Published by Communications and Public Affairs (519) 824-4120, Ext. 56982 or 53338
April 05, 2001
‘Harmless-looking' trees really predators; partners with fungi to eat insects alive, new research shows
The white pine tree -- known for its majestic heights and soft blue-green needles -- is a predator under the soil, teaming up with fungi to eat insects alive, University of Guelph researchers have found.
The findings of botany professor John Klironomos and graduate student Miranda Hart will appear in the April 5 edition of Nature magazine and have the potential to change how science looks at nutrient cycling in forests.
Klironomos and Hart found that white pine trees form a deadly partnership underground with the fungus Laccaria bicolor, which grows from the tree’s root. The two work as mutualists, with the fungus preying on insects to get animal-origin nitrogen, then using it to “barter” with the host tree for the carbon it needs to synthesize enzymes.
In this way, white pine trees are acting indirectly as predators to supply themselves with life-sustaining nutrition, Klironomos said. It also means that forest nutrient cycling may be more complicated than was previously thought. “Above-ground, these trees look so harmless, but it turns out that below the surface, they are feeding on live animals.”
The researchers made the discovery while conducting a routine study that involved white pines. “When we would introduce insects to the soil – mostly springtails – they would die immediately, and we wondered why,” Klironomos said.
“Upon closer examination, we discovered that the insects were really being attacked by this fungus. We think the fungus releases a toxin that paralyzes the insect, then it infects them, grows inside them and eats them alive.”
To verify the results, the researchers conducted a series of controlled experiments with white pine seedlings and L. bicolor. They found that springtails in the soil did not die in the presence of other fungi or in tests that were fungus-free. Likewise, when white pine seedlings were grown in controlled environments with a different fungus or in the absence of fungus, they were only able to acquire nitrogen from dead insects.
“It is the specific combination of the white pine tree and the L. bicolor fungus that proves lethal for insects and most effective for the tree,” Klironomos said.
Science has long recognized the importance of the partnership between trees and ectomycorrhizal fungi (fungi that grow from the trees’ root) in plant nutrition. Until now, however, it has been commonly believed that trees and their associated fungi derive nitrogen from dead organic matter in the soil, he said.
Klironomos added that more studies must be conducted to determine if their findings are an isolated incident. “When you are dealing with soil, it really is a big black box; it is so difficult to figure out what is going on down there. But if this phenomenon proves to be widespread, it changes everything.”
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