Dormancy patterns in buried seeds of Datura ferox and D. stramonium

Abstract

Seasonal changes in seed dormancy of Datura ferox L. and D. stramonium L. were studied during 2 years in seeds buried in the field and compared with changes in dormancy of dry-stored seeds. Dormancy levels were evaluated by measuring the germination of exhumed and dry-stored seeds under 32:27 °C (nondormant seeds) or 32:12 °C (relatively dormant seeds). Levels of relative or full dormancy did not change during 2 years of dry storage in either species. Seed burial at 20 cm accelerated after-ripening, and primary dormancy disappeared earlier than at 5 cm. However, burial depths greater than 10 cm prevented germination in situ. This inhibition was not due to smaller daily fluctuations of soil temperature with increasing depth, since seeds buried at 20 cm and kept at 32:12 °C also failed to germinate. Transferring seeds to shallower soil layers allowed their germination. Cyclic seasonal changes in dormancy were found in buried seeds of D. ferox but not in D. stramonium. In D. ferox, dormancy was alleviated during the winter and germinability was maximal in early spring; the increase in dormancy was preceded by high late spring – summer temperatures. In D. stramonium most seeds near the soil surface germinated in the field in a brief flush in early winter, at temperatures under which D. ferox did not germinate. Key words: Datura, germination, dormancy, buried seeds, temperature.