AUTUMN LEAF ABSCISSION

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

*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

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

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