How nutrients get into plants

> From: Stephen.Pushak at hcsd_hac.com
> <a few questions>

Holy Question Barrage, Batman!

I have archived an exchange from rec.aqauria from Aug 1990, where I
was treated to a discourse by Jeff Frank on laterite and heating coils
and the goodness of same.  Here is an excerpt (e-mail me if you want
the whole 40 kbytes) regarding nutrient uptake by plant roots:

| If other plant growth factors are present in reasonable amounts, we
| will have good root growth.  By good root growth, I dont mean lots
| of roots.  You can have hardy plants with big thick masses of roots
| in other systems.  I mean here root hair profiferation.  Only under
| the special conditions including substrates relatively high in
| cation exchange capacity, and O2 content can the tremendous surface
| area and nutrient adsorbing power of root hairs be optimized in an
| aquarium.  (Adsorption is the direct echange of a nutrient cation
| such as NH4 from an exchange site on a substrate for a H+ from
| H2(CO2) from a root hair)  Plants in other systems have no cation
| rich substrate for roots to exploit, so don't mass root hairs.  They
| are less effiecient.  Plants in these other systems can do quite
| well taking nutrients up from the water by absorption.  (Absorption
| is the drawing in of nutrients as the plant draws in water.)
| Higher plants have developed vascular systems which prefer to
| adsorb thru roots.  The Dupla book doesn't say this stuff.  I think
| they want it to remain a bit mystical.