CaO-modified hydrochar reduces soil cadmium bioavailability by altering soil properties, shifting bacterial community, and promoting microbial metabolisms

Abstract

The efficient remediation of cadmium (Cd)-contaminated soil is of great significance for reducing the threats to ecosystem and human health. At present, the carbon-rich hydrochar with abundant oxygen-containing functional groups as environmental remediation material gains numerous attention due to its cost-effectiveness and sustainability. A pot experiment was performed to investigate the Cd immobilization efficiency and microbial response in soil with the presence of pristine corn stalk hydrochar and CaO-modified hydrochars. Results showed that compared with pristine hydrochar, fresh biomass of plant shoot was promoted by 0.904–15.6% with CaO-modified hydrochar amendment, and the bioavailable Cd content and correspoding Cd uptake by shoot were decreased by 8.19–16.2% and 4.18–17.0%, respectively. Additionally, the relative abundance of Actinobacteriota benefiting Cd immobilization in soil was elevated from 30.3% to 34.4–44.6% after CaO-modified hydrochar amendment. The microbial metabolisms (e.g., carbohydrate metabolism, amino acid metabolism, and citrate cycle) were also enhanced by CaO-modified hydrochar, contributing to reduce Cd bioavailability. Redundancy analysis revealed that bacterial community structure in rhizosphere soil was significantly influenced by soil dissolved organic carbon and electric conductivity (p＜0.05). Overall, the cost-effective CaO-modified hydrochar with reduced phytotoxicity was a promising remediation material for Cd immobilization in metal-contaminated soil.