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Making red plants really red


I'm glad this subject has come up again. I remember speculating, some time
back, that _blue_ light was used more by red plants.  My simplistic
reasoning at the time was that red plants reflected more of the red end of
the spectrum, so therefore they must use more of the blue spectrum.  I
placed all my red plants underneath where I'd installed a 9W blue, 7100K
compact fluorescent.  Perhaps coincidentally, the plants there were quite
red. Not long after I'd installed the blue light, though I changed the
lighting in my hood, and made a host of other changes, all of which caused
my plants problems for quite a while, so I don't know whether the red
growth I'd seen suggests anything meaningful about the effects of blue
light.  However, the most amazing redness I've seen is in a 60 gal tank
with 270watts of VHO, actinic white lighting, which I presume has a lot of
blue in it.  The substrate is a thin layer of silica sand, with regular
aquarium gravel over it.  The horemannii "Red" in there is indeed an
almost black purple/red.  There is also a bunch plant whose i.d. escapes
me, which also has incredibly dark purple 'red' leaves.  When I get over
there to re-charge the CO2, and add some fertilizer (Flourish, cichlid
salts and potassium nitrate) the bushiness of this red bunch plant
increases, and leaf growth begins further down the plant.  I had
attributed the redness to the blueness of the light, but that was before I
knew about anthocyanins, and before I'd read about Neil's Rotala
macrandra, which was maroon in a 70 gal w/ a mere 80watts of light.  At
any rate, I took a snipping off the the bunch plant, placed it in a cup
with a thin layer of sand, and the rest Flourite, and moved it in to a 10
gal with 27 watts (1 13 watt 5000K compact fluorescent, 1 aquari-lux, a
bulb that has a nice M shaped spectrum, but is not very intense, at least
in lumens, fwiw).  The tank has CO2 injection and according to the KH/pH
charts, maintains CO2 in the 10 to 15 range.  Strangely, though other
plants in there are thriving, the red bunch plant is not maintaining its
redness, and neither are the Red Melon Swords. It's been a few months.
Last week, I moved the bunch plant in to my 25 gal, which has 70watts of
T-8 lighting and CO2 etc.  We'll see what happens.  The bulbs in there are
two 5000K, two 6500K, and the macrandra "pink" is indeed a nice pink
colour.  I still suspect that it is blue light which can really bring out
the redness of plants, but i suppose we'll have to see what real
scientific experimentation tells us.

			Andrew  



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