The magic of mushrooms
U plant biologists unearth mysteries
of fungi in forests
By Nina Shepherd
For some people, mushrooms are evocative
of fairies and other mythological creatures. "They're
almost magical," says David McLaughlin, a plant biology
professor and curator of fungi for the University's
herbarium. "They can suddenly appear almost overnight."
But for McLaughlin, the lure of mushrooms is their importance
to the real world. "They're mysterious mostly because
they haven't been well studied," he says, "yet they
are a critical environmental indicator of a forest's
health."
Mushrooms can be classified into three
categories based on their relationship to other plants.
There are decay-causing mushrooms, which are essential
to forest ecosystems because they recycle dead matter
into nutrients for new growth; parasitic mushrooms,
which threaten and sometimes destroy the life of the
host plant; and mycorrhizal mushrooms, which bond with
a plant's root system, extracting nutrients from the
plant while helping its host absorb nutrients from the
soil.
"Mycorrhizal mushrooms form a distinctive
structure around the root of the tree, which acts as
a protective, absorptive, and sometimes disease-repelling
agent," says McLaughlin. "They can actually serve as
a bridge between the root systems of different types
of trees, bringing nutrients to smaller, shaded trees
that might not otherwise stand a chance of developing."
In fact, the relationship can be so interdependent that
trees thrive only in the presence of a particular species
of mycorrhizal mushroom.
The importance of mycorrhizal mushrooms
to the survival of trees makes them a key indicator
of forest health, says McLaughlin. He points out that
dramatic declines in these mushrooms throughout Europe
over the last 20 years have been attributed to air pollution
and agricultural runoff. And just as the number and
diversity of Europe's mycorrhizal mushrooms have declined,
so have its forests.
That led McLaughlin to look at Minnesota
forests. For the past 10 years, he has worked to establish
baseline data on mycorrhizal mushroom diversity in the
old-growth and mature (100 years old) red pine forests
and hardwood conifer forests of northern Minnesota.
Armed with knives, collecting baskets, and paper bags,
McLaughlin and his students sometimes travel miles into
a forest in search of samples. Closer to the Twin Cities,
at CBS's Cedar Creek Natural History Area in Bethel,
McLaughlin has begun to look at mycorrhizal mushroom
activity both above and beneath the forest floor. Because
mycorrhizal mushrooms don't always fruit -- or produce
a mushroom -- above ground, tracking them gets tricky.
McLaughlin and his students must drill deep underground,
into a tree's root system, to extract specimens -- which
can vary in color from brilliant yellow to bright, electric
blue.
Despite the difficulties, McLaughlin
and his students have found a startlingly high level
of diversity of mycorrhizal mushrooms in the red pine
and northern hardwood-conifer forests they studied --
more than 300 species when the expectation had been
25 to 50 per forest type, based on reports from the
eastern U.S. and Europe. About half these species have
never before been recorded in Minnesota. But more importantly,
the researchers noticed that some species are restricted
to old-growth forests and some to mature forests --
suggesting the importance of maintaining forests of
different ages in order to maintain biodiversity.
While Minnesota's mushroom population
appears healthy, McLaughlin sees the disappearance of
Europe's mushrooms as a warning. "We don't understand
fully what these fungi do, nor do we know all the mushrooms
that are here yet. If we wipe them out, or allow them
to die off, we may lose our forests forever."
by Nina Shepherd
Back to Frontiers spring
1999
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The magic of mushrooms