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Not_Leopard_Seal t1_irru494 wrote

>I’d always just assumed “that’s the colour of a maple leaf without the chlorophyll bits,” but I’m realizing now that that seems naive.

That's actually pretty much it. Leaves don't just have chlorophyll serving as an energy acceptor from sunlight but also other antioxidants in less concentration who accept energy from red and yellow, but also from green light unlike chlorophylls who accept red, yellow and violet light.

Here is the absorption spectra of chlorophyll A and B as well as Beta-Carotine. You'll notice that Beta-carotine absorpts quite a bit of green light.

Once it becomes fall, trees notice a change in the red light ratio during dusk and dawn and begin a process that is called "reverse clorophyll biosynthesis". Because chlorophyll is a very expensive molecule plants don't really degrade it. They save it from the leaves and suck it up into the wood, where it stays in a different form for the winter. That's why the leaves, now empty of chlorophyll, have this yellow and red color. Once the leaf loses the antioxidants as well, it becomes brown and dies. The chlorophyll will become active again in spring and will provide energy again in new leafs.

So the vibrant colors are not really a signal for anything. Just a change in light accepting molecules.

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bitemark01 t1_irs4c7h wrote

That's interesting, I didn't know they pulled back the chlorophyll, thanks for the explanation!

Recently a few maples in our neighbourhood got infested with moths, one had all of its leaves eaten by mid-June. I thought it might kill the tree, but it popped out all of the empty leaf stems and simply regrew (smaller) the leaves. I always wondered what kind of energy expenditure it was for the tree to d o that, now it seems like more than I realized.

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Highwaymantechforcer t1_irs7lyj wrote

Complete defoliation of a bonsai maple can be performed in late June to encourage a full second flush of smaller leaves in a beautiful deep red colour, the tree has more than enough stored energy to do this. It only takes around 4 weeks to get back to a full dense canopy. Not recommended every year as it does consume energy but you can do it every few years. I assume a full size maple can withstand a similar treatment, certain seems so according to your observations.

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phred14 t1_irsr35m wrote

We had a major spongy moth caterpillar problem this year, hitting mostly oak, but our crabapple and a few other trees as well. All refoliated. I had wondered about the metabolic costs and trade-off, thanks.

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phred14 t1_irw7pax wrote

I forgot one exception. We have a white oak, and I've been told that they're wonderful trees to have. So I worked hard at keeping it clear of caterpillars, with some success. It partially refoliated where there was more damage, but kept on with the lightly damaged leaves. An interesting question in how much damage calls for refoliation.

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Krail t1_irsyyvq wrote

So, to summarize, there's a wide variety of different chemicals plants use for photosynthesis that all look different colors to us, and we just see the reds and yellows because plants are sucking up chlorophyl to store in wood for winter?

And then late leaves look brown because the leaves lose these other chemicals? Do they also store these other chemicals in their trunks over winter?

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IrvineRyan t1_iruq7sw wrote

Is there any noticeable effect on size, color, weight or any sort of composition of the tree when it pulls the chlorophyll back in?

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Not_Leopard_Seal t1_irvdjnh wrote

Size -> No

Color -> No

Weight -> Yes. It would lose multiple kg of weight because it gets rid of all it's leafs

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IrvineRyan t1_irvdrc3 wrote

No, that wasn't my question. Let me rephrase. You said chlorophyll is sucked up into the wood. I'm asking, after its sucked into the wood, if there's any change in the composition of the wood specifically. Especially in weight.

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kidnoki t1_irv7cd4 wrote

The colors actually aid in frost and UV protection. In the north as winter comes Carotenoids and anthocyanins will be produced at a higher rate, while reverse biosynthesis occurs revealing the deeper, reds, oranges, blues and purples. At least in cannabis, I can usually play with the final colors, by tweaking temps and also the pH on my feetigation, this can also change the sap and pistil color.

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