| With the rapid development of China’s industrialization,urbanization,and modernization,the problem of soil metal pollution caused by industrial "three wastes" emissions,mining,sewage irrigation,and irrational application of pesticides and fertilizers has become increasingly serious.Sedum plumbizincicola has been widely used in phytoremediation of cadmium contaminated soil.In the actual remediating process,S.plumbizincicola generally suffers from problems such as small biomass,slower growth rate,and negative impacts of soil environmental conditions,which leads to inconsistent plant growth and low remediation efficiency.Earthworms,as large soil animals,have been studied on the improvement of soil nutrient and the promotion of plant growth,but their effects on the growth of hyperaccumulator S.plumbizincicola and the metal uptake efficiency have been rarely reported.In order to explore the enhancement effect of Eisenia fetida on S.plumbizincicola and the mechanisms,and to provide support and reference for the application of Eisenia fetida in the enhancement of remediation using S.plumbizincicola,the following main researches were studied:(1)Through soil culture experiments the effects of Eisenia fetida on soil nutrients and metal availability in Perudic Luvisols,Stagnic Anthrosols,and Udic Cambisols were investigated.(2)using potted test method the effect of Eisenia fetida on S.plumbizincicola growth and metal uptake was conducted for the above three soils and(3)the combining effects of rice straw and Eisenia fetida on the growth of S.plumbizincicola and the uptake of cadmium and zinc was further studied.The main research results and conclusions are as follows:(1)The results of soil culture test showed that Eisenia fetida lowers the soil p H of Perudic Luvisols,Stagnic Anthrosols,and Udic Cambisols,of which the p H of Stagnic Anthrosols decreases the most;the combination of Eisenia fetida and straw can increase the soil DOC of the Peruvian Luvisols.Eisenia fetida has obvious activation effect on the availability of nitrogen in Periodic Luvisols.Under the combined treatment of straw and Eisenia fetida,the available phosphorus of Periodic Luvisols and Stagnic Anthrosols can be increased.The combination can increase the available potassium of all soils;the availability of calcium can be increased by Eisenia fetida for all soils.The availability of soil cadmium and zinc in Stagnic Anthrosols after Eisenia fetida increased significantly,and the highest increased of soil cadmium availability could be by 136%,and the available zinc increased by 33.3%.The cadmium availability of Perudic Luvisols and Udic Cambisols under aging sampling in the treatment of Eisenia fetida and straw increased significantly,with increases of 14.9% and 32.3% respectively.(2)The results of pot experiment showed that inoculation of Eisenia fetida in Perudic Luvisols promoted S.plumbizincicola’s absorption of soil nitrogen,phosphorus,potassium,calcium,and magnesium,which in turn promoted the growth;Compared with the control treatment Eisenia fetida inoculation increased the biomass and cadmium absorption by 106% and 72% respectively.The addition of Eisenia fetida to Stagnic Anthrosols and Udic Cambisols did not show the effect of promoting the growth of S.plumbizincicola and enhancing the absorption of cadmium and zinc.The possible reason is that Eisenia fetida only promoted the absorption of nitrogen by S.plumbizincicola,and had no obvious effect on the absorption of other nutrients,and the unbalance absorption of nutrients might be the problem.In the second season pot experiment,single application of rice straw made the increases in shoot cadmium concentration of S.plumbizincicola in Stagnic Anthrosols,and the remediation efficiency increased by 36.3% compared with control,and the combine application Eisenia fetida and rice straw increased the remediation efficiency of S.plumbizincicola by 66.3%. |
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