Ammonium uptake and incorporation by Chesapeake Bay phytoplankton: Short term uptake kinetics1
Abstract
Using 15N‑labeled NH4+, we assessed the time‑course of NH4+ uptake, the parameters of saturation kinetics, and the rates of incorporation of NH4+ into trichloroacetic acid‑insoluble material by Chesapeake Bay phytoplankton. The amount of NH4+ taken up by the phytoplankton increased linearly with time for 2 h for all samples growing on or exposed to high concentrations (>1 µg‑atom N · liter−1) of NH4+, but extrapolations to time zero did not intercept the origin. These results could be explained by rapid isotopic equilibration of internal and external NH4+ pools. For stations for which ambient NH4+ bordered on detection limits, rapid but nonsaturable uptake was observed in 1‑ and 5‑min incubations, whereas saturation was attained in 15–60‑min incubations. The experiments on rates of NH4+ incorporation into TCA‑insoluble material demonstrated that most (>85%) of the 15N label was incorporated into the macromolecular fraction by ≈15 min. These data thus demonstrate that rates of NH4+ uptake may become limited within minutes by rates of assimilation and incorporation into macromolecules and that reported kinetic parameters reflect these metabolic rates rather than transport rates.
- Publication:
-
Limnology and Oceanography
- Pub Date:
- November 1982
- DOI:
- 10.4319/lo.1982.27.6.1113
- Bibcode:
- 1982LimOc..27.1113W