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| 中国热带亚热带木本被子植物叶片功能属性的种间变异格局及其生态学意义 | |
| 其他题名 | INTERSPECIFIC VARIATIONS OF LEAF FUNCTIONAL TRAITS AMONG WOODY ANGIOSPERMS IN TROPICAL-SUBTROPICAL FORESTS IN CHINA AND THEIR ECOLOGICAL SIGNIFICANCE |
| 李乐 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 郭大立 ; 牛书丽 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 植物功能属性研究对深入理解植物多样化的生态策略和物种共存机制等具有重要的科学意义。与叶片碳构建成本和回报相关的叶片经济学属性、与叶片水气交换相关的叶片水分属性、与细胞构建相关的叶片细胞大小属性等在理解和预测生态系统过程及其对全球变化的响应中起到重要作用，因而受到研究者的广泛重视。尽管叶片经济学属性和水分属性内部的变异关系已被研究者广泛认同，然而这两套属性之间的关系及其与叶片细胞大小的关系仍然处于争议之中。近年来，越来越多的研究结果表明植物内部存在多个功能属性维度，而非只有叶片经济学谱这一个属性轴。 为了更好地认识被子植物进化过程中叶片生态策略的分化，揭示叶片不同结构和功能之间的关系，理解叶片经济学属性和水分属性之间、细胞大小与不同属性之间的权衡制约关系，本文以中国5个热带亚热带森林中广泛分布的85个常见木本被子植物为主要研究对象，分析了3类9个重要叶片功能属性(叶片氮浓度、比叶重、气孔密度、气孔保卫细胞长度、叶脉密度、末端叶脉直径、上表皮细胞的长度、下表皮细胞的长度、栅栏细胞的宽度等)的变异格局及相互作用关系。同时，结合文献数据，集成分析了全球尺度上不同生物群区和生活型中被子植物的比叶重和叶脉密度的变异格局。最后，本文提出了叶片模块化构造的理论假说，该假说可用于解释叶片尺度上的多维性变异格局和多样的生态策略。主要研究结果如下：在我国热带亚热带森林，木本被子植物叶片内部存在多维性的变异格局。在叶片水分属性内部，气孔密度(SD)和叶脉密度(VD)呈现正相关关系(r = 0.35, P < 0.01)。在叶片经济学属性内部，比叶重(LMA)和单位重量叶片氮浓度(Nmass)之间则呈现显著负相关关系(r = -0.562, P < 0.01)。然而，叶片水分属性(包括气孔密度、气孔保卫细胞长度、叶脉密度等)和叶片经济学属性(包括Nmass与LMA等)则呈现相互独立(即正交)的关系，从而构成了叶片尺度上属性变异的两个重要维度，其中叶片经济学维度主要对应于叶片光捕获和组织构建等功能，而叶片水分维度主要对应于叶片水分利用和气体交换等功能。在不同物种中，这两套属性可以自由组合，形成了叶片的结构和功能的多样的分化，有助于解释热带亚热带地区较高的物种多样性，也对理解植物生态策略及生态系统的功能多样性有理论价值。在全球尺度上，不同被子植物比叶重和叶脉密度呈现独立变异的格局。在全球尺度上(包括热带雨林、热带季节性干旱森林、亚热带季雨林、温带森林、地中海群区、荒漠等)，叶脉密度(代表叶片水分属性)和比叶重(代表叶片经济学属性)呈现独立格局，这种格局不仅存在于我国热带亚热带森林，也存在于温带群区(r = 0.144, P = 0.140)；在每个生活型(包括乔木、灌木、草本等)，两者也都呈现出独立的种间变异格局。这种独立的变异格局对完善全球植被模型具有重要意义。在细胞构建尺度上，木本被子植物叶片细胞大小与叶片水分属性相关，而与叶片经济学属性呈现独立变异的格局。不同细胞大小与水分属性密切相关，但与叶片经济学属性相互独立。其中，保卫细胞长度和下表皮细胞长度可以共同解释气孔密度41%的变异，栅栏细胞宽度和保卫细胞长度可以共同解释叶脉密度50%的变异。叶脉密度和栅栏细胞与保卫细胞之间的权衡关系，进一步体现了叶脉供应栅栏组织光合用水和表皮细胞蒸腾用水的双重功能。重要的是，叶脉密度和栅栏细胞宽度的权衡关系呈现分段式，分段点出现在叶脉密度为6.1mm mm-2，这种分段性的变异格局体现了被子植物在进化过程中是分阶段的，这是被子植物适应不同生境的过程，也是被子植物生态策略分化的过程，这对深入理解被子植物的进化过程具有重要意义。木本被子植物叶片模块化构造的理论假说。本研究提出木本被子植物叶片可以被分解为三个重要的模块： 光捕获模块、水分养分运输模块和气体交换模块。每个模块都由一组叶片结构和组织构成，主要用于获取叶片必需的一类重要资源。在不同环境条件下，不同模块在数量上的组合方式和在空间上的排列样式都各有不同，正是这种多样式的组合方式造就了地球上被子植物叶片多样化的结构和功能。这种模块化的视角区别于从叶片整体结构出发的叶片经济学理论，有利于研究者从进化的角度追溯叶片结构和功能的演化过程，并为预测未来全球变化情景下植物叶片的响应模式提供参考依据。未来进一步研究在不同环境条件下不同模块的组合方式及其在叶片功能上的意义，将有助于深入理解和阐释地球生物圈上植物多样性的生态学意义和变异来源。 |
| 英文摘要 | Studies of plant functional traits across species and biomes have greatly advanced our understanding of plant form and function. Among various plant traits, those related to leaf-level construction cost and payback time, CO2 and water exchange, and cellular construction have probably received most attention, reflecting the critical importance of these processes in global primary production and functioning of the biosphere. Despite that the significant correlations within both leaf economics traits and leaf hydraulic traits have been widely recognized by researchers, it still remains doubted that whether leaf economics traits are correlated with leaf economics traits and their relationships with different leaf cell sizes. In recent years, evidence is accumulating in support of multiple dimensions in plant functional traits, opposing a single spectrum of world-wide plant trait economics. Tropical-subtropical woody angiosperms are one of the largest plant functional group and encompass high plant diversity. The use of multiple phylogenetic lineages allows for a better understanding of trait relationships in a phylogenetically-informed manner. Further examination of the relationships among leaf economics traits, leaf hydraulic traits and different leaf cell sizes will help researchers better understand diverse leaf ecological strategies and the evolutionary pathway of angiosperms in the long history. Here, I chose 85 woody angiosperms from five tropical-subtropical forests in China, and analyzed the relationships among leaf economics traits (i.e., leaf nitrogen concentration and leaf dry mass per area), leaf hydraulic traits (i.e., stomatal density, stomatal guard cell length, and vein density), and different leaf cell sizes (i.e., minor vein diameter, upper epidermal cell length, lower epidermal cell length, palisade cell width) across species. Besides, by collecting data from published papers, I analyzed the variation pattern between leaf dry mass per area and vein density across different biomes and different functional types at the global scale. Last but not least, by reviewing literature related to leaf structure and function, I propose a modularized-leaf design perspective for better understanding the multidimensional variation pattern of leaf functional traits. Below are the main results of my studies:(1) Multi-dimensional variation at the leaf level among woody angiosperms in the tropical-subtropical forests in China. Within leaf hydraulic traits, leaf stomatal density (SD) was positively correlated with vein density (VD) (r = 0.35, P < 0.01). Within leaf economics traits, leaf dry mass per area (LMA) was negatively correlated with leaf nitrogen concentration (Nmass) (r = -0.562, P < 0.01). By contrast, these two suites of traits were statistically decoupled. This decoupling suggests that independent trait dimensions exist within a leaf, with leaf economics dimension corresponding to light capture and tissue longevity, and leaf hydraulic dimension to water use and gas exchange. Clearly, leaf economics and hydraulic traits can vary independently, thus allowing for more possible plant trait combinations. Compared with a single trait dimension, multiple trait dimensions may better enable species adaptations to multifarious niche dimensions, promote diverse plant strategies and facilitate species coexistence.(2) Independent variation between leaf dry mass per area and vein density among angiosperms at the global scale. In general, non-significant relationship between LMA and vein density was found across different biomes and in the entire global dataset. We found that the independence between LMA and leaf vein density occurred not only in the subtropics we studied, but also in the temperate biome (r = 0.144, P = 0.140, n=106), whereas patterns within other biomes differed somewhat. Subdividing the dataset into different plant functional types further supported overall independence of these traits.(3) Correlations between different leaf cell sizes and leaf hydraulic traits, but independent variation exist between leaf cell sizes and leaf economics traits among woody angiosperms in tropical-subtropical forests in China. Different leaf cell sizes were significantly correlated with leaf hydraulic traits, but were decoupled from leaf economics traits. In particular, stomatal guard cell length and lower epidermal cell length can together explain 41% variation of stomatal density. Palisade cell width and stomatal guard cell length can together explain 50% variation of vein density, which suggests that leaf veins have the function of both supplying water for photosynthesis in the palisade tissue and supplying water for transpiration in the epidermal tissues. More importantly, a stepwise decrease of palisade cell width was found when vein density equals to 6.1mm mm-2, forming one platform of large width-low density among Magnoliaceae to another of small width-high density among more advanced angiosperms. We suggest that this modification may have been a critical step that contributed to leaf evolution in the radiation of angiosperms from understory shaded environment to open habitats, and that divergence of angiosperms was associated with higher vein density, stomatal density and smaller cell sizes of leaves.(4) Modularized leaf design among woody angiosperms. Here I propose a new perspective for linking leaf structure and function in woody angiosperms by arguing that a leaf may be divided into three key sub-modules, the light capture module, the water-nutrient flow module and the gas exchange module. Each module consists of a set of leaf structures corresponding to a certain resource acquisition function, and the combination and configuration of different modules may differ depending on overall leaf functioning in a given environment. This modularized-leaf perspective differs from the whole-leaf perspective used in leaf economics theory and may serve as a valuable tool for tracing the evolution of leaf form and function. This perspective also implies that the evolutionary direction of various leaf designs is not to optimize a single critical trait, but to optimize the combination of different traits to better adapt to the historical and current environments. Future studies examining how different modules are synchronized for overall leaf functioning in different environments should offer critical insights into the diversity of leaf designs worldwide. |
| 中文关键词 | 木本被子植物 ; 叶脉密度 ; 气孔密度 |
| 英文关键词 | woody angiosperms vein density stomatal density |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生态学 |
| 来源机构 | 中国科学院地理科学与资源研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287869 |
| 推荐引用方式 GB/T 7714 | 李乐. 中国热带亚热带木本被子植物叶片功能属性的种间变异格局及其生态学意义[D]. 中国科学院大学,2017. |
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