Enhanced cadmium phytoremediation by ryegrass (Lolium perenne L.) through a synergistic earthworm-selenium strategy

Cadmium (Cd) contamination in soil poses a severe threat to ecosystem stability and human health. While phytoremediation using ryegrass is a sustainable remediation strategy; however, its efficacy is frequently constrained by Cd-induced phytotoxicity. Selenium (Se) and earthworms have been identified as potential ameliorative agents; Se acts as an antioxidant enhancer and metabolic regulator, while earthworms improve soil structure and nutrient availability. However, the synergistic impacts of their combined application on Cd phytoextraction efficiency remain insufficiently characterized. The present study aimed to investigate the individual and combined effects of Se (1 µg/g) and earthworms ( Eisenia fetida , E) on ryegrass biomass, Cd accumulation and restoration efficiency, and antioxidant defense mechanisms in Cd-contaminated soil (30 µg/g). A pot experiment was conducted and the findings demonstrated that the combined earthworm-Se treatment most effectively promoted ryegrass growth, increasing shoot fresh and dry weight by 60.24% and 60.00%, respectively, compared to Cd-stressed plants. While Se alone significantly increased Cd biotranslocation to shoots, the co-application with earthworms strategically redirected Cd accumulation towards the roots, achieving in the highest root Cd concentration (377.35 µg/g), an enhanced root bioaccumulation factor (BAF Root−Cd ), and a reduced biotranslocation factor (BTF). Consequently, the combined earthworm-Se treatment achieved the highest total Cd phytoextraction (89.06 µg/plant) and soil Cd removal rate (0.59%/plant). Physiological analysis revealed that Se alleviated Cd-induced oxidative stress by enhancing the activities of CAT and POD, and increasing soluble protein content, thereby maintaining cellular integrity and metabolic function. The synergy between Se and earthworms establishes a robust bio-strategy for assisted phytoremediation. Earthworms optimize the rhizosphere habitat and promote biomass production, while Se fortifies the internal antioxidant defense system. This integrated approach simultaneously boosts plant biomass, enhances root sequestration of Cd, and strengthens plant resilience, offering a highly effective and sustainable solution for the remediation of Cd-contaminated soils while minimizing ecological risks.