Data from: Smooth brome invasion increases rare soil bacterial species prevalence and alters soil bacterial community composition

Plant and soil communities are tightly linked, but the mechanisms by which the invasion of an exotic plant and the resulting shifts in plant diversity and productivity influence soil bacterial community structure remain poorly understood. We investigated the effects of invasive smooth brome (Bromus inermis) on grassland soil bacterial community structure using massively-parallel sequencing of the 16S rRNA gene to determine bacterial community richness, evenness, composition, and beta diversity (UniFrac indices) of soils collected along a gradient of smooth brome abundance. We evaluated several hypotheses including: a) that the declines in native plant diversity associated with smooth brome invasion would cause declines in bacterial community diversity, and b) that mechanisms driving smooth brome effects on bacterial community structure involved altered soil edaphic properties rather than preferential invasion in areas of high soil nitrogen and distinct soil microbial communities. Smooth brome invasion led to increased soil nitrogen, soil carbon and root biomass. Bacterial evenness and bacterial richness increased with increasing smooth brome cover, while bacterial beta diversity declined. We found no evidence of a dominant direct link between the alteration of soil edaphic properties by brome and the changes in the soil bacterial community. Rather, the main controls on the soil bacterial community were direct effects of pH and smooth brome that could not be linked to the edaphic changes. The most important effect of brome on the bacterial community was the selective suppression of dominant bacterial species, which allowed rarer bacteria to increase in relative abundance. Synthesis: Here we show that plant community composition influences bacterial community structure at a very fine scale, but that these changes are not due to altered soil total nitrogen or carbon content. The dominant direct effect of smooth brome invasion on soil communities suggests non-edaphic, i.e. inter and intra-trophic, interactions among smooth brome and non-bacterial components of the soil ecosystem are key drivers of soil community structure. Some of the data in this repository were also reported in the following paper: Piper, C.L., Lamb, E.G. & Siciliano, S.D. (In Press) Smooth brome changes gross soil nitrogen cycling processes during invasion of a rough fescue grassland. Plant Ecology. doi:10.1007/s11258-014-0431-y

植物群落与土壤群落紧密关联，但外来植物入侵及其引发的植物多样性、生产力变化如何影响土壤细菌群落结构，其背后的调控机制仍未得到充分阐明。本研究以入侵性无芒雀麦（Bromus inermis）为研究对象，通过16S核糖体RNA（16S rRNA）基因大规模平行测序技术，对沿无芒雀麦盖度梯度采集的草地土壤样品进行分析，以明确入侵植物对土壤细菌群落丰富度、均匀度、组成及β多样性（beta diversity，UniFrac指数）的影响。本研究验证了两项假说：其一，与无芒雀麦入侵相关的本土植物多样性下降，会导致细菌群落多样性降低；其二，无芒雀麦对细菌群落结构的调控机制主要通过改变土壤理化性质介导，而非仅因高氮土壤区域或独特土壤微生物群落更易被其优先入侵。实验结果显示，无芒雀麦入侵会提升土壤氮、土壤碳含量与根系生物量。随着无芒雀麦盖度的升高，土壤细菌群落的均匀度与丰富度均有所提升，而细菌β多样性则呈下降趋势。本研究未发现无芒雀麦对土壤理化性质的改变与土壤细菌群落变化之间存在显著直接关联。反之，调控土壤细菌群落的主要因素为土壤pH值与无芒雀麦的直接作用，且该作用与土壤理化性质的改变无关。无芒雀麦对细菌群落最关键的影响，是选择性抑制优势细菌类群，从而使稀有细菌类群的相对丰度得以提升。综合分析结果表明：植物群落组成可在极精细的尺度上调控细菌群落结构，但此类变化并非由土壤总氮或总碳含量改变所介导。无芒雀麦入侵对土壤群落的显著直接作用表明，非土壤理化性质介导的过程——即无芒雀麦与土壤生态系统中非细菌组分之间的营养级内与营养级间互作——是调控土壤群落结构的核心驱动因素。本数据集的部分内容已发表于以下论文：Piper, C.L.、Lamb, E.G. 与 Siciliano, S.D.（已接收），《入侵紫羊茅草地过程中无芒雀麦改变土壤总氮循环过程》，《Plant Ecology》，doi:10.1007/s11258-014-0431-y