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Energy use in plants

A subscriber wrote:

<<This is where I break down to speculation, and someone else could probably
give a better answer.  It seems inevitable to me that the plant's task of
providing oxygen to its roots places an energy burden on the plant.  If
the roots are kept under aerobic conditions, then the plant doesn't have
that burden, and the energy can be used for growth or fruiting. >>

I think this is a common misunderstanding as to "how plants work." Plants are
not animals - the movement of chemicals, water, sugars, etc., in a plant is
governed by physics, and the plant does not expend any energy to move these
things. Plants can conveniently be thought of as "plumbing systems," where
fluids and dissolved substances move through tubes solely by means of
physical forces that do not depend upon energy input from the plant. IOW, in
terrestrial plants, water moves UP the stem to the leaves by capillary
attraction, and the much heavier sap with sugars from photosynthesis moves
DOWN by weight.  I realize that is a DRASTIC oversimplification, but we
should remember that plants do NOT have pumping organs that move things
about, like an animal's bloodstream. 

Aquatic plants (Also a large number of terrestrial plants) move oxygen down
to their roots with essentially inert physical mechanisms, i.e. they don't do
any work or use any energy to move the oxygen. The movement of oxygen is
entirely due to the STRUCTURE of the roots.

Still, it is common for us to say things like "Pin Oaks are very weak at
extracting Iron from Alkaline Soils." even though we know full well that this
is not true. We even say "Pin Oaks LIKE (emphasis supplied) Acid Soils." Pin
Oaks do not think, so they really cannot accurately be said to "like"
anything.  I suppose we should not be surprised at how we say things - after
all, who has not cussed out an inanimate object they they have just stubbed
their bare toe on?  <ggggg>

Pin Oaks do not obtain iron from Alkaline Soils, because Iron is tightly tied
up chemically in Alkaline Soils. Lower the pH of the soil, and the amount of
"free" iron goes up. (In Pin Oaks, there is another mechanism that causes
trouble - Highly alkaline soils give highly basic soil moisture, and the
basic moisture reacts with the iron already present in the tree to chemically
tie it up. Thus, a very young Pin Oak, planted "Balled and Burlapped" in a
calcareous soil may grow quite well, until its roots grow into the
surrounding soil, thus absorbing the alkaline materials, transporting the
alkaline materials throughout the tree, and pretty much dooming the young
plant to Iron Deficiency Chlorosis.) Same with Aquatic Plants. It is much
"easier" to keep iron "available" to our Aquatic Plants when we keep the pH
LOW. 

Anyway, don't worry about our Aquatic Plants using energy to move anything
through their tissues. In fact, the only reason DEAD trees stop moving water
through their tissues is the simple fact that, when the top dies, the roots
no longer get carbohydrates from photosynthesis, and simply die of
starvation. The dead roots can't move water because they are decomposing, not
just because they are no longer living. Or, the roots die from, for example,
Phytophera Root Rot, and the rest of the tree dies of dehydration because the
dead roots and root hairs have decomposed and thus stopped moving soil
moisture UP through the tree structure.

I hope this helps.

Cheers!

Jean Olson
JOlson8590 at AOL_com
Out in the Boonies, near
Cambridge, Iowa