[APD] Re: Gw/NH4

["Steve Pushak" <teban at powersonic_bc.ca>]

Well the spelling "virii" should win on pure cuteness alone! ;-)

You should also training yourselves to say:
"The data are conclusive!"

Thomas Barr wrote:
> >> When a healthy well growing plant is supplied with a
> >> fair amount of NH4 as a nitrogen source (fish/critter
> >> wastes) and suddenly you stop adding things like
> >> PO4/K/Traces, the plant growth stops/shuts down.
> >> So does NH4 uptake.
>
> > Sorry, I have to disagree on this theory Thomas. Aquatic plants
> can store
> > reserves of nitrogen and will do so quite efficiently.

You have said above that a tank with lots of nitrogen in it will stop
growing because you're not adding a) enough phosphate b) enough potassium or
c) enough trace. And then you are saying that because its not growing, it
will stop absorbing nitrogen.

When you are away, you have stopped adding fish food so a major source of
nitrogen & phosphates has been removed. Plant growth should still continue
because the plants were not starved or deficient of phosphorus. Usually with
a tank populated with fish, if you are going to keep growth not limited by
nitrogen, you are going to have to add additional nitrogen & other
nutrients. If you are doing it properly, you have a surplus of potassium &
enough to last several weeks. You don't have to worry about excess potassium
causing problems. Phosphates & trace should not be a problem because these
are sequestered in the substrate through accumulation of fish poop.
Phosphates become soluble within the substrate and are absorbed by the
roots; they are also readily absorbed in solution from plant leaves. Normal
senescence will supply enough phosphates to keep the plants growing new
leaves and if there is a shortage, old leaves die & there is always enough P
in the water to support growth. I don't know how much P can be stored in
plant tissue. Trace nutrients should not be limiting because you've been
supplying these in surplus with most fish foods & certainly if you are
adding trace elements ala PMDD or other trace supplements.

Someone who knows about plant nutrient analysis & typical ratios could help
this discussion.

When a plant has a surplus of nitrogen & a reduced supply of phosphate, you
will still get growth along with senescence of the older leaves. The new
growth will be succulent and lack strength in the tissues. Leaves become
much larger. In your garden, the growth in an overly rich nitrogen
environment, becomes succulent & highly attractive to insects as a food
source.

>
> A) If you run the NO3 levels at zero ppm for more than 2 days at high
light,
> stem plants stunt. I've done this enough times the wrong way to
> know. Trying
> to get plants to have a nice red colour using N limiting methods
> really gave
> me a lot of experience. Some plants are more tolerant, but if the fast
> growers are maintained well, then it follows the slower growers
> will also do
> well. A number of other folks on this list can attest to this.
>
> B) I'm saying that a PO4(or trace/K+) limited tank/plant is going to have
> slower uptake and growth than one that is non limited. Make this
> limitation
> severe enough, and the ability to remove/assimilate NH4 from the water
> column will be reduced.
>
> That's all I said in the above statement.
> Still disagree?

You've said something entirely different here Thomas. You've said that a
nitrogen limited tank stops growing immediately when you stop adding fish
food or other nitrogen sources. That's true but not at all the point I
disagreed with. Paragraph A) talks about N limitation. Paragraph B) talks
about P limitation and P deficiency. I think P limitation & P deficiency are
not the same. With P limitation but a steady supply of P, you should have
luxuriant growth right out of the top of the tank. A P deficient tank has a
problem keeping the plants alive & I don't think fish would survive long
without fish food which supplies a healthy & adequate supply of P.

> > Nutrient uptake is
> > independent of growth (but not vice versa).
>
> Okay, then where is the plant going to put the nutrient's it
> brings in?

See above. Storage is in the new succulent growth.

> Small amounts/brief time periods may be independent, but there is
> certainly
> interdependence with nutrient uptake and growth.

Granted over time & depending upon which nutrients we're talking about.

[snip]

> This statement above I made was about why the NH4 uptake is
> reduced and NH4
> 's relationship to GW causes. This something I've actually done a fair
> amount of work on and talked and helped many folks over a number of years.
> I can get into the biochem if you wish on how plant's regulate Nitrogen
> metabolism. I've posted some info before not too long ago on N
> assimilation.

Are you saying you've done controlled lab experiments or that you've done
research into N assimilation? Severe P limitation (deficiency) would be
different. I do not think that is a normal condition of aquaria with fishes.
(sic) ;-)

My understanding of the affect of surplus N is based on gardening experience
& common gardening books. My experience with P limitation is limited too.
;-)

I suppose that if the green water (GW) were incipient, that an increase in
GW would rapidly absorb most available P from the water column. Perhaps this
GW observation only occurs under certain types of conditions? If the GW gets
think enough, it can curtail plant growth by competing for light! Another
thought is that plants getting lots of P & trace elements from the water
might not develop an adequate root system & thus be at a disadvantage
getting P from the substrate in times of shortage? Another thought is that
with the curtailment of food, perhaps Ca has become deficient 7 curtailing
growth enough to permit a GW bloom?

I think we do agree that if P shortage is SEVERE enough to curtail growth,
that N uptake would be reduced. I just don't think that's common.

Maybe for truly healthy tanks, we should think about having growth limited
by light instead of nutrients?!!

Steve

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