Undaunted by microbes. Purple loosestrife and other invasive plants can withstand soil diseases.

Invaders Get Support From Underground

Invasive plants, one of the greatest threats to biodiversity worldwide, may owe their success to friendly relations with underground microbes. A new study finds that soil fungal diseases have little impact on invaders, whereas they are a major factor in reducing the growth of native plants. The finding may suggest ways to counteract weedy invasions.

Invasive plants drain as much as $35 billion a year from the U.S. economy. Farmers and ranchers must spend money to control the weeds or risk crop and livestock losses. And the plants' rampant growth threatens fragile species and ecosystems. Ecologists have speculated that some exotic plants become invaders because they compete better, disperse further, or tolerate predators. But these ideas only partially explain what goes on in nature. John Klironomos, an ecologist at the University of Guelph in Canada, thought another factor might lie underground, with the fungal diseases that attack plant roots.

To find out if rare, native plants and their invasive competitors differ in their relationships with soil organisms, Klironomos studied plants from a Canadian grassland. In one set of experiments, he planted five rare and five invasive species in individual pots to allow the diseases particular to each species to build up. He then planted new seeds in soil that previously hosted either the same species or a different species. Rare plants were stunted by soil that their own species had grown in, but four of the five invasive plants fared better in soils where their own species had grown. The team showed that invaders are better able to tolerate fungal diseases by manipulating the pathogens in the pots.

The study, published in the 2 May issue of Nature, "tells us that invasive plants may have escaped their pathogens," says Klironomos, suggesting that new pathogens might control them. Other researchers were guardedly enthusiastic. David Tilman, an ecologist at the University of Minnesota, Twin Cities, says, "plant pathogens, long overlooked, may turn out to rival insects and mammals in their effects on plant abundances."

Related Sites
John Klironomos's home page
Fact book on invasive plants
Invasive Plants.net