Effects of nitrate nitrogen fertilizer combined with ethylenediamine disuccinic acid on the growth and active oxygen metabolism of Bidens pilosa under Cd stress

To explore the physiological, biochemical, and antioxidant mechanisms of Bidens pilosa in response to cadmium (Cd) stress under the combined action of nitrate nitrogen fertilizer and ethylenediamine disuccinic acid (EDDS), an indoor pot experiment was conducted to study the effects of 75 mg·kg⁻¹ (as nitrogen) nitrate nitrogen fertilizer combined with 1 mmol·L⁻¹ EDDS on the growth and active oxygen metabolism of Bidens pilosa under 15 mg·kg⁻¹ Cd stress. Under Cd stress, plant height, root length, chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl), and soluble protein (SP) content of B. pilosa reached maximum values with the addition of nitrate nitrogen fertilizer alone. The addition of EDDS alone resulted in the highest soluble sugar (SS) content. Under Cd stress, the combination of nitrate-nitrogen fertilizer and EDDS increased the plant height, Chl a, and Chl content of B. pilosa by 24.29%, 51.06%, and 21.09%, respectively, compared with Cd treatment alone. It significantly enhanced the activities of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) by 37.04%, 22.92%, 18.31%, and 197.81%, respectively, compared to the Cd treatment alone, reaching maximum values among all treatments. Additionally, the SP and SS contents were maximized, whereas the malondialdehyde (MDA) content and relative electrical conductivity (REC) decreased significantly by 45.77% and 21.25%, respectively, compared to the Cd treatment alone. In summary, 75 mg·kg⁻¹ nitrate nitrogen fertilizer combined with 1 mmol·L⁻¹ EDDS can improve the tolerance of B. pilosa to Cd stress. Combined remediation technologies can promote the growth of aboveground parts and maintain the normal accumulation of biomass by increasing the Chl a and Chl content in plants. By enhancing the antioxidant enzyme activities and increasing osmotic adjustment content, the membrane lipid peroxidation damage caused by Cd was alleviated, and the cell membrane was maintained.