Invasive species pose one of the largest threats to the stability of native ecosystem functions. This is most evident in the disruption of vegetative structure and demography, but invasion by non-native plants can also affect nutrient cycling and ecosystem engineering processes. My research investigates the effects imposed upon the soil community by invasion of Alliaria petiolata (Garlic Mustard) in an oak-maple-hickory woodland undergoing restoration.

A non-mycorrhizal member of the Brassicaceae family, A. petiolata secretes a glucosinolate compound into the rhizosphere which has been shown to have allelopathic properties that disrupt the Arbuscular Mycorrhizal Fungi (AMF) associated with neighboring root systems. Mycorrhizae serve a critical function in ecosystem processes, providing water, nitrogen, and phosphorous uptake services to their root partners, and receiving a reliable source of carbon in return, something they can not produce for themselves. A. petiolata's allelopathy is most pronounced toward seedlings of AMF associated hardwood species, such as Maples and Ashes, resulting in a lack of sufficient numbers of juvenile trees. The net effect is a significant opening of the forest canopy as adult hardwoods die back unreplaced, and eventually major shifts in the vegetative structure of the woodland away from the stable native demography.

I am working with Dr. Louise Egerton-Warburton to investigate several questions associated with Garlic Mustard's allelopathy. First, can we directly observe the effects of allelopathy associated with Garlic Mustard invasion in a natural woodland? Most investigations of this phenomenon are conducted as pot trials, and we hope to make direct observations in the field setting that will correlate well with published greenhouse results. (Stinson 2006) Our study involves planting bare-root seedlings of Sugar Maple and Red Oak into invaded soils in the MacDonald Woods habitat at the Chicago Botanic Garden, a woodland that is currently undergoing restoration efforts. As well, we are planting seedlings in an uninvaded Bur-Oak Savannah as a control, though we are aware of the unfortunate differences in the control and experimental habitats, a necessary flaw in our experimental design in a region with little or no pristine woodlands. At season's end, the seedlings will be harvested and observations made on their root systems to identify the presence or lack of fungal associates, percentage of colonization, and possible species shifts.

Second, we wish to know if allelopathy is also observed toward ectomycorrhizal fungi? Our study is looking at both Sugar Maples (AMF associates) and Red Oaks (ectomycorrhizal associates), and we hypothesize the presence of a similar disruption toward Red Oak fungal root-associations as that seen in Sugar Maples. Third, what effect, if any, will disruptions in the mycorrhizal community have on microarthropod populations in the soil, most notably for collembola species that are mycorrhizal grazers? Our working hypothesis is the expectation of a disruption of collembola populations in our study sites, either in terms of lowered abundance of microarthropods, a species shift, or both.

Coupled with the mycorrhizal and microarthropod studies we are also measuring various soil factors including structure, pH, conductivity, total Carbon, Nitrogen, and Phosphorous, and available Nitrogen. We hope to publish the results of our study in the Summer of 2007.