Comparison of organic and synthetic amendments for poplar phytomanagement in copper and lead-contaminated calcareous soil

Soil remediation can be achieved through organic and synthetic amendments, but the differences in the phytomanagement of trace metal-contaminated land are unclear. We conducted an outdoor microcosm experiment to simulate the effects of organic amendment citric acid and synthetic amendments EDTA and EGTA on poplar phytomanagement of copper (Cu)- and lead (Pb)-contaminated calcareous land at doses of 0, 1, 3, and 9 mmol kg−1. We found that soil-bioavailable Cu and Pb contents increased by 2.11–27.27 and 1.48−269 times compared to the control, respectively. Additionally, synthetic amendments had a long-lasting (within 25 days) effect on metal bioavailability relative to organic amendments. Consequently, organic amendments increased the root Cu and Pb contents by 2.68–48.61% and 6.60−49.51%, respectively, whereas synthetic amendments increased them by 65.94–260% and 12.50−103%. The Cu and Pb contents in the leaves were lower than those in the roots, and increased significantly by 47.04–179% and 237−601%, respectively, only under synthetic amendments. Interestingly, none of the amendments increased the Cu and Pb content in poplar stems (<5 mg kg−1), which remained within the normal range for terrestrial plants. Regardless of the type and addition level, the amendments did not affect poplar growth. Nevertheless, synthetic amendments caused a significant redistribution of metals (Cu: 22−32%; Pb: 23−53%) from the topsoil into the subsoil within the root zone at medium and high levels relative to organic amendments. Therefore, organic and synthetic amendments can assist poplar phytomanagement with a phytostabilization strategy for Cu- and Pb-contaminated calcareous land and obtain marketable wood biomass. Moreover, collecting leaf litter is crucial when using synthetic amendments at optimum concentration levels.