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Leaf Abscission: Definition & Purpose

Leaf Abscission: Definition & Purpose
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  • 0:01 What Is a Leaf Abscission?
  • 0:48 How Does Abscission Work?
  • 2:27 Why Do Leaves Abscise?
  • 2:58 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista
Every year we see trees drop their leaves in anticipation of winter. This actually has a specific purpose and reason. Abscission occurs in many different plants for a variety of reasons, and in this lesson, we will look at the specifics of abscission.

What Is a Leaf Abscission?

Abscission is the shedding away or cutting off of different parts of an organism, generally a plant. When you see a plant dropping its leaves or its fruits, this is a form of abscission. Leaf abscission is simply when a plant drops its leaves.

As is commonly seen, deciduous, or leaf bearing trees, drop their leaves in preparation for wintertime. Coniferous, or cone bearing trees, also drop some of their needle-shaped leaves, though not all of them, just before winter. But coniferous trees also drop their needles periodically throughout the year. That's why if you look at the ground around a pine tree, you will probably see lots of needles.

How Does Abscission Work?

In terms of how leaf falling occurs, we can look at the environment at the time of abscission. This process generally occurs during the fall when we see the weather beginning to cool and the growing season ending. As the autumn and winter months approach, the leaves from all leaf-bearing trees and the needles from some pine trees, such as the larch, will drop.

Oftentimes, the process of abscission is brought on by a number of factors, including lack of chlorophyll, which is the light-absorbing pigment that makes leaves green. In the autumn months, we see a reduction in the number of hours of sunlight. This causes a slow-down of photosynthesis, the method by which plants make food by absorbing sunlight and taking in carbon dioxide and water. When photosynthesis slows down, there is a reduction of chlorophyll in plant leaves. This then allows the leaf to turn colors, depending on the other pigments in that particular leaf. The pigments xanthophylls, carotenoids, and anthocyanins will cause the leaf to turn yellow, orange, or red. Which color the leaf turns will depend upon the particular pigment in the leaf. The leaf then falls off.

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