Invasive plants can be relentless in crowding out native species. They thrive because they lack natural enemies, grow faster, or reproduce more and therefore outcompete new neighbors for nutrients and other resources. And that's not all: New research shows they also engage in underground guerilla tactics, disrupting key relationships between roots and certain fungi. This strategy has enabled at least one species to get a foothold in well-established forests.
Typically, invasives do best in disturbed areas or along the edges of forests, where grasses and shrubs dominate. But garlic mustard (Alliaria petiolata) also thrives underneath the forest's canopy. There, the native plants' prosperity depends in a large part on microscopic organisms called arbuscular mycorrhizal fungi. The fungi send out long microscopic threads called hyphae that create a subterranean network enabling plants to exchange nutrients. This partnership enriches the forest (Science, 11 June 2004, p. 1620). Five years ago, researchers found that, in the lab, extracts of garlic mustard leaves impaired fungal reproduction and the fungus's ability to establish linkages with tomato roots, but no one knew whether this happened in the wild.
To find out, ecologists Kristina Stinson of Harvard University and John Klironomos of the University of Guelph in Canada and other colleagues examined a natural forest dominated by red and sugar maples and white ash. They found that mustard-occupied sites had fewer fungal-root connections and that the trees in those plots grew more slowly than did trees at mustard-free sites.
The researchers also planted tree seedlings in plots containing either mustard, sugar maple, red maple, or ash trees. The fungi paired up with less than 10% of the seedlings growing side by side with mustard, compared to up to 65% in the other plots, the researchers report in the May PLoS Biology. The tree-fungi partnerships were similarly impaired when the researchers added garlic mustard extract to an otherwise mustard-free site, they reported. Out 16 plant species subsequently evaluated, those most dependent on the fungi were the most compromised by the garlic mustard.
"It's chemical warfare, but in an indirect way," says Marcel van der Heijden, an ecologist at the Vrije University in Amsterdam. In addition, he notes, the results point to the importance of plant-fungi relationships in determining the composition of plant communities--and their vulnerability.
Related site
)
)
)
)
)
)
)
)
