[APD] Re: Aquatic vs Aquarium Plants - and cuticles

["Stephan Mifsud" <labmdp at waldonet_net.mt>]

Steve P's Hypothesis: "I don't think we know if the ability to grow a thin
or absent cuticle is
an adaptation to grow underwater. I submit that plants which adapt to
seasonal flooding need to have this ability, whereas obligate
terrestrial plants lack this ability."

There are some notable exceptions to this hypothesis, since I have been
studying them closely this winter. One is Crassula vaillantii, a very small
succulent, very close relative to the xerophyllic succulents in the genus
Crassula, but which is restricted to shallow temporary rainwater pools, here
in the Mediterranean. The plant germinates naturally underwater so it can be
considered a true aquatic, but it does so in very shallow pools with regular
drying and flooding according to rain fall. It may be submerged for a few
weeks, completely emmersed for another week, in the baking Mediterranean
sun, then submerged again. There is no time to thicken/thin a cuticle. This
is obviously always present-yet it grows very well submerged.

Another plant particular to this habitat is Elatine gussonei, even more of
an aquatic, which also grows in deeper pools. It also has a cuticle present
while submerged. You can even see its particular shine. The water level can
drop within a couple of days leaving these plants high and dry, and yet they
do not dry out, at least not before their substrate has dried out - at the
end of winter.

These plants need an already formed cuticle for such a rapidly changing
water level. But one thing is for sure it does not not stop them thriving
underwater.

The physiology of these plants appears to be different in an aquariums,
enriched with CO2, lower light (not sunlight), and higher nutrients: The
particular shine appears to be reduced, and the growth pattern is very
different to that in nature: they appear to grow better! Maybe it is a
reduction in the cuticle which allows better respiration, and better growth.
Which may also partly explain Steve's observations on his plants. Plants in
aquariums can behave very differently than in nature. If you had to see just
these aquarium-grown plants, you might make some very wrong assumptions on
their actual 'behaviour' in nature. I think that this might hold true for
other plants we grow in our tanks, but I have not seen them in their natural
habitat so I should not comment

Steve this is a good Brainstorming session. I find its useful, hope others
do.

Best regards

Stephan
Malta




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