GERMINATION REQUIREMENTS OF OENOTHERA-BIENNIS SEEDS DURING BURIAL UNDER NATURAL SEASONAL TEMPERATURE CYCLES

Buried seeds of Oenothera biennis, which have the potential to form lo ng-lived seed banks, were investigated to determine whether or not the y (i) undergo seasonal changes in their dormancy states and (ii) requi re light for germination. Seeds were buried in soil and exposed to nat ural seasonal temperature changes. Samples of seeds were exhumed at mo nthly intervals for 31 months and tested for germination in light and darkness at 12-h daily thermoperiods of 15:6, 20:10, 25:15, 30:15, and 35:20 degrees C. At maturity in autumn, seeds germinated to 84-95% in light at 30:15 and 35:20 degrees C, but to 0-69% at other test condit ions. By late winter, seeds germinated to 95-100% at the five thermope riods in light and in darkness. In summer and autumn, germination in l ight decreased at 15:6 degrees C, and in darkness it dropped to 0% at 15:6 degrees C and decreased at 20:10, 25:15, 30:15, and 35:20 degrees C. Following the second winter of burial, seeds germinated to near 10 0% at all thermoperiods in light and darkness. Thus, seeds exhibited a n annual nondormancy - conditional dormancy cycle, being nondormant fr om midwinter to late spring and conditionally dormant in summer and au tumn. Oenothera biennis is 1 of 10 species whose seeds live for 39-40 years or longer in soil and also have an annual conditional dormancy - nondormancy cycle. Seeds of six of these species, including O. bienni s, can germinate in darkness in spring or summer at simulated habitat temperatures. Therefore, a light requirement for germination is not ne cessarily a prerequisite for long-term survival of buried seeds, and s omething other than darkness prevents germination of seeds of some spe cies buried in soil.