AAUUTTUUMMNN LLEEAAFF

AABBSSCCIISSSSIIOONN

AAuuttuummnn Leaf Leaf AbscissionAbscission

A process that occurs inA process that occurs in deciduous plants deciduous plants inin

preparation for the onset preparation for the onset of winter.of winter.

As the growing season ends in As the growing season ends in the northern hemisphere, and the northern hemisphere, and

winter approaches, the winter approaches, the amount of sunlight in a 24 amount of sunlight in a 24

hour period of time begins to hour period of time begins to decrease. decrease.

*decrease in number of hours *decrease in number of hours

for photosynthesis to occur.for photosynthesis to occur.

*decrease in the intensity of *decrease in the intensity of sunlightsunlight

*Additional factors that contribute*Additional factors that contribute

to leaf coloration:to leaf coloration:

- - TemperatureTemperature

- - MoistureMoisture- - WindWind (can cause leaves to fall before full color (can cause leaves to fall before full color develops)develops)

•Sunny days

•Cool nights (but not below freezing)

•Low rainfall

Factors that

create the best

fall color!

Steps in the Steps in the Process:Process:

1. 1. ABSCISSION LAYERABSCISSION LAYER forms = a corky layer forms = a corky layer of cells that blocks of cells that blocks the flow of water the flow of water into the leaf and into the leaf and the exit of the exit of carbohydrates carbohydrates out of the leaf. out of the leaf.

2. Due to the lack of water, 2. Due to the lack of water, chlorophyllchlorophyll production ceases = production ceases = existing chlorophyll degrades = existing chlorophyll degrades =

greengreen color gone! color gone!

3. Once the green color is gone, all 3. Once the green color is gone, all of the other accessory pigmentsof the other accessory pigments

(help collect sunlight for photosynthesis)(help collect sunlight for photosynthesis)

are revealedare revealed. .

* The first to become visible are * The first to become visible are

the the yellow yellow XANTHOPHYLLSXANTHOPHYLLS and the and the orange orange

CAROTENOIDSCAROTENOIDS. .

4. New pigments, called 4. New pigments, called ANANTHOTHOCYCYANANINSINS, are , are

manufactured from the manufactured from the sugars that are trapped in sugars that are trapped in the leaf. These pigments the leaf. These pigments

create create redred and and purplepurple colors. colors.

*This pigment is not typically *This pigment is not typically present in all leaves during the present in all leaves during the

growing season. growing season.

4. The abscission layer 4. The abscission layer becomes more dry and the becomes more dry and the

leaves fall from the tree. leaves fall from the tree.

* Eventually the xanthophyll, * Eventually the xanthophyll, caretonoid, and anthocyanin caretonoid, and anthocyanin

pigments degrade and the only pigments degrade and the only pigments that remain are thepigments that remain are the

TANINSTANINS which arewhich are brownbrown. .

*Area with intense color for *Area with intense color for a short period of time = a short period of time =

New England New England

*Area with gradual change that *Area with gradual change that lasts for weeks = lasts for weeks =

Southern Appalachian Mountain Southern Appalachian Mountain range.range.

PA Grand Canyon

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