Different Germination Strategies Displayed by Three Potamogeton Species: P. natans, P. lucens, and P. pectinatus

Aquatic plants may rely on seeds to promote population persistence after severe disturbances, such as droughts. We characterized the seed germination dynamics for three Potamogeton species following seed storage under dry versus submerged conditions. Overall germination levels were highest for P. lucens and, more specifically, were higher after submerged storage (70.4%) than dry storage (56.0%). Overall germination levels were lower for the two other species and displayed a different response to storage conditions; they were higher after dry storage (P. natans: 24.6%; P. pectinatus: 28.1%) than submerged storage (10.8 and 7.1%, respectively). Only P. natans would have likely made a large seed bank contribution as follows: 42.2% of its seeds remained ungerminated and viable after submerged storage, while this figure was 17.4% for seeds that had experienced dry storage. Our results suggest the species differ in their reproductive strategies. Sexual reproduction plays an important role in Potamogeton lucens, adding new individuals to plant populations every year; however, the low viability of the species’ ungerminated seeds suggest its seed bank contribution may be small, rendering it vulnerable to long periods of unfavourable environmental conditions. In contrast, P. natans would likely make a larger seed bank contribution, underscoring the role its seeds may play in population persistence across years. Potamogeton pectinatus may minimally rely on its seeds, which fits with its predominant use of vegetative reproduction in the field. While its seeds might contribute little to population persistence, they may nonetheless promote genetic variability among populations.