Nitrogen application rate and transplanting regime shape rhizosphere soil microenvironment, microbial community and leaf quality of flue‑cured tobacco

Abstract

Excessive nitrogen fertilizer application in Guizhou’s tobacco-producing regions has degraded soil fertility and reduced leaf quality. Although different transplanting methods strongly influence tobacco growth and productivity, the interactive effects of nitrogen application rates and transplanting methods on rhizosphere soil and tobacco quality remain insufficiently studied. Using flue-cured tobacco cultivar Yunyan 87, a two-factor experiment with three nitrogen application rates and five transplanting methods was conducted. Based on high-throughput sequencing, we systematically analyzed rhizosphere soil physicochemical properties, microbial community characteristics, and their relationships with tobacco leaf quality. The results showed that nitrogen rate and transplanting method significantly affected soil physicochemical properties, and duckbill transplanting combined with low nitrogen application maintained the highest soil organic matter and available potassium contents. Sequencing identified 34 bacterial phyla and 13 fungal phyla. Proteobacteria and Ascomycota were the dominant bacterial and fungal phyla, respectively. Low nitrogen combined with duckbill transplanting significantly enriched nitrogen-cycling taxa such as Nitrospira and Nitrosomonas, and altered the relative abundance of dominant genera including Sphingomonas, Pseudomonas, Botryotrichum, and Mortierella. LEfSe analysis revealed distinct microbial biomarkers among treatments, with Sphingomonas and Sphingomonadaceae significantly enriched under low nitrogen, whereas specific fungal taxa including Agaricomycetes were indicative of certain transplanting regimes. Tobacco leaf chemical components were optimized under the N1T3 treatment (N1: 121.5 kg/hm²; T3: duckbill transplanting), and Pearson correlation analysis revealed close linkages among key rhizosphere microbes, soil properties, and tobacco quality indices. These findings suggest that a nitrogen application rate of 121.5 kg/hm² combined with duckbill transplanting optimizes rhizosphere microbial community structure, enriches N-cycling functional microbiota, regulates key metabolic functions, and improves tobacco leaf quality. This reduced-nitrogen strategy is environmentally sustainable and provides a scientific basis for green and sustainable tobacco cultivation.