Background and aims Rapeseed, a globally important oil crop with high nitrogen demand, exhibits rhizosphere microbial responses influenced by both nitrogen fertilization and species. However, the differential effects of nitrogen and rapeseed species on root morphology, rhizosphere enzyme activity, and microbial communities have not been adequately evaluated. Methods A rhizo-box experiment was conducted over 21 days using clay loam soil from a long-term paddy field. We compared the effects of urea application (0 vs. 0.12 g N kg⁻1 dry soil) and two rapeseed species (Brassica napus, cabbage-type; Brassica juncea, mustard-type) on root morphology, rhizosphere enzyme activity, and bacterial community structure. By integrating in situ soil zymography and bacterial amplicon sequencing, we comprehensively analyzed enzyme dynamics and microbial community responses in the rhizosphere. Results Rapeseed species primarily affected root morphology and the spatial distribution of rhizosphere enzymes, with cabbage-type rapeseed exhibiting broader rhizo-enzyme diffusion and larger hotspot areas than mustard-type rapeseed. Compared with rapeseed species, nitrogen fertilization not only enhanced enzyme activities and expanded root tip diffusion and hotspot areas but also significantly influenced bacterial β-diversity and functional profiles. Nitrogen fertilization increased gram-negative bacteria associated with bio-originated carbon decomposition (e.g., chitinolysis) and reduced gram-positive and aerobic bacteria linked to complex carbon degradation (cellulose degradation, fermentation, and aromatic compound degradation). Conclusions Compared with the rapeseed species, nitrogen fertilization is the dominant driver of microbial community structure and function. These findings underscore the potential ecological consequences of nitrogen fertilization, particularly its role in shaping microbial-mediated rhizo-nutrient cycling. Graphical Abstract The left side of the figure represents cabbage-type rapeseed (B. napus). The right side of the figure represents mustard-type rapeseed (B. juncea). Notes: One-way analysis of variance was performed using IBM SPSS Statistics 27. The PLS-SEM was constructed using the plspm package. R/S refers to the root-to-shoot ratio. : p < 0.05, : p < 0.01, : p < 0.001;↓followed after letters represent reduce, ↑followed after letters represent increase.

Nitrogen fertilization surpasses rapeseed species in shaping rhizosphere enzyme activities and bacterial community structure

期刊论文
发表日期：

2026年3月17日

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Zhirong Qiu,
Donghai Jiang,
Wangxin Cui,
Ziwei Zhao,
Zhenhua Zhang

摘要

Background and aims

Rapeseed, a globally important oil crop with high nitrogen demand, exhibits rhizosphere microbial responses influenced by both nitrogen fertilization and species. However, the differential effects of nitrogen and rapeseed species on root morphology, rhizosphere enzyme activity, and microbial communities have not been adequately evaluated.

Methods

A rhizo-box experiment was conducted over 21 days using clay loam soil from a long-term paddy field. We compared the effects of urea application (0 vs. 0.12 g N kg⁻¹ dry soil) and two rapeseed species (Brassica napus, cabbage-type; Brassica juncea, mustard-type) on root morphology, rhizosphere enzyme activity, and bacterial community structure. By integrating in situ soil zymography and bacterial amplicon sequencing, we comprehensively analyzed enzyme dynamics and microbial community responses in the rhizosphere.

Results

Rapeseed species primarily affected root morphology and the spatial distribution of rhizosphere enzymes, with cabbage-type rapeseed exhibiting broader rhizo-enzyme diffusion and larger hotspot areas than mustard-type rapeseed. Compared with rapeseed species, nitrogen fertilization not only enhanced enzyme activities and expanded root tip diffusion and hotspot areas but also significantly influenced bacterial β-diversity and functional profiles. Nitrogen fertilization increased gram-negative bacteria associated with bio-originated carbon decomposition (e.g., chitinolysis) and reduced gram-positive and aerobic bacteria linked to complex carbon degradation (cellulose degradation, fermentation, and aromatic compound degradation).

Conclusions

Compared with the rapeseed species, nitrogen fertilization is the dominant driver of microbial community structure and function. These findings underscore the potential ecological consequences of nitrogen fertilization, particularly its role in shaping microbial-mediated rhizo-nutrient cycling.

Graphical Abstract

The left side of the figure represents cabbage-type rapeseed (B. napus). The right side of the figure represents mustard-type rapeseed (B. juncea). Notes: One-way analysis of variance was performed using IBM SPSS Statistics 27. The PLS-SEM was constructed using the plspm package. R/S refers to the root-to-shoot ratio. *: p < 0.05, **: p < 0.01, ***: p < 0.001;↓followed after letters represent reduce, ↑followed after letters represent increase.