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Re: Green light
> As far as I know, green light is not a requirement for normal growth and
> is used much less efficiently than other wavelengths.
> On another note, freshwater ecosystems do absorb light with fairly high
> extinction coefficients. Particulates, DOC, phytoplankton, zooplankton
> all absorb at particular wavelengths... the result is a light spectrum
> that is vastly different from incident radiation and one that is CHANGING
> all the time. IMHO this makes aquatic plants extremely well adapted to
> scavenging any and all PAR.
The generalization I've read is that in freshwater bodies both the blue
light and the red light are strongly attenuated with depth; red light
being attenuated by the water itself and blue light being attenuated
mostly by organic material in the water. The result is that the middle
(greenish) part of the spectrum might be expected to predominate at depth
in fresh water. Personally, when I've been in deep fresh water it usually
just looked dark.
Given that, I expect that plants adapted to growing submersed in deep
freshwater will be able to use every last scrap of available PAR. I think
that describes some Potamogetons and Isoetes - probably some others, as
I don't know that very many of the plants we keep in aquaria are adapted
to that setting. From what I've seen and read, it seems to me that most
are either emergent plants (e.g. most crypts, many echinodorus and
sagittaria), floating plants (water sprite, etc.) or plants adapted to
shallow water where their leaves lie on or just under the water surface
(e.g. val, probably aponogetons and many stem plants). It don't think
that these plants would need to scavenge for their light.
Sorry about the speculation. Sometimes there's just no substitute for