Re: [APD] RE: algae growing on leaky plants

[Roger Miller <roger at spinn_net>]

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 
dim light. 

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.


Roger Miller
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