Development of negative soil feedback by an invasive plant near the northern limit of its invaded range

Abstract

In the Canadian subarctic, the non-native plant Linaria vulgarishas invaded human-disturbed soils in and around the town of Churchill, Manitoba (58.8ºN), but for decades has failed to spread into nearby tundra and taiga communities. One possible explanation for this stasis might be greater resistance by soil communities in uninvaded areas relative to areas where this plant has been long established; however, no local evidence for such 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 within anthropogenically-disturbed areas, and measured plant performance (biomass) over three greenhouse iterations. We also conducted basic soil chemical analyses to determine whether pH, and carbon, nitrogen, and phosphorous contents differ between invaded and uninvaded areas. There was no initial difference in plant biomass between soil inoculation treatments in the first two iterations. However, by iteration 3, 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. Soil chemistry did not differ significantly between invaded and uninvaded soils, though there was a tendency for invaded soils to contain slightly more carbon and nitrogen. These results reject the possibility than L. vulgaris is absent from uncolonized sites because their soil communities resist invasion. Instead, they provide evidence that L. vulgaris is inhibited by plant-soil feedbacks in invaded soils, while feedbacks in native-dominated soils do not represent a barrier to further local spread. Thus, explanations for the restriction of this species to anthropogenically modified areas must lie elsewhere.