Archimedes Plutonium wrote in message ...
Inyo wrote:


We have a Liquidambar (Sweetgum) planted in our front yard (the tree closely
resembles an Amur Maple, of course--and, yes, I know I know: Liquidamber is a
member of the Hamamelidaceae, not Aceraceae). The tree gets all kinds of water,
not only from the winter rainy season, but from our regular irrigation of the
lawn during summer, all the way up until the leaves fall completely off. The
tree seldom develops a stunning brilliant red Autumnal display that virtually
every other Liquidambar reveals around town during Fall. Our Liquidambar's
leaves remain, most years, a dull yellow, bordering on dingy brown. Depressing,
in the main. As I recollect, our Liquidambar does indeed seem to demonstrate at
least a modicum of reddish Autumnal glory when we've not watered nearly as much
during the summer, or early Fall. Could be merely coincidence, though; or,
perhaps the change is influenced by microclimates, or even differences in
ground chemistry caused by irrigation leaching ions from the
soil during our years of heavy watering.

Or it could be that the molecule responsible red color in Amur maple when combined
with water becomes red whereas a similar molecule in Sweetgum is the reverse color
of yellow. So that the molecule with alot of water is red for amur but yellow for
sweetgum.

No, the molecules are chemically unrelated. They are not in any way
identical or similar molecules that differ in hydration or anything of
the sort.

Yellow and orange pigments are various carotenes and xanthophylls.
These are pigments that are already present in leaf tissue when leaf
senescence (aging) begins. Destruction of chlorophyll causes these
pigments to become visible.

Red pigments are anthocyanins. Their biochemistry is well-known but
still the subject of much current study, because they are responsible
for red, purple, and blue color in many important ornamental and food
plants, and because there is medical and nutritional interest in their
antioxidant properties.

It is not fully understood what the adaptive value of leaf
anthocyanins is. Unlike the other fall color pigments, they are
synthesized rather than merely exposed. One hypothesis is that they
regulate light uptake or prevent oxidation damage, prolonging the life
of aging leaves under harsh fall conditions.

In trees that have variable fall color, environmental conditions do
influence anthocyanin production and thus influence fall color.
Anything that acts to send the tree into early dormancy, such as an
early hard frost, will impair anthocyanin production and thus impair
the red fall color display.

Water dependency makes sense on another dimension. When we cut a branch off of a
tree it never turns from green to red but always to yellow brown because the water
has been reduced.

Almost. It goes yellow-brown because it needs to remain healthy to
turn red. Cut it off, so that it won't live to produce anthocyanin,
and it won't turn red.

Now if this Liquidambar branch was broken does it tend to turn a reddish tint
before going yellow-brown? And why is it called "Liquid" and "ambar" in the first
place? Is it because it has something to do with red and water.

Proper coloring and abscission require that the leaf go through its
stages of aging while still attached to a tree that is supplying
nutrients. Break the branch off, and it loses its supply and just
dies.

The ornamental Liquidambar is Liquidambar styraciflua, sometimes
called Sweet Gum: it produces a viscous, amber-colored liquid that is
a usable substitute for styrax in medicinal and cosmetic applications.
Nothing at all to do with the leaf color.

As with other trees grown for fall color, there are varieties that
show one color reliably, and there are varieties that are variable.
Liquidambar is a common garden ornamental in mild-winter places,
because its varieties color reliably even in the absence of dormancy
signals such as chill. (I have Liquidambar trees that never see frost
but color reliably every November.)



On the other hand, the Chinese Pistache in our back yard receives prodigious
amounts of water during the summer and early Autumn--and that tree has no
problem turning brilliant red each and every year.

Finally, one last observation: most of the Liquidambars around our town are
pretty much neglected--the trees along the main streets and such. The only
water they apparently receive is from the customary winter and early Spring
rain cycles; and those Liquidambars, each and every year, virtually explode in
a brilliant display of vivid reds--gorgeous. They put our tree to shame.

Ornamental Liquidambars are bred to march to their own drummer, so to
speak. They color consistently with seemingly little dependence on
fall conditions. That's what makes them valuable in places that don't
have a sharp fall and winter. If only the big old ones didn't turn
into pavement-wreckers...

So, if the hypothesis that links reddish Autumnal leaf colors with the amount
of water delivered to a tree during the time the leaves begin to turn color
"holds water," bears credence, then our situation is directly opposite of
yours, at least with regard to the Liquidambar.


It maybe in that the chemistry of leaves and water are reverse of that between
amur-maple and sweetgum.

No, the chemistry of leaves is just about the same in both trees. What
you are overlooking is the operation (or lack thereof) of the
mechanisms of leaf aging. If the conditions are not conducive to
anthocyanin production *in that tree in that place*, you get no red or
reduced red color. Temperature is usually the most important
environmental condition: the more chill before killing frost, the
better the fall color. Early killing frost impairs fall color.
Adequate water during color formation improves fall color; drought or
flooding will more likely impair it.

--
Chris Green