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Erosion, on the down low.

Scientists have for the first time observed how the tiny fungi that live on plant roots physically erode rocks and set the stage for chemical breakdown. Steeve Bonneville of the University of Leeds in England and his colleagues set up a lab test to study the effects of the fungi Paxillus involutus on biotite, a potassium-rich mineral found in granite and other rock types. In the test, reported in the July Geology, the researchers planted a pine seedling with fungi-covered roots in a dry nutrient-poor soil free of other microorganisms (right). A flake of biotite (arrow) near the tree's roots provided nourishment and was the only source of potassium in the soil, Bonneville says. After three months, the team analyzed the flake in areas where fungi filaments, known as hyphae, had attached. Microscopy revealed that mineral layers beneath the attachments were wedged apart by at least 14 degrees. Material near the attachment had lost as much as 70 percent of its potassium. These changes allowed iron-bearing compounds in the rocks to react with oxygen from the air, encouraging further erosion, the team reports.

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Title Annotation:Earth
Author:Perkins, Sid
Publication:Science News
Article Type:Brief article
Geographic Code:4EUUK
Date:Aug 1, 2009
Words:185
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