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Re: [APD] RE: allelopathic thoughts & Algae

Thanks Tom,

I need to re-read your post a few times to digest it and further think about the scheme of things in nature. Its always fascinating to me (an electronics engineer)..

How does our aquatic pest algae attach itself to leaves and glass? Some are really well glued while others come off easily.

Bangalore, South India.

> Tom,
>  My thoughts on this..

> During evolution of the aquatic plants, they have evolved a way to
> keep off the algae. If this was not true then all these plant species
> have gone the Dodo way.

Herbivores(yummy algae), light blockage, they also both occupy different
environments(algae the microscale- so called microphytes while the larger
scale macrophytes occupy another environment even if they live on the
plant). Plants also relocate the resources to the new growth, you'll see a
stem coming up from the substrate then  branching to cover the surface
blocking light below. Many plants are amphibous also, few algae are(but
there are some like Cladophora which lives on Turtle and Gator backs and
other situations). Light is the main advantage plants have over algae.
Why would algae not kill off all other species of algae and go the way of
the Dodo as well? There many more species of algae, some macroscopic, than
aquatic plants.
Think about that one for awhile.

Any allelopathic chemicals they produce would be
> only local acting and would be found on the surface of the plant.

But every plant species out of 200-300 species has this same surface bound

I could see a few plants MAYBE, but  __I study periphyton on aquatic
plants__ and this is my research. I scape off plant leaves and mark them.
Then come back 30 days later and scrub them for algae epeiphytes.
There are very often more algae on plant leaves than on other non living
These plants have been submerged for at least 300 years, likely longer.
The species composition is also different on the plants vs the non living
By comparing glass substrates, plastic plant leaves, live plant leaves in a
very stable environment where plants have been for hundreds of years, you
can tell if this occurs to any significance.  So far, I'll stick with my
original contention, it is nothing more than a very subtle(insignificant)
interaction on periphyton in terms of CHL a.
Species composition is different though on the substrates.

The plant provides a good structure/surface area for algae/habitat for
critters(nutrients), some leaching losses thereby providing some nutrients
and also a good place above the non living substrate for light.

 In nature
> most of these plants are growing in large water bodies or rivers and any
> chemicals given off by them would be very diluted and miniscule and
> probably have little or no effect.

Well why make them and go to that trouble then? It'd be a greater advantage
to grow up faster to the sucface or relocate the resources to new
growth.Also, why then is growth so good and stable in these systems for
hundreds of years?

Also: how would a plant make it impossible for ALL ALGAE SPECIES NOT TO
I could see a few plants and few algae not being able to, but we do not see
this occur in nature.
Nor in our tanks.BBA has no problem growing on all plants for example.
If a plant can beat this algae, it does through new growth, blocking light
Aquatic plants can outgrow most plants since they do not have to provide so
much support and are mostly water/water is non limiting.
Anytime a herbivore eats a plant, algae grows on the surface etc, the plant
can can try and make something that deters the animal from grazing on the
plant. Similarly, algae can keep pace with this chemical warfare and
prevent a plant from effecting the algae's growth.
Algae are not static in the competitive race, they have ways to get around
plant defenses, just as plants has the potential to retard periphyton.

But in nature, plant epiphytes are tough customers.

 In a aquariums these chemicals might
> accumulate and have some effect on algae on all surfaces.

Wait a minute, these occur on _plant surfaces_, not accumulating in the
water column, which is it?
Also, why doesn't algae occur in BOTH non CO2 tanks where I do no water
changes, and also CO2 tanks where I do large frequent waters, even every
day water changes of 50-90% will still do great?

 Regular water
> changes should keep these chemicals from accumulating. This would favour
> newer aquariums having algae problems and older ones being free from

Why would newer tanks be affected any different if accumulation is the
issue? I do the same water change routine in a new, perhaps even more so,
than an older tank.

I would suggest a stable substrate/filter is the ONLY difference in a new
versus an old mature tank.
The glass is the same, filter itself, the nature of gravel, the plants, the
light etc.

The only difference is the substrate and filter are colonized with
bacteria/organic matter.
If you remove the plants, you still will get algae with these bacteria and
the organic matter still present.
So you cannot blame the bacteria or organic matter to any large degree for
this effect. Bacteria perhaps for converting NH4=> NO3 but if the plants
are in good shape and there enough plant biomass, then all ther NH4 is

If you add mulm/peat to the substrate and mulm to the filter, this adds
what is missing from a new tank and you do not have any new tank issues.

>          Allelopathic chemical produced by the root should be stunting or
> blocking the roots of other species and therefore giving it an advantage
> and helping it spread.

But rooting /substrate space is not the issue, light competition is with
aquatic plants. There's plenty of nutrients and water in lakes, the issue
is light availability.
It would be better to allocate the resources for canopy growth rather than
root warfare or deep roots and not get washed down stream like Crypts and
Swords or just be a slow grower underwater and wait till you are above the
water surface when the dry season comes.

 so there may be more than one chemical produced by
> aquatic plants. Water movements in the substrate gravel will reduce these
> effects.

I have never observed anything I could view as root warfare in aquatic
plants. I've kept many species, I've also used RFUG's which would blow out
any chemical.
Then I've kept plants without any flow through the substrate and also used
cables.I found the best growth with all species without any in/outflow
thorugh the gravel.
I would say the observations do not match the theory, I see better, not
worse growth with less flow/flux.

The problem with root allelopathic chemicals are the same as ones in the
water column, they diffuse out and are diluted into the water column above
in our tanks, the aerenchyma will transport these out, the bacteria in the
sediment will break these chemicals down .............if they exist at all
in aquariums.
I say they do not pay a significant role at all. Also, why with Riccia/moss
and other non rooted plants do we still observe the reduction in algae?

And if you happen upon a special case where it does, another algae will
come along and find a way around it or another plant.
The chemical "arms race" is a two way street.
Light is a more dominate issue.

You can add activated carbon to the substrate also, like the water column
to remove the effects of any suspected allelopathic chemicals, but I've
never observed any in the root zones.

But root chemicals doesn't explain why the __water column__ is free of
algae either.....................

Tom Barr

> Raj

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