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Marine Ecology Progress Series

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MEPS 605:87-101 (2018)  -  DOI: https://doi.org/10.3354/meps12755

Dinitrogen (N2) fixation rates in a subtropical seagrass meadow measured with a direct 15N-N2 tracer method

Natasha L. Carlson-Perret*, Dirk V. Erler, Bradley D. Eyre

Centre for Coastal Biogeochemistry, School of Environmental Science and Engineering, Southern Cross University, Lismore, NSW 2480, Australia
*Corresponding author:

ABSTRACT: This study used a direct 15N stable isotope labelling technique to measure rates of dinitrogen (N2) fixation within above- and belowground loci of a subtropical seagrass meadow (Zostera muelleri). The total rate of N2 fixation (i.e. sum of the above- and belowground rates) was ~38 µmol N2 m-2 h-1, similar to other rates measured in subtropical systems. Rates of N2 fixation were higher when the 15N-N2 label was added to the surface water compared to when it was added to the sediments. Furthermore, the lowest rates of N2 fixation were observed in the root/rhizome material regardless of whether the 15N-N2 label was added directly to the rhizosphere (0.12 µmol N2 m-2 h-1) or the overlying water column (7.3 µmol N2 m-2 h-1). These results suggest that there was active transport of fixed N from the leaves to the roots of the seagrass plants, in contrast to other studies in which N2 fixation was more active in the rhizosphere. Our study demonstrates the utility of the direct 15N-N2 tracer approach for quantifying the spatial heterogeneity of N2 fixation in complex seagrass environments.


KEY WORDS: Nitrogen fixation · Stable isotope tracer · Zostera muelleri


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Cite this article as: Carlson-Perret NL, Erler DV, Eyre BD (2018) Dinitrogen (N2) fixation rates in a subtropical seagrass meadow measured with a direct 15N-N2 tracer method. Mar Ecol Prog Ser 605:87-101. https://doi.org/10.3354/meps12755

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