Unravelling the invasion success: How do climate and pollination mode shape seed germination of a non-native plant in native and invaded ranges?

Understanding how invasive plants germinate in response to shifting climatic conditions and biotic interactions is crucial for predicting and preventing their spread. Species may possess a broad germination capacity that allows them to germinate under a wide range of environmental conditions, or they may exhibit specific germination responses tailored to local environments. We investigated the germination responses of the invasive shrub Nicotiana glauca, using seeds from its native range (South America) and from two invaded areas (South Africa and Spain) with different climates and pollination environments. We evaluated the proportion and timing of germination at different temperatures, water potentials simulating hydric stress, and pollination treatments to assess the importance of pollinators and autonomous selfing. The germination response to temperature reflected broad tolerance, with a trend towards specificity, especially in the non-native ranges. In all regions, seeds reduced their germination under water stress, but how this reduction occurred showed different strategies in each region. Germination responses to pollination treatments were specific and consistent with the reproductive modes of N. glauca in each region. Although autonomous self-pollination effectively produced germinable seeds in non-native areas, the acquisition of pollinators may facilitate adaptation to climatic conditions. Our results suggest that rapid post-introduction evolution tailored to the local environment, rather than broad tolerance, would have allowed N. glauca to maximise germination under the specific conditions of the novel habitats. This finding indicates the potential for this species to invade diverse locations worldwide, as climatic and pollination environments do not appear to limit its expansion.