MEPS 409:1-15 (2010)  -  doi:10.3354/meps08639

Burrowing deeper into benthic nitrogen cycling: the impact of bioturbation on nitrogen fixation coupled to sulfate reduction

Victoria J. Bertics1,2,*, Jill A. Sohm1,*, Tina Treude1,2, Cheryl-Emiliane T. Chow1, Douglas G. Capone1, Jed A. Fuhrman1, Wiebke Ziebis1,**

1Dept. of Biological Sciences and Wrigley Institute for Environmental Studies, University of Southern California, 3616 Trousdale Parkway, Allan Hancock Foundation Building, Los Angeles, California 90089-0371, USA
2Leibniz Institute of Marine Sciences, Wischhofstr. 1–3, GEB. 4, Kiel 24148, Germany
*These authors contributed equally to this manuscript
**Corresponding author. Email:

ABSTRACT: Biological dinitrogen (N2) fixation is the primary input of fixed nitrogen (N) into the marine biosphere, making it an essential process contributing to the biological functions of all organisms. Because biologically available N often limits marine productivity, microbial processes leading to its loss and gain (e.g. denitrification and N2 fixation, respectively) play an important role in global biogeochemical cycles. Bioturbation is known to influence benthic N cycling, most often reported as enhancement of denitrification and a subsequent loss of N2 from the system. N2 fixation has rarely been addressed in bioturbation studies. Instead, sedimentary N2 fixation typically has been considered important in relatively rare, localized habitats such as rhizosphere and phototrophic microbial mat environments. However, the potential for N2 fixation in marine sediments may be more widespread. We show here that nitrogenase activity can be very high (up to 5 nmol C2H4 cm–3 h–1) in coastal sediments bioturbated by the ghost shrimp Neotrypaea californiensis and at depths below 5 cm. Integrated subsurface N2-fixation rates were greater than those previously found for un-vegetated estuarine sediments and were comparable to rates from photosynthetic microbial mats and rhizospheres. Inhibition experiments and genetic analysis showed that this activity was mainly linked to sulfate reduction. Sulfate-reducing bacteria (SRB) are widespread and abundant in marine sediments, with many possessing the genetic capacity to fix N2. Our results show that N2 fixation by SRB in bioturbated sediments may be an important process leading to new N input into marine sediments. Given the ubiquity of bioturbation and of SRB in marine sediments, this overlooked benthic N2 fixation may play an important role in marine N and carbon (C) cycles.

KEY WORDS: Bioturbation · Crustaceans · Marine sediment · Microniche · Nitrogen fixation · Sulfate reduction

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Cite this article as: Bertics VJ, Sohm JA, Treude T, Chow CET, Capone DG, Fuhrman JA, Ziebis W (2010) Burrowing deeper into benthic nitrogen cycling: the impact of bioturbation on nitrogen fixation coupled to sulfate reduction. Mar Ecol Prog Ser 409:1-15

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