A comparative study of the seed germination biology of a narrow endemic and two geographically-widespread species of Solidago (Asteraceae). 3. Photoecology of germination

Regardless of whether or not seeds of the geographically-widespread Solidago altissima and S. nemoralis were exposed to light in autumn, those 'dispersed' in autumn (15/6°c) or winter (5°c) required 12 weeks of light in winter to germinate to ≤80% in darkness in spring (2 weeks at 20/10°c). On the other hand, seeds of the narrow-endemic S. shortii dispersed in autumn and exposed to ≤2 weeks of light in early winter germinated to ≤77% in darkness in spring, and those dispersed in winter and exposed to ≤6 weeks of light germinated to ≤82%. S. altissima and S. nemoralis seeds not exposed to light during any season germinated to only 0-1% in darkness in spring, whereas S. shortii seeds germinated to 45-56%. Seeds of S. altissima and S. nemoralis kept in darkness in autumn and winter needed a 1-day (14-h photoperiod) light exposure in spring to germinate to ≤75% in darkness, whereas those of S. shortii required only one 5-s exposure. Cold-stratified (nondormant) seeds of S. altissima, S. nemoralis and S. shortii exposed to light with a high far-red/red ratio germinated to significantly higher percentages than dark controls and freshly-matured and lab-stored seeds. Results of this study suggest that a soil seed bank of S. shortii should be smaller and be depleted at a faster rate than those of S. altissima and S. nemoralis, and portions of the seeds of the three species can germinate in the far-red-enriched light under plant canopies.