Increasing soil contamination with nickel (Ni) and copper (Cu) is a growing environmental concern, adversely affecting ecosystems and the survival of both plants and animals. This study investigated the morphological and physiological responses of Euphorbia marginata Pursh seedlings to varying concentrations of Ni and Cu over a 45-day period. The findings revealed that low concentrations of Ni and Cu enhanced morphological indexes, root indexes, biomass, and photosynthetic pigment content of E. marginata, while high concentrations inhibited these parameters. Compared to the control, Ni and Cu stresses induced membrane peroxidation, increased cell membrane permeability, and inhibited the synthesis of soluble proteins and proline in the leaves. The seedlings demonstrated an ability to mitigate Ni and Cu toxicity by increasing soluble sugar content and enhancing the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Notably, E. marginata exhibited a higher capacity for Cu²⁺ enrichment and translocation compared to Ni²⁺. Combined Ni and Cu treatments reduced the maximum enrichment and translocation levels of both metals in E. marginata. This study highlights the superior tolerance of E. marginata to Ni and Cu stresses and elucidates the mechanisms underlying its response, providing a theoretical basis for the use of landscape plants in the remediation of heavy-metal-contaminated soils.

It is of great importance to explore how plants respond to excess accumulation of Cu and Ni in soil, yet the mechanisms by which Euphorbia marginata, a common ornamental plant in China, responds to heavy metal stress remain unclear. In this study, E. marginata seedlings were subjected to CK, Ni 500 mg/kg, and Cu 900 mg/kg, with Ni-Cu combined stress, and their growth, physiological indexes, heavy metal accumulation, and their corresponding gene expression were evaluated after 45 d. The results showed that the two heavy metals mainly accumulated in plant roots and severely inhibited root growth, while the combined stress promoted the accumulation of heavy metals to a small extent. Either Cu or Ni stresses inhibit photosynthetic pigment synthesis as well as activate antioxidant and osmoregulatory systems, but there are differences in their effects. Combined stress has a synergistic stress effect, severely damaging the cell membrane structure and leading to dysregulation of antioxidant and osmoregulatory systems. The expression of CDPK, CaMCML, MEKK3/6 signaling factors, UFGT, and COMT was severely suppressed under the combined stresses of Cu and Ni compared to the single stress of both. These results provide evidence of a specific defense response to heavy metal stress in E. marginata, which could help guide new research efforts and support the development of strategies for phytoremediation using E. marginata.