Physiological Adaptation Strategy of the Pseudo-Metallophyte Lotus corniculatus L. to Long-Term Metal Contamination

Lotus corniculatus L. can spontaneously colonize metal-contaminated areas like the old Zn-Pb calamine tailings. This study compared two L. corniculatus ecotypes collected from metal-contaminated (HM) and non-contaminated (NM) sites to identify physiological adaptations to long-term metal exposure. The results indicated that HM ecotype accumulates Zn, Pb, and Cd in shoots without showing any toxic symptoms at the ultrastructural level. The HM ecotype exhibited a different composition of photosynthetic pigments, lower lipid peroxidation, and oxidative stress levels and increased the efficiency of the antioxidant defense system and antioxidant activity compared to the NM ecotype. Leaf antioxidant enzymes such as SOD, CAT, POX, and GPX were more active in the shoots of the HM ecotype, while GR and APX showed lower activity compared to the NM ecotype. In addition, the HM ecotype was characterized by higher glutathione and total phenolics content (mainly catechin, rutin, ferulic, and salicylic acids); however, these non-enzymatic metabolites primarily function in metal chelation alongside their role in oxidative stress mitigation. The results showed that calamine Lotus plants exhibit effective adaptation to long-term metal exposure by keeping metals away from metabolically active compartments and strengthening antioxidant defenses. These coordinated mechanisms reduce oxidative stress and contribute to the enhanced metal tolerance of calamine plants.