Knotweed (Fallopiaspp.) Invasion of North America Utilizes Hybridization, Epigenetics, Seed Dispersal (Unexpectedly), and an Arsenal of Physiological Tactics

Abstract

More than 100 years ago, Japanese knotweed was introduced to North America. Given its vigorous rhizome system and capability to grow from rhizome and stem fragments, it persists and spreads locally, forming monotypic stands. The Japanese knotweed clone originally introduced was a male sterile female clone; thus, early in the invasion, reproduction from seed was not an issue. The implication was that long-distance dispersal was relatively rare. However, recently, widespread hybridization between Japanese knotweed and Sakhalin (giant) knotweed has been reported, with the hybrid species, Bohemian knotweed, forming the majority of knotweed plants in many areas and possessing higher variability than the parent species. The hybrids produce large numbers of wind-dispersed viable seeds that germinate at rates approaching 100% in some populations. As temperatures increase, knotweed is predicted to expand its range farther north and to higher elevations. With the ability to regenerate from vegetative fragments and disperse via seeds, invasive knotweed species are on the move. An arsenal of chemical weapons, the ability to shade out competitors, and the ability to adapt rapidly through epigenetic change makes knotweed a formidable invader. We observed that knotweed species clearly possess 8 of the 12 ideal weed characteristics, with Bohemian knotweed likely exhibiting still more because of prolific seed production. More research is needed to answer pressing questions. How does hybridization affect knotweed epigenetics? Under what conditions might seed production become more frequent? What kind of niche expansion is possible with the increased variability? Given the considerable challenges posed by knotweed species that promise to become even greater with the proliferation and spread of Bohemian ecotypes, only a thoroughly researched, well-informed approach to knotweed management across North America can be successful.

Microwave soil heating reduces seedling emergence of a wide range of species including invasives

“…The experiments were performed on a seed bank contained in soil extracted in situ and also on seeds of three important plant species invasive in Europe ( Datura stramonium , Reynoutria × bohemica , and Solidago gigantea ), which are abundant seed‐producers (Weaver & Warwick ; Weber & Jakobs ; Gillies et al ). Information about D. stramonium , R. × bohemica , and S. gigantea ecology and invasion history is available in Appendix S1.…”

“…This seed introduction was intended (1) to test the effect of microwaves directly on three important invasive plant species and (2) to evaluate the percentage of seedlings able to emerge after each treatment, when directly mixed with soil. The three species, noxious in some European countries (Weber ; Weber & Jakobs ; Van Kleunen et al ), were chosen not only because they reproduce by seeds (Saayman ; Weber & Jakobs ; Gillies et al ) but also mostly because their seeds differ in shape and size. Indeed, these characteristics are known as major determinants of seed sensitivity to microwave heating (Bebawi et al ; Brodie et al ).…”

Modeling invasive alien plant species in river systems: Interaction with native ecosystem engineers and effects on hydro‐morphodynamic processes

“…This hybrid has similar characteristics as F. japonica , some even more vigorous, but it is also able to reproduce via seeds. These seeds are buoyant, while water increases their germination rate [ Gillies et al ., ]. This means that the distribution of Fallopia hybrids toward downstream areas can expand even more rapidly in riparian areas.…”

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“…F. japonica is closely related to two other members of the Fallopia genus, F. sachalinensis and Fallopia x bohemica, which have similar invasive ranges and have similar impacts. Of note, in some parts of its invasive range, Fallopia x bohemica spreads via the production of large numbers of wind-dispersed viable seeds that germinate at rates approaching 100% in some populations (Gillies, Clements & Grenz, 2016). However, in the UK, spread by this means does not currently occur in the UK.…”

“…On a global scale its reputation as a problematic invasive alien species (IAS) primarily stems from its vigorous growth and impacts on riparian habitats (Child & Wade, 2000) coupled with difficulty of eradication (Bailey, 2013;Jones et al, 2018). Verified impacts include the creation of dense monodominant stands (Gillies, Clements & Grenz, 2016;MDNR, 2012); reductions in ecosystem services in riparian zones, e.g. by impeding access (Environment Agency, 2013;Gerber et al, 2008;Kidd, 2000;Urgenson, 2006); negative effects on native plant and invertebrate assemblages in riparian habitats (Gerber 2008); reductions in species richness (Aguilera et al, 2010;Hejda et al, 2009;Urgenson, 2006) and abundance of native understory herbs, shrubs, and juvenile trees in riparian woodlands (Urgenson, 2006); modifications to nutrient cycles (Urgenson, 2006); and impacts on flood defence through impeding water flow and facilitation of riverbank erosion (Booy, Wade & Roy, 2015; Environment Agency, 2013; Kidd, 2000).…”