Don received a letter from Research Scientist, Dr Dugald Close, who is associated with the Cooperative Research Centre for Sustainable Production Forestry, at the University of Tasmania. In the letter, Dr Close explains why leaves colour reddish shades in autumn, and why the new growth on some plants is red.
Leafy solar panels
Leaves collect light, just like solar panels, but too much light can actually damage the leaves. In new shoots the chloroplasts (which contain green chlorophyll) are not yet developed. So plants replace the green chlorophyll with red pigment (or anthocyanins) as a kind of sun block for the new growth.
Autumn colour
Deciduous trees and shrubs draw back all the valuable chemical nutrients from the leaves before they drop. As the chlorophyll is taken out, the plants pump anthocyanins back into the leaves to stop them being damaged by the sun.
Frost damage?
Dr Close also pointed out that when leaves are very cold after a frost, they can’t protect themselves from sunlight. So damage after frost is actually photo damage, or sunburn.
Further information
CRC for Sustainable Production Forestry
Website: www.forestry.crc.org.au/