|Place of Degree Grantor
|土壤古菌，土壤细菌，群落组成和分布特征，生态系统类型，扩散限制， 环境筛选，生态位理论，中性理论，空间因子，环境因子，结构方程模型，荧光 实时定量 PCR，高通量测序， soil archaea, soil bacteria, community composition and distribution, ecosystem types, dispersal limitation, environmental filting, niche theory, neutral theory, spatial factors, environmental factors, Structural Equation Modeling, real-time PCR, high-throughput sequencing
|Distribution patterns and the ecological mechanisms of soil microorganism in typical ecosystems
| 土壤微生物是生态系统的重要组成部分，在生态系统的物质循环和能量转换过程中起着重要作用。本文在积极吸收和借鉴分子生物学的技术和研究方法的基础上，充分发挥我国多种自然地理条件下生物多样性的优势，通过系统取样，广泛收集我国不同典型生态系统的土壤样品，获取土壤微生物基因组 DNA，在此基础上，通过 Real-time PCR、高通量测序等技术手段，重点考察土壤微生物的群落结构多样性及生态分布特征，探讨土壤微生物的空间分布格局及其形成机制。本研究选取典型的草地生态系统、灌丛生态系统和荒漠生态系统，跨越五省两个自治区，分别为黑龙江省、内蒙古自治区、河北省、山西省、甘肃省、青海省、新疆维吾尔自治区，共计 156个土壤样品，其中草地生态系统包括 99个样点、灌丛生态系统 21个样点、荒漠生态系统 36个样点。深入比较 3种生态系统中土壤古菌和细菌的数量和群落组成特征；通过多样性指数分析、空间距离或环境异质性与土壤微生物群落多样性关系、影响因素的直接和间接分析模型（结构方程模型）等方面的研究，阐释了生物因子、非生物因子、确定和随机过程的相对重要性，进而解释了影响土壤微生物群落构建的生态位和中性理论的相对贡献。在比较和借鉴宏观生态学理论及微生物生态学研究进展的基础上，在研究的框架范围内明确了土壤微生物地理学分布特征和可能的生态学驱动机制。论文的主要研究内容与成果如下：
1.草地生态系统中土壤微生物群落的组成和分布特征：选取内蒙等七省区典型草地生境，共采集 99个土壤样品，包括禾草草原、盐生草甸、沼泽草甸、温带草丛、草甸草原、荒漠草原、杂草草甸、高寒草甸、灌木草原和高寒草原10种子类型。研究结果表明，土壤古菌占原核生物量（细菌与古菌之和）的比例在 0.04% ~ 9.26%之间，细菌数量显著高于古菌数量 2~3个数量级。古菌与细菌数量呈显著正相关关系。草地生态系统中土壤微生物群落共产生 23个门，主要由变形菌门、放线菌门、酸杆菌门、绿弯菌门、浮霉菌门组成。土壤微生物群落受最干季均温、最干燥月降水量、纬度等的影响显著，生境差异和空间位置的变化共同影响了土壤微生物群落组成和多样性。
2.灌丛生态系统中土壤微生物群落的组成和分布特征：以内蒙、河北、青海为研究区域，共采集 21个土壤样品。结果表明，土壤古菌 16S rRNA基因拷贝数变化范围在 5.32× 107 ~ 1.31 × 109 copies g-1 dry soil，土壤细菌 16S rRNA基因拷贝数在 3.70 × 109 ~ 3.50× 1011 copies g-1 dry soil之间，古菌 16S rRNA基因拷贝数显著低于细菌。灌丛生态系统中土壤微生物群落共产生 16个门，主要由变形菌门、放线菌门、酸杆菌门、绿弯菌门、浮霉菌门、疣微菌门组成。由NMDS分析表明不同灌丛生态系统类型的微生物群落 β多样性差异显著。产生这种分布格局的主要影响因素是最湿润月降水量、年降水量、经度等。空间和环境因子共同影响了土壤微生物群落分布格局。这也证实了气候因子影响作用的连续性，对验证前期草地生态系统分析结果，以及明确影响不同生态系统中土壤微生物群落分布格局的空间和环境因子起着非常重要的印证和参考作用，并为后续研究提供思路。
3.荒漠生态系统中土壤微生物群落的组成和分布特征：以内蒙、甘肃、青海、新疆为研究区域，共采集 36个土壤样品。结果表明，古菌数量占原核生物比例为 0.10 % ~ 4.02 %。总体上，细菌数量显著高于古菌数量 2~3个数量级。古菌与细菌数量呈显著正相关关系。荒漠生态系统中土壤微生物群落共产生16个门，主要为变形菌门、放线菌门、酸杆菌门、绿弯菌门、浮霉菌门。由 NMDS分析群落的β多样性变化可知，不同荒漠生态系统类型的微生物群落β多样性差异显著。土壤微生物群落的 RDA分析结果显示，群落组成变化主要受最干季均温、最暖月均温、最冷季均温等的影响显著影响。对验证前期草地和灌丛生态系统分析结果，以及明确影响不同生态系统中土壤微生物群落分布格局的空间和环境因子起着重要作用，并为后续研究提供思路，但对于产生这种分布格局的驱动机制尚待进一步研究，而微生物群落构建和物种多度分布格局的形成是否如大型动植物存在一定的生态学驱动机制，也成为我们关注的重点。
4.典型生态系统中土壤微生物群落的分布特征及生态学机制：长期以来，对生物地理分布特征的研究一直是生态学的研究重点，尽管得益于分子生物学技术发展，使研究微生物的分布特征成为可能，但是微生物是否一如大型生物存在生物地理分布特征一直困扰着我们。相较之大型生物的研究依旧微乎其微，并且许多的研究并未考虑空间距离和生态系统类型对群落构建的影响，抑或未考虑空间距离与环境因子间的相互关系。本研究中，不同生态系统类型中植物和土壤微生物群落 β多样性差异显著。土壤微生物 β多样性与植物 β多样性显著正相关，说明地上部植被群落组成的复杂度一定程度上影响了地下部微生物群落组成。β多样性（相异指数）与地理距离存在显著正相关关系，体现出明显的扩散限制作用；与环境因子间存在显著正相关关系，体现出环境筛选作用，说明随环境异质性增加，微生物群落多样性加大。通过对环境因子与地理距离间的相关分析表明，环境因子与地理距离间存在显著交互作用。结构方程研究表明，除去多样性指标本身（α多样性），气候因子对微生物群落 β多样性影响最大，而作为土壤微生物的生存环境——土壤性质成为最直接的影响因素，二者属于环境因子的一部分，说明物种多样性变化受到环境筛选的作用影响。
| Soil microorganisms are important parts of the ecosystem, and are essential to virtually all ecological processes, such as the material cycle and energy transformation. As there are several typical ecosystems, the distribution patterns and community diversity of soil microorganisms could be fully tested in China. In this thesis, 156 soil samples were collected from three different ecosystem types used for community abundance and diversity analysis. The ninety-nine soil samples of them got from grassland, twenty-one from shrubland, and the remain from desert ecosystem. Firstly, the abudance and diversity of soil bacterial and archaeal 16S rRNA gene were mesured by real-time PCR and high-throughput sequencing. Then, comparing the abundance and compostion of soil bacteria and archaea communites, diversity indices,and partitioning the influence of spatial or environmental factors on microbial communites under different ecotypes, improve our understanding of soil microbial biogeography and its driving mechanism, and further indicated whether the microorganisms followed the distribution patterns of macroorganisms. The major contents and findings of the dissertaion are as follows:
1. Distribution patterns of soil microbial communities in grassland ecosystem: 99 soil samples were collected from seven provinces in China, which were separated into ten different subclass ecotypes, to clarify the biogeography of soil microbial communities and examine the dominant ecological mechanism in structuring soil microbial communities. The percentage of archaea in prokaryotes ranged from 0.04% ~ 9.26%. The archaeal abundance was significantly correlated with bacteria, but 2~3 magnitude lower than it. The soil microbial communities recovered in the present
study affiliated within Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi,Planctomycetes. RDA analysis revealed that mean temperature of driest quarter, precipitation of driest month and latitude were ignificantly related to the soil microbial community composition. The habitat heterogeneity and spatial distance both influenced the composition and diversity of soil icroorganisms.
2. Distribution patterns of soil microbial communities in shrubland ecosystem: 21 samples were selected in shrubland ecosystem. The archaeal 16S rRNA gene copy numbers ranged between 5.32 × 107 and 1.31 × 109 copies g-1 dry soil and bacterial 16S rRNA gene copy numbers varied from 3.70 × 109 to 3.50 × 1011 copies g-1 dry soil. Bacterial abundance was significantly higher than archaeal abundance.Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Planctomycetes and Verrucomicrobia were the dominant phyla, but the relative abundance was different among each site. The NMDS analysis also indicated that beta diversity was different in subclass ecotypes. Furthermore, the result of RDA indicated that distribution patterns of archaeal communites was impacted by both spatial and environmental factors. Precipitation of wettest month, annual precipitation and longitude were significantly related to the community composition. These indicated the coherence influence of climate factors, and also demonstrated the results of grassland ecosystem.
3. Distribution patterns of soil microbial communities in desert ecosystem: 36 samples were selected in desert area. The result indicated that the percentage of archaea in prokaryotes ranged from 0.10 % ~ 4.02 %. The abundance of bacteria was significant larger than archaea. Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi and Planctomycetes were the dominant groups, but there relative abundance were different among each site. The spatial and environmental factors were analyzed to tackle the mechanisms that generate the patterns of microbial biogeography under multiple ecotypes. Using RDA analysis, the communities pattern
changed mainly with the variety of mean temperature of driest quarter, mean temperature of wettest month, and mean temperature of coldest quarter, to conduct a comparative study to distinguish the impact of environmental and spatial factors in the individual habitats. The results extended and deepened our understanding of microbial ecology.
4. Distribution patterns and the ecological mechanisms of soil microorganism in typical ecosystems: Biogeography is the study of the distribution of biodiversity over space and time. For decades, knowledge about the biogeography of organisms has been a focus in ecological research, including the mechanisms that generate and maintain diversity. It has been shown that macroorganisms have obvious zonal distributions along gradients of water and energy. Whether or not microorganisms follow similar distribution patterns to macroorganisms is still a matter of debate,although we have benefited from recent advances in molecular biological techniques which make it possible to examine geographic distributions of microbes.Understanding the patterns and determinants of species turnover between two or more sites, often referred to as beta diversity, is one of the central goals of community ecology and has long been a focus of studies of biodiversity. The PCoA analysis indicated beta-diversity of plant and soil microbial community was significantly different among three ecosystems. Furthmore, beta diversity of soil microbial community has a positive correlationship with plant, which showed the below-ground diversity (the diversity of soil microbial community) would related to the complexity of above-ground (the diversity of plant). Besides, microbial beta diversity showed a positive correlated with geographic and environmental ditance, which stated a obviously distance-decay relationship or environmental filting process. We also detected that there was positive relationship between environmental and geographic distance. In order to decided the main driving factors, SEM analysis was applied. The results indicated beta diversity of soil microbial community was mainly impacted by climate factors, which showed a clear enviromental filting effect.
In this thesis, structure and distribution patterns of soil microorganisms were similar with macroorganism, and influenced by both spatial and environmental factors.Knowledge of the distribution patterns of soil archaea and bacteria, the driving mechanisms in different nvirionmental conditions and the relative influence of environmental and spatial factors could improve our understanding of soil processes mediated by microorganisms, structuring a framework for microbial ecology and also provide theoretical foundation for management and regulation of terrestrial ecosystems.