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Frontiers
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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