Anthocyanin Crimson

I have been looking for words to express the red color of anthocyanins in fall leaves. The thesaurus gives me many delightful words for red such as the color of blood, bittersweet, bloodshot, blooming, blush, brick, burgundy, cardinal, carmine, cerise, cherry, chestnut, claret, copper, coral, crimson, dahlia, flaming, florid, flushed, fuchsia, garnet, geranium, glowing, healthy, inflamed, infrared, magenta, maroon, pink, puce, rose, roseate, rosy, rubicund, ruby, ruddy, rufescent, russet, rust, salmon, sanguine, scarlet, titian, vermilion, and wine - some of which (anyone heard of cerise?) are a bit obscure. Whatever you call it, red is definitely one of God's favorite colors, especially around fall.

Anthocyanins (an-though-SIGH-un-ins) are what makes fall leaves red. These pigments are produced in the leaves of deciduous trees as they transition to winter. The leaves will soon be lost, so the trees withdraw their nutrients and store them away as the leaves die off or senesce. Unlike carotenoids, which are present in the leaves throughout the year and are revealed by fading chlorophyll, anthocyanins are produced in the leaves as the leaves are dying.

But it seems illogical to use energy produce new compounds in a leaf that is already on its way out, right? This question has stumped scientists for a long while. They have proposed all kinds of interesting theories for why leaves produce anthocyanins in the fall. One theory that has recently stood out is that anthocyanins are protective compounds that keep the leaves on as long as possible to make sure the tree can suck all the nitrogen out before they fall. Anthocyanins, like carotenoids, are powerful antioxidants and could be protecting the leaves from oxidative stress. In addition, anthocyanins absorb UV and can act like a sunscreen to protect the leaf from light stress (and here I thought that trees couldn't get sunburned).

So the anthocyanin is like a shield detachment sent to cover the retreat of nutrients from the leaves. With anthocyanins, the leaves stay on longer and the tree can store away more nitrogen. But the anthocyanins still cost energy to produce, so trees that grow in nitrogen-rich conditions will be less red because the extra nitrogen that they get isn't worth the investment in the sunscreening anthocyanins. Trees that grow in nitrogen-poor conditions, on the other hand, will glow like red-hot embers as they try to protect as much of their nitrogen as they can.

American Goldfinch

Today I have seen a handsome American Goldfinch (Carduelis tristis (L)) on my balcony feeder for the first time. He surprised me when I first saw him, small and unassuming in shape but bright big-bird yellow with black wings crossing his back and clashing with his yellow like crime scene tape. He's been visiting it frequently all day as I watch from the couch, alternately falling asleep, working, and wasting my afternoon. My Audubon guide says that American Goldfinches wait to pair up until late in the summer when tasty seeds tend to be more plentiful. Other species with broader diets are already busy parents, laying eggs and rearing multiple broods of chicks while the Goldfinches are still flocking around in big irresponsible groups.

This makes me smile. The goldfinches have their appointed time for relationship and parenthood, but it's later than the other birds' time. They flock together like anxious graduate students waiting to see how the seeds will shake out before they settle down and start that family. I wonder if my goldfinch has transitioned into family life or if he's still hanging out with all his yellow friends.

Photo by Flickr user Jason Means licensed for non-commercial use by Creative Commons.