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[APD] The "seed" theory with why algae does not grow when plants are

I've suggested for some time that algae "know" when to grow and when not to

I've argued that nutrient limitation is not the causitive mechanism for
algae decline when plants are growing.
I've aruged that allelopathy does not seem to have much role/effect.
I've agued for and against photorespiration(I did a test with algae's
responses to a variety of CO2/O2 conditions and measured the algal biomass
by Chl a measurements).
I've argued these mechanisms for some time but I have still felt that algae
"know when to grow" and "when not to grow". I think it might make more
sense to folks to consider spores like plant seeds to understand and
consider this concept. 
There are other issues, like herbivory, pruning the plants and replanting
the tops, water changes, us picking off algae etc.

I think if you think about algae spores like one often does a seed, it
might help to understand this idea better.

Seeds often will not germinate unless they have precise conditions.
I would argue the same is true for algae.

Seeds will often not germinate if there are other competitors around
already, they will wait till they die back, or something causes the
competitor's demise.
Algae spores are very tough and have similar approachs in the water column.

How do they sense this? 
I'm not sure about some, some algae certainly sense NH4+, I've shown this
with Green water and staghorn, Urea can also be included there.
It often seems anytime the plants slow down or stop growing, then the algae
start up.

I think of my gravel as my seed back of algae spores.
I have been using a pelagic plant, Utricularia stellaris to investigate the
effect of well growing plant on the algae. 
Since it has no roots, there is nothing disturbing it and the weight,
sampling it easier.
Hornwort, Riccia etc can be used also.

This Bladderwort grows very quickly(several inches a day) and can be added
and removed easily to note algae growth differences with and without plants
at the same nutrient levels. This removes the plant's cycling with the
substrate and better isolates the issue of what is causing the algae not to
grow even when there are plenty of nutrients available.

This may relate to the alternate stable states theory that Bachmann and
Hoyer have put forth and other limnologist focusing on macrophyte dominated
sub and tropical lakes.

I think some of the key things they are already done has opened more
questions than answers. The paper tells me what is not the case(eg high
nutrients do not mean the lake will become algae covered and turbid), but
also has cases where the lake is pea soup with similar conditions. Both
states are stable.

So perhaps it's NH4 cycling that occurs too fast to measure, but can be
traced using isotopes(which is what I'm doing now with a Sag).
But out of 319 lakes over  wide range, there's no pattern to suggest that
nutrients cause a lake to be full of plants and gin clear or pea soup with
Planted Aquariums might be able to isolate these issue better.

I think many folks have the attitude that everything is know etc in
science. Few people study tropical macrophyte dominated lakes and rivers
There's very little known really.
But they spend roughly 50 million a year in the state of Florida alone on
weed and algal management, so it's getting more attention.

Tom Barr



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