I guess I thought that a tree's leaves all changed color at the same time, but I have noticed that this is not the case. It seems that the leaves that recieve the most sunlight change color first, but why? And why are there so many different colors? Most trees have leaves that are some shade of green, so why do they change to a miriad of different colors- red, orange, yellow...?
I decided to research these questions and was suprised to find that there are not any easy answers. In fact, I was a bit confused at times. This is the simple explanation I came up-
- All leaves contain chlorophyll (green color) and carotenoids (yellow and orange color). Cholorophyll is necessary for photosynthesis (conversion of carbon dioxide and water to oxygen and sugar).
- When the days become shorter and there is less light available for photosynthesis, trees start to conserve energy by decreasing the rate of cholorophyll production in the leaves (keeping it from doing photosynthesis, basically killing it). This makes them turn from green to yellow, orange.
- The red color in leaves is sugar that was made inside of the leaf by photosynthesis but then trapped there because the cold weather closed the leaf's veins and made it unable to send the sugar into the tree. That's why the leaves on the outer part of a tree's canopy turn color first, because they get more sunlight but then get colder and "die" faster that the leaves that are protected inside the canopy.