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  • Writer's picturemeredith conaty

The science of autumn leaves

Did you know that the changing colours of leaves in autumn is so dramatic in some parts of the world, that you can even see it from space? One of the few pleasures of this COVID-19 lockdown is that its such a beautiful time of the year - so at least in our daily exercise we have something nice to look at.

So next time you walk past a tree which is changing colours have a good look, and take some leaves so you can look at them in detail and work out what is happening. It's fun for the kids to line them up and see how the leaves are changing.

Did you know that the leaves don't just go red, but they go through a very specific progression of colours as particular nutrients are "remobilised"? Nutrients are moved from where they've been stored or used in the leaves and then can be stored in the plant's branches, trunk or roots over winter. Each year deciduous trees and plants carry out this mass movement of these nutrients essential to their survival, to enable them to grow again in spring.

The different colours represent complicated processes occurring in the leaves, as the plant prepares itself for cold temperatures and low light in winter. Several complex compounds are broken down into small molecules, which can be stored in the plant ready for when temperatures and light levels increase again in spring, and some of these compounds are plant pigments.

One of the first compounds to break down in autumn is chlorophyll - which is the name of the pigment that gives leaves their green colour. As this breaks down the leaves lose their green colour and other pigments have their turn to shine.

Carrotenoids make plant tissue look yellow and orange, and after the chlorophyll starts to break down the carotenoids begin to take over the colouring of the leaves.

Once these begin to breakdown, another set of pigments can shine through - the anthocyanins, which make leaves turn red and sometimes almost purple.

So have a look at the leaves around you! Beautiful and complicated and definitely something to enjoy.

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