The Atriplex genus: a promising resource for phytoremediation of heavy metal and metalloid-contaminated sites in arid regions

Phytoremediation of areas polluted by heavy metals and toxic metalloids is challenging, particularly in arid regions where limited water availability compromises plant establishment. This study shows that several Atriplex species ( A. halimus, A. canescens, A. nummularia, A. atacamensis, A. hortensis , etc.) can be used in a phytostabilization and/or phytoextraction strategy. Many of these species are xero-halophytic plants with C 4 metabolism that are adapted to harsh conditions. A deep root system allows contaminants to be removed from deep within the soil. These species can accumulate heavy metals and toxic metalloid elements and develop tolerance mechanisms associated with the synthesis of osmoprotective compounds (proline and glycinebetaine), phytochelatins and metallothioneins, and endogenous antioxidant compounds. Sequestration of toxic elements in cell walls or excretion into leaf trichomes contributes to this tolerance. In many cases, transfer factors greater than 1 suggest that these plants can be used to decontaminate polluted sites. Adult plants can produce 3 t.ha -1 of dry matter, and the quantities of pollutants effectively removed from the soil can be significant (from 500 g to several kg per hectare in a single harvest, depending on the pollutant). The application of chelating agents can be useful in increasing the bioavailability of toxic elements, and fertilization, mainly with nitrogen, may be required when the soil is not very fertile and a high plant density (up to 4,000 plants per hectare) is used to help combat erosion. Species of the genus Atriplex are characterized by significant intraspecific genetic variability, and their use therefore requires prior identification of the material best suited to the various pollutants present. Many species of this fascinating genus constitute particularly promising plant material for the low-cost management of large areas of polluted land in arid regions, helping to combat erosion, gradually decontaminate the soil, and restore the ecological balance of marginal areas.