GLDA-enhanced phytoremediation of Cd-contaminated soil by Tagetes Patula L.: effects on soil Cd fractions and microbial communities

This study investigated the efficacy of GLDA (C9H9NNa4O8) for the remediation of moderately Cd-contaminated soil (total Cd, 0.47 mg/kg). A 50-day pot experiment was carried out with T. patula (Tagetes patula L.) subjected to five GLDA treatments (0, 0.25, 0.5, 1 and 2 mmol/kg). The GLDA doses were administered in two equal parts, with a 15-day time interval between them. Our results indicated that GLDA treatments significantly increased the Cd content in the aboveground and root of T. patula, as well as soil pH and soil DTPA-Cd content compared with the control treatment (CK) (P < 0.05). Under 2 mmol/kg, an average reduction of 9.85% occurred in soil Cd content compared with the CK. Furthermore, GLDA enhanced the transformation of residual and organic-bound Cd into exchangeable and iron-manganese oxide forms. At concentrations of 0 and 0.25 mmol/kg, GLDA increased the richness of soil bacterial communities, whereas inhibition occurred at higher application rates (1 and 2 mmol/kg). The Chao1 and Shannon indices of 1 and 0.5 mmol/kg significantly increased by 29.9% and 7.98%, respectively, compared with the CK (P < 0.05). Proteobacteria, Acidobacteria, Chloroflexia, and Myxococcota were the dominant bacterial phyla in Cd remediation by T. patula induced by GLDA, reflecting their high tolerance to Cd contamination. Altogether, this study elucidates how GLDA enhances Cd remediation through its impacts on soil Cd mobility/fractionation and soil microbial composition, presenting a novel and sustainable/ecofriendly phytoremediation strategy for moderately Cd-contaminated soils.