Germination responses of Mediterranean populations of Cakile maritima to light, salinity and temperature

Soil salinity is among the main factors influencing seed germination in coastal dunes, acting as a major determinant of species establishment and growth. Tolerance to salinity during the germination process is crucial especially for species of the drift line, which are exposed to high levels. Cakile maritima is an annual species of coastal dunes which can suffer from the effects of salt-spray and seawater inundation. We investigated the effect of light, temperature and salinity on seed germination of C. maritima in three populations of the Mediterranean Basin (central Italy, Sardinia and Mallorca). Results showed higher germination percentage in the dark, although the species was only weekly photoinhibited. Germination increased at 25°C and decreased under NaCl conditions. Exposure to NaCl increased mortality, especially at high temperature, suggesting a toxic effect on seeds. However, the response to salinity differed between populations, seemingly depending on the degree of aridity of collection sites: seeds from Sardinia (the most arid collection site) were the most salt-tolerant, while seeds from Mallorca (with the highest values of precipitation, especially in spring), were the least salt-tolerant. These germination patterns suggest that although being under the same macroclimate conditions, beach populations can be subjected to local conditions, such as aridity, influencing population responses at fine scale. In the context of global climate change, the investigation of germination under varying environmental factors can provide important information for understanding population dynamics, predicting the response of species to climate change and setting restoration plans.