Why do leaves change color in the fall? This is a question that many people have asked themselves as they observe the plants in a forest change from shades of green to warm autumn colors. We can observe that the leaves seem to change when the morning and evening starts to get cooler and when the amount of daily sunlight decreases, but what is going on inside the leaf?
Thankfully, scientists have tools and a desire to know how things work that have led some of them to study this natural phenomenon and illuminate a bit of this everyday mystery, though they still don't understand all of it.
The short answer is that the leaf is made up of many plant cells and each cell contains many different components - all doing a specific job. The chloroplasts are the part of a plant that gives it the ability to photosynthesize or make its own food. The chloroplasts contain green pigments called chloraphyll.
During the growing season, the leaves look green, but as the air cools and the sunlight decreases, the
hlorophyll starts to break down. The green color goes away and the yellow and orange pigments, the carotenoids, that have always been in the leaf show through. The carotenoids absorb lightwaves that the chlorophyll cannot, increasing the plants ability to photosynthesize.
The red and purple colors occur from chemical reactions that take place in the plant leaves in the fall that produce anthocyanin pigments. These act like a sunscreen as the tree pulls in the last bit of sap from its leaves. There are more red pigments seen in years when it is sunny and dry, because the sugar in the sap is more concentrated and the tree is trying to get all of it stored before it goes dormant for the winter.
So next time you are enjoying the autumn landscape, take a moment to consider the complexity that allows it all to be and your sense of awe will increase.