Plants possess 0.06% Fe by dry weight.
The energy difference is hardly significant in the total energy budget for a plant.

Plants almost exclusively are adapted to Fe3+ uptake as Fe2+ is chelated to Fe3+ once inside the plant cell for transport anyway............

So...........

You may read the Fe/Mn article here if you are interested in the BarrReport articles.
It goes over uptake mechanisms and what is known.

Unchelated Fe will not exists in the free form in our water, we need to have it bound by a chelator to have it be taken up by the plant leaves.

Note, in the sediment, reduction via the roots and bacteria(under the right conditions) will provide the usable form of Fe by that uptake method.

But never in the water column.


Regards,
Tom Barr