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Invasive Species Harms Native Hardwoods by Killing Soil Fungus [From Harvard University Press Release 4/26/2006] CAMBRIDGE, Mass., April 24, 2006 – An invasive weed that has spread across much of the U.S. harms native maples, ashes, and other hardwood trees by releasing chemicals harmful to a soil fungus the trees depend on for growth and survival, scientists report this week in the Public Library of Science. The tree‐stifling alien, garlic mustard (Alliaria petiolata), first introduced into the U.S. in the 1860s, has since spread to Canada and 30 states in the A forest understory in Massachusetts invaded by East and Midwest, with recent sightings as garlic mustard. Photo by Ben Wolfe. far west as Oregon. While many mechanisms – from the absence of natural predators or parasites to and the UFZ Centre for Environmental the disruption of long‐established Research in Germany. “While vanishing habitat caused by interactions among native organisms – have been proposed to explain the success of human activity is the number one threat to invasive species, this new work is the first to biodiversity, there is great concern over the show that an invasive plant harms native impact of accidental and intentional dispersal plants by thwarting the biological “friends” of alien invasive species across the globe,” upon which they depend for growth. says Kristina A. Stinson, a plant population biologist at the Harvard Forest, Harvard’s The work, which provides striking evidence for a unique process by which ecology and conservation center in invaders harm native species, was Petersham, Mass. “In North America, conducted by researchers at Harvard thousands of nonnative plants and animals University, the University of Guelph, the have become established since European University of Montana, Purdue University, settlement and many more continue to be introduced. Some alien species cause little 1
harm, while others can become very mustard invasion. Three species – sugar aggressive and radically transfigure their maple, red maple, and white ash – had new habitat. significantly less AMF root colonization and “The mechanisms for this grew only about one‐tenth as fast in the phenomenon and its potential long term infested soil. Seedlings grown in sterilized, impacts remain poorly understood,” Stinson AMF‐free soil taken from invaded and pest‐
adds, “but one possibility is that invasive free locations showed similar reductions, species may disrupt fragile ecological suggesting that diminished microbial activity relationships that evolved over millions of had suppressed tree growth. Other years.” experiments showed that adding garlic Stinson and her colleagues found mustard extracts to soil impaired AMF that garlic mustard targets arbuscular colonization and seedling growth, implying mycorrhizal fungi (AMF), which form that the weed uses phytochemical poisons to mutually beneficial relationships with many disrupt native plants’ mycorrhizal associations forest trees. These fungi have long filaments and stunt their growth. that penetrate the roots of plants, forming an When the study was subsequently intricate interwoven network that effectively replicated with seedlings of 16 other native extends the plant’s root system. AMF plants, only the hardwoods and other woody depend on plants for energy and plants plants were harmed by the presence of garlic depend on the fungi for nutrients. When mustard. tree seedlings, which depend strongly on “This suggests garlic mustard invades AMF, began to decline in the presence of the understory of mature forests by poisoning garlic mustard, the researchers suspected the allies of its main competitors,” Stinson that the invasive plant might thwart this says. “By killing off native soil fungi, the symbiotic relationship. appearance of this weed in an intact forest could stifle the next generation of dominant To test this possibility, they collected soil from five forests in Ontario canopy trees. It could also invite other native dominated by four species of native and nonnative weedy plants that currently hardwoods. First, the researchers tested grow in low‐AMF habitats, such as those seedlings’ ability to form mycorrhizal disturbed by logging or development.” The researchers plan to study which relationships in soil with a history of garlic phytochemicals in garlic mustard may kill 2
Research. The work was funded by the National Science Foundation’s Long Term Ecological Research Program at Harvard Forest, the Natural Sciences and Engineering Research Council of Canada, and Harvard’s Bullard Foundation. ‐‐ Steve Bradt, Harvard University Communications Offices 617‐496‐8070 [email protected]
Harvard Forest Contact: [email protected]
Link to article at PLoS Biology: Top left (BW ): Microscope view of a plant root colonized by AMF
spores (stained in dark blue); top right (BW): flowering adult garlic
mustard plant; bottom left (JK): spore of an AMF in the genus
Glomus; bottom right(BW): crushed spore of an AMF in the genus
Acaulaspora. Photos credits: Ben Wolfe (BW) and John
Klironomos (JK).
AMF, how these chemicals interact with http://biology.plosjournals.org/perlserv/?requ
other beneficial soil microbes, and how est=get‐
plants and fungi in garlic mustard’s native document&doi=10.1371/journal.pbio.0040140
European habitat coexist with the noxious species. Stinson’s co‐authors are Stuart A. Campbell, Jeff R. Powell, Benjamin E. Wolfe, and John N. Klironomos at the University of Guelph; Ragan M. Callaway and Giles C. Thelen at the University of Montana; Steven G. Hallett at Purdue University; and Daniel Prati at the UFZ Centre for Environmental 3