Autumn Trivia | Why do leaves change color?

Autumn Trivia | Why do leaves change color?
November is the time of year when the autumn leaves are at their best throughout the country. Have you already made plans to go see the autumn foliage?
This time, I would like to introduce a trivia on the mechanism of autumn leaves.
So how do the fascinating red and yellow colored leaves get their color?

The autumn foliage is the preparation for the shedding of leaves

紅葉
During the spring and summer seasons when the temperature is high, the tree's leaves gain nutrients in the chloroplast from energy obtained through sunlight. This process is called photosynthesis.
However when autumn comes and the temperature falls, the tree cannot gain enough energy to hold all of its leaves.
For this reason, the tree prepares to drop its leaves, and the leaves change color as if to finish their roles.

Carotenoids are responsible for turning leaves yellow

北海道大学
▲The carpet of golden maidenhair trees lined up at Hokkaido University
While some kinds of trees turn red, there are other kinds that turn yellow. In any case, the colors change in the order of "Green→Yellow→Red".

First, I would like to talk about the process of how the green leaves turn to yellow.
When temperatures fall and the leaves stop photosynthesis, the amount of chlorophyll that controls photosynthesis in the leaves decrease.
Originally, leaves have a pigment called carotenoids that support the photosynthesis of the chlorophyll. As photosynthesis decreases, the chlorophylls break down and their green color fades, causing the yellow color of the carotenoids to stand out. This is how the leaves turn yellow.

Anthocyanin turns the leaves into a red color

毘沙門堂
▲The stone steps of Bishamondo filled with blazing red maple leaves
Next, the transformation of color from yellow to red is caused by the increase of anthocyanin.
There are various theories explaining the increase of anthocyanin, so I would like to introduce one of them.

When the temperatures drastically fall (lowest temperature of 5~8°C), the pace of the two functions of gaining energy from the sun and creating nutrition from the energy become imbalanced.
When this happens, the tree creates new anthocyanin to maintain this balance and to continue photosynthesis until the last minute before the leaves fall.
Therefore, the cooling down of the temperature causes the leaves to turn red.

紅葉のメカニズム

▲The mechanism of the autumn leaves changing color


In conclusion, this was some trivia on the process of how autumn leaves get its color.
The vivid colors of the autumn trees are very impressive. Try remembering these mysterious mechanisms the next time you walk under autumn leaves.


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