【冻土区土壤微生物群落】Antje Gittel et al. Distinct microbial communities associated with buried soils in the Siberian tundra. The ISME Journal (2014) 8 841–853

Abstract

Cryoturbation the burial of topsoil material into deeper soil horizons by repeated freeze–thaw events is an important storage mechanism for soil organic matter (SOM) in permafrost-affected soils. Besides abiotic conditions microbial community structure and the accessibility of SOM to the decomposer community are hypothesized to control SOM decomposition and thus have a crucial role in SOM accumulation in buried soils. We surveyed the microbial community structure in cryoturbated soils from nine soil profiles in the northeastern Siberian tundra using high-throughput sequencing and quantification of bacterial archaeal and fungal marker genes. We found that bacterial abundances in buried topsoils were as high as in unburied topsoils. In contrast fungal abundances decreased with depth and were significantly lower in buried than in unburied topsoils resulting in remarkably low fungal to bacterial ratios in buried topsoils. Fungal community profiling revealed an associated decrease in presumably ectomycorrhizal (ECM) fungi. The abiotic conditions (low to subzero temperatures anoxia) and the reduced abundance of fungi likely provide a niche for bacterial facultative anaerobic decomposers of SOM such as members of the Actinobacteria which were found in significantly higher relative abundances in buried than in unburied topsoils. Our study expands the knowledge on the microbial community structure in soils of Northern latitude permafrost regions and attributes the delayed decomposition of SOM in buried soils to specific microbial taxa and particularly to a decrease in abundance and activity of ECM fungi and to the extent to which bacterial decomposers are able to act as their functional substitutes.

【根际微生物与植物生长】Jacqueline M Chaparro et al. Rhizosphere microbiome assemblage is affected by plant development. The ISME Journal (2014) 8 790–803

Abstract

There is a concerted understanding of the ability of root exudates to influence the structure of rhizosphere microbial communities. However our knowledge of the connection between plant development root exudation and microbiome assemblage is limited. Here we analyzed the structure of the rhizospheric bacterial community associated with Arabidopsis at four time points corresponding to distinct stages of plant development: seedling vegetative bolting and flowering. Overall there were no significant differences in bacterial community structure but we observed that the microbial community at the seedling stage was distinct from the other developmental time points. At a closer level phylum such as Acidobacteria Actinobacteria Bacteroidetes Cyanobacteria and specific genera within those phyla followed distinct patterns associated with plant development and root exudation. These results suggested that the plant can select a subset of microbes at different stages of development presumably for specific functions. Accordingly metatranscriptomics analysis of the rhizosphere microbiome revealed that 81 unique transcripts were significantly (P<0.05) expressed at different stages of plant development. For instance genes involved in streptomycin synthesis were significantly induced at bolting and flowering stages presumably for disease suppression. We surmise that plants secrete blends of compounds and specific phytochemicals in the root exudates that are differentially pr