Regeneration niche of Cortaderia selloana in an invaded region: Flower predation, environmental stress, and transgenerational effects

Background and aims: Biological invasions are causing massive environmental, social, and economic impacts worldwide. Understanding the ecological factors that affect the regeneration of invasive plants is critical to develop action plans based on empirical biological evidence. In this study, we investigate ecological limits in the regeneration of Cortaderia selloana, an invasive species with a strong impact in temperate regions. Methods: We sampled 22 sites invaded by C. selloana along an environmental gradient in northern Spain to evaluate the influence of flower predation, environmental stress, and transgenerational effects on the performance of C. selloana offspring. Key results: We found that over half of the sampled flowers per individual contained larvae of Spanolepis selloanae, a recently discovered predator of C. selloana. This finding suggests that the presence of this natural enemy extends over a larger area than previously thought, which might drastically reduce seed production. A common-garden experiment conducted with over 5,200 seeds revealed that seed germination is significantly enhanced with increasing temperatures (with an optimum temperature of 22/12 °C day/night temperatures), and that seedling survival and growth are highest under waterlogged soil conditions. Our experiments also suggest that the minimum temperature for germination of C. selloana is 10 °C, and that seedlings can survive up to one month without water. These findings can improve management programs by delineating which areas are at high risk of invasion and which ones are unsuitable for the regeneration of C. selloana. We also found that seed mass and maternal plant size are positively correlated with seed germination and early seedling growth. Progeny from dry maternal environments performed better under continuous drought conditions and the opposite was found under wet conditions. Conclusions: Overall, our results suggest that flower predators, environmental stress, and transgenerational effects have complex and profound effects on early demographic stages of C. selloana, influencing seed production, seed germination, seedling growth, and seedling survival.