# Plant Allelopathy



## ItsDubC (Jan 12, 2008)

I know that many aquarists don't feel that plant allelopathy is a significant concern in planted tanks but isn't it true that it is more of an issue in NPTs because of the infrequent water changes? That being said, has anyone come across a compiled list of common aquarium plants and their respective allelopathic effects on other common aquarium plants?

Ecology of the Planted Aquarium mentions a few such relations. Yellow water lillies causing duckweed death and a species of eleocharis slowing the growth of certain pondweeds were described as examples of competitive allelopathy. I have also read about certain symbiotic allelopathic relationships, such as one in which growing crypts next to madagascar lace plants actually improves the growth of these lace plants. Is anyone compiling this information? Has anyone else had experiences that may be attributed to allelopathy in their planted tank(s)?


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## Hubert (Feb 2, 2008)

Sorry, don't know that anyone is compiling this information as far as I'm aware. I did read somewhere about hornwort having an allelopathic effect on algae though, which sounded useful.


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## HeyPK (Jan 23, 2004)

I am the one who reported on the beneficial effect of crypts on lace plants. I think it is just the aeration of the substrate by the crypt roots that aids the lace plant. 

Allelopathy is hard to prove. There are so many other factors that limit plant growth---competition for nutrients, light and CO2 as well as space in the substrate for the roots, and I also suspect that in an aquarium crowded with plants there is a kind of crowding effect that limits growth and that can not be overcome by more light, nutrients, or CO2. That crowding effect might be allelopathy, but I don't know how it could be verified. Giving a plant lots of room---lots of open water---makes it easy to get the healthiest growth. A number of our aquarium plants are pretty large and usually are not in tanks large enough to allow them to reach full size even if they were the only plant in the tank.


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## ItsDubC (Jan 12, 2008)

Practical Fishkeeping's Peter Bradley (also a member on these forums) reported on the benefits of growing lace plants w/ crypts as well:

http://www.aquaticplantcentral.com/...thumb-forum-allelopathy-planted-aquarium.html
http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=51

If the lace plant's better growth can indeed be attributed to the crypt's ability to aerate the substrate, then surely there are other plants out there w/ similar rooting behavior that can help the lace plant grow just as well, but I haven't found any information related to this.

I also remember reading somewhere about hornwort releasing allelopathic chemicals to inhibit algae growth, but the fact that some of my hornwort has algae growing on it leads me to believe that hornwort is just better at out-competing algae in most cases.

Even Ms. Walstad in the thread linked to above admits that allelopathy is *probably* a minor factor in most aquariums, but any information or explanations as to why certain plants are growing better or worse for ppl would be beneficial to others. But again, I agree that there are too many other factors to consider in attempting to prove the existence of allelopathy in the aquarium.


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