In the Forum there have been many links to scholarly explanations of how fall colors form. The 'standard' theory is that by default the color would be yellow due to the carotenoids already present except when anthocyanins are produced which will mix with the carotenoids to give all the hues from orange to fiery red depending on the amount of anthocyanins produced. The mystery as to why the plant would embark in the synthesis of this new molecule at the time when the leaf is going to drop appears to be now solved: anthocyanins are a 'low cost' sun-screen that will give more time to the plant to recover all the sugars stored in the leaf. It ensues, if this explanation is correct, that no-sun ==> no reds. That's why we see often the outer leaves red and the inner ones (receiving less or no sun) yellow. That's also why we see variations from year to year depending on the amount of sunshine in the fall. In my experience with the maples in my garden, all species and cultivars, seem to confirm this for all of them with one exception. This exception is Acer amoenum and its cultivars: they take the same color, year after year, irrespective of exposition and amount of sunshine. An 'Osakazuki' will turn the same red in sun, shade, fog, sleet or snow :) . I do not have an explanation for this, are amoenums genetically designed to produce the anthocyanins without external trigger? The picture is of Acer amoenum 'Mon zukushi'.It is planted behind the (3-story) house, north side under a terrace. It sees some dappled sunshine until early September after which no sun whatsoever. It turns the same red each year by mid-November. Gomero
Thanks gamero for observation of red amoenum, i appreciate. I have some young ' oh-momiji ' (seeds collected in Japan) they need some more light in october to turn yellow and orange in 10/20 november. A 3 years 'yama-momiji' (from seed) becomes bright red without direct sun. (southwest of France too) We can also said : Resulting of the chimical modifications , in autumn leaves keep green and blue light but throw out red and yellow . (refering to sun spectrum). Very interesting forum. Sorry for my english.
This is my Acer, In 2012 it went extremely red (UK) Its the reddest its ever been. Its never been fed, watered only in the height of summer. It got every element wind/rain/snow etc, never bothers it. Its my favorite Acer.
