Wheat morphological and biochemical responses to copper oxide nanoparticles in two soils

The widespread application of copper oxide nanoparticles (CuO NPs) in agricultural production has caused growing concerns about their impact on crops. In this study, wheat root elongation was used to evaluate the toxic effect concentrations of CuO NPs in two soils with differing properties, collected from farmlands in Guangdong (GD) and Shandong (SD) provinces, China. Plant morphological and biochemical properties were also assessed to explore the toxicity mechanism of CuO NPs on wheat seedlings. The root elongation results revealed lower toxic effect concentration values in the plants grown in GD soil than in SD soil. Furthermore, the treatment with CuO NPs at 200 mg Cu kg^-1 significantly reduced wheat root and shoot biomass by 35.8% and 15.8%, respectively, in GD soil. Electron microscopy showed that CuO NPs deformed wheat roots and entered leaf cells, causing deformation and damaging the cell structure. The CuO NP treatments also decreased chlorophyll content, increased antioxidant enzyme activity, and increased membrane lipid peroxidation in wheat leaves. The addition of CuO NPs significantly reduced the Zn (by 17.3%) and Fe (by 26.9%) contents in the leaves of plants grown in GD and SD soils, respectively. However, the contents of Cu, Mg, and Mn were increased by 27.4%–52.5% in GD soil and by 17.9%–71.6% in SD soil. These results suggested that CuO NPs showed greater toxicity to wheat plants grown in acidic soil than in alkaline soil and that the adverse effects of CuO NP treatments on wheat seedlings were due to a combination of CuO NPs and released Cu²⁺.