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calcium for roots? yes!

Steve Pushak wrote wrote:
> there is no point in putting calcium tablets in the substrate for your
> plants; they absorb it from the water and terrestrial plants transpire
> Ca from roots only with difficulty. See apd archives. Paul K or Dave H
> might have a few more comments on the subject.

Actually, adding calcium to the substrate works very well.  It works
well enough to provide a practical long-term solution for all but one of
the plants I treated.  The lone exception was Ammania senegalensis and
under less extreme conditions calcium additions to the substrate will
probably work well for that plant, too.

Of course, you could also add calcium to the water, but that would
probably require larger additions.  For instance, last weekend I treated
a large H. corymbosa in my 55 gallon tank with half of a 500 mg tablet. 
It's now growing nice, healthy new leaves.  If instead I managed to
dissolve the calcium into the water it would have increased the calcium
content in the tank by about 1.4 mg/l -- a whopping (and unmeasurable)
0.2 degrees GH.  I doubt that would have cured anything. 

Several of the plants I've treated with substrate additions of calcium
are naturally emergent plants (H. corymbosa, E. osiris, E.
cordifolius).  As emergent plants they would probably die if they
couldn't take up calcium through their roots.  Terrestrial plants *must*
take up calcium through their roots; they have no choice.  Many of our
aquarium plants are members of plant families - even genera - that are
mostly terrestrial plants.  It's difficult for me to imagine why or how
an adaptation to submersed growth would cause those plants to lose the
ability to take calcium through their roots.

That isn't to say that all aquatic plants act the same.

I have successfully treated what I believe was a calcium deficiency in
Vallisneria americana (an obligate submersed plant) by adding calcium
carbonate to the substrate below the plant.  However, the symptoms in V.
americana suggests to me that the plant is at least partly dependent on
calcium in the water.

Severe symptoms of what I treated as calcium deficiency stop the growth
of new leaves.  Milder symptoms effect only the first couple inches (or
less) of a new leaf, and the rest of the leaf is normal.  I speculate
that new leaves are initially supplied with calcium from the roots.  If
the roots can't get and transport enough calcium to supply the new leaf
then the early growth is calcium deficient and stunted.  As the new leaf
grows it soon reaches a size where it obtains it's own calcium supply
directly from the water.  If there's enough calcium in the water then
the leaf continues to grow normally; if there isn't enough calcium in
the water then growth stops.

At any rate, calcium in the substrate is a proven treatment for calcium
deficiency in aquatic plants.

Roger Miller