Annual dormancy cycle and influence of flooding in buried seeds of mudflat populations of the summer annual Leucospora multifida

Dormant seeds of Leucospora multifida (Michx) Nutt. were used to determine: (1) temperature requirements for loss of dormancy; (2) if buried seeds undergo seasonal changes in their dormancy states; and (3) effects of flooding on dormancy loss and induction. Seeds came out of dormancy when buried at 5 degrees C and 15/6 degrees C for 12 weeks, but at 20/10 degrees C, 25/15 degrees C and 30/15 degrees C, they gained the ability to germinate only at 30/15 degrees C and 35/20 degrees C. Seeds buried in soil and exposed to natural seasonal temperature changes under non-flooded conditions exhibited an annual conditional dormancy/non-dormancy cycle, being non-dormant in spring and early summer, and conditionally dormant in late summer and autumn. Non-dormant seeds required light for germination at all thermoperiods, and they did not germinate in light or darkness at 15/6 degrees C. Flooding prevented non-dormant seeds from entering conditional dormancy in summer, and it prevented dormant seeds from coming out of dormancy in winter. However, if dormancy loss had started in late autumn prior to flooding, it continued during flooding in winter. Dormant seeds exposed to high temperatures become conditionally dormant, thus those that fail to come out of dormancy during flooding in winter could gain the ability to germinate at summer temperatures on exposed mudflats in summer. Responses of seeds to annual temperature and flooding cycles indicate that they could germinate from April to September or October, depending on when mudflats are dewatered.