An invasive plant does not escape negative soil feedback near the northern limit of its invaded range

Abstract In the Canadian subarctic, the non-native plant Linaria vulgaris has invaded human-disturbed soils in and around the town of Churchill, Manitoba (58.8ºN), but has failed to spread into nearby tundra and taiga communities. This lack of spread over decades suggests that interactions with native soil communities might be a barrier to L. vulgaris, in contrast to areas where this plant has been long established; however, no local evidence for plant-soil feedbacks yet exists. In one of the first studies to investigate the role of plant-soil feedbacks in an invasion at high latitudes, we planted L. vulgaris in soil serially inoculated with live and sterilized field-collected soil that was sampled either from invaded or uninvaded plots, and measured plant performance (biomass) over three greenhouse generations. We also conducted soil chemical analyses on all soil samples to determine whether pH, and carbon, nitrogen, and phosphorous contents may contribute to feedbacks. There was no significant difference in soil chemistry detected between invaded and uninvaded areas. Additionally, there was no initial difference in plant biomass between soil treatments in the first two generations. However, by generation three, we found that sterilization significantly increased L. vulgaris biomass in invaded soils, indicating feedback gradually becomes more negative in invaded soils compared to uninvaded soils. These results suggest both that this non-native plant is not modifying the soil biota to its benefit in invaded soils, and that feedbacks in native-dominated soils do not represent a barrier to further range expansion. Thus, explanations for the restriction of this species to anthropogenically modified areas must lie elsewhere.