Carotenoids, xanthophylls and anthocyanins – these plant pigments ensure that leaves shine in bright colors in autumn: they usually turn yellow, orange, red and even violet, blue or blue-black in September and October. The color of the leaves depends on the tree species: Poplar leaves turn golden yellow, maple leaves usually glow yellow and orange and red oaks get fiery red foliage. But why do the leaves change color in the first place?
This is why leaves change color
The coloring of the foliage is in a way a preparation for the winter – and a survival instinct. Before the cold winter months, trees shed their leaves to protect themselves from drying out. Because a tree evaporates a lot of water through its leaves – and less water can be drawn from the frosty winter ground than in summer. In winter, the leaves would not survive possible frost damage anyway. So you can leave. But before that, the tree secures a molecule that is essential for its survival: chlorophyll.
Dye in leaves: chlorophyll turns them green in spring and summer
Chlorophyll is necessary for photosynthesis. It enables trees to absorb carbon dioxide from the atmosphere and process it into glucose using light energy and water. The sugar obtained serves as an energy source for the tree. When it gets colder in autumn, the days get shorter and there is less light, the trees react: they strip the leaves of the chlorophyll to store it in other parts of the tree – in branches, roots and the trunk – until next spring . The trees slow down their metabolism. The process is triggered by plant hormones.
And chlorophyll has another property: it is the pigment that turns leaves green in spring and summer. Due to the decline in the green pigment, the other pigments in the leaf – carotenoids, xanthophylls and anthocyanins – become visible in autumn and ensure colorful foliage.