Ole's refute to allelopathy having any significant effect on algae in aquariums

Mar 20, 2013
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There is an assumption that the lower the concentrations, the less of an effect there is. However, it is possible that the concentration of allelochemicals are so small that they go undetected by the target plant and thus, the target plant cannot mount an immune response. This allows the allelochemicals to enter the plant and inhibit growth.

So far, from what I've read, some tests have used massive amounts of allelochemicals by the blender method to extract toxins. Has there been any test that uses far smaller amounts in the ppb range or smaller to see if there is an effect?
 

Tom Barr

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Solcielo lawrencia;112204 said:
There is an assumption that the lower the concentrations, the less of an effect there is. However, it is possible that the concentration of allelochemicals are so small that they go undetected by the target plant and thus, the target plant cannot mount an immune response. This allows the allelochemicals to enter the plant and inhibit growth.

So far, from what I've read, some tests have used massive amounts of allelochemicals by the blender method to extract toxins. Has there been any test that uses far smaller amounts in the ppb range or smaller to see if there is an effect?



There are many examples of specific inhibitors that are in the ppb ranges, herbicides are just one such group.
But these are not allelopathic chemicals, there's just no ecological/evolutionary need for such chemicals. They just outgrow the issue and head for the surface: high light use efficacy, ability to grow with very limiting CO2 ppm, honey comb structure to reduce the resources required, heterophylly etc. These are fast growing herbaceous weeds. There are simply too many species, genera and families that produce a wide array of secondary chemicals that are unrelated for this observation we see to ever possibly be true. Well, there's always a chance, but the chance is extremely small. Unless someone had some serious repeated proof, no one is even going to buy this claim, statistically, it's extremely improbable.

They generally test at higher concentrations, at lower levels, much lower, there's even less effect and whether the plants give these off naturally is yet another issue.
This hypothesis goes from really bad to even worse.

How does work in unidirectional systems like rivers?
Large bodies of waters where massive dilution and current also removes such chemicals from the system?
How do you provide a control in a natural system?

None of the aquatic plants tested with such controls in mesocosms have shown evidence of these hypothesis.
Does it occur in natural systems?
No one can say.

But few would say there's much if any effect in an aquatic system.
If you do a dose response curve over a wide concentration, which many have done and used regression to fill in the lower ranges, the effect is not statistically significant. This assumes you ground up the plants and released the chemicals.
Dilutions of 100-1000X is not going to do much. Test well experiments already showed that.

Herbicides applied to natural systems to kill aquatic weeds often release the chemicals from decaying plants at massive levels, and yet many species are not susceptible to the various classes of herbicides. This has no effect on algae, in fact, it helps the algae grow.

I'll happily eat my words if someone can show this.
That was 15 or so years ago, no takers, not even remotely close have come along in that time.
The evidence against this meanwhile has only grown stronger.
The funding has dried up as well.