| One of the most difficulties in cultivating Chinese medical herbals is continuous cropping obstacles, which would reduce the total output of medical herbals to a high degree, or even no yield. Therefore, resolutions to continuous cropping obstacles would advance the cultivation of Chinese medical herbals greatly. Coptis chinensis is one of the most common Chinese medical herbals, but continuous cropping obstacle is serious in cultivation. Generally, the farmland that was used to cultivate Coptis chinensis must be left free or shifted for other crops, and Coptis chinensis could be re-cultivated after 4-5 years, which would delay the further development of this important Chinese medical herbal. Accordingly, it is urgent to discover the mechanisms of continuous cropping obstacle of Coptis chinensis.In the market, Coptis consists of the roots of three Coptis (Ranunculaceae) species, respectively as C. chinensis, C. deltoidea and C. teeta. For traditional Chinese medical herbals, genuine production areas are very important because the Chinese medical herbals from these areas are considered to be more effective for cures than those from other areas. Shizhu in Chongqing is considered as the genuine production area of C. chinensis, accounting for the 40% of the total production of Coptis chinensis in China. In this thesis, in order to understand the mechanisms of continuous cropping obstacle to Coptis chinensis and provide a model study on the continuous cropping obstacle to other Chinese medical herbals and crops, we studied the differences in the fields with and without Coptis chinensis. Based on ultraviolet spectrophotometry, HPLC, LC-MS and GC-MS, I isolated and identified the phenolic acids that was reported to have allelopathy on plants and microbes. I also studied the variations of phenolic acids, microbes in the soils and soil traits based on investigations and experiments, with the aim to analyze the mechanisms of continuous cropping obstacle to Coptis chinensis. Detailed results are in the following.1. Eight kinds of phenolic acids, respectively as protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, vanillin, ferulic acid, salicylic acid, cinnamic acid and p-coumaricacid, were isolated and identified from the soils that were used to cultivate Coptis chinensis. By potting experiments, three of them, respectively as vanillic acid, ferulic acid and p-coumaricacid, were found to be produced by the roots of Coptis chinensis.2. The inter-annual variations of phenolic acids were examined and compared in the fields with and without Coptis chinensis based on ultraviolet spectrophotometry, HPLC and LC-MS. In the soils that were used to cultivate Coptis chinensis, the contents of total phenolic acids, vanillic acid, ferulic acid and p-coumaricacidincreased significantly with the extension of Coptis cultivation, and the content of total phenolic acids was the highest in the third years after cultivation. The content of p-coumaricaciddecreased on the first four years after cultivation, but increased in the following years. In contrast, in the soils that were left free, except the content of p-coumaricacid, the contents of others phenolic acids decreased significantly in the followed years after Coptis chinensis cultivations were ceased.3. We analyzed the microbial communities in the soils with and without Coptis chinensis based on phospholipid fatty acid (PLFAs). Principle component analysis (PCA) suggested that microbial communities were affected significantly by the total amounts of microbes, the number of bacteria, fungi, gram-positive bacteria and gram-negative bacteria. With the extension of Coptis chinensis cultivation, the total amount of microbes, the numbers of bacteria and fungi around the Coptis chinensis roots decreased significantly, indicating that the balances of microbial communities would be destroyed after three years of initial cultivation. In contrast, when the farmland were left free, the total amount of microbes, the numbers of bacteria and fungi increased significantly with the extension of time, indicating that micro-environments in the soil were improved.4. We analyzed the soil traits, including organic matters, micro-elements, PH and soil conductivity based on commonly used methods. We found that, except the total nitrogen that did not changes significantly across years, other traits, including organic matters, total phosphorus, available phosphorus, available boron, PH and soil conductivity increased in the farmlands that were used to cultivate Coptis chinensis. In contrast, in the farmland that was left free, available phosphorus, available boron, PH and soil conductivity decreased with the extension of time in the soil, but there were no obvious changes for other traits.5. Correlation analysis among the contents of phenolic acids, the amounts of microbes and the soil traits suggested that the three variables correlated with each other, and there was a significant correlation between the contents of phenolic acids and the soil traits.Collectively, I concluded that the phenolic acids produced by the roots of Coptis chinensis have destroyed the microbial communities and the soil traits, resulting in the changes in the soil micro-environment, which might be facilitated by the allelopathy from phenolic acids. The comprehensive effects of these factors might have played an important role in the continuous cropping obstacle of Coptis chinensis, and this might open a window for the continuous cropping of the famous Chinese medical herbal.Generally, I have perform a comprehensive study with a focus on the chemical constituents produced by the roots, microbial communities and micro-elements in the soil, aiming to uncover the mechanisms of continuous cropping obstacles to Coptis chinensis. My results provided the experimental supports for the continuous cropping of this Chinese medical herbal, which could be a model study on overcoming the continuous cropping obstacles of Chinese medical herbals and crops. |
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