The winter storm that caused havoc across the country dropped temperatures into the teens in the Georgia Piedmont. Gusty, freezing weather would keep me by the fire. But Gunter the German shepherd is oblivious to cold. He insists on a couple of miles a day. After the brisk walk, he rests on the porch and crunches ice. He loves ice cubes, regardless of season.
If you are going to walk, you might as well try to learn something about the world. So I’ve been looking at lichens.
The suggestion comes from Richard Headstrom, a wonderful science teacher of my grandfather’s generation. Headstrom was a New Englander. He pointed out you could find lichens flourishing in snow.
Lichens are a community of organisms — commonly a partnership between fungi and algae — rather than a single plant.
The filaments of fungi provide a foundation and some protection for the algae, which provides the food through photosynthesis. (In some lichens, cyanobacteria, instead of algae, do the photosynthesis.)
Biologists call the relationship mutualistic. But there’s some debate about how to describe it: how much is mutually beneficial and how much is parasitic.
Headstrom says lichens are at their best in winter. They aren’t hurt by the cold and they like moisture.
His remark made me wonder how much cold lichens can take.
Australian scientists studying lichens in the Arctic say lichens can “exhibit net photosynthesis” — generate more energy for food than they use in making it — at temperatures as low as minus 4 degrees Fahrenheit.
They’ve found lichens as far south as 86.30 degrees. Lichens can absorb water from the atmosphere, as well as in the forms of snow and ice. They can grow even when covered by a layer of snow, which offers it some protection. In those extreme climates, a centimeter’s growth might take a thousand years.
The winter storm that hit the Piedmont has been impressive to me, but the lichens here don’t seem to have been hurt.
Lichens come in different colors. Headstrom says this about the most common kinds:
When dry, most lichens are chalky gray color, because the colorless fungal filaments so effectively cover the algal cells that their bright green is obscured. But when moist, the same lichens will appear green, because the moistened filaments transmit light quite well; hence the green algal cells can be seen through them.
After the walk, I can report that the lichens are green and the dog is happy.
I’m going to stay by the fire.
• Sources: Richard Headstrom, Nature Discoveries with a Hand Lens; New York: Dover Publications, Inc., 1968, pp. 12-16. The quotation is on p. 13.
For information on the Australian Antarctic Program, see:
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