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[APD] Re: changing light

"Message: 10
Date: Wed, 19 Nov 2003 08:11:57 -0600
From: "Ann Viverette" <annv777 at houston_rr.com>
Subject: [APD] Amano's comments on light spectrum
To: <aquatic-plants at actwin_com>

I just got Amaon's Aquarium Plant Paradise (bookcloseouts.com!) and read on
pp 55-56 (about red plants)..."Moreover, frequently changing the colors of
light injures the plants and can even kill them.  The reason for this is
that besides chlorophyll, the green leaf pigment, additional plant pigments
corresponding to the spectrum of light provided are produced, which can
occur unproblematically only in young leaves. Therefore, when the light is
changed the old leaves are dropped and new leaves are formed.""

No, this is too simplistic a view.
Think about the spectral changes that occur daily or even with in the few seconds.
In the AM, the light is generally redder in color as the air/atmosphere filters the blue light out, then midday it's around 6500K and then gets redder towards evening.
Light is filtered as plant leaves block other plant leaves light out. Clouds etc.....all these influence light and spectrum daily, but we do not see leaf losses/algae etc due to this on a daily time scale.
I do not think you can kill a plant with aquarium bulbs by changing them often, I guess if you changed them daily with a wide range etc, you might be able to...but it'd be very hard and something I've never heard of or seen due directly to lighting.

Carotenoid formation et al, "other pigments" most certainly can and do get produced in older leaves, not just new growth.
Many color variable plant's older leaves can and do change color, the reason why you see so much red color in young leaves is the plant's cells have not matured yet and the red pigments are not masked by chlorophyll yet. As the chloroplast mature and develop, they will become greener in color due to possessing more CHL. If the plant is NO3/NH4 limited, the strongest visual indication on a plant is where growth is strongest, the young new leaf. 

I wonder if these folks think about plant biology when they write this stuff. 
If you want to say "why" you need to know why or at least have a good idea, these are just wrong. If they want to say "in Cryptcoryne affinis leaf cartenoid production ceases in mature leaves yadadyada...." but that's not what was said.

I've given several reasons why they are wrong. I can also back it up in practical terms. 

I really don't know what he means by that, every month or every year or????
Plants are very well adapted to spectral changes.  Older leaves can a dn DO adapt to spectral changes, they do not get "damaged", they take some time to change the light gathering pigments, but only a few plants will lose the leaves due to light changes in the bulbs. 
But generally it's a good idea not to change things around a lot. That is the point he's making, his reason's why are not well founbded and some are just plain incorrect. Perhaps something is lost in the trasnlation, but that does not seem too likely either

"Does this explain the common outbreak of algae in newly planted tanks?"

Hehe. no. 

" Is
the algae an attack on newly weakened leaves, in advance of their being shed
anyhow? Is the remedy then to prune them away as soon as reasonable as new
growth appears?"

Yes. Cull the weaklings!!!! Same goes for breeding fish.
Do not "top" plants but rather uproot them and replant the tops with the new young growth which has not had time to get any algal film growing on it.

After 2-3 weeks, generally there is very little left on any leave 

"Furthermore, in my new PSL hood with 4 x 55 watts, one bank of lights is
6500K, the other 9325K, and the run times are slightly staggered -- am I
confusing the plants by doing this?"

No, perhaps yourself, but not the plants:)

" Forgive me if this is old info, it is simply new to me. I am seeing a minor
outbreak of algae in the new tank similar to what occured after I changed
the lights from double flourescents to PC, when pruning and patience (and
nutrients) proved to be the best answer. However, even when nutrients were
adjusted, nearly all old leaves had to be removed."

You added more light by doing this, the color changes are minor influences.
The addition of more light can cause algae as you may niot have adjusted the CO2/nutrients to match the increase in lighting.

"It makes sense to me that all plants would have a response not unlike a
minor version of crypt melt when placed into a new situation, I've seen it
happen with terrestial plants in response to changed sunlight."

Crypts often will melt in response to changes in light, generally changes in light in submersed plants means a seasonal change, turbidity increasing etc, nutrient changes etc, not just light alone. But generalizing for all plants? No, you cannot say this because I know it does not occur. You can this in your own plants at home and find this not to be the case in the research and the text books.

"Ann V"

Tom Barr
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