| Artemisia annua L., a compositae annual herb, is one of the commonly used Chinese herbal medicines.It has activities of heat-clearing and detoxifying since used as a medicine for over2000years. It has become the only medicinal materials since Chinese scientist isolated artemisinin from A. annua in the seventies of the20th century. Now, Artemisinin combination treatments are now first-line drugs, as recommended by World Health Organization (WHO), because about40%of the world’s population is threatened by malaria.In the growth process of A. annua, allelochemicals which are secreted by its roots or produced via volatilization and eluviation of the aerial parts and through decomposition of plant body remnants so on, are released into soil and severely affect the growth of around and after culture crop, harm soil animals, at last reduce the land productivity. Soil is a place plant growing, soil microorganisms, which are important components of soil, deeply effect physical and chemical properties and health level of it because they are involved in soil metabolism and energy transformation. The area of cultivated A. annua and yield of artemisinin in Southwest of China accounted for more than80%of the world, it was not much reported that A. annua long-term cultivated on large-scale had effect on soil microorganisms. It is importantly significant to reduce the ecological risk resulted from intensive cultivation of A. annua and alleviate the harm on soil that soil microorganisms and anti-malaria-related compounds of A. annua is studied. Soil microorganism, enzymatic activity, nutrient, concentration and distribution of anti-malaria-related compounds of A. annua were studied, which was based on the theory and method of major knowledge including pedology, microbiology, analytical chemistry and modern instrumental analysis. Correlation between microorganism, enzymatic activity and nutrient in soil, and the relationship of rhizosphere microorganism and anti-malaria-related compounds of A. annua was researched. Ecological pressure of A. annua cultivation on soil microorganism was evaluated further, and the following results were obtained:1Soil nutrient and enzymatic properties of A. annuaThe concentration of nitrogen (N), phosphorus (P) and potassium (K) in soil of wild A. annua changes with environment and soil type, same as soil pH, invertase, urease and phosphatase. The concentration of N, P and K, and the activities of invertase, urease and phosphatase in rhizosphere soil of A. annua were higher than non-rhizosphere, it was suggested that A. annua could activate soil nutrient, which might be related to the ability of resistance to nutritional deficiency. Soil nutrient and enzymatic activities of cultivated A. annua changed with fertilization and soil type. The available nutrient, organic matter and enzymatic activities in rhizosphere soil were higher or significantly higher than non-rhizosphere, and fertilization improved the concentration of soil nutrient in rhizosphere and non-rhizosphere, so it was useful for fertilizer to promote supply of soil nutrient, at last improve the growth of A.. annua.2Soil microbial biomass C, N and phospholipid fatty acids (PLFAs) of A. annuaIn soil of wild A. annua, microbial biomass C, N changed with sample sites, while in soil of cultivated A. annua, fertilization significantly affected microbial biomass C and N. It was suggested that root secretion of A. annua was the important C and N sources of soil microorganism since microbial biomass C and N in rhizosphere was higher than non-rhizosphere. As far as microbial biomass C, N were concerned, they were most highest in no fertilizer rhizosphere soil, fertilization lead to decreasing concentration of them on different degree, but the declined percent in soil of combination of chemical fertilizer and manure (CFM) was lower than inorganic fertilizer (CF), it was suggested that CFM improved the growth, reproduction and amount of soil microorganism. In addition, not only wild in wild but also cultivated soil, total concentration of PLFAs in rhizosphere soil was higher than non-rhizosphere, and significantly or highly significantly related with microbial biomass C, which indicated that microbial biomass could be measured by PLFAs.24PLFAs were detected in wild A. annua, the concentration of them general in rhizosphere soil was higher than non-rhizosphere, and changed with sample sites; while21PLFAs were detected in cultivated A. annua soil. These PLFAs included19bacterial biomarkers (11~19C); The sum of10Me18:0represented Actinomycetes PLFA; the fungi were represented by18:2cω6,9,18:1ω9c and18:1ω9t;20:0represented nematode. Fertilization led to significantly drop of PLFAs in rhizosphere soil, addition to the Gram positive bacteria (G+). Diversity index of microorganism in no fertilizer soil was lower than CFM, which showed that rational fertilization could improve diversity and population structure of soil microorganism.3. Correction of soil microorganism and nutrientIn wild A. annua soil, microbial biomass C and N were significantly positively related to concentration of organic matter, available N, P and K, while there were no significantly relationship in cultivated A. annua soil. It was suggested that soil microorganism could activated nutrient, and support plant with available nutrient, but fertilization highly increased the concentration of soil nutrient, which reduced the ability of microorganism activating and supporting nutrient. No significant correlations of soil enzymatic activities with microbial biomass C, N and the concentration of PLFAs of soil microorganism, the roots and residues of A. annua were main sources of it and significantly affect nutrient transformation and utilization of soil. Broadly adaptive abilities of A. annua growth were future explain.4. Concentration and contribution of anti-malaria-related compounds in A. annuaIn A. annua, the content of terpene compounds including artemisinin, deoxyartemisinin and artemisinin acid, Phenols including polyphenols, scopoletin, chrysosplenol-D and chrysosplenetin were following trend:leaf> stem> root, it was indicated that leaves were the main organs of these compounds synthesis and storage. The antioxidant activities of the leaf extracts were highest in all organs, and related positively with the concentration of polyphenols, scopoletin, chrysosplenol-D and chrysosplenetin. The growth, concentration of anti-malaria-related compounds and antioxidant activities in wild A. annua changed with sample plots, and the variation was large. In cultivated A. annua, the plant biomass and concentration of terpene compounds under no fertilization were lower than fertilization, contrast to polyphenols, chrysosplenol-D and chrysosplenetin. In all, fertilization not only improved the growth, production of polyphenols, scopoletin, chrysosplenol-D and chrysosplenetin of A. annua, but also increased the concentration and production of artemisinin, deoxyartemisinin and artemisinin acid, and the variation was narrow, CFM was most significant in all treatments, it might be related with improvement of nutrient.5Correlation between soil microorganism and anti-malaria-related compounds of A. annuaCorrelation analysis showed that the phenols in rhizosphere soil of wild and cultivated A. annua were significantly or extremely significantly positively related with certain or some groups of microbes, such as scopoletin was significantly positively related with bacteria, G-bacteria and fungi PLFAs. Contrast to them, artemisinin acid in rhizosphere soil of wild A. annua significantly positively related with bacteria, G-bacteria, Actinomycetes and fungi PLFAs, because the concentration was low and not produce inhibitory effect on soil microorganisms, while provided then with carbon source and promoted their growth, but in cultivated A. annua soil, the concentration of artemisinin acid was2times of wild soil, and was significantly negatively related with bacteria, G-bacteria and fungi PLFAs, it showed that artemisinin acid inhibited the growth and propagation of soil microorganism.6Effect of A. annua extracts and artemisinin on soil microorganismThe concentration of soil microbial PLFAs was decreased by water extract solution from roots, leaves and rhizosphere soil of A. annua, and the declining variation was affected by sources of water extract solution and microbial group. It showed that soil microorganism was inhibited, and the inhibitory effect increased with the extension of incubation time within culturing time (1～12d), the ratio variations of inhibition on bacteria, fungi and Actinomycetes were5.59%～75.10%,15.13%～69.77%,23.81%～63.82%. It was suggested that soil health was affected indirectly because of differently sensitive degree of soil microorganism to secretions and leaching from A. annua. In addition to, different concentration (24,48mg/L) artemisinin severely affected the growth and propagation, carbon source utilization ratio of PSB with increasing its concentrations, organic acid secretion reduced, and P solubilization of PSB decreased1.02%-49.49%at the same time. Microbial population structure were changed, biomass (PLFAs content) were reduced, the growth and propagation of them were inhibited, and at last production capacity of the soil was reduced in soil of cultivated A. annua. |
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