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[APD] Re: plant/algae competition

Roger wrote:

> I hate to butt in, but this is one of my pet topics, so I will anyway.

Thanks for jumping in!

> I have an article coauthored by one of the most respected limnologists
> in which the authors suggest not only that this is a mechanism for algae
> growth on leaves, but that it is an evolved-in defense mechanism.  The
> "intentionally" promote growth of algae on their leaves so that herbivores
> more likely to eat the algae and less likely to eat the leaves.
> I won't comment on whether that makes a lot of sense, but that is what
they said.

Maybe it is to attract slimy nasty bitter tasting algae that no one wants to

> > Is it possible that when something is in short supply, the other (now)
> > excess nutrients leak out, attracting algae as scavengers to absorb that
> > leakage?
> I talked to Claus Christensen about this at the AGA conference in Houston.
> agreed that plants will leak inorganic nutrients into the water.  I don't
> recall whether he also agreed that the leakage was accelerated by a
> limitation.  It makes sense that it would be.
> I'm not sure what significance this would have.  If those nutrients are
> to the plants then they are probably already present in the water at
> concentrations that are more than sufficient for algae growth.

But the plants ought to be leaking "plant products" not "plant intakes" this
would help explain why it isn't so easy to say what is lacking, if the algae
growth is reflecting the leakage of what is in the plant, stored reserves,
not necessarily the inputs that are in excess now.

> Now extending that thought a little ...
> According to at least one authoritative source some -- perhaps most --
> are capable of autotrophic behavior.  They can use sugars and other fixed
> carbon sources from their environment as direct replacements for the
> they would fix by their own photosynthesis.
> That made me wonder if plants might leak simple sugars with that leakage
> increasing under at least some conditions of nutrient limitation.  I asked
> around at the local university and a biology professor there told me that
> algae are known to lose quite a bit of fixed carbon when they are nutrient
> stressed, but he wasn't sure that plants did.  More recently I read that
> nutrient-stressed algae can lose as much as 50% of the carbon they fix.
> are a major source of dissolved organics.

And if the plant is short on nitrogen that sugar might differ by being short
of N? And if it were short of P could the sugar reflect that? Some things
are mobile and some are not, according to something on the Krib or
elsewhere, maybe that has something to do wth what leaks out.

> If plants show the same or similar behavior then they could leak organics
> the water that some algae -- acting autotrophically -- might use.  If so
> we would have not only an explanation for why algae problems crop up when
> plants are nutrient-stressed, but also a part of the answer to why such a
> small number of algaes (out of the thousands out there) seem to reach
> levels in mature planted aquariums.
> This is all a rather complicated speculation that needs quite a bit of
> experimental work.  Just the same, the concept is to me an appealing
> explanation for some of the odd plant-algae relationships we see in
> Roger Miller

I observe that when I add new plants to a tank, they frequently develop
algae and then the old leaves decay, aided by the snails that come to feast.
Removal of the old leaves is the best solution, for the new leaves are not
as prone to the algae it seems. Sometimes this happens with a lighting
change also. I'm suspecting that the changes, possibly primarily a nutrient
problem due to different lighting causing different growth rates not
necessarily well matched with additional nutrients from the laging aquarist.
I suspect, though, that the new lighting actually requires slightly
differnet leaves to optimally process the light.

In trees, leaf fall is when the tree withdraws the nutrients to the trunk
and roots for later use in making new leaves. Perhaps my plants are capable
of the same thing. Sort of like crypt meltdown but really slow. Anyhow the
new leaves are different, stronger, maybe a small adaptation of something to
the new situation is required and so the old leaves are sucked of nutrients
by either the plant and/or the algaes. Maybe the plant takes what it can
move to growing new adapted leaves and the algae gets the leftovers.

Ann Viverette

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