0000-0001-8819-189X (Mulholland)

Document Type


Publication Date




Publication Title

Frontiers in Microbiology




1380179 (1-22)


Understanding nitrogen (N) uptake rates respect to nutrient availability and the biogeography of phytoplankton communities is crucial for untangling the complexities of marine ecosystems and the physical, biological, and chemical forces shaping them. In the summer of 2016, we conducted measurements of bulk microbial uptake rates for six ¹⁵N-labeled substrates: nitrate, nitrite, ammonium, urea, cyanate, and dissolve free amino acids across distinct marine provinces, including the continental shelf of the Mid-and South Atlantic Bights (MAB and SAB), the Slope Sea, and the Gulf Stream, marking the first instance of simultaneously measuring six different N uptake rates in this dynamic region. Total measured N uptake rates were lowest in the Gulf Stream followed by the SAB. Notably, the MAB exhibited significantly higher N uptake rates compared to the SAB, likely due to the excess levels of pre-existing phosphorus present in the MAB. Together, urea and nitrate uptake contributed approximately 50% of the total N uptake across the study region. Although cyanate uptake rates were consistently low, they accounted for up to 11% of the total measured N uptake at some Gulf Stream stations. Phytoplankton groups were identified based on specific pigment markers, revealing a dominance of diatoms in the shelf community, while Synechococcus, Prochlorococcus, and pico-eukaryotes dominated in oligotrophic Gulf Stream waters. The reported uptake rates in this study were mostly in agreement with previous studies conducted in coastal waters of the North Atlantic Ocean. This study suggests there are distinct regional patterns of N uptake in this physically dynamic region, correlating with nutrient availability and phytoplankton community composition. These findings contribute valuable insights into the intricate interplay of biological and chemical factors shaping N dynamics in disparate marine ecosystems.


© 2024 Zhu, Mulholland, Bernhardt, Neeley, Widner, Tapia and Echevarria.

This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0). The use, distribution or reproduction in other forums is permitted, provided the original authors and the copyright owners are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

Data Availability

Article states: "The datasets presented in this study can be found in online repositories. The CTD, nutrient, and PNPC and nitrogen uptake rates data can be accessed via https://www.bco-dmo.org/project/683923. The phytoplankton pigment data are available at https://seabass.gsfc.nasa.gov/cruise/cyanate2016."

Original Publication Citation

Zhu, Y., Mulholland, M. R., Bernhardt, P. W., Neeley, A. R., Widner, B., Tapia, A. M., & Echevarria, M. A. (2024). Nitrogen uptake rates and phytoplankton composition across contrasting north Atlantic Ocean coastal regimes north and south of Cape Hatteras. Frontiers in Microbiology, 15, 1-22, Article 1380179. https://doi.org/10.3389/fmicb.2024.1380179

Mulholland-2024-SuppMaterialNitrogenUptakeRat.docx (2116 kB)
Supplementary Material


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