# Nitrogen and its affect on plant color



## plantbrain (Jan 23, 2004)

Phil, if red need more light, why are cactus and desert plants all green and why are tropical rainforest plants deep in the jungle red?

That's counter to the entire notion of red needs more light.
Few emergent plants are red, red plants that grow out of the water become green.

It takes a lot of N to produce Chl, not much to make red which will catch lots of light and make the Chl a more efficient and the plants can have far less N per unit of leaf area.

There are many things a plant can do to get more light or reduce the amount of light. 

I do not buy that red plants need more light nor iron. Never have. 

Regards, 
Tom Barr


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## Phil Edwards (Jan 22, 2004)

Tom,

That's interesting stuff!! "Feed me, Seymour!" :shock:

*if red need more light, why are cactus and desert plants all green and why are tropical rainforest plants deep in the jungle red? *

Desert plants are green because ChloroPhil (hahaha) is more efficient. They've got other adaptations, like photosynthetic trunks or needles rather than leaves (generally). Why aren't all tropical plants red?

Understory plants/autotrophs in any super dense/highly filtered ecosystem, be it a rainforest or 200' under water will have high percentages of red pigments. Only the highest energy light (blue to ultraviolet on down) is able to penetrate to those depths. Since red pigments are the most efficient at capturing that higher energy radiation the plants will produce more red than anything else. That's not to say that others aren't produced as well on the off chance that a large tree might fall and create an extra light situation. I've got a lot of Begonia species in the conservatory at school with green tops and red bottoms to capture the greatest spectrum possible.

*That's counter to the entire notion of red needs more light. 
Few emergent plants are red, red plants that grow out of the water become green. *

True enough. However, with the increase in the red spectra once out of the filtering/reflective capacity of the water the plants are better able to utilize the lower energy end of the spectrum and start producing Chlorophyll in amounts able to mask the Carotenoids.

*It takes a lot of N to produce Chl, not much to make red which will catch lots of light and make the Chl a more efficient and the plants can have far less N per unit of leaf area. *

If the red pigments are so useful why aren't they the dominant pigment?  I've got no argument with you there, the combination of pigments is most effective.

*There are many things a plant can do to get more light or reduce the amount of light. *

I wasn't trying to suggest that the plant is attempting to reduce the amount of light, rather, they build more red pigments to capture the increased blue light and so harness the higher energy radiation rather than let it affect their physiology.

*I do not buy that red plants need more light nor iron. Never have.*

I would argue that plants with higher percentages of caretoids to chlorophyll will need more light simply because of the decreased ability of the carotenoids to capture and utilize the light.

Even so, I still believe that Nitrogen deficiency is the main cause of red coloration in plants. I've had some pretty green "red" plants under some pretty strong light in some well supplimented aquariums.

Best,
Phil


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## MantisX (Sep 2, 2004)

I dont know what either of you just said  but if you would like my personal experience with reds, its this; my reds didnt turn red until I added phosphate. Also way back when I was clueless and didnt dose nitrates, my reds still came out pretty deep. I will also mention that the lighting at the time was 72 watts over a 10 gallon. Pardon if my info is totally irrelevant. :shock:


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## Sir_BlackhOle (Jan 25, 2004)

These are my favorite type of threads! Lets hear some more!


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## Hanzo (Mar 9, 2004)

Clue me in! Love this in deepth kinda things. I lost my wonderfull red color when I installed MH lightning (all daylight). After trying to dose No3 and Po4 like crazy and still not getting the color I want, I'm going back to tubes for now :evil:


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## defdac (May 10, 2004)

It took my tank a couple of months with 2.75 ppm PO4 + 2 ppm NO3 dosage 2-3 times a week before I started getting good red colors.

Before my dosage was 0.5 ppm PO4 + 11 ppm NO3 each dose and the NO3-levels hovered around 10-20 ppm when I measured it with JBL-test kit.


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## HeyPK (Jan 23, 2004)

Let me trot out a theory that may explain why some aquarium plants are more red when N deficient. The theory is that, when N deficient, plants make an excess of carbohydrates. They wouldn't have an excess of carbohydrates if they had enough nitrogen because they could convert the carbohydrates into amino acids and then into proteins which would be used for growth. Since growth is slowed for lack of protein, the carbohydrates build up and some of these are diverted into making red pigments.


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## SCMurphy (Jan 28, 2004)

I thought that when plants have red leaves it's because they are reflecting red light and absorbing blue light.


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## plantbrain (Jan 23, 2004)

You can see the arguement of past on the APD.

Name one red desert plant.
Why aren't more desert plants C4?
Many are CAM or else annuals.

Significant filtering doesn't occur in the upper 3ft of water where most submersed plants occur in clear water.



> I've got a lot of Begonia species in the conservatory at school with green tops and red bottoms to capture the greatest spectrum possible.


?
Well you are proving my arguement, you need less light for reds then?



> the red pigments are so useful why aren't they the dominant pigment?


Err, they are in many cases. Depends on the leaf/plant/phenology/development/nutrient status etc

Phil, give me one good reason a submersed plant would bebefit from blue light?

Blue light will cause the stomata to open more.
Hydrilla has no stomata, what is the advantage in an aquatic system then?

Diffusion through the very thin leaves of many aquatic plants is enough.
SAM's have reduce cuticles and many other adaptions to increase CO2 gathering.

I have never seen nor heard of any blue light=> increase growth rates in SAM's to date.

There may be some, I've never seen one yet though.
Terrestrial systems yes, but not SAM's.(Submersed Aquatic macrophytes)



> would argue that plants with higher percentages of caretoids to chlorophyll will need more light simply because of the decreased ability of the carotenoids to capture and utilize the light.


 Carotenoids help make Chl more efficient, not the reverse. 
If you have less N, then you can only build a few Chl molecules.
So more Carots would help run the Chl you do have at a more efficient rate.

Heck, you can try it your self and see.
Use less light.

BTW, adding PO4 does what to NO3 levels?
Causes them to drop.

PO4 buyself does not play that large of a role with color, N is the main player with most plants.

Having less light will allow more stable NO3 levels(and/or more reliance from fish waste) vs higher light.

Regards, 
Tom Barr


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## Phil Edwards (Jan 22, 2004)

plantbrain said:


> You can see the arguement of past on the APD.
> 
> Name one red desert plant.
> 
> ...


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