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You're listening to Shortwave from NPR.

Hey, shortwavers, Emily Kwong here.

Now, depending on where you live in the U.S., 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 NPR'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.

They're 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.

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 not 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 is 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

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