【作者】 徐怀同；

【导师】 陈存根；

【作者基本信息】 西北农林科技大学 ， 生态学， 2013， 博士

【摘要】 北美香柏是北部森林重要树种，被北美的许多州/省列为濒危物种。对其种群动态、遗传结构和多样性等进行深入研究，对维持生态系统稳定、种质和基因资源保护、可持续森林管理等方面具有重要意义。本研究通过分析气候、自然干扰、森林演替、破碎化等对其种群动态和遗传结构的影响，旨在：1)揭示纬度梯度和破碎化对其种群遗传多样性的影响；2)阐明火后森林演替过程中，有性和无性繁殖模式对其森林更新的相对重要性，以及干扰历史对其遗传结构的影响；3)阐明景观特征对其遗传多样性的影响，及其火后森林残留的保护价值。本文运用时间和空间，以及分子标记技术的研究方法，同时整合气候因子、历史纪录、干扰因子、遗传数据。得出的主要结论如下：1)沿着从加拿大北部森林南端的混交林森林到其北端的针叶林森林的纬度梯度，没有出现显著的遗传多样性（等位基因丰度，基因多样性，种群分化）的纬度效应。种群隔离和破碎化的加剧不与遗传多样性显著降低相关。在边缘区种群(F_is=0.244；P_HW=0.0042)和不连续区种群(F_is=0.166；P_HW=0.0042)中存显著的正近交系数和杂合子缺乏，表明存在较高的近亲繁殖。连续区种群符合Hardy-Weinberg平衡(F_is=-0.007; P_HW=0.3625)。贝叶斯分析和近邻结合树分析都显示存在种群遗传结构，且与地理来源部分一致。总体上，北美香柏种群存在一定程度的遗传分化(F_st=0.077)。大部分种群的规模显示近期扩大，而少数几个边缘种群经历了近期规模变小。总体而言，破碎化对其遗传多样性的影响是沿纬度梯度产生正近交系数，并且破碎化的北美香柏种群对近亲繁殖而导致的遗传侵蚀影响有缓冲能力。2)沿火后250年的演替梯度，无性更新所占的百分比略有增加（样点1916，22.8%；样点1823，27.0%；样点1760，30.9%），基因型多样性则相应的下降。大部分的基因扩散是在样方内实现（花粉，88.5％；种子，79.4％）。最年轻的样点（1916）从两个古老样点（1823；1760）获得了很大比例的通过花粉和种子介导的基因（75.8％）。平均有效种子传播距离为1079.4m，最大距离为7.2km；平均有效授粉距离为536.6m，最大距离为4.4km。树苗和成龄树之间的微观尺度空间遗传结构存在鲜明对比。树苗的微观尺度空间遗传结构较强且显著，成年树的则较弱且不显著。克隆生长在短距离内增加了树苗的微观尺度空间遗传结构。沿演替梯度，树苗（不含克隆）在第一距离间隔内的微观尺度空间遗传结构的强度逐渐减弱。离种子源的距离，火后更新中出现产种子树木的时间，以及适宜的微环境大量出现是控制火后森林演替过程中北美香柏数量（丰富度）的主要因素。3)在破碎化森林景观中火后遗漏的北美香柏森林小补丁，天然破碎化湖泊景观中其岛屿林分，以及非破碎化森林景观中其陆地古老森林之间存在高水平的基因流。其基因流格局存在源–汇动态。其森林小补丁通过接收陆地古老森林的基因而维持一定程度的遗传多样性。三种景观类型之间存在着等位基因多样性的显著区别，也存在种群分化的显著区别。破碎化森林景观中火后遗漏的森林小补丁具有最低等位基因丰富度（AR=5.06），最高的种群分化(F_st=0.052)，以及数量最少的私有等位基因（PA=5）。气候（风）和景观特征共同塑造北美香柏在这景观中的遗传结构。北美香柏陆地古老森林或其大斑块具高遗传保存价值。因此，应采取适当保护措施，避免其进一步退化，以防其变小成为森林小补丁及出现伴随的遗传变异显著降低；确保其能继续为火敏感物种提供重要栖息地。更多还原

【Abstract】 Eastern white cedar （EWC; Thuja occidentalis L.） is an important late-successional treespecies in the Boreal forest. It is listed as an endangered species by many states/provinces inNorth America. Conducting in-depth research on its population dynamics, genetic structureand diversity, is essential for the maintenance of ecosystem stability, the conservation of itsgermplasm and genetic resources, and the sustainable forest management. The long-termobjective of this study was to understanding the relative influence of climate, naturaldisturbances, forest succession and fragmentation upon the dynamics and genetic structure ofEWC populations in the boreal forest. Specifically, we used molecular markers to:1) examinethe impact of latitudinal gradient and fragmentation on its population genetic diversity;2)investigate the relative importance of the mode of regeneration along a post-fire succession aswell as the effect of disturbance history on its genetic structure;3) estimate the effects oflandscape features on its genetic diversity, and the conservation value of fire residuals. Weintroduced a spatial-temporal approach, as well as integrating climate factors, stand history,disturbance factors, and genetic data. The main conclusions are as follows:1) There were no significant latitudinal effects on population genetic diversity (Genediversity, H_s; Allelic richness, AR; Population differentiation, F_st) along the latitudinalgradient from the boreal mixed-wood to northern coniferous forest. Increased populationisolation and fragmentation was not correlated with a significant decrease in geneticdiversity.Positive Fisvalues and heterozygote deficiency were observed in populations fromthe marginal (F_is=0.244; P_HW=0.0042) and discontinuous zones (F_is=0.166; P_HW=0.0042)indicating inbreeding. However, populations from the continuous zone were in HWequilibrium (F_is=-0.007; P_HW=0.3625). Bayesian and NJT （neighbour-joining tree） analysesdemonstrated the presence of a population structure that was partly consistent with thegeographic origins of the populations. In general, there was substantial genetic differentiationamong EWC populations (F_st=0.077). Several marginal populations experienced recentpopulation decline, the remaining populations showed a signal of recent expansion. Overall,the impact of population fragmentation on the genetic structure of EWC is the presence of a positive inbreeding coefficient along the latitudinal gradient. The fragmented populations ofEWC appear well-buffered against effects of inbreeding on genetic erosion.2) The percentage of asexual regeneration slightly increased with stand development（1916,22.8%;1823,27.0%;1760,30.9%） along a250-year-long post-fire successionalgradient, while genotypic diversity decreased. Most gene dispersal was realised within site（pollen,88.5%; seed,79.4%）. The youngest site （1916） received a great portion （75.8%） ofgenes mediated by pollen and seed dispersal from older sites （1823,1760）. Mean seeddispersal distance was estimated to be1079.4m, with a maximum distance of7.2km, whilethe pollination between mates occurred over a mean distance of536.6m （maximum=4.4km）. Fine-scale spatial genetic structure （SGS） analysis showed contrasting patterns of SGSbetween saplings and adult trees. SGS was high and significant in saplings, and weaker inadult trees. Clonal growth increased SGS in saplings over short distances, together with SGSintensity （Sp）. Fine-scale SGS among saplings （excluding clonal individuals） in the firstdistance interval gradually weakened along the post-fire successional gradient. The distancefrom seed sources and the time needed for post-fire regeneration to produce seed-bearing treesare among the factors that controlled EWC abundance along the post-fire succession, togetherwith the abundance of suitable microsites.3) There were high levels of gene flow among small EWC fire residuals from thefragmented terrestrial landscape, naturally fragmented EWC islands from the lacustrinelandscape, and mainland EWC old forests from the non-fragmented terrestrial landscape. Ourresults revealed that a source-sink dynamic pattern of gene flow. Small EWC fire residualsmaintained high genetic diversity by receiving replenishment from mainland populations.There were significant differences in several genetic estimates among the three landscapetypes with small EWC fire residuals having the lowest allelic richness （AR=5.06）, highestpopulation differentiation (F_st=0.052), and lowest number of private alleles （PA=5）. Bothclimate （wind） and landscape features shaped the genetic structure of EWC in the landscape.Our study provides empirical evidences on the top conservation value of mainland EWCold-growth forest or its large patches. Therefore, appropriate protection measures should betaken before they turn to small patches that characterised with reduced genetic variation, asthey can continue to provide crucial habitat reserves for fire sensitive species.更多还原