Protists are abundant, diverse and perform essential functions in soils. Protistan community structure and its change across time or space are traditionally studied at the species level but the relative importance of the processes shaping these patterns depends on the taxon phylogenetic resolution. Using 18S rDNA amplicon data of the Cercozoa, a group of dominant soil protists, from an agricultural field in western Germany, we observed a turnover of relatively closely related taxa (from sequence variants to genus-level clades) across soil depth; while across soil habitats (rhizosphere, bulk soil, drilosphere), we observed turnover of relatively distantly related taxa, confirming Paracercomonadidae as a rhizosphere-associated clade. We extended our approach to show that closely related Cercozoa encounter divergent arbuscular mycorrhizal (AM) fungi across soil depth and that distantly related Cercozoa encounter closely related AM fungi across soil compartments. This study suggests that soil Cercozoa community assembly at the field scale is driven by niche-based processes shaped by evolutionary legacy of adaptation to conditions primarily related to the soil compartment, followed by the soil layer, giving a deeper understanding on the selection pressures that shaped their evolution.

中文翻译：

---

温带农田土壤原生生物的等级系统发育群落组装

原生生物丰富多样，在土壤中发挥着重要的作用。Protistan 社区结构及其跨时间或空间的变化传统上是在物种水平上研究的，但塑造这些模式的过程的相对重要性取决于分类单元系统发育分辨率。使用来自德国西部农田的一组优势土壤原生生物尾虫的 18S rDNA 扩增子数据，我们观察到相对密切相关的分类群（从序列变异到属级进化枝）在土壤深度上的更替；而在土壤生境（根际、大块土壤、根际）中，我们观察到相对较远相关的分类群的更替，证实了 Paracercomonadidae 是与根际相关的进化枝。我们扩展了我们的方法，以表明密切相关的尾椎动物在整个土壤深度遇到不同的丛枝菌根 (AM) 真菌，而远缘尾椎动物在土壤隔室中遇到密切相关的丛枝菌根 (AM) 真菌。这项研究表明，田间规模的土壤尾生动物群落组装是由基于生态位的过程驱动的，这些过程是由适应主要与土壤隔室相关的条件的进化遗产形成的，其次是土壤层，从而更深入地了解形成的选择压力他们的进化。