Polyphenols and antioxidant activity of Sulla pallida from mining sites of Morocco: Implication for phytoremediation of heavy metal-contaminated pastures

An on-field survey was conducted to assess the physiological and symbiotic response of Sulla pallida in an abandoned mining site in Northeast Morocco. Results indicated that S. pallida maintained high nodulation and nitrogen efficiency even at late growth stages while accumulating significant levels of Fe, Pb, Zn, and Cu in its aerial parts. Phenol content varied significantly (p<0.05) by phenological stage and plant part, with a high concentration of total extractable polyphenols (7.73 %DM) and tannins (6.97 %DM) recorded during the vegetative stage. Antioxidant activity, as shown by DPPH radical scavenging (IC ₅₀ of 0.126 mg/mL), was comparable to the control (BHT, IC ₅₀ of 0.110 mg/mL). Anti-lipid peroxidation and ferric reduction potential were highest during flowering, with values outperforming controls in some assays. HPLC-ESI-MS/MS analysis identified 38 compounds, with high levels of 4-Hydroxy benzoic acid, rutin, vanillic, gallic, and p-coumaric acids. These findings highlighted S. pallid as a promising forage species for remediating heavy metal-contaminated pastures and promoting sustainable land use.