Tree change
The shorter days of autumn and winter mean there is less light for plants to use photosynthesis, and trees will close up food production and allow chlorophyll to disappear from the leaves. This is when we start to see the lovely colours of orange, red, pink, purple and yellow.
The fact is that these colours have been in the leaves the whole time but we can’t see them because the green chlorophyll covers them up. At the leaf base there is a layer of cells called the abscission layer that forms a seal between leaf and tree, through which water and nutrients pass during summer.
In autumn, these cells swell into a corky material and eventually cut off the supply chain from the tree to the leaves. The leaf can trap only waste material and glucose and, without a supply of water, the leaves lose their chlorophyll.
Red and purple hues are caused by the presence of antioxidants called anthocyanin pigments, which incidentally colour beetroot, red apples and red wine. It’s interesting to know the antioxidants in the leaves of trees also can be found in other food groups. The brown colour comes from tannin, the orange from carotene (same as carrots) and the yellow colour comes from xanthophyll, as seen in bananas and egg yolks.
These pigments help protect the leaves from frost and sunburn and any remaining sugars and nutrients can be fed back into the tree for a longer period of time. Some scientists believe that when the dried leaves finally fall to the ground, anthocyanins seep into the ground and inhibit germination of competing species.
