Why do some leaves turn yellow in autumn, while others turn red?
• Leaves contain various coloured pigments. The pigments carotene (orange), xanthophyll (yellow) and chlorophyll (green) are found in leaves all the way through spring and summer. Chlorophyll is the dominant one, effectively hiding the other two pigments and giving the leaves their green colour.
In autumn, chlorophyll is typically the first pigment to break down and disappear from the leaf, leaving behind the yellow and orange to show through.
Advertisement
Anthocyanin (a red pigment) is a little different. Only a few types of tree can produce it and, even in those that can, it is not present throughout the growing season, but is only made in the autumn. Anthocyanin production increases in dry, sunny autumns. It is thought that the pigment protects the leaves from the sun, slowing down the process of leaf death. This gives the tree a little longer to gather useful nutrients from the leaves before they drop.
Jo Dempster, Glasgow, UK
We pay £25 for every answer published in ¿ìè¶ÌÊÓƵ. To answer this question – or ask a new one – email lastword@newscientist.com.
Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.
¿ìè¶ÌÊÓƵ retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.
You can also submit answers by post to: The Last Word, ¿ìè¶ÌÊÓƵ, 25 Bedford Street, London WC2E 9ES.