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Light and Node Distance

Michael Cordero wrote:

>hi all .. i would like to ask if light intensity, spectrum, etc
>would affect the way my stem plants grow .. meaning that how light
>affects node distance .. i think it was K randall who stated .. that
>more blue light makes the plant grow bushy and smaller leaves .. and
>shorter nodes .. i would like to establish that my stem plants have
>leaves with closely packed nodes this makes a few stalks look like
>a bunch of plants clumped together .. PLEASE COMMENT

>PS - correct me if im wrong karen

Thanks, I will.<g>  I did say that blue light promotes shorter, bushier
growth, while red light promotes taller, lankier growth.  This wasn't an
original statement on my part though, it's pretty well documented in
horticultural literature. I didn't say anything about leaf size.  The
trouble is that people have taken the above statement to mean that you can
(should?) emphasize one end of the spectrum over the other.  What I was
trying to get across (and obviously failed, since this has come up numerous
times<g>) is that with our present knowledge or lack thereof, it would seem
prudent to provide good balanced coverage at both ends of the spectrum.

As far as long internodes and small leaves, in my experience, this is most
likely a sign of inadequate intensity, rather than the "wrong" spectrum,
what ever that is.  Aquatic plants are remarkably adaptable, and live in a
_very_ complex environment.  It is tempting to make assumptions about cause
and effect, but unless the same response is seen by a large number of
people under a wide variety of "other" conditions (varying substrates,
nutrient supplementation, CO2 supplementation, plant species, etc) I would
hesitate to say that the ONE factor involved with any difference in growth
pattern is the specific spectrum used.

This is one of the reasons that "scientific" experiments are interesting,
but not always very useful for aquatic gardening.  The experiments are
usually done with a limited number of species, often not those commonly
used in aquaria, in very strictly controlled environments for relatively
short periods of time.  It's not that the finding are not valid, it's just
that there may be many other factors that can skew the results in the
working aquarium.

For instance, and I'm _NOT!!!_ suggesting that this is true... it is a
hypothetical example -

What if an experiment was set up to run for 60 days showing the effect of
red spectrum light and blue spectrum light over a specific plant.  At the
end of the 60 days, it is clear that the plants in the blue light are
shorter, but bushier.  What happens if you extend the blue only light
regime indefinitely?  Do those plants continue their growth pattern?  Do
they eventually dwarf themselves?  Is the fact that they are shorter a
response to spreading out under the blue light, or is it a sign that the
uptake of a specific mineral is being blocked, leading indirectly to the
shorter growth?  If you can isolate the mineral shortage, can it be
compensated for by adding more of this nutrient?

We don't know the answers to any of those questions.

It is good to discuss all this, and I think very helpful to share
experience.  But I think we need to be _very_ careful about drawing

Karen Randall
Aquatic Gardeners Association