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High CO2 Stimulates Soil-Building "Glue"

By Don Comis
August 12, 1999

In the first examination of the effects of high atmospheric carbon dioxide levels on soil structure, an Agricultural Research Service scientist and cooperators found that the gas stimulates soil-dwelling fungi to produce more of a unique protein that greatly amplifies a soil's ability to store carbon.

The study's results are described in a letter published in the August 12 issue of Nature magazine. One of the letter's authors, ARS soil scientist Sara F. Wright, previously discovered the protein and named it glomalin. She suspects it may be the primary glue that holds soil together. Now it appears that a little of this glue goes a long way toward helping soils keep carbon out of the atmosphere in the form of carbon dioxide.

Carbon dioxide is a greenhouse gas contributing to possible global warming.

The lead author, Matthias C. Rillig, is with the Carnegie Institution of Washington at Stanford, Calif., as is Christopher B. Field. The fourth author, Michael F. Allen, is with the University of California at Riverside. The researchers studied three different ecosystems: two grasslands in northern California and chaparral in southern California. In all three, they found that as more carbon dioxide was pumped into open-top chambers placed over grassland plants growing outdoors, or in a greenhouse built around shrubs, glomalin levels rose, along with soil stability.

The high carbon dioxide levels in the air increase the amount of carbon taken in by plant roots. That gives the fungi more food and enables them to produce more glomalin. The glomalin glues soil particles together and helps them clump, improving soil structure. This eases the passage of air and water through soil, boosting plant yields. It also helps soil resist erosion and hold in soil carbon--valuable organic matter that holds nutrients to recycle slowly to plants.

Farmers can increase glomalin levels further by avoiding plowing and by growing cover crops year-round if feasible. Fungi need live roots to produce glomalin.

Scientific contact: Sara F. Wright, ARS Soil Microbial Systems Laboratory, Beltsville, Md., phone (301) 504-8156, fax 504-8370,