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2,069 Posts
Discussion Starter · #1 ·
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.

Tom Barr

2,069 Posts
Discussion Starter · #9 ·
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.

Tom Barr
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