Re: [AGA Member] Plant Pigmentation Discussion (somewhat long)

["Roger Miller" <roger@spinn.net>]

On Tue, 23 Sep 2003 14:36:41 -0400, Phil Edwards wrote

> I've been told by people who have been to the tropical jungles that 
> there is almost no light in the understory/ground level.  In a 
> jungle {aquatic or not :)} all of the overstory plants use Red-
> Violet light.  Taking into account the density of green reflecting 
> leaves in the canopy, very little green light makes it into the 
> understories of a jungle.  This is also true of red light and the 
> spectra more to the left side of our visable spectrum.  This is 
> caused by the longer wavelength and decrease in penetrating power of 
> those spectra.  The farther right we go on the spectrum the shorter 
> the wavelength and higher the penetrating power of the light.

My statement that light in a forest understory is strongly green was based on
reported measurements of spectral intensity in forest understories.  So
despite the reasoning there is some data that has to be dealt with :).

> A forest/jungle canopy is almost totally analagous with water.  The 
> farther down one goes the more attenuated the spectrum is and the 
> more blue the light gets.

Umm, light transmitted through a fresh water body -- aside from getting dim
real fast -- should get more green with depth.  That is because a) water
adsorbs more light at the red end of the spectrum, b) organic compounds in the
water adsorb more light at the blue end of the spectrum and c) phytoplankton
in the water transmit or reflect light in the middle of the spectrum, but
adsorb light at both ends of the spectrum.  Obviously the whole effect will
vary a lot from water body to water body depending on the relative roles of
the water itself, organic compounds in the water and phytoplankton in the
water.  In sea water where organic constituents and phytoplankton are rare the
light tends to get blue with depth.

As I think Scott and others were getting to, the reddish pigments in plants
probably have more than one role.  The pigment has a role in plants growing
under bright light that seems different from the role it plays in forest
understory plants.  That multiplicity may cause problems in your research.


Roger Miller

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