Salinity effects on the germination and reproduction of Eryngium maritimum L. (Apiaceae)

Abstract

Coastal ecosystems are globally threatened. As sea level rises, flooding, salt-water intrusion and coastal regression are dramatically changing their environmental conditions. Eryngium maritimum L. (Apiaceae) mainly inhabits white dunes of the Mediterranean and Atlantic coasts. The present study aimed to analyse the effect of salinity on the germination and reproduction of the species. Seeds from Mallorca (Spain) were germinated with four different salts (NaCl, Na2SO4, MgCl2, MgSO4) at concentrations ranging from 0 to 0.4 M. On the other hand, seedlings were grown and watered with different seawater (SW) concentrations ranging from 6.25% SW to full SW. Reproductive investment was assessed considering the number of inflorescences, fruit set and seed set per plant per whorl in the different treatments. Complementarily, field electrical conductivity measurements were carried out in a natural population to assess its variability along the dune. Germination was inhibited by salts, with nearly null germination at concentrations higher than 0.1 M, with significant differences among salts. Specifically, Na2SO4 and MgCl2 strongly affected germination rather than NaCl and MgSO4. Plant dieback increased in concentrations higher than 50% SW. Fruit and seed production was inhibited by the presence of salts even at concentrations of 12.5% SW. Embryonic dune was the most saline area, with decreasing electrical conductivity in white and semi-fixed dunes. These results suggest that E. maritimum can deal with high salt concentrations along its life cycle. However, to germinate and reproduce, it tolerates only low salt concentrations. So, it should be considered as a halotolerant species. Considering its distribution along the dune, the salinity of the strandline could be, along with other factors, responsible for its decrease in fitness in front dunes. As a result of sea-level rise and coastal salinization, it can be hypothesized that the optimal distribution of E. maritimum along the dune will change, shifting from actual foredunes to dune-crests.