A fall mystery: why do only certain leaves turn red?
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What is the main topic discussed in this episode?
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You're listening to Shortwave. From NPR. Hey short wavers, Emily Quang here. Now, depending on where you live in the US, you may be enjoying some fall foliage. You know, the result of colder days, trees preparing for winter, and in some, their chlorophyll, the green pigment, is breaking down. And instead of green, we're seeing these amazing colors: yellow, orange, and red. Colors you might tuck into a home decoration. Along with some of those mutant squash you get at the farmer's market, the really warty ones. Hey Nell. Hey! That's NPier's Nell Greenfield Boyce. And Nell, from what I understand, you have been getting really into autumn leaves lately. Well, some of them, some of them.
Particularly the red
ones. I love the red ones.
So beautiful. People like red leaves. And you know, when I met up with this biologist named Nikki Hughes in North Carolina, she told me My
dad always was talking about his quest for the perfect red leaf. Mm, respect. So it's
been this lifetime thing, but she's on her own quest now, and that is just to understand red leaves. Why red leaves? Why why
not yellow?
Why do some leaves turn red in the fall while others stay yellow?
So yellow is in the leaves all along. It's kind of hiding in there, right? And so you mentioned chlorophyll breaking down in the fall. And when that happens, it's because the tree wants to recover some key nutrients like nitrogen. Nitrogen's really precious to a plant. It's needed for everything from photosynthesis to making proteins and DNA and so You know, the tree is going dormant kind of in winter, but it doesn't want to lose that nitrogen. It wants to hang on to it. So the chlorophyll gets busted up, the green is going away, and this exposes yellow, right? Okay. And scientists agree on that. The yellow is there, it gets exposed. The red is this completely different thing. Oh. Because the red is actually made brand new in the fall.
Like Mickey picked up this one maple leaf, which was this kind
of mottled red on yellow. The red was not there beforehand, or you would have seen it, so the leaf would have been purple, because green plus red equals purple. So the question is
Why does the tree bother to make this red?
Especially since the leaf is about to fall and die anyway. Why go through?
Exactly. Like within l days, the leaf is doomed. So why go to the effort, why go to the trouble of making new red colors? And I should note here that these red pigments are also responsible for the leaves we see as orange. Okay. Like Nikki Hughes picked up this other leaf from like a tupelo tree that was red and dark orange. And she said if you looked at what appeared to be orange. Under a microscope, you see lots of red freckles.
Red freckles, that's so cute.
How does chlorophyll breakdown reveal yellow pigments in autumn leaves?
Okay, today on the show, the mystery of red leaves. What are scientists' best ideas about what a tree might get from going
ginger? Join us as we rustle up some autumn leaf biology here on Shortwave, the science podcast from NPR.
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Chapters
6 chapters
1
What is the main topic discussed in this episode?
0:00–1:34
2
Why do some leaves turn red in the fall while others stay yellow?
1:34–3:10
3
How does chlorophyll breakdown reveal yellow pigments in autumn leaves?
3:10–7:11
4
What biochemical process creates the new red pigment in dying leaves?
7:11–11:59
5
Can red leaf pigments act as a sunscreen to protect leaves from excess light?
11:59–15:28
6
Do red leaves help trees avoid insect damage and herbivory?
15:28–16:49
Speakers
4 identifiedMore from Short Wave
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