Abstract: To clarify the regulatory mechanism of soil pH on the quality formation of cigar tobacco leaves and rhizosphere microecology, a pot experiment was conducted using the cigar wrapper variety Chuxue 26, with soils of different natural pH values and pH gradients amended with quicklime. The effects of soil pH on tobacco plant agronomic traits, leaf chemical composition, rhizosphere metabolite profiles, and bacterial community structure were systematically analyzed. The results indicated that the soil pH range of 5.5-6.5 was suitable for the growth of cigar tobacco plants, under which plant height, number of effective leaves, and maximum leaf area were significantly superior to those under strongly acidic (pH 4.5) and strongly alkaline treatments (pH 8.1-8.5). Under the S3（pH 5.5） and S5(pH 6.5±0.15) treatments, the total potassium content of tobacco leaves was relatively high at 5.5% and 6.3%, respectively, representing significant increases of 205.6% and 250.0% compared with the S4(pH 4.5) treatment. Metabolomic analysis revealed that the optimal soil pH significantly promoted the accumulation of membrane lipid components such as phosphatidylglycerol (PG) and antioxidant substances, while significantly reducing the relative abundance of stress-responsive metabolites such as 2-deoxyribose-5-phosphate. Microbial community analysis showed that under soil pH 5.5-6.5, rhizosphere bacterial alpha diversity was higher, and the rhizosphere soil was significantly enriched with potentially beneficial bacterial groups such as Actinobacteria and Gemmatimonadota. In conclusion, maintaining a slightly acidic soil environment effectively alleviated acid stress and synergistically improved the agronomic traits and chemical quality of cigar wrapper leaves by remodeling rhizosphere metabolite profiles and optimizing bacterial community structure.

Key words: soil, pH, cigar tobacco leaves, chemical composition, rhizosphere bacteria, diversity, metabolites