You can't see it.

But it's associated with nearly everything you can see from the ground up — trees, grasses, food crops — as a microscopic cling-on that helps plant roots absorb water and nutrients.

It's mycorrhizal fungi.

And in the midst of their search for solutions to worldwide buildup of carbon dioxide, scientists are looking underground to learn more about its role.

"One hopeful dream is our fungi will help buffer the rise of carbon dioxide in the air by growing more. This is a big deal," said Northern Arizona University environmental sciences professor Nancy Johnson, whose work focuses on the possibility.

Johnson said researchers throughout the world are puzzled because they've measured the amount of carbon dioxide going into the air from fossil fuel-burning and forest fires, and they're measuring the carbon dioxide in the atmosphere — but the numbers don't jibe.

"Carbon dioxide in the atmosphere is going up, but it's not going up nearly fast enough to account for what's being produced," Johnson said. "The oceans aren't doing it."

And mycorrhizal fungi, she explained, may just be "the missing sink," a sink being a part of the environment helping to absorb the excess.

"This is a big deal right now. U.S. leaders are reticent to reduce carbon dioxide emissions and they're looking for any possible sink," she said.

Johnson and graduate student Julie Wolf have recently contributed another piece to the greenhouse gas puzzle with research funded by $500,000 from the National Science Foundation.

Wolf defended a thesis in December and handed in the final copies last week. Her work shows that changing levels of carbon dioxide, some of them mirroring what the world can expect with the sustained burning of fossil fuels, will affect the fungi that grow in hidden partnerships with plants.

Deciphering the potential extent of the changes — and what they could mean for plant communities all over the globe — is a long way off. But piece by piece, Johnson and Wolf are plugging away.

For the part of the NSF work included in Wolf's thesis, she set up Free Air CO2 Enrichment (FACE) rings, designed by students in NAU's engineering program, around six plots at a study site north of Twin Cities, Minn.

Then Wolf's work centered in on Flagstaff, as she used soil samples that were Fed-Exed to her in plastic bags from the site. Wolf measured how much fungi were growing in each of the plots — thereby exploring whether varying levels of carbon dioxide would change the amounts of the microscopic fungi in the soil.

She began by scooping cupfuls of soil, and she says each one contained miles of fungal branches called hyphae.

"It's kind of like DNA," she said, meaning that the fungus is thin and coiled tightly in its limited space.

"I make mudslides," she explained. "I put some in water and I blend it for a little while, then put it on a small sieve. All the hyphae will stay on top."

Of course, Wolf still can't see her study subject matter at that point — until she swipes it on a microscope slide. Magnified 250 times, the hyphae are "branched, kind of clear to yellow-colored … they're beautiful."

Wolf counted the hyphae in each gram of soil. She also counted how many spores, the fungal version of seeds, were produced each year.

She found that fungal hyphae length did increase as a whole, and one of the 12 species she explored increased its spore production.

Wolf points out that any changes in underground fungus would naturally make conditions more or less favorable for the specific plants it associates with — so changes in the fungal community could beget changes in plant communities on a broad scale, she said.

"You hear about global warming all the time. This is another big potential problem. We could have changes in plant diversity," she said.

Now that Wolf has completed her master's degree, she'll stay on as project manager for the next phase of the research.

Johnson laughs heartily when she describes her recent trip across the country in a Ryder truck filled with Minnesota soil.

Using that soil, the scientists have begun a more controlled experiment in the university's greenhouse to tease out differences in the responses of individual plant and fungal species to changing levels of carbon dioxide.

Anne Minard can be reached at aminard@azdailysun.com or 556-2253.

— Arizona Daily Sun

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