Dec 06, 2021 | written by: Lara Zambonelli
If you type #autumncolors or #autumnvibes into Instagram, you’ll get about 300 million results. We’re all crazy about autumn colours, but how many of us know why leaves turn yellow, red and orange at this time of year? It’s the kind of question a child would ask, in that it’s only seemingly straightforward.
Why do leaves change colour in autumn?
Because life gets harder in winter.
To protect ourselves from the cold, we humans take our jumpers out of the wardrobe, turn on the heating and put on our warm shoes. Trees can’t do this, but they can protect themselves in other ways.
They slowly start to withhold precious chlorophyll from their leaves. Chlorophyll is the green pigment that enables leaves to convert sunlight and water into sugars through photosynthesis. In other words, it’s what allows trees to eat.
So, at the time of year when the days become shorter and the temperatures drop, trees break down chlorophyll to extract its nutrients and store them safely in their roots. They build up reserves.
And without chlorophyll, the leaves lose their green colour.
Why do some leaves turn yellow and others red or orange?
Because in the absence of chlorophyll, other chemicals become visible and finally get their 15 minutes of fame:
- carotene, which gives the leaves a yellow colour;
- anthocyanins, which turn them red and purple.
This way, the nutrients are safe in the roots, and we get to see the multicoloured vistas we love so much. When not a single drop of chlorophyll is left, the leaves dry up and fall off. At our latitude, this happens in autumn and winter, but that's not the case all over the world. Tropical trees, for example, shed their leaves during the dry season: they’re discarded to reduce transpiration and conserve available water.
If you’ve made it this far, you’re a curious person. Have you ever wondered if trees move? And how do they do it? And what are the Dynamite Tree and the Chewing Gum Tree?
Sources
- http://www.scifun.org/chemweek/fallcolr/fallcolr.html
- https://www.americanscientist.org/sites/americanscientist.org/files/200610285126_306.pdf
- https://www.nature.com/articles/449982a
- https://www.nationalgeographic.org/encyclopedia/rain-forest/
- http://www.trafioriepiante.it/infogardening/giardino/Coloriautunno.htm
