Research highlights: Our study is the first to explore the genetic composition of ancient Cryptomeria trees across a distribution range in China. Background and objectives: Cryptomeria japonica var. sinensis is a native forest species of China; it is widely planted in the south of the country to create forests and for wood production. Unlike Cryptomeria in Japan, genetic Chinese Cryptomeria has seldom been studied, although there is ample evidence of its great ecological and economic value. Materials and methods: Because of overcutting, natural populations are rare in the wild. In this study, we investigated seven ancient tree populations to explore the genetic composition of Chinese Cryptomeria through ddRAD-seq technology. Results: The results reveal a lower genetic variation but higher genetic differentiation (Ho = 0.143, F_ST = 0.1204) than Japanese Cryptomeria (Ho = 0.245, F_ST = 0.0455). The 86% within-population variation is based on an analysis of molecular variance (AMOVA). Significant excess heterozygosity was detected in three populations and some outlier loci were found; these were considered to be the consequence of selection or chance. Structure analysis and dendrogram construction divided the seven ancient tree populations into four groups corresponding to the geographical provinces in which the populations are located, but there was no obvious correlation between genetic distance and geographic distance. A demographic history analysis conducted by a Stairway Plot showed that the effective population size of Chinese Cryptomeria had experienced a continuing decline from the mid-Pleistocene to the present. Our findings suggest that the strong genetic drift caused by climate fluctuation and intense anthropogenic disturbance together contributed to the current low diversity and structure. Considering the species’ unfavorable conservation status, strategies are urgently required to preserve the remaining genetic resources.

The adaptive capacity of tree species is crucial for their survival under environmental change. Liushan (Cryptomeria japonica var. sinensis), an allogamous conifer species, is widely distributed across southern China. However, despite its broad distribution, there have been few investigations on the geographical variation and environmental adaptability of this species. Here, we combined the phenotypic (eight needle traits) and genetic data (14 nSSR loci) to fill this gap by assessing the genetic variation of geographical populations and exploring environmental adaptations of this species. Both phenotypic and molecular genetic analyses indicated a strong genetic differentiation among geographic populations. All populations could be clustered into three groups that were consistent with their geography. Most of the needle traits showed significantly correlated with geography and environmental factors. Geographical isolation and environmental differences are the main factors that have shaped current morphological traits and patterns of genetic variation. We suggest conservation measures to be implemented on a population level with existing populations, especially those with rare phenotypes as the main goal. Our findings shed light on the geographic variation in Liushan and expanded the knowledge of its putative adaptive mechanisms, ultimately benefiting the conservation of this species.