But have you ever wondered why trees shed their leaves, or what's responsible for the stunning colours of autumn?
When groundwater freezes it becomes difficult to draw up enough water to replace the water lost by transpiration, so in autumn, deciduous plants shed their leaves to reduce water loss.
One of the first chemicals in the leaves that's broken down is chlorophyll. Chlorophyll is the green pigment that absorbs light to fuel photosynthesis. The plant absorbs the products of breakdown and stores it for spring. When the chlorophyll breaks down, other photosynthetic pigments are revealed.
Carotenoids are 'accessory pigments' that absorb light energy and pass it to chlorophyll, and also protect chloropyll from being damaged by high energy ultraviolet (UV) radiation from the sun. A famous carotenoid is beta-carotene in carrots, which is good for you because it's an antioxidant, and it can be turned into vitamin A. Fucoxanthin is what makes some seaweed and algae brown. Anthocyanins also protect plant tissues from UV.
|Wavelengths of visible light absorbed by chlorophylls and carotenoids|
From LED Grow Lights
The most stunning range of autumn colours is produced with sunny days and cool nights. The sunny days promotes the synthesis of yellow pigments, which makes the colours more intense. Cool nights slows down the transport of sugars from the leaves to the roots, so the extra sugars left in the leaves get turned into red anthocyanins.