Comprehensive effects of functional agents on growth, nutrient accumulation, and rhizosphere bacterial communities in flue-cured tobacco (Nicotiana tabacum L.)

Introduction Sustained nutrient supply and dry matter accumulation during the late field growth stage are crucial for the final yield and quality of flue-cured tobacco. However, the slow nutrient release of conventional organic fertilizers often restricts plant growth during this critical period. Methods This study evaluated the comprehensive effects of supplementing conventional organic fertilizer with a carbon polymer water-soluble fertilizer alone (T2), or in further combination with an anti-continuous cropping agent (T3) and a microbial inoculant (T4). Results The results demonstrated that, compared to the sole application of organic fertilizer, both the T3 and T4 combined treatments effectively promoted late-stage growth. Specifically, the T4 and T3 treatments significantly increased leaf dry matter accumulation by 39.84% and 29.62%, respectively. Regarding nutrient uptake, the T4 treatment significantly enhanced whole-plant nitrogen and phosphorus accumulation by 41.76% and 154.28%, respectively. Meanwhile, the T3 treatment significantly boosted whole-plant and leaf potassium accumulation by 62.43% and 124.59%, respectively. Crucially, multivariate analysis confirmed that the T4 treatment maximized dry matter by alleviating soil compaction (reducing bulk density), increasing soil available nutrients, and significantly activating glutamine synthetase and invertase in the leaves while maintaining the stable abundance of core dominant bacterial taxa. In contrast, the T3 treatment significantly altered soil acid-base conditions and selectively enriched specific taxa, including Tepidisphaera and Gp16 , thereby improving the root zone microenvironment to facilitate a unique source-sink nutrient allocation. Discussion In conclusion, supplementing the organic and carbon polymer fertilizer base with either an anti-continuous cropping agent or a microbial inoculant effectively overcomes late-stage growth bottlenecks. Specifically, the microbial inoculant combination (T4) demonstrated the optimal overall performance in maximizing dry matter accumulation and nitrogen/phosphorus uptake, while the anti-continuous cropping agent combination (T3) was optimal for enhancing leaf potassium accumulation. These combined applications achieve this by ameliorating soil physicochemical properties, improving the rhizosphere microenvironment, promoting carbon and nitrogen metabolism, and optimizing source-sink nutrient allocation. Ultimately, these findings provide practical fertilization strategies to alleviate late-stage premature senescence and optimize field nutrient management in flue-cured tobacco.