Relationship of Senescence Characteristic Difference Between Flue-cured Tobacco Varieties at Maturity Stage with NH₃ Compensation Points Thereof

To better understand the relationship of senescence characteristic difference between different flue-cured tobacco varieties at maturity stage with NH₃ compensation points, pot experiments on three varieties (ZY90, K326 and NC89) were carried out, foliar apoplastic NH₄⁺ concentration and pH were determined, and their NH₃ compensation points (χ_s, 25℃) were calculated. The results showed that an increase trend was observed in the apoplastic NH4+ concentration in all the three varieties at maturity stage; comparing with slow senescing cultivar, the leaves of fast senescing tobacco cultivar possessed lower N content, lower glutamine synthetase activity, higher absolute value of NH₃ compensation point (χ_s, 25℃) and larger increasing extent. Therefore, the fast senescing tobacco cultivar featured a higher potential of NH₃ emission from senescing leaves at maturity stage, and the difference of senescence characteristics between varieties related to their difference of NH₃ compensation points.