Autumn is upon us in many parts of the country. This beautiful time of year is brought on by changing light levels and to a lesser extent cooler temperatures. A decrease in light levels causes chlorophyll inside the leaves of deciduous trees to fade away- essentially not be replaced. As the chlorophyll fades other pigments present all year begin to shine through. Some tree species only have one other type of pigment- like tulip poplars only contain yellow pigments. Other tree species like maple can have more than one type of pigment, yellow and red. In maple leaves other factors determine the final color during autumn. While the exact process is not fully understood, it is believed that temperature and pH differences determine if the yellow or red pigments predominate.
Several types of pigments are listed in the table below. Ask your students, why do they think plants need more than one type of pigment? (An answer suggestion can be found on our Facebook or Twitter page.)
| Pigment Type | Color | Wavelength (in nanometers) |
| Carotenoids | Yellow, orange, red | 400-500 nm |
| Chlorophyll a & b | Green | 350-490 nm & 625-675 nm |
| Anthocyanins | Red | 450-590 nm |
| Flavonoid | Yellow, red, blue, magenta, purple | 225-465 nm |
Use the web links below to help you:
http://www.hometrainingtools.com/leaf-experiments/a/1235/
http://www.uaf.edu/olcg/globalchange/phenology/pigment.pdf
