BASKIN, CAROL C.1,2*, OLLE ZACKRISSON3, and JERRY M. BASKIN3. 1School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225; 2Department of Agronomy, University of Kentucky, Lexington, KY 40546-0091; 3Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences S-901 83 Umea, Sweden. - Role of warm plus cold stratification in promoting germination of seeds with stony endocarps: Empetrum hermaphroditum.
Seeds (true seed + endocarp, hereafter seeds) of Empetrum
hermaphroditum are dormant at maturity in September and October,
and fresh seeds collected at various sites in Sweden germinated to
only 2-5% in light at daily alternating temperature regimes of 15/6,
20/10, and 25/15C. Dormancy was not due to impermeability of the stony
endocarp surrounding each seed, and embryos did not grow prior to
radicle emergence. Thus, seeds did not have physical dormancy or
morphological dormancy. Long periods of cold stratification (32 wk)
and of warm stratification (16 wk) given separately resulted in a
maximum of only 25 and 10% germination, respectively, in light at
25/15C. After 12 wk warm stratification plus 20 wk cold
stratification, however, seeds germinated to 83-93% in light at the
three temperature regimes. When length of the cold stratification
period was constant (e.g. 20 wk), germination increased with increase
in length of the warm stratification treatment preceding cold
stratification. Gibberellic acid promoted germination in a high
percentage of the seeds. Based on dormancy-breaking requirements and
response to gibberellic acid, seeds have intermediate physiological
dormancy. In regions where summers are relatively short and cool (or
if seeds become buried in soils that are cool during summer), the
requirement for warm plus cold stratification to break dormancy may
cause germination of a cohort of seeds to be spread over time, thus
helping explain the occurrence of persistent soil seed banks in this
species.
Key words: life cycle biology, plant ecology, reproductive biology, seed dormancy, seed germination