Influence of hydraulics on the uptake of ammonium by two freshwater plants

Authors

  • Kris D. Bal,

    Corresponding author
    1. Department of Biology, Ecosystem Management Research Group, University of Antwerp, Wilrijk, Belgium
    2. Department of Biodiversity, School of Molecular and Life Sciences, University of Limpopo, Sovenga, South Africa
    • Correspondence: Kris D. Bal, University of Limpopo, Department of Biodiversity, School of Molecular and Life Sciences, Sovenga 0727, South Africa.

      E-mail: kris.bal@ua.ac.be

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  • Natacha Brion,

    1. Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
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  • Veronique Woulé-Ebongué,

    1. Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
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  • Jonas Schoelynck,

    1. Department of Biology, Ecosystem Management Research Group, University of Antwerp, Wilrijk, Belgium
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  • Antoinette Jooste,

    1. Department of Biodiversity, School of Molecular and Life Sciences, University of Limpopo, Sovenga, South Africa
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  • Cristina Barrón,

    1. Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
    2. Departamento de Biología, Centro Andaluz Superior de Estudios Marinos (CASEM), Universidad de Cádiz, Cádiz, Spain
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  • Frank Dehairs,

    1. Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
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  • Patrick Meire,

    1. Department of Biology, Ecosystem Management Research Group, University of Antwerp, Wilrijk, Belgium
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  • Tjeerd J. Bouma

    1. Centre for Estuarine and Marine Ecology (CEME), Netherlands Institute of Ecology (NIOO-KNAW), Yerseke, The Netherlands
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Summary

  1. Macrophytes are important in the biogeochemistry of flowing rivers, although most information so far has relied on measurements of nutrients in plant tissues. This yields only indirect information on the nutrient uptake fluxes by roots and shoots and about nutrient translocation between roots and shoots. Here, we studied nitrogen uptake through experiments with enriched 15N stable isotopes.
  2. Two macrophytes (Potamogeton natans and Ranunculus fluitans) were grown in a closed race track-shaped flume, allowing us to control the hydraulic conditions in and around the plants. Overall ammonium uptake rates (μmol g−1 dry mass h−1) were higher for R. fluitans than P. natans.
  3. In addition to differences between the species, the spatial position of individuals within the plant patch and water flow were also important in explaining ammonium uptake. Thus, ammonium uptake was high at the leading edge of the patch and increased with velocity.
  4. Plant characteristic, such as the angle at which the plants bent in the flow, was also correlated with ammonium uptake. Differences in nutrient uptake associated with hydrodynamic parameters raised the question of how the two are related. For both species, uptake was not correlated with Reynolds stress, indicating the poor effect of turbulent mixing in determining ammonium uptake.

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