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Plants That Don't Do Well Together


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I changed the title from just Alleopathy in hopes of more discussion and in recognizing that alleopathy is quite narrowly defined. So, let's just talk about our experiences with plants that we think interfered with our success growing others.

 

Let's talk about allelopathy in planted tanks. What have you read? What have you seen in your own experience? Facts (opinions?) are all over the place on this topic, even my go-to Wikipedia hedges their bets as to what allelopathy is. Wikipedia's final sentence in their intro is "Today, most ecologists recognize the existence of allelopathy, however many particular cases remain controversial." It should be fun and enlightening for us to see what we think.

Edited by Ken
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It's really hard to study and I don't think that people have done that many experiments. Personally I think it's really a thing with significant impacts. I'm guessing it's why plants sometimes don't do well in one tank but if moved to another tank with the same tap water, light, substrate, etc. they can thrive (or vice versa). Walstad's book talks about allelopathy with some examples, notably water lilies (Nymphaea) were found to produce a lot of these chemicals.

In my tanks I haven't observed any noticeable effects from this. But I'm mindful to try to plant species in clumps to reduce the possibility. Probably most plants we use --- many which grow together in large masses in nature --- are not allelopathic against their own species.

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So as promised, I will chime in here.  I do think allelopathy is an interesting topic.  There are absolutely cases of it that have been studied in terrestrial plants and corals.   A few other things too.  Actually, if you grow strawberries, they are known to show "autotoxicity" where higher densities inhibit their own growth, and there are some suggested chemicals, which when increased as observed in dense stands reduce growth of the plants.  But it's still not conclusive.

The thing to remember about allelopathy, and this goes for everyone, scientists included, is that it is not the commonest cause of many of the patterns attributed to it.  It the zebra problem: if you hear clopping hooves coming don't assume it's a zebra, because it is more likely a horse.

The patterns attributed to allelopathy are often caused by other things.  Because is not known to be the commonest cause, claims of allelopathy bear the burden of proof (BTW, this applies to anoxic nitrate filters in home aquaria too).  Essentially for allelopathy this means you need to show it is not being caused by the more common drivers of negative correlations between species, and then even better, show there is a likely chemical mechanism driving the observed pattern.  This involves studying populations, species interactions, physiology, and chemical ecology.  It's challenging to show definitively, but an easy thing to suggest. 

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On 10/12/2021 at 8:55 PM, Streetwise said:

where the leaves dropped in the fall bias the soil chemistry for new trees in the spring

That is absolutely true!  Though it happens through several mechanisms not just allelopathy.  One of the predominant drivers is nutrient cycling, which is impacted by ECM (ectomycorrhizae) and AM (arbuscular mycorrhizae) associations. 

Woah, I just read that last sentence and realized I am on a fish forum.  Let me slow down.  Yup.  Deciduous forests have a good example of allelopathy from falling leaves: walnuts.  It's a really interesting process. 

Honestly, in the rare cases where allelopathy happens, it is really interesting.  The thing is, it's expensive.  As a plant you have to exude piles of chemicals to try to get an advantage over your neighbors.  Energy you could otherwise use to grow faster than your neighbors, or make more seeds than them, or defend yourself from predators, etc.  It's uncommon because it is a fairly desperate and extreme adaptation; like carnivory in plants. 

Now, in an aquarium setting, where there is often significantly less water available and less is exchanged, as @MJV Aquatics would point out, there is the potential for various, what are referred to as, secondary metabolites to build up to levels not seen in habitat.  Those could, under these artificial conditions, cause negative impacts to neighboring species for which they were not intended.  It's possible.  I don't know of a single study showing that; but it remains a possibility.  Is this "allelopathy" then?  Are those "allelopathic plants"?  Again, under the artificial conditions of an aquarium, I don't know that that has been defined by botanists or ecologists, who think about what has evolved for competition in habitat.  I genuinely think that aspect is wide open to discussion.  And yes, under those conditions, observations by individuals are a great starting point. 

So as a scientist, who has experience in this arena, I'm as curious as @Ken is about what people observe.

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I started reading about this again a few months ago. I’m not sciencey so can only say what I see and guess. Elodea does great for me but if I put hornwort in a tank with it it stops growing but not suffering. Brazilian pennywort does great with or without hornwort. Brazilian pennywort and elodea do well next to each other in the same tank. If I put pennywort in with hornwort the hornwort suffers. 
I started reading about this to see if that was it. The chemistry component that goes into this is beyond my chemistry understanding or plant physiology understanding. But it could also be which is stronger at competing for different nutrients and in what quantities.   🤷‍♀️

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Still on terrestrial plants. Here in Utah the first thing done when someone wants to increase cattle range productivity is "chain the cedars". Cedar is what we call the Utah Juniper. When any local municipality wants to increase the amount of water that gets into an aquifer (by decreasing runoff) they "chain the cedars" so other plants can survive allowing more water to soak in. The fact that cedars don't allow anything to grow near them is accepted but the experts shy away from calling it all allelopathy. BYU did a paper that debunks the theory that allelopathy is involved at all. The ranchers and Water Conservancy Districts don't particularly care what it's called.

Maybe the title of thread should be What Aquarium Plants Grow Well Together?

I have a personal aquarium example that I'll type up in the next day or two. Rough week.

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I have this theory that there's some chemical war that goes on between plants and algae.  To me it explains how EI method can work and why the "algae can eat any one nutrient" idea is such a pervasive explanation for why "unbalanced" tanks grow algae even know it doesn't make sense*.  It also explains why my java fern has no algae on it and my anubias 1" away grows algae.  both are slow growers but I presume my java fern is a better fighter.

I also have a tank full of algae I can't beat, so if I'm right I still clearly don't know what to do with my knowledge. 

 

 

*unless algae can have tiny nuclear fusion/fission reactors to make their own elements they need NPK + trace like everyone else.

Edited by CT_
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On 10/13/2021 at 8:33 PM, OnlyGenusCaps said:

Now, in an aquarium setting, where there is often significantly less water available and less is exchanged, as @MJV Aquatics would point out, there is the potential for various, what are referred to as, secondary metabolites to build up to levels not seen in habitat.

Yes, the average aquarium has less 'fresh' water than we most often see in nature. But it would be a stretch to blame allelopathy for any plant failure. New plants often 'melt' back due to how they're grown for sale. Often plants just don't get the nutrients they require for optimum growth. And then there's lighting. I quite like fast growing floating plants to aid in water quality as they more quickly convert nutrients (aka pollution) into plant tissue, eventually trimmed and removed. But of course these shade rooted plants already at a disadvantage due to tank depth. So if allelopathy is a factor in plant growth, it could be the least of several other issues. But if/when in doubt, up the anti on partial water changes in frequency and/or volume as generally speaking, 'there's no such thing as too much clean, fresh water' 🙂

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When I added Hornwort to my 40 gallon community tank within a couple of weeks it became "balanced" and the algae pretty much vanished. Months later my then new 20 long wouldn't stop growing algae so looking back at how well the Hornwort had worked in the other tank I grabbed a big handful from the 40 and put it in the 20. Within weeks the algae had was all but gone.

The interesting part is later when I thought I wanted some algae in the 20 for the Borneo Loaches, shrimp and snails I took the Hornwort out and put in Amazon Frogbit. The algae came back after about a month. No changes to lighting, stocking, water change schedule or fertilizing.

Can my results be explained otherwise? Probably. But if ever have a stubborn algae problem again in goes the Hornwort.

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On 10/15/2021 at 6:45 PM, Ken said:

Can my results be explained otherwise? Probably. But if ever have a stubborn algae problem again in goes the Hornwor

Ive heard forever so many times the chemicals hornwort puts out deter algae. I used to believe it but now I’m starting to think it just hogs up all the nutrients 🤷‍♀️  I had a piece of hornwort not doing great but not dropping needles that grew a piece of hair algae, diatom algae and some other type. 

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I touched on this topic briefly in August. Plants that don't do well together is probably a better title. 

When I took a job working in a vineyard, I inquired as to the why the different grape varieties weren't planted closer together, and why new vines weren't planted where an old vine had died?  They claimed the answer was alleopathy, one variety would produce chemicals detrimental to new vines and other varieties.. 

In my aquarium Hornwort and Elodea don't get along.  Hornwort was introduced in part, to help control algae, The Hornwort thrived but also became an algae island  The snails loved it.  Later I added Elodea to help consume excess nutrients. When the planted Elodea eventually made it to the surface and began to spread, the Hornwort began dying.  Hornwort moved to different tanks died anyway. Healthy Hornwort reintroduced to the aquarium also died.  I don't think that the Elodea out competed the Hornwort for food, but something wiped it out. 

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I have had Elodea densa completely destroy my Java fern 'Windelov' in a matter of a few weeks. This was after replacing the hornwort with that anacharis because my Veiltail Betta was shredding his fins on the stiffer needles.

I moved what was left of the Java fern to another tank and it is very, very slowly recovering. The Anubias petite 'Nana' seems to get along with the Elodea densa, but the water wisteria l just got from the Coop looks stunted, and yet it is thriving in all the other tanks. Go figure!

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Now you folks have me thinking. I’ve always been cautious to not put hornwort with plants I really love. I love elodea and have it in all my tanks but my Java fern does seem less wow and struggles a bit when next to elodea. As well as an Asian water fern that sent new plants then the mother plant died next to elodea. However my ludwiga repens is surrounded by elodea and thrives and gets pink and some red. I wonder if it’s trace elements that some plants need more of and two competing for the same where as other plants use less of certain trace 🤔

Edited by Guppysnail
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On 10/17/2021 at 3:30 AM, Guppysnail said:

Now you folks have me thinking. I’ve always been cautious to not put hornwort with plants I really love. I love elodea and have it in all my tanks but my Java fern does seem less wow and struggles a bit when next to elodea. As well as an Asian water fern that sent new plants then the mother plant died next to elodea. However my ludwiga repens is surrounded by elodea and thrives and gets pink and some red. I wonder if it’s trace elements that some plants need more of and two competing for the same where as other plants use less of certain trace 🤔

You started me thinking, because I was just tutoring on how the RDA was developed (I'm omitting a lot here). Quick summary:

Top cut off (max RDA)  happens when test subjects started showing adverse effects, and the lethality was determined when half the subjects died.

Minimum RDA is anything below that, test subjects began getting sick, and lethally low was when 50% died.

What doctors, nutritionists, and other health care providers are *not* taught, unless they take biomed ethics courses with an instructor who believes in the whole truth, is who they tested on, and how they ran the tests (meaning a lot of the data can't be replicated, and shouldn't be considered valid).

 

I suspect that we have a tendency to bring that same lens to many other aspects of science.

 

Completely off topic for aquariums, and still meaningful research to read, is the search for grandmother trees in old groves, and how they use myrchozia (I spelled it wrong, I think) to not only communicate with younger trees, they share their stores of tree sugars with younger trees as well. 

When fire is being blown towards a stand of trees, the grandmother tree communicates what the rest of the trees need to do to increase survival rates. 

I wonder how much of that is happening in our aquariums, and how would we test/ measure it?🤔

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