Responses of Halophyte Salicornia bigelovii to Different Forms of Nitrogen Source

Salt-affected soils are agricultural and environmental problems on a global scale. Plants suffer from saline stresses in these soils and show nitrogen (N) deficiency symptoms. However, halophytes grow soundly under saline conditions. In order to clarify the N nutrition of the halophyte Salicornia bigelovii, it was grown at several N levels (1, 2, 3, and 4 mmol L−1), supplied in the form of NO−3 or ammonium (NH+4), under high NaCl conditions (200 mmol L−1). NH+4 -fed plants showed better growth than NO−3 -fed plants at 1–3 mmol L−1 N, and plants in both treatments showed the same growth at 4 mmol L−1 N. Nitrogen contents in NO−3 -fed plants increased with the N concentrations in solution; competitive inhibition of NO−3 absorption by Cl− was observed under lower N conditions. In addition, shoot dry weight was significantly correlated only with shoot N content. Therefore, growth of NO−3 -fed plants was regulated by N absorption. In contrast, N contents of shoots in NH+4 -fed plants did not change with N concentration. Shoot Na content decreased with increasing N concentration, while K content increased. Dry weight was highly correlated only with K content in NH+4 -fed plants. These observations indicated that growth of NH+4 -fed plants was mainly regulated by K absorption.