The Miracle of Autumn Colour

The Miracle of Autumn Colour This year has seen a brilliant display of autumn colour as leaves change from green to reds and yellows. The green colour of leaves is through the presence of chlorophyll, a highly complex molecule – C₅₅H₇₂O₅N₄Mg – that absorbs radiation from the sun from 400nm to 700nm wavelength. Through the highly complex process of photosythesis this energy is used to form glucose – 6CO2 + 6H2O + E → C6H12O6 + 6O2 In springtime, warmer temperatures bring about the physiological activity that leads to new growth, formation of xylem and phloem and the transfer of nutrients and rising sapflow. Macro nutrients such as Nitrogen and Magnesium are essential for formation of Chlorophyll and micronutrients such as Iron and Manganese. As leaves start to flush photosynthesis begins to produce Carbohydrates. During the summer months the tree needs to produce more Carbohydrates than it uses thus providing a store for the winter and the following spring. During the Autumn period the cooler temperatures and lower light light levels reduces the photosythesis and production of Chlorophyll starts to slow. As the Chlorophyll is gradually broken down, Carotenoids such as Beta Carotene – C40H56 and Flavonoids such as Flavonol – C15H10O3 which provide the yellow and orange colours start to dominate. These colours are present in the leaf throughout the season but we only see the green. However if there is a nutrient deficiency that limits the ability of the tree to produce chlorophyll we see the leaves turning to yellow during the growing season. This is called Chlorosis. The Carotenoids absorb light from the green and blue spectrum but strongly reflects red and yellow light, hence the orange appearance. The Carotenoids also start to degrade at the same time as the Chlorophyll but much slower. In the autumn the physiological changes initiate the production of anthocyanins – C15H11O+ bringing out the strong red colour. It is generally thought that as the chlorophyll is broken down, the production of anthocyanins help to protect the leaf from the sunlight allowing the recovery of the last of the nutrients. Whatever the physiological processes are, to us we are privileged to see this glorious display of colour during the autumn season!!

For more information on The Miracle of Autumn Colour talk to Iros Arboriculture Ltd