The characteristics of the rhizosphere microbial community across different cultivation years (from 1, 3, 5, 15, 20, and 50 years) in saline-alkaline paddy soils in Songnen Plain of China were investigated based on sequence variation of 16S rDNA using Illumina MiSeq sequencing. The results showed that the microbial community diversity varied across cultivation years, showing higher diversity in cultivation years >15 than in cultivation years <15. The dominant microbial community of the rhizosphere was mainly composed of Proteobacteria, Acidobacteria, Firmicutes, and Bacteroidetes. Furthermore, soil microbial diversity appeared to be affected directly by changes in soil properties corresponding to cultivated years. Diversity of Proteobacteria decreased as cultivated years increased; however, that of Acidobacteria showed the opposite direction. In addition, the soil microbial communities were clustered into two main groups: one from the sites cultivated for fewer than 15 years, and the other from the sites cultivated for more than 15 years. The abundance of nitrogen-fixing microorganisms in the soil sample was significantly higher in soils cultivated for under 15 years than in those cultivated for over 15 years (P < 0.05). Moreover, there was an obvious negative correlation between the cultivated years and Methanosarcina. Our findings on the dynamics of microbial community and its specific function in response to variable soil conditions are important for understanding and improving physical and chemical characteristics of saline-alkaline soil in Songnen Plain of China.

Fungal and bacterial community structure in tussock, intertussock and shrub organic and mineral soils at Toolik Lake, Alaska were evaluated. Community structure was examined by constructing clone libraries of partial 16S and 18S rRNA genes. The soil communities were sampled at the end of the growing season in August 2004 and just after the soils thawed in June 2005. The communities differed greatly between vegetation types, although tussock and intertussock soil communities were very similar at the phyla level. The communities were relatively stable between sample dates at the phyla and subphyla levels, but differed significantly at finer phylogenetic scales. Tussock and intertussock bacterial communities were dominated by Acidobacteria, while shrub soils were dominated by Proteobacteria. These results appear consistent with previous work demonstrating that shrub soils contain an active, bioavailable C fraction, while tussock soils are dominated by more recalcitrant substrates. Tussock fungi communities had higher proportions of Ascomycota than shrub soils, while Zygomycota were more abundant in shrub soils. Recent documentation of increasing shrub abundance in the Arctic suggests that soil microbial communities and their functioning are likely to be altered by climate change.

本研究以荒漠草原达茂旗毛刺锦鸡儿（Caragana tibetica）灌丛沙堆为研究对象，通过16S rRNA高通量测序和土壤理化性质分析，探究不同规格（大、中、小）灌丛及无灌丛生长的对照地（CK）土壤细菌群落结构和多样性以及与土壤理化性质的关系。结果表明：不同规格灌丛根际土和对照地（CK）土壤样品中，蛋白酶活性、含水量和全氮含量存在显著差异（P大灌丛>对照地（CK）>中灌丛，其中Alpha多样性的物种数、Chao1和ACE指数存在显著差异（PP<0.05），RDA分析表明蛋白酶活性、全氮含量和脲酶活性是驱动细菌群落组成的关键因子。综上所述，不同规格灌丛根际土与对照地（CK）土壤细菌群落存在一定差异，且土壤环境因子对微生物群落产生影响。

为了解干旱半干旱地区荒漠草原不同发育阶段柠条灌丛堆土壤细菌群落结构与多样性特征及影响因素,选取宁夏荒漠草原生长期、成熟期和衰退期3种不同发育阶段柠条灌丛堆,通过高通量测序技术分析其土壤细菌的群落结构及多样性特征,探究发育阶段和土壤理化因子演变对土壤细菌群落结构和功能的影响因素,最后利用PICRUSt方法预测不同发育阶段柠条灌丛堆土壤细菌的功能。结果表明,获得的15 383个细菌操作分类单元（operational taxonomic unit,OTU）属于50门146纲364目590科1 111属,其中生长期细菌数量最多,优势菌门为放线菌门（Actinobacteriota）、变形菌门（Proteobacteria）、酸杆菌门（Acidobacteriota）、绿弯菌门（Chloroflexi）等9个菌门,占微生物总数90%以上,优势菌门门类与大多数研究相似。柠条灌丛堆不同发育阶段土壤AP、EC存在显著差异,表现为成熟期>生长期>衰退期,其他土壤养分差异不显著,但数值同样表现为成熟期>生长期>衰退期。细菌群落的多样性和丰富度没有显著性差异,但数值上表现为成熟期最高。AP、SOC是柠条灌丛堆土壤细菌群落多样性的主要影响因子,EC、pH等其他环境因子也显著影响多个菌群丰富度。基于柠条灌丛堆不同发育阶段土壤细菌基因组的16S rRNA序列对其功能的预测发现,土壤细菌的主要功能表现为代谢方面。以上结果丰富了半干旱荒漠草原地区土壤微生物多样性的相关理论知识,为柠条植被的恢复提供一定的依据。

Soil bacteria play key roles in regulating terrestrial carbon dynamics, nutrient cycles, and plant productivity. However, the natural histories and distributions of these organisms remain largely undocumented. Delgado-Baquerizo et al. provide a survey of the dominant bacterial taxa found around the world. In soil collections from six continents, they found that only 2% of bacterial taxa account for nearly half of the soil bacterial communities across the globe. These dominant taxa could be clustered into ecological groups of co-occurring bacteria that share habitat preferences. The findings will allow for a more predictive understanding of soil bacterial diversity and distribution.\n

Although researchers have begun cataloging the incredible diversity of bacteria found in soil, we are largely unable to interpret this information in an ecological context, including which groups of bacteria are most abundant in different soils and why. With this study, we examined how the abundances of major soil bacterial phyla correspond to the biotic and abiotic characteristics of the soil environment to determine if they can be divided into ecologically meaningful categories. To do this, we collected 71 unique soil samples from a wide range of ecosystems across North America and looked for relationships between soil properties and the relative abundances of six dominant bacterial phyla (Acidobacteria, Bacteroidetes, Firmicutes, Actinobacteria, alpha-Proteobacteria, and the beta-Proteobacteria). Of the soil properties measured, net carbon (C) mineralization rate (an index of C availability) was the best predictor of phylum-level abundances. There was a negative correlation between Acidobacteria abundance and C mineralization rates (r2 = 0.26, P < 0.001), while the abundances of beta-Proteobacteria and Bacteroidetes were positively correlated with C mineralization rates (r2 = 0.35, P < 0.001 and r2 = 0.34, P < 0.001, respectively). These patterns were explored further using both experimental and meta-analytical approaches. We amended soil cores from a specific site with varying levels of sucrose over a 12-month period to maintain a gradient of elevated C availabilities. This experiment confirmed our survey results: there was a negative relationship between C amendment level and the abundance of Acidobacteria (r2 = 0.42, P < 0.01) and a positive relationship for both Bacteroidetes and beta-Proteobacteria (r2 = 0.38 and 0.70, respectively; P < 0.01 for each). Further support for a relationship between the relative abundances of these bacterial phyla and C availability was garnered from an analysis of published bacterial clone libraries from bulk and rhizosphere soils. Together our survey, experimental, and meta-analytical results suggest that certain bacterial phyla can be differentiated into copiotrophic and oligotrophic categories that correspond to the r- and K-selected categories used to describe the ecological attributes of plants and animals. By applying the copiotroph-oligotroph concept to soil microorganisms we can make specific predictions about the ecological attributes of various bacterial taxa and better understand the structure and function of soil bacterial communities.

Soil microbes play a key role in controlling ecosystem functions and providing ecosystem services. Yet, microbial communities in urban green space soils remain poorly characterized. Here we compared soil microbial communities in 41 urban parks of (i) divergent plant functional types (evergreen trees, deciduous trees and lawn) and (ii) different ages (constructed 10, ∼50 and >100 years ago). These microbial communities were also compared to those in 5 control forests in southern Finland. Our results indicate that, despite frequent disturbances in urban parks, urban soil microbes still followed the classic patterns typical of plant-microbe associations in natural environments: both bacterial and fungal communities in urban parks responded to plant functional groups, but fungi were under tighter control of plants than bacteria. We show that park age shaped the composition of microbial communities, possibly because vegetation in old parks have had a longer time to modify soil properties and microbial communities than in young parks. Furthermore, control forests harboured distinct but less diverse soil microbial communities than urban parks that are under continuous anthropogenic disturbance. Our results highlight the importance of maintaining a diverse portfolio of urban green spaces and plant communities therein to facilitate complex microbial communities and functions in urban systems.© 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

Fertilization has a large impact on the soil microbial communities, which play pivotal roles in soil biogeochemical cycling and ecological processes. While the effects of changes in nutrient availability due to fertilization on the soil microbial communities have received considerable attention, specific microbial taxa strongly influenced by long-term organic and inorganic fertilization, their potential effects and associations with soil nutrients remain unclear. Here, we use deep 16S amplicon sequencing to investigate bacterial community characteristics in a fluvo-aquic soil treated for 24 years with inorganic fertilizers and organics (manure and straw)-inorganic fertilizers, and uncover potential links between soil nutrient parameters and specific bacterial taxa. Our results showed that combined organic-inorganic fertilization increased soil organic carbon (SOC) and total nitrogen (TN) contents and altered bacterial community composition, while inorganic fertilization had little impact on soil nutrients and bacterial community composition. SOC and TN emerged as the major determinants of community composition. The abundances of specific taxa, especially Arenimonas, Gemmatimonas, and an unclassified member of Xanthomonadaceae, were substantially increased by organic-inorganic amendments rather than inorganic amendments only. A co-occurrence based network analysis demonstrated that SOC and TN had strong positive associations with some taxa (Gemmatimonas and the members of Acidobacteria subgroup 6, Myxococcales, Betaproteobacteria, and Bacteroidetes), and Gemmatimonas, Flavobacterium, and an unclassified member of Verrucomicrobia were identified as the keystone taxa. These specific taxa identified above are implicated in the decomposition of complex organic matters and soil carbon, nitrogen, and phosphorus transformations. The present work strengthens our current understanding of the soil microbial community structure and functions under long-term fertilization management and provides certain theoretical support for selection of rational fertilization strategies.