Effects of EDTA and plant growth-promoting rhizobacteria on plant growth and heavy metal uptake of hyperaccumulator Sedum alfredii Hance

Phytoremediation is a cost-effective and environment-friendly strategy for decontaminating heavy-metal-contaminated soil. However, the practical use of phytoremediation is constrained by the low biomass of plants and low bioavailability of heavy metals in soil. A pot experiment was conducted to investigate the effects of the metal chelator ethylenediaminetetraacetic acid (EDTA) and EDTA in combination with plant growth-promoting rhizobacteria (Burkholderia sp. D54 or Burkholderia sp. D416) on the growth and metal uptake of the hyperaccumulator Sedum alfredii Hance. According to the results, EDTA application decreased shoot and root biomass by 50% and 43%, respectively. The soil respiration and Cd, Pb, Zn uptake were depressed, while the photosynthetic rate, glutathione and phytochelatin (PC) contents were increased by EDTA application. Interestingly, Burkholderia sp. D54 and Burkholderia sp. D416 inoculation significantly relieved the inhibitory effects of EDTA on plant growth and soil respiration. Compared with the control, EDTA + D416 treatment increased the Cd concentration in shoots and decreased the Pb concentration in shoots and roots, but did not change the Zn concentration in S. alfredii plants. Furthermore, EDTA, EDTA + D54 and EDTA + D416 application increased the cysteine and PC contents in S. alfredii (p < 0.05); among all tested PCs, the most abundant species was PC2, and compared with the control, the PC2 content was increased by 371.0%, 1158.6% and 815.6%, respectively. These results will provide some insights into the practical use of EDTA and PGPR in the phytoremediation of heavy-metal-contaminated soil by S. alfredii.