Release from belowground enemies and shifts in root traits as interrelated drivers of alien plant invasion success: a hypothesis

Abstract

Our understanding of the interrelated mechanisms driving plant invasions, such as the interplay between enemy release and resource‐acquisition traits, is biased by an aboveground perspective. To address this bias, I hypothesize that plant release from belowground enemies (especially fungal pathogens) will give invasive plant species a fitness advantage in the alien range, via shifts in root traits (e.g., increased specific root length and branching intensity) that increase resource uptake and competitive ability compared to native species in the alien range, and compared to plants of the invader in its native range. Such root‐trait changes could be ecological or evolutionary in nature. I explain how shifts in root traits could occur as a consequence of enemy release and contribute to invasion success of alien plants, and how they could be interrelated with other potential belowground drivers of invasion success (allelopathy, mutualist enhancement). Finally, I outline the approaches that could be taken to test whether belowground enemy release results in increased competitive ability and nutrient uptake by invasive alien plants, via changes in root traits in the alien range.

Release from Above- and Belowground Insect Herbivory Mediates Invasion Dynamics and Impact of an Exotic Plant

“…There is increasing evidence that belowground enemies can be as important for species co-existence and community dynamics as aboveground enemies [62] and may even drive the positive biodiversity-productivity relationships in native plant communities [63]. Nevertheless, surprisingly few studies have looked on enemy release from belowground enemies [52,64] and most of them concentrated on plant-soil feedback (e.g., [65][66][67][68][69][70][71][72]. These studies frequently demonstrated that release from soil-borne pathogens may favor plant invasions [52,64], but the role of belowground insect herbivory is still insufficiently understood and studied.…”

“…Nevertheless, surprisingly few studies have looked on enemy release from belowground enemies [52,64] and most of them concentrated on plant-soil feedback (e.g., [65][66][67][68][69][70][71][72]. These studies frequently demonstrated that release from soil-borne pathogens may favor plant invasions [52,64], but the role of belowground insect herbivory is still insufficiently understood and studied. Root herbivores are increasingly used as biocontrol agents [73] as they are highly specific and can effectively reduce growth and survival of focal plants species (e.g., [74].…”

“…Besides the release from specialist belowground enemies, the novel chemistry of exotic plants may also act against co-evolutionary naïve insect herbivores feeding belowground [62]. Therefore, current theories on the importance of insect herbivores for plant invasions seem to apply also for the belowground compartment of terrestrial ecosystems [52]. According to theory, invasion success of exotic plants depends on either a competitive advantage over resident species, or on niche differences from the native residents [40].…”

“…Moreover, there is increasing evidence that belowground herbivores are equally or even more important in structuring plant communities as aboveground herbivores [1]. However, there are still few studies on effects of belowground herbivores for biological invasions (see review by [52]).…”

Soil ecology of the exotic dune grass Leymus arenarius.

“…These belowground differences between Leymus and Ammophila were unaltered by interactions with AMF or PPN. Inherent differences in root architecture, and the associated differences in response to root herbivores, including PPN, may provide a possible explanation for the invasion success of many exotic invasive plant species (Dawson 2015).…”