1. AUTUMN LEAF ABSCISSION

2. Autumn Leaf Abscission
A process that occurs in deciduous plants in preparation for the onset of winter.

3. *decrease in number of hours for photosynthesis to occur.
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

4. Factors that create the best fall color!
*Additional factors that contribute
to leaf coloration:
- Temperature
- Moisture
- Wind (can cause leaves to fall before full color develops)
Factors that create the best fall color!
Sunny days
Cool nights (but not below freezing)
Low rainfall

5. 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.

6. 2. Due to the lack of water, chlorophyll production ceases = existing chlorophyll degrades =
green color gone!

7. 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.

10. 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.

12. 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.

16. *Area with intense color for a short period of time = New England

17. *Area with gradual change that lasts for weeks =
Southern Appalachian Mountain range.

19. PA Grand Canyon

24. *Area with intense, but not very diverse color =Rocky Mountain Area