Dissolved organic nitrogen: A relevant, complementary source of nitrogen for the seagrass Zostera marina

Alexandre, A. and Hill, P.W. and Jones, D.L. and Santos, R. (2015) Dissolved organic nitrogen: A relevant, complementary source of nitrogen for the seagrass Zostera marina. Limnology and Oceanography, 60 (5). pp. 1477-1483. DOI: 10.1002/lno.10084

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Dissolved organic nitrogen (DON) forms a significant pool of bioavailable N in the water column (62%) and in sediments of Ria Formosa lagoon (53%). We assessed the uptake rates of inorganic and organic nitrogen and its interactions in the seagrass Zostera marina, and further explored the possibility of seagrasses to use complex organic substrates (peptides). Uptake rates by leaves and roots were quantified in choice-uptake experiments where plants were exposed to mixed N solutions containing both 15N inorganic (ammonium�+�nitrate) and 13C15N organic (alanine�+�trialanine) nitrogen at field-relevant concentrations, and compared with uptake rates of single inorganic or organic N forms. Ammonia was the preferred N source, but plants preferred DON to nitrate. DON uptake was significantly higher through roots than leaves, coinciding with the one-order of magnitude higher concentration of DON in the sediment than in the water. Not only amino acids, as reported elsewhere for other seagrasses, but also peptides constitute relevant N sources for Z. marina (10% and 4% of the total N uptake). Seagrasses may thus compete with microbes for organic substrates at an earlier stage of protein degradation in the N cycle than previously thought. Because no interactions occurred between inorganic and organic N sources, the total N uptake by Z. marina was higher when both sources were present, showing that organic nitrogen is a complementary rather than alternative source of nitrogen. The uptake of organic nitrogen should be included in future studies assessing the total N budgets of seagrass meadows.

Item Type: Article
Subjects: Research Publications
Departments: College of Natural Sciences > School of Environment, Natural Resources and Geography
Date Deposited: 05 Nov 2015 04:46
Last Modified: 05 Nov 2015 04:46
ISSN: 0024-3590
URI: http://e.bangor.ac.uk/id/eprint/5819
Identification Number: DOI: 10.1002/lno.10084
Publisher: Wiley
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