Leafy chemistry: What happens when a leaf changes colour in autumn?

Discover the science behind autumn's vibrant leaf coloiurs and their role in trees' life cycles and survival strategies.

For a moment, close your eyes and imagine yourself in the fall season. The cold, chilly wind kisses your face, and the leaves begin to dance gracefully as they fall off the tree. What’s the first thing you notice about the leaves? That they change colour before they fall off. But how? Asked and answered.

Usually the trees that are deciduous (plants or trees that shed leaves annually) have leaves that change colour. They have large and broad leaves.

Most of the year, these trees are green throughout the year because of chlorophyll content. And if you have learnt in school, chlorophyll is important to absorb sunlight during photosynthesis, and the leaves convert sunlight into energy and energy into sugars to feed the tree. This pigment is constantly produced throughout the spring and summer. Other pigments are present, but in much lesser quantities.

As seasons change, the weather gets colder towards the last few months of the year. Days also get shorter with time. Trees get less direct sunlight, and hence, the chlorophyll in the leaves begins to break down. This in turn leads to other pigments being produced in higher quantities, marking the trees’ preparation for winter.

The leaves eventually fall off when nutrition is cut off, and they decompose, enriching the soil for the next life cycle.

Visitors walk inside a Mughal garden as they enjoy during the autumn season, in Srinagar, Kashmir. | Photo Credit: IMRAN NISSAR/The Hindu