Legacy nicotine stimulates soil nitrification and available nitrogen in long-term tobacco cropping system via microbial priming and nitrogen supply

The legacy effects of nicotine, alkaloid from tobacco, on soil bacteria and nutrient cycling functions are not fully understood. In this microcosm study using soil from a decade-long tobacco monoculture field. Nicotine exhibited a persistent influence on nitrification for 42 days via direct nicotine-N supply and priming nitrifier activity. Gross nitrification rates and available nitrogen (NH ₄ ⁺ and NO ₃ ⁻ ) content were significantly higher at 100 mg kg ^− 1 nicotine than those at 10 mg kg ^− 1 . Nicotine significantly altered soil bacterial dynamics (contribution = 0.22) and increased the abundance of Intrasporangiaceae and Bryobacter . Changes in nitrification rates were positively correlated with increases in ammonia-oxidizing bacteria (AOB)- amoA copy numbers. Phylogenetic analysis revealed dominant AOB Operational Taxonomic Units (OTUs) affiliated with the genus Nirosospira , closely related to ‘ Nitrosospira sp. Np 39 − 19’ (99% identity). Dominant ammonia-oxidizing archaea (AOA) include Nitrosopumilaceae (> 70% of sequences) and Nitrosopumilus . This study enhances understanding nicotine’s role in microbial function shifts and suggests potential strategies for rhizodeposition-based nitrogen management in tobacco fields.