Environmental conditions affect the allelopathic potential of three invasive alien plants species in North‐Eastern France

Abstract Invasive alien plants species (IAPs) pose significant challenges worldwide, affecting the economy, public health and biodiversity conservation. Their global success can be partially attributed to the release of new exogenous molecules into the environment, known as allelochemicals. The synthesis and concentration of these compounds in vivo are referred to as the allelopathic potential, which exhibits plasticity in response to the environment. Here, we investigated how the expression of this allelopathic potential of three IAPs in Alsace, North‐Eastern (NE) France, responds to various environmental variables. Phytotoxicity tests were conducted to evaluate the root length in two target species: Lactuca sativa and either Medicago sativa or Bromus catharticus , measuring the allelopathic potential expression of the IAPs. The tests utilized leaves collected from multiple IAP populations in the fields. At each sampling site, a total of 22 environmental variables were recorded, encompassing diverse factors across five categories, including micro‐environmental parameters, land cover, soil properties, ecological indicator values and climate. Additionally, genetic analysis was conducted to characterize the genetic diversity of each IAP. The three IAPs under investigation exhibited varying levels of genetic diversity. We found one unique genotype for Ailanthus altissima , six different genotypes for Phytolacca americana and 10 genotypes for the Reynoutria spp. complex, with a majority one corresponding to Reynoutria japonica . Each IAP species presents an environmental plasticity, higher for A. altissima and P. americana than R. japonica, regarding their allelopathic potential expression. A variety of environmental factors contributed to this plasticity, with effect on the expression of allelopathic potential specific to the IAP species studied. Synthesis : Overall, the findings highlighted the significant role of environmental variables in influencing the allelopathic potential expression, with varying degrees of impact depending on the species under study. Understanding how environmental conditions affect the production of allelochemicals provides valuable insights for managing these invasive alien plant species. This knowledge can guide the prioritization of interventions for controlling the most competitive invasive populations.