Understanding how plant-associated microbial communities assemble and the role they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, community assembly is generally driven by host plant selection and soil conditions. Here, we aimed to determine the relative importance of neutral and deterministic processes in the assembly of bacterial communities of root nodules of a legume shrub adapted to extreme nutrient limitation, rooibos (Aspalathus linearis Burm. Dahlgren). We grew rooibos seedlings in soil from cultivated land and wild habitats, and mixtures of these soils, sampled from a wide geographic area, and with a fertilization treatment. Bacterial communities were characterized using next generation sequencing of part of the nodA gene (i.e. common to the core rhizobial symbionts of rooibos), and part of the gyrB gene (i.e. common to all bacterial taxa). Ecological drift alone was a major driver of taxonomic turnover in the bacterial communities of root nodules (62.6% of gyrB communities). In contrast, the assembly of core rhizobial communities (genus Mesorhizobium) was driven by dispersal limitation in concert with drift (81.1% of nodA communities). This agrees with a scenario of rooibos-Mesorhizobium specificity in spatially separated subpopulations, and low host filtering of other bacteria colonizing root nodules in a stochastic manner.

中文翻译：

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实验结果表明，生态漂移是木本豆类作物中根瘤细菌多样性的主要驱动力。

理解与植物相关的微生物群落如何组装以及它们在植物性能中的作用是微生物生态学的主要目标。对于固氮根瘤菌，群落组装通常由寄主植物选择和土壤条件驱动。在这里，我们旨在确定中性和确定性过程在豆类灌木根瘤细菌群落的装配中的相对重要性，该菌群适应于极端营养限制的路易波氏菌（Aspalathus linearis Burm。Dahlgren）。我们在耕地和野生动植物的土壤中种植了如意宝种子，并通过施肥对这些土壤的混合物进行了采样，这些土壤来自广泛的地理区域。通过对部分nodA基因（即如意宝的核心根瘤菌共生菌）进行下一代测序来鉴定细菌群落，和部分gyrB基因（即所有细菌类群共有）。单独的生态漂移是根瘤细菌群落（gyrB群落的62.6％）分类学更新的主要驱动力。相反，核心的根瘤菌群落（中生根瘤菌属）的组装是由扩散限制和漂移共同驱动的（占nodA群落的81.1％）。这与在空间上分离的亚群中的路易波杆菌-中生根瘤菌特异性以及以随机方式在定居根瘤中的其他细菌的低宿主过滤率一致。核心的根瘤菌群落（中生根瘤菌属）的组装是由扩散限制和漂移共同驱动的（占nodA群落的81.1％）。这与在空间上分离的亚群中的路易波杆菌-中生根虫特异性以及以随机方式对定居在根瘤中的其他细菌的低宿主过滤的情况相一致。核心的根瘤菌群落（中生根瘤菌属）的组装是由扩散限制和漂移共同驱动的（占nodA群落的81.1％）。这与在空间上分离的亚群中的路易波杆菌-中生根瘤菌特异性以及以随机方式在定居根瘤中的其他细菌的低宿主过滤率一致。