The Fungi-Tree Connection
Posted February 1, 1998
A commonly held view of a community of plants is that they are in competition with one another for resources. Recent studies show that this model may need to be changed.
Biologists have known for many years that fungi and trees have a symbiotic relationship. Trees, like all plants, remove carbon dioxide from the air in the process of photosynthesis.
Carbon compounds made by the trees are then used by the fungi for their own metabolism. Fungi fix atmospheric nitrogen and phosphorus and convert them into compounds that the trees can
use. Both fungi and trees benefit from this association.
But, underground, fungi can cover a large area with their mycelia, connecting with many individual trees and different tree species. Suzanne Simard, a forest ecologist
with the Ministry of Forests in British Columbia, wondered whether these connections benefit trees in a forest community. She planted seedlings of Douglas fir and paper birch, two species
that grow together naturally, and waited for them to become infected with the local soil fungi. After a year of growth, she provided each species of tree with a different isotope of
carbon dioxide. Nine days later, she harvested the trees, ground them up, extracted the isotopes, and measured how much of the isotopes each of the trees retained.
Simard found some interesting results. She discovered that the isotopes absorbed by one tree often ended up in another tree, and that the trees in the shade had proportionately
more carbon from the trees located in sunny areas. In other words, isotopes given to birch trees in the sun often ended up in fir trees in the shade. This finding shows that trees in
a community are not necessarily in competition with one another for resources; in fact, they appear to be sharing resources. But how did the carbon isotopes get from one tree to another?
Simard concluded that the fungi were extracting carbon from trees in the sun and releasing it to trees in the shade.
Simard's research has a practical application for forest management. In many forests, the Douglas fir is considered to be a desirable species and the birch to be
a "weed" species to be disposed of quickly. But if birch trees actually support fir trees by releasing carbon through their combined root fungi, then destroying all the birch trees is
not a good idea. The results of her study lend strength to the theory that species diversity may in fact be key to maintaining a healthy forest community.
References
Zimmer, Carl. "For the Good of a Fungus." Discover, Vol. 18, No. 11, p. 44.
Strauss, E. "Communism in Trees Goes Underground." Science News, August 9, 1997, Vol. 152, No. 6, p.87.
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