Fermented spent coffee grounds affect cadmium toxicity and accumulation in Lolium perenne : implications for phytoremediation

Cadmium (Cd) pollution poses severe threats to ecosystems and human health. Phytoremediation using fast‑growing plants offers a promising solution, but Cd toxicity restricts plant performance. This study investigated whether fermented spent coffee grounds (FSCG) can alleviate Cd stress in Lolium perenne and enhance Cd accumulation. In a greenhouse experiment, L. perenne was subject to four Cd levels (0, 0.5, 5, and 50 mg kg−1) fully crossed with two FSCG treatments (with or without FSCG). Cd significantly inhibited seed germination and biomass. The addition of FSCG increased the germination rate, root mass, root-shoot ratio, and root tolerance. However, the shoot mass was lower, except at the Cd level of 5 mg kg−1, where FSCG increased the shoot mass. Moreover, the chlorophyll and MDA content were reduced. Notably, FSCG reduced shoot Cd concentration across all Cd levels. The interactive effects between Cd and FSCG were significant for growth, with the greatest promotion occurring at the Cd level of 5 mg kg−1. This study reveals a dual role of FSCG in waste valorization and phytoremediation enhancement, demonstrating that FSCG protects L. perenne from Cd toxicity by improving root development, mitigating oxidative stress, and concurrently limiting Cd translocation to shoots. Although FSCG reduced shoot Cd concentration per unit biomass, its promotion of root development and plant health may favor sustained biomass production over repeated harvests, thereby enhancing long‑term phytoextraction efficiency. These findings provide new insights into the physiological mechanisms by which FSCG protects plants under Cd stress and offer a synergistic strategy for organic waste reuse coupled with soil remediation.