Sunday, November 4, 2007

Red: the color of health. Sourwoods, dogwoods, and sweetgums.

Inspired by the "French paradox" of long lifespans in a population with a high-fat diet, some of us hope to stay healthy by drinking plenty of red wine. Many plants adopt a similar strategy by producing red leaf pigments in the fall. The spectacular reds and maroons that light up the autumn landscape are the colors of anthocyanins, a family of antioxidant compounds. These antioxidants protect plants (and us) against chemical injury caused by oxygen, a highly reactive and dangerous molecule.(1)

Some of the best red foliage is visible in Plainfield now. Red maples, sugar maples, and Japanese maples are famous for their red foliage. One of my favorite small trees is sourwood, Oxydendrum arboreum, a native of the southeastern United States that is scattered around Plainfield in small numbers. A fine example is at Watchung Avenue near the corner of Kensington.

The tree highlights its maroon leaves with cream-colored seeds.

One of the many charms of our native dogwood is its beautiful maroon fall foliage.

Sweetgums, maligned for their production of difficult-to-rake gumballs, more than make up for whatever maintenance problems they cause with a panoply of red fall colors.

Some sweetgums have autumn foliage in yellow tones.

Deciduous plants don't just passively lose their leaves in the fall. They make elaborate preparations for winter. Red antioxidant coloration is part of that preparation. Green leaves are colored by chlorophyll, the molecule that allows plants to capture the energy of sunlight. When the leaves are shed, plants don't allow the chlorophyll to go to waste. They break it down and move the breakdown products to the roots, where they are stored over the winter. With their energy-generating machinery moving into storage, plants are in a vulnerable state. As they lose their chlorophyll, the leaves of some plants gain protective anthocyanins and reddish colors. The latest scientific thinking about why the leaves of those plants turn red in the fall is that additional antioxidative protection in dying leaves permits orderly breakdown and withdrawal of the chlorophyll before the leaves fall. This subject is nicely summarized by Colin Tudge in his recent book, The Tree.(2)

Some autumn leaves develop yellowish tints. Where do those colors come from? Yellow autumn leaf pigments are generally chemicals that have been present all during the growing season and that are unmasked by the absence of chlorophyll. Yellow and orange carotenoids play a role in photosynthesis. They are also antioxidants.(3)

(1) Blueberries are touted as good sources of anthocyanins. A widely cited study found that elderly rats had an improved sense of balance after being fed large quantities of blueberries for weeks.

(2) Colin Tudge, The Tree, A Natural History of What Trees Are, How They Live, and Why They Matter, Crown Publishers, 2006, pp. 357-359. The author points out that new spring leaves and shoots, also particularly vulnerable to injury, have a red tinge in many plants.

(3) Beta-carotene has been a widely used dietary supplement. I suspect that its popularity fell off after scientific studies seemed to indicate that taking it did not offer the hoped-for cardiovascular benefits. Better, it seems, to get your antioxidants by eating plants, not pills.

Copyright Gregory Palermo

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