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Dissolved organic nitrogen: an important source of nitrogen for the microphytobenthos insandy sediment
University of Gothenburg. (MPEA)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (MPEA)
2011 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 63, no 1, p. 89-100Article in journal (Refereed) Published
Abstract [en]

To test the hypothesis that dissolved organic nitrogen (DON) is important for sustaining microphytobenthic (MPB) primary production during nitrogen-limited conditions, the uptake of 15N-labelled urea, the amino acids glycine (GLY) and glutamic acid (GLU), and nitrate and ammonium were measured under simulated in-situ light and temperature conditions. Microphytobenthic primary production and chlorophyll a (Chl a) were also measured. MPB was dominated by diatoms attached to sand grains, cyanobacteria making up ~30% of the biomass. Activities of the hydrolytic ectoenzymes leucin aminopeptidase (AMA), alkaline phosphatase (APA), and β-glucosidase (GLA) in filter-fractionated sediment showed that the microbenthic community was strongly N deficient, with the bacterial fraction (<1 µm) also phosphorus limited. DON uptake (urea + glutamic acid + glycine) accounted for ~ 50–65% of the uptake of 15N-labeled substrates, with higher proportion of DON uptake at low substrate concentrations (≤2 µM). Except for nitrate, the kinetics fitted a linear model. Calculated relative preference index (RPI) based on porewater concentrations, suggested that the order of preference of the microbenthic community was NH4+ > urea > GLU > NO3- > GLY. Using a prokaryotic inhibitor (chloramphenicol) and theoretical calculations of algal uptake based on C/Chl a ratios, it was estimated that “algal” nitrogen uptake accounted for ~ 55-90% of DON uptake. Uptake rates were, however, estimated to cover only 26% –50% of the N-demand of MPB, suggesting that porewater N concentrations were not sufficient to meet the microalgal demand in early summer and that MPB in sandy sediments of micro-tidal waters may often be severely N-limited.

Place, publisher, year, edition, pages
2011. Vol. 63, no 1, p. 89-100
Keywords [en]
Microphytobenthos, Nitrogen, DON, Urea, Amino acids, Ectoenzymes
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-7586DOI: 10.3354/ame01479Scopus ID: 2-s2.0-79956304465OAI: oai:DiVA.org:lnu-7586DiVA, id: diva2:344756
Available from: 2010-08-20 Created: 2010-08-20 Last updated: 2017-12-12Bibliographically approved

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Lindehoff, ElinGranéli, Edna

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