From seed to seedling: A critical transitional stage for the Mediterranean psammophilous species Dianthus morisianus (Caryophyllaceae)

Seed germination, seedling emergence and seed persistence in the soil were investigated for Dianthus morisianus (Caryophyllaceae), a psammophilous endemic species of Sardinia. Stored and freshly collected seeds were incubated in a range of constant temperatures (5-25 degrees C) and an alternating temperature regime (25/10 degrees C). The effect of seed burial depth on seedling emergence was investigated under controlled environmental conditions. Seed persistence in the soil was verified by in situ experimental seed burials. Seeds of this species were non-dormant, and all seed lots germinated both in the light and darkness, mainly at low temperatures (<= 20 degrees C), with a maximum at 15 degrees C (>= 95%). Optimal seedling emergence was obtained when seeds were buried at a depth of 1-2 cm, and a declining emergence with increasing depth was observed. D. morisianus was also unable to form a persistent soil seed bank. The fate of the seeds that, after dispersal, do not emerge from the soil in the spring is, therefore, presumably to die before the next favourable growing season.