Why do autumn leaves change colours?
Friday, November 6th, 2009Going out for a walk today, I was enthralled by the beautiful play of autumnal colours. Varying from green over yellow to ochre, bright red and brown – autumn lets the tree’s leafs so beautifully coloured.
Why do autumn leaves change colours | Picture: Gerhard W.
But what is the clue about this brightness of colour? In spring and summer, these leafs are green. This green colour is due to the presence of so called chlorophyll, which is the most important biological pigment for plants, because it absorbs the sunlight and makes it available for Photosynthesis. Photosynthesis is the biochemical process which allows the plants to obtain energy from sunlight. In summer, the yellow to reddish pigments like Carotene, Xanthophyll and Anthocyanin are superimposed by the green pigments of the chlorophyll. Leafs contain many important nutrients, the plant needs for its growth in the next spring. This is the reason why in autumn the chlorophyll in the leafs is being broken down into its constituent parts. Particularly the “staple foods” – Nitrogen and Phosphate – go into the branches and the trunk where they are stored.
The yellow to reddish colours remain and give the leafs the bright colours. But this isn’t the whole clue yet: Chemical metabolism processes increase the formation of Anthocyanes in the dying leafs. These can even turn the cells colour into a deep red.