Knowledge Resource Center for Ecological Environment in Arid Area
| 大尺度梯度下羊草表型分化及驱动机制研究 | |
| 其他题名 | Phenotypic differentiation and driving mechanisms in Leymus chinensis along a large-scale gradient |
| 袁珊 | |
| 出版年 | 2015 |
| 学位类型 | 博士 |
| 导师 | 王仁忠 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 羊草（Leymus chinensis）为禾本科赖草属多年生根茎型禾草，是欧亚大陆东部草原区建群种之一。因其生产力高、适口性好、营养丰富等特性成为一种优质牧草，具有重要经济价值。羊草适应性强，耐旱、耐盐碱、耐贫瘠，在多种复杂生境下均有大面积分布。在大尺度梯度范围内，多变的气候和土壤等环境因素导致羊草表型分化显著，不仅体现在种群性状水平，而且在自然条件下存在两种叶色差异明显的生态型（灰绿型和黄绿型）。目前对羊草研究多集中于其物种生态适应性或优良抗性的挖掘等方面，对羊草种内表型分化的驱动因素和机制鲜见报道，这方面研究对了解物种适应策略与进化方向具有重要意义。本实验以我国东北草原124°E - 114°E梯度下的羊草为研究对象，通过野外种群调查、温室同质栽培（北京）和分子标记等实验获得数量性状和遗传分化数据，探讨羊草种内表型分化的驱动因素和机制，得出以下结论： 1）大尺度梯度下，气候变化（包括年均降水量和年均温度）是羊草种群表型分化的主要驱动因素。自然环境下，东部羊草种群（草甸草原）和西部种群（典型草原和荒漠草原）在植株密度、形态性状和生理调节能力各方面均发生剧烈分化，西部种群通过增强保水能力和减少蒸腾作用来应对干旱环境（如增加叶片相对含水量和单位面积叶重等），并将物质分配集中于营养繁殖，缩减有性生殖投入（如减小种子干重和穗长等）以维持种群生长。但同质园栽培后种群间形态和生理性状的变异系数显著减小，西部种群有向东部种群趋同的变化趋势（如株高和叶面积显著增加、脯氨酸和可溶性糖含量显著下降等），表明羊草表型受环境影响显著，环境因子分异与否很大程度上决定了种群表型分化程度。自然种群的株高、叶长、种子重和穗长等多个形态性状和生理指标（脯氨酸、可溶性糖含量等）与年平均降水量（MAP）和年均温度（MAT）呈显著相关关系，而与土壤pH值和土壤氮含量等无显著相关性，表明水分和温度是驱动羊草种群表型分化的关键因素。 2）大尺度梯度下，各羊草种群间遗传分化也是导致其表型趋异的一个重要原因。基于微卫星标记的遗传结构指派分析（STRUCTURE assignment analysis）和分子变异率分析（AMOVA）显示，尽管羊草种群间由花粉和种子传播产生的丰富基因流可能会削弱遗传结构，但东部和西部羊草种群之间仍存在一定分化。数量性状和中性分子分化的聚类结果均将18个种群分为东-西两大分支，证明东-西部种群间存在遗传分化。两种聚类结果的分界点略有差异表明羊草种群表型变异呈连续渐进性。中性分子遗传分化系数（FST = 0.041）显著低于数量性状分化系数（QST = 0.221），说明歧化选择是导致羊草种群表型分化的重要原因之一。气候变化下的歧化选择和遗传分化共同驱动大尺度梯度下羊草表型变异。 3）自然种群中，两种生态型羊草（灰绿型（GG）和黄绿型（YG））在种群密度、形态性状（株高、叶面积、叶干重、种子重等）及生理性状（叶绿素含量、脯氨酸和可溶性糖含量等）均发生差异显著（P < 0.05），体现出两种生态型羊草在生殖生长策略、光能利用效率和渗透调节能力等方面的差异。同质栽培后两种生态型分化仍然存在，说明其分化受环境因子影响较小。通过微卫星分子标记得出的邻接树和贝叶斯指派分析结果也显示两种生态型羊草在分子水平上分化显著，表明内在遗传差异也是导致其分化的主要驱动力，推测羊草在未来气候变化情况下仍有遗传潜力维持其性状差异。 综上所述，在本研究区域内气候变化和分子遗传分化是羊草表型分化的关键驱动因素。大尺度梯度下由东向西随干旱加剧，羊草表型性状发生显著分化（如西部种群在种群密度、形态性状和生理调节能力上均呈旱生化特征）。表型变异与气候因子（MAP和MAT）相关性显著，而同质栽培后羊草种群表型分化程度明显减小，西部种群有向东部种群趋同的效应，呈现出高降水量下的表型特征（株高增加、RWC减小、生理调节物质含量减少），表明干旱对其表型分化起重要驱动作用。数量性状聚类支持将这些种群分为东-西部两分支，分子变异分析也支持东-西部羊草种群的遗传分化，两种生态型之间也存在一定分化，故分子遗传分化也是羊草种内表型分异的重要驱动力之一。 |
| 英文摘要 | Leymus chinensis (Trin.) Tzvel., a perennial rhizomatous, is one of the constructive species in eastern Eurasian steppe and a high-quality economic forage for its high productivity, palatability and nutrient-rich features. This species exhibits strong adaptability on drought, salinity and infertility and habitats a wide distribution covering complex environments. Phenotypes of the species differentiate largely not only on population level, but also on the two ecotypes (gray-green (GG) and yellow-green (YG) by their leaf colors) at large-scale gradient with significant variations of climate and soil properties. Previous studies mainly focused on the ecological adaptability in L. chinensis and its excellent resistance, however, the driving mechanism of the phenotypic divergence in this species along large-scale gradient has not yet been addressed, and this knowledge is essential for understanding the evolutionary trajectory of plant species under global climate change. In this study, wild population surveys along a broad scale longitude gradient (124 °E - 114 °E) in Northeast China grassland, greenhouse transplanted experiments (Beijing) and molecular genetic differentiation of L. chinensis (both populations and ecotypes) were conducted, demographical, morphological and physiological traits and molecular genetic data were analyzed to reveal the driving factors of L. chinensis phenotypic divergence. The followings are the main conclusions: 1) Climatic variations, including mean annual precipitation (MAP) and mean annual temperature (MAT), were the dominant drivers for L. chinensis population phenotypic differentiation along the large-scale gradient. In wild sites, the eastern populations (meadow sites) and western populations (sites from typical steppes and desert steppes) showed dramatic differentiation in shoot densities, morphological and physiological traits. Western populations responded adaptively to drought by enhancing the water-holding capacity and reducing transpiration (such as the increase of leaf relative water content and leaf mass per area), magnifying vegetative reproduction assignment and diminishing sexual reproduction investment (decreases of seed dry weights and spike lengths) to maintain a certain population size. After transplantation, however, the variation coefficients of both morphological and physiological traits declined under the identical conditions with sufficient water supply and the western populations transformed toward the eastern ones (such as shoot heights and leaf area increased, proline and soluble sugar contents decreased in western populations), indicating that the L. chinensis phenotype divergences were largely depended on climatic changes. Most of leaf and seed traits were significantly correlated with MAP and MAT in wild sites, but not with soil pH and soil N content, suggesting that climatic variables play a vital role rather than soil pH and nutrition in phenotypic divergence in the species. 2）Genetic differentiation also drove phenotypic differentiation in L. chinensis populations along the large-scale gradient. STRUCTURE assignment analysis and analysis of molecular variance (AMOVA) based on microsatellite markers showed low but significant differentiation between eastern-western populations, in spite of a wealth of gene flow by seed and pollen dispersals which would weaken the genetic differentiation. The discrepancies of the dividing points between quantitative traits clustering and molecular neighbor-joining tree indicated the gradual and continuous variations among L. chinensis populations. Neutral genetic differentiation (FST = 0.041) was greatly lower than phenotypic differentiation (QST = 0.221), indicating that divergent natural selection was critical in determining the phenotypic divergences among L. chinensis populations. Divergent selections under climate change and the neutral genetic differentiation were both major contributors in driving L. chinensis phenotypic divergences along the large-scale gradient. 3）Population demographical and morphological traits and physiological adjustments differed significantly between two ecotypes in wild sites, suggesting the variations of growth strategies, light use efficiency and osmotic adjustments between ecotypes probably caused the ecotype differentiation. Transplanted populations in a common garden exhibited significant differentiation on physiological traits between GG and YG ecotypes, implying ecotype divergence could be rarely driven by environmental variations. Neighbor joining tree and Bayesian assignment generated into two groups mainly according to ecotypes, indicating molecular genetic differentiation was significant under the two ecotypes’ phenotypic divergences. We concluded that L. chinensis ecotypes have potential to maintain their genetic differentiation under climate change in future. In summary, climate variations and molecular genetic differentiation were the driving factors for L. chinensis phenotype divergences along the large-scale gradient. Phenotypes in L. chinensis differentiated greatly, western populations with lower population densities and relative greater LMA, proline and soluble sugar contents, exhibiting more drought-resistant tendency with MAP and MAT decreased from east to west. In transplanted experiments, the phenotypic variations decreased significantly with the western populations exhibited the eastern-like characters (higher shoot heights, lower RWC and osmotic adjustment substance contents), suggesting climatic variations played a vital role in driving the phenotypic differentiation. The clustering on quantitative traits divided the 18 populations into eastern-western groups, and the population differentiations on neutral molecular markers indicated that the genetic differentiation was another critical factor for the L. chinensis intraspecific phenotypic divergences. |
| 中文关键词 | 表型分化 ; 气候变化 ; 微卫星标记 ; 羊草 ; 生态型 |
| 英文关键词 | phenotypic divergence climate variation microsatellite markers Leymus chinensis ecotype |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院植物研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287632 |
| 推荐引用方式 GB/T 7714 | 袁珊. 大尺度梯度下羊草表型分化及驱动机制研究[D]. 中国科学院大学,2015. |
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