Thanks. Theoretical physics is more my thing, really...


Thanks for explaining. I understand now and I agree it is a persuasive result.


However, one thing bothers me:


It seems to me that this is exactly what you would expect to see.

All aquatic plants compete with algae in nature.

As far as I can tell, the same general kinds (not the same species, most likely, but certainly species that fill similar niches) occur in aquaria all over the world. Here in Australia I have green spot algae that looks like like photos of green spot algae in an aquarium in Britain, or the USA. I don't know if its the same species, but it certainly seems to fill the same niche.

It makes total sense to me that a native aquatic plant in Australia would have to come up with a system of defense against green spot algae, just as a plant in the USA or anywhere else in the world would have to do so.

If (this is the if, I do realise) plants are defending themselves against algae with allelopathy, I would expect it to be very common. Because all plants have need to defend against similar things. Whatever a good defense is against alage, whether it is allelopathy or something else entirely, I would expect many species to come up with variations on this particular defense. I would expect it to be normal. If very ancient species had come up with it, I would expect it to be present in descendants of those ancient species, which might be many many different species today (I don't actually know anything about plant evolution, so maybe I'm talking nonsense here).

Maybe this should be rephrased to "all plants in similar ecosystems". But then presumably most aquarium plants actually are from reasonably similar ecosystems, since they all grow in aquariums.

Maybe there is a flaw in this observation. But I just have to ask about it, because I hate it when people say it is so unlikely that things would happen when in fact natural selection has worked in favour of that thing happening, so it actually isn't that unlikely, given billions of years of natural selection (don't get me started on people who believe that life itself is so unlikely as to make it impossible it occurred via natural selection...)

I totally buy your comments about the problems with mashing up a plant and testing it in some agar on some algae. I hadn't thought of those complications but of course it makes perfect sense.

Thanks again for the discussion and explanations. I'm learning, and hopefully others reading this are too.

Helen

They are the same actually.
Sort of amazing, but algae are excellent indicators of environmental parameters, we use them in water assessments for streams among other indicators.
I use them to pin point aquarium issues without ever picking up a test kit.
Know thy enemy(or weed).


How long has evolution worked in the aquatic plant hobby for this to occur?
Not long enough.

Algae in natural systems are subjected to many strategies and cycles. NH4 influx due to seasonal rains, light cycles season to season(day length), temperature changes, presence/absense of herbivores(algae or plants).....no people pruning selectively........not very stable conditions.

A plant can simply out grow the algae if there are ample nutrients and CO2.
It'll just lose that leaf and grow a new one before the algae can colonize.
It will grow to the surface and form a canopy and block the light below.

Sometimes it may not be worth while to fight the algae, allow it to live on the leaf and by the time the water recedes, the algae dies and the plant flowers goes to seed or forms emergent leaves.

Most aquatic plants are amphibious.

And like CA, USA, Oz is pretty seasonal when it comes to the rains near as I can tell. At least that's what Dave Wilson keeps saying. He collects aquatic plants lot down there.

GSA(green spot algae), is generally correlated well with low CO2 and low PO4, all good things for most fish keepers. But we can induce it by reducing the PO4 and also remove it and go back and forth 4-5-6x on a planted tank using this method. Likewise, we can do the same if we change just the CO2 and keep PO4 high. However, reducing the CO2 for a few days typically induces other algae under higher light........


But why do it chemically and waste if if the plant lives in a river or a seasonal pool?
The impact of algae is minimal in seasonal systems.
Just like wet rice cultivation.
Why do it if you live in a river?
It'll all be wasted downstream.........


And they all would be the same intensity over a very wide range of aquariums and species combinations? That would not be "normal".


No not at all...........if that trait had selective pressure, then yes, but there's really not a strong selective pressure to beat algae chemically. Plants have many other methods that are much more adaptable to the varied ecology that aquatic plants are exposed too in nature and our aquariums.

Likewise, what induces algae should really be the question.......we know why plants grow, the real question is why does X species of algae bloom and grow?

Better and more specific yet: what induces an algae spore to germinate?
Then you can better understand cause and effect rather than correlation and infinite uncertainy (No relation to Heisenberg's principle!).

I used that to determine why(at least one or two reasons) certain species of algae grow in aquariums. I induce algae on purpose using a well run tank as a control and then apply the treatment. Few aquarist are willing to do this.

I culture algae so it's not an issue for me.
I can also kill it and start over faster than most anyone.


Ammania never sees water in most cases, Egeria has to live it's entire life in water. Banana plants: from very acidic pools, Crypts: faster flowing water.
Every year I take folks to see an enormously wide range of parameters that submersed aquatic plants exist in nature. Some are dry most of the year, some are hot, some cool.........they exist everywhere virtually. Snow capped mountains, alpine regions, even the deserts, deep dark forest, open bright marshes.......the list goes on and on.



You are preaching to the choir.
Plants has been around for perhaps 400 million years. They evolved from algae.
Angiosperms maybe 120 million years. I think focusing on natural selection and is the pressure real or needed for chemical defense vs ecology. Same is true for algae-algae interactions.


It's a popular topic
One folks in th hobby have been pondering for many decades.
I've gotten much further than any using some rather simple methods.
It's a step by step slow process.
Ruling things out one at a time.

There are some nice methods such as N15 stable isotopes that can answer a lot of the questions I have that I cannot answer with simpler methods hobbyist might use.

But that's another thread.

Regards,
Tom Barr