Fri, 08 Oct 2004 07:15:55 GMT Sean Houtman wrote:
(snipped)


Leaf color has been studied. More important than soil moisture is the
combination of day length and air temperature. Deciduous trees in
temperate zones start to shut down leaf metabolism based on day length.
If the cool weather of fall arrives at a different stage of the
shutdown, then tissues in the leaf will die at different parts of the
cycle, leading to different colors.

Red colors come from Anthocyanins and Betaines in the leaf, which are
carried in vacuoles of the epithelial cells. Yellow colors are from
Xanthophylls, which are in the plastids of the pallisade cells. Those
plastids also have a lot of chlorophyll in them, which in deciduous
trees dies at a certain temperature. If the red pigments have been
removed from the epithelial cells by the time cool weather kills the
chlorophyll, then the leaves are yellow, if not, then you get red
leaves.

Soil moisture has some effect, as it influences the amount of sugars
that are in the leaf. The sugars don't actually react with anything to
make the colors, but they do affect the timing that the red pigments
are removed. In addition, if a tree never produces the red pigments,
you will never get red leaves.

This is simplified somewhat, you should be able to find some articles
on the web that go into more detail.

Sean

Okay, thanks, that explains why one year the amur maples were all yellow
and why this year they are mostly red.

I need to know something about trees and plants taking in water during
Autumn and Winter months.

I need an answer on whether plants and trees like a wet Autumn or prefer a
dry Autumn considering that they need to get water and sap out of their
systems in preparation for winter. And whether trees during winter take in
water and by how much? I guess they take in some water such as
strawberries.

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