Effect of Removal of Garlic Mustard (Alliaria petiolata, Brassicaeae) on Arbuscular Mycorrhizal Fungi Inoculum Potential in Forest Soils

Garlic mustard (Alliaria petiolata), a biennial species, is considered to be among the most troublesome of the invasive plants in the Eastern Deciduous forest of North America. It has been shown to prevent or reduce mycorrhizal colonization of native herbaceous ground layer plants and trees in these forests. It is estimated that 70-90% or more of herbaceous native ground layer plant species form associations with arbuscular mycorrhizal fungi (AMF). Loss of the mycorrhizal association can reduce growth, reproductive success, and competitiveness of plant species. Using a corn root bioassay, we examined the effect of garlic mustard removal on the soil AMF mycorrhizal inoculum potential (MIP), in control plots and plots that had second-year garlic mustard removed annually for the past five years (2005-2009). Removal treatment plots had significantly (P = 0.0240, df = 28) greater MIP than control plots (25.72±2.26% and 18.29±2.04%, respectively). MIP was negatively correlated with cover of garlic mustard (r = 0.1325, P < 0.05, df = 30), which accounted for 13.2% of the variation in MIP. Cover of native vegetation in removal treatment plots (104.50±2.6%) was greater than that of the control plots (95.14±3.66%), (P = 0.0236, df = 115). These results show that removal of garlic mustard results in an increase in soil MIP and cover of native species; however, there is not a complete loss of MIP associated with garlic mustard invasion. Following removal of garlic mustard, our data suggest that mycorrhizal plants recover more slowly than non-mycorrhizal species, apparently due to a delay in the establishment of a well-functioning mycorrhizal association. Our study is the first to demonstrate that the MIP of native soils and cover of native species increase following reduction in the cover of garlic mustard.