| Studies on the eco-toxicology and techniques for remediation of Cd polluted farmlands have been the most interesting research points in agriculture and environmental sciences, since Cd pollution was reported to have caused the disease of "Itai-itai" in Japan in 1961. Controlling policies mainly focuses on two strategies of soil purification and detoxicification before the middle of the eighties in the 20th century, when the idea of ecological controlling was put forward and was primarily applied to plant stabilization. However all these strategies have apparently both positive significances and marketable limitations, for they could hardly meet the needs of remediation of Cd polluted farming soils. Therefore, based on ecological harm avoidance theory, the new strategy of "agro-ecological regulation and safe-and-efficient utilization of cadmium polluted farmlands" is put forward by the author. Regarding Cd polluted soil as a special farming resource, this strategy built up a new and ecological safe-and-efficient model, by way of selecting cultivated plants with strong Cd tolerance physiologically and little pollution in their products to replace Cd sensitive ones. Cd pollution controlling is therefore well integrated in the course of safe and efficient utilization of farmlands. In order to successfully applying this strategy, main cultivated plants in south China with strong Cd tolerance (both with high yield and high quality) were selected and certified. Meanwhile, systematic and comparative studies on Cd transporting behavior, and the eco-toxicologic effect in different soil- plant (animal) systems was studied. Moreover, a confirmatory study on the feasibility of using ramie as phytoextractor to purify Cd polluted soils were conducted seperately. Main research results are as follows:1. Cereals, no matter they have a strong or a weak tolerance to Cd toxicity physiologically, belong to Cd-sensitive crops, for their products (grains) are easy to be polluted and hence lose their edible value. So it is improper to plant them in Cd polluted soils. Oil plants such as Brassica napus and Arachis hypogaea, etc. have a strong tolerance to Cd stress physiologically and can be cultivated in Cd polluted farmlands, since Cd residue stocks in their products (oil or sugar) are at a lower level than that of the food hygienic standard. But the straw and dregs of oil crops is not suitable to use them as manure or stock food. Saccharum offwinarum and citrus L. also have a strong tolerance to Cd pollution. Since there is little effect on hygienic quality as little Cd migrate to the products of sugar and orange pulps, they can be selected as Cd tolerant plants for slightly polluted soil. But sugarcane bagasse and citrus peels should be properly treated as pollutants. Fibre crops like Gossypium hirsutum, Hibiscus cannabinus, Boehmeria nivea and Morus alba are tolerant towards soil Cdstress to different degrees. Basically soil Cd pollution has no unfavorable effects on the products to fibre crops. Moreover, there was scarcely any Cd entering the human food chain through these crops. Therefore, they would be a good replacement for those sensitive crops in the polluted region.2. Effects of Cd pollution stress on rice various with its different growing stages. The principal toxic effects of Cd on rice before ear initiation were the reduction of the photosynthetic production and the inhibition of vegetative growth. In the stages of ear initiation to heading, the main phytotoxicity of Cd was the inhibition of the differentiation and development of the reproductive organs. After the heading statge, the main effects of Cd toxicity were the transport and redistribution of in vivo nutrients. The most sensitive stage of rice to Cd toxicity was from ear initiation to heading. Comparatively speaking, hybrid rice was more sensitive than conventional rice to Cd pollution, which is shown in the greater reduction of biomass and economical yielding, and slower speed in recovering after Cd stress.3. The absorption ability of rice to soil Cd di...
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