Seasonal Changes in the Germination Responses of Buried Seeds of Arabidopsis thaliana and Ecological Interpretation

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Abstract
Buried seeds of A. thaliana exposed to natural seasonal temperature changes exhibited an annual dormancy/nondormancy cycle. The majority of freshly matured seeds were dormant. During burial in summer, fresh seeds and those that had been buried for 1 and 2 yr afterripened. During afterripening, seeds first germinated at 15.degree./6.degree. C and then at progressively higher temperatures until they were nondormant by Oct., when they germinated to high percentages at all thermoperiods except 35.degree./20.degree. C. Light was required for germination of both conditionally dormant and nondormant seeds. During autumn and winter, seeds reentered dormancy, first losing the ability to germinate at high and then at low temperatures. Thus, seeds can germinate in the field only in autumn, and germination is restricted to those seeds on or near the soil surface where both light and moisture can be nonlimiting. In spring, seeds are dormant; in summer, temperatures are too high for germination, and in winter, they are too low. Consequently, A. thaliana behaves as a winter annual.