Fall colours: Why summer’s weird weather has affected the leaves – Canada – CBC News
Canada has had some weird weather this year and that has had an impact on the fall colours now on display in some areas. As well, historic patterns of when trees are at their most colourful, and how colourful, may be shifting due to climate change.
Before autumn, the healthy leaves on deciduous trees get their green colour from the chlorophyll molecules in their microscopic factories, or chloroplasts, that convert water and carbon dioxide into sugars, other carbohydrates and oxygen.
The chlorophyll hides the yellow and orange pigments present in the leaves because it is so intense. In autumn, trees stop replacing the chlorophyll in their leaves, which then breaks down, allowing the other pigments to become more and more visible.
The proportion of pigments varies by species. Maples have lots of anthocyanin, for example, which gives a red colour. Anthocyanin is abundant in leaves in early spring but as the leaves grow it breaks down.
Scientists debate why some autumn leaves on some tree species turn red. “The best guess is that some of the pigments, such as carotenoids [which produce the yellow and orange pigments], help absorb sunlight, while carotenoids and anthocyanins help protect the chlorophyll from UV damage, which leaves are especially prone to in cold weather,” Gorelick explains.