Effects of increased nitrogen fertilizer on lead accumulation of Suaeda salsa in heavy metal-contaminated saline land

Halophytes are the most commonly used plants for bioremediation of heavy metal pollution in saline lands. To assess the effects of nitrogen fertilizer on the growth and lead (Pb)-accumulating capacity of Suaeda salsa in heavy metal-contaminated saline land, we conducted a pot experiment to analyze the growth, Pb accumulation, and osmotic regulation characteristics of S. salsa at three soil salt levels. The results revealed that nitrogen fertilization can promote significant increases in the aboveground biomass of plants, and that in this regard, the effects of base fertilization were more pronounced than those attributable to topdressing (P < 0.05). In response to the application of base fertilizer under high salt conditions, the highest Pb content in the aboveground parts was 34.53 mg·kg⁻¹, and the highest Pb enrichment was 350.77 mg. In addition, under moderate- and high-salt conditions, the dry weight and Pb content of plants were higher than those in plants without fertilizer treatment. Nitrogen fertilization was also found to have an effect on osmotic regulatory substances. Proline was the main osmotic regulator detected in plants receiving base fertilizer, whereas soluble sugars were the main osmotic regulators in plants receiving no fertilizer or a topdressing. Furthermore, base fertilization promoted a significant increase in Ca²⁺ accumulation. These findings reveal that by promoting increases in aboveground biomass, the application of nitrogen fertilizer in Pb-polluted saline soil can contribute to enhancing the biological remediation effects of halophytes.