| Artemisia annua L., also called sweet wormwood, is an annual or biennial herbaceous plant used as a sole material for artemisinin extraction. Around40%of the populations in the world are now facing malaria infection. Artemisinin is recommended by World Health Organization (WHO) as a drug for the initial treatment of malaria.About90%of A. annua and artemisinin in the world was grown and produced in China. Chongqing is the place for growing A. annua with high-quality and the yield of artemisinin and planting area of A. annua accounted for70%and80%, respectively, in China. Artemisinin is one of the allelochemicals effused from A. annua which could exist in soils for a long time, which could reduce land productivity, inhibit the growth of surrounding plants, and damage soil and water ecsystems.In the process of artificial cutivation of A. annua, artemisinin released into environments increased significantly with contents and yield of artemisinin increased, resulting in more serious allelopathic effect. Through field, quadrate survey, solution culture, greeenhouse pot and field experiments, we investigated colony characters of wild A. annua, species and growth of surrounding plants, the allelopathic effect and mechanism of artemisinin on terrestrial and aquatic plants. The influence of cropping pattern, fertilization and water management on A. annua itself and after-crops were also studied. Plant growth, concentration and yield of artemisinin were recorded in field and greenhouse pot experiments. The cultivation techniques for high yield of artemisinin and efficient soil utilization were primarily developed on the base of our studies. The main results are as follows:The investigation of wild A. annua colonies in9southern provinces and cities with48samples showed that A. annua colonies were relatively stable.In the highest frequency of the9species pairs among different communities of wild A. annua,5species were Compositae,3Gramineae, and they were low connective. Few species of Cruciferae and Cyphomandra betacea were observed in or around the communities of wild A. annua, indicating allelopathic effects of A. annua on those plants, which inhibited significantly their growth and development.Adding artemisinin produced by the A. annua into soils inhibited growth of after-crops such as wheat, rape and pickle. The biomass decreased by41.1～51.7%. The growth inhibition of pickle was much lower than rape and wheat. The inhibition of artemisinin on the growth of other plants was beneficial to enlarge living space of A. annua, by competition. Selection of after-crops with strong anti-allelopathic effect could increase whole soil productivity by improving land utilization. The high artemisinin reduced chlorophyll but increased carotenoid in the leaves of after-crops, indicating that artemisinin might promote chlorophyll decomposition, reduce photosynthetic rate, and decrease dry matter accumulation.In addition, artemisinin significantly inhibited the absorption of nitrogen, phosphorus and potassium, which might be related to the decreased root and nitrate reductase activities. Moderately late sowing and transplanting of after-crops following A. annua harvest might reduce the harm to the succeeding crop.In solution culture, artemisinin inhibit the growth of green algae, and the density was reduced by74.5%(Chlorella pyrenoidosa) and61.8%(Scenedesmus obliquus), respectively. The decease in dissolved oxygen, chlorophyll and protein in green algae indicated that the poor growth might be due to slow photosynthesis and disorder protein synthesis caused by artemisinin. Cultivation of A. annua in large scale might reduce self-purification ability and productivity of water systems, leading to low pollution load and low fish production even their disappearances. Dispersive cultivation and fine recovery of A. annua at harvest could reduce artemisinin in water in the growing areas and eliminate the ecological risk.In addition, artemisinin increased the electric conductivity of culture medium and malondialdehyde in green algae cells, showing cell membrane damage, efflux of intracellular solution, and cell death by adding artemisinin into culture solutions. Low concentrations of artemisinin, however, increased the activities of superoxide dismutase, peroxide, and catalase in green algae, beneficial to fast elimination of active oxygen and free radicals, which could thus reduce the hazards to green algae cells.In A. annua planting areas in Chongqing, the content and yield of artemisinin and the annual income per land unit were significantly higher under the cropping pattern of A. annua-B.juncea than A. annua-T aestivum L. and A. annua-B. napus L. Organic fertilization, especially organic and inorganic fertilizers, significantly promoted the growth of A. annua, improved the artemisinin content and yield, reduced the inhibitory effect of A annua on bacteria, fungi and actinomycetes in soils. Meanwhile, the activities of urease, invertase and phosphatasein soils with A. annua grown were increased and nutrient absorption by A. annua was also improved. Under drought stress, the biomass of A. annua was reduced by69.36%and artemisinin production by81.56%.Simultaneously, cell membrane permeability of leaves increased in contrast to leaf water potential, chlorophyll, root activity, and nutrient absorption (N, P, K) which were reduced significantly. Under mild drought stress, however, increased content of artemisinin in leaves and phosphorus and potassium in roots suggested that more phosphorus and potassium fertilizers might be beneficial to improve the drought resistance of A. annua. In addition, the proline in A. annua increased10times at least under drought stress, much more than the increament of chlorophyll, root activity, nutrient uptake, and reduction of artemisinin content. It seems reasonable to indicate that proline accumulation might be a protective biochemical reaction of A. annua under drought stress. In A. annua cultivation process, moderate drought stress applied to seedlings before transplanting might increase proline, beneficial to A. annua. resistant to drought.In summary, in the A. annua planting area in Chongqing, friendly cultivation includes the cropping patterns of A. annua-B.juncea, moderate late sowing and transplanting of after-crops, organic fertilization, water management, disperse cultivation, and fine recovery at harvest. |
