Temporal And Spatial Distribution Of Leaf Nitrogen/Carbon And Its Relationships With Nitrogen Utilization Efficiency In Winter Wheat

Nitrogen uptake and utilization in crops is regulated by genetics, ecological environment and cultivation measurements. Efficient genotypes and reasonable nitrogen fertilization management are effective methods to increase nitrogen use efficiency. So it is important to elucidate the physiological mechanism of nitrogen use for increasing NUE in wheat. In the present study, the field experiments were conducted using 4 wheat cultivars, Ningmai 9, Yangmai 10, Huaimai 20 and Xumai 26, to study temporal and spatial distribution of nitrogen content and its relationship with nitrogen use efficiency in wheat. The main results were summarized as follows:1. The results showed that the yield, protein content and gluten content increased with nitrogen level, but 1000-grain weight and yield reduced with excessive nitrogen. The starch content reduced with nitrogen levels. NRE of all wheat cultivars increased and then reduced with nitrogen level, however, NDE, NYE and NAE lowered with nitrogen level.The yield, protein content and gluten content were negative with NDE and NYE, the starch content was on the contrary. Four wheat cultivars were classified as: low efficiency and slow response (Ningmai 9), low efficiency and rapid response (Huaimai 20), high efficiency and slow response (Yangmai 10), high efficiency and rapid response (Xumai 26).2. The distribution characteristics of leaf nitrogen content affected by different nitrogen application rates and the relationships with plant nitrogen status was investigated. The results showed leaf nitrogen content declined as the order of the 1st leaf＞2nd leaf＞3rd leaf＞4th leaf from the top. The total soluble sugar content increased with the leaf positions declining, but 4th leaf was lower than 3rd. The C/N increased with the leaf positions declining. For Ningmai 9, the differences of nitrogen content between 4th leaf and top three leaves were enlarged. Leaf nitrogen content in different leaf positions were the highest at anther connective stage under nitrogen fertilization treatments. The correlation analysis showed that leaf nitrogen contents were significantly positively correlated with plant nitrogen content. LND_4-1 and LND_4-2 exhibited positively significant correlation with plant nitrogen content. The total soluble sugar content and C/N were significantly negatively with plant nitrogen content. The nitrogen content of 1st and 2nd leaf was significantly negatively with NDE and NAE at anther connective and anthesis stage. 3. The temporal and spatial distribution of different nitrogen forms and relationships with nitrogen use efficiency was investigated. The results indicated that the protein nitrogen content and non-protein nitrogen content decreased with leaf position from the top. The content of free amino acid increased as the order of 1st＜2nd＜4th＜3rd at jointing stage and did with leaf position declining at booting, anthesis and filling stage. The chlorophyll content declined with the leaf position from the top. The total nitrogen content and protein nitrogen content were significantly positively with other nitrogen forms. The correlation analysis showed that the content of different nitrogen forms was negative with NDE, NYE, NAE and NRE.4. The characterization of carbon and nitrogen metabolism and its relationships with NUE was investigated. The results showed that the photosynthesis, stomata conductance and transpiration rate, which was the highest at anthesis stage, increased with the increasing of nitrogen applying but declined with the excessive nitrogen applying. GS and GPT activity increased as the order of 1st＞2nd＞3rd＞4th though there were slightly difference between 2 wheat cultivars. TA, TR and NCG increased with the increasing of applying nitrogen, but became lower with excessive nitrogen applying. The correlation analysis showed that GS and GPT activity were significantly negative with NRE, and TA of nitrogen and dry matter was significantly negatively with NDE.5. The characteristics of leaf color distribution and nutrition diagnosis for nitrogen in wheat was investigated. The results indicated that the characteristics of leaf color (SPAD value) order decreased with the leaf positions, but 1st was lower than 2nd before booting stage. The SPAD value of all leaves increased as the plant nitrogen content increased. But that of 4th was the largest in all the leaves, that of 1st smallest. The correlation analysis showed that the SPAD value of different leaf was significantly positive with leaf nitrogen content and plant nitrogen content except for that of 1st leaf at jointing and booting stage. The leaf SPAD value was significantly negatively with NDE and NAE. ILSD_4/1 was significantly negative with plant nitrogen content in both 2 cultivars. The results suggested that plant nitrogen status in wheat might be predicted by monitoring the ILSD_4/1, but the optimum stage for mornitoring was different for 2 cultivars.