How Does Ammonium Nutrition Influence Salt Tolerance in Spartina alterniflora Loisel?

Abstract

Spartina alternifl ora (Poaceae), commonly known as smooth cordgrass is originated from hydro-morph and salted marginal lands. In these regions, hypoxic and salt stress conditions strongly inhibit nitrifi cation and promote denitrifi cation. Distribution and yield of this species depend on its capacity to tolerate salinity and to use ammonium as the predominant source of nitrogen. S. alternifl ora grown on medium containing varying ammonium:nitrate ratio were treated with 500 mol m −3 NaCl. In absence of NaCl, the highest growth rate was observed in the mixed medium and the lowest one in medium containing nitrate alone. However, growth was higher in ammonium than in nitrate medium, indicating that S. alternifl ora was one of the scarce species which prefered ammonium as nitrogen source. The addition of 500 mol m −3 NaCl affected plant growth in both nitrate and mixed-media, but did not affect when ammonium was supplied. In absence or in presence of 500 mM NaCl, differences in growth between the treatments were due to difference in photosynthesis activity. In the same way the mean secretion of ions, especially Na + by shoots of S. alternifl ora was increased by ammonium treatment. Ammonium treatment probably improved salt tolerance of S. alternifl ora by increasing secretion activity of salt glands leading to a decrease in salt content of leaves mesophyll and consequently to avoiding toxic buildup of Na + in the apoplastic tissues of the leaves.