Dissolved Organic Nitrogen Uptake by Seagrasses

We examined the ability of seagrasses to take up dissolved organic nitrogen (DON) with leaves (in situ) and roots (laboratory) in an oligotrophic tropical offshore meadow in Indonesia using $^{{\rm{15}}} {\rm{N}}$-labeled nitrogen (N) substrates. We compared the uptake of urea and amino acids with t...

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Bibliographic Details
Published in:Limnology and oceanography 2008-03, Vol.53 (2), p.542-548
Main Authors: Vonk, Jan Arie, Middelburg, Jack J., Stapel, Johan, Bouma, Tjeerd J.
Format: Article
Language:English
Subjects:
Amino acids
Animal and plant ecology
Animal, plant and microbial ecology
Biological and medical sciences
Cymodocea rotundata
Fundamental and applied biological sciences. Psychology
General aspects
Halodule uninervis
Kinetics
Leaves
Macroalgae
Macrophytes
Marine
Meadows
Nitrogen
Padina
Plant roots
Sargassum
Sea water
Sediments
Synecology
Thalassia hemprichii
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Summary:We examined the ability of seagrasses to take up dissolved organic nitrogen (DON) with leaves (in situ) and roots (laboratory) in an oligotrophic tropical offshore meadow in Indonesia using $^{{\rm{15}}} {\rm{N}}$-labeled nitrogen (N) substrates. We compared the uptake of urea and amino acids with that of ammonium $({\rm{NH}}_{\rm{4}}^{\rm{ + }})$ and nitrate $({\rm{NO}}_{\rm{3}}^{\rm{ - }})$ and determined uptake kinetics of amino acids for the seagrasses "Thalassia hemprichii", "Halodule uninervis", and "Cymodocea rotundata" in comparison with the macroalgae "Sargassum" sp. and Padina sp. Uptake rates of small DON substrates for macroalgae were higher than those for seagrass leaves for all N substrates, but the seagrass roots also had a considerable uptake capacity. Seagrass leaves preferred urea, ${\rm{NH}}_{\rm{4}}^{\rm{ + },}$ and ${\rm{NO}}_{\rm{3}}^{\rm{ - }}$ over amino acids, and there were differences between species. Seagrass roots, however, took up amino acids at rates comparable to ${\rm{NH}}_{\rm{4}}^{\rm{ + },}$, whereas uptake rates of urea and ${\rm{NO}}_{\rm{3}}^{\rm{ - }}$ were much lower. The ability to take up DON enables seagrasses and macroalgae to shortcut N cycling and gives them access to additional N resources. In oligotrophic environments, uptake of amino acids by roots may provide seagrasses with a competitive advantage over macroalgae.
ISSN:0024-3590
1939-5590
DOI:10.4319/lo.2008.53.2.0542