# Allelopathy and CO2



## dwalstad (Apr 14, 2006)

Philosophos said:


> I don't think there's any good tautology showing why CO2 prevents algae.
> 
> I am talking about allelopathy as a possibility though, despite what Texgal said. I'm not talking about plant killing plant through elevating the phenol levels and such throughout the entire column. I don't think that a healthy tank should have enough decaying plant matter to manage something like that.
> 
> ...


There's considerable information about allelopathy in scientific literature. My book contains an entire chapter devoted to allelopathy (pp. 33-52) with 90 plus scientific references.

Allelopathy is subtle and difficult to demonstrate experimentally. Nevertheless, several experimental studies have _proven_ alleopathy where:


a plant species inhibits another plant species via the water
a plant species inhibits another plant species via the sediment
a plant species inhibits an algae species (e.g., the alga-inhibiting chemical Tellimagrandin II was isolated from _Myriophyllum spicatum_)
an alga species inhibits another alga species

You can't really think about allelopathy without thinking about chemical evolution and the plant's native habitat. A plant species develops (over eons of evolution) to protect itself against the other plant species and algae within its native habitat. It produces and releases specific chemicals designed to compete with the specific plants and algae in its environment. Plants are "master chemists" (realize here that they have no other protection). Individuals of a plant species that "design" (via a mutation) a better protective chemical are the ones that survive and propogate.

Allelopathy is chemical warfare developed over eons, and there are _a lot of _chemicals.

These chemicals may or may not work when you throw this plant species into an aquarium. Here, the plant species is confronted with a completely different assortment of plants an algae that may (or may not) be susceptible.

As to allelopathy and CO2. Allelochemicals are not essential to plant metabolism; they are strictly for defense. Therefore, if a plant is barely hanging on, it might not be able to produce allelochemicals. In contrast, if the plant is healthy and getting enough CO2, it will be better able to produce compounds that may (or may not) protect it.


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## mudboots (Jun 24, 2009)

Very interesting thread.

Thanks for posting this dwalstad; it's threads like this that help to actually TEACH us newbies why we're experiencing what's going on in our aquariums...ESPECIALLY when it sparks debates that cause us to rethink and analyze and...gasp...LEARN...

Anyway, just wanted to show some appreciation for all of the awesome threads I've been pouring through and participating in since I joined. I've learned a lot and the fish and plants are thankful.


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## Zapins (Jul 28, 2004)

Interesting. But I wonder to what extent does allelopathy actually affects algae levels in our tanks...?


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## mudboots (Jun 24, 2009)

> ...to what extent does allelopathy actually affects algae levels in our tanks...?


Great question Zapins. I can't imagine it'd be much, but it goes back to those "it depends" deals with everyone have different set ups, plants species, et cetera. But I am certainly interested in learning more about this simply because a couple of months ago I couldn't even pronounce the names of the plants I had, much less did I have a clue that water millfoil secreted "Tellimagrandin II" (not to mention that I've never even heard of that before).:-s


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## Dustymac (Apr 26, 2008)

I have one 10 gal npt that only houses three plant species: a little duckweed, a couple swords and a giant anubias which is about 20 inches tall and is growing mostly emmersed. I can't get anything else to grow in this tank, not even an algae film on the glass. The duckweed grows poorly and the swords hardly grow at all. There is a 2" diameter root star growing from the anubias rhizome with 50+ tentacles filtering the water.

Is this monster anubias exhibiting allelopathy? I can't think of any other explanation.


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## Zapins (Jul 28, 2004)

Its lack of light. Without energy plants and algae can't grow.


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## Dustymac (Apr 26, 2008)

Zapins said:


> Its lack of light. Without energy plants and algae can't grow.


Maybe I wasn't clear enough; the Anubias is growing like crazy. I even repositioned the light to the sword end of the tank.


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## Zapins (Jul 28, 2004)

What light are you using?

I highly doubt its allelopathy since if it was then everyone trying to grow the plants you have in the same combination wouldn't be able to grow them. The fact that plants in the hobby are common and the fact that you can basically mix up nearly every combination of plants together and still have them all thrive under good ideal lighting and nutrient conditions basically proves that allelopathy's effects in the tank are minimal or sketchy at best. Thus it is much more likely that your growth problems come from a lack of a basic requirement rather then allelopathy whose effects are basically not determinable under hobbyist conditions.


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## Dustymac (Apr 26, 2008)

Zapins said:


> What light are you using?


It's a 13w compact fluorescent daylight color. 


> I highly doubt its allelopathy since if it was then everyone trying to grow the plants you have in the same combination wouldn't be able to grow them. The fact that plants in the hobby are common and the fact that you can basically mix up nearly every combination of plants together and still have them all thrive under good ideal lighting and nutrient conditions basically proves that allelopathy's effects in the tank are minimal or sketchy at best. Thus it is much more likely that your growth problems come from a lack of a basic requirement rather then allelopathy whose effects are basically not determinable under hobbyist conditions.


You really need to buy "Ecology of the Planted Aquarium" to understand all the concepts behind how npts work. The only advantage hi-tech has over the npt pertains to avoiding allelopathy through frequent water changing. Seriously, get the book. It's full of tons of important info.


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## mudboots (Jun 24, 2009)

Dustymac - I'm still trying to imagine a 20+ inch Anubias in a 10 gallon tank - goodness...

I can certainly imagine, assuming you are getting the light where it needs for the other plants (the duckweed is a given of course) that if this tank is set up NPT-style that there should be plenty of "food" and light for your swords to grow, and therefore it's not unreasonable to think that your Anubias has declared war on the intruders :fencing:

My tanks are still relatively new, but I am watching very closely where the algae grows and doesn't grow, though in my case it's a matter of available goodies as the plants are still filling in and adjusting to my inability to keep my hands out of their home.


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## Dustymac (Apr 26, 2008)

mudboots said:


> Dustymac - I'm still trying to imagine a 20+ inch Anubias in a 10 gallon tank - goodness...












Well, ever since I put the light on the other side, the leaves aren't growing straight up anymore. But 16 inches tall is OK, right? 

Jim


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## mistergreen (Mar 3, 2007)

Hi,
Just curious, what are some of the chemical make up of Allelochemicals. And if it's hard to do experiment with, how do we know it has any affect?


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## f1ea (Jul 7, 2009)

I think there is another interesting component in the plant/algae 'equilibrium' in a natural or simulated environment.

So far 1) Alleopathy (in the form of chemicals released by the plants) and 2) nutrient competition (light, CO2, macros/micros) have been discussed here... But another component that might very well either assist or complement the Plant vs Algae battle in water systems is BACTERIAL COLONIZATION.

These bacteria could be 'hosted' by plants in a symbiotic relationship to help them outcompete algae, or they can be present in the water column, substrate etc... in this case, rather than wonder which and how much of a certain chemical a plants secretes that kills algae, we may be dealing with how much and which type of bacterial colony do we have in our tank that erradicates algae. It would also be easier to identify specific bacterial colonies in healthy water/tanks (with a microscope) rather than specific chemicals which may or may not harm algae and which may or may not have been released by plants...

I came accross this very interesting talk (link below), and if we humans live with an incredibly large number of bacteria performing protective and vital functions for us... why not plants as well??

http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html

Perhaps this is another way of plants beating out algae and another reason why sudden changes in conditions trigger algae: the bacterial colonies living on plants, the water column etc being much more primitive and simple organisms than plants/fish are much more susceptible to environmental conditions and therefore die easily, triggering algae outbreaks.

Not an easy subject anyway, but there went a few cents......


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## dwalstad (Apr 14, 2006)

mistergreen said:


> Hi,
> Just curious, what are some of the chemical make up of Allelochemicals. And if it's hard to do experiment with, how do we know it has any affect?


The list of about 30 specific inhibitory chemicals (e.g., nicotine, vitexin, etc) found in aquatic plants is in my book on pages 37-39.

Even though its very hard to do these experiments, a few investigators have done the job. I've discussed their work in my book. The hard part is showing that the other plant species didn't simply outcompete the other plant species for nutrients. The scientists doing these investigations were able to eliminate that variable and still show significant inhibition.

Allelopathy is real. Might (or might not be) relevant to aquariums. What intrigued me about allelopathy is the great effort that plants go to protect themselves with these chemicals. BTW, much of allelopathy is directed against herbivores. When you think of it, its pretty amazing that so few fish eat aquatic plants.


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## mistergreen (Mar 3, 2007)

So in a healthy plant environment in the aquarium, what's the contributing factor that keeps the algae at bay? Is it the allelochemicals? Or many other factors as well.

I've always wondered why/how healthy plants can create an environment that keeps the algae spores from blooming.


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## Dustymac (Apr 26, 2008)

f1ea said:


> These bacteria could be 'hosted' by plants in a symbiotic relationship to help them outcompete algae, or they can be present in the water column, substrate etc... in this case, rather than wonder which and how much of a certain chemical a plants secretes that kills algae, we may be dealing with how much and which type of bacterial colony do we have in our tank that erradicates algae. It would also be easier to identify specific bacterial colonies in healthy water/tanks (with a microscope) rather than specific chemicals which may or may not harm algae and which may or may not have been released by plants...


interesting idea...but I would have to ask why there aren't similar bacteria which attack living underwater plants. Afterall, natural selection would suggest an equal opportunity for evolution. On the other hand, there certainly are plenty of bacteria in a fish tank. I see them in nearly every tank sample under the microscope.


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## f1ea (Jul 7, 2009)

Dustymac said:


> interesting idea...but I would have to ask why there aren't similar bacteria which attack living underwater plants.


In the same vein: why would alleopathy work in a plant vs algae and not so much plant vs plant scenario? (perhaps minus some of the extra-invasive species).

Its not uncommon to see LOTS of plants coexisting in a small space with no algae (sure, there is nutrient competition and so on, but from a chemical point of view?).

Also, there is bacteria that 'attack' plants: cyanobacteria. But plants are much more complex than bacteria/algae, so it would seem reasonable that plants can form symbiotic relationships with bacteria to deter algae rather than algae to deter plants. Basicially, the most complex being has the advantage to form the symbiotic relationship.



> On the other hand, there certainly are plenty of bacteria in a fish tank. I see them in nearly every tank sample under the microscope.


Exactly, there is always bacteria present in water/soil; but the task would be to find which bacteria colony (and size) is present in tanks without algae that is not present in tanks with algae, and which plants are better at having such relationships. Maybe even someone could actually get to SEE a certain type of bacteria destroying algae cells in the way we've seen bacteria digesting, decomposing, nitrifying, attacking other cells etc....

I dont really have the experience/background to give 'solid' statements on these matters, but perhaps the more knowledgeable folks in here do or are able to deduct something more elaborate; so i guess nothing's wrong with a little bit of innocence....


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## Diana K (Dec 20, 2007)

It has been shown that land plants do indeed have symbiotic relationships with bacteria and fungi. One of the most obvious is legumes (Peas, beans, alfalfa...) that have nodules on the roots. These nodules are Gram negative bacteria that have invaded the roots. They remove nitrogen from the atmosphere and make it available to the plants. 
There are many other bacteria and fungi that are both positive and negative toward land plants, but not quite so many algae. It is possible to buy an innoculant for the soil to aid the plants in getting a good start by boosting the population of beneficial microorganisms. 
http://en.wikipedia.org/wiki/Soil_inoculant

I would not be surprised that similar associations can be found in aquaria. I think this is part of what is going on when someone specifies that a certain fish or plant will thrive in a 'mature' tank, not a recently set up tank, even if it has a good nitrogen cycle going. It is all the 'other' microorganisms that are still sorting themselves out that must mean something to help or hinder fish and plants.

Land plants also display allelopathy. Some common examples: Look at how few plants grow under certain trees. Eucalyptus, Pine and Walnut are among the plants known to inhibit the growth of plants under their canopy. Even if plants do mange to grow under these trees the plants are often spindly, poor growing, and not dense, healthy plants. 
On the other hand, there are plants that thrive under trees. Look at the Coast Redwood community on the west coast of North America. The plants that thrive here are specialists in their way, but the chemicals from the redwoods and other trees do not inhibit them.


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## dwalstad (Apr 14, 2006)

I have hi-jacked this quote about allelopathy from another thread, because I think its a good addition to the allelopathy discussion.



Philosophos said:


> the cuticle is a waxy compound that often contains allelopathic chemicals; no need to suspend into the water. Even if it does end up in the water, there's something called the barrier zone on leaves that creates a dead water zone, and it takes some decent current to defeat it meaning that the allelochemicals wouldn't be distributed into the rest of the column at the same rate. Philosophos


Philosophos, I think you're on to something here. Rather than assuming that allelochemicals quickly disappear into the bulk water, I suspect they hang around long enough to inhibit algae. (Earlier I talked about how my_ Cryptocoryne cordata_ never has algae on its leaves, while other plant species easily succumb to algae.)

It is well known (by scientists) that the boundary layer (an unstirred region on leaf surface) is always present in aquatic plants. Water movement decreases the boundary layer, but it never becomes zero. Could released allelochemicals hang around within this layer long enough to impact algae?

As to waxy cuticles.... Deep-water rice actually brings air oxygen down to its root area on the _outside_ of the plant. A waxy cuticle on leaf surface provides air layer whereby air can move downward to roots. The total volume of the air layers on both sides of the leaf is about 45% of the leaf blade itself.*

So these cuticles, waxes and boundary layers are micro-environments where allelochemicals could be concentrated enough to truly protect the plant.

*Raskin I and Kende H. 1983. How does deep water rice solve its aeration problem. Plant Physiology 72: 447-454.


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## mudboots (Jun 24, 2009)

> Well, ever since I put the light on the other side, the leaves aren't growing straight up anymore. But 16 inches tall is OK, right?
> 
> Jim


Nice indeed Dustymac.



> It is well known (by scientists) that the boundary layer (an unstirred region on leaf surface) is always present in aquatic plants. Water movement decreases the boundary layer, but it never becomes zero. Could released allelochemicals hang around within this layer long enough to impact algae?


Good thought provoking conversation. I have 0 water movement (this will change after I add a Koralia next week in the 125), and while I get lots of settling of "stuff" on leaves while the tanks heal from my inability to leave them alone, the only leaves with noticeable algae are my young anubias plants and some java "needle leaf". It's interesting that the regular Java fern is algae free while the needle leaf is not faring quite so well. Other than that it's just the driftwood (or deco regarding Abby's 10 gallon).


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## Philosophos (Mar 1, 2009)

Well... crap... I've got to stop routinely clicking the, "New threads" and "subscriptions" buttons in place of browsing the forums. It's been half a month since this thread started and I was never aware of it 

I'm glad I could contribute something to the discussion. While allelopathy as a column-wide concept in aquariums may not be confirmed, it's sort of hard to believe that similarly small populations of plants within nature would be defenseless. I've yet to find something in a system so open and varied as the littoral zone that lacks the ability to defend its self. The immobility and necessary coloration from pigment of SAM's sort of leaves limited options; spread fast and become unpleasant.

I had no idea some rice actually managed to pull oxygen down that way; very interesting. Does this mean that high current interferes with root growth in this type of plant?

One quick thought; a plant without cuticle or allelopathic compounds that does not succumb to algae in a non-limiting environment would definitely prove to be a point of falsifiability for all of this. I'm not sure if or how this could be produced, but it'd sure be neat to see what would happen. Anything that removes the cuticle that I'm aware of would also turn the plant to goo, save for some genetic engineering. Anyone here work for Monsanto? 

-Philosophos


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## RestlessCrow (Nov 5, 2009)

I've got to add my two cents here too... In my former life as a professional plant geek I have stumbled across this subject many times. I once had a customer that no matter WHAT he did would kill any plant he planted. (He even killed FORSYTHIA!) I finally went out to the gentleman's house and before I even got out of my truck I saw the problem. There was a MASSIVE Black Walnut (Juglans *****) directly over the planting bed he was trying to establish. I know someone mentioned this before. Walnuts release a substance into the soil called "Juglone". I provided the gentleman with a list of juglone resistant plants, and he was back in the gardening business.

Now..... for my question. There has been a considerable "wholistic" approach in the horticultural scene in the last few years. People have started realizing that the years and years of intensive farming, chemical applications have basically killed the soil. There exists, at least in terrestrial plants, a very important symbiosis between higher plants and Mycrorhizial fungi.

One company I used to deal with, Plant Health Care Inc. markets a large number of fertilizers containing the mycrorhyzae, and I have personally seen tremendous effects on plants that were near dead.

I'm borrowing the following from PHC's website:

"Millions of years ago a symbiotic partnership developed between plants and mycorrhizal fungi dwelling in the soil among plant roots. Both faced many natural stresses, and to survive each needed something the other could provide. The fungi needed sugars plants could manufacture for them as food. The plants needed greater root reach and numbers to draw in more nutrients so they could grow stronger, and stronger.

Mycorrhizal fungi began to serve as a secondary root system, organizing and extending themselves far out into the soil with tubular structures that extract mineral elements and water from soil and transport them to the roots of their host plant. The fungi in turn live off the plant's sugars translocated to them by the roots."

Their website is Planthealtcare.com

I wonder if anyone has investigated whether or not similar symbiotic relationships in the root zone exist in the aquatic realm. If so I would be curious if it was a fungal or bacterial partnership. Anyone have any input on this?

It's a well known fact that human beings also have such relationships. All you have to do is watch an "Activia" yogurt commercial to see that people are starting to become more aware of such things. And it has been proven that a Candidia fungus overgrowth in the human body can cause cancer.


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## dwalstad (Apr 14, 2006)

RestlessCrow said:


> Walnuts release a substance into the soil called "Juglone". I provided the gentleman with a list of juglone resistant plants, and he was back in the gardening business.QUOTE]
> 
> RestlessCrow,
> 
> ...


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