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Abstract. As a key biogeochemical pathway in the marine nitrogen cycle, nitrification (ammonia oxidation and nitrite oxidation) converts the most reduced form of nitrogen – ammonium–ammonia (NH4+–NH3) – into the oxidized species nitrite (NO2-) and nitrate (NO3-). In the ocean, these processes are mainly performed by ammonia-oxidizing archaea (AOA) and bacteria (AOB) and nitrite-oxidizing bacteria (NOB). By transforming nitrogen speciation and providing substrates for nitrogen removal, nitrification affects microbial community structure; marine productivity (including chemoautotrophic carbon fixation); and the production of a powerful greenhouse gas, nitrous oxide (N2O). Nitrification is hypothesized to be regulated by temperature, oxygen, light, substrate concentration, substrate flux, pH and other environmental factors. Although the number of field observations from various oceanic regions has increased considerably over the last few decades, a global synthesis is lacking, and understanding how environmental factors control nitrification remains elusive. Therefore, we have compiled a database of nitrification rates and nitrifier abundance in the global ocean from published literature and unpublished datasets. This database includes 2393 and 1006 measurements of ammonia oxidation and nitrite oxidation rates and 2242 and 631 quantifications of ammonia oxidizers and nitrite oxidizers, respectively. This community effort confirms and enhances our understanding of the spatial distribution of nitrification and nitrifiers and their corresponding drivers such as the important role of substrate concentration in controlling nitrification rates and nitrifier abundance. Some conundrums are also revealed, including the inconsistent observations of light limitation and high rates of nitrite oxidation reported from anoxic waters. This database can be used to constrain the distribution of marine nitrification, to evaluate and improve biogeochemical models of nitrification, and to quantify the impact of nitrification on ecosystem functions like marine productivity and N2O production. This database additionally sets a baseline for comparison with future observations and guides future exploration (e.g., measurements in the poorly sampled regions such as the Indian Ocean and method comparison and/or standardization). The database is publicly available at the Zenodo repository: https://doi.org/10.5281/zenodo.8355912 (Tang et al., 2023).
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This content will become publicly available on June 1, 2027
Ocean Genes CURE: The influence of ocean microbes on global carbon cycling
The global ocean is a profoundly important ecosystem that regulates Earth’s climate and is responsible for nearly half of the oxygen we breathe. Oceanographic concepts and marine microbial ecology are often excluded from undergraduate curricula despite their significance. Specifically, phytoplankton in the surface ocean fix atmospheric CO2 into organic molecules, which are released into the water where they serve as substrates for heterotrophic bacteria. Upon release, bacteria use transporter proteins to move these substrates across their membranes for metabolism inside their cells. However, the substrate preference and specificity of many microbial transporters in the ocean remains unknown. To address these curricular and scientific gaps, we developed the Ocean Genes course-based undergraduate research experience (CURE). In this five-session CURE lesson, students perform growth assays with a mutant library of the ecologically relevant marine bacterium Ruegeria pomeroyi DSS-3 on different carbon sources. The scientific goal of their investigation is to identify the substrate specificity of the bacterium’s 126 transporter genes, most of which remain uncharacterized despite their critical role in the food web that underpins global carbon cycles. Through this lesson, students develop their skills in interpreting scientific literature, performing microbiological techniques, analyzing data using relevant statistical tests, interpreting experimental results, and making arguments from evidence. This lesson aims to broaden engagement of undergraduate students with authentic marine science research. In doing so, the Ocean Genes CURE offers a novel avenue to increase diversity in the marine science and expand ocean literacy of undergraduate students.
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- PAR ID:
- 10674682
- Publisher / Repository:
- CourseSource
- Date Published:
- Journal Name:
- CourseSource
- ISSN:
- 2332-6530
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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