| This thesis is based on the study of root medicinal plant Platycodon grandiflorum (Jacq.) A.DC. Both field experiment and pot experiment combined with laboratory analyses were performed. The dynamic accumulation of dry matter in Platycodon grandiflorum plants, the absorption of nitrogen (N), phosphorous (P2O5) and potassium (K2O) by Platycodon grandiflorum plants, and the seasonal change of the contents of trace elements in different organs of Platycodon grandiflorum were investigated. In addition, the effect of Zinc spraying on the growth and effective ingredients of Platycodon grandiflorum was studied based on pot experiment. More importantly, the effect of N, P2O5and K2O on the growth and secondary product metabolism of Platycodon grandiflorum was studied. Furthermore, the effect functions of nitrogen, phosphorus and potassium application codes on the yield and total platycodin of Platycodon grandiflorum were established based on the field experiments using mathematical modeling methods, which is expected to provide scientific basis for accurate fertilizing of Platycodon grandiflorum plants in practical cultivation.1. The accumulation amount of dry matter in root, stem and leave of Platycodon grandiflorum increased with growth. In the first90days after the emergence of seedlings, above-ground plant parts grew more rapidly. Instead, root of Platycodon grandiflorum intensively developed in the period between the150th day and the180th day after the emergence of seedlings. The nitrogen content in stem and leave reached maximal in the120th day after the emergence of seedlings, and the peak values of the phosphorous and potassium contents appeared relatively later. The accumulation amount of nutritional elements in all organs was in the sequence of nitrogen> potassium> phosphorous. Moreover, the accumulation of dry matter scaled linearly with the accumulation of nutritional elements.2. The contents of Ca and Fe were the most in all organs of Platycodon grandiflorum. Thereinto, the maximal Ca content reached15963.73μg/g in leave and the maximal content of Fe reached1869.52μg/g in root. Conversely, the content of Cu was the least in all organs. As the main part for medicinal usages, root possessed abundant Fe, Mn, Cu and Zn elements, and the content of all elements reached maximal in September, to be1869.52μg/g,28.15μg/g,3.56μg/g and24.98μg/g respectively. The contents of Ca, Mn and Zn in leave were obviously higher than those in root and stem over the entire growth period.3. Proper application of N, P2O5and K2O can promote the growth of Platycodon grandiflorum and also enhance the yield and effective ingredients of Platycodon grandiflorum. The effect of N on the growth was the most pronounced. However, too much N application can lower the transfer ratio of photosynthetic products to root. Therefore, it is not good to apply too much N to Platycodon grandiflorum plants. The effect of different nutritional elements on the yield and total saponin of Platycodon grandiflorum was N> K> P. The effect of nitrogen, phosphorus and potassium application on the content of polysaccharide was P> N> K. Nevertheless, both nitrogen and phosphorus had a negative effect on the accumulation of total flavone in Platycodon grandiflorum.4. Reasonable application of N, P2O5and K2O can improve photosynthetic pigments and also photosynthetic performance in Platycodon grandiflorum plants. The fertilization combination of N150kg-hm·2, P2O5225kg·hm-2and K2O79.41kg-hm-2obviously enhanced the contents of chlorophyll and carotenoid in leaves of Platycodon grandiflorum seedlings, and also significantly lowered the initial fluorescence Fo to reduce invalid optical energy loss. Moreover, it increased the maximal fluorescence Fm, the variable fluorescence Fv and accordingly enhanced the net photosynthetic rate of Platycodon grandiflorum seedlings noticeably.5. The effect functions of nitrogen, phosphorus and potassium application codes on the yield and total platycodin of both Platycodon grandiflorum growing for one year and biennial Platycodon grandiflorum were established respectively based on the field experiments using mathematical modeling methods. The effect of N, P and K on the yield of Platycodon grandiflorum was N> K> P. The effect of N, P and K on the total saponin of Platycodon grandiflorum was N> P> K. For Platycodon grandiflorum growing for one year, as the target yield was set as4200～4800kg/hm2and the target content of total saponin was set as>5.5%, the optimal fertilization combination was found to be N113.37～119.41kg/hm2, P2O585.96～134.39kg/hm2, K2O78.80～136.38kg/hm2and the corresponding fertilization ratio of N, P2O5and K2O was1:0.72～1.18:0.66～1.20. For biennial Platycodon grandiflorum, as the target yield was set as more than7000kg/hm2and the target content of total saponin was set as more than8%, the optimal fertilization combination was found to be N102.44～129.86 kg/hm2, P2O5P2O581.96～114.36kg/hm2, K2O126.00～172.32kg/hm2and the corresponding fertilization ratio of N, P2O5andK2O was1:0.63～1.12:1.23～1.68.6. Zn spraying with proper Zn concentration can apparently enhance the contents of chlorophyll and carotenoid in leaves of Platycodon grandiflorum seedlings, increase photo synthetic performance, reduce the fractional-root number, and increase the content of total saponin. It was found that the optimal spraying concentration was800mg/L. |
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