Germination characteristics of shingle beach species, effects of seed ageing and their implications for vegetation restoration.
Restoration of coastal-shingle vegetation at Sizewell, Suffolk, UK, after construction of a power station, was underpinned by an investigation into the germination ecology of six key species: Crambe maritima, Eryngium maritimum, Glaucium flavum, Honckenya peploides, Lathyrus japonicus and Rumex crispus. The use of indigenous seed, collected from the site before the 6-year construction project, necessitated long-term storage. The effects of seed aging on viability and germination responses to temperature, light and salinity were examined to determine how any reduction in germination might be mitigated. Innate seed dormancy was important in all species, except R. crispus. C. maritima and L. japonicus showed hard-seed dormancy. Stratification of E. maritimum, G. flavum and H. peploides effectively softened the pericarp or testa, and satisfied their varying requirements for low temperature to overcome physiological dormancy. All species germinated well in diurnally alternating temperature regimes. Germination of H. peploides was promoted by light, but the other species were insensitive to light. Increasing salinity progressively reduced germination rate relative to that in distilled water, and sea water at concentrations of 50% or more completely inhibited germination. Seed storage at low temperature and humidity for 7 years did not affect innate dormancy, except in H. peploides, where the requirement for stratification was lost. Storage reduced germination rate in all species, except R. crispus. Aging resulted in considerably less germination at higher temperatures in some species. Salinity-enforced dormancy was significantly greater in aged seed for four of the species. The promotion of germination by light in H. peploides disappeared with age. These changes represented a narrowing of the environmental conditions that allow germination, even when viability only declined slightly.