Nutritional and osmotic roles of nitrate in a euhalophyte and a xerophyte in saline conditions.

The effects of salinity and nitrogen (N) on growth and the role of NO3- in osmotic adjustment in the leaf-succulent euhalophyte Suaeda physophora and the stem-succulent xerophyte Haloxylon persicum were evaluated. Seedlings were exposed to 1 or 300 mm NaCl in 0.05, 1 or 10 mm NO3- -N treatments for 24 d. At 10 mm NO3-, 300 mm NaCl had no adverse effect on the concentration of NO3-, the content of organic N, and the estimated contribution of NO3- to osmotic potential in leaves of S. physophora, but markedly reduced these in stems of H. persicum. At 300 mm NaCl, more NO3- but less Cl- and Na+ were involved in osmotic adjustment in leaves of S. physophora compared with that in stems of H. persicum. The contribution of NO3- to osmotic potential was much higher in S. physophora, but lower in H. persicum, than that of amino acids at 300 mm NaCl. The nutritional and osmotic roles of NO3- -N seem to be more important in the euhalophyte S. physophora than in the xerophyte H. persicum under saline conditions. These characteristics may determine the natural distributions of the two species in saline or arid environments.