Intraspecific variation in Potamogeton illinoensis life history and seed germination has implications for restoration in eutrophic lakes

Potamogeton illinoensis is a North American macrophyte, commonly the focus of management, but limited knowledge of its life history hampers conservation and restoration efforts. We conducted greenhouse and growth chamber experiments and field monitoring to understand intraspecific variation in P. illinoensis reproduction and germination traits, monitoring one restored and three natural populations in Central Florida, USA. We assessed reproductive phenology, seed banks in the fall and spring, and germination across different light, temperature, sediment, and ethylene treatments. Flowering and seeding occurred spring through fall, with the highest seed bank densities in fall and minimal seeds detected in late spring. Seeds germinated at the highest percentages in light from 20 to 25°C, and at higher percentages in highly organic field-collected soil. Seeds treated with ethephon, which emits ethylene (commonly produced by submerged organic sediments), germinated at nearly twice the percentage as those exposed to water alone. While these reproductive and germination patterns were true across populations, there was variation among populations in seed bank densities, the most favorable germination temperatures, and overall germination percentages, indicating population differences contribute to reproductive performance. These results suggest restoration via seeds will be limited in conditions with low light or in unconsolidated sediments where burial is likely.