| The nitrogen (N) concentration of winter wheat (Triticum aestivum L.) plants is strongly related to its grain yields and grain protein content, which is important for baking and nutritional quality. The relationship between canopy N dynamic and grain quality can be considered the principal condition for prediction of grain quality in winter wheat. The timely obtained information of wheat growth status, especially N status, will help us to apply fertilizer and irrigation management and achieve preliminary classification of grain quality. Aim to detect the feasibility of the diagnosis of canopy N status and the prediction of grain quality in winter wheat, the relationship between plant N dynamic and grain quality, and the relationship between leaf and canopy N and ground measured canopy reflectance were investigated in this study. The results are summarized as below.1. The temporal and spatial N distributions characters on both single leaf and canopy levels of winter wheat genotypes, differed in grain protein content and plant type, were preliminary illustrated. The maximum value of leaf N concentration of both grain protein genotypes appeared at different growth stages. Jingdong8, a semi-hard winter wheat, appeared at jointing stage, but Zhongyou9507, a hard winter wheat, appeared at rising stage. N in stem and sheath decreased gradually in the whole growth stages for both grain protein genotypes. Plant N concentration decreased quicker in Zhongyou9507 than in Jingdong8 at grain filling stage. N exporting in leaf of Jingdong8 was higher than in Zhongyou9507 at earlier growth stages, but opposite at later growth stages. N exporting in stem and sheath of Zhongyou9507 was higher than that of Jingdong8 in the whole growth stages. There appared the same change trends of canopy nitrogen density (CND) for both the cultivars. Apparent difference of CND among all N treatments showed before early grain filling stages in Jingdong8, but post-anthesis in Zhongyou9507.There appeared apparent vertical gradients of both leaf N concentration and CND in canopy. Leaf N concentration decreased gradually from top to bottom layer in both Jingdong8 and Zhongyou9507, but the highest CND exhibited in middle layers for most cultivars with different plant types. There was no apparent vertical gradient in culm and sheath and in Zhongyou9507 compared with that in leaf and in Jingdong8. CND in top layer of the horizontal leaf type cultivars were higher than that of the erect leaf type, but opposite in the middle and bottom layer. CND in the bottom layer decreased quicker in the horizontal leaf type than that of the erect leaf type after anthesis.There was less discrepancy of leaf N concentration with different amount N application in Zhongyou9507, but opposite in Jingdong8. Zhongyou9507 had higher nitrate reductase activity (NRA) and vertical NRA gradient than that of Jingdong8. There were significant relationship between NRA and leaf N concentration in top layer of Jingdong8. But the NRA both in top and middle layer of Zhongyou9507 could reflect its leaf N status.2. N in dirrerent organs exhibited different contribution to the grain quality for both grain protein content cultivars. There were better relationship between leaf N concentration and grain quality than the relationship between grain quality and N in stem and sheath, and the N exporting amount in leaf, stemand sheath. The greatest correlation coefficient between leaf N concentration and grain quality appeared at anthesis in Jingdong8, but at middle grain filling in Zhongyou9507. The correlation coefficients between CND and grain protein content, wet gluten content and sedimentation value were lower than those of between CND and grain protein yield and wet gluten yield. N in different layers of leaf, stem . and sheath had different contribution to grain quality. Leaf N in layer 1 and layer 2 significantly contributed to the grain protein content and wet gluten content in Jingdong8. Grain quality parameters were significantly related to leaf N in layer 1...
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