A COMPARATIVE-STUDY OF THE SEED-GERMINATION BIOLOGY OF A NARROW ENDEMIC AND 2 GEOGRAPHICALLY-WIDESPREAD SPECIES OF SOLIDAGO (ASTERACEAE) .2. GERMINATION RESPONSES OF BURIED SEEDS IN RELATION TO SEASONAL TEMPERATURE CYCLES

Seeds of the narrow-endemic Solidago shortii and of the geographically -widespread S. altissima and S. nemoralis collected and buried in 1992 and 1993 were incubated in light and in darkness at 15/6 degrees, 20/ 10 degrees, 25/15 degrees, 30/15 degrees or 35/20 degrees C following various periods of burial in soil in a non-temperature-controlled glas shouse. At maturity in November, seeds of the three species germinated to 0-1% in light at 15/6 degrees C and to 10-77% at 20/10 degrees, 25 /15 degrees, 30/15 degrees and 35/20 degrees C. Seeds exhumed each Apr il from 1993 to 1996 and incubated in light at 15/6 degrees and 20/10 degrees C germinated to greater than or equal to 83% and greater than or equal to 90%, respectively, whereas those exhumed each September of 1993-96 germinated to less than or equal to 2% and less than or equal to 40%, respectively. At 25/15 degrees, 30/15 degrees and 35/20 degre es C in light, seeds of S. altissima and S. shortii germinated to grea ter than or equal to 52% and those of S. nemoralis to greater than or equal to 19%, regardless of when they were exhumed. Timson's index, wh ich integrates percentages, rates and times for onset of germination, was higher at all temperature regimes for seeds exhumed in April 1995 than for those exhumed in September 1995. Freshly-matured seeds of the three species germinated to 0-11% in darkness. Furthermore, regardles s of when they were exhumed, seeds of S. altissima and S. nemoralis in cubated in darkness germinated mostly to only 0-9% over the range of t emperature regimes. In contrast, less than or equal to 88% and less th an or equal to 6% of the seeds of S. shortii exhumed and incubated in darkness each April and September of 1993-96, respectively, germinated , less than or equal to 1% of them germinating while buried in soil. T hus, although buried seeds of all three species exhibited an annual co nditional dormancy/non-dormancy cycle, only those of S. shortii exhibi ted cyclic changes in their germination response in darkness.