MEPS 616:1-11 (2019)  -  DOI: https://doi.org/10.3354/meps12961

ABSTRACT: Highly productive seagrass meadows often occur in oligotrophic waters, and nitrogen (N) fixation may play a role in supporting the N demand of the meadows. To date, most studies of N fixation in seagrass sediments have relied on indirect measurements via the acetylene reduction technique. Recent measurements of N fixation in submerged estuarine sediments using direct methods (e.g. N₂:Ar ratio) in laboratory core incubations have shown higher rates than acetylene reduction measurements. Direct methods have not yet been applied to seagrass sediments in situ. In this study, we used a new in situ ³⁰N₂ push-pull method to measure N fixation rates in seagrass sediments and compared those rates to traditional acetylene reduction slurries. On average, hourly rates of N fixation measured via the ³⁰N₂ push-pull method were more than an order of magnitude greater than the acetylene reduction rates during summer (388 and 7.8 µmol m^-2 h^-1, respectively). These push-pull rates exceeded other published rates of N fixation in seagrass sediments (measured via acetylene reduction) but were within the range of reported rates for direct measurements of N fixation in submerged estuarine sediments. These results indicate the need for further investigation of N fixation rates in seagrass sediments via direct and in situ measurements. In order to fully understand the role of seagrass meadows in coastal N cycling, it is critical to accurately determine the magnitude of N fixation that occurs in these highly productive ecosystems.

KEY WORDS: Nitrogen fixation · Seagrass · Zostera marina · Push-pull · ³⁰N₂

Full text in pdf format Information about this Feature Article

Cite this article as: Aoki LR, McGlathery KJ (2019) High rates of N fixation in seagrass sediments measured via a direct 30N2 push-pull method. Mar Ecol Prog Ser 616:1-11. https://doi.org/10.3354/meps12961 Export citation Share:    Facebook - - linkedIn