salinity research and (ii) the main barriers and potentials of saline agriculture for addressing food security and environmental sustainability in terms of population growth and climate change.

Arbuscular mycorrhizal fungi regulate amino acid metabolism, phytohormones and glycolysis pathway to promote the growth of Suaeda salsa under combined Cd and NaCl stresses

The use of halophytes in conjunction with arbuscular mycorrhizal (AM) fungi has been found to enhance the removal efficacy of heavy metals and salts in heavy metals contaminated saline soil. The mechanisms of AM fungi on promoting halophyte growth and regulating metabolism remain unclear. In this study, combinations of 0 g kg−1 NaCl and 3 mg kg−1 Cd (S0Cd3), 6 g kg−1 NaCl and 3 mg kg−1 Cd (S6Cd3), and 12 g kg−1 NaCl and 3 mg kg−1 Cd (S12Cd3) were employed to explore the impact of Funneliformis mosseae on the growth and metabolism of Suaeda salsa. The results showed that AM fungi increased the biomass and the P, K+, Ca2+, and Mg2+ accumulations, reduced the Cd and Na+ concentrations in S0Cd3 and S6Cd3, and increased the Cd concentrations in S12Cd3. AM fungi inoculation reduced the Cd and Na+ transfer factors and increased the Cd and Na+ accumulations in S6Cd3. The metabolomics of S6Cd3 showed that AM fungi upregulated the expression of 5-hydroxy-L-tryptophan and 3-indoleacid acid in tryptophan metabolism, potentially acting as crucial antioxidants enabling plants to actively cope with abiotic stresses. AM fungi upregulated the expression of arbutin in glycolysis process, enhancing the plants’ osmoregulation capacity. AM fungi upregulated the expression of 2-hydroxycinnamic acid in phenylalanine metabolism and dopaquinone in tyrosine metabolism. These two metabolites help effectively remove reactive oxygen species. Correspondingly, AM fungi decreased MDA content and increased soluble sugar content. These results indicate that AM fungi improve the stress resistance of S. salsa by increasing nutrient uptake and regulating physiological and metabolic changes.

Improving crop salt tolerance through soil legacy effects.

Soil salinization poses a critical problem, adversely affecting plant development and sustainable agriculture. Plants can produce soil legacy effects through interactions with the soil environments. Salt tolerance of plants in saline soils is not only determined by their own stress tolerance but is also closely related to soil legacy effects. Creating positive soil legacy effects for crops, thereby alleviating crop salt stress, presents a new perspective for improving soil conditions and increasing productivity in saline farmlands. Firstly, the formation and role of soil legacy effects in natural ecosystems are summarized. Then, the processes by which plants and soil microbial assistance respond to salt stress are outlined, as well as the potential soil legacy effects they may produce. Using this as a foundation, proposed the application of salt tolerance mechanisms related to soil legacy effects in natural ecosystems to saline farmlands production. One aspect involves leveraging the soil legacy effects created by plants to cope with salt stress, including the direct use of halophytes and salt-tolerant crops and the design of cropping patterns with the specific crop functional groups. Another aspect focuses on the utilization of soil legacy effects created synergistically by soil microorganisms. This includes the inoculation of specific strains, functional microbiota, entire soil which legacy with beneficial microorganisms and tolerant substances, as well as the application of novel technologies such as direct use of rhizosphere secretions or microbial transmission mechanisms. These approaches capitalize on the characteristics of beneficial microorganisms to help crops against salinity. Consequently, we concluded that by the screening suitable salt-tolerant crops, the development rational cropping patterns, and the inoculation of safe functional soils, positive soil legacy effects could be created to enhance crop salt tolerance. It could also improve the practical significance of soil legacy effects in the application of saline farmlands.

Valorization of Salicornia patula Duval-Jouve Young Shoots in Healthy and Sustainable Diets.

The revalorization of natural resources in food production is increasing, and the effect of climate change is negatively affecting the production of conventional crops. In recent years, edible halophytes have received more attention due to their ability to tolerate a wide range of salinities. Thus, the use of halophytes that require less water and are strongly adapted to high-salinity soil and coastal areas can provide sustainable agriculture in certain areas. In addition, there is growing interest in the study of the possibilities that these species offer as foods due to their excellent nutritional profile and antioxidant properties. For that reason, the exploitation of plants adapted to these areas is nowadays even more important than in the past to guarantee food security in arid or semiarid salinized territories. The available data about the nutrients and bioactive compounds composition of many non-cultivated edible vegetables traditionally used in the Mediterranean area, such as Salicornia edible young shoots, are still scarce. With the aim of improving the knowledge on their nutritional value, the present study provides new data about the content of some compounds with biological activity, such as fiber and organic acids, in eight samples of young shoots of S. patula Duval-Jouve gathered in great mainland and coastal salt marshes in Southwest and Central Spain. Results showed that this vegetable can be considered a healthy food and a very good source of dietary fiber (4.81-6.30 g/100 g fw total fiber). Its organic acid profile showed oxalic, malic, citric and succinic acids. Oxalic acid was the major one, with mean values of 0.151-1.691 g/100 g fw. From the results obtained in this study, S. patula shoots could be recommended as an alternative source of fiber for healthy and sustainable diets in the general adult population with no risk of renal disease.

Evaluating the Enzyme Activities and Soil Physicochemical Properties of Four Typical Halophytic Communities in Saline-Sodic Soil

Four typical halophytic communities found in saline-sodic soil, including Phragmites australis, Suaeda glauca, Leymus chinensis, and Puccinellia parl, were investigated in this study. A comparison was made among the electrical conductivity (EC) value, pH value, soil organic carbon (SOC), and soil enzyme activity across various soil depths. The findings of this study indicate that the EC and pH levels of the soil at the 0–40 cm depth vary among the four communities, with Suaeda glauca having the highest values, followed by Puccinellia parl, Phragmites australis, and Leymus chinensis. The highest value of SOC among the four communities was observed in the Leymus chinensis community (0.85–0.94 g/kg), followed by the Phragmites australis community (0.50–0.77 g/kg), and the lowest levels were observed in the Puccinellia parl community (0.37–0.78 g/kg). As the soil depth increases, there is a decline in the amount of SOC. With an increase in soil depth, the content of SOC in the soil decreased, and the content of total nitrogen (TN) and the activity of six enzymes in the soil of each community increased. Furthermore, at the soil layer of 0–20 cm, the TN content in the soils was negatively correlated with pH and EC (p < 0.01), and so was the total phosphorus (TP). Additionally, the TP content is considerably positively connected with alkaline phosphatase (ALP) activity, whereas the TN content is significantly positively correlated with Soil Urease (S-UE) activity. Within the soil depth of 20–40 cm, the levels of TN, TP, and SOC exhibit a negative association with pH and EC. However, this link is weaker compared to that observed in the surface soil. A strong inverse correlation (p < 0.05) exists between the TP concentration and the ALP activity. The objective of this study was to investigate the use of halophytes in various saline-sodic soils for diverse avenues of restoration, and to establish a database on the role and efficacy of plant roots in enhancing saline-sodic soil.

Evaluation of the potential of two halophytes to extract Cd and Zn from contaminated saltwater.

The contamination of saltwater by toxic heavy metals has become a worldwide problem. The application of phytoextraction to remove these pollutants seems to be more efficient and cheaper compared to physicochemical methods. In this work, we evaluated the potential of two halophyte species to accumulate cadmium and zinc from contaminated water. Seedlings of Carpobrotus edulis L. and Sesuvium portulacastrum L. were cultivated during 1 month on pots filled with saltwater (200 mM NaCl) containing different concentrations of Cd2+ (0, 50, 100 μM) and of Zn2+ (0, 200, and 400 μM) applied separately. Results showed that both halophytes were more resistant to Zn2+ than Cd2+ and that Sesuvium better tolerates the two metals. Zn2+ and Cd2+ concentrations in the shoot as well as the values of translocation factors suggest that these species are able to absorb and to concentrate Cd2+ and Zn2+ in their roots and shoots. Hence, after 1 month of culture on 50 μM Cd2+, plants were able to extract 31% and 21% of Cd, respectively, in S. portulacastrum and C. edulis. The Zn-extraction efficiency was less important and reached 18 and 19%, respectively, in S. portulacastrum and C. edulis cultivated under 200 μM Zn2+. Given together, data demonstrate the efficiency of the use of halophytes, especially S. portulacastrum, to extract Zn2+ and Cd2+ from salt wastewater.

Floristic Inventory of Ethnobotanically Important Halophytes of North-Western Mediterranean Coastal Brackish Areas, Tuscany, Italy

Plants have always been used by people for multiple purposes, but over the centuries knowledge of useful plants has largely been lost. Through ethnobotanical studies it is possible to retrieve information on the uses of plants and renew the ancient attention to plants which could be useful to apply in modern applications. In this context, the ethnobotanical use of halophytes has not been explored in depth. The present study focused on the flora of two brackish areas of the north-western Mediterranean sited in Tuscany, Italy. This research aimed to identify the halophyte species of ethnobotanical interest and create a relative map database of the study areas. The floristic list of the two areas, including 78 halophyte and non-halophyte species, was created following periodic field sampling, localization of the species by GPS, and taxonomic identification. The ethnobotanical information was acquired through a bibliographic survey. Botanical, geographic, and ethnobotanical information was filed and included in floristic maps produced using the free Open Source QGIS software. Of the total wild species surveyed, 50% were halophytes with ethnobotanical properties, with a predominance for medicinal ones. Some of them are the subject of numerous studies today such as those on antioxidants. Both investigated areas showed a high floristic and ethnobotanical value. This makes them interesting as potential germplasm banks to be used in various application contexts of ethnobotany.

Halophytes as Medicinal Plants against Human Infectious Diseases

Halophytes have long been used for medicinal purposes. However, for many decades, their use was entirely empirical, with virtually no knowledge of the bioactive compounds underlying the different applications. In recent decades, the growing problem of antibiotic resistance triggered the research on alternative antimicrobial approaches, and halophytes, along with other medicinal plants, regained attention as an underexplored pharmacological vein. Furthermore, the high nutritional/nutraceutical/pharmacological value of some halophytic species may represent added value to the emerging activity of saline agriculture and targeted modification of the rhizosphere, with plant-growth-promoting bacteria being attempted to be used as a tool to modulate the plant metabolome and enhance the expression of interesting metabolites. The objective of this review is to highlight the potential of halophytes as a valuable, and still unexplored, source of antimicrobial compounds for clinical applications. For that, we provide a critical perspective on the empirical use of halophytes in traditional medicine and a state-or-the-art overview of the most relevant plant species and metabolites related with antiviral, antifungal and antibacterial activities.

Salicornia dolichostachya organosolv fractionation: towards establishing a halophyte biorefinery.

Halophytes are a potential source of lignocellulosic material for biorefinery, as they can be grown in areas unsuitable for the cultivation of crops aimed at food production. To enable the viable use of halophytes in biorefineries, the present study investigated how different organosolv process parameters affected the fractionation of green pressed fibers of Salicornia dolichostachya. We produced pretreated solids characterized by up to 51.3% ± 1.7% cellulose, a significant increase from 25.6% ± 1.3% in untreated fibers. A delignification yield of as high as 60.7%, and hemicellulose removal of as high as 86.1% were also achieved in the current study. The obtained cellulose could be completely converted to glucose via enzymatic hydrolysis within 24 h. The lignin fractions obtained were of high purity, with sugar contamination of only 1.22% w/w and ashes below 1% w/w in most samples. Finally, up to 29.1% ± 0.4% hemicellulose was recovered as a separate product, whose proportion of oligomers to total sugars was 69.9% ± 3.0%. To the best of our knowledge, this is the first report in which Salicornia fibers are shown to be a suitable feedstock for organosolv biomass fractionation. These results expand the portfolio of biomass sources for biorefinery applications.

Comprehensive transcriptome and metabolome profiling reveal metabolic mechanisms of Nitraria sibirica Pall. to salt stress

Nitraria sibirica Pall., a typical halophyte that can survive under extreme drought conditions and in saline-alkali environments, exhibits strong salt tolerance and environmental adaptability. Understanding the mechanism of molecular and physiological metabolic response to salt stress of plant will better promote the cultivation and use of halophytes. To explore the mechanism of molecular and physiological metabolic of N. sibirica response to salt stress, two-month-old seedlings were treated with 0, 100, and 400 mM NaCl. The results showed that the differentially expressed genes between 100 and 400 mmol L−1 NaCl and unsalted treatment showed significant enrichment in GO terms such as binding, cell wall, extemal encapsulating structure, extracellular region and nucleotide binding. KEGG enrichment analysis found that NaCl treatment had a significant effect on the metabolic pathways in N. sibirica leaves, which mainly including plant-pathogen interaction, amino acid metabolism of the beta alanine, arginine, proline and glycine metabolism, carbon metabolism of glycolysis, gluconeogenesis, galactose, starch and sucrose metabolism, plant hormone signal transduction and spliceosome. Metabolomics analysis found that the differential metabolites between the unsalted treatment and the NaCl treatment are mainly amino acids (proline, aspartic acid, methionine, etc.), organic acids (oxaloacetic acid, fumaric acid, nicotinic acid, etc.) and polyhydric alcohols (inositol, ribitol, etc.), etc. KEGG annotation and enrichment analysis showed that 100 mmol L−1 NaCl treatment had a greater effect on the sulfur metabolism, cysteine and methionine metabolism in N. sibirica leaves, while various amino acid metabolism, TCA cycle, photosynthetic carbon fixation and sulfur metabolism and other metabolic pathways have been significantly affected by 400 mmol L−1 NaCl treatment. Correlation analysis of differential genes in transcriptome and differential metabolites in metabolome have found that the genes of AMY2, BAM1, GPAT3, ASP1, CML38 and RPL4 and the metabolites of L-cysteine, proline, 4-aminobutyric acid and oxaloacetate played an important role in N. sibirica salt tolerance control. This is a further improvement of the salt tolerance mechanism of N. sibirica, and it will provide a theoretical basis and technical support for treatment of saline-alkali soil and the cultivation of halophytes.

Increasing the value of Salicornia bigelovii green biomass grown in a desert environment through biorefining

Utilizing saline soil and water resources are essential in meeting future demands for food, feed, and biofuels in a world of increasing freshwater scarcity, by use of halophytes (salt-loving plants). The succulent halophyte Salicornia bigelovii Tor. was cultivated as a green biomass crop irrigated with saline aquaculture effluents, and bio-fractionation was tested as a way to improve the value of the crop. Bio-fractionation proved to be an effective way of extracting ash and nitrogen into the green juice fraction, from which a protein concentrate was produced with 15 % crude protein and 33 % ash. The fiber fraction was not found useful as fodder due to a relatively low crude protein content of 4.1 % and 10–12 % remaining ash. However, the high digestibility of the structural carbohydrates in the fiber demonstrated its potential as a feedstock for biorefining with estimated bioethanol yields around 2500 L/ha.

Mathematical modeling and quality parameters of Salicornia fruticosa dried by convective drying.

The effect of convective drying at 50, 60 and 70°C on the drying kinetics and quality parameters of Salicornia fruticosa was investigated. To estimate the equilibrium moisture content a desorption isotherm was performed using five empirical models: Halsey, Caurie, Henderson, Smith and Oswin. The experimental data was also fitted to different drying kinetic models (Logarithmic, Two-Terms, Midilli-Kucuk and Exponential Two-Terms). A numerical simulation using the Finite Volume Method allowed us to describe the evolution of temperature and moisture content distributions during drying. The Henderson model was found to be the most suitable for predicting the equilibrium moisture content of S. fruticosa, with values of X we in the drying process of 1.51; 1.54 and 1.36g water/g d.m for 50, 60 and 70°C, respectively. A good agreement was found between the numerical and experimental results of temperature and moisture during Salicornia drying. The Midilli-Kucuk model presented the best fitting to the drying curves. The effects of drying on S. fruticosa were significant in two quality parameters. Antioxidant capacity decreased in ca. 45% and lightness (> L*) significantly increased at a drying temperature of 70°C, compared to the fresh samples. The optimum drying temperature where drying time and nutrients loss was minimum was 70°C. These results can be used to estimate the best drying conditions for producing dehydrated Salicornia. The use of halophytes as sustainable crops is promising, and the vision of their commercial production must be evaluated and considered, given water scarcity in many areas of the planet.

Biochemical and Molecular Genetics Identification of Salicornia sp. and Sarcocornia sp. in the North Coast of Egypt

Because water scarcity anticipated to increase within the destiny in particular with growing global population and the rise in prosperity problem of the shortage of water suitable for cultivation of meals plants inside the global is growing in arid and semi-arid regions. There is the call to discover some other plant resource that doesn’t need freshwater i.e. able to grow using seawater. It is worth to note that Salicornia sp. and Sarcocornia sp. may be grown at the seawater. Currently, considered one of the most crucial issues dealing with Egypt is a way to provide food within the frame of limiting to be had soils for cultivation, limitation of water resources, especially after Ethiopian Nahda Dam and growing in population. Accordingly, the use of halophytes forage plants (Salicornia and Sarcocornia) using seawater has emerged as one in all the most exciting and intelligent research points. Therefore, a case observe was carried out in 2018 and 2019 to evaluate the nutritional status of Salicornia and Sarcocornia plants which can be grown on salty water in the North Coast of Egypt. Five samples of Salicornia and Sarcocornia amassed from Damietta Port Said coastal road and identified depends on phenotypic homes to Sarcocornia perennis (DA), Sarcocornia perennis (PS), Sarcocornia fruticosa, Salicornia europaea and Salicornia herbacea. Proximate composition analyses were carried out. It turned into obtrusive that, among dry biomass, carbohydrate has become in the most important proximate compositions in the Sarcocornia sp. and Salicornia sp. Tissues observed through ash. Molecular evaluation by SCoT techniques turned into done for Salicornia and Sarcocornia. The SCoT molecular marker techniques reach producing reproducible and dependable amplicons. Even though that the SCoT technique became higher in assessment for molecular variety and discrimination ability for all studied Salicornia and Sarcocornia.The results obtained have shown that the high nutritional value of the plant in terms of protein content, carbohydrates content and as a result, it is suitable for food

Presowing seed treatment with glycine betaine confers NaCl tolerance in quinoa by modulating some physiological processes and antioxidant machinery

Soil salinity threatens the yield and food security worldwide and use of halophytes might be a valid option to cope with devastating salinity effects. The present investigation was accomplished to evaluate the role of glycine betaine (GB) as presowing seed treatment on growth parameters, photosynthetic pigments, gas exchange attributes, enzymatic antioxidants, lipid peroxidation (MDA), hydrogen peroxide (H2 O2 ), endogenous GB, total soluble proteins (TSP), and yield in quinoa (Chenopodium quinoa) under saline conditions. Ames-13737 (Q7) and PI-634919 (Q9) quinoa accessions were used for this trial. The plants were applied with two salt stress treatments (Control and 450 mM NaCl) after 45 days of sowing. Presowing seed treatments with GB (water, 10 and 20 mM) were given for 12 h. Each treatment replicated four times through completely randomized design. Imposition of salinity triggered a major decrease in growth, photosynthetic pigments, net CO2 assimilation rate (A), transpiration rate (E), and stomatal conductance (gs ), while the level of lipid peroxidation and activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced. Slight increment in total soluble proteins was observed along with higher endogenous GB in quinoa under salinity. Both levels of GB increased the shoot length, shoot fresh, and dry weights in accession PI-634919 under saline regime. Photosynthetic attributes, E and gs were increased when 20 mM of GB was applied under saline conditions. Activities of antioxidant enzymes, TSP, endogenous glycine betaine and yield parameters were also increased when GB was applied. Presowing treatment with GB in quinoa plants prominently decreased the MDA and H2 O2 concentration. The concentration of 10 mM GB enhanced the panicle length while 20 mM GB showed same results for 1000 seed weight and TSP under saline conditions. Overall, quinoa accession Ames-13737 was better as compared to PI-634919 in terms of growth rate, photosynthetic properties, gas exchange parameters, enzymatic antioxidants, and yield.

Beneficial Effects of Salt on Halophyte Growth: Morphology, Cells, and Genes.

Halophytes can survive and complete their life cycle in the presence of ≥200 mM NaCl. These remarkable plants have developed various strategies to tolerate salinity and thrive in high-salt environments. At the appropriate levels, salt has a beneficial effect on the vegetative growth of halophytes but inhibits the growth of non-halophytes. In recent years, many studies have focused on elucidating the salt-tolerance mechanisms of halophytes at the molecular, physiological, and individual level. In this review, we focus on the mechanisms, from the macroscopic to the molecular, underlying the successful growth of halophytes in saline environments to explain why salt has beneficial effects on halophytes but harmful effects on non-halophytes. These mechanisms include the specialized organs of halophytes (for example, ion compartmentalization in succulent leaves), their unique structures (salt glands and hydrophobic barriers in roots), and their salt-tolerance genes. We hope to shed light on the use of halophytes for engineering salt-tolerant crops, soil conservation, and the protection of freshwater resources in the near future.

Towards saving freshwater: halophytes as unconventional feedstuffs in livestock feed: a review.

Water represents 71% of all earth area and about 97% of this water is salty water. So, only 3% of the overall world water quantity is freshwater. Human can benefit only from 1% of this water and the remaining 2% freeze at both poles of earth. Therefore, it is important to preserve the freshwater through increasing the plants consuming salty water. The future prosperity of feed resources in arid and semi-arid countries depends on economic use of alternative resources that have been marginalized for long periods of time, such as halophytic plants, which are one such potential future resource. Halophyte plants can grow in high salinity water and soil and to some extent during drought. The growth of these plants depends on the contact of the salted water with plant roots as in semi-desert saline water, mangrove swamps, marshes, and seashores. Halophyte plants need high levels of sodium chloride in the soil water for growth, and the soil water must also contain high levels of salts, as sodium hydroxide or magnesium sulfate. There are many uses for halophyte plants, including feed for animals, vegetables, drugs, sand dune stabilizers, wind shelter, soil cover, wetland cultivation, laundry detergents, and paper production. This paper will focus on the use of halophytes as a feed additive for animals. In spite of the good nutritional value of halophytes, some anti-nutritional factors as nitrates, nitrite complexes, tannins, glycosides, phenolic compounds, saponins, oxalates, and alkaloids may be present in some of them. The presence of such anti-nutritional agents makes halophytes unpalatable to animals, which tends to reduce feed intake and nutrient use. Therefore, the negative effects of these plants on animal performance are the only objection against using halophytes in animal feed diets. This review article highlights the beneficial impact of considering halophytes in animal feeding on saving freshwater and illustrates its nutritive value for livestock from different aspects.

Phytoremediation of heavy metal contaminated saline soils using halophytes: current progress and future perspectives

Soil salinity is a destructive environmental stressor that greatly reduces plant growth and productivity. In recent years, large tracts of farmland in arid and semiarid regions have been simultaneously affected by salinity and heavy metal pollution, arousing widespread environmental concern. Phytoremediation, defined as the use of plants to remove pollutants from the environment and (or) to render them harmless, is a low cost, environmentally friendly, and effective method for the decontamination of soils polluted by heavy metals. Halophytes, which can survive and reproduce in high-salt environments, are potentially ideal candidates for phytoremediation of heavy metal contaminated saline soils. In this review, we discuss the current progress on the use of halophytes, their tolerance mechanisms to salt and heavy metal toxicity, and their potential for phytoremediation in heavy metal contaminated saline soils. The relative mechanisms are discussed and the future perspectives are proposed.

Use of halophytes in pilot-scale horizontal flow constructed wetland treating domestic wastewater.

Recent findings encourage the use of halophytes in constructed wetlands for domestic wastewater treatment due to their special physiological characteristics as the ability to accumulate heavy metals and salts in their tissues makes them ideal candidates for constructed wetland vegetation. In this particular study, we investigated the application of halophytic plants in a horizontal flow constructed wetland for domestic wastewater treatment purposes. The pilot plant which was situated in Crete (Greece) was planted with a polyculture of halophytes (Tamarix parviflora, Juncus acutus, Sarcocornia perrenis, and Limoniastrum monopetalum). The system's performance was monitored for a period of 11months during which it received primary treated wastewater from the local wastewater treatment plant. Results show that halophytes developed successfully in the constructed wetland and achieved organic matter and pathogen removal efficiencies comparable to those reported for reeds in previous works (63% and 1.6 log units, respectively). In addition, boron concentration in the effluent was reduced by 40% in comparison with the influent. Salinity as expressed by electrical conductivity did not change during the treatment, indicating that the accumulation of salts in the leaves is not able to overcome electrical conductivity increasing due to evapotranspiration. The results indicate an improvement in the treatment of domestic wastewater via the use of halophyte-planted CWs.

Cadmium hampers salt tolerance of Sesuvium portulacastrum

It is well known that salinity reduces cadmium toxicity in halophytes. However, the possible interference of Cd with the mechanisms of salt tolerance is poorly explored. The aim of this study was to see whether Cd affects salt tolerance mechanisms in the halophyte Sesuvium portulacastrum. S. portulacastrum plants obtained from cuttings were grown in hydroponics for 3 weeks and then exposed to low (0.09 mM) or moderate (200 mM) NaCl concentrations, alone or in combination with 25 μM CdCl2. Microscopy observation revealed two strategies of salt tolerance: euhalophytism and secretion of salt by bladder cells. Cadmium exposure hardly influenced the total leaf Na+ concentrations. However, Cd supply delayed the salt–induced upregulation of AHA1 (plasma membrane H+-ATPase 1) and SOS1 (plasma membrane Na+ transporter “Salt Overly Sensitive 1”), genes that are essential for salt tolerance. Moreover, Cd induced the activation of BADH, coding for betaine aldehyde dehydrogenase, indicating enhanced osmotic stress due to Cd. Sodium-green fluorescence in protoplasts from plants grown with low or high NaCl, alone or in combination with Cd, revealed higher Na+ concentrations in the cytoplasm of Cd-exposed plants. Taken together the results indicate interference of Cd with salt tolerance mechanisms in S. portulacastrum. This may have consequences for the efficient use of halophytes in phytoremediation of Cd-contaminated saline soils.

Halophytes as vertical-flow constructed wetland vegetation for domestic wastewater treatment

Recent findings show that halophytes have the ability to accumulate salts in their tissues, making them a very interesting group of plants for domestic wastewater treatment in constructed wetlands (CWs). In that case, it might be possible to reduce the salinity of the final effluent, which is a crucial parameter for wastewater reuse in agriculture. During this study three halophytes, Atriplex halimus, Juncus acutus and Sarcocornia perennis, were tested for phyto-desalination of domestic wastewater in a vertical flow constructed wetland (VFCW) and compared with common reeds (Phragmites australis). In addition, the effect of this alternative vegetation on the overall performance of the system regarding organic matter, nutrients, boron and pathogen removal was monitored. The organic loading rate (OLR) was about 21gCOD/m2/d and the hydraulic loading rate (HLR) was 95mm/d in both cases. Promising results were obtained for A. halimus, which shows high biomass productivity and significant capability to accumulate salts, mainly Na, in its tissues. A positive effect on pathogen removal efficiency was also recorded. However, nitrogen concentration in the effluent of the VFCW planted with halophytes was found to be higher than in the effluent of the VFCW planted with reeds. Finally, no significant effect on organic matter and phosphorus removal efficiency was observed from the use of halophytes in place of reeds.