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Re: Nutrient Uptake: Roots v. Leaves

On Thu, 14 Oct 1999, Aquatic Plants Digest wrote:

> Also remember that nutrient uptake in terrestrial
> plants is usually driven by transpiration... water
> taken in at the roots, and pulled up the plant
> through the osmotic gradient (evaporation at the
> leaves leave a lower gradient
  <er, I think you mean "potential">
> there, so the water
> is pulled up).  If you don't transpire your water,
> it's pretty hard to get those nutrients up there.

That's what I figured, too.  Then I read the research article posted at
the Tropica site (is it still there?) that shows guttation in aquatic
plants.  I think that means that aquatic plants can maintain a
transpiration stream even in the absence of evaporation from the leaves.
Karen Randall has on a number of occasions sited this result as a
mechanism for plants to induce circulation in the substrate.

I don't know how they do that in the absence of evaporation, but I think
Jean Olson once said that the flow of water (and nutrients) up from the
roots was coupled to the flow of denser carbohydrate-bearing fluid
from the leaves to the roots.  With that coupling, gravity driving the
heavier carbohydrate-bearing fluids down also drives the lighter
nutrient-bearing fluids up.

Pretty cool, IMHO.

Roger Miller