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Re: [APD] Re: Aquatic-Plants Digest, Vol 15, Issue 3

Michi Henning wrote:
From: Thomas Barr <tcbiii at earthlink_net>

No, it's not limiting to the plants, they have plenty of NO3.
So the N is still being supplied to the plants but little NH4 causes the

algae not to bloom and cause probelms.

Plants do not need NH4 at all. they do fine with nothing but NO3.
They are huge and have plenty of reserves to convert NO3=>NH4. Algae

don't, they exist in a different niche, the microscale.

Just a question here: NH4 --> NO2 is an exothermic reaction, as is NO2 -->
NO3 (after all, that's where the bacteria
colonies get their energy from). So, if I offer both NH4 and NO3 to plants,
wouldn't the plants preferentially take
up NH4 because it takes less energy for them to get at the N?

If this assumption is correct, then that might help to explain why healthy
and actively growing plants
help to control algae: a healthy plant is biologically active and would have
"a go" at any NH4 as
soon as it appears, thereby removing it from the water and depriving algae
spores of an essential nutrient.
On the other hand, a plant that isn't growing well would take some time to
activate and remove
the NH4, thereby allowing the spores to get at it first and establish
themselves as algae. Then, once the
algae are established, it doesn't matter much any more what the plants are
doing because, once established,
algae can get their N from NO3 just as well as the plants can, and the NH4
concentration becomes a
secondary factor.

If all this (admittedly surmise) is correct, that would help to explain why
a well-planted and fertilized
tank tends not to get algae and why, once algae are present, it's so
difficult to get rid of them again.

If understood it correctly it goes exactly the other way. If plant would prefer ammonia to NO3 it would take all NH4 even in absence of NO3 and there would be no algae problem. Rate of uptake of NH3/4 by higher plants must be lower than of NO3 in order for mechanism described by Tom Barr to work. Am I right here? The other point could be that algae spores need very little NH4 to bloom and in order to minimize NH4 you want pants to function as efficient as possible, which you do by providing sufficient amount of nutrients, such as NO3 which do not affect blooming of algae spores. It is my understanding that evolutionary plants are competitors with algae. That is so because algae reduces, for example, amount of light which could reach plant and therefore there are chemical mechanisms which can push balance in one way or the other. Plants could have other offensive mechanisms besides those which depend on NH3/NO3 ratio. And as far as stored chemical energy, it is probably too crude way of looking at the process. We, humans, could also consume compounds with larger stored energy but they would be toxic for us. Same with plants or fish.

Dmitri Priimak

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