Cardamine amara L. (Brassicaceae) in dynamic habitats: Genetic composition and diversity of seed bank and established populations

We investigated the distribution of genetic diversity in the strictly outcrossing plant species Cardamine amara using isozyme analysis. We investigated 36 populations from an area of approximately 900 square kilometres in a geographically well-defined region in Northwestern Germany. For these 36 populations we did not find any geographical structuring of genetic diversity. For ten out of the 36 populations we compared the genetic diversity of established population and soil seed bank from two different depths. At these ten sites we also studied differences in the species composition of soil seed bank and of established vegetation as an indicator of environmental dynamics. The corresponding results indicate that increasing dynamics of the habitat decreased the similarity between aboveground vegetation and soil seed bank and the homogeneity of the vertical distribution of seeds. Moreover, increasing environmental dynamics non-significantly increased heterozygosity. In typical, disturbed wet woodland habitats, Cardamine amara established a long-term persistent seed bank with up to 35,900 seeds m(-2). Here the overall genetic diversity stored in the seed bank was similar to the one of the actually established population. Nevertheless, wet woodland seed bank subpopulations from different depths were more similar to each other genetically than compared to the established populations. Most established and seed bank populations were genetically close to Hardy-Weinberg equilibrium. Our study demonstrates that established C. amara populations do not represent simple representative genetic subsets of the underlying seed banks.