55-Iron uptake: Difference between revisions
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=== Recent applications === | === Recent applications === | ||
* | * For recent applications, including probing the iron nutritional status of natural phytoplankton, see review chapter by Marchetti and Maldonado 2016<ref name="Marchetti and Maldonado 2016">A. Marchetti and M. T. Maldonado, “Iron” in “The Physiology of Microalgae. 1 ed. Cham Switzerland: Springer, 2016. 681 p. doi: 10.1007/978-3-319-24945-2</ref>. | ||
=== Common calculations/conversions === | === Common calculations/conversions === | ||
Latest revision as of 16:21, 21 September 2026
| Iron uptake (55Fe) |
|---|
| Approach: radiotracer (55Fe) incubation |
| Context: incubation, lab |
| Spatial scale: point sample |
| Temporal scale: 4–24 h |
| Units: (x)mol Fe biomass-1 d-1; (x)mol Fe L-1 d-1 |
| Community captured: all (usually > 0.2 or 0.7 µm) |
| Co-measurements: biomass (Chl, cells, POC, cell volume) |
Method Overview
Iron uptake rates are measured by adding 55Fe (a low-energy gamma/X-ray emitter, half-life ~2.7 years) as a radiolabelled FeCl3 tracer to seawater samples under trace-metal-clean conditions. The 55Fe spike is added at concentrations comparable to ambient dissolved iron concentrations and allowed to equilibrate with the ambient iron-binding ligand pool before incubation. After a 4–24 h dark or light incubation, the particulate fraction is collected by filtration, washed with oxalate solution[1] to remove adsorbed (extracellular) iron, and the filter radioactivity is measured by liquid scintillation counting. The uptake rate is calculated from the fraction of 55Fe incorporated relative to the total dissolved 55Fe in the incubation[2].
Scale of measurement
Sampling after 4–24 h incubation. Trace-metal-clean sampling and handling are essential throughout to avoid iron contamination.
Data generated
Iron uptake rates normalized to biomass (mol Fe cell-1 d-1, mol Fe mol C-1 d-1) or expressed as volumetric rates (mol Fe L-1 d-1). When combined with iron quotas (cellular Fe content), growth-rate-specific iron requirements (KFe) can be derived.
Units & currency
Units are (x)mol Fe biomass-1 d-1 or (x)mol Fe L-1 d-1. The currency is Fe.
Sample size
Typical samples are < 1 L in volume.
Repositories & databases
Limitations
The method assumes minimal isotopic fractionation between 55Fe and ambient 56/54Fe. In field incubations, bottle effects can alter iron speciation and uptake rates relative to in situ conditions. The distribution of iron between the organic-ligand-bound and inorganic forms (bioavailability) must equilibrate before incubation; inadequate equilibration leads to inaccurate estimates. Radiotracer recycling (released iron taken up again) can overestimate rates in longer incubations.
Example Applications & Protocols
Classic examples
- Hudson & Morel (1990) Iron transport in marine phytoplankton: kinetics of cellular and medium coordination reactions [2]
Recent applications
- For recent applications, including probing the iron nutritional status of natural phytoplankton, see review chapter by Marchetti and Maldonado 2016[3].
Common calculations/conversions
- Fe uptake rate (mol Fe L-1 d-1) = (cpmcells / cpmtotal dissolved) × [Fedissolved] / incubation time.
- Biomass-specific rate = volumetric rate / [biomass]; requires cell counts or POC measurements.
References
- ↑ Tang D, Morel FMM (2006) Distinguishing between cellular and Fe-oxide-associated trace elements in phytoplankton. Marine Chemistry,98, 18–30. https://doi:10.1016/j.marchem.2005.06.003
- ↑ 2.0 2.1 Hudson, R. J. M., & Morel, F. M. M. (1990). Iron transport in marine phytoplankton: kinetics of cellular and medium coordination reactions. Limnology and Oceanography, 35(5), 1002–1020. https://doi.org/10.4319/lo.1990.35.5.1002
- ↑ A. Marchetti and M. T. Maldonado, “Iron” in “The Physiology of Microalgae. 1 ed. Cham Switzerland: Springer, 2016. 681 p. doi: 10.1007/978-3-319-24945-2