The Research On Decontamination Impact And Its Mechanism In The Habitat Of Pai-tsai By Co-cropping With The Cd Hyperaccumulator Oilseed Rape

It is estimated that thousands of sites in our country have been polluted with heavy metals. It results in huge losing on ecosystem and economy, and threatens health of the people. Cadmium is one of the most important heavy metal elements for its mobile ability and high toxicity, so it is very urgent for us to find a way to solve soil cadmium pollution. In order to provide theory basis and technical measure of the remediation method in which phytoremediation and nomal agriculture production could work together, we studied the effects of interspecific interactions on Cd uptake by co-cropping a Cd hyperaccumulator and a less Cd-tolerant plant in our experiments.The experiment was designed to see whether the reduction of Cd in the rhizosphere of ZhongyouzaⅠ, one breed of oilseed rapes (Brassica junica) which can hyperaccumulate cadmium from the soil, could improve the living condition of less Cd-tolerant plant pai-tsai (Brassia chinensis) with their roots permitted to intermingle and develop coincident rhizosphere. The extent of rhizosphere interactions between ZhongyouzaⅠand pai-tsai in this experiment were controlled by different root barriers, or without barrier. Data showed that in the 10 and 20mg·kg^-1Cd treated soils, pai-tsai got higher shoot mass and less Cd accumulation in its shoot than in the barrier treatments or in the mono cultures, when its roots were permitted to intermingle with those of ZhongyouzaⅠ. Meanwhile, soil decontamination rates of ZhongyouzaⅠwere not affected much by co-cropping with pai-tsai, they were 80.0% and 91.8% as that in the mono cultures of ZhongyouzaⅠ. However, the co-cropping method in meliorating the living condition of pai-tsai was not obviously when Cd concentration in soil raised to 40mg·kg^-1, and soil decontamination rate decreased to 0.14, which was 58.3% compared to that in the mono culture. These results indicate that the oilseed rape ZhongyouzaⅠmight alleviate Cd toxicity of surrounding less-tolerant species, and its ability of phytoremediation was not affected much at the same time, especially in the middle polluted soil.In the latter experiment, we added organic manure in the co-cropping system to study more about the extraction action. As organic manure added into the soils, dry shoot mass of this two plants increased in both mix and mono cultures. And in the lower Cd concentration soils, Cd content in the shoots of them increased with the increasing mass of organic manure too. However, in the 40 mg·kg^-1 Cd treated soils, organic manure gave a positive effect on decreasing the Cd content in shoots. When co-cropped with oilseed rape, Cd content in the shoot of pai-tsai was 75.5% and 68.1% in the M50 and M100 treatments, respectively, as compared to that in the M0 treatment. We can conclude that the interaction of organic manure and co-cropping method only show an advanced effect on relieving Cd toxicity of pai-tsai on high Cd concentration soils.