群落的时间和空间变异是生态学研究的基本问题之一。人们通过大量的实验观察和理论推导揭示了群落的时空变异模式，并提出了各种假说来解释这些模式。然而相关的工作主要集中在大型生物中。微生物作为地球上数量最多，分布最广，生态功能不可替代的生物类群，被研究的并不充分。本文研究了内蒙古草原土壤总细菌群落和活性细菌群落的时空变异，以及环境因子与细菌群落组成的关系。在两个时间点，我们分别对六个生境进行取样，采集了72份土壤样品，并收集每个生境内的环境因子，包括土壤pH，土壤含水量，土壤碳氮比，地上植物多样性等。通过高通量焦磷酸平行测序和实时定量PCR技术获取土壤细菌群落的物种组成和生物量数据。总细菌群落和活性细菌群落的物种丰富度均很高，总细菌群落有多达20个门，活性细菌群落有17个门，两种群落均有6个相同的门相对多度超过1%。同一生境下，总细菌群落与活性细菌群落组成不同，特别是在极端环境，如河边和沙地环境中。在同一时间的不同生境中，蓝藻细菌基本只出现在活性细菌群落中。总细菌和活性细菌群落的α多样性与环境因子之间没有显著相关。而群落间物种组成的差异与土壤含水量，土壤碳氮比，地上植物丰富度等环境因子显著相关。随着土壤含水量，土壤碳氮比，地上植物丰富度差异的变大，群落物种组成的差异越大。基于以上内容，我们可以知道，同一生境中的总细菌和活性细菌有明显差异。随着时间和生境的变化，总细菌和活性细菌群落的物种组成也发生明显变化，土壤含水量，土壤碳氮比和地上植物丰富度是影响微生物群落组成的主要因素。

Understanding temporal and spatial patterns in the abundance and distribution of communities has been a fundamental quest in ecology. Ecologists have conducted a lot of theoretical and empirical studies to unravel patterns of spatial and temperal variation in different communities, and to understand the underlying processes that determine these patterns. However, most of these studies focus on macroorganisms. While microorganisms are the most abundant and widespread organisms on earth and mediate important ecosystem processes, little is known about their spatial and temperal variation. In this research, we implemented a field survey to describe the spatial and temperal variation of both total and active soil bacteria in the Inner Mongolia grassland. Also, we tried to understand the relationship between community composition and environmental factors. We sampled six different types of habitats in summer and early spring respectively, getting 72 samples in total, and collected data of soil pH, water content and C:N ratio of soil, and above ground plants. Taxa richness of soil bacteria and their relative abundance were measured by massively parallel high-throughput pyrosequencing and biomass of total and active bacteria was quatified by real-time PCR.Taxa richness of both total and total bacteria in the Inner Mongolia grassland was high, and thousands of operational taxonomic units (OTUs) were defined. Total bacteria sequences belonged to 20 phyla, while active bacteria sequences belonged to 17 phyla, among which 6 of the phyla were recorded with relative abundance over 1%. The community composition was significantly different between total and active bacteria got from the same habitats, especially in extreme habitats like riverside and sandy soil. Cyanobacteria only existed in active communities wherever the samples were collected. There was no significant correlation between environmental factors and α diversity of total and active bacteria. However, significant correlation was found between community composition and water content, C:N ratio and richness of above ground plants. That is to say, community composition was more dissimiliar when the difference of water content, C:N ratio and richness of above ground plants between two samples was bigger. In conclusion, community composition of total and active bacteria varied along spatial and temperal changes. water content, C:N ratio and richness of above ground plants were the main environmental factors influencing the community composition of bacteria.