Eleni Manousaki

Halophytes—An Emerging Trend in Phytoremediation

Halophytic plants are of special interest because these plants are naturally present in environments characterized by an excess of toxic ions, mainly sodium and chloride. Several studies have revealed that these plants may also tolerate other stresses including heavy metals based on the findings that tolerance to salt and to heavy metals may, at least partly, rely on common physiological mechanisms. In addition, it has been shown that salt-tolerant plants may also be able to accumulate metals. Therefore, halophytes have been suggested to be naturally better adapted to cope with environmental stresses, including heavy metals compared to salt-sensitive crop plants commonly chosen for phytoextraction purposes. Thus, potentially halophytes are ideal candidates for phytoextraction or phytostabilization of heavy metal polluted soils and moreover of heavy metal polluted soils affected by salinity. Some halophytes use excretion processes in order to remove the excess of salt ions from their sensitive tissues and in some cases these glandular structures are not always specific to Na+ and Cl− and other toxic elements such as cadmium, zinc, lead, or copper are accumulated and excreted by salt glands or trichomes on the surface of the leaves—a novel phytoremediation process called “phytoexcretion.” Finally, the use of halophytes has also been proposed for soil desalination through salt accumulation in the plant tissue or dissolution of soil calcite in the rhizosphere to provide Ca2+ that can be exchanged with Na+ at cation exchange sites.

Pb and Cd Accumulation and Phyto-Excretion by Salt Cedar (Tamarix Smyrnensis Bunge)

The accumulation and excretion of lead (Pb) and cadmium (Cd) by salt cedar (Tamarix smyrnensis Bunge) were investigated in this study. Tamarix smyrnensis plants were exposed to the mixtures of Pb and Cd and high salinity for 10 wk. Subsequently, Pb and Cd uptake was quantified in the shoots and roots of the plants by ICP-AES. In addition, physiological parameters such as biomass production, shoot length, plant appearance, and chlorophyll content were examined. The roots accumulated the highest amount of Pb. Salinity was found to not have an important effect on Pb translocation to the leaves. Cd was translocated into the aerial part in a higher portion than Pb. Cd content in leaves of T. smyrnensis increased with the increasing salinity. The visible toxicity symptoms, if present, were connected only to the high salinity. The excretion of Pb and Cd by salt glands was observed and quantified. T. smyrnensis excreted a significant amount of metals on the leaf surface. This characteristic of salt cedar plants can be viewed as a novel phytoremediation process for the remediation of sites contaminated with heavy metals that we have termed “phyto-excretion.

Mitigation measures for chromium-VI contaminated groundwater - The role of endophytic bacteria in rhizofiltration.

A constructed wetland pilot with Juncus acutus L. plants was investigated for its rhizofiltration efficiency in treating Cr(VI)-contaminated groundwater. Measurements of Cr(VI) and total Cr were performed to estimate the rate of removal. In addition, Cr concentration in plant tissues was measured and the role of endophytic bacteria on plants tolerance to Cr(VI) toxicity was investigated. The results support that J. acutus is able to rhizofiltrate Cr(VI) from contaminated water with up to 140μg/L while Cr content analysis in plant tissues revealed that the majority of Cr was accumulated by the plants. Moreover, two leaf (Acidovorax sp. strain U3 and Ralstonia sp. strain U36) isolated endophytic bacteria were found to tolerated 100mg/L Cr(VI) while nine root isolates showed resistance to 500mg/L Cr(VI). The endophytic bacteria Pseudomonas sp. strain R16 and Ochrobactrum sp. strain R24 were chosen for Cr(VI) reduction assays. All four strains exhibited a strong potential to reduce Cr(VI) to Cr(III) aerobically. Among them Pseudomonas sp. strain R16 was found able to completely reduced 100mg/L Cr(VI) after 150h of incubation. These results suggest that J. acutus is an excellent choice for CWs whose function is the removal of Cr(VI) from contaminated groundwater for subsequent use in crop irrigation.

Metal Phytoremediation by the Halophyte Limoniastrum monopetalum (L.) Boiss: Two Contrasting Ecotypes

The phytoremediation potential of the halophyte Limoniastrum monopetalum for the removal of Cd and Pb from polluted sites is assessed in this work. Two pot experiments were conducted; the first with wild L. monopetalum grown on soil polluted with Cd and Pb irrigated at different salinities, and the second with commonly cultivated ornamental L. monopetalum grown on soil polluted with Cd irrigated also at different salinities. The data revealed that wild L. monopetalum is a Cd and Pb tolerant plant able to accumulate at least 100 ppm of cadmium in its shoots without showing any significant decrease in terms of biomass production, chlorophyll content or water content suggesting that it could be an accumulator of Cd. Pb above-ground accumulation was kept at low levels with the majority of Pb localized in the roots. On the other hand, contrasting results were obtained for ornamental L. monopetalum which although it was found to be also Cd tolerant, Cd accumulation in its tissues was kept at significantly lower levels especially compared to that of the wild ecotype. In addition for ornamental L. monopetalum salinity did not have a positive effect on Cd accumulation and translocation as observed in the wild type and in other halophytes. Analysis of the salt excretion crystals on the leaf surface confirmed that wild and cultivated ornamental L. monopetalum excrete cadmium and lead through their salt glands as a possible metal detoxification mechanism, although the amount excreted by the ornamental L. monopetalum is significantly less.

11th International Phytotechnologies Conference, Heraklion, Crete, Greece, September 30−October 3, 2014

11th International Phytotechnologies Conference, Heraklion, Crete, Greece, September 30−October 3, 2014 Nicolas Kalogerakis , Thrassyvoulos Manios & Eleni Manousaki To cite this article: Nicolas Kalogerakis , Thrassyvoulos Manios & Eleni Manousaki (2016) 11th International Phytotechnologies Conference, Heraklion, Crete, Greece, September 30−October 3, 2014, International Journal of Phytoremediation, 18:6, 535-535, DOI: 10.1080/15226514.2016.1144428 To link to this article: http://dx.doi.org/10.1080/15226514.2016.1144428