Table5.DOCX

Genetic fingerprinting demonstrated in previous studies that differently sized soil particle fractions (PSFs; clay, silt, and sand with particulate organic matter (POM)) harbor microbial communities that differ in structure, functional potentials and sensitivity to environmental conditions. To elucidate whether specific bacterial or archaeal taxa exhibit preference for specific PSFs, we examined the diversity of PCR-amplified 16S rRNA genes by high-throughput sequencing using total DNA extracted from three long-term fertilization variants (unfertilized, fertilized with minerals, and fertilized with animal manure) of an agricultural loamy sand soil and their PSFs. The PSFs were obtained by gentle ultrasonic dispersion, wet sieving, and centrifugation. The abundance of bacterial taxa assigned to operational taxonomic units (OTUs) differed less than 2.7% between unfractionated soil and soil based on combined PSFs. Across the three soil variants, no archaeal OTUs, but many bacterial OTUs, the latter representing 34–56% of all amplicon sequences, showed significant preferences for specific PSFs. The sand-sized fraction with POM was the preferred site for members of Bacteroidetes and Alphaproteobacteria, while Gemmatimonadales preferred coarse silt, Actinobacteria and Nitrosospira fine silt, and Planctomycetales clay. Firmicutes were depleted in the sand-sized fraction. In contrast, archaea, which represented 0.8% of all 16S rRNA gene sequences, showed only little preference for specific PSFs. We conclude that differently sized soil particles represent distinct microenvironments that support specific bacterial taxa and that these preferences could strongly contribute to the spatial heterogeneity and bacterial diversity found in soils.

过往研究通过基因指纹分析（genetic fingerprinting）技术证实，不同粒径的土壤颗粒组分（PSFs）——即黏粒、粉粒及携带有颗粒态有机质（POM）的砂粒——所承载的微生物群落在群落结构、功能潜能以及对环境条件的敏感性上均存在差异。为阐明特定细菌或古菌类群是否对特定土壤颗粒组分存在偏好，本研究针对某农业壤质砂土的3种长期施肥处理组（不施肥组、矿物肥料施肥组及动物有机肥施肥组）及其分离得到的土壤颗粒组分，采用高通量测序技术分析了经聚合酶链式反应（PCR）扩增的16S rRNA基因的多样性，总DNA提取自上述土壤样品及对应的颗粒组分。土壤颗粒组分通过温和超声分散、湿筛法及离心法分离得到。未分级土壤与合并所有颗粒组分的土壤之间，归属于操作分类单元（OTUs）的细菌类群丰度差异不超过2.7%。在3种土壤处理组中，未发现古菌OTUs对特定粒径组分存在显著偏好，但存在大量细菌OTUs，这类OTUs占所有扩增子序列的34%~56%，且多数对特定土壤颗粒组分表现出显著偏好。携带有颗粒态有机质的砂粒组分是拟杆菌门（Bacteroidetes）与α-变形菌纲（Alphaproteobacteria）类群的偏好生境；芽单胞菌目（Gemmatimonadales）偏好粗粉粒组分，放线菌门（Actinobacteria）与亚硝化螺菌属（Nitrosospira）偏好细粉粒组分，浮霉菌目（Planctomycetales）则偏好黏粒组分。厚壁菌门（Firmicutes）在砂粒组分中相对匮乏。与之相反，占所有16S rRNA基因序列0.8%的古菌类群，仅表现出极弱的粒径偏好性。本研究得出结论：不同粒径的土壤颗粒代表了各具特色的微环境，可支撑特定细菌类群的定植；这类类群的粒径偏好性可能极大地推动了土壤空间异质性与细菌多样性的形成。