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Re: Roots

On Thu, 14 Oct 1999, Ronnie wrote:

> > Aquatic plants can take in nutrients at either roots or leave.  I've read
> > that that aquatic plants switch from root feeding to foliar feeding when
> > dissolved nutrients are high enough to supply the plant.
> >From where did you come across this info?  If you have the book's title
> or ISBN #, I'd like to read up.

The information was from the review section of a US Gov - sponsored
publication about the response of aquatic vascular plant communities to
environmental change.  I don't have the reference with me now but can post
it later.  The paper is actually very interesting because it has an
excellent summary section on factors that influence growth of vascular
plants (as opposed to algae, which are the focus of most academic "aquatic
plant" literature).  It includes a big graphic describing the natural
environment of a large number of native plants.

Being a fairly academic, government (EPA?) sponsored work it didn't get
widely circulated, and probably won't be readily available in Singapore.

> > Taken literally this means that even if the substrate is very rich the
> > plant won't use nutrients in the substrate if there are sufficient
> > nutrients in the water column to supply the plants.  I'm not sure that was
> > the author's intent in writing that passage, but that's how it was
> > written.
> Is this absorption particular to specific plants or all plants in
> general?  I was under the impression that root-feeders like Echinodorus
> and crypts rely on substrate fertilization and draw nutrients more from
> the roots than it's foliage, thus the practice of shoving Jobes' sticks,
> laterite balls and whatnots into the gravel.

Root feeding abilities vary from species to species, from (as Tom Barr
pointed out) rootless aquatics like hornwort and riccia that don't have
the root feeding alternative at all to plants with highly developed roots
that normally depend on root feeding for their nutrient supply.  There are
even examples that are exclusively dependent on root feeding for one or
more nutrient, e.g. Isoetes ferns that can only take CO2 through their

Personally I don't like fertilizing several times a week or adding big
fertilizer doses to the water column, so without root feeding I have a
hard time keeping up with the nutrient demands of heavy feeders like large

I doubt that there are any aquarium plants that are exclusively dependent
on root feeding for all their nutrients.  Even completely nonaquatic
vegetable crops can get nutrients through foliage feeding! (Or at least
that's what the fertilizer manufacturers claim).

Some plants may exhibit different growth patterns depending on whether
they are root feeding or foliage feeding, but I can't attest to that.

The principle advantages to root feeding, as I see it are:

	1)  You do it infrequently
	2)  You do very few water tests
	3)  You feed the plants, not the algae.

The disadvantages are:

	1)  Successes (as Onis Cogburn pointed out) can be difficult to
	2)  Feeding (as Tom Barr pointed out) can be messy
	3)  Some nutrients (as Dave Huebert once pointed out) can't be fed
	    exclusively at the roots.

I hope that helps,

Roger Miller

In smokey Albuquerque, where the US Forest Service started a controlled
forest fire in the nearby mountains and caused the City to violate US
air quality standards.  Ain't that just peachy?