Not So Simply Red

Last Updated (Monday, 02 November 2009 15:56) Written by Raymond Nakamura

While exploring secrets of the universe on Facebook, I noticed a friend's comment in Toronto wondering where the reds were this fall. As I raked through the internet for information, the true colours of this question turned out to be more complex than I expected. 

Leaves contain different pigments. The yellows and orangey ones are always in the leaves, along with the green. They capture different colours of light and help with photosynthesis. When the green chlorophyll breaks down in the fall, these colours remain. You can separate the pigments in a leaf using chromatography. The red, however, is actually manufactured in the leaf. It varies in intensity from leaf to leaf and from year to year.

So the physical explanation for why leaves change colour seems pretty well understood. But the metaphysical explanation still seem up in the air.

Some scientists think that the colours of the leaves can be used as information. The colours of flowers and fruits attract animals. The bright colours of certain animals often indicate  they taste bad (unless they are pretending to be something that tastes bad). The changing colour of leaf might tell insects to bugger off because the leaf was: A) falling off soon; B) developing toxins; C) losing nutrients; or D) not green anymore.

SIMCHA LEV-YADUN; KEVIN S. GOULD. What Do Red and Yellow Autumn Leaves Signal? The Botanical Review 73 no4 279-89 O/D 2007.)

The red colour in leaves has two leading explanations about the pigment: E) it protects the leaf tissues from the sun and F) it absorbs free radicals produced when the leaf is under stress.I don't know about you, but thinking about autumn colours in this way felt like I was turning over a new leaf, and it wasn't just a pigment of my imagination.