# Deep enrichment of soil Proteobacteria and its coupled response to carbon, nitrogen, and phosphorus cycles under quizalofop-p-ethyl stress

## TL;DR

This study shows how a herbicide affects soil bacteria, especially Proteobacteria, and how this impacts carbon, nitrogen, and phosphorus cycles in deep soil layers.

## Contribution

The study reveals the vertical enrichment of Proteobacteria and its role in regulating soil C/N/P cycles under quizalofop-p-ethyl stress.

## Key findings

- Proteobacteria abundance increases with soil depth under herbicide stress.
- Herbicide exposure upregulates key metabolic pathways for carbon, nitrogen, and phosphorus cycles.
- Proteobacteria promote nutrient cycling through gene expression related to nitrogen assimilation and phosphorus utilization.

## Abstract

To investigate the vertical impacts of quizalofop-p-ethyl stress on soil bacterial communities and their ecological functional responses in wheat fields, this study collected soil samples from three depths (0–30 cm, 30–60 cm, and 60–90 cm) using a grid sampling method in typical wheat fields of Inner Mongolia Autonomous Region. Through quizalofop-p-ethyl acclimation experiments with concentration gradients (50–300 mg/L), combined with bacterial community structure and functional analyses, this study focused on revealing the dominant enrichment of Proteobacteria in deep soil and its key regulatory role in carbon (C), nitrogen (N), and phosphorus (P) cycles. The results showed that quizalofop-p-ethyl treatment significantly altered soil microbial community structure and induced obvious functional remodeling. As a core responsive taxon, the relative abundance of Proteobacteria increased significantly with increasing soil depth, becoming the absolute dominant phylum in deep soil layers. This change was significantly positively correlated with the upregulation of key metabolic pathways involved in soil C, N, and P cycles (including the citrate cycle, nitrogen metabolism, phosphonate metabolism, etc.). Functional gene analysis further indicated that the expression of multiple genes related to nitrogen assimilation and phosphorus utilization was closely associated with the abundance of Proteobacteria, directly promoting N and P cycling processes. Meanwhile, the activation of quizalofop-p-ethyl degradation-related pathways provided additional carbon sources for microorganisms, synergistically enhancing the C cycle. From the perspective of “dominant bacterial taxa driving element cycling,” this study clarified the vertical differentiation mechanism of soil microbial ecological functions under quizalofop-p-ethyl stress, which deepens the understanding of the soil microecological effects of herbicides.

Split illustration contrasting two crop fields and their soil layers to elucidate the impact of quizalofop-p-ethyl herbicide on soil C/N/P cycling. The left panel shows the herbicide-sprayed field with lighter-colored soil (indicating higher maturity), sparser vegetation, and enhanced carbon, nitrogen, and phosphorus nutrient cycling (marked by large directional arrows and “C/N/P”). The right panel depicts the non-herbicide field with darker soil, denser vegetation, a clear 0–90 centimeter soil depth scale, and natural soil microbial distribution. The illustration clearly contrasts the soil maturity, vegetation, and microbial-driven nutrient cycling differences between the two systems.