Gradients in invader allelochemistry determine native plant growth and restoration strategies

Background/Question/Methods Invasive species often evolve rapidly following introduction, creating phenotypic differences between the native and introduced range, but also among populations within the new range. Across their introduced range, Alliaria petiolata populations vary in their investment in allelopathic traits according to invasion history, which could, in turn, lead to gradients of impact on native plant species. To test these impacts, I transplanted red oak (Quercus rubra) into eight A. petiolata invaded sites across Illinois. At each site, I imposed a A. petiolata removal and a soil microbial inoculation treatment to simulate alternate restoration strategies.

Results/Conclusions

Red oak (Quercus rubra) seedlings grew faster in populations with a longer history of invasion and lower allelochemical concentrations in the invader. Experimental removal of A.petiolata and inoculation with soil microbial communities interacted to determine seedling growth, with the benefits of soil community inoculation increasing in younger or more highly allelopathic invader populations. These results suggest that the impact of this invader varies across landscapes, and that knowledge of this variation could improve the efficacy and efficiency of restoration activities.