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Re: [APD] RE: Allelopathy

Interesting hypothesizing but are there no experimental
scientists out there, only theoretical ones?  ;-)

Scott H.

--- Raj <ggrk at blr_vsnl.net.in> wrote:
> 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 would 
> have gone the Dodo way.. Any allelopathic chemicals they
> produce would be 
> only local acting and would be found on the surface of
> the plant. 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. In a aquariums these
> chemicals might 
> accumulate and have some effect on algae on all
> surfaces.. Regular water 
> changes should keep these chemicals from accumulating.
> This would favour 
> newer aquariums having algae problems and older ones
> being free from algae..
>          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.. so there may be more than one
> chemical produced by 
> aquatic plants. Water movements in the substrate gravel
> will reduce these 
> effects.
> Raj
> >From: "Thomas Barr" <tcbiii at earthlink_net>
> >
> >A couple of problems with the allelopathic effect being
> a reason for
> >significant algae decline/presence:
> >
> >One issue that is very tough to get around about
> allelopathy's potenital
> >role in aquariums: we see/observe a reduction in algae
> with _all plant
> >species_ present in the tank, there's close to
> 300species of aquatic plants
> >in this hobby, and no matter how you mix it it up, they
> are produce the
> >same effect when plants are healthy on algae presence.
> >
> >Riccia to Hornwort, to Ammannia which doesn't live even
> close to water
> >normally, to crypts, to har-grass, to Micrantherum to
> Lugwigia, to Chara(an
> >algae) to Green water(an algae), Gloss or just about
> anything you want to
> >choose. CO2 high light methods, non CO2 etc, large
> frequent water changes,
> >no water changes, adding carbon/UV(which may cleave the
> chemicals bonds) or
> >not.
> >
> >Now what are the odds that each and every one of the
> these 300 species
> >retards all the same algae in the same manner through
> allelopathic
> >chemicals?
> >
> >Does each/all plant species produce some secret algae
> killing allelopathic
> >chemical?
> >_Perhaps_ a few might, but those effects are _subtle_ at
> best.
> >
> >Review the research studies on these compounds, they
> involve grinding the
> >plant/algae up and dumping a concentrated pulp into an
> algal culture.This
> >is not the same as a live plants growing natrually in
> the tank or in
> >nature. Some active chemicals have been isolated, BUT,
> these are much
> >higher concentrations than would be found in natural
> systems.
> >
> >But all 300species produce the same allelopathic
> conpounds or similar ones
> >that significantly reduce algae?
> >I'm skeptical. **You can have the same nutrient levels
> in each tank and add
> >nutrients to *match* relative uptake by the plants(fast
> or slow growers
> >etc) and get the same effect no matter what the plant
> species. All 300
> >plant species have the same allelopathic potential that
> is this effective?
> >  What about the algae<=> algae interactions?
> >
> >I think it's something much more general based on
> observations with all
> >these plant species and I think it's quite rare and
> subtle if it exist in
> >our tanks.
> >But you can always add activated carbon to see as it
> will remove these just
> >like it removes tannins and humic acids and many organic
> compounds.
> >
> >I skeptical about the notion that the allelopathic
> chemical somehow are
> >"emmedded" on the plant's surface/cuticle. Again, all
> 300 species do this?
> >Also, why does algae not grow elsewhere in there tank
> besides the plant
> >surface which also leak out nutrients for algae?  You
> will often find
> >different species growing on plant surfaces than rocks
> or wood in nature,
> >not less algae biomass but often more. Adding carbon
> will take out the
> >active chemicals(and a few plant nutrients, but these
> can be
> >resupplied/added to the substrate) from the water column
> but the surfaces
> >but it still seems unlikely that _all_ the plant species
> do this.
> >
> >Another issue: How does a plant know how large of a
> water body does it live
> >in? If it released the chemical compounds, it would be
> diluted in large
> >lake but fair well in small pool. What about flowing
> water? Rivers/streams
> >are unidirectional so any chemicals released would wash
> down stream and you
> >should see a decrease in the algae down stream also.
> Many plants do
> >extremely well in flowing rivers/springs.
> >
> >While it might be an unknown, perhaps an entertaining
> idea, I have grave
> >doubts about its effect and the significance of it's
> role in planted
> >aquariums.
> >
> >
> >Regards,
> >Tom Barr
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> Aquatic-Plants at actwin_com
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S. Hieber

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