Effects of Biochar on Purslane-Mediated Transfer and Uptake of Soil Bioavailable Cadmium

As a carbon-negative emission technology, biochar has attracted extensive attention for application in fields for soil improvement and pollution control. The interactions between biochar and soil cadmium via the coupling of physical and chemical processes with extensive application and the correlation between the speciation of soil heavy metals and bioavailability are current research hotspots. However, the effect of biochar on Cd immobilization in soil and its transfer to purslanes have seldom been addressed. Thus, this study sought to determine the effects of wheat straw biochar on purslane biomass and Cd distribution in soil and purslane. Biochar application was found to increase purslane gross biomass, especially its stem, by 27.52-43.26% (root and aboveground parts) relative to the control. Biochar application also significantly decreased Cd levels by 10.88-46.04% and 14.07-35.30% in purslane shoots and roots; this effect was enhanced by the increase in biochar application rate. Biochar application increased soil pH by 0.33-0.90 and soil organic carbon (SOC) by 157.28-553.50%, markedly contributing to Cd immobilization in the soil. The soil available Cd concentration decreased by 2.19% and 15.89% with biochar application. The functional groups of biochar have also been shown to facilitate Cd complexation, which contributes to the immobilization and stabilization of soil Cd.