Abstract
Soil contamination by toxic heavy metals represents a critical ecological challenge, threatening agricultural sustainability and human health. Phytoremediation using high-biomass hyperaccumulators, such as Helianthus annuus (sunflower), offers a viable green remediation strategy; however, severe metal phytotoxicity often impairs plant growth and extraction efficiency. In this study, we investigated the synergistic role of two novel endophytic fungal strains, Trichoderma virens (HAE-2) and Epicoccum nigrum (HAE-7), in enhancing cadmium (Cd) and lead (Pb) sequestration and physiological resilience in H. annuus grown in co-contaminated soils. Plants were inoculated individually and in consortium under controlled greenhouse conditions across varying metal concentrations (Cd: 25 mg/kg; Pb: 300 mg/kg). Dual inoculation significantly mitigated metal-induced phytotoxicity, yielding a 44.6% increase in shoot dry biomass and a 58.2% increase in root dry biomass relative to non-inoculated contaminated controls. Bioaccumulation metrics revealed that fungal colonization enhanced total metal extraction, skewing metal partitioning toward the root systems (translocation factors < 0.65 for Pb and < 0.85 for Cd), primarily through intracellular chelation and cell-wall immobilization. Furthermore, inoculated plants demonstrated pronounced attenuation of oxidative stress, marked by a 37.1% reduction in lipid peroxidation (malondialdehyde content) and coordinated up-regulation of superoxide dismutase, catalase, and ascorbate peroxidase activities. These findings demonstrate that fungal endophytes functionally bolster the phytostabilization and phytoextraction potential of H. annuus, presenting a robust, biologically driven remediation framework for metalliferous soils.
