Role of nitrate in nitrogen nutrition of the mangrove Avicennia marina

A crucial role of nitrate uptake in the nitrogen nutrition of the mangrove Avicennia marina (Forsk.)Vierh.has been indicated from 2 laboratory pot culture experiments: (1) Seedlings grown for 63 d in 'SNH,'-e~iched anaerobic soil exhibited markedly reduced (by 50 %) nitrogen uptake when a nitrification inhibitor (N-serve) was added to the soil, compared to controls where no Nserve was added.(2) Seedlings grown for 158 d in aerobic solution culture showed poor growth, complete lack of fine root development and low nitrogen uptake when supplled wlth ammonium as the sole nitrogen source.Increased ammonium supply, at 5, 10, 30 and 50 ppm (N) levels, did not significantly enhance growth in any of the plant components (leaves, stems, roots).Conversely, seedlings supplied with nitrate (only) showed extensive fine root development and good aboveground growth which was significantly enhanced by increased nitrate supply up to 30 ppm (N).