Seed dormancy cycling and mortality differ between two locally adapted populations of Arabidopsis thaliana

Intraspecific variation in seed bank dynamics should contribute to local adaptation, but is not well studied. The extent to which genetic and environmental factors affect dormancy cycling and seed mortality was investigated in the annual herb Arabidopsis thaliana by conducting a reciprocal seed burial experiment.

Seeds from two locally adapted populations (from Italy and Sweden) were buried at both of the sites of origin, and seed mortality and germinability were determined during the following 2 years for initially non-dormant glasshouse-matured seeds and dormant field-matured seeds.

Mean soil temperature was higher at the Italian site compared with the Swedish site throughout the year, and the germination proportions were in general higher for seeds buried in Italy than in Sweden. The rate of secondary dormancy induction of the Italian genotype was faster than that of the Swedish genotype at both sites, while the opposite was true for the rate of dormancy release, at least at the Swedish site. The comparison of non-dormant glasshouse seeds with dormant field seeds demonstrated that A. thaliana seeds can adjust their dormancy levels to current environmental conditions, and suggests that maternal environmental conditions have only minor effects on dormancy cycles. At both sites, locally produced seeds had low germinability in the first year compared with the second year, suggesting that a considerable fraction of the seeds would enter the seed bank. In Italy, but not in Sweden, seed mortality increased rapidly during the second year of burial.

This is the first demonstration of intraspecific genetic differentiation in the annual seed dormancy cycle of any species, and the documented difference is likely to contribute to local adaptation. The results suggest that the contribution of a seed bank to seedling recruitment should vary among environments due to differences in the rate of seed mortality.