Effects of seed traits and dormancy break treatments on germination of four aquatic plant species

Germination biology and dormancy-breaking requirements of fully aquatic (submerged and floating) plant species remain relatively understudied. This is a significant impediment to efforts to restore vegetation in freshwater systems, where the abundance of seeds, and possibility of sowing them in large numbers, suggests underutilized potential for active revegetation. We assessed the influence of seed traits (mass and shape) and two treatments to break dormancy (scarification and gibberellic acid) on the germination of seeds of four macrophyte species after cold-stratification. For all species, untreated seeds did not germinate (0% rate), despite relatively high seed viability (42–90% across species). For Potamogeton illinoensis and P. natans, scarification plus gibberellic acid increased germination the most, to 83% and 35%, respectively (corrected for viability). The other two species remained wholly (Brasenia schreberi) or overwhelmingly (Nuphar variegata) ungerminated. For the two species that did germinate, germination probability increased with seed mass (P. natans and P. illinoensis) and elongation (P. natans). While the small size of trait effects relative to seed treatment effects suggests the latter are more important for revegetation work, the trait patterns highlight evolutionary tradeoffs in seed-size investments. The two Potamogeton species we examined show promise for use in revegetation via seeding, whereas B. schreberi and N. variegata dormancy break has not been adequately developed for these species to be used in seeding-based revegetation.