Temporal variation in regeneration events affecting population structure in different size- and life-stages contributes to overall genetic diversity of natural Zelkova serrata population

Abstract

ABSTRACT To clarify the mechanisms underlying the maintenance of genetic diversity in long-lived forest tree populations, it is important to understand the influence of temporal variation in regeneration sites and its effect on population structure (i.e., nonrandom distribution of trees in spatial location and size) and the spatial genetic structure. Features of population structure in four different life stages (current-year seedlings, saplings, juveniles, and adults) were investigated in a natural population of Zelkova serrata. The genetic diversity and genetic structure of these life stages were evaluated using eight microsatellite markers, and the regeneration processes required for maintaining the genetic diversity of the adult tree population were inferred. Within a study plot, differences in spatial distribution among life stages and size classes, and significantly positive spatial autocorrelation of tree sizes (Km(r) statistic) at the adult stage were observed. Analysis of standardized measures of genetic differentiation showed a clear genetic difference among life stages (F’ST = 0.095), with the adult stage exhibiting the highest allelic richness, the highest estimated effective number of contributing parents (N eb), and the highest estimator of spatial genetic structure (Sp statistic). The adult stage may comprise many different cohorts (subpopulations), contributed by different compositions of parents, due to spatially and temporarily distinct regeneration events, and the resulting genetic heterogeneity would contribute to an increase in genetic diversity within the population.