>1)In spite of my intuition, the soil does become alkaline.
>2)Instead of needing alkaline, the Pings benefit from the Ca++ ions.
>3)This is something ineffectual the CPer does to please him/her self.
>4)Something else is going on (aka the cover your a** possibility)
>Comments on acid/base reactions, Rob M? On the usefulness of Ca++ to plants,
A good question. Something which got me scratching the noggin'. You
are right: peat is weakly acidic and CaCO3 (and Ca(OH)2) are highly
aqueous insoluble alkaline salts. However, one would expect that the
small amount that dissolves in H2O (ie., moist substrate) will react in
an acid/base fashion with the peat moss (Hypothesis A). To rationalize
this assumption, we need to know that peat moss (and Sphagnum moss) are
cationic ion exchangers, that is, they can exchange cations (eg., Ca++,
Na+, Mg++, NH4+, etc., including H+ which confers acidity) with those in
the growing medium. In particular, H+ ions in unspent or fresh peat,
with Ca++ ions from the CaCO3. In chemical parlance:
(peat moss)--2(H+) + CaCO3 ------> (peat moss)--Ca++ + H2CO3
H2CO3 ---------> H2O + CO2
(carbonic acid)
Given that acid/base reactions are facile and proceed to completion to give
a salt and water [(peat moss)--Ca++ and H2O in this case] and that the
exchange capacity of the peat most has not been exceeded (since after all
we've just added a smidgen of CaCO3), then we have SOME peat moss in the
salt form (ie., (peat moss)--Ca++) and ALL of the CaCO3 has reacted (none
remains in the medium). The benefit that the calciphilic Pings would gain -
if you believe this hypothesis - would have to derived from the calcium salt
form of the peat moss or from free Ca++ ions itself, as Ca++ can dissociate
from the peat moss through exchange with other ions in the substate. Ca++ may
be the important substance for proper growth in calciphilous plants.
The other possible explaination, Hypothesis B, is simpler: CaCO3 may be
deposited in the clefts of the vermiculite, leaching out as aqueous CaCO3
which is actually basic because of free OH- ions from the reaction:
CaCO3 + H2O ---------------> Ca++ + CO3--
CO3-- + H20 ----------------> HCO3- + OH-
If the Ping roots are in the vicinity of the CaCO3, then they may be able to
directly absorb OH- ions BEFORE it gets a chance to be neutralized by the
acidic peat moss. So, it may be that OH- ions is the mystery ingredient or
active ingredient behind the pinch of CaCO3 recipe.
Which hypo is more likely to be correct? I tend to think its B. Ca++ salts
in the growing medium, tend to be water insoluble retarding or minimizing
absorption which, if my knowlege of freshman biology serves correctly, is
accomplished via a thin film of water on the root surface. Also, the CaCO3
(or Ca(OH)2) needs to be indroduced regularily, as by fornightly waterings
or frequent repottings with fresh CaCO3 impregnated mixes. This would lend
support for Hypo B as OH- ions cannot be expected to have an indefinite life-
time in a predominantly acidic medium. My third best guess would be
equivalent to Barry's #4 possibility.
>On a similar subject, do crosses with bicalcarata inherit the fangs?
Yep, there's at least one cross - made by Cliff Dodd and recorded as a
cultivar in CPN - with N. X dyeriana, which supports the fangs. I
believe that he named it after his wife, Nina. I have a bical. X gracilis
cross but I'm told that it does not have fangs (mine has yet to pitcher).
Rob (M)