A COMPARATIVE-STUDY OF THE SEED-GERMINATION BIOLOGY OF A NARROW ENDEMIC AND 2 GEOGRAPHICALLY-WIDESPREAD SPECIES OF SOLIDAGO (ASTERACEAE) .3. PHOTOECOLOGY OF GERMINATION

Regardless of whether or not seeds geographically-widespread Solidago altissima nemoralis were exposed to light in autumn, those 'dispersed' in autumn (15/6 degrees C) or winter (5 degrees C) required 12 weeks of light in winter to germinate to greater than or equal to 80% in dar kness in spring (2 weeks at 20/10 degrees C). On the other hand, seeds of the narrow-endemic S. shortii dispersed in autumn and exposed to g reater than or equal to 2 weeks of light in early winter germinated to greater than or equal to 77% in darkness in spring, and those dispers ed in winter and exposed to greater than or equal to 6 weeks of light germinated to greater than or equal to 82%. S. altissima and S. nemora lis 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 a nd winter needed a 1-day (14-h photoperiod) light exposure in spring t o germinate to greater than or equal to 75% in darkness, whereas those of S. shortii required only one 5-s exposure. Cold-stratified (nondor mant) seeds of S. altissima, S. nemoralis and S. shortii exposed to li ght with a high far-red/red ratio germinated to significantly higher p ercentages than dark controls and freshly-matured and lab-stored seeds . Results of this study suggest that a soil seed bank of S. shortii sh ould be smaller and be depleted at a faster rate than those of S. alti ssima and S. nemoralis, and portions of the seeds of the three species can germinate in the far-red-enriched light under plant canopies.