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Discussion Starter · #1 ·
Why do certain species of aquatic plant colour up under intense light? That they do is something we often observe in all well lighted planted tanks. That this change in colouration becomes more prominent with the intensity of light is also a common observation. I will concede that some specie of aquatic plants will not show any perceptible change in their colouration and some others do not need very intense light to be other than green.

There are and always had been nutritional factors which can change the colouration of plants – but those need not be addressed here.

As I see it, when a plant does change its colour under lights, it does not stop reflecting the green part of the light spectrum it normally did, but is now reflecting an additional part of the spectrum, and this causes the change in colouration. Conversely this means that the plant is reducing the range of the light spectrum it was absorbing. Therefore it follows that the plant is reducing its energy absorption from those parts which are in more intense light. Why?

Additional energy when there is no lack of nutrients for the plant to increase synthesis of its growth substances should have been an advantage to the plant; still the plant is opting to reduce it energy absorption. Nature never induces curtailment of any action (or omission) which is of advantage to any specie; then why is such an advantage to the plant being curtailed? The answer must be that behind the obvious advantage lies some hidden disadvantage.

Reflecting over the question, it suddenly struck me the answer must be oxygen. Oxygen is synonymous with life, as we know it, but it is a dangerous poison. Man regularly uses oxygen and oxidising agents to kill living organisms. The most abundant byproduct of photosynthesis is oxygen. Therefore the plants that change colour with more intense light must have a limited capacity to handle the byproduct oxygen in its photosynthetic action. The change of colour is a defensive mechanism to reduce the quantum of the byproduct – oxygen.

I am no scientist, but I do like my queries answered. So I put questions to myself and try to find logical answers to them, not all my beliefs are true but this time I think I am on the right track.
 

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Children Boogie
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no, I don't think the color change has anything to do with any supposed harmful effected of O2. How do you explain plants that don't change color, and stay green even in extreme light?

It's probably genetic where certain plants don't need certain wavelengths to aid in photosynthesis.
 

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Discussion Starter · #3 ·
Nature does nothing without reason. The propensity to change colour must have a purpose, especially as synthesising those pigments need effort and expense of nutrient elements of these plant specie. No plant would evolve such an unnecessary and costly (extravagant) behaviour.

Genetically the threshold of different plants in handling of oxygen or the mechanism by which different specie control the threshold may differ. The explanation why some plants do not change colour would be there.

The range of the spectrum chosen by the plant would naturally be fixed by their genetic evolution, yes.

PS

Even if the trigger for additional pigments is linked to the byproduct oxygen from photosynthesis only; it would explain nutritional deficiencies and/or availabilities causing colour change in plants.

Any nutritional deficiency which affects the plants efficiency in handling the oxygen – or a nutritional excess of any element that increases the plants photosynthesis; can and will cause a change of the colour of the plant, when the threshold is breached.
 

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Something tells me the "answer" to the question being asked in this thread lies more in the realm of philosophy and speculation, than science.

I choose to think that the plants know how beautiful they are, and have developed the pigments for that purpose.

Prove me wrong.
 

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Plant Whisperer
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I seem to remember from botany class that the answer to this question has to do with the photosynthesis mechanism becoming overloaded with light. When it is under very intense light it becomes damaged and so blocking light is a benefit for this reason. I am not sure exactly what causes the damage but I think it has to do with the delicate structure of the chlorophyll and the way accessory pigments pass the electrons to the main iron molecule.

My best guess/analogy is that just like overloading a house's circuits with too many devices and causing the wires to heat up, the photosynthesis mechanism can be overused and overheat or deteriorate in some way.
 

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I seem to remember from botany class that the answer to this question has to do with the photosynthesis mechanism becoming overloaded with light. When it is under very intense light it becomes damaged and so blocking light is a benefit for this reason. I am not sure exactly what causes the damage but I think it has to do with the delicate structure of the chlorophyll and the way accessory pigments pass the electrons to the main iron molecule.

My best guess/analogy is that just like overloading a house's circuits with too many devices and causing the wires to heat up, the photosynthesis mechanism can be overused and overheat or deteriorate in some way.
Exactly right. Green plants reflect green light naturally anyway and use mostly red and blue light. If the light intensity is higher than what the plant can safely use, it may develop a red tint to it. This way it blocks green along with the majority of red light and keeps the chlorophyll from getting damaged.

Pretty much like a natural sunscreen for plants :)
 

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Isn't it possible that the change in coloration is a secondary effect of something else? If so, there may not be a logical reason for why plants begin to reflect more red light when they live in intense light.

I think Tom Barr is away right now, or we could send out a call for his explanation of this.
 

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I know that the color change can be affected by the amount of nutrients the plants take in too (like Fe, P, N and a few micros), but I'm not really sure how they affect the color change. I just know that they do somehow.

I've noticed that some plants like Rotala rotundifolia will pretty much turn pink as it nears the light no matter what. But something like Blyxa japonica needs lots of macros and Fe along with a huge amount of light to turn reddish. I think it probably depends on the species of plant too.

So from that, I would assume that lighting is the main factor. Maybe nutrient uptake just assists the process?
 

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Here's something else to think about: Blue light is a higher energy intensity light than red. If a plant is has just enough light, it's going to use everything available to it to keep it's photosynthesis going. But if there is a surplus of Blue light and using primarily blue wavelengths makes its photosynthesis more efficient it stands to reason that it would be to the plants benefit to "ignore" the red light and focus on absorbing the blue. Another side effect of the blue light intensity is that too much blue light can destroy the green pigments. That's why some plants will yellow and die if they get too much light. Now it just so happens that the darker pigments that reflect red light also absorb more blue light. When you think about it in terms of energy conservation and efficiency it makes a lot of sense.

As for nutrients affecting the change, that also stands to reason. You need more iron and other trace metals to produce red pigment than you do to make green pigment. Even if there is an abundance of blue light, if the plant doesn't have the raw materials necessary to manufacture the red pigment, it can't turn red.
 

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^ I think that's a very good theory right there! But I want to know is this: Why would a plant which is healthy in every apparent way only start to turn red once N is limited? I've seen this on terrestrial plants as well as aquatic ones, but for this example I'll use the L. aromatica that was in my 10g. I was dosing KNO3, KH2PO4, and K2SO4, along with CSM+B, and everything was beautiful, growing well, just GREEN. So then, while keeping everything else exactly the same, but eliminating KNO3, the plant became very red.

It seems in my example, the plant ran out of the raw materials necessary to hide the red pigment, causing it to turn from green to red. Why is that?

I've always thought that the red pigment was there all along. It's there "underneath" the chlorophyll the whole time. But when the conditions to showcase the chlorophyll start to fall apart, then the red comes out. I actually always thought that was what explained how green leaves turn red in the fall every year.

But I'm no expert in this matter. :(
 

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^ I think that's a very good theory right there! But I want to know is this: Why would a plant which is healthy in every apparent way only start to turn red once N is limited? I've seen this on terrestrial plants as well as aquatic ones, but for this example I'll use the L. aromatica that was in my 10g. I was dosing KNO3, KH2PO4, and K2SO4, along with CSM+B, and everything was beautiful, growing well, just GREEN. So then, while keeping everything else exactly the same, but eliminating KNO3, the plant became very red.

It seems in my example, the plant ran out of the raw materials necessary to hide the red pigment, causing it to turn from green to red. Why is that?

I've always thought that the red pigment was there all along. It's there "underneath" the chlorophyll the whole time. But when the conditions to showcase the chlorophyll start to fall apart, then the red comes out. I actually always thought that was what explained how green leaves turn red in the fall every year.

But I'm no expert in this matter. :(
This sounds very reasonable and it slightly rings a bell for me.....unless someone is at the front door?:biggrin:
 

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Discussion Starter · #14 · (Edited)
Here's something else to think about: Blue light is a higher energy intensity light than red. If a plant is has just enough light, it's going to use everything available to it to keep it's photosynthesis going. But if there is a surplus of Blue light and using primarily blue wavelengths makes its photosynthesis more efficient it stands to reason that it would be to the plants benefit to "ignore" the red light and focus on absorbing the blue. Another side effect of the blue light intensity is that too much blue light can destroy the green pigments. That's why some plants will yellow and die if they get too much light. Now it just so happens that the darker pigments that reflect red light also absorb more blue light. When you think about it in terms of energy conservation and efficiency it makes a lot of sense.

As for nutrients affecting the change, that also stands to reason. You need more iron and other trace metals to produce red pigment than you do to make green pigment. Even if there is an abundance of blue light, if the plant doesn't have the raw materials necessary to manufacture the red pigment, it can't turn red.
I agree with you about why some of the plant specie prefers to block out the red part of the spectrum and opt to use the blue part. I had also agreed that these plants do need to use a lot of effort and hard to get nutrients to build these additional pigments to block out the non-preferred part of the spectrum. In my original post I was trying to deduce the NEED for blocking out any part of the spectrum by plant specie. My explanation was that oxygen handling becomes a problem which triggers this action of additional pigments.

My deduction is that once the oxygen produced becomes too much to handle - a threshold position is reached where the plant needs to curtail further oxygen production to save itself from being damaged by this element. If it cannot then the plant will be damaged and may even die.

PS: Not all plants use the same mechanism to prevent this suspected oxygen damage. Neither do all plants colour up red, some even colour up violet which means some blue part of the spectrum is also blocked. Why plants don't colour up BLUE maybe because in nature a truly blue pigment is missing.
 

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Children Boogie
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Just did a little reading. Nitrogen is important in chlorophyll, the green stuff. Seems like church might be right. Too much light, even uv will damage the chlorophyll and also limiting N will contribute to the damage. The color red is underneath the damaged green.
 

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Fresh Fish Freak
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It's been a LOOOONG time since I studied photosynthesis in high school, but isn't "oxygen handling" just via osmosis? So no energy required on the plant's part?

Here's what makes sense to me-

Light triggers photosynthesis aka plant growth. The more light, the more more the plants are triggered to grow, the more nutrients they need. If they start to run low on nitrates, which they need plenty of, then it would make sense for them to produce red pigments to slow down their light intake.
 

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Discussion Starter · #20 ·
If they start to run low on nitrates, which they need plenty of, then it would make sense for them to produce red pigments to slow down their light intake.

No Laura. Nature does not work in that fashion. Any extra tax of work or material requirement to evolve will need to be triggered by some serious need linked to survival. The nutrient deficiency would itself stop/slow photosynthesis. The deficiency should also cause damage to the plant tissue from the ongoing photosynthesis for the plant to evolve any defensive mechanism.
 
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