Effects of Different Forms of Sulfur on Plant Growth and Soil Properties in Cadmium-Contaminated Soils

Sulfur (S), an indispensable plant nutrient and a recognized amendment for ecosystem restoration, which holds promise in the remediation of Cd-contaminated soil. This study aims to unravel the impacts of elemental sulfur (ES) and sodium sulfate (SS) on soil properties, Cd bioavailability, and their interplay with tomato seedling growth in Cd-contaminated soil. The added concentration of ES or SS was 100 and 200 mg S·kg− 1 soil and incubated for 7 d with the soil. The tomato seeds germinated and growth for 21 d in vermiculite, then transferred to different soil growth for 30 or 60 d, during which Cd accumulation and soil properties were monitored. Treatment with ES and SS significantly promoted the growth of seedlings, with SS showing a stronger effect. Cd content were decreased by two concentrations of ES and SS in the root and shoot. Plant uptake factor (PUF) and transportation factor (TF) of Cd also significantly reduced by S, with 100 mg S·kg− 1 treatment being the most effective. Additionally, two forms of S increased soil organic matter (SOM) and NO3−-N, decrease NH4+-N, available phosphorus (AP) and available potassium (AK), while affecting soil enzyme activity. The addition of S obviously decreased the proportion of acid-extractable Cd (Aci-Cd) and increased the proportion of residual Cd (Res-Cd), the contents of DTPA-Cd were reduced with different treatments, effectively prevented Cd from entering the plants. In Cd-contaminated soils, S acts as a potent soil conditioner, fostering plant growth by curbing Cd availability. This finding holds profound implications for the secure cultivation of crops in Cd-contaminated environments, showcasing the multifaceted role of S in mitigating the deleterious effects of HMs contamination.