Digging into: why leaves change colors
Autumn has passed and winter is upon us. I often try to be outside as much as I can, especially since I work in a lab that doesn’t have a lot of access to windows or sunlight. No, it is not a dungeon.
Something that came to me while sitting on a bench outside during one of my lunch breaks was the magic behind the changing colors of the leaves on the trees around me. It led me to question how many people know why leaves change colors or how many people miss this golden opportunity to connect with nature in one of the most subtle ways.
So, why do leaves change colors? Let’s get digging.
Leave color depends on sunlight. Plain and simple.
During the summer and fall, our days are longer so the trees have more access to sunlight. Now, let’s get down to the smallest element of this process: chloroplasts.
Just like humans, plants are made up of hundreds of thousands of cells. They are different cells than human cells, but they have the same purpose: they allow the living organism to do what it needs to do to survive and reproduce.
Chloroplasts are present in every single plant cell, but why are they important?
This is where photosynthesis occurs. Photosynthesis is how the plant survives and creates its own '“food” or energy sources. Instead of going to the nearest grocery store, like the rest of us humans do for our energy supplies, plants have to make their own energy sources. They do this by absorbing sunlight (this is why plants need a lot of sunlight), carbon dioxide and water. Well, that is all fine and dandy that all of the ingredients are in the plant, but how do they get processed to be useable? Think: we can eat enough food for energy, but, if our stomach is not working to digest the food, then we won’t be able to get the energy or nutrients from the food.
That is where chlorophyll comes in. Chlorophyll is present inside chloroplasts that are inside all plant cells. Chlorophyll are a type of pigment that have the ability to absorb sunlight. Pigment is a common term we use for all sorts of things, like skin color, makeup, and dyes. There are four main pigments in plant leaves: chlorophyll, xanthophylls (zan-tho-phil), carotenoids (car-ra-ten-oids), and anthocyanins (antho-sigh-a-nins). Enough of the fancy words, let’s get to the important stuff.
Chlorophyll is a green pigment that has the role of absorbing sunlight and converting the carbon dioxide and water that the plant absorbs into oxygen that is realized into the environment.
Here is the take away: plants are green in the summer and fall, because this is the time of year when there is the most sunlight, and the plant is producing the highest amount of chlorophyll that can absorb the sunlight.
Now, what happens as winter approaches?
Our days get shorter, the air gets more chilled, we pull out our sweaters - the whole 9 yards. The leaves will start to transition from green to yellow to orange to red. After this transition, they will eventually fall off the tree and become a crispy pile on the ground that we get to play in or have the satisfaction of stomping on You know you can’t resist the urge to step on a nice crunchy leaf on the floor - we all do it.
As the amount of sunlight lessens, the less chlorophyll is made which is why the leaves start to transition from green to yellow. Unfortunately, I have to bring up those fancy pigment names again but I promise it is worth it:
Xanthophylls: These are yellow pigments made by the plant and start to become abundant in the leaves as less chlorophyll is made and less sunlight is available.
Carotenoids: These are orange pigments and start to takeover the xanthophylls as winter approaches.
Side note: Ever wonder why carrots are orange? The main pigment in carrots is beta-carotene, which is a carotenoid. BOOM.
Anthocyanins: Last but not least, these provide the red pigment to leaves and are most abundant when there is less sunlight available.
So, the leave color trend depends on which pigment is being made the most, and all of this depends on the amount of sunlight.
I hope you learned a little something about the world around you. Don’t forget to stomp on that crunchy leaf you walk by today and allow yourself to smile a little bit.
As always, stay humble.
- Emily
