Tuesday, September 28, 2010

Autumn Colors

One thing I am downright baffled by as I continue writing the Mycelial Network is how people who have real jobs maintain their blogs. I guess I’m just lazy. But not today!

It’s officially fall. The moon says so. And the leaves in my neighborhood have already started to change colors. This is one of those events, like that sun rising every morning, that we all expect. But how and why does this occur?

Chemistry of course! Most of us are probably familiar with one of the molecules in tree leaves that gives them their green color: chlorophyll. But tree leaves have other pigments in them as well from two major classes of molecules: carotenoids (I may have ranted about these when I talked about the red aphids. Carotenoids give most red things in nature their color.) and anthocyanins. These compounds aide the work of chlorophyll by absorbing additional wavelengths of light.

A quick note about color for those who’ve forgotten their high school physics: colors are produced by rays of light with different amounts of energy or wavelengths. So red, orange, yellow, etc. each have a very specific amount of energy associated with that color. When white light strikes an object some of those wavelengths are absorbed by the pigments in the object. The colors that are not absorbed are reflected to our eyes and that produces the color we see. For example: a red object is actually absorbing all or most wavelengths of light except for red. The red is then reflected to our eyes and we perceive that color.

So when autumn comes the days start getting shorter and the nights get longer. This begins to trigger trees’ response to get ready for winter. Deciduous trees’ leaves are not capable of surviving frost so they have evolved to drop them off to conserve energy during cold months and months of low sunlight. It’s simply not worth while to try to photosynthesize only a few hours a day. As this happens the chlorophyll begins to degrade but the carotenoids and anthocyanins remain, showing the pigments that were always present in the leaves but were unnoticed due to the presence of chlorophyll. Sometimes leaves simply turn brown and shrivel instead of turning a brilliant red, purple or yellow. This is because the other pigments have also degraded and waste material is building up in the leaves, giving them a brown color.

The range and intensity of the color change can vary greatly depending on weather especially rainfall and sunlight. These processes are still not entirely understood and scientists are working on figuring out the more precise patterns of autumn color change in leaves.

What other fall-related natural history topics would you like to see on the Network? Leave me a note and stay tuned for (hopefully) more from me soon.


University Of Wisconsin: http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html

USDA: http://www.na.fs.fed.us/fhp/pubs/leaves/leaves.shtm

Science Made Simple: http://www.sciencemadesimple.com/leaves.html

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