Hey guys, when leaves change colour, it’s generally from green to yellow, to orange, to red to brown. My son asked me why the leaves the change colour and I vaguely know that chlorophyll makes them green, but I don’t know what happens to make the other colours. I guess the chlorophyll is leaving (heh) the leaves, so that takes away the green, but what drives the other colours? Thanks in advance!
It’s partially a result of chemicals that were already there, and partially chemicals that are made at the same time as the chlorophyll is broken down. And it’s different for different plants, which is why there’s such a range of colors.
And the yellow carotinoids have important functions in the leaf. Chlorophyll is green because it reflects rather than absorbs green light. The main job of the carotinoids is to absorb those middle wavelengths that chlorophyll reflects and pass their energy on to chlorophyll so it can be used in photosynthesis. (They can also serve to dissipate excess energy.)
And here’s a fun fact- even though Europe has the same types of trees that show vivid fall colors in North America, like maples and oaks, those trees in Europe don’t display the same vivid bright reds and deep oranges that they do here. The reason for that has to do with mountain ranges and insect migration patterns:
As I understand it, warm days and cool nights change the sugars within the leaves. This causes the formation of the above-mentioned anthocyanin, which makes the red colors. Cooler days or warmer nights prevent that formation, leaving the browns and yellows.
here in the high desert in ca most of the leaves don’t fall …. they just turn to leaf dust when they freeze
It’s my understanding that the reds, oranges, and yellows are always there but they are hidden by the chlorophyll. The best analogy is a bucket of green paint filled with red marbles. All you see is green until the paint is drained.
See the second post. Yellows and oranges are from carotinoids which are always there. Reds are from anthocyanins which are manufactured in the fall.
I’m glad this has been clarified. I’ve seen people asset that all of the colours were there all along, including the reds, and that never made sense to me.
Leaves that turn red often* (when fresh) look green both by reflection and transmission - if there was some ‘hidden red’ in there, I would expect them not to look green in both of those cases.
*I know there are leaves that have a red underside or similar, but I’m not talking about those.
Is there some magic high/low temperature combination that causes leaves to turn the brilliant colors that they do in the north? Here in South Texas (and my limited experience with North Texas in the winter) most deciduous tree leaves just turn slowly brown and gradually fall off from December to February. Some will have a yellow stage, but it’s not the bright yellow, and definitely none of the oranges and reds, you would see in the Ozarks, Appalachians or New England(I have no experience of the northern plains or the Rockies).
The first part of October here in central Ohio was considerably warmer than normal and leaves showed little sign of turning color. The latter part has been more like November, and especially in the last week the leaves have been changing over to fall plumage.
This is supposed to be a banner year for Texas foliage.
There are some anthocyanins present in leaves year-round, as you can find by separating the colors using filter paper. But there are more of them in the fall.
As a fun fact, anthocyanins are also the reason why many fruits turn red as they sweeten and ripen. The pigment is made from sugars, and so only shows up when enough sugar is present. Hence why maples, with their sugary sap, turn such bright red.