Co-application of indole-3-acetic acid/gibberellin and oxalic acid for phytoextraction of cadmium and lead with Sedum alfredii Hance from contaminated soil

Exogenous application of plant-growth promoting substances in combination with chelators is a common way to enhance the phytoextraction of heavy metals. A pot experiment was used to explore the influences of indole-3acetic acid (IAA)/gibberellin (GA3) alone or together with oxalic acid (OA) on the growth, physiological response, and nutrient contents of hyperaccumulator Sedum alfredii Hance, and cadmium (Cd) and lead (Pb) phytoextraction efficiency. The results showed that a foliar spray of IAA/GA3 alone or together with OA increased plant growth. The largest shoot biomass with increase by 29.7% was produced by the 50 mu mol L-1 IAA combined with 2.5 mmol kg-1 OA (50I+2.5OA) treatment as compared with the control treatment (CK). The presence of IAA and GA3 enhanced the chlorophyll a, carotenoid, and potassium contents in leaves and decreased the malondialdehyde content. The Cd content in leaf and the translocation factor (TFshoot) value from 50I+2.5OA treatment was increased by 4.29% and 21.4%, and the Pb content in stem and shoot, and the TFshoot of Pb after applying 50 mu mol L-1 GA3 combined with 2.5 mmol kg- 1 OA was enhanced by 32.5%, 13.4%, and 57.6%, compared with CK, respectively. The optimal Cd and Pb phytoextraction efficiency occurred from 50I+2.5OA treatment with increase by 82.4% and 79.3% as compared with CK, respectively. Therefore, the results showed that a combined application of 50 mu mol L-1 IAA and 2.5 mmol kg- 1 OA could effectively enhance S. alfredii Hance phytoremediation of Cd and Pb co-contaminated soil.