Germination response of the freshwater invasive Iris pseudacorus to brackish and marine salinity as well as implications for coastal invasion

Abstract

AbstractConventionally considered a freshwater species, evidence indicates that yellow flag iris (Iris pseudacorus) tolerates saline conditions. As a water-dispersed species, clarifying howI. pseudacorusseeds respond to seawater immersion is critical to understanding marine dispersal and invasion risk for coastal habitat. Using seeds from marine and freshwaterI. pseudacoruspopulations, we assessed how the duration of immersion (15, 30, 60, and 90 days) in varying salinities (0, 13–15, 33–35 practical salinity units) affected the germination response of seeds, and whether immersion in freshwater following saline exposure impacted germination success or seed viability. Freshwater-produced seeds consistently outperformed those produced by plants persisting in marine conditions. Neither salinity concentration nor duration of immersion had a statistically significant impact on germination success. Exposure to saline conditions fully inhibited germination unless seeds received a freshwater recovery. Seed coat thickness was statistically significantly greater among the freshwater population, but there was no discernible difference in mean seed weight. Seeds from both populations remained viable following prolonged exposure to salinity. We posit that observed differences in germination between the two populations may arise from dormancy mechanisms rather than seed fitness. Overall, our results suggest thatI. pseudacorushas the capacity to disperse vast distances through the marine environment, potentially habitat-hopping to reach ecosystems characterized by freshwater input, such as estuaries or saltmarshes. Management efforts should target early detection of the species in freshwater-enriched coastal habitats and react rapidly to remove individuals before they become established.