天山一号冰川底部沉积层及其前沿退缩带微生物群落时空演替格局对环境分异的响应

Microorganisms are the most abundant and potentially most diverse organisms in the biosphere. They play critical roles in many ecosystem processes and thereby control key pathways of biogeochemical cycling. However, to date, knowledge of the origin, maintenance and distribution of diversity on terrestrial microorganisms remains limited. .Forefields of receding glaciers are pristine and sensitive environments representing natural chronosequences and the spatial heterogeneities. One consequence is the acceleration of glacier retreat, exposing new habitats that are colonized by microorganisms whose diversity and function are unknown. Thus，these glacier forefields provide excellent opportunities to study microbial succession, biogeochemical weathering processes, and the conversion of glacial till into fertile soils along the chronosequence in regionally defined landscape..The objective of this project is to use a combination of culture-independent methods, namely rRNA gene clone library analyses，pyrosequencing , DGGE fingerprinting，quantitative PCR (q-PCR), to determine the microbial diversity and community composition present within the supra-, sub-, and proglacial sediments of the Glacier No.1 in the Tianshan Mountains. A comparison of multiple microbial community along a chronosequence of a glacier forefield is carried out by using phylogenetic-diatance based approaches and the UniFrac software. In addition, multivariate analysis of ecological data will be used to demonstrate the geographical distrubation patterns of phylogenetic groups of the Glacier No.1 foreland soils at different level of taxonomic organization. .To conclude, our objectives are: (ⅰ) to test whether the deeper branches of the ribosomal RNA-derived phylogenetic tree in the pristine terrestrial systems, such as the phyla or class level, have ecological coherence. (ⅱ) to determine whether the subglacial microbiota are allochthonous (originating from adjacent environments) or autochthonous (indigenous communities unique and potentially adapted to the subglacial environment). (ⅲ) to link environmental variables to shifts in the structure and composition of the microbial community, and to investigate whether, or to what extent, environmental variables that vary over space and time induce succession of the nitrogen, carbon and sulfur cycling microbial communities. .The implementation of the project contributes greatly to our understanding of how the ecosystem prosesses of receding glaciers varies in response to global climate change, and thereby possibly shedding light onto the tendency of environmental changes in a regionally defined landscape.

近二十年来，全球气候变暖使冰川呈现加速融化和退缩趋势，但目前对冰川退缩前后生态系统发生的微生物地球化学过程缺乏全面的比较研究。我们前期研究发现天山一号冰川前沿生境具有明显的时间序列性和空间异质性，其微生物类群空间分布格局明显不同于高纬度极地环境。本项目拟采用不同分辨率的分子生物学技术(克隆文库、定量PCR、高通量测序)，结合土壤理化特征、功能酶活等分析，系统开展中、低纬度典型冰川退缩前后生境微生物群落时空演替的模式研究。通过处理海量DNA序列数据结合生态多元统计：揭示一号冰川底部沉积层及其退缩前沿微生物群落在不同分类学层次上的空间分布格局，尤其阐明高层次微生物分类单元是否对环境异质表现出生态凝聚力；揭示介导碳、氮、硫循环的功能微生物类群在退缩过程中的演替规律及其对环境分异的响应机制。为比较和科学评价全球不同冰川退缩生态系统微生物地球化学过程差异，以及为区域环境变化趋势的预测提供理论依据。

项目采用不同分辨率的分子生物学技术(克隆文库、定量PCR、高通量测序)，揭示介导碳、氮、硫循环的功能微生物类群在退缩过程中的演替规律及其对环境分异的响应机制。高通量测序结果显示，天山一号冰川底部沉积层及其前沿环境中的细菌，在高层次分类单元（taxon）门（phylum）一级水平共有34个系统发育类群。依据冰川末端距离的增加所代表的演替时间的增加，细菌多样性指数、操作分类单元OUT数明显增加，但不同系统发育类群对多样性变化的贡献差异显著。.通过对天山一号冰川不同融水和天山表面粉尘、积雪以及冰川底部沉积层的16S rRNA基因7个克隆文库统计，共有的细菌门有α-Proteobacteria、β-Proteobacteria、γ-Proteobacteria、Bacteriodates和Actinobacteria，β-Proteobacteria是所有克隆文库中的优势菌群，Bacteriodates次之。Cyanobacteria在TSFC克隆文库中最多；在TSMW和TSD克隆文库中也分别检测到一条与Desinococcus-Thermus和Gemmatimonadetes相关的克隆序列。TSD克隆文库中的序列包括Proteobacteria（55%）、Actinobacteria（9%）、Gemmatimonadetes（1%）、Bacteriodates（35%）和Cyanobacteria（1%）以及1个未确定分类的细菌克隆（1%）克隆文库序列；隶属于Proteobacteria和CFB类序列在整个文库中占绝对优势。天山1号冰川中真菌以担子菌门(Basidiomycota)、子囊菌门(Ascomycota)占绝对优势，子囊菌门的真菌在Fz、Dz文库中的比例分别为27%、57%。依据99%相似性共得到26个真菌OTU，表面冰尘和底部沉积层分别为21、22个，17个为共有OTU。Aspergillus、Simplicillium在冰川底部沉积物中占优势。天山一号冰川表面粉尘101个蓝细菌克隆序列基于97%的相似性被划分为12个OTU，shannon多样性指数为1.522，系统发育分析显示主要隶属于颤蓝细菌目(Oscillatoriales)和色球蓝细菌目(Chroococcales)。