Dinitrogen Fixation and Release of Ammonium and Dissolved Organic Nitrogen by Trichodesmium IMS101

Authors

Margaret R. Mulholland, Old Dominion UniversityFollow
Deborah A. Bronk
Douglas G. Capone

ORCID

0000-0001-8819-189X (Mulholland)

Document Type

Article

Publication Date

2004

DOI

10.3354/ame037085

Publication Title

Aquatic Microbial Ecology

Volume

37

Issue

1

Pages

85-94

Abstract

Two methods used to measure dinitrogen (N₂) fixation (acetylene reduction and ¹⁵N₂ uptake) often result in different N₂ fixation rates. Part of the discrepancy may arise from the observation that Trichodesmium can release a fraction of their recently fixed N₂ as dissolved organic nitrogen (DON) and/or ammonium (NH4 ⁺). To resolve outstanding issues regarding N₂ fixation and the production of dissolved combined nitrogen (N) by Trichodesmium, we conducted a comprehensive analysis of N₂ fixation and the production of DON and NH₄⁺ in cultures of Trichodesmium IMS101. We performed ¹⁵N₂ uptake experiments in parallel with acetylene (C₂H₂) reduction assays, and measured production of ¹⁵NH₄⁺ and DO¹⁵N from ¹⁵N₂, and ¹⁵NH₄ ⁺ uptake and regeneration by isotope dilution. Four main results are highlighted. First, ¹⁵N₂ uptake appears to provide a better approximation of net N-specific growth rates than N₂ fixation estimates made using C₂H₂ reduction. Second, the C₂H₂ reduction method provides a closer approximation of gross N₂ fixation. Third, simultaneous measurements of relevant N pools and pathways by several methods enabled us to rigorously evaluate deviations from theoretical conversion factors and to interpret the basis for those deviations. Our results suggest that a conversion ratio (mol C₂H₂ reduced: mol N₂ reduced to PON, ammonium and DON) of 4:1 may be more appropriate for total N₂ fixation. Fourth, the difference between estimates of gross N₂ fixation, made using the C₂H₂ reduction technique, and net ¹⁵N₂ uptake into particulate N may be a good indicator of N release from N₂ fixation.

Original Publication Citation

Mulholland, M. R., Bronk, D. A., & Capone, D. G. (2004). Dinitrogen fixation and release of ammonium and dissolved organic nitrogen by Trichodesmium IMS101. Aquatic Microbial Ecology, 37(1), 85-94. doi:10.3354/ame037085

Repository Citation

Mulholland, Margaret R.; Bronk, Deborah A.; and Capone, Douglas G., "Dinitrogen Fixation and Release of Ammonium and Dissolved Organic Nitrogen by Trichodesmium IMS101" (2004). OES Faculty Publications. 305.
https://digitalcommons.odu.edu/oeas_fac_pubs/305