CHAMPAIGN, Ill. Like most invasive plants introduced to the U.S. from Europe and other places, garlic mustard first found it easy to dominate the natives. A new study indicates that eventually, however, its primary weapon a fungus-killing toxin injected into the soil becomes less potent.
The study, in Proceedings of the National Academy of Sciences, is one of the first to show that evolutionary forces can alter the very attributes that give an invasive plant its advantage. In fact, the study suggests the plant's defenses are undermined by its own success.
Garlic mustard comes from a family of smelly, sharp-tasting plants that includes cabbage, radish, horseradish and wasabi. Unlike most plants, which rely on soil fungi to supplement them with phosphorous, nitrogen and water, garlic mustard gets by without the extra help, said Richard Lankau, a postdoctoral researcher at the Illinois Natural History Survey (INHS) at the University of Illinois. Lankau led the study with INHS plant ecologist Greg Spyreas.
"For whatever reason, these plants just don't hook up with the soil fungus," Lankau said. Instead, garlic mustard produces glucosinolates, pungent compounds that leach into the soil and kill off many soil fungi, especially those native to North America. This weakens the native plants. As a result, garlic mustard now grows in dense patches in many North American woodlands, its preferred habitat. Those patches are often devoid of native plants.
Lankau began the new study with a seemingly obvious question: Once garlic mustard has vanquished most of its competitors, why would it invest as much in maintaining its toxic arsenal? He predicted correctly, it turns out that levels of glucosinolates in the plant would diminish over time.
"When you're in a situation where the only thing you're competing with is other garlic mustard, it may be that making lots of this chemical is not a very good idea," he said.
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign