Continuing the theme of our sly silent nonhuman companions (many of whom are dying around here, too):
We moved our Book Scanning computer (“doesticks”) to our upstairs office from our basement today. As I mentioned earlier, it was a brilliant clear day. Sunlight reflected from the fall-foliaged maple tree in the treelawn filled the office with orange sunset colors, all afternoon. This is not just “orange” in the sense of a bright crayon, you know; this is fluorescence on a vast and brilliant scale. The sugar maple is re-emitting light in wavelengths quite different from what’s hitting it and reflecting off its leaves. All you need to do is look at it with funny-colored sunglasses to see the extra colors.
Now, it’s Autumn. And we all know why trees change colors.
But I was once a molecular botanist, see, and so I have, like secret knowledge only available to people who read obscure journals and teach biochemistry and stuff, all about phytochrome and other plant photoreceptors. And, dude, I’m sitting there in that glowing orange office thinking: they have to be able to see themselves. Where “see” is some odd distributed light-detection response.
Yes, sure, the coloration arises due to the breakdown of chlorophyll and related carotenoid photosynthetic pigments, and shifts in the colors of anthocyanins. And sure, the leaves are destined for abscission, and of course it would be stupid for the tree to hang onto them and risk dehydration by passive transpiration in the dry cold months of winter. And I can see where you’re going evolutionarily, with your just-so adaptive stories: there’s no animal reader for a tree to signal in Fall, no pollinators, not even many pests to speak of. And yet some species make what looks for all the world an extra effort to be brilliant and fluorescent.
What are they up to? Who are they waving these red flags at? Because of my secret molecular botanist training, I just don’t trust ‘em to be as dumb as their popular reputation would imply. Because, when you get right down to it: there are many trees that don’t bother with a showy display in autumn.
Who are these showoffs talking to, and what are they saying?
I don’t know who they’re talking to or what they’re saying, but green leaves give off light that is not just re-emitted (chemiluminescence, presumably). We were once looking to measure the spectrum of this very weak light using a monochromator and a very sensitive photomultiplier when one of the fellows in the dark room put a small tear in the leaf. The PMT saturated immediately. It was as if the leaf was screaming.
One can’t help thinking of Mullah Nasruddin searching for his lost car keys under the streetlight.
I was just told in passing (but in a forest ecology course) that fluorescence was often a way of dumping extra light, when the light/water ratio was too low for non-damaging photosynthesis.
Does the fall color come after the tree shuts off the water to its leaves? Is the blazing color the bremsstrahlung as the abandoned leaves rage against the dying of the light?
(Could I fit more half-baked metaphors in?)