| The plant nitrogen nutrition efficiency is the adaptability of plant to soil nitrogen conditions in the long-term living process and is controlled by multiple genes. It has specific morphological, physiological and biochemical characteristics. Study on the nitrogen nutrition efficiency and its mechanism is one of the hottest issues in plant nutrient genetics. The difference of nitrogen nutrition efficiency of seven tea clones, Yabukita, Huangdan, Maoxie, Xiuhong, Yingshuang, Fuding Dabaicha and Longjing 43, and its mechanism had been investigated. The following is the summary of the results.1. Significant difference has been observed in N use efficiency (NE), which was defined as biomass based on dry weight of increased value/ available N, among seven genotypes at four N levels, the difference was expressed by the difference of physiological characteristics, such as N uptake rate, N assimilation rate and physiological utilization efficiency, etc. and was expressed by the difference of biomass dry weight of increased value finally. The difference of physiological characteristics was determined by gene (genotypic difference at the same N level) and gene+environment (G+ N), but it was determined by gene fundamentally. Based on the NE and N responsiveness of the different seven clones, they are grouped into three types, (1) Yabukita and Huangdan are low efficient and high responsive, (2) Maoxie, Xiuhong and Yingshuang are high efficient and low responsive, and (3) Fuding Dabaicha and Longjing 43 are high efficient and high responsive, respectively.2. The major factors that determine the NE of tea plant are N uptake efficiency (NUE), which was defined as plant total N increase value/ available N (r=0.8543, p<0.01), as well as N physiological utilization efficiency (NPE), which was defined as biomass increase value [dry weight]/ total N increase value (r=0.2757, p>0.05), respectively.. Furthermore, N economic efficiency (NEE), which is defined as new shoots and leaves increase value [dry weight]/ available N, has extremely significant correlation with NE (r=0.8050, p<0.01). The ideal tea genotype is which has high NUE, NPE and strong N transport ability.3. The results of root dry weight, volume, active uptake area, activity, N uptake rate, N assimilation ratio and GS activity indicate that there are significant difference among the seven clones at four different N levels. The correlation analysis between these parameters suggest that they affected NE via NUE. The correlations between them and NUE are either significant or extremely significant except root active uptake area, which has significant correlation to NPE. All of the parameters except GS activity have significant or extremely significant correlation with NE. Meanwhile, root volume, activity, N uptake rate and N assimilation rate have significant or extremely significant correlation with NEE. And positive correlations have also been observed between all the parameters, they compose a complex system to influence the NE of tea plant.4. According to the demand of breeding and the results of this experiment, root volume, activity and GS activity could be considered as indices to select and breed high NE new tea genotype.5. Significant difference has been observed in NH4+ kinetic parameters (Km and Vmax) among the seven clones. Km and Vmax could be also considered as referential indices to select and breed high NE tea plant genotype.6.15N labeled isotope experiment indicates that there is difference of N fertilizer utilization efficiency (FNUE) among seven clones. However, it is not consistent with NE. Leaves and stem is the prior to getting N for high NE tea plant genotype when the soil has sufficient N.In conclusion, the main factors, which make tea plant genotypes have nitrogen nutrition differences, have been preliminarily elucidated, and some indices which had close relationship with NE have been selected. It will give theoretical benefit and guidance to high NE tea breeding and tea nutrient genetics.
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