Effects of sodium on nitrate uptake and osmotic adjustment of Suaeda physophora

Na(+) ions play an important role in the growth of halophyte. The effect of Na(+) ions on nitrate uptake and osmotic adjustment in the euhalophyte Suaeda physophora was investigated under glasshouse conditions. Seedlings were exposed to 1 mmol/L NaCl (control), 300 mmol/L NaCl, 150 mmol/L NaCl plus 150 mmol/L KCl or 300 mmol/L KCl treatments for 24 d. Dry weight was not affected greatly by different salt treatments, but water content and succulence in leaves of S. physophora were significantly increased at 300 mmol/L NaCl and 150 mmol/L NaCl plus 150 mmol/L KCl treatments. The concentrations of Na(+) and NO(3)(-) in leaves of S. physophora were the highest at 150 mmol/L NaCl plus 150 mmol/L KCl, but lowest at 300 mmol/L KCl treatment. Moreover, the increase of NO(3)(-) concentration did not result in the decrease of Cl(-) concentration at 150 mmol/L NaCl plus 150 mmol/L KCl treatments. The estimated contribution of NO(3)(-) to osmotic potential (C(NO3)) in leaves of S. physophora was 9.8% at 150 mmol/L NaCl plus 150 mmol/L KCl, and C(Na) and Cc, were 31.0% and 23.3%, respectively. However, C(NO3), C(Na) and C(Cl) were respectively 1.6%, 7.9% and 11.9% at 300 mmol/L KCl treatment. It is concluded that Na(+) stimulates NO(3)(-) absorption and the stimulation is independent on the internal or the external Cl- concentration in the euhalophyte S. physophora. These characteristics may explain the high levels of N in leaves of saline desert plants in arid ecosystem.