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Abstract Picoplankton populations dominate the planktonic community in the surface oligotrophic ocean. Yet, their strategies in the acquisition and the partitioning of organic and inorganic sources of nitrogen (N) and carbon (C) are poorly described. Here, we measured at the single‐cell level the uptake of dissolved inorganic C (C‐fixation), C‐leucine, N‐leucine, nitrate (NO3−), ammonium (NH4+), and N‐urea in pigmented and nonpigmented picoplankton groups at six low‐N stations in the northwestern Atlantic Ocean. Our study highlights important differences in trophic strategies betweenProchlorococcus,Synechococcus, photosynthetic pico‐eukaryotes, and nonpigmented prokaryotes. Nonpigmented prokaryotes were characterized by high leucine uptake rates, nonsignificant C‐fixation and relatively low NH4+, N‐urea, and NO3−uptake rates. Nonpigmented prokaryotes contributed to 7% ± 3%, 2% ± 2%, and 9% ± 5% of the NH4+, NO3−, and N‐urea community uptake, respectively. In contrast, pigmented groups displayed relatively high C‐fixation rates, NH4+and N‐urea uptake rates, but lower leucine uptake rates than nonpigmented prokaryotes.Synechococcusand photosynthetic pico‐eukaryotes NO3−uptake rates were higher thanProchlorococcusones. Pico‐sized pigmented groups accounted for a significant fraction of the community C‐fixation (63% ± 27%), NH4+uptake (47% ± 27%), NO3−uptake (62% ± 49%), and N‐urea uptake (81% ± 35%). Interestingly,Prochlorococcusand photosynthetic pico‐eukaryotes showed a greater reliance on C‐ and N‐leucine thanSynechococcuson average, suggesting a greater reliance on organic C and N sources. Taken together, our single‐cell results decipher the wide diversity of C and N trophic strategies between and within marine picoplankton groups, but a clear partitioning between pigmented and nonpigmented groups still remains.
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Size dependence of metabolism within marine picoplankton populations
Abstract Cell size is broadly applied as a convenient parameterization of ecosystem models and is widely applicable to constrain the activities of organisms spanning large size ranges. However, the size structure of the majority of the marine picoplankton assemblage is narrow and beneath the lower size limit of the empirical allometric relationships established so far (typically >1 μm). We applied a fine‐resolution (0.05 μm increments) size fractionation method to estimate the size dependence of metabolic activities of picoplankton populations in the 0.10–1.00 μm size interval within the surface North Pacific Subtropical Gyre microbial assemblage. Group‐specific carbon retained on each filter was quantified by flow cytometric conversion of light scatter to cellular carbon quotas. Median carbon quotas were 25.7, 22.6, and 5.9 fg C cell−1for populations of the picocyanobacteriumProchlorococcus, high‐scatter heterotrophs, and low‐scatter heterotrophs, respectively. Carbon‐specific rates of primary production as a function of cell size, using the14C method, and phosphate transport, using33P radiotracers, resulted in negative power scalings (b) within populations ofProchlorococcusand heterotrophs ofb = −1.3 andb = −1.1, respectively. These findings are in contrast to the positive empirical power scaling comprising the broader and larger prokaryote category (b = 0.7) and point to within‐population variability in cell physiology and metabolism for these important microbial groups.
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- PAR ID:
- 10448834
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 64
- Issue:
- 4
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 1819-1827
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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