黄土高原是世界上生境破碎化和生物多样性衰减最为严重地区之一，探讨生境隔离对植物种群遗传效应及影响机制一直是生态学、保护生物学、种群遗传学研究的热点之一。中国沙棘广泛分布于该地区不同微生境中，近年来，由于人类活动和气候变化的影响导致不同中国沙棘种群之间生态隔离加剧。本文选取中国沙棘作为试验材料，以黄土高原西部为主要研究区，在不同空间尺度上，以ISSR、SSR分子标记作为遗传分析手段，采用点格局、空间自相关分析、Mantel检验作为空间统计工具，以父本分析、TwoGener模型作为花粉流估测方法，对中国沙棘进行了遗传多样性本底调查、对其遗传结构进行了空间分析以及对交配系统与花粉流等进行了广泛研究，初步探讨了环境长期破碎化对中国沙棘各群体遗传效应的影响以及各群体对生境的响应。主要结论如下：1．按照中国沙棘的分布区进行取样，采用ISSR分子标记技术在2000km范围的18个种群进行了遗传多样性本底调查，结果发现：18个种群物种水平的多态位点百分率为98.9%，种群水平从40.74%（甘肃子午岭种群GanZi）变化到74.07%（河北双月种群HeSY），平均为55.14%。在物种水平用Shannon信息指数(I)估计的遗传多样性指数为0.4255，Nei基因多样性指数（H）为0.2778，都表明中国沙棘遗传多样性丰富，是中国沙棘分布广、适应性强的遗传学基础。基于Nei的基因分化系数为Gst为0.4087，也就是40.87%的遗传分化存在于种群之间，AMOVA分析结果也证明群体间存在高度的遗传分化（Fst=0.257），基因流的结果（Nm<1）显示种群之间基因交流少；聚类分析结果显示各地种群聚在一起，表现出明显的地方特色。经Mantel检验发现遗传距离与地理距离具有显著的正相关关系（r=0.436，P＜0.001），表明生境差异与距离隔离驱动着中国沙棘不同种群分异加重。 2．利用点格局分析方法以及空间自相关统计方法对黄土高原500km范围的自东向西分布的中国沙棘六个种群进行了空间分布格局分析，按照初始分布状态将六个种群分为两大类：即随机或近随机的大种群包括子午岭（ZWL）、定西（DX）以及马坡（MP）以及聚集或近聚集分布的小种群包括六盘山东（LPSE）、六盘山西（LPSW）以及兴隆山（XLS），结果表明大种群内个体聚集程度受环境影响较大，随着生境自东向西降雨量减少温度降低聚集程度增强，小种群受微生境影响较大，山体阻碍了中国沙棘的有效扩散。植株形体大小与空间分布格局密切相关，幼小植株具有明显的聚集分布趋势，高大植株则表现为随机分布。利用ISSR位点进行遗传变异的空间自相关分析发现绝大部分位点不具有空间结构，呈随机分布，呈显著相关位点所表现出的共同趋势是随着距离的增加个体相似度下降，相距9m以内六个种群的中国沙棘植株在遗传变异上的相似度较高, 而此距离范围以外的植株遗传相似性较低, 说明中国沙棘的有效传粉距离可能主要集中在9m左右。 3．采用微卫星分子标记技术（SSR）对受农田干扰强烈的马坡地区300m范围内四个隔离的中国沙棘小群体共67个成熟个体以及348个幼苗进行了遗传变异分析，结果表明中国沙棘种群子代与亲代相比显著偏离哈温平衡系数（Fis=0.119），表明后代个体部分等位基因来自共同祖先概率较高。个体亲缘性与地理距离相关性分析表明中国沙棘存在邻体效应，符合风媒植物传粉特性，即随着距离增加个体亲缘性降低，这种现象在后代个体中表现更为突出。 4．对四个小群体交配格局的比较研究发现，群体大小与异交率没有直接的对应关系，而是与种群中的雌雄比例密切相关，当雌雄比例越接近1时，异交率趋向增高。另外，比较了四个小群体的近交衰退动态，结果表明四个小群体出现了一定程度的近交衰退现象，近亲交配比例较高，存在近交衰退风险。父本分析和TwoGener模型估测花粉散布的分析结果显示中国沙棘花粉扩散与雌雄比例和繁殖体密度密切相关，花粉的最佳扩散距离为3～12米，超过12米花粉扩散的有效性显著降低。 综上所述，黄土高原生境异质性及破碎化导致中国沙棘群体间分异加剧，种群内个体间聚集程度增加，产生邻体效应，进而近亲交配风险增加，降低种群的生态适合度，不利于该物种的可持续利用，结果表明， 在人工栽培管理中维持良好的种群密度以及雌雄比例是发挥黄土高原防护林可持续效应的必备策略。

Loess Plateau is one of the most severe areas where habitat fragmentation and biodiversity attenuation occur worldwide. To reveal genetic effects of habitat fragmentation on plant populations and its functional mechanism have been one of the hotpoints in ecology, conservation biology and population genetics. Chinese seabuckthorn (Hippophae rhamnoides subsp. Sinensis), as a typical pioneer species, is widely distributed in the different microhabitat of Loess Plateau. In recent years, ecological isolation has been intensified in different populations of H.rhamnoides due to human activities and climate change. In this study, H.rhamnoides was chosen as experimental material and the basal survey of Chinese seabuckthorn genetic diversity had been made. At the scales of various haitats, genetic diversity, mating system feature and gene flow dynamics had been investigated using ISSR and SSR molecular marker as a method of genetic analysis, using a point pattern analysis and spatial autocorrelation analysis and Mantel test as a statistical tool, and using paternal analysis and TwoGener model as a method of estimating pollen flow. The objective of this study is to reveal the effect of long-term habitat fragmentation on genetic variation of Chiense seabuckthorn population and the response of these populations to habitat fragmentation. Major results were listed as follows:1. Sample leaves were collected from individuals of 18 natural Chinese seabuckthorn populations along with its distribution regions within the range of 2000 km. Genetic variation among and within 18 populations of H. rhamnoides was investigated using ISSR markers. Thirteen primers used in this study amplified 188 reproducible bands with 186(98.9%) polymorphic at species level. The percentage of polymorphic bands at the population level ranged from 40.74 to 74.07. The Nei’s genetic and Shannon’s information index were 0.2778 and 0.4255 respective1y at the species level. Based Nei’s GST value and analysis of molecular variance(AMOVA), it showed that higher genetic differentiation had occurred among populations. Gene flow (Nm)was 0.7235.The results showed that subpopulation of H. rhamnoides had higher genetic diversity and higher genetic differentiation among populations. The results of UPGMA cluster analysis showed that 18 populations of H.rhamnoides got together one by one in according with their province. It indicated that they had obvious geographic distribution character. Mantel test showed that genetic distance was significant positively correlated with geographical distance（r=0.436，P<0.001）.These results suggested that the levels of genetic diversity of the present populations of H.rhamnoides are still high. The difference in habitat and isolation by distance are the driver of increasing the diversity of different populations in H.rhamnoides.2. Spatial distribution pattern was analyzed for six Chinese seabuckthorn populations within the area of 500 km ranging from east to west in Loess Plateau using the methods of point pattern analysis and spatial autocorrelation statistics. Six populations will be divided into two categories according to the initial scatter plot:large populations in the form of random or near random distribution, including Ziwuling(ZWL) population,Dingxi(DX) population and Mapo(MP) population; small populations in the form of clumped or near clumped distribution,including Liupanshan east(LPSE) population, Liupanshan west(LPSW) population and Xinglongshan(XLS)population. The results showed that climate environment have an effect on the level of aggregation of individual within large population, with the rainfall to reduce and the temperature lower from east to west, the level of aggregation of individual within large population enhanced. Microhabitat has impact on small popultion, by reason of mountain hindered the effective spread of H.rhamnoides. Plant physical size closely related to spatial distribution pattern.Short plants have trends in the form of clumped distribution, while tall plants have trends in the form of random distribution. Spatial autocorrelation analysis of Genetic variation using ISSR locus found that most of locus have no spatial structure,which showed a random distribution. Few locus that have significant correlation with spatial distance had the common trend in which individual similarity decline with spatial distance increased.Genetic variation of H.rhamnoides between the individual showed similarity within 9m apart.It indicated that the effective pollination distance of H.rhamnoides may be mainly concentrated in about 9m.3. Sixty-seven adult individuals and three hundred and forty-eight seedlings were selected from four small Chinese seabuckthorn population which were separated mutually in Mapo county where ecosystem had been strongly disturbed by the farmland, to analyze the genetic varation using SSR molecular marker. The results showed offspring populations compared to parentage showed significant deviations from Hardy-weinberg equilibrium(Fis=0.119), it indicated that the probability from the common ancestor is very high in the offspring individual alleles. The correlation analysis between individual relatedness and geographic distance showed that there is neighborhood effect in H.rhamnoides population. The relatedness between individuals reduced with an increase of distance, especially in offspring individuals.4. Outcrossing rates of four populations were calculated by using MLTR program.The results showed that outcrossing rate of H.rhamnoides is closely related with the proportion of male and female, while is not closely related with population size.The proportion of male and female is closer to 1, outcrossing rate is higher.Further analysis of inbreeding depression was found that there was inbreeding depression in four populations of H.rhamnoides, However, the proportion of mating close relatives was high. It suggested that there exists high inbreeding depression risk in H.rhamnoides populations. The average of pollen flow distance was measured by both paternity and TwoGener analysis. The observed short-pollen dispersal distance is probably related to the proportion of male and female and the density of reproductive trees. The optimal dispersal distance of H.rhamnoides is 3-12m, if more than 12m, pollen dispersal is easy to be limited.In conclusion, habitat fragmentation of Loess Plateau caused the differentiation intensified among populations of H.rhamnoides,the level of aggregation increased between individuals within populations. H.rhamnoides between individuals has strong neighborhood effect,thereby increasing the risk of mating close relatives,consequently it will reduce the ecological fitness of the population,not conductive to the sustainable use of the species.The results suggested that keeping a good proportion of male and female and population density in artifical cultivation management is a necessary strategy for sustainable effect of shelterbelt on Loess Plateau.