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Re: Aquatic Plants Digest V3 #373

Luca Specchio asked:
>1) The FeEDTA or any other chelated micronutrients (such as Zn, Cu, Mn
>etc.) can be adsorbed by plants withOUT waiting that link between EDTA and
>Fe is broken? I suppose they can.

A text book sitting on my bookshelves (_Soil Science_, R G McLaren & K 
C  Cameron, 1990, Oxford University Press, Auckland) shows metals such 
as iron, manganese, copper etc. being taken up by plants as the 
divalent ionic form only (eg Fe2+  etc.).  I suspect that a 
metal/chelate complex molecule is too large to pass through the cell 
membranes of the plant.  No reason to suspect that this doesn't apply 
under water as well.

Presumably as ionic iron etc is taken up by plant roots it 
is replaced by iron being released from the chelated form by shifts 
in equilibria.  Of course, whether that replacement process is fast 
enough to satisfy impatient aquarists.....

Don't forget that the anaerobic environment around the roots in the 
substrate will result in some unoxidised iron being present which can 
be taken up.
If there are any soil scientists on the group they may like to 

Nick Miller
Rotorua, New Zealand