Effects of nitrogen addition on the growth of the salt marsh grass Elymus athericus

Effects of nitrogen addition on the growth of the salt marsh grass Elymus athericus were studied under greenhouse conditions. The addition of inorganic nitrogen (in the form of nitrate or ammonium and ranging from 0-24 g N/m2) stimulated the growth of Elymus athericus at the highest addition. Addition of nitrogen led to an increase of the soil nitrate concentrations both in the nitrate and ammonium treated soil in the first period of the experiment, whereas no differences were present at the end of the experiment. Ammonium in the ammonium treatments was transformed to nitrate within 15 days. In another experiment the values of the stable isotope nitrogen-15 - expressed as δ15N- in nitrogen compounds used as fertilizer, in salt marsh soil and of Elymus athericus were measured. The δ15N of the N-compounds added (between - 3.2 and + 2.6 %c) were lower than the soil (ca. +10 %c) and plants (ca. + 8 %). During growth in water culture the δ15N of the leaves, stems and roots of Elymus athericus decreased from + 9% to - 1 %. The latter value was close to the δ15N of the N-compounds used in the water solution. Addition of N-compounds in soil culture, however, did not lead to such a decrease of the δ15N of Elymus athericus. The difference in δ15N between soil nitrogen and the N-compounds added may be too small to be used successfully in ecological studies of nitrogen fluxes in the salt marsh environment.