Abstract: Genetic changes over space and time provide insights into the relative roles of evolutionary factors in shaping genetic patterns within plant populations. However, compared with spatial genetic structure, few studies have been conducted on genetic changes over time. In this study, we used six polymorphic microsatellite loci to assess genetic variation of six size-classes of the population of Liushan, Cryptomeria japonica var. sinensis, in the Tianmushan National Nature Reserve, whose origin was debatable. The mean number of alleles per locus and expected heterozygosity were 4.583 and 0.599 9 respectively, lower than other conifers with the same life history characteristics. FST was 0.002 ± 0.003, and the pairwise test revealed no significant differentiation in any pair of size classes. Significant heterozygosity excesses were detected in five size classes except the oldest one, indicating bottleneck event(s). The above results support the hypothesis that Tianmushan population was introduced and followed by natural regeneration.

Key words: Cryptomeria japonica var. sinensis, founder effect, genetic variation, microsatellites, size class