Dynamic assembly in the rhizosphere microbial community of oilseed rape under uranium stress: On temporal and spatial scales

Abstract

Phytoextraction has emerged as a prominent strategy for remediating uranium-contaminated soils, where the assembly dynamics of plant rhizosphere microbial communities critically influence uranium speciation, plant growth promotion, and stress adaptation. This study systematically explored the temporal (fast-growing and mature periods) and spatial (from soil to leaves) scales in microbial community composition and assembly patterns—defined as the structured reorganization of microbial taxa across niches and time—within the rhizosphere of uranium-exposed oilseed rape (Brassica napus) using high-throughput 16S rRNA sequencing. Our study revealed that oilseed rape maintained normal growth without visible phytotoxicity under uranium stress, supported by rhizosphere-driven microbial recruitment. Notably, Proteobacteria enrichment in the rhizosphere correlated with uranium detoxification through stress-alleviating phytohormone production and nitrogen cycling, while Actinobacteriota and Streptomyces mediated uranium immobilization via biosorption and redox transformations, reducing its bioavailability. Rhizosphere and bulk soil microbial diversity declined during the mature stage (Shannon index decreased from 5.91 to 5.43) compared to the fast-growing period. Uranium treatment significantly reduced the relative abundance of root endophytes during the fast-growing period (e.g., Actinobacteriota decreased from 36.9 % to 8.34 %), while leaf-associated microbial communities exhibited the opposite trend (Actinobacteriota increased from 11.7 % to 49.9 %), reflecting microbial adaptation to uranium speciation shifts. Spatially, microbial communities displayed a progressive diversity gradient, decreasing from the soil to plant (Shannon index: bulk soil 10.2 > rhizosphere soil 10.1 > roots 8.19 > leaves 5.22), with root- and leaf-associated phyla (>1 % abundance) representing subsets of bulk soil taxa. These assembly patterns highlight hierarchical microbial filtering, where plants selectively recruit stress-tolerant taxa to enhance uranium mobilization or stabilization. These insights advance our understanding of rhizosphere microbiome dynamics in uranium phytoextraction and inform strategies to optimize remediation efficiency through targeted microbial consortia engineering.