A hydroponic experiment with six treatments,i.e.,0% seawater(control),10% seawater,25% seawater,0% seawater +N(7.5 mmol L-1 NaNO3),10% seawater + N(7.5 mmol L-1 NaNO3),and 25% seawater +N(7.5 mmol L-1 NaNO3),was carried out to study the effect of nitrogen addition on the growth and physiological and biochemical characteristics of Jerusalem artichoke(Helianthus tuberosus)seedlings under seawater stress.The 10% seawater stress treatment had the least effect on plant growth while at 25% seawater growth was significantly inhibited.The malondialdehyde content and electrolyte leakage in leaves under 10% seawater were similar to those of the control,but significantly higher under the 25% seawater stress.The activities of superoxide dismutase,peroxidase and catalase in the leaves increased concomitantly with increasing seawater concentration and time.Proline and soluble-sugars in the leaves and Na+,K+,and Cl- contents in shoots and roots increased significantly with the concentration of seawater increasing.Nitrogen addition resulted in increasing fresh and dry weights of shoots and roots compared with seawater treatment without N.Nitrogen supplemen-tation also significantly enhanced the activities of antioxidant enzymes in leaves.Addition of N to seawater enhanced the contents of proline and soluble-sugars in the leaves and K+ and total-N in the aerial parts and roots of H.tuberosus,but it resulted in declined concentrations of Na+ and Cl- in the aerial parts and roots.Nitrogen addition ameliorated the toxicity of seawater by improving the antioxidative enzymes,accumulating of proline and soluble-sugars,and altering the distribution of inorganic ions in H.tuberosus.