Physiological mechanisms for the difference of nitrate accumulation in two cultivars of non-heading Chinese cabbage

Two cultivars of non-heading Chinese cabbage(Shanghaiqing,cultivar of lower nitrate content;Liangbaiye 1,cultivar of higher nitrate content)were hydroponically grown in four different nutrient solutions containing 0.5,2.0,5.0 mmol·L-1 NO3 and 3.75 mmol·L-1 NO3-mixing with 1.25 mmol·L-1 NH4+,respectively.Effects of N supplement on nitrate reductase activity(NRA),NO3-content and photosynthetic rate were studied.The results were listed as follows:NO3-content in Liangbaiye 1 was higher than that in Shanghaiqing and also showed significant differences between their organs(P0.05).NO3-contents in organs were in the decreasing order of petiole,leaf blade and root.NO3-content increased with the increasing of NO3-concentrations outside.Proper enhancing NH4+ reduced NO3-content.Shanghaiqing got higher NRA than that of Liangbaiye 1 under all treatments(P0.05).NRA in different organs was in the decreasing order of leaf blade,root and petiole.NRA of leaf blade and root increased with the increasing of NO3-concentrations outside,while reduced when NO3-was partially replaced by NH4+.Under the treatment of NO3-,photosynthetic rate in leaf blades of Shanghaiqing was significantly higher than that of Liangbaiye 1(P0.05).Increase of NO3-concentrations outside promoted photosynthetic rate of leaf blades,while some supply of NH4+ reduced it.In general,Shanghaiqing had the higher NRA and photosynthetic rate compared with Liangbaiye 1,which was helpful for the reduction and assimilation of NO3