Why Do Leaves Change Colors in the Fall?

I recently shared some of the ways trees are awesome. They are also awesome because their leaves turn to pretty colors when the weather starts to get cooler. But…why?

One of the important things plants do is photosynthesis, which is capturing light energy and turning it into sugar, which can be used later by the plant or eaten by another species and used as fuel. The capturing of light energy is done by a pigment called chlorophyll. A pigment is a chemical in a cell that has color, which doesn’t sound like a very good definition, but it tells you a lot about what chlorophyll does. Chlorophyll appears green, which is why leaves and other plants look green. If something appears green, it’s because it is reflecting green light back into our eyes and absorbing of the other colors in the rainbow. Chlorophyll works so well because, although it reflects green, it absorbs other colors in sunlight, like red and orange and purple. It can then use this light to make food.

Leaves don’t only have chlorophyll, though. They have other pigments like carotenes, which look orange.

When the temperatures start to cool and the hours of sunlight start to decrease, many plants stop making chlorophyll because, well, why bother? If there’s not enough sunlight, it’s better to save the resources and hunker down until spring. As green chlorophyll starts to break down, some of the other pigments, like orange carotenes, remain. Carotenes are always there, but are usually hidden beneath all that chlorophyll.

The plants also start producing pigments like anthrocyanins, which makes some leaves reddish-purple. Anthrocyanins also protect the leaves against damaging UV rays, kind of like sunscreen does for us.

Eventually, the plants give up on the leaves altogether, and they fall to the ground, leaving the branches bare until they start making new leaves in spring.

Not only are fall leaves pretty, but they also show a pretty cool way the trees save their resources for months with longer hours of sunlight!

Sources:

https://www.thoughtco.com/pigment-definition-4141440

https://www.esf.edu/pubprog/brochure/leaves/leaves.htm