The application of nitrogen improved the remediation ability of Hydrangea macrophylla to cadmium-contaminated soil

Hydrangea macrophylla is a potential plant for cadmium (Cd) remediation. Many studies have shown that nitrogen (N) can enhance the remediation efficiency of plants for heavy metals. However, little research has been conducted on the nitrogen-enhanced remediation efficiency of Hydrangea macrophylla in high Cd concentrations. This study employed two cultivars of Hydrangea macrophylla in pot experiments with CO(NH₂)₂, NH₄Cl, and NaNO₃ to investigate the effects of N application on growth physiology, Cd accumulation and translocation, and soil physicochemical properties under high Cd stress, aiming to determine the optimal fertilization strategy. The results demonstrated that NH₄Cl significantly increased the fresh weights of the shoots and roots and nitrate reductase activity in two cultivars. The medium concentration of CO(NH₂)₂ significantly enhanced the activities of peroxidase, elevated the contents of glutathione, free proline, soluble proteins, and soluble sugars of two cultivars. In addition, NH₄Cl and NaNO₃ greatly promoted the uptake and accumulation of Cd in two cultivars and reduced the percentage of Cd in the residue form in the soil. The combined affiliation function analysis yields that the 0.8 g kg^-1 of NaNO₃ (N3A3) and 0.2 g kg^-1 of NH₄Cl (N2B6) were the most effective treatments for enhancing the Cd-contaminated soil remediation potential of the two cultivars.