Relationship of Senescence Characteristic Difference Between Flue-cured Tobacco Varieties at Maturity Stage with NH 3 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(χs,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(χs,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.