Germination response of dimorphic seeds of two halophyte species to environmentally controlled and natural conditions

To determine whether or not tolerance limits at the germination stage of development and annual germination patterns affect plant distribution in an inland salt marsh, we assessed germination of dimorphic seeds for Atriplex prostrata Boucher ex DC. and Salicornia europaea L. under field and laboratory conditions. Statistically significant differences were found in germination across marsh zones for both species in the field. However, germination percentages for small seeds of A. prostrata and S. europaea were above 50% and 75%, respectively, across all zones for seeds placed on the surface. For large seeds of each species placed on the surface, germination was above 90% across all zones. Small seeds for both species had primary dormancy, a light requirement for germination, and appeared to exhibit dormancy cycling. Large seeds of A. prostrata were nondormant from December through March, whereas large seeds of S. europaea were nondormant when produced. Persistent seed banks were most likely to be formed from small seeds of both species. Seeds typically germinate in the spring when salinity across the marsh is sufficiently low for seeds to germinate in all zones, indicating that the germination stage of development does not effect the spatial distribution of A. prostrata or S. europaea on the marsh.Key words: Atriplex prostrata, seed dormancy and germination, halophyte, Salicornia europaea, seed dimorphism, salt marsh zonation.