Effect of salt stress on the germination of Silene hicesiae (Caryophyllaceae), an insular endemic from the Tyrrhenian hot-spot

The increase in soil salinity, being a global trend in the actual scenario of environmental changes, may represent a threat to the conservation of endangered plant species. The effect of salt stress is stronger during earlier stages of plant life and to study its effect on seed germination is crucial when planning seed-based restoration of endangered plant populations. Silene hicesiae is a threatened endemic species of the Aeolian Islands (Italy). The effect of salt stress on seed germination was evaluated using NaCl and its alleviation by KNO3 was tested in two factorial experiments, investigating, respectively, the interactive effect of salt stress, KNO3 and temperature and the interactive effect of NaCl, KNO3 and seed size. To assess the recovery ability of seeds, non-germinated seeds were re-sown in water-agar. Final germination percentage of S. hicesiae decreased with increasing NaCl concentration and temperature. KNO3 did not alleviate salt stress. Seed size did not influence germination as main effect but in interactions with NaCl and KNO3. Seed viability was not excessively compromised by salinity but recovery was lower for seeds incubated at 20 °C and for small seeds. These findings should be considered when planning in-situ reinforcement action by direct seed sowing.