Autumn is my favorite season of the year. Temperature are getting lower and trees become yellow, orange and red.

To understand why leaves change color, we must first learn why they are green.

The green color of leaves is due to a chemical compound called chlorophyll. When sunlight hits the leaves, chlorophyll absorbs the red and blue components of light and reflects the green one, which is the color that we see.

Chlorophyll is not the only pigment present in leaves, we can also find carotenoids. These pigments absorb the blue-green and blue components of light and reflect the yellow one.

A third class of pigments is characterized by anthocyanins. They absorb the blue, blue-green and green components of light and reflect the red one.

During the summer these three types of pigments are all present in the leaves, but chlorophyll is the most abundant, leading to the green color of leaves.

Autumn causes a great change in trees, all pigments are slowly destroyed, but this process is faster for chlorophyll. While the abundance of chlorophyll decreases, carotenoids and anthocyanins are still there and by reflecting yellow and red light, allow us to enjoy the amazing color of autumn.

What is your favorite season of the year?

References:

Ougham et al., “The Colors of Autumn Leaves as Symptoms of Cellular Recycling and Defenses Against Environmental Stresses,” (2005), 10.1016/S0070-2153(05)66004-8

Keskitalo et al., “A Cellular Timetable of Autumn Senescence,” (2005), https://doi.org/10.1104/pp.105.066845

“The chemicals behind the colours of autumn leaves”, https://www.compoundchem.com/2014/09/11/autumnleaves/