A comparison of chelator‐facilitated metal uptake by a halophyte and a glycophyte

Abstract

Phytoextraction is the use of plants to remove contaminants, in particular metals, from soil via root uptake and translocation to the shoots. Efficient phytoextraction requires high-biomass plants with efficient translocating properties. Halophytes characteristically accumulate large quantities of salts in above ground tissue material and can have high biomass production. It has been speculated that salt-tolerant plants may also be heavy metal tolerant and, further, may be able to accumulate metals. This study compared growth and metal uptake by a halophyte, Atriplex nummularia, and a common glycophyte, Zea mays, in a mine-tailing contaminated soil:mulch mixture. Two chelators, ethylenediaminetetraacetic acid (EDTA) and rhamnolipid, were used to facilitate plant metal uptake. Despite a lower growth rate (2% growth/d) in the contaminated soil, the halophyte accumulated roughly the same amount of metals as the glycophyte on a mass basis (30-40 mg/kg dry wt). Neither plant, however, hyperaccumulated any of the metals tested. When treated with EDTA, specific differences in patterns of metal uptake between the two plants emerged. The halophyte accumulated significantly more Cu (2x) and Pb (1x) in the shoots than the glycophyte, but root metal concentrations were generally higher for the glycophyte, indicating that the halophyte translocated more metal from the root to the shoot than the glycophyte. For example, Zn shoot-to-root ratios ranged from 1.4 to 2.1 for Atriplex and from 0.5 to 0.6 for Z. mays. The biodegradable chelator rhamnolipid was not effective at enhancing shoot metal concentrations, even though radiolabeled chelator was found in the shoot material of both plants. Our results suggest that halophytes, despite their slower growth rates, may have greater potential to selectively phytoextract metals from contaminated soils than glycophytes.

Effects of humic acid and competing cations on metal uptake by Lolium perenne

“…Humic acid stimulated the transport of Cu, as well as that of Pb and Fe, from the roots to the shoots, whereas it decreased the transport of Mn ( p < 0.05). The increased transport of Cu and Pb to the shoots in the presence of a ligand has been demonstrated before, when EDTA was used as a ligand in a soil experiment [40]. In the present study, the increased transport (expressed as the ratio of shoot and root content) of Cu, Pb, and Fe was caused by a decreased metal content in the roots rather than by an increased metal content in the shoots, whereas the decreased transport of Mn was caused by an increased content in the roots rather than by a decreased content in the shoots.…”

“…Zinc and Ni were transported relatively easily through the plant, whereas Cd, Cu, Pb, Fe, and Mn accumulated mainly in the root system. In an earlier experiment of metal uptake by plants in soil, it also was found that Cu and Pb accumulated in the root system but that Zn was transported mainly to the shoots [40].…”

Uranium complexation and uptake by a green alga in relation to chemical speciation: The importance of the free uranyl ion

“…The EDTA is known to be a persistent nonassimilable ligand (although recent evidence observed with higher plants argues that intact metal EDTA complexes can be assimilated [38–40]), while citrate can be assimilated and in some occasions was shown to increase metal uptake and toxicity beyond the prediction of the FIAM [17,18]. Uptake of uranium gradually decreased with the addition of EDTA and citrate, as expected from the complexation of the free UO 2+ 2 ion (Fig.…”

Production of the forage halophyte Atriplex amnicola in metal‐contaminated soils

“…In particular, Atriplex species have a high tolerance to metal stress (Lutts et al ., ; Sai Kachout et al ., ). They can be irrigated with saline water and can also tolerate drought, freezing and heat (Thomas et al ., ; Jordan et al ., ; Lutts et al ., ).…”