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The salinization of freshwater habitats from winter road salt application is a growing concern. Understanding how taxa exposed to road salt run-off respond to this salinity exposure across life history transitions will be important for predicting the impacts of increasing salinity. We show that Leucorrhinia intacta Hagen, 1861 (Odonata: Libellulidae) dragonflies are robust to environmentally relevant levels of salt pollution across intrinsically stressful life history transitions (hatching, growth, and metamorphosis). Additionally, we observed no carry-over effects into adult dragonfly morphology. However, in a multiple-stressor setting, we see negative interactive effects of warming and salinity on activity, and we found that chronically warmed dragonfly larvae consumed fewer mosquitoes. Despite showing relatively high tolerance to salinity individually, we expect that decreased dragonfly performance in multiple-stressor environments could limit dragonflies’ contribution to ecosystem services such as mosquito pest control in urban freshwater environments.

Although relatively infrequent, invasions by non-native plants at high latitudes are increasingly recognized as an emerging problem. Churchill, Manitoba, is unusual as over a hundred non-native species have been found in human-disturbed areas, making it an outlier amongst subarctic habitats. Although these non-native species have persisted almost exclusively within town, some occur in isolated locations throughout the local road network. Most of these non-native species have been observed in areas with a history of soil movement (e.g., for construction or road repairs), suggesting that they have been moved within the soil, likely either germinating from seeds or growing clonally from root and rhizome fragments. Using a greenhouse experiment, we found evidence that soils from human-disturbed sites can contain a substantial non-native seed bank. In particular, we grew a significantly higher number of non-native seedlings from translocated soils compared to uninvaded soils. These germinated non-native species are native to Europe but have widely invaded temperate regions. This study provides the first direct evidence that movement of seed-contaminated soil is a significant source of local non-native species spread. Future warming in arctic regions may increase seed production of these species, leading to increased spread and persistence via contaminated soil.

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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.