Garlic mustard, Alliaria petiolata, is an invasive species native to Eurasia that is now common in vegetation throughout the eastern United States and adjacent Canada. It is a member of the non-mycorrhizal and glucosinolate-producing Brassicaceae family and its invasive and competitive capacity may derive from its ability to disturb mycorrhizal interactions of native species. Glomus intraradice is a fungus that participates in these symbiotic relationships and is actively added to the common potting soil marketed as Pro-Mix BX. We investigated the effect of garlic mustard on the growth of mycorrhizae-dependent native species by growing them in Pro-Mix previously occupied by garlic mustard. Since garlic mustard produces glucosinolates, the fitness of mycorrhizal species is likely to be suppressed relative to those grown in soil not exposed to garlic mustard. Garlic mustard was planted in nine pots containing Pro-Mix BX soil and allowed to grow for one month. Native species Oenothera biennis L. and the exotic species Ageratina altissima Spach were planted into the pots that previously contained garlic mustard and nine pots that contained fresh Pro-Mix BX. Relative chlorophyll content using a SPAD meter, biomass, leaf area, and height were measured on harvest for all plants.
Results/Conclusions
After three weeks of measurements, both species grown in soil mix previously containing garlic mustard showed significantly decreased vigor and smaller size compared to those grown in soil mix without garlic mustard. Thus, the presence of garlic mustard in soil could be responsible for suppressing populations of native species in invaded habitats and enhancing the invasive impact of garlic mustard. However, it is clear that the effects could be due simply to nutrient depletion by garlic mustard, and have nothing to do with Glomus – garlic mustard interactions. We conducted a further experiment to determine the effect of garlic mustard presence in the soil while accounting for nutrient depletion using a control species, Brassica oleracea. This species is closely related to garlic mustard but has been shown to produce extremely low levels of glucosinolates. By growing plants in control soils, Brassica soils and garlic mustard soils, we will be able to tease apart nutrient depletion and glucosinolate effects of garlic mustard on native communities.
