Why do leaves change color in autumn?

2023-10-13

Every autumn, most of the trees will wear red and yellow autumn clothes, so the question is: why do the leaves turn yellow in autumn? What is the reason? Although this is a very common phenomenon, maybe you can't really explain it when you explain it. Let's find out.

Before introducing the color change of leaves, we must first popularize several substances that cause the color of leaves: chlorophyll, carotenoids, anthocyanins.

Chlorophyll: In chlorophyll, there are many different family partners, the most common being chlorophyll A and chlorophyll B. They are insoluble in water, but soluble in organic solvents such as ethanol, acetone, etc. The chlorophyll in the plant body is mainly involved in the light absorption process in photosynthesis, it can absorb most of the red light and purple light, but reflects green light, so chlorophyll appears green, the secret is here!

Like other substances in the living body, chlorophyll is constantly being synthesized and broken down. Its synthesis process requires strong light and higher temperature. In spring and summer, because the amount of chlorophyll synthesis is greater than the amount of decomposition, the decomposed chlorophyll can be replenished in time; In autumn and winter, the amount of synthesis is not as good as the amount of decomposition, and the decomposed chlorophyll is often not supplemented. So that's why, the leaves turn green in spring and degreen in autumn.

Carotenoids: Speaking of carotenoids, we want to introduce carotenes and lutein. They are also insoluble in water, soluble in organic solvents, photosynthesis, they mainly absorb blue-violet light, which can assist chlorophyll to capture light energy. Carotenoids are relatively stable compared to chlorophyll and are not easily affected by changes in the external environment, so when the content of chlorophyll decreases in autumn, the proportion of carotenoids increases accordingly, so that the leaves appear yellow.

Anthocyanins: Anthocyanins have a large family with more than 300 siblings in nature. The colorful flowers, fruits and vegetables we usually see are related to anthocyanin accumulation. The anthocyanins in cells are mainly found in vacuoles, which itself has no color, but after dissolving in water, it will produce different colors under different pH conditions.

In late autumn, as the temperature decreases, the ability of the leaves to transport sugars and water is weakened, and glucose continues to accumulate, resulting in higher and higher concentrations. The increase in soluble sugars makes the cells acidic, and under acidic conditions, anthocyanins turn red, so the leaves turn red.

The chlorophyll in the leaves usually breaks down when autumn comes, and the nutrients in the leaves are also redistributed to the trunk and roots to help the trees survive the winter when the sun is scarce, and after the leaves lose chlorophyll, the yellow carotenoids that are already present will be revealed, which is the reason why the leaves of some trees turn yellow in autumn.

The redness of leaves is mainly caused by anthocyanins, which are usually produced by leaves when autumn arrives, the purpose of which is to delay the time of leaf withering to ensure more nutrients for wintering.

Botanists also point out that the color of autumn leaves and the morning and evening of leaf fall are related to the amount of rainfall or snowfall. If in a dry year, the color of the leaves will not change much, and the leaves will fall earlier, this is to retain more water for the tree. It seems that storing nutrients, retaining more water, and falling leaves are a means for trees to "lose their pawns and protect themselves".

Whether it is yellow leaves, red leaves, or beautiful autumn scenery, under the cold winter wind, the leaves of deciduous trees will eventually fall, leaving only bare trunks. Therefore, please cherish the beauty that trees bring to you every season.