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Why do leaves change colour?


Why do leaves change colour?

Autumn foliage is fully on display. A dramatic mix of colours like purple, red, yellow and orange. 

But have you ever asked why we see this palette of colour?
The result is part of a chemical process that's underway.  

The Green leaf

During the warmer months, the leaves on trees serve as food factories; manufacturing and storing the necessary nutrients needed for the tree's growth. In the leaf, there are numerous cells containing chlorophyll - a pigment which gives the leaf its green colour.  This magical chlorophyll chemical absorbs sunlight, carbon dioxide, and water then converts it into energy-conserving carbohydrates, such as sugars and starch. This gets stored in the roots and in the leaves.

The turn and fall

When the days get shorter and temperatures change the leaf struggles to run its food-making factory. The trees start moving their nutrients from the leaves to the roots. The chlorophyll breaks down into smaller particles, the green fades and other pigments start to overpower. Once the tree uses the leaves supply it drops the leaf and seals the patch, conserving its energy for winter.

So, why the different colours?

This colour changing transformation occurs with deciduous trees, seasonal shredding trees.
Let's break down the colour pigments.
Carotenoids are common pigment in the leaf, they produce yellow and orange.
Anthocyanins are more complicated, not all trees have this pigment. They show the red, pink, and purple colors. The prevailing theory is that anthocyanins are triggered to protect leaves from excess sunlight so the leaf doesn't dry out and the tree can recover the remaining nutrients. Sunlight increases sugar concentration. The tree releases anthocyanins so it can panic grab the nutrients before the leaf goes dry.

The weather plays a major role in this autumnal transformation. Still, sunny days will produce vibrant reds, add brilliance and longevity colour turning trees. Freezing, wet, overcast days will cause trees to make their seasonal drop sooner than later.