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April 24, 2000

John Bluck

NASA Ames Research Center, Moffett Field, CA

650/604-5026 or 604-9000



Tiny fungi that make forests possible are significantly affected by clear-cutting tree stands, perhaps altering forests and plant types that re-grow, according to a recent paper in the Canadian Journal of Botany.

The paper reports on ecological fungi research by NASA at Yellowstone National Park, WY, where scientists used a police technique, "DNA finger printing," to investigate biodiversity and the importance of human changes to ecosystems. An ecosystem is the combination of living things and raw materials, such as water, gases and minerals, that life uses in the environment. Clear-cutting refers to the practice of cutting a stand of trees in its entirety.

"If the fungi in ecosystems change in large areas of the world, then the kind of plant life could also change," said Dr. Ken Cullings, a scientist at NASA Ames Research Center, in California’s Silicon Valley, who co-authored the paper with team member Kristin Byrd. "These fungal changes in the soil may begin to explain why it is more difficult for certain species of trees to re-grow. Our results identify the need for further research to understand how fungi remained after clear-cutting," Cullings said.

"The fungi we study are related to the big mushrooms you see when walking through the forests," he said. "If you go to the market, you’ll also see them; they are chanterelles and king bolete, expensive mushrooms that are also mycorrhizal fungi."

"Mycorrhizal fungi are important because, without them, trees could not get nutrients such as nitrogen and phosphorus from the soil," he said. "The fungi get carbon from tree roots in exchange for providing nitrogen and phosphorus to the trees."

If a tree does not have nitrogen, it cannot survive. Most plants on Earth, including trees in the tropical rainforests, form associations with fungi. "The things we are learning in Yellowstone can apply to ecosystems across the world," said Cullings.

The paper reports that the research team took soil cores at both undisturbed and clear-cut forest sites. Researchers found 48 species of ectomycorrhizal fungi in clear-cut areas, and 70 species in undisturbed Yellowstone forests. The research team also found nine of the 14 most common "clear-cut" species in the undisturbed sites, but at a much lower abundance.

"We’re using DNA finger printing to identify these different kinds of microbes," he said. "We work with a root hair the size of a pin head. Just like forensic detectives, we amplify the DNA by taking a gene, and we put it in a machine with the chemical building blocks of DNA." Scientists use an enzyme, first discovered in a Yellowstone Hot Springs bacterium in the 1960s, to make several billion copies of each gene under study. Cullings was the first scientist to use this process to categorize Yellowstone microbes.

"We measure biodiversity; and one way to do it is to measure the species that are present in the soil," Cullings said. "My group is counting microorganisms and what kinds live in Yellowstone’s soil. We’re looking at how clear-cutting, forest fires and other disturbances are affecting the microbe populations."

"We have found there is a big difference between how clear-cutting a forest affects microbes and how fires affect those populations," he said. "After a fire, or clearing of timber in a given area, the number of microbe species may be the same, but different kinds survive a fire versus survive clear-cutting."

Because some types of fungi may help certain tree varieties to survive, but not others, the kind of forest in the area may change after a fire or a clear-cut. The historic cycle of forest recovery may also change. During decades or even hundreds of years, many Yellowstone and Rocky Mountain forests change from lodge pole pines, to firs and spruce. Human-made disturbances, such as acid rain and changes in atmospheric gases (including carbon dioxide levels or damage to Earth’s ozone layer), can also alter the repeating cycle of tree growth, Cullings’ study suggests. The Cullings paper appeared in the Canadian Journal of Botany, February 2000, Vol. 78, No. 2.



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