226
On the other hand, Halimione portulacoides (L.) Aellen is a halophytic shrub
frequently found on sandy and muddy sea-shores and middle salt marshes around
the coasts of Europe, North Africa and South-West Asia. This species is frequently
the physiognomic dominant on well-drained middle marshes, often fringing channels and pools that are flooded at high tide (Chapman 1950). In several estuaries of
the Iberian Peninsula, H. portulacoides grows in sediments featuring extremely
high concentrations of metals. Several studies have explored the phytoremediation
potential of H. portulacoides under different factors, such as the presence of organic
pollutants (e.g., Duarte et al. 2007) and heavy metals (e.g., Andrades et al. 2013).
Moreover, H. portulacoides have been highlighted as having the potential for phytoextraction (Milić et al. 2012). Cambrollé et al. (2012a, b) evaluated the effects of
Zn and Cu on this species in greenhouse experiments. They concluded that this species can tolerate extremely high tissue concentrations of Cu and Zn without suffering adverse physiological effects, producing significant amounts of biomass while
sequestrating high concentrations of these metals. In this regard, Sousa et al. (2008)
stated that compartmentation and detoxification mechanisms are crucial to allow H.
portulacoides to tolerate high levels of heavy metals, and found that this halophyte
is able to retain a considerable quantity of metals in its root cell wall. Latest
approaches investigating H. portulacoides potential for remediation are focused on
the use of stem cuttings directly planted in the marsh. In this sense, Cambrollé et al.
(2016) found that this species is able to survive and grow at external Zn concentrations of 130 mmol l
−1
(approximately 9000 mg kg
−1
) during a greenhouse experiment, and determined that the use of stem cuttings with a minimum size of
approximately 10 cm in length and a minimum biomass of 100 mg dry weight
would be advisable to use to remediate soils highly polluted with Zn showing concentrations from 50 mmol l
−1
. Nevertheless, despite these promising results, this
approach still needs to be comprehensively tested on the field.
Although known to be highly salt tolerant, Salicornia spp. tolerance to heavy metals has been poorly studied (Rosso et al. 2005). Compared to results from uncontaminated sites, it has been observed that Salicornia spp. accumulate high levels of certain
metals when growing in metal-polluted sites (Bryan and Gibbs 1983). In contrast,
other studies show that metal concentration in the Salicornia spp. tissues is generally
lower in comparison with values recorded in the associated sediments (Williams
et al. 1994), with the exception of Zn, which has been observed to be hyperaccumulated. In this sense, the annual S. ramosissima has shown high capacity for Cd accumulation (Pérez-Romero et al. 2016). A recent study stated that Salicornia spp.
appears to be a suitable tool for biomonitoring Zn and Cu (Smillie 2015).
The potential of the extreme halophyte Arthrocnemum macrostachyum has been
analyzed by Redondo-Gómez et al. (2010) to determine its tolerance and ability to
accumulate Cd for phytoremediation purposes. This species, growing at high salt
marshes and salt pans, has demonstrated hypertolerance to stress by Cd, showing no
phytotoxicity at shoot concentration as high as 70 mg kg
−1
. Therefore, it has been
suggested to be a valuable species for restoring Cd-contaminated sites.
On the other hand, the high salt marsh plant species Limoniastrum monopetalum could be used in the revegetation of Cu-contaminated soils since it is able to
S.M. Vallés et al.
On the other hand, Halimione portulacoides (L.) Aellen is a halophytic shrub
frequently found on sandy and muddy sea-shores and middle salt marshes around
the coasts of Europe, North Africa and South-West Asia. This species is frequently
the physiognomic dominant on well-drained middle marshes, often fringing channels and pools that are flooded at high tide (Chapman 1950). In several estuaries of
the Iberian Peninsula, H. portulacoides grows in sediments featuring extremely
high concentrations of metals. Several studies have explored the phytoremediation
potential of H. portulacoides under different factors, such as the presence of organic
pollutants (e.g., Duarte et al. 2007) and heavy metals (e.g., Andrades et al. 2013).
Moreover, H. portulacoides have been highlighted as having the potential for phytoextraction (Milić et al. 2012). Cambrollé et al. (2012a, b) evaluated the effects of
Zn and Cu on this species in greenhouse experiments. They concluded that this species can tolerate extremely high tissue concentrations of Cu and Zn without suffering adverse physiological effects, producing significant amounts of biomass while
sequestrating high concentrations of these metals. In this regard, Sousa et al. (2008)
stated that compartmentation and detoxification mechanisms are crucial to allow H.
portulacoides to tolerate high levels of heavy metals, and found that this halophyte
is able to retain a considerable quantity of metals in its root cell wall. Latest
approaches investigating H. portulacoides potential for remediation are focused on
the use of stem cuttings directly planted in the marsh. In this sense, Cambrollé et al.
(2016) found that this species is able to survive and grow at external Zn concentrations of 130 mmol l
−1
(approximately 9000 mg kg
−1
) during a greenhouse experiment, and determined that the use of stem cuttings with a minimum size of
approximately 10 cm in length and a minimum biomass of 100 mg dry weight
would be advisable to use to remediate soils highly polluted with Zn showing concentrations from 50 mmol l
−1
. Nevertheless, despite these promising results, this
approach still needs to be comprehensively tested on the field.
Although known to be highly salt tolerant, Salicornia spp. tolerance to heavy metals has been poorly studied (Rosso et al. 2005). Compared to results from uncontaminated sites, it has been observed that Salicornia spp. accumulate high levels of certain
metals when growing in metal-polluted sites (Bryan and Gibbs 1983). In contrast,
other studies show that metal concentration in the Salicornia spp. tissues is generally
lower in comparison with values recorded in the associated sediments (Williams
et al. 1994), with the exception of Zn, which has been observed to be hyperaccumulated. In this sense, the annual S. ramosissima has shown high capacity for Cd accumulation (Pérez-Romero et al. 2016). A recent study stated that Salicornia spp.
appears to be a suitable tool for biomonitoring Zn and Cu (Smillie 2015).
The potential of the extreme halophyte Arthrocnemum macrostachyum has been
analyzed by Redondo-Gómez et al. (2010) to determine its tolerance and ability to
accumulate Cd for phytoremediation purposes. This species, growing at high salt
marshes and salt pans, has demonstrated hypertolerance to stress by Cd, showing no
phytotoxicity at shoot concentration as high as 70 mg kg
−1
. Therefore, it has been
suggested to be a valuable species for restoring Cd-contaminated sites.
On the other hand, the high salt marsh plant species Limoniastrum monopetalum could be used in the revegetation of Cu-contaminated soils since it is able to
S.M. Vallés et al.