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Biotron's Cutaway View Reveals Underside of Life

March 1996

With windows that look out on brownish hair-like roots and earthworms, the University of Michigan's Soil Biotron is one of few places in the world to see the underside of a natural system.

The biotron resembles a basement with glass walls. It was built with NSF funding, under a grove of trembling aspen, red oak, and red maples at the university's Biological Station near Pellston.

Experiments here help ecologists study problems such as global change, gauge their effects, and enhance overall knowledge of the under-studied underworld.

"We know a lot about the top of a tree," says ecologist Kurt Pregitzer of Michigan Technological University. "For example, we know about leaf longevity, leaf size and rate of growth. But we know next to nothing about what happens underground."

To learn more about how roots grow, Pregitzer designed a computer driven time-lapse video system.

The camera records not only roots, but movements of soil animals and growth of fungi. The whole system of removable windows and cameras is a great advance for soil ecologists, says Bob Fogel, Biotron Director and University of Michigan biologist. Before the biotron was in place, soil was studied by coring "where you drive a tube into the ground. That disrupts the spatial relationships of the roots, animals and fungi."

With the help of the biotron and another NSF grant, Fogel and his colleague John Lussenhop, a biologist from the University of Illinois, Chicago Circle, have learned how important fungi are to roots and vice versa. Roots give carbon to fungi, and fungi provide phosphorus to roots.

"Almost all plants rely on fungi as auxiliary roots," says Lussenhop. "The particular fungi, seen through the biotron windows, store phosphorus for use by the trees. So they can be thought of as the gas tank of the forest."

Work is under way to measure the gas held by fungi and exchanged with roots. "Clearly the trees can't live without fungi. But how much gas is intercepted by soil animals chewing on the roots?" he asks.

While Lussenhop and Fogel are closing in on answers to some of these questions about normal life in the forest's soil, Pregitzer asks what would happen if the soil system changed.

To search for the answers, Pregitzer added extra water and nitrogen to certain soil plots, then trained his camera on the plots and waited. He discovered that roots actively seek out patches of soil with extra nutrients, growing toward the pool with extra water and nitrogen. In another study, he showed that if atmospheric carbon dioxide is increased, aspen roots grow faster--and die faster.

What does this mean? Too early to say, Pregitzer thinks. "There is great biological diversity in the soil system. If we tried the same experiment in different communities, we may not see the same results."

So the work goes on. "If we're ever going to develop a more fundamental understanding of how plant communities live," says Pregitzer, "we need to understand root growth and mortality."

The biotron was built as a multi-investigator research facility. For more information send an e-mail message to Bob Fogel at rfogel@umich.edu.

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