VARIATION IN THE ANNUAL DORMANCY CYCLE IN BURIED SEEDS OF THE WEEDY WINTER ANNUAL VIOLA-ARVENSIS

Seeds of Viola arvensis collected in different years and in different months within those years were buried in soil under natural seasonal t emperature cycles, and changes in their germination requirements monit ored. Seeds were dormant at maturity in May or June, but nondormant by autumn. During winter, some seeds entered dormancy, while others ente red conditional dormancy, i.e. retained the ability to germinate at 15 /6 and 20/10 degrees C but not at other thermoperiods. Dormant and con ditionally dormant seeds became nondormant the following summer. Seeds collected in 1981 exhibited an annual dormancy:nondormancy cycle, whi le those collected in 1982 exhibited an annual conditional dormancy:no ndormancy cycle. The type of dormancy cycle found in these seed lots d uring their first year of burial persisted in subsequent years. Thirty -five and 36% of seeds collected in May 1983 and 1986, respectively, w ere conditionally dormant the following May, while only 5 and 9% of th ose collected in the same field in June 1983 and 1986, respectively, w ere conditionally dormant. Dormant seeds collected in 1981, 1982 and 1 984 and buried at 5 degrees C during summer germinated to 0, 33 and 0% respectively, at 15/6 degrees C in autumn. After the 1982 seeds becam e nondormant during summer, only 25% entered conditional dormancy when buried at 5 degrees C, but after the 1981 and 1984 seeds became nondo rmant, 100% entered conditional dormancy at 5 degrees C. Thus, the per sistent seed bank of V. arvensis at a population site may consist of s eeds with an annual dormancy:nondormancy cycle and others with an annu al conditional dormancy:nondormancy cycle. This is the first report of the two types of annual seed dormancy cycles in the same species.