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Re: [APD] RE: algae growing on leaky plants
On Tuesday 20 January 2004 16:54, Tom wrote:
> >are capable of autotrophic behavior. They can use sugars and other fixed
> >carbon sources from their environment as direct replacements for the
> > sugars they would fix by their own photosynthesis.
> Heterotrophic not autotrophic? They are already autotrophes(most).
> It's have to be a fairly nutrient poor system such as the oceanic gyres I
> would think rather than the rich nutrient planted tank.
Yeah, heterotrophic. I realized the error after I sent the letter but by
then it was too late to correct the problem. Thanks for giving me the
opportunity to correct it.
> I can give you some feedback as I need to do some researching on this issue
> coming uop soon anyway, it's one of the topics for a review paper myself
> and a couple of other folks hope to publish. It'll be more based with
> natural systems though.
I had a totally wasted day at work due to a flu onset, so I took the time to
do some internet searching.
One of the more interesting things I found was a study from Lake Tahoe, where
aquatic plants were grown in Tahoe water and substrate, then some of the
water with all the plant exhudates was transfered to a plant-free microcosm
with algae. Algae in the microcosms with exudate were more productive than
in the control; water from M. spicatum prompted more production than water
from E. canadensis. It was a simple and interesting technique.
This doesn't support a role of allelopathy. Unfortunately, the researchers
did not characterize the exudates, so they didn't know if the effect was
created by mineral exudates or by organic exudates or by both.
Regarding allelopathy in M. spicatum, researchers have identified another of
plant-toxic compounds in extracts from M. spicatum. One of the studies I
found today tested plants grown in microcosms and the water they grew in for
presence of the known toxins. The chemicals were readily identifiable in the
extracts but were not found in the water.
It does seem that algae production from plant exudates may not be a
significant factor unless mineral nutrients are very low. There are two
other factors that might increase that significance.
First is light limitation. In my tanks the algae problems that would be most
easily explained as heterotrophic growth are those where algae is growing in
Second I find it unusual that algae would preserve all of the machinery
necessary to grow heterotrophically if they didn't use the capability on a
regular basis. Is it possible that algae will by preference extract some
ligands from organic compounds rather than synthesizing them internally? If
so, then at least some algae could be dependent on the presence of certain
organic molecules in the water.
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