Researcher: Spotted knapweed may suppress natives via root chemicals and fungi

Rick Holloway, a researcher in the University of Montana Division of Biological Sciences, told a public lecture in Missoula that spotted knapweed (Centaurea maculosa) is able to form large monocultures on Mount Jumbo and Sentinel and that multiple research lines point to both direct and indirect mechanisms explaining its competitive success.

Holloway summarized experiments from his lab showing that festuca (Idaho fescue) roots slowed or stopped elongation when they encountered knapweed roots unless activated carbon was added to the soil. "With activated carbon the fescue roots grew much faster," Holloway said, describing the experiment in which activated carbon (added at roughly a 1:100 proportion) reduced the negative effect on fescue root growth. He framed those results as evidence that knapweed roots exude organic compounds that can inhibit native-root growth.

The nut graf: Holloway said allelopathic root exudation is only part of the picture. His team also reported that mycorrhizal fungi — the arbuscular mycorrhizae common on grassland plants — can change outcomes of competition. In…