Figure 4.

Schematic representation of experimental probing and calculation of the uptake rate constant – k_up – exemplified with Fe-limited Emiliania huxleyi uptake data. Note that the complexing ligand L for strong ligands such as DFB should be in sufficient excess of Fe to rule out the presence of Fe′ (which would bias uptake rate since Fe′ is taken up more readily than FeL). But L:Fe should be minimal to prevent ligand from competing with cells for Fe (and thus decreasing uptake rates).