The importance of vegetative and sexual dispersal of Luronium natans

Luronium natans (L.) Rafin. is a very rare macrophyte even though it has the ability to grow in a wide variety of habitat types. Previous studies leave two possibilities for this pattern: the species has a poor ability to disperse and establish or it is unable to grow and develop a sustainable population after colonization.Experiments on establishment of shoots, seed bank dynamics, seed germination and genetic analysis (AFLP) were conducted to establish whether L. natans disperse to new habitats within hydrologically linked water systems by means of vegetative shoots or by seeds. Shoots had high ability to establish by roots (52% in autumn shoots), but only when subjected to water depths <4 cm. Seeds of L. natans has a high germinate rate (mean of 51–60%), and the density of seeds in the seed bank ranged from 635 to 3354 m−2 during a year. Analysis of the genetic diversity showed that samples could be differentiated to individuals with higher diversity between populations than within population. Low ability of shoots to establish if not subjected to low water depth, high germination rate of seeds, substantial seed bank and a high genetic diversity all indicate that most colonization events depend on sexual reproduction.Genetic diversity in L. natans seems to depend on habitat type and management. Habitats subjected to high water velocities or management with weed cutting generally have a lower genetic diversity (5–6%) than habitats subjected to dredging (11%), indicating that the latter habitats favor sexual reproduction.