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Abscission Layers Forming

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As the days grow shorter and the nights longer, cells near where a leaf’s stem joins a tree’s branch start to divide rapidly. This is the start of the creation of the corky layer of cells known as the abcission layer.

The annual growth of a tree ends with the formation of the abcission layer. This layer prevents the transport of materials such as carbohydrates from the leaf to the branch and it blocks the flow of minerals from the roots into the leaves. Chlorophyll, critical to the process of photosynthesis, breaks down with exposure to light and is replaced continually by the leaves during the summer. When the abcission layer forms, this is no longer possible.  The chlorophyll slowly breaks down and disappears, revealing the underlying xanthophylls (yellow pigments) and carotenoids (orange pigments) that the chlorophyll was masking. These pigments, in addition to the red pigments (anthocyanins) that are manufactured from sugars trapped in the leaf, provide us with our brilliant foliage.

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10 responses

  1. Elizabeth

    Thanks for this. Best, clearest explanation I’ve seen for why leaves change color in the fall.

    October 17, 2016 at 8:24 am

  2. I second Elizabeth’s comment – thanks for this clear explanation! The only question I still have relates to the chlorophyll: where does it come from? Is it “manufactured” chemically by the plant, from other compounds? How does this work?
    What a wonderful leaf you found to photograph, to lead us into all this!

    October 17, 2016 at 8:49 am

  3. Tom Jones

    Very nice, as always Mary – just a note that not all trees have abscission layers – white oaks & Beech for example. You know more of this than I, just a note. Your blogs are an important part of my day, I love them. Thank you so much. – Tom

    October 17, 2016 at 9:10 am

    • You’re absolutely right, Tom, and I thank you for mentioning that not all deciduous trees form abcission layers. I think marcescence is the term used to describe leaf retention and I believe it’s most common with many of the oak species, American beech, witch hazel, hornbeam (musclewood), and hophornbeam (ironwood). Thanks again!

      October 17, 2016 at 9:44 am

  4. Kathryn

    And brilliant, it is! I have never seen or imagined color like we have this year. Makes any minute outside (from a walk in the yard to a long drive) colorfully magical!

    October 17, 2016 at 10:07 am

  5. Kevin Thompson

    Is the abscission layer formed prior to the color change? I believe I heard an explanation on NPR that said at the end of the season the tree reclaims the nitrogen from the leaves as the chlorophyll breaks down, and only then forms the abscission layer.

    October 17, 2016 at 10:22 am

    • I honestly have not heard this sequence before, but will do some research. It obviously conflicts with what I wrote, so I’d like to know if I’m correct or not!

      October 17, 2016 at 11:06 am

  6. https://en.wikipedia.org/wiki/Photosynthesishttps://en.wikipedia.org/wiki/Photosynthesis for dellwvt and I couldn’t agree with you more, Kathryn! What a foliage extravaganza! Mary, as always, loved this post. I know have 2 new scientific terms to use! Thank you!

    October 17, 2016 at 10:54 am

  7. Cheron barton

    VERY interesting!!

    Sent from my iPhone

    >

    October 17, 2016 at 7:22 pm

  8. Susan Wind

    There’s the word I was trying to think of on our walk. Abscission Layers. Please share with ALex. LOVNG U!!!!!!!!

    October 21, 2016 at 6:54 pm

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