The role of mycorrhizal fungi in suppression of weeds. . Healthy native ecosystems are resistant to weed invasion, an effect promoted by vigorous, mycorrhizal native plants. Several mechanisms account for resistance to invasion, and none are completely understood. In such locations, weeds win the competitive struggle against greatly incapacitated natives.
Weeds usually require relatively higher soil fertility than native species.
Healthy, mycorrhizal natives rapidly remove mobile nutrient ions from the soil, making the site inhospitable to weeds. Some weeds react to mycorrhizal fungi as they would to root pathogens. Seedlings of Russian thistle, an important weed in the western United States, soon die if the soil is full of mycorrhizal hyphae. In the future we may discover other weed species that are intolerant of mycorrhizal fungi. Other factors also influence the competition between weeds and natives, but mycorrhizal inoculation is one essential step in winning the battle.