Archimedes Plutonium wrote in
:



Thu, 07 Oct 2004 12:59:54 -0500 Archimedes Plutonium wrote:
(all snipped except)


Water movement explains the variability.


It maybe something in the sap of the tree as it starts its Autumn
migration and hibernation for winter.

So I need some chemical compound in photosynthesis of tree leaves
(amur maples in particular) and I need both sap and water as to
how sap and water can alter the visual appearance of this chemical
compound from green to purple to yellow to red to brown.

It maybe how fast the sap migrates out of the tree. Or water
migration. Or both sap and water. It maybe the sap itself is the
color determinant.

But it is obvious that sap and water are the key determinants
because the explanation of why a amur maple has fringed red on its
outermost leaves. Fringing is a pattern that follows the sap and
water movement.

Chris, you have not done too well on this discussion and in fact
done very poorly. So let me ask you a new question. Do plants and
trees prefer or is it in their interest or to their advantage to
have a wet Autumn considering that they are readying themselves
for sap migration and hibernation for the winter. So do they
prefer a "dry Fall" or do they prefer a wet Fall?


I agree that Chris has done poorly in the discussion, preferring to
scoff at your lack of knowledge instead of showing the way that you are
mistaken.

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