Species-specific responses of invasive plants to parasitism are modified by climate warming

Parasitic plants can inflict significant damage to invasive plants and are considered biocontrol agents. Climate warming can affect the fitness of invasive plants and the efficacy of their biocontrol agents. However, the impact of climate warming on the responses of invasive plants to parasitism remains inadequately explored. To investigate this critical issue, we conducted a controlled warming experiment to assess the impact of a constant, continuous +2 °C temperature increase, consistent with projected global warming scenarios reported by the Intergovernmental Panel on Climate Change, on the responses of two common invasive plants in China, Solidago canadensis and Bidens pilosa to the parasitic plant Cuscuta gronovii. Our findings indicate that parasitism significantly reduces the growth of both invasive species irrespective of temperature increases. A significant interaction was observed between Cuscuta parasitism and the different host species, particularly affecting stem diameter, plant height, and root-to-shoot ratio of the host plants. Interestingly, while increased temperature independently did not significantly impact total biomass, aboveground biomass, or leaf number of the host plants, it exhibited marginal interactions with parasitism and the different hosts regarding belowground biomass of the hosts. Moreover, C. gronovii biomass was significantly influenced by host type; however, increased temperatures did not significantly affect the biomass of C. gronovii or its deleterious effects on host plants. Overall, these findings highlight the complex interplay among parasitism, host species, and environmental factors, which are crucial for comprehensively understanding invasive species dynamics and their ecological implications.