Tuesday 3 November 2015

WHAT IS AUTUMN COLOUR?


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Autumn is my favourite time of year because the changing leaf colour always reminds me of the start a new year at school or college, having fun trudging through the leaves and bonfire night.

 Trees during the autumn mirror the bright fireworks in the sky, with leaves turning red, yellow, purple, black, orange, pink, magenta, blue and brown. This autumn colour can be stunning and is certainly worth a visit to a woodland or arboretum to observe.
Deciduous plants shed their leaves in autumn due to a number of factors including high level of maintenance required for a vastly reduced return via photosynthesis, insect predation, water loss, and damage from high winds or snowfall.

 The shortening of daylight hours and reduction in temperature triggers the dormancy of trees and therefore autumn colour. A special cork layer forms at the base of each leaf, reducing the fluids carried into and out of the leaf.  As this cork layer develops, water and mineral intake into the leaf is reduced, slowly at first, and then more rapidly. It is during this time that the chlorophyll begins to decrease.

 Autumn colour occurs due to a number of chemical changes within leaves, which affect the coloured pigments within them. Pigments within the leaves give leaves their distinctive colour; Chlorophyll (green), Carotenoids (orange-yellow) and Anthocyanins (reds and purples).  

 The brown colour of leaves is not the result of a pigment, but rather cell walls, which may be evident when no colouring pigment is visible.The amino acids released from degradation of these pigments are stored all winter in the tree's roots, branches, stems, and trunk until next spring when they are recycled to re‑leaf the tree.

Chlorophyll

 Chlorophyll plays an essential part in photosynthesis, converting the sun's rays into energy. Chlorophyll is therefore most abundant during the growing season (summer). It is the presence of chlorophyll within a leave makes it green, which masks out other colour pigments that may be present in the leaf.
In late summer, as daylight hours shorten and temperatures cool, the level of chlorophyll reduce and the leaves lose their green colouring. As the chlorophyll's degrade, the hidden pigments of yellow and orange are revealed. Red pigments form when half the chlorophyll has been degraded. 

 Carotenoids

Carotenoids are present in leaves the whole year round, although are masked when chlorophyll is present. As the level of chlorophyll reduce at the end of summer this masking effect fades away and the pigments begin to show through. 

 Anthocyanins

A group of pigments in the cells called anthocyanins are responsible for the reds, the purples, and their blended combinations. Unlike the carotenoids, these pigments are not present in the leaf throughout the growing season but are actively produced towards the end of summer.

 Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced. The brighter the light during this period, the greater the production of anthocyanins. The brightest colour display results when the days of autumn are bright and cool, and the nights are chilly but not freezing.
For related articles click onto:
What is the difference between a woodland and a forest?

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