Nitrogen nutrition in the estuarine zone: the case of Suaeda maritima var. macrocarpa

Abstract

Suaeda rnaritima L. var. macrocarpa is a halophytic species distributed in the lower parts of salt marshes of the French coasts. The influence of salinity on nitrogen nutrition and on levels of the key enzymes involved in nitrogen assimilation is analyzed by growing Suaeda under experimental conditions. Use of 15N-labelled NO~ and NH + shows that both ions are effective sources of inorganic nitrogen for Suaeda. The plant is found to use NH4 + ions with a good yield, chiefly at high salinities (up to 130 mM). Nitrate reduction and ammonium assimilation by the glutamine synthetase/glutamate synthase pathway occurs mainly in leaves when Suaeda is grown at optimal saline conditions (130 mM NaC1). Absence of NaC1 creates less favourable conditions and lowers the activity of nitrate reductase and glutamine synthetase but leads to an important activity of glutamate dehydrogenase in roots. This enzyme could play a major role under suboptimal environmental conditions (i.e., absence of NaC1 for Suaeda maritima).