[APD] RE: Aquatic vs Aquarium Plants

["Steve Pushak" <teban at powersonic_bc.ca>]

Scott wrote:
> Surely living underwater is a criterion? Hmmm, some times
> slow death is counted as living submerged. How fast does a
> plant have to die to be counted as non-aquatic? I guess one
> could try to draw a line between never getting better after
> being submerged and not getting worse.

Here there is a clear biological definition, at least for the term
growth. Growth means that the net carbon content of the specimen is
increasing; it implies that CO2 is being absorbed & that photosynthesis
is occurring above the rate necessary to keep the plant growth areas
ahead of the places where tissue is senescing (dying). This implies that
the plant can continue to exist indefinitely under those conditions. As
an example, I've used soil that contained grass seeds or roots which
actually began growing underwater. In this case the plant was viable but
I would consider it unsuitable because it wasn't attractive. It also
didn't grow fast enough or well enough to create a bunch formation that
would have been suitable for an aquascape.

Alternanthera is another border-line plant. If you take a specimen that
has grown emerse, as was commonly sold in fish stores a few years back,
and put it underwater, it could not absorb enough CO2 through its leaves
in order to keep them alive. I'm not sure where I acquired the specimen
that I've got today; I think it was a survivor from some stems that had
lost all their leaves. It was probably about the time I first started
injecting yeast CO2. This plant grows quite well for me now; I keep the
roots in soil & give it plenty of light, CO2 & other nutrients. When I
first started bringing cuttings to the LFS for credit, the store owner
didn't even want it because his experiences with the plant had been so
disastrous in the past. The suppliers had been culturing it emerse
because they could grow massive amounts of the plant & reap huge
profits.

In many cases, the difference between being able to grow & survive long
term is whether you have a nice viable specimen to start with that has
roots & functional underwater leaves. You can't just take a plant you
find growing in your garden & stick it under water & expect it to grow.
You can often take a nice healthy piece of weed, such as chickweed and
stick the base under water & leave some of the leaves above water in the
air. The above surface leaves provide enough sugars to permit the bits
under water to begin forming viable underwater leaves. I'm not saying
that chickweed would work but its a specimen that's probably worth
trying. If it would grow underwater, I bet it would look a lot like
Glossostigma! It was Dr. Paul Krombholz who suggested that we try
experimenting with unconventional plants to see if we couldn't get them
acclimatized.

Here's a question for our biologists to answer, if they can. Do all of
these borderline plants start growing leaves without a waxy cuticle on
the leaves so that they can respire CO2 more easily? If so, how
universal is this adaptation? Is it absolutely necessary for a plant to
survive underwater? I've suspected that some types of leaves such as
Anubias, could indeed be viable out of water too.

Steve P

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