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Fungi necessary for growth

While fungi are thought to cause harm to many plants, this certain type helps prairie plants.

By Staci Hauschild



Burning and grazing practices are vital components for sustaining the tallgrass prairie ecosystem, but an organism under the earth's surface is also essential for the growth and regrowth of dominant plant species.

Unlike fungi that are usually thought to cause harm and kill many plants, a certain type of fungus provides numerous benefits to prairie plants, said David Hartnett, professor of biology at Kansas State University, and director of the Konza Prairie Biological Station.

Hartnett said the symbiotic association between the fungi and the roots of prairie plants is called mycorrhizae, a Latin word meaning "fungus root."

"Fungi colonize the roots of the plants and help plants take up nutrients, help increase plants' resistance to disease and help increase drought tolerance -- all contributing to markedly enhanced growth," Hartnett said. "Plants return the favor by providing a food source to the fungus because the fungus is an organism that doesn't make its own food by photosynthesis."

Researchers have discovered that these beneficial fungi occur in more than 80 percent of the world's plants. After studying about 100 tallgrass prairie plant species, all were found to have the symbiotic relationship.

"There is quite a bit of variability between the species in the prairie as to how critical the symbiosis is to their production," Hartnett said. "The dominant tallgrasses of the prairie absolutely require the fungus. It they don't have the fungus infecting their roots, they won't survive at all. It's an absolute requirement."

The dominant native grasses such as big bluestem, Indian grass and switchgrass are also the native grasses that cattle consume as forage.

"When the plants are grazed by cattle or bison they must have enough resources -- water and nutrients -- in the soil," he said. "If you took the fungi away, the plants wouldn't be able to take up enough nutrients to regrow. If it weren't for these fungi you wouldn't have beef to eat."

Hartnett said many times researchers assume that the vegetation on tallgrass prairies is responding to grazing or the effects of fire, but some of these influences on the ecosystem are indirect effects through the fungi.

When the prairie is burned in the spring, fires remove the dead layer of vegetation from the soil surface and the soil receives more direct sunlight on the soil. The higher soil temperatures incubate the fungi, stimulating the fungi to develop. The fungi colonize the plants, and the plants get all the benefits, Hartnett said.

In addition to native tallgrass plants, agricultural crops, such as wheat and corn, also benefit from being colonized by fungi. Hartnett said that varieties differ, but wheat and corn typically show a 20 to 80 percent reduction in production without the symbiotic relationship.

"They can still grow, and they can still function without it, but they do much better if they are colonized by the fungi," he said.

June 2002