Root activity, copper distribution, and leaf physiology of golden dewdrop (Duranta erecta) under different concentrations of Cu2+ in a hydroponic culture experiment

Abstract

Copper (Cu), as an essential microelement for plant growth, may have impacts on root activity and function under excessive conditions, thereby affecting the physiology and growth of plants. One-year-old golden dewdrop (Duranta erecta) cuttings were treated with six Cu2+ levels of 0.2, 2.0, 20.0, 200.0, and 2000.0 mmol L−1 for 7, 21, and 35 days by hydroponic culture with 0.0 mmol L−1 as the control. The obvious negative effects of 200.0 and 2000.0 mmol L−1 Cu2+ on the aboveground and belowground parts of D. erecta were observed after 35 days of treatment. The root activity at 20.0, 200.0, and 2000.0 mmol L−1 Cu2+ was 16%, 21%, and 22% lower than the control, while no significant difference between 2.0 mmol L−1 Cu2+ and the control. The net photosynthetic rate and transpiration rate showed a decreasing trend with treatment time when Cu2+ concentration was higher than 20.0 mmol L−1. The chlorophyll contents, leaf circumference, and leaf area at 2.0 mmol L−1 Cu2+ were significantly higher than the control and other Cu2+ treatments. The Cu concentration of roots, stems, and leaves at 2000.0 mmol L−1 Cu2+ was 22.9, 3.3, and 2.7 times higher than the control. Our results indicate that 2000.0 mmol L−1 Cu2+ destroyed the root function, causing excessive Cu accumulation in the roots, stems and leaves, consequently decreasing plant physiology and growth. Based on the short-term results, 2.0 mmol L−1 Cu2+ was the suitable concentration for D. erecta in hydroponic culture.