& Key message Tetracentron sinense Oliver, an endangered species from China, displays a low within-population genetic diversity and high genetic differentiation among populations, and the existing populations could be divided into three conservation and management units. & Context The endangered tree Tetracentron sinense Oliver has great value; however, little is known regarding the withinpopulation genetic diversity and differentiation among T. sinense populations. & Aims We examined the genetic diversity and differentiation of T. sinense wild populations, and we tested the effect of small-size population on the level of genetic diversity within these populations. & Methods Using inter-simple sequence repeat (ISSR), we assessed the genetic variation and structure among 174 individuals from 26 natural populations of T. sinense sampled across its distribution range in China. & Results The ISSR primers yielded 180 amplified loci (123 were polymorphic). At the species level, the percentage of polymorphic loci (PPL), Nei's gene diversity (H), and Shannon's information index (I) were 68.3%, 0.196 and 0.300, respectively. The average population level PPL was 20.0%, and the Na, Ne, H, and I were 1.20, 1.13, 0.076, and 0.112, respectively. AMOVA revealed high genetic differentiation among populations (52.0% of total variance, P = 0.001), consistent with the gene differentiation coefficient (Gst = 0.607) and gene flow (Nm = 0.326). The 174 individuals of the 26 T. sinense populations clustered into three groups, and T. sinense geographic and genetic distance were significantly correlated. & Conclusions T. sinense exhibited intermediate within-species genetic diversity, indicating preserved evolutionary potential. The low within-population genetic diversity and high genetic differentiation among T. sinense populations may be one of important factors causing endangerment. Three conservation units were determined based on genetic difference and structure. Inter-population introduction of individuals within units via appropriate propagation and seedling management might be an effective strategy for increasing T. sinense within-population genetic diversity and population size.

Background: Tetracentron sinense Oliv., is an endangered, broad-leaved tree distributed in south-central China. Structural characteristics of the community and dominant tree population niches in T. sinense communities are currently unclear. Questions: (1) What is the status of T. sinense populations in the community? (2) What are the interspecies interactions between T. sinense populations and its associated species. Study sites and dates: T. sinense communities in Meigu Dafengding Nature Reserve in southwest China in 2014. Methods: Six sites of 400 m 2 were studied for importance value, special diversity, niche breadth, and overlap of dominant tree populations. Results: There were 80 species, 67 genera, and 41 families of vascular plants. Sixty-one genera of seed plants in T. sinense communities were classified into 9 types. The North Temperate genus was the largest, accounting for 44.26 %. Species richness, species diversity, and evenness indexes were all low. There were 6 dominant tree populations in T. sinense communities, and the importance values and niche breadths of T. sinense populations were significantly higher than other species. Horizontal niche overlaps between T. sinense and Pterocarya stenoptera, Acer pictum subsp. mono, and Cercidiphyllum japonicum were high; the vertical niche overlaps between T. sinense and these species were all greater than 0.7. Conclusions: T. sinense communities have North Temperate character, and are immature and unstable communities, still in the early stage of succession. T. sinense is the edificator tree in the communities. A high similarity of habitat demand and strong interspecific competition for light exist between T. sinense and its associated trees.

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Tetracentron sinense Oliver, as a tertiary living fossil, a dramatic decline in T. sinense population amounts, genetic resources depletion and recent human activities have shaped habitat fragmentation of relict and endangered plants, although there is ample evidence of its great medicinal, economic and ecological value. However, little is known about the genetic evolution of T. sinense. With this work, 193 individuals from 22 natural T. sinense populations regarding its genetic diversity, genetic differentiation, and demographic history using simple sequence repeat (SSR) markers to clarify its evolution models and develop scientific conservation strategies. We evaluated the genetic diversity, population structure and demographic history of 193 T. sinense individuals based on 14 SSR markers. At the species level, PPL, I and He were 100%, 1.631 and 0.559, respectively. At the population level, Na, Ne, I, Ho and He were 3.221, 2.505, 0.937, 0.434 and 0.566, respectively. The results revealed high genetic diversity at the species level and within populations. Individuals were structured into three main clusters (K = 3) with significant genetic differentiation (Fst = 0.31). Demographic history analysis showed that T. sinense differentiated according to the radial differentiation model. The differentiation occurred 1.115×104 to 2.23×104 years ago during Last Glacial Maximum. The twenty–two T. sinense populations revealed moderate genetic diversity and seemed to be structured into three clusters with high differentiation suggesting its preserved the evolutionary potential and the Hengduan Mountains and Qinling Mountains act as the two major glacial refuges. High differentiation caused by long–term geographic isolation may lead to the population extinction. The radial differentiation model suggested that T. sinense originated from common ancestor.