The New England office of Cambridge Polymer Group is fortunate to see the brilliant color display every fall as the foliage undergoes its autumnal transformation. Our work in polymer chemistry naturally starts us down the path of wondering what is happening to the leaves to cause this color change.
The colors in leaves come from three principle sources:
Chlorophyll is responsible for photosynthesis in leaves, and provides them with their green color.
Anthocyanins provide the reddish colors found in fruits such as cherries, strawberries, and cranberries.
Carotenoids provide the orange, brown, and yellow colors in fruits and vegetables like bananas and corn, as well as egg yolks and flowers.
Chemical composition of leaf color
Chlorophyll is produced during the growth of plants, typically in the spring and summer when there is more daylight, resulting in the lush green appearance we associate with those seasons. When the days start to grow shorter resulting in less light, chlorophyll production slows and eventually stops. The chlorophyll eventually degrades and disappears, along with its green color. The remaining pigment types, anthocyanins and carotenoids, which were there all along but dominated by the green chlorophyll, now emerge.
Species vs. Weather
The amount and type of color will depend on the species of tree or bush, but also depend on the weather leading up the fall. Warm days and cool nights will result in the production of sugars in the leaves during the day, with the cool nights keeping the sugars in place by closing off the veins in the leaves. The sugars aid in production of anthocyanin, or the red colors we clamor to see in late September in the New England area.