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substrate circulation and oxygen

Roger Miller wrote an excellent posting discussing the micro
environments present in substrates. I want to clarify something he
attributed to me.

> Steve brought up two points that seem to be at odds with one another.  On
> one hand he said that anaerobic conditions in the substrate were necessary
> to keep typically insoluble nutrients like iron and phosphorus in a
> biologically available state.  On the other hand he said that rooted
> plants circulate water in and aerate the substrate.  If the latter were
> completely true, then the former would not happen.

I don't believe I said that the transpiration stream of submerged
aquatics is responsible for aeration of the substrate. I have said at
other times that the aerenchyma of stems and roots DOES provide oxygen
in the substrate and that in some circumstances, plant roots could grow
so densely over time that the reduction of iron would be greatly

I'm not going to repeat what Roger already said so eloquently about the
micro environments. Well explained!

Steve, feeling a bit notorious with all the name dropping going on!