Comparative germination ecology and seedling growth of two Ibero-Levantine endemic species belonging to the Silene mollissima aggregate (Caryophyllaceae)

The present study was focused on the seed germination and seedling growth of Silene mollissima and S. hifacensis, endemics of the Mediterranean Ibero-Levantine biogeographic province, in order to better understand what environmental factors (e.g. temperature, salinity) influence their ecology and rarity causing their narrow distribution. Inter- and intra-specific variability in the responses to light (12 h light/12 h dark) and darkness, constant and alternating temperatures, salinity tolerance and germination recovery after washing seeds with distilled water were evaluated. Moreover, the biomass production and the growth rate during the early stages of seedling development were measured at several temperatures. Seeds of the two species were non-dormant and light did not affect their germination. For both species, germination was high at the lowest tested temperatures, while at the highest temperatures inter-specific differences were observed. Seeds of the two species were able to germinate up to 250 mM NaCl, furthermore the highest germination occurred in the non-saline control and decreased with increasing salinity. Independently from the tested temperature, S. mollissima and S. hifacensis seeds totally recovered their germination after the NaCl exposure. For both S. mollissima populations the increasing temperature promoted the seedling dry weight and the growth rate, while this pattern was observed only for one S. hifacensis population. This study highlighted that although these species have different needs during their seed germination, they share several common traits in same critical phases of their life cycle. From the ecological viewpoint, our results are consistent with field germination from autumn until spring for S. mollissima and limited to the autumn–winter months for S. hifacensis, when soil moisture is high and salinity levels are low due to the seasonal washout by rainfall. These findings may partially explain the limited distribution of the two species, although further investigation would be needed.