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  National Geographic 21 Nov 05
Army of Tiny Fungi Keeps Forests Healthy, Study Suggests
 John Roach

Communities of microscopic fungi that live inside trees might help protect their hosts from disease and predators, new research suggests.

These fungi, called endophytes, are found throughout various types of plants from the roots to the leaves. Many different endophyte species can live together in a single plant.

"We really don't understand exactly what [endophytes] do," said fungi researcher Rebecca Ganley. "But we are slowly coming to understand how they might be involved in resistance, tolerance, and other ecological processes that go on in the plant."

Ganley works for Scion, a sustainable biomaterials development company based in Rotorua, New Zealand. Before joining Scion, she conducted graduate research at the University of Idaho in Moscow that focused on harnessing the power of the tiny fungi to keep trees healthy.

Ganley's research suggested that trees with diverse communities of endophytes are more resistant to diseases, such as blister rust, than forests with fewer endophytes. Blister rust has caused widespread deaths in several species of white pine, an important family of trees in the Pacific Northwest U.S.

Ganley also found that diversity among the fungi is greatest in native, old-growth forests and lowest in plantations and nurseries.

Small Fungus, Big Business

Ganley and her colleagues at Scion now hope to figure out which endophytes are important for disease resistance. They can then reintroduce the fungi to new forests, boosting the resistance of new trees to the spread of lethal diseases.

The researchers must first determine which endophytes live in which types of trees. "For most tree species, we don't know what's in the tree at all," Ganley said. Then she and her colleagues want to figure out how the endophyte communities in the trees work together.

James White is a plant pathologist at Rutgers University in New Brunswick, New Jersey. He said researchers have learned in recent years to harness endophytes in certain grasses to make the plants resistant to disease, drought, and insects.

Such endophyte research is "big business," he said, especially for turf grasses: the sorts that adorn front lawns. "The benefits are tremendous," he said. "It means no or little herbicide has to be applied, less water to be put on the plants, and few insecticides." In grasses many endophytes boost insect resistance, White said.

Scientists believe the endophytes release nitrogen-containing compounds known as alkaloids that often have a bitter taste. Insects and animals learn to avoid plants that release alkaloids, which can cause adverse reactions when ingested.

For example, horses in the southwestern U.S. might eat sleepy grass (Stipa robusta). Eating the grass makes the animals stumble around and then fall into a deep sleep that can last for days. Once they wake, the horses never eat the grass again.

Researchers studying the grass discovered that the endophyte-released alkaloid in sleepy grass is a cousin to the psychedelic drug LSD, White said.

In another study researchers found that an endophyte allows certain species of plant to thrive in the hot, volcanic soils of Yellowstone National Park. "In that case the endophyte species in those small-space plants was required for tolerance to high temperature," Ganley said.

Fungal Army

In grasses the endophyte community is limited to one or two species. But in trees a single pine needle can host tens or even hundreds of species, Ganley said.

According to White, endophyte diversity may be high in trees because an army of internal fungi may be required to thwart the myriad threats trees face from diseases and predators. "Overall there's bigger protection. I think that's the concept there," he said.

In general, Ganley believes diversity is the key to the smooth operation of any ecosystem.

"If you lose one animal, that has a lot of impact on the ecosystem," she said. "And fungal species can potentially be the same."
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