Transcript autumn leaf abscission - Dallastown Area School District Moodle

AUTUMN LEAF
ABSCISSION
Autumn Leaf
Abscission
A process that occurs in
deciduous plants in
preparation for the onset
of winter.

As the growing season ends in the
northern hemisphere, and winter
approaches, the amount of
sunlight in a 24 hour period of
time begins to decrease.
*decrease in number of hours for
photosynthesis to occur.
*decrease in the intensity of
sunlight
*Additional factors that contribute
to leaf coloration:
- Temperature
- Moisture
- Wind (can cause leaves to fall before full color develops)
•Sunny days
•Cool nights (but not below freezing)
•Low rainfall
Factors
that
create
the best
fall color!
Steps in the Process:
1. ABSCISSION LAYER
forms = a corky layer
of cells that blocks
the flow of water
into the leaf and
the exit of
carbohydrates
out of the leaf.
2. Due to the lack of water, chlorophyll
production ceases = existing
chlorophyll degrades =
green color gone!
3. Once the green color is gone, all
of the other accessory pigments
(help collect sunlight for photosynthesis)
are revealed.
* The first to become visible are the
yellow XANTHOPHYLLS and
the orange CAROTENOIDS.
4. New pigments, called
ANTHOCYANINS, are
manufactured from the sugars
that are trapped in the leaf.
These pigments create red and
purple colors.
*This pigment is not typically present in
all leaves during the growing season.
4. The abscission layer becomes
more dry and the leaves fall from
the tree.
* Eventually the xanthophyll, caretonoid,
and anthocyanin pigments degrade and
the only pigments that remain are the
TANINS which are brown.
*Area with intense color for a
short period of time =
New England
*Area with gradual change that lasts
for weeks =
Southern Appalachian Mountain
range.
PA Grand Canyon
*Area with intense, but not very diverse
color =Rocky Mountain Area