The timing of germination is a key life-history trait in plants, which
is strongly affected by the strength of seed dormancy. Continental-wide
variation in seed dormancy has been related to differences in climate
and the timing of conditions suitable for seedling establishment.
However, for predictions of adaptive potential and consequences of
climatic change, information is needed regarding the extent to which
seed dormancy varies within climatic regions and the factors driving
such variation We planted 17 Italian and 28 Fennoscandian populations of
Arabidopsis thaliana in the greenhouse and at two field sites in Italy
and Sweden. To identify possible drivers of among-population variation
in seed dormancy, we examined the relationship between seed dormancy and
climate at the sites where populations were originally sampled. Seed
dormancy was on average stronger in the Italian compared to the
Fennoscandian populations, but also varied widely within both regions.
Estimates of seed dormancy in the three maternal environments were
positively correlated, but seeds had on average stronger dormancy when
produced in the greenhouse than at the two field sites. Among
Fennoscandian populations, seed dormancy tended to increase with
increasing summer temperature and decreasing precipitation at the site
of origin. In the smaller sample of Italian populations, no significant
association was detected between mean seed dormancy and climate at the
site of origin. The correlation between seed dormancy and climatic
factors in Fennoscandia suggests that at least some of the
among-population variation is adaptive and that climate change will
affect selection on this trait.