54-Manganese uptake

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Manganese uptake (⁵⁴Mn)
Approach: radiotracer (⁵⁴Mn) incubation
Context: incubation, lab
Spatial scale: point sample
Temporal scale: 4–24 h
Units: (x)mol Mn biomass^-1 d^-1; (x)mol Mn L^-1 d^-1
Community captured: all (usually > 0.2 or 0.7 µm)
Co-measurements: biomass (Chl, cells, POC, cell volume)

Method Overview

Manganese uptake rates are measured by adding ⁵⁴Mn (a gamma emitter, half-life ~312 days) to seawater samples under trace-metal-clean conditions. The ⁵⁴Mn tracer (as MnCl₂) is equilibrated with the sample before incubation. After 4–24 h, cells are collected by filtration; intracellular Mn is distinguished from surface-adsorbed Mn by a titanium(III) citrate EDTA wash, and filter radioactivity is counted by gamma spectrometry. Uptake rates are calculated from the fraction of ⁵⁴Mn in the cellular fraction relative to total dissolved ⁵⁴Mn^[1]. Mn is a micronutrient required for superoxide dismutase (MnSOD) and for photosystem II (the water-splitting Mn₄Ca cluster).

Scale of measurement

4–24 h incubation under trace-metal-clean conditions.

Data generated

Manganese uptake rates (mol Mn L^-1 d^-1 or mol Mn biomass^-1 d^-1). Combined with Mn quotas, elemental Mn:C ratios can be derived.

Units & currency

Units are (x)mol Mn L^-1 d^-1 or (x)mol Mn biomass^-1 d^-1. The currency is Mn.

Sample size

Typical samples are < 1 L in volume.

Repositories & databases

Limitations

Minimal isotopic fractionation is assumed. Mn speciation (dissolved Mn²⁺ vs. colloidal Mn oxides) strongly affects bioavailability; the equilibration step must establish realistic speciation. Steady-state conditions (short-term vs. long-term rates) may differ, and natural ligands can alter uptake rates relative to simple MnCl₂-spiked systems.

Example Applications & Protocols

Classic examples

Peers & Price (2004) A role for manganese in superoxide dismutases and growth of iron-deficient diatoms ^[1]

Recent applications

Common calculations/conversions

Mn uptake rate = (cpm_cells / cpm_dissolved) × [Mn_dissolved] / incubation time.

References

↑ ^1.0 ^1.1 Peers, G., & Price, N. M. (2004). A role for manganese in superoxide dismutases and growth of iron-deficient diatoms. Limnology and Oceanography, 49(5), 1774–1783. https://doi.org/10.4319/lo.2004.49.5.1774

[Peers2004-1] 1.0 ^1.1 Peers, G., & Price, N. M. (2004). A role for manganese in superoxide dismutases and growth of iron-deficient diatoms. Limnology and Oceanography, 49(5), 1774–1783. https://doi.org/10.4319/lo.2004.49.5.1774

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