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re: nutrient deficiency symptoms related to lighting?
I'm following up on my own post. Shortest possible review; plants
in one of my tanks showed symptoms that could be caused by nutrient
deficiency, but which went away abruptly after I replaced half my
Ultralume lights with Gro-Lux wide spectrum lights.
Since last I visited this topic I've been searching for spectral output
info on the Philips Ultralume and GE Gro-Lux lights and looking for
reason's why my change from one light to the other might apparently
"cure" nutrient deficiency symptoms.
This doesn't mean I'm going to drop the substrate angle on the issue,
just that I'm covering the bases.
There is a big difference between the lights in the red and far red bands.
According to the tables at George Booth's site, red is 630 to 700 nm and
far red is above 700. The Ultralume has a big spike in the orange band,
very little output in the red band, and a small spike in the far-red at
about 710 nm. The Gro-Lux has a big spike in the red band and tapers off
in the orange and far red.
The topic of red light, far red light and the ratio between them has been
discussed on this list before. Plants have a pigment (or set of pigments)
called phytochromes that are sensitive to light in the red and far-red
bands. Phytochromes are important in controlling plant morphology and
seem to play roles in many other functions. Dr. Dave reasoned that
phytochrome was relatively less important to aquatic plants because they
are adapted to submersed growth where the quality of red light will be
highly variable. He can correct me or flesh that statement out if he'd
After some searching, I found a faculty member at the University of North
Carolina at Chapel Hill (Dr. Jason Reed), who's research interests seemed
related to my problem, so I wrote up my questions and sent them off to him.
Remarkably, Dr. Reed didn't just trash my letter! Instead, he forwarded
my questions to a colleaque, Enrique Lopez at the University of London.
Dr. Lopez was kind enough to provide some speculation about possible
mechanisms for the symptoms.
In short, I asked if the absence of red light in an artificial light
source could cause damage to plants grown under those lights. I can't
paraphrase Dr. Lopez's ideas as well as he expressed them himself, so I'm
including a part of his letter here and cc'ing him on this note to insure
that he isn't misrepresented.
Dr. Lopez wrote:
> One possibility is induced senescence. I don't know whether the damage you
> observed could be related to senescence in any way. In many terrestrial
> species, as far as I know, senescence accelerates in the dark, and this is
> because it is under the control of phytochrome photoequilibrium.
> Phytochrome slowly reverts to supposedly inactive (Pr) in the dark. Dutch
> flower carriers use red diodes inside trucks and containers to prolongue
> the life of cut flowers. Might it be that the fluorescent lamps used first
> contained very little red, and an overall spectrum which actually reverted
> phytochrome to an inactive form? This would be a little surprising, but not
> impossible. If so adding red would obviously solve the problem.
> Another highly speculative alternative would be that the spectrum is such
> that photosynthesis is made to sense a low amount of light. Primarily the
> amount of light, but also the balance of energy between the two
> photosystems in which the light reactions happen, affects the state of a
> carrier between them, and this carrier appears to inform plants of whether
> they are in high or low light. If the plants are made to believe they are
> in low light, when they are not, they will gear themselves for maximum
> light harvest, but then light absorption would result in various kinds of
> photodamage, particularly "photoinhibition", the destruction of the primary
> light energy acceptor.
Dr. Lopez's ideas are presented as speculation but I find them very
interesting just the same, and I thought others on this list might be
For my part, I'll probably replace my remaining Ultralumes with full
Incidentally, it appears that Ultralume isn't the only trichromatic bulb
on the market with a dirth of red light and a small spike in the far red
band. The spectrum for the "Gamma Visible Spettro Triton" that I posted
on my site (http://www.rt66.com/~rgrmill/philips/spectra.html) shows the
same pattern. Interestingly, the spectrum for the "Triton Tube" on Jeff
Dietsch's site (http://www.voicenet.com/~dietsch/fishpics/lightspc.jpg)
(thanks, Jeff) has a spike at slightly lower wavelengths, in the red band
instead of the far red.
In Albuquerque where its windy... no, its raining... no, its dry.