濒危物种保护是生物多样性理论和应用研究的重要内容，濒危物种遗传多样性和种群间遗传分化的研究能为合理有效保护对策的制定提供重要的理论依据。如果是历史时间尺度上种群瓶颈等因素导致种群遗传多样性低，那么大尺度上的基因流或者近缘种的基因流引入可能是更合理的保护对策。如果是近期局部种群遗传多样性降低，那么促进种群间基因流可能是合理的保护对策。所以，濒危物种的遗传风险评估主要集中在种群内遗传多样性水平和种群间遗传分化这两个参数上。巴山水青冈（Fagus pashanica C. C. Yang）是壳斗科（Fagaceae）水青冈属落叶乔木，是中国特有植物，主要分布在大巴山山脉一带，浙江地区也有零星分布。近年来，由于人类活动过于频繁，巴山水青冈分布面积和数量都在减少。本研究以巴山水青冈为研究对象，根据种群遗传学相关理论，并利用分子生态学手段，分析巴山水青冈的遗传多样性、种群遗传结构以及种群历史动态，为巴山水青冈的管理提供一定的科学依据。

本研究采用15个微卫星（也称SSR）位点，对22个巴山水青冈种群、1个台湾水青冈种群，共690个个体，着重从遗传多样性和种群间遗传分化两个方面展开了种群遗传学分析。台湾种群与大陆其他种群遗传分化明显，表明台湾种群可能是台湾水青冈，而大陆种群是巴山水青冈。针对巴山水青冈种群遗传变异的分析结果显示：（1）巴山水青冈种群遗传多样性相对较低，其中大巴山-神农架区域种群遗传多样性相对较高。等位基因数目A平均值为3.930，有效等位基因数目A_e平均值为2.000，观测杂合度H_o平均值为0.413，期望杂合度H_e平均值为0.416，无偏期望杂合度UH_e平均值为0.424，等位基因丰富度Ar平均值为3.142，特有等位基因丰富度情况P_A平均值为0.058。（2）巴山水青冈种群聚类分析表明，巴山水青冈种群分布没有明显的地理格局，种群间遗传分化程度较低，F_st值为0.048。（3）种群历史动态分析发现，巴山水青冈大约在1.37万年前经历过非常严重的瓶颈，导致巴山水青冈的有效种群大小非常小。

综上所述，巴山水青冈遗传多样性水平相对较低，种群间遗传分化程度低，没有明显的种群遗传结构。这表明当前巴山水青冈分布区的地理隔离，可能是近期一些过程导致的。大巴山-神农架区域可能是巴山水青冈度过第四纪冰期的避难所。经历严重的瓶颈后，巴山水青冈有效种群大小急剧降低，丢失大量遗传变异。巴山水青冈的保护，一方面对其生境进行保护，另一方面，如果巴山水青冈种群越来越小，遗传多样性持续降低，可能要考虑适当引入近缘种基因流，提高遗传多样性水平。

The evaluation of genetic risks of endangered species is crutial for its conservative strategies. The information of genetic diversity and genetic differentiation among populations could provide important theoretical basis for the effective managements of endangered species. If the historical bottleneck and other factors lead to low population genetic diversity, the introduction of gene flow on a large scale or from related species may be more effective. If the genetic diversity of local populations has decreased recently, the promotion of gene flow among populations may be essential. Therefore, genetic risk assessment of endangered species focused on the genetic diversity within populations and the genetic differentiation among populations. Fagus pashanica C. C. Yang, a tree species from Fagaceae, which is endemic to China as a deciduous tree, mainly distributed in the Dabashan Mountains and there was a little of the beech distributing in Zhejiang. In recent years, due to human activities, the distribution area and the number of this beech were on the decline. Therefore, this study aimed to analyze the genetic diversity, genetic structure and historical dynamics of the endangered F. pashanica populations, and to provide suggestions on its conservation.

In this study, 15 nuclear simple repeat sequences (SSR) loci were used to analyze 22 populations of F. pashanica and one population of F. hayatae Palibin., with a total of 690 individuals. The Taiwan population was significantly different from other populations in mainland China in genetic variation, which supported the point that the Taiwan population was F. hayatae and the mainland populations were F. pashanica. The population genetics analyses of the F. pashanica populations showed: (1) The genetic diversity of F. pashanica was relatively low. The average value of number of alleles (A) was 3.930, the average value of effective number of allele (A_e) was 2.000, the average value of observed heterozygosity (H_o) value was 0.413, the average value of expected heterozygosity (H_e) was 0.416, the average value of unbiased expected heterozygosity (UH_e) was 0.424, the average value of the allele richness (Ar) was 3.142, the average value of the unique allele richness (P_A) was 0.058; (2) The populations were not genetically clustered. The degree of genetic differentiation among populations was low, with the F_st of 0.048; (3) the F. pashanica populations have experienced a significant bottleneck 13,700 years ago, which led to a very small effective population size of this endangered species.

As a summary, both the within-population genetic diversity and the among-population genetic differentiation were low, which suggested that the fragmented population spatial structure resulted from some recent processes by combining the positive correlation between genetic and geographic distance. The Dabashan-Shennongjia area may be the refuge of this beech through the Quaternary glacial period as indicated by the highest genetic diversity in this area. The effective population size declined dramatively because of a bottleneck event. According to the genetic variation of F. pashanica, if the population size became smaller, the effective conservation strategy may focus on the increase of genetic diversity by introducing gene flow from related species. In addition to this strategy, protecting the habitat of F. pashanica was necessary.