I was thumbing through a well known, but older Limnology text (Hutchinson, 1975, Vol 3 Limnological Botany pg 351-357) when I saw a nice graph showing growth rate vs NO3 concentration.

It seems Paul had found that 20 ppm and above was the ideal range for submersed plant growth(Vallisneria americana) back in the 1960's(1966). I suppose I redisocovered this range(20-75ppm) independently some 30 years later.

What is interesting is that we both arrived at the same range. At progressively high concentrations, this high rate of growth slowly decline, but very slowly.....even at 100ppm etc.

This also mirrors my own observations when I did longer term NO3 at 75ppm for several weeks.

What is really interesting is how rapid the growth rate increases when the level is maintained.

For example:
At 5 ppm the rate of growth is greatly reduce, about 2.2/0.7= 3.14 times less growth (dry weight mass).
At 10ppm, the growth was about 1/2, 2.2/1.1 = 2x less growth than at 20-80ppm.
After 20ppm, the plant's growth is no longer nitrogen limited.

Fast forward to the molecular age of plant biology.
Why might these plants show this pattern? How would they control it?
Given what is known about LAT and HAT transportors for NO3, it may now be suggested that when plants have all their constitutive and inducible transporters upregulated and maintained, they grow faster and have non limited growth.

In order for the plants to do this, 20-30ppm of NO3 needs to be present in the medium(the water column). Now we have a plant that is healthy and can grow at a maximum rate. If the NO3 levels varies between say 2-15ppm, then the various transporters will be degraded and more efficient transports(the HATs) specific to low NO3 levels will be put in their place. As a result, the plants growth rate will be reduced.

It takes more energy to concentrate nutrients when there is less in the external environment. So at higher levels, the plants use different transportors that take full advantage of the higher NO3 levels and grow faster as result.

PO4 data was also discussed. But no such graph was provided, other than tissue analysis for PO4.Still if one assumes a ratio for PO4, then a 6:1 to 10:1 relationship would suggest about 2ppm or higher for PO4(Conversion from N:P to NO3:PO4 is addressed FYI).

Which is about what we find to be optimal for growth in the water column.
Seems the data was and has been there all along, just no one bothered to listen to Paul, nor look stuff up.

He looked at many lakes and plants and did a lot of tissue analysis beside this as well. Below is my personal favorite of Paul at the plant fest, he should stick to plants:-)

Reference:

Gerloff, G.C., and Krombholz, P.H., 1966. Tissue analysis as measure of nutrient availability for the growth of aquatic plants. Limnological Oceanography, 11:529-537. (Hutchinson, 351-357)

Regards,
Tom Barr

http://links.jstor.org/sici?sici=002...3E2.0.CO%3B2-X

Regards,
Tom Barr

So are you suggesting that planted tanks should run at 20-30ppm NO3 and about 2ppm PO4? I run 1ppm PO4 and 5-10ppm NO3 with high light and CO2 should I increase PO4 and NO3? Should the increase occur incrementally over time or all at once? Thanks.

All I am saying is that Paul's data suggest this.It may not apply to every plant species, but does for some certainly, such as M umbrosum, a known NO3 loving plant.


Regards,
Tom Barr

Interesting fact. It poses conflicting issues : maintaining high concentration of NO3might interfere with our wishes of increasing the plant's red colors as we always say that we need to lower NO3 concentration to increase anthocyanin concentration, hence redder plants.
So in light of that I have 2 questions :
1. How do we maintain stronger red color in plants (ignoring the fact that redder plant means stressed plant).
2. When anthocyanin concentration increases, what role exactly do they play with photosynthesis? (do they photosynthesize themselves or just aid the clr (a and b) to themselves?

Why is a stressed red plant a desired condition?
There are plenty of red plant species that do not require low NO3, many red species look pretty red when given good nutrition.

Anth's play a few plausible roles.
UV protection and anti herbivory are the most popluar.

When folks talk about plant growth and what it prefers, I think it's very safe to say that over expression of red is bad and sign of stress, hardly preference or optimal conditions for the plants.

Many species are available that will be a very nice red color without playing that razor's edge with NO3.

The main point of the research I see is that you have a large decrease in plant growth with only 10-15ppm decline in NO3 from 20 to 5ppm.

Very large.
400% less growth.

If you think that is a trivial amount, you may want to think again.

What happens if you drop the NO3 to 2ppm?
Or only a sub ppm?

BGA pops up pretty fast. Adding more CO2 and NO3 helps address that.
If there is little NO3 and decent NH4 and organic matter(leaching from stressed plants), makes sense, the BGA have good place to grow since the plants cannot.
Same deal with CO2 changes, and BBA, GW with NH4 and so on........

If you really want to maintain a low NO3, it's actually not that hard, but you need to use low light.

Low light=> less uptake demand for CO2=> less demand for NO3.
You have a lot more wiggle room between red stressed plant and permanent deficiency as demands and growth rates are less.

But then someone claims high light helps.
No, it does not.

High light increases NO3 uptake(and CO2 as well) and if you had a nice stable 5ppm, now the plant get redder because the growth rate increased, but you did not add more NO3. Often such tanks have troubles over time maintaining such red color but it's possible, just hard to do consistently over time.

So you get a few pics of super red plants here and there, some re touched photos etc.

Perception of color from person to person is very arbitrary as well.

R macrandra has done best at about 2-3w/gal of normal output FL's.
That's about 1 to 2.2 w/gal of PC.

Regards,
Tom Barr

bonjour,
(first sorry for my bad english, wish i could developpe more...)

i have some R.mancranda for a while...and doing grate whit it.
last month my co2 was empty...
it take me 2 week to refile it...

first...my set up:
~200g (60x36x22inch)
10x 32watts T8 zoo-med (flora sun + reef sun)
flourite and sand (50-50% where the mancranda take place)
no liquid ferts added (only dry Kno3, when needed)
no water change for 3-4 month now.
No3 = 5ppm
po4 = 0ppm
co2= 20-25ppm

on the picture
#1 is the color that R.mancrada have whit CO2
#2 is new leaf (one week) whit no CO2


for now, my CO2 is back on track...and new leef of R.macranda is red again...

what can we suppose in that case ?
red color need CO2 or the poor CO2 make no more carence of no3 ?

Hi Tom, can you name the red plant species that do ok in high NO3 conditions.

Sure, these damn weeds:
L pantanal, L cuba, L arcuata

All at high NO3, 30ppm etc
Also note the red color without CO2.
Then look at the lighter color with CO2.

Developmentally, the plant can produce a lot more Red color if .........it's grown better. While less CO2 will help slow growth, at 1.5 to 1.6w/gal of T8 lighting in a large tank can go either way, but a plant can produce more anthocyanins if it has more carbon as those colored pigments are mainly unsaturated carbon chains.


Regards,
Tom Barr

I've heard that some plants are red not because of anthocyanins, but due to betalains, which contain nitrogen atoms. Maybe L. pantanal, L. cuba and L. arcuata contain betalains, therefore they are red at high NO3?