Role of nitrate in nitrogen nutrition of the mangrove Avicennia marina

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Abstract
A crucial role of nitrate uptake in the N nutrition of the mangrove, A. marina (Forsk.) Vierh., was indicated from 2 laboratory pot culture experiments. Seedlings grown for 63 d [days] in 15NH4+-enriched anaerobic soil exhibited markedly reduced (by 50%) N uptake when a nitrification inhibitor (N-Serve) was added to the soil, compared to controls where no N-Serve was added. Seedlings grown for 158 d in aerobic solution culture showed poor growth, complete lack of fine root development and low N uptake when supplied with ammonium as the sole N source. Increased ammonium supply, at 5, 10, 30 and 50 ppm (N) levels, did not signficantly enhance growth in any of the plant components (leaves, stems, roots). 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).