Increasing presence of non-native plants and arbuscular mycorrhizal fungi during a 10-year survey along subarctic mountains roads

Mycorrhiza surveysThe mycorrhiza surveys were conducted in a selection of the sample sites along which the vegetation surveys were done, resulting in mycorrhizal samples being taken in 20 of the total of 60 sample sites, 7 along R2 and R3, and 6 along the shorter R1 (resources were not available to sample all 60 sample sites).In each of these sample sites, soil samples (henceforth called background samples, in line with Clavel et al. 2019) were taken for AM fungal measurement in roots both in the roadside plot and the first adjacent plot.A background sample consisted of three pooled topsoil cores of 5 cm diameter and 5 cm depth, randomly taken inside a 20 x 20 cm square after removing the litter layer.The soil was then sieved to isolate the roots before freezing them until analysis.During the first year of survey in 2017, 5 background samples were taken in each roadside plot but, ultimately, only two could be analyzed due to resource constraints.In 2019 and 2021, three background samples were taken and analyzed in each roadside plot, at 5, 25, and 45 m along the long axis of the plot (Fig. 1).In the adjacent plots, two samples were taken each year, one 10 m away from the roadside plot and one 40 m away from the roadside plot, to test for a potential effect of distance from the road (Fig. 1).