Root hemiparasites suppress invasive alien clonal plants: evidence from a cultivation experiment

 Alien invasive plants threaten biodiversity by rapid spread and competitive exclusion of native plant species. Especially, tall clonal invasives can rapidly attain strong dominance in vegetation. Root-hemiparasitic plants are known to suppress the growth of clonal plants by the uptake of resources from their below-ground organs and reduce their abundance. However, root-hemiparasites’ ability to interact with alien clonal plants has not yet been tested. We explored the interactions between native root-hemiparasitic species, Melampyrum arvense and Rhinanthus alectorolophus and invasive aliens, Solidago gigantea and Symphyotrichum lanceolatum. We investigated the haustorial connections and conducted a pot experiment. We used seeds from wild hemiparasite populations and those cultivated in monostands of the invasive plants to identify a possible selection of lineages with increased compatibility with these alien hosts. The hemiparasitic species significantly suppressed the growth of the invasive plants. Melampyrum inflicted the most substantial growth reduction on Solidago (78%), followed by Rhinanthus (49%). Both hemiparasitic species reduced Symphyotrichum biomass by one-third. Additionally, Melampyrum reduced the shoot density of both host species. We also observed some transgenerational effects possibly facilitating the growth of hemiparasites sourced from subpopulations experienced with the host. Native root hemiparasites can effectively decrease alien clonal plants’ biomass production and shoot density. The outcomes of these interactions are species-specific and may be associated with the level of clonal integration of the hosts. The putative selection of lineages with higher performance when attached to the invasive novel hosts may increase hemiparasites’ efficiency in future biocontrol applications.