Interspecific competition and plant–soil feedbacks are powerful drivers of plant community structure. However, across a range of edaphic conditions the interactive effects of these drivers on complex plant communities remain unclear. For example, plant–soil feedback studies focus on soil trained by a single plant species. We developed a method to assess effects of plant–microbial interactions (PMI) on a complex plant community. We established mesocosms with 13 grassland species, grown individually or together, in overgrazed or restored soil, with or without soil microbial inoculum collected from a productive and diverse native grassland. We assessed biomass production as influenced by edaphic conditions, interspecific competition and PMI. Furthermore, we assessed potential influences of interspecific competition and edaphic conditions on strength and direction of PMI. Our results indicate PMI drives negative growth responses for graminoids while forbs experience positive growth responses. Generally, interspecific competition did not alter the magnitude or direction of PMI‐mediated growth responses. Edaphic conditions altered the influence of soil microbial communities on individual plant growth while PMI facilitated plant evenness. In plant community mesocosms, PMI‐associated benefits were observed in overgrazed soil. However, interspecific competition overwhelmed plant growth benefits associated with soil microbial communities when plant communities were grown in restored soil. In mesocosms containing dominant grass species, interspecific competition had negative effects on species coexistence, but both positive and negative PMI partially counterbalanced this influence on plant species evenness. Understanding these mechanisms may improve our capacity to manage diverse and productive grasslands by enabling prediction of plant community composition following disturbance and subsequent restoration.

中文翻译：

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植物与微生物的相互作用促进了草地物种在社区一级的共存

种间竞争和植物土壤反馈是植物群落结构的强大驱动力。但是，在一系列广泛的条件下，这些驱动因素对复杂植物群落的相互作用影响仍然不清楚。例如，植物-土壤反馈研究集中于由单一植物物种训练的土壤。我们开发了一种方法来评估植物-微生物相互作用（PMI）对复杂植物群落的影响。我们建立了由13种草原物种组成的中观世界，它们单独或一起生长在过度放牧或恢复的土壤中，有无土壤微生物接种物都来自生产性和多样性的原生草地。我们评估了生物质生产受环境条件，种间竞争和PMI的影响。此外，我们评估了种间竞争和前卫条件对PMI强度和方向的潜在影响。我们的结果表明，PMI推动了类胡萝卜素的负增长响应，而Forb则经历了正增长响应。通常，种间竞争不会改变PMI介导的生长反应的大小或方向。磷化条件改变了土壤微生物群落对个体植物生长的影响，而PMI促进了植物的均匀性。在植物群落的中观世界中，在过度放牧的土壤中观察到了与PMI相关的益处。但是，当植物群落在恢复的土壤中生长时，种间竞争使与土壤微生物群落相关的植物生长优势不堪重负。在含有优势草种的中观世界中，种间竞争对物种共存具有负面影响，但正负PMI均部分抵消了这种对植物物种均匀度的影响。了解这些机制可以通过预测干扰和随后的恢复后植物群落组成，从而提高我们管理多样化和多产草原的能力。