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- photoperiodism (plants sensitive to lack of light), sensitivity to daylength results from light-sensitive pigment (phytochrome), exists in 2 forms (Pr and Pfr, each absorbing diff type of light and ratio changes depending on light levels)
- summer has high temps and long days, autumn has opposite, lengthened dark period triggers abscission and periods of dormancy
- less light means less auxins so leaves form ethene, abscission zone (made up of 2 layers of cells sensitive to ethene) at base of leaf stalk, ethene initiates gene switching here to form enzymes that digest/weaken cell walls in outer layer of abscission zone (seperation zone), vascular bundles (carrying materials) sealed off and fatty material deposited in cells on stem side of seperation layer (forming protective scar when leaf falls), cells deep in seperation zone swell with water and strain outer layer further, and abiotic factors finish process (leaf falls)
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