Relationship between leaf SPAD values and the nitrate content and nitrate reductase activity in cucumber at different nitrogen rates | 不同施氮水平下黄瓜叶片SPAD值与硝态氮含量及硝酸还原酶活性的关系

chinois. 确定黄瓜氮素营养缺乏诊断的最佳时期、最佳部位和临界浓度。采用溶液培养法，研究不同氮素水平（0，70，140，210和280 mg/kg）下，黄瓜不同生育期（幼苗期，开花期和结果期）、不同叶位叶片的SPAD值、硝酸还原酶活性（NRA）和叶柄硝态氮含量的变化特征。黄瓜不同叶位叶片的SPAD值对施氮水平反应的敏感程度存在显著差异。随施氮量的增加,黄瓜各叶位叶片SPAD值均有所增加，但不同叶位叶片SPAD值增长的幅度明显不同；黄瓜叶片的SPAD值、NRA和叶柄硝态氮含量3个参数的变化，因黄瓜生育时期的不同而有明显差异，幼苗期和开花期三者显著相关，开花期叶片SPAD值和叶柄硝态氮含量极显著相关。黄瓜幼苗期和开花期的第3叶、结果期的第7叶对施氮水平的反应最敏感，可以作为黄瓜氮素缺乏诊断的最佳部位；氮素缺乏的临界浓度为210 mg/kg；诊断的最佳时期为开花期。

anglais. The study was to confirm the best period, best location and critical nitrogen concentration of plant diagnosis in cucumber. A hydroponic experiment was conducted to investigate the changing characters of the leaf SPAD values, nitrate reductase activity and the leafstalks nitrate nitrogen content at different growth stages of cucumber under the conditions of different nitrogen supplying rates respectively. The results showed that the leaf SPAD values increased significantly with the increase of N rate, and they all could be used as indices for plant nitrogen nutrition diagnosis. The leaf SPAD values at different positions of leaf responded differently to the increase of N rate. The leaf SPAD values, the nitrate reductase activity and the leafstalks nitrate nitrogen content have changed significantly at the different growth stages and there was a significant relationship in seedling stage and florescence. Therefore, the 3L's SPAD values at seedling stage and in florescence and the 7L's in fruiting were more sensitive, which were suggested to be the best leaf position to diagnose the nitrogen nutrition status of the cucumber plants; The best period and critical nitrogen concentration of cucumber plant diagnosis were florescence and 210 mg/kg.