Soil chemistry exerts a more significant influence on bacterial responses to nitrogen disturbances than root exudates

Abstract Atmospheric nitrogen (N) deposition is anticipated to stabilize or decline in numerous global regions. However, the residual effects of historical N enrichment on soil microbial communities—particularly their regulatory mechanisms—remain poorly understood. Our 18-year grassland experiment indicated that bacterial communities in bulk soil exhibited greater sensitivity to N addition compared to those in rhizosphere soil, suggesting host plants affect the response of soil bacteria to N enrichment. Following cessation of N addition, there was limited bacterial community recovery, especially in the rhizosphere soil of forb species. Although root exudates from plants underwent significant alterations under N enrichment, the sensitivity of bacterial communities was primarily governed by changes in soil properties and root traits. In contrast to host selection, environmental filtering factors, particularly soil pH and metal ions, mainly determined the resilience of the overall community by differentially affecting bacterial groups with distinct life-history strategies. Oligotrophic bacteria were negatively impacted by reduced pH and elevated metal ion levels, leading to a decline following N enrichment. Conversely, copiotrophic bacteria initially benefited from metal ions, exhibiting an increase followed by a decrease after the addition and subsequent cessation of N enrichment. These findings indicate that soil environmental filtration exerts a more substantial influence than host selection on bacterial communities in response to N disturbances, thereby enhancing our understanding of the mechanisms underlying plant–microbial interactions under ongoing global changes.