COS 107-8
Can below-ground interactions drive the spread of an invader?

Thursday, August 13, 2015: 10:30 AM
338, Baltimore Convention Center
Krystal A. Nunes, Ecology and Evolutionary Biology, University of Toronto, Mississauga, ON, Canada
Peter M. Kotanen, Ecology and Evolutionary Biology, University of Toronto, Mississauga, ON, Canada

The majority of research and management efforts for invasive plant species have been centred on above-ground herbivory.  The importance of the below-ground biotic community on invader success remains understudied. For instance, do local or regional variations in below-ground impacts have the potential to help or hinder invasions? To address this question, the noxious weed Cirsium arvense (Canada thistle) was used as a study system. Soil was collected inside and outside established thistle populations at 8 locations, which spanned a 700 kilometre transect from agricultural southern Ontario to boreal northern Ontario, Canada.  Seeds were grown in pots prepared with a 1:5 ratio of live field soil to sterilized potting soil, with sterile controls.  Growth rate measurements were taken throughout the experiment, and forty days following seedling transplant the above- and below-ground biomass were harvested, dried, and weighed in order to provide a measure of overall plant performance.


Plants grown in soils sourced from northern Ontario or from outside thistle populations performed better than those grown in southern Ontario soils (p<0.0001) or those from inside thistle populations (p<0.0001).  This suggests that subterranean herbivores and pathogens accumulate in pre-existing thistle populations, and that such accumulation is more likely at southern sites than in more isolated northern locations. As a result, those individuals who are able to establish outside of existing populations and in geographically marginal areas more likely to succeed.  In this way, below-ground interactions may be driving the success and spread of C. arvense northwards.