Figure 1.

Schematic of the hypothesis that belowground enemy release in the rhizosphere of plants results in root‐trait changes, comparing the alien (red lines) and native range (red lines; A). Alien plants are expected to benefit from belowground enemy release, through expressing root traits such as greater branching and specific root length (A) which in turn allow greater rates of soil resource uptake in the alien compared to the native range (B). The shift in root traits toward values promoting greater resource uptake could be ecological or evolutionary, but should result in greater fitness for plants in the alien versus native range (C). The native range expectations in B and C could also represent native species in the alien range. While main groups of belowground enemies are depicted and are expected to be absent/less abundant in the alien range, root traits are expected to respond most strongly to release from fungal pathogens. Arbuscular mycorrhizal fungi should associate with plant roots at similar frequency in both ranges, but effects on plant growth may differ, with potential consequences for root‐trait expression (see “Integrating alternative belowground mechanisms explaining invasion success”).