Effect of varying Alliaria petiolata populations on myrosinase and sinigrin concentration in field soils

Background/Question/Methods

Alliaria petiolata is a biennial plant in the Brassicaceae family.  It is an exotic, invasive that has been invading Northeastern U.S. forest understories since the early 20^th century. Recent research has suggested that chemical exudates from A. petiolata in the soil suppress native species.  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 and possibly fungi species. 

Populations of biennial A. petiolata tend to alternate being dominated by juvenile and adult plants, although mixed populations occur.  If soil sinigrin concentrations are dependent on population age structure, then A. petiolata’s allelopathic impact is likely to fluctuate over time and space.  We modified a method used in literature to assay soil sinigrin concentrations, using HPLC analysis of soil extracts. Current work is developing a model to measure field soil myrosinase concentrations using size separation columns and spectroscopy. Soil samples from sites dominated by either adult or juvenile plants will be assayed during the growing season in 2011. The patterns of enzyme and substrate concentrations in the soil may explain invasiveness and reveal dynamic interactions with native species.

Results/Conclusions

Trial assays from the 2010 season indicated that soils under juvenile populations have higher concentrations of sinigrin than those under 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 and will be responsive to changes in myrosinase.

The resulting patterns revealed by the sinigrin assays will be integrated with the enzymatic assay in which the concentration of myrosinase is determined. The combination and timing of the two exudates during A. petiolata’s life cycle may reveal important patterns that impact recruitment, growth and success of native species as well as invasive behavior.