Effect of citric acid and biochar addition on combined remediation of ryegrass-Streptomyces spp.

Soil cadmium (Cd) contamination poses significant risks to ecosystems and human health, necessitating effective remediation strategies. Plant-microbe combined remediation has shown promise, but its efficiency can be further enhanced by amendments such as citric acid and biochar. This study investigated the effects of citric acid and biochar on the potential of ryegrass (Lolium perenne)-Streptomyces combined remediation for Cd-contaminated soil. A pot experiment was conducted to determine: (1) soil Cd concentration and speciation, (2) plant biomass and Cd uptake in shoots/roots, and (3) antioxidant defense system responses (e.g., catalase, peroxidase, malondialdehyde). Results demonstrated that Streptomyces inoculation alone significantly promoted ryegrass root growth (18.9-22.3% biomass increase) and total Cd accumulation (up to 25.9%), while enhancing antioxidant defenses (179.3% and 135.1% increases in catalase and peroxidase activities, respectively). However, adding citric acid or biochar inhibited plant growth and compromised remediation efficiency. Furthermore, Cd distribution patterns in plants varied across treatments. These findings provide critical insights for optimizing plant-microbe remediation systems.