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1042 Views 6 Replies 5 Participants Last post by  aquabillpers
The term "allelopathy" refers to the ability of some plants to produce chemicals that prevent the growth of different plant species near them. The concept is well documented in terrestrial plants, but it is controversial in aquatic plants.

Below is a link to a thread that I started at Tom Barr's site. In it I maintained that a large number of C. wenditii was killing all of the other plants in a 29 gallon aquarium. Most people there disagreed with me, BTW.

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Do you still have this tank going, and is it still inhospitable to other plants? It would be nice to see a picture of it.
This is a discussion that comes up now and again. I read through the thread at Tom's site. I think this time I'll take Tom's position that allelopathy is possible, but as yet unproven.

Chemical warfare is pretty common in the world of biology. That's how penicillin was "discovered." A great percentage of the earth's population is around today because we or our ancestors were saved by timely administration of antibiotics.

If you really think about it, you must admit that there are a variety of possible explanations about what you're observing in that particular aquarium. A tank that has been full of crypts for 4 years will be LOADED with roots. The extensive root system would be expected to alter the local biology of the substrate, presumably in ways that favor crypt growth. This could include mechanical changes, nutrient or gas transport, and other factors that have nothing to do with allelopathy. It's also possible that water column conditions are not favorable to the particular stem plants that you've tried.

Personally, I'd try a variety of species - swords, vals, sag, bacopas, rotalas, etc just to see what happens. I'm guessing you'll see some pretty good success with some if not most of them. The "experiment" wouldn't prove anything, but it's pretty easy, and it might help you understand why certain things don't grow well in that particular tank.
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As I said in the thread, the 50 crypts occupied the left side of the tank. I planted vals, E. tenellus, and hygros, and even tossed in some duckweed.

None survived, and none of the rooted plants developed new roots.

Before that, other plants occupied the right side of the tank, and over a 6 month period all died, including a large stand of Java fern that had been there for 3 years.

When I took down the tank, the roots of the crypts had not spread much beyond the half-tank where they were planted. There was no sign of "root binding", and the duckweed and the hygros wouldn't have cared, anyway.

So, test your theory by adding a significant portion of water from the crypt tank to another planted tank and see if it nukes any of the plants in there.

My C. wendtii has always played nicely w/ my other species, but that doesn't mean you don't have a more hostile variety.
I too have had large stands of C. wendtii without any problems with the other plants. Put me on the 'possible though doubtful' group.
This aquarium had been set up for 4 years, and the crypts had been the dominant plant for at least the last two. It might be that the allelopathic chemical(s) build up over time. The effect, if any, would be more pronounced in a NPT which doesn't get a lot of water changing.

The crypts and other plants lived in harmony for all but the last 6 to 9 months of the tanks existence, when all of the other plants slowly died and new ones died real fast.

But I don't know for sure.

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