Phytochemicals produced by Alliaria petiolata have been implicated in reduced seed germination and growth of native plants and are believed to be a key factor in its ability to invade understory vegetation. We used treatments of activated carbon as a way to potentially absorb A. petiolata phytotoxins and tested the effects of carbon-mediated and unmediated Alliaria extracts and soil on seed germination and seedling growth of a native herbaceous perennial, Aguilegia canadensis. We predicted that treatments with activated carbon would result in better germination and growth for A. canadensis when exposed to A. petiolata. Three experiments were used to test the effects of activated carbon treatments. In a lab experiment with germination, groups of 10 A. canadensis seeds were exposed to filter paper soaked with extracts of A. petiolata with and without activated carbon. A greenhouse experiment tested the effect on germination and growth of A. canadensis of adding carbon directly to potting soil from A. petiolata plants. Finally, activated carbon was applied in a field experiment using existing soil in a natural infestation of A. petiolata at the Pierce Cedar Creek Institute in Barry County, Michigan. Stem elongation was measured in A. canadensis seedlings grown in these field treatments.

Results/Conclusions

A. canadensis seeds grown in extract that had been pre-soaked with activated carbon had a better germination success rate of 54% compared with 40% for the extract alone (N=25, t-test, p=0.005). There was no significant difference between seed germination rate for seeds grown in soil from A. petiolata plants with and without activated carbon. Stem elongation rate twenty days after germination did not differ between these treatments but a control treatment of activated carbon alone reduced stem elongation rate by 50% (ANOVA, F_2,36=5.9, p= 0.006). In field infestations of A. petiolata, A. canadensis had longer stems in the carbon-treated areas after four weeks of growth than in the control areas with no activated carbon treatments (average stem length with carbon =19.9 cm , average without carbon =17.2 cm, N=8, Wilcoxon, p=0.04). We concluded that while activated carbon can be used to mediate the negative effects of A. petiolata on seed germination and seedling growth of A. canadensis in the field, activated carbon by itself has negative impacts, possibly through reduction in soil fertility, and may have limited use in controlling the impacts of this invasive plant.