Title

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

Document Type

Article

Publication details

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', Marine Ecology Progress Series, vol. 605, pp. 87-101.

Published version available from:

https://dx.doi.org/10.3354/meps12755

Peer Reviewed

Peer-Reviewed

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 N2fixation in complex seagrass environments.

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