Enhanced heavy metal phytoextraction by Echinochloa crus-galli using root exudates

Heavy metal uptake and growth by Echinochloa crus-galli were investigated to determine if the use of root exudates enhanced phytoextraction. E. crus-galli were planted in soils contaminated with 600 mg kg− 1 Pb, 40 mg kg− 1 Cd and 100 mg kg− 1 Cu. E. crus-galli were then cultivated with and without root exudates from Belamcanda chinensis for 4 weeks. The growth of E. crus-galli in metal-contaminated soils that contained root exudates showed increased roots and shoots when compared to E. crus-galli grown without root exudates (p < 0.05). In addition, the accumulation of metal in E. crus-galli that was cultivated with the root exudates was two- to fourfold higher than in plants that were cultivated without the root exudates. The exchangeable soil fraction in the rhizosphere of E. crus-galli grown with root exudates was greater than when E. crus-galli was grown without root exudates. Finally, the BCF and TF values of Cd, Cu and Pb were greater when the root exudates were added (p < 0.05). Taken together, these results indicate that root exudates can be used as a natural chelating agent to enhance phytoextraction.