Root exudates increase metal accumulation in mixed cultures : implications for naturally enhanced phytoextraction

Abstract

Soluble root exudates collected from the barley grown in Fe deficient-nutrition solutions were added to soil to study their effects on metal solubility. The results showed that the addition of barley root exudates from the Fe deficient-nutrition solutions resulted in a 4.7-, 3.2-, 9.7-, 4.9- and 11.5-fold increase in the concentrations of soluble Cu, Pb, Zn, Cd and Fe, respectively, in comparison with the root exudates from the full-nutrition solutions. When peas were placed in a mixed culture with barley in pots, the concentrations of Cu, Pb, Zn, Cd and Fe in the shoots of the peas were 1.5-, 1.8-, 1.4-, 1.4- and 1.3 times higher than those grown in sole (single culture pots). It was hypothesized that the root exudates from barley in the mixed culture system played an important role in the process of solubilizing metals in soil and facilitating the uptake of metals by peas. Although the improved efficiency from the current experiments was relatively low, it may indicate a potential approach to the remediation of metal-contaminated soils in a naturally enhanced way.