Differences in light and temperature responses determine autumn versus spring germination for seeds of Schoenolirion croceum

Seeds of the southeastern North American Schoenolirion croceum (Michx.) Wood are dormant when dispersed in late spring to early summer. Fresh seeds buried in soil after dispersal germinate in autumn, whereas those sown on the soil surface do so the following late winter – early spring. To understand this difference in germination phenology, we examined the light and temperature requirements for dormancy break and germination. Seeds germinated to high percentages in darkness over 12:12 h thermoperiods ranging from 15:6 to 35:20 °C following warm stratification (25:15 °C) in darkness, whereas no seeds germinated in light following stratification in light. On the other hand, seeds germinated to high percentages in light and in darkness following cold stratification (5 °C) in light or darkness. Seeds exposed to light during autumn germinated in winter–spring regardless of the light regime in summer or winter–spring, whereas those in darkness during autumn germinated in autumn regardless of the light regime in summer. Thus, light conditions during autumn are critical for determining whether seeds will germinate in autumn versus early spring. In contrast with many other species in which germination phenology is mostly temperature controlled, timing of germination for S. croceum depends on the light conditions in relation to temperatures experienced during dormancy release.Key words: dark, germination phenology, Hyacinthaceae, negative photoblastic seeds, photoecology, seed dormancy.