Invasive plants escape from suppressive soil biota at regional scales

Summary 1. A prominent hypothesis for plant invasions is escape from the inhibitory effects of soil biota. Although the strength of these inhibitory effects, measured as soil feedbacks, has been assessed between natives and exotics in non-native ranges, few studies have compared the strength of plant–soil feedbacks for exotic species in soils from non-native versus native ranges. 2. We examined whether 6 perennial European forb species that are widespread invaders in North American grasslands (Centaurea stoebe, Euphorbia esula, Hypericum perforatum, Linaria vulgaris, Potentilla recta and Leucanthemum vulgare) experienced different suppressive effects of soil biota collected from 21 sites across both ranges. 3. Four of the six species tested exhibited substantially reduced shoot biomass in ‘live’ versus sterile soil from Europe. In contrast, North American soils produced no significant feedbacks on any of the invasive species tested indicating a broad scale escape from the inhibitory effects of soil biota. 4. Negative feedbacks generated by European soil varied idiosyncratically among sites and species. Since this variation did not correspond with the presence of the target species at field sites, it suggests that negative feedbacks can be generated from soil biota that are widely distributed in native ranges in the absence of density-dependent effects. 5. Synthesis. Our results show that for some invasives, native soils have strong suppressive potential, whereas this is not the case in soils from across the introduced range. Differences in regional-scale evolutionary history among plants and soil biota could ultimately help explain why some exotics are able to occur at higher abundance in the introduced versus native range