Summer ends, and the only solace before the arrival of winter is the beauty of autumn. Fall colors are seen in deciduous trees and shrubs before they shed their leaves to conserve water in bitter winters. I immensely enjoy watching the lush greens transition to yellow-red; it’s like a rainbow on the ground. Why do the leaves present us this colorful visual treat before falling off? Before I reveal the mystery of these colors, think about how the bacteria in Grand prismatic spring display such distinct colors. If you know the answer now, read on. If not, take a look at this.

Yellow colored leaves are due to carotenoids

Yes, the answer, in this case, is also pigments. The pigments responsible for fall colors actually exist in the leaves throughout the year; we just don’t see them! The green color of the leaves is due to a pigment called chlorophyll, which helps them produce energy in the presence of sunlight. When the days are long with plenty of sunlight, this pigment is abundant in the leaves, masking all other colored pigments. As the days shorten after summer, there are physical changes in the plant that cut-off food supply to the leaves. So, chlorophyll production becomes lesser over time, unmasking the other pigments like carotenoids, which are yellow and orange in color. Need proof? Check out this simple experiment to confirm the presence of different pigments in leaves: https://www.education.com/activity/article/Leaves_Change_fifth/.

Green, yellow, and red colors in leaves are due to pigments chlorophyll, carotenoids, and anthocyanin, respectively

Why are these pigments present in the leaves anyway? Carotenoids help in photosynthesis and protect chlorophyll from harsh sunlight. However, the red colored pigment, anthocyanin, is not present in the leaves throughout the year. It is produced only in fall from the remaining carbohydrates from the leaves. One idea of its use involves co-evolution: insects and plants usually exist in symbiotic relationships¹. So, indicating their poor health with the red pigment is a signal to insects to lay their eggs somewhere else. The trees, in turn, benefit by getting rid of their parasites through this honest signaling. Think of it as showing off your empty pockets to discourage muggers from targeting you!

Once again nature impresses me with its plans, and beauty, of course. Meanwhile, looking forward to a spirit-uplifting fall!

Further reading

1. Archetti, Marco. “The origin of autumn colours by coevolution.” Journal of Theoretical Biology 205.4 (2000): 625-630.