Abstract: To investigate the physiological and biochemical traits in the formation of robust flavor style, apoplast extraction was used to assay the variations of nitrogen metabolites and the activity of related enzymes during leaf senescence and the ammonia compensation point was calculated in flue-cured tobacco cv. NC89 and cv. 89112 (the control), which possessed typical robust flavor style. The results showed that: comparing with 89112, NC89 contained more total nitrogen and soluble protein, during senescence stage, it displayed less decline in glutamine synthetase (GS) activity, lower glutamate dehydrogenase (GDH) activity, relatively flattened apoplastic NH₄⁺ concentration and pH variations, and less reduction of total nitrogen due to lower ammonia emission potential indicated by lower ammonia compensation point at the peak volatilized stage.