Germination Response of the Freshwater Invasive Iris pseudacorus to Brackish and Marine Salinity as Well as Implications for Coastal Invasion

Abstract

Clarifying the conditions in which a species can germinate helps elucidate dispersal and establishment patterns. Conventionally considered a freshwater species, evidence indicates that the invasive Yellow flag iris (Iris pseudacorus), originally from North Africa, East Asia and Europe, tolerates saline conditions. Clarifying how water-dispersed I. pseudacorus seeds respond to seawater immersion is critical to understanding marine dispersal and invasion risk for coastal habitats. Accordingly, we evaluated the impact of salinity on the germination of I. pseudacorus. Using seeds from marine and freshwater I. pseudacorus populations, we assessed how the duration of immersion (15, 30, 60, and 90 days) in varying salinities (0, 13–15, 33–35 practical salinity units [PSU]) affected germination, and whether immersion in freshwater following saline exposure impacted germination or seed viability. Seeds sourced from freshwater consistently outperformed seeds from the marine population. Neither salinity concentration nor immersion duration had a statistically significant impact on germination, and nearly all seeds remained buoyant in marine saltwater (33–35 PSU) for 90 days. Saline immersion and germination conditions inhibited germination unless seeds received a freshwater recovery. The freshwater population of seeds had statistically significantly thicker seed coats, but there was no discernible difference in mean seed weight. Seeds from both populations remained viable after prolonged salinity exposure (90–165 days). We posit that observed differences in germination between the two populations may arise from seed dormancy mechanisms rather than seed fitness. Our results suggest that I. pseudacorus seeds could disperse vast distances through the marine environment, possibly habitat-hopping to reach increasingly suitable ecosystems.