From Salt-Affected Marginal Land Resource to Remediation Agent: Halophyte-Derived Biochar for Ameliorating Cd-Contaminated Acidic Soil

Cadmium (Cd) contamination of acidic soils poses a significant threat to ecosystem stability and crop health. This study evaluated the potential of biochar derived from the halophyte Salicornia europaea (SBC), a salt-tolerant plant that grows on saline-alkali marginal land, to remediate Cd-contaminated acidic soil. A pot experiment was conducted using acidic soil spiked with 3 mg kg⁻¹ Cd and amended with SBC at 0%, 1%, and 2% (w/w). The results showed that compared to the control, 1% and 2% SBC treatments increased the rhizosphere soil pH by 0.7 and 1.4 units, respectively, and significantly enhanced organic matter content and cation exchange capacity. In addition, these treatments reduced the concentration of available Cd in rhizosphere soil by 14.0% and 33.9%, respectively. Furthermore, biochar promoted plant growth and increased the photosynthetic rate, while Cd accumulation in plants was significantly reduced by 51.3% and 52.6%. Metabolomic analysis revealed that SBC upregulated the tryptophan metabolic pathway, with indoleacetic acid and 5-hydroxyindoleacetic acid being the predominant metabolites. Their accumulation in rhizosphere soil was associated with enhanced plant stress tolerance and growth. Although the soil electrical conductivity increased with SBC addition, no negative effects on plant growth were observed. These findings indicate that SBC can effectively immobilize Cd, improve soil quality, and facilitate plant growth in acidic contaminated soils, thus offering a promising strategy for sustainable remediation. This approach suggests a potential pathway for utilizing resources from marginal lands to remediate acidic contaminated soils, thereby contributing to sustainable land management and environmental protection.