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Re: Carbon dioxide concentration in water

Stepen wrote:

> That would seem to suggest that a leaf in water fitting the above
> description would be exposed to more CO2 than the same sized leaf in air.
> Does it follow then that plants have more trouble extracting the CO2 from 
> water than air?

Yes.  The trouble comes from the fact that water is thicker than air. 
Plants pull the CO2 out of a thin film of water around the leaves. 
After that the plant's CO2 uptake rate depends on how quickly CO2 can
get across that layer to reach the leaf.  The same process happens in
air, but air is so thin (compared to water) that the layer of
CO2-depleted air near the leaf is nearly non-existent and the CO2 can
get to the leaf very easily.

Dave Huebert often made the point that keeping good water movement in
the tank helps break down the CO2-depleted zone around the leaves. 
Improving water movement in a tank is an effective way of increasing the
CO2 supply for the plants.  In some cases it may be more effective then
turning up the CO2.

Roger Miller