A plant's neighborhood context can alter its interactions with other organisms, but little is known about how these dynamics occur belowground, especially with soil microbes. Microbial communities in rhizosphere soil are influenced by many factors, including abiotic conditions and root-derived signals. In particular, root exudates have strong effects on rhizosphere assembly, respond to changes in abiotic conditions, and help plants interact with neighbors. Therefore, we predicted that root exudates likely play a central role in neighbor-induced shifts in rhizosphere communities. We conducted a greenhouse experiment to test this and determine how the rhizosphere bacterial community of a focal plant, Panicum virgatum, changed when beside different neighbors, and whether these shifts were mediated by neighbor-induced changes in root exudation. We found that neighbor altered both focal plant exudates and rhizosphere community, and that changes were largest when the focal plant was beside the most competitive neighbor, Rudbeckia hirta, which reduced both focal plant growth and nitrogen uptake. Several factors contributed to neighbor impacts on rhizosphere assembly, including neighbor-induced changes in root exudates during nitrogen-limitation and microbial spillover from roots of larger neighbors. Using an additional soil incubation, we also found that these changes in exudates can have even greater effects on soil nutrients than on microbial assembly. Overall, we show that neighbors influence one another's microbiomes, and highlight neighbor-induced changes in root exudates as one mechanism through which this may occur. This work suggests that rhizosphere assembly may differ in mixed-species communities and thus emphasizes a need for microbiome studies that consider neighborhood context.

植物的邻域环境可以改变它与其他生物的相互作用，但对于这些动态如何在地下发生，尤其是与土壤微生物的相互作用知之甚少。根际土壤中的微生物群落受到许多因素的影响，包括非生物条件和根源信号。特别是，根系分泌物对根际组装、响应非生物条件的变化以及帮助植物与邻居相互作用具有很强的影响。因此，我们预测根系分泌物可能在邻居引起的根际群落变化中起核心作用。我们进行了一个温室实验来测试这一点，并确定一种焦点植物Panicum virgatum的根际细菌群落如何，在不同邻居旁边时发生变化，以及这些变化是否由邻居引起的根系分泌变化介导。我们发现邻居改变了焦点植物的分泌物和根际群落，当焦点植物在最具竞争力的邻居金光菊旁边时变化最大，这减少了焦点植物的生长和氮的吸收。有几个因素导致了邻居对根际组装的影响，包括在氮限制期间邻居引起的根系分泌物变化和较大邻居根部的微生物溢出。使用额外的土壤孵化，我们还发现渗出物的这些变化对土壤养分的影响比对微生物组装的影响更大。总体而言，我们表明邻居会影响彼此的微生物组，并强调邻居引起的根系分泌物变化是可能发生这种情况的一种机制。这项工作表明，混合物种群落中的根际组装可能不同，因此强调了考虑邻里环境的微生物组研究的必要性。