Plant rhizosphere microbes play a key role in plant-soil feedbacks. However, the intrinsic principles governing the assembly of the rhizosphere microbial community remain unclear. To understand these principles, we studied the taxonomical and functional characteristics of the reassembled maize rhizosphere bacterial communities after transplanting between soils. The composition of the rhizosphere bacterial community was measured by high-throughput amplicon-based Illumina MiSeq sequencing of the V4 region of the 16S ribosomal RNA (rRNA) gene. The rhizosphere functional profile was assessed using 16S rRNA data in the PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved State) software. We found that the reassembled rhizosphere bacterial community was recruited from both soil and endosphere communities. The assembly and functional traits of the rhizosphere bacterial community were associated with the concentrations of soil available nutrients. The most important rhizospheric functions were to improve host stress tolerance, followed by nutrient cycling functions. The rhizosphere bacterial taxa that improved host stress tolerance were in low abundance and were primarily derived from the surrounding bulk soil. Moreover, the rhizosphere nutrient cycling functions were marginalized in nutrient-excessive soils. Plants may sacrifice stress tolerance functions and enhance compensatory colonization of nutrient cycling-related endophytes in the rhizosphere in nutrient-deficient soils. Our results demonstrate that the levels of soil available nutrients mediate the assembly of rhizosphere bacterial communities to satisfy plant-required functions. This assembly principle is useful for manipulating the bacterial communities of plant roots to improve agricultural sustainability.

植物根际微生物在植物-土壤反馈中起关键作用。但是，控制根际微生物群落组装的内在原则仍然不清楚。为了理解这些原理，我们研究了在土壤之间移植后重新组装的玉米根际细菌群落的分类学和功能特征。根际细菌群落的组成是通过对16S核糖体RNA（rRNA）基因的V4区进行基于高通量扩增子的Illumina MiSeq测序来测量的。使用PICRUSt（通过未观察到的状态重建社区的系统发育调查）软件中的16S rRNA数据评估了根际功能特征。我们发现，重组后的根际细菌群落是从土壤和内球群落中募集的。根际细菌群落的组装和功能性状与土壤有效养分的浓度有关。根际最重要的功能是提高宿主抗逆性，其次是养分循环功能。改善寄主耐性的根际细菌类群的丰度较低，并且主要来自周围的散装土壤。此外，在养分过多的土壤中，根际养分循环功能被边缘化。在营养缺乏的土壤中，植物可能会牺牲胁迫的耐受功能并增强根际中与营养循环相关的内生菌的补偿定居。我们的结果表明，土壤有效养分的水平介导了根际细菌群落的组装，以满足植物所需的功能。