Alliaria petiolata is a biennial plant that is part of the Brassicaceae family and is a exotic, invasive species of plant that has been invading local forest understories since the early 20^th century. Recent research has suggested that chemical exudates from A. petiolata  in the soil affect the mycorrhizal relationships of native plants, suppressing them and enhancing invasiveness.  Some of these exudates include sinigrin, a glucosinolate that is degraded by myrosinase, an enzyme that is common in the soil and also present in A. petiolata.  The product of this degradation, isothiocyanate, negatively impacts the growth and survival of neighboring, indigenous plants.  Populations of biennial A. petiolata tend to alternate being dominated by juvenile and adult plants.  If accumulation of sinigrin in soil is dependent on population age structure, then the relative impact of A. petiolata is likely to fluctuate over time.  We modified a method used in agricultural systems to assay soil sinigrin concentrations, using a commonly available glucose oxidase/peroxidase test.  The enzyme in that test kit degrades sinigrin into easily detectable glucose, the concentration of which is measured using spectrophotometry. Soil samples from nine sites with predominantly adult or juvenile populations were used for the preliminary study and 20 more were used during the 2010 growing season. 

Results/Conclusions

Trial assays indicated that soils in juvenile populations have higher concentrations of sinigrin than those from populations dominated by adults.  It is likely that this chemical defense compound is reallocated from roots and leaves in juveniles to seeds and fruits in adults, thus reducing soil concentrations, since sinigrin can dissipate quickly in soils.  Thus, because the amount of sinigrin detected associates strongly with population age structure, the timing and intensity of this mode of ecological interaction for A. petiolata is likely to vary substantially throughout the year as well as between years.  If the timing of sinigrin exudation matches the timing of seedling recruitment and development of mycorrhizal associations for native species, this may help explain garlic mustard’s negative invasive impacts.