A sustainable management strategy for continuous flue-cured tobacco: Organic amendments reshape rhizosphere health to suppress autotoxicity and soil-borne pathogens

Continuous cropping poses a severe threat to the sustainability of industrial crops like flue-cured tobacco (Nicotiana tabacum L.) by degrading the rhizosphere micro-ecosystem. Organic amendments offer a promising remediation strategy, yet the systemic mechanisms linking amendment-induced changes in the rhizosphere environment to plant performance remain poorly quantified. Using a multi-omics approach—integrating rhizosphere soil microbial profiling (16S rRNA and ITS sequencing) with root exudate metabolomics (UHPLC-MS/MS)—this study investigated how four organic amendments (corn straw, cattle manure, rapeseed cake, and humic acid fertilizer) alleviate this obstacle in a continuous flue-cured tobacco system. Cattle manure and humic acid fertilizer were most effective in promoting plant growth, increasing plant height by 6.78% and 7.31%, and root dry weight by 55.51% and 71.26%, respectively, compared to the non-amended control. These amendments consistently elevated rhizosphere pH and organic matter, while reducing nutrient availability. The re-engineered soil environment was associated with a marked reduction in autotoxic phenolic acids (e.g., benzoic and cinnamic acid) and suppression of pathogenic fungi such as Fusarium and Plectosphaerella. Partial least squares path modeling (PLS-PM) integrated these disparate observations, verifying that the improvements in plant growth were primarily mediated through the rhizosphere soil property-driven suppression of autotoxins and pathogenic fungi, rather than through direct effects. These findings provide a mechanistic framework for selectively deploying organic amendments to manage rhizosphere health, offering a sustainable strategy to enhance productivity and break the cycle of soil sickness in continuous cropping systems for tobacco and other susceptible industrial crops.