Tobacco-rice rotation drives soil microbial communities to establish a "nicotine-molybdenum (Mo)-nitrogen" coupling...

Long-term continuous rice cultivation depletes soil nutrients and disrupts microbial nitrogen cycling, whereas tobacco-rice rotation (TRR) serves as a potential strategy for restoring soil functionality. This study reveals that TRR integrates the plant secondary metabolite nicotine into the nitrogen cycle through synergistic bacterial-archaeal metabolism, forming a "nicotine-molybdenum (Mo)-nitrogen" coupled metabolic network. Nicotine is degraded into ammonia and other nitrogen-containing intermediates via cross-domain collaboration involving bacteria (e.g., Ramlibacter, Streptomyces) and archaea (e.g., Nitrososphaera, Methanopereden). This process is supported by significant upregulation of key nitrogen cycling genes in TRR soils, including nifK (nitrogen fixation), nasA (nitrate reduction), and ndhABC (nicotine degradation. Available Mo content in TRR soils is significantly reduced (0.27 ± 0.02 mg/kg compared to 0.35 ± 0.03 mg/kg in continuous rice cultivation, p < 0.05), indicating that Mo ions are a critical factor in this process. However, long-term TRR may deplete soil Mo reserves, potentially limiting nitrogen availability and highlighting the need for Mo supplementation strategies. This study proposes a "nicotine-Mo-nitrogen" theoretical model, refining the conventional understanding of soil nitrogen cycling and providing a theoretical foundation and practical insights for microbially driven soil health management in sustainable agriculture.