National Geographic : 2009 Sep
PHOTO: DOUGLAS SMITH ENVIRONMENT Mushroom Breath Fungi that pop up in the forest are "like CO chimneys," says researcher Steven Allison. Back in 2005 he measured the carbon dioxide emitted by mushrooms after their rootlike mycelia ate carbon from the soil. He was "shocked" by their output---and concerned, since CO traps heat in the atmosphere. Allison figured that as the planet warmed up, fungi would thrive, belching out even more CO . To test the theory, he and a colleague from the University of California, Irvine, built small greenhouses in a central Alaska forest, with soil half a degree Celsius warmer than in control plots. To his surprise, the greenhouse mushrooms fell dormant or died; the soil likely dried out too much for them. The failing fungi consumed less carbon; their CO emissions diminished. A drop in mushroom CO can't make up for human releases: One exhaled breath equals about the amount a large mushroom exudes in an hour. And southern fungi might not act the same as the north- ern ones studied. Nonetheless, learning how ecosystems affect CO levels is critical in predicting Earth's temperature rise. "Bacteria are the next frontier," Allison says. "They also eat carbon, but we're not sure how much or how fast." He aims to find out. ---Karen E. Lange Mushrooms like this specimen, genus Sarcodon, spew carbon dioxide. But as tem- peratures warm in the north, emissions drop.