Effects of sulfate-reducing bacteria on the plant uptake of heavy metals in chelator-washed soil with residual heavy metal-chelant complexes.

Abstract

The application of sulfate-reducing bacteria (SRB) for stabilizing heavy metals in chelator-washed soils is critical for enabling agricultural reuse, yet its impact on plant uptake of heavy metals remains understudied. In this study, a pot experiment was conducted to examine the effects of SRB-which include Shewanella JN01 (S), Clostridium ZG01 (C), and a mixture of the two strains (M)-on stabilization of heavy metal-chelant complexes and the uptake of heavy metals (Cd, Pb, Cu, and Zn) by Chinese cabbage. The results revealed that all SRB treatments significantly reduced available Pb, Cu, and Zn by 8.23-34.85%, 8.78-15.72%, and 19.83-29.49% in the chelator-washed soils after planting Chinese cabbage, respectively. However, there was no significant change in available Cd contents in all SRB treatments because the formation of CdS with higher solubility constants was more difficult than the formation of CuS and PbS. Clostridium ZG01 reduced Cd, Pb, Cu, and Zn concentrations in shoots by 41.85%, 83.02%, 14.55%, and 23.49%, respectively, and lowered transfer coefficients by 48.18-90.00%, outperforming other treatments. This strain enhanced soil bacterial diversity and organic matter content, likely through metabolic synergies and rhizosphere interactions. Our findings demonstrated Clostridium ZG01 has excellent efficacy in stabilizing metal-chelant complexes and mitigating phytoavailability in alkaline soils, though crop selection or integrated remediation strategies are necessary for safe reuse. Collectively, this study provided an efficient, green and economical strategy for the remediation of heavy metals-contaminated farmland after being washed by chelators.