【作者】 姜慧敏；

【导师】 杨俊诚；

【作者基本信息】 中国农业科学院 ， 生物物理， 2006， 硕士

【摘要】 正文:重金属污染土壤具有累积性、滞后性、隐蔽性和不可逆性,是目前国内亟待解决的环境问题。本研究针对我国农田土壤污染现状,在综合分析国内外研究的基础上,结合国内农业生产实际。应用农艺措施（施用不同浓度外源性磷）对镉、锌复合污染的农田土壤进行修复机理研究,为重金属镉、锌复合污染的农田土壤修复提供科学依据。 首先利用¹⁰⁹Cd、⁶⁵Zn双标记核素示踪技术研究不同浓度磷水平下,玉米对镉、锌单一及镉、锌复合污染的吸收动力学,探索磷、镉、锌之间的交互作用,取得以下试验结果:（1）随着时间的延长,根系对镉、锌的吸收存在两个过程,即快速吸收过程和缓慢的吸收过程,直至达到一个相对稳定的平衡状态;（2）无论是单一元素污染还是复合污染,随着外源性磷浓度的升高,植物根系及地上部对重金属镉、锌的吸收量都呈现先增加后降低的趋势,而且根系积累的重金属的量显著高于地上部（p<0.05）;（3）在外源性磷浓度相同条件下,当植物受到镉、锌复合污染时,根系及地上部对重金属镉、锌的吸收量明显高于单独施加镉、锌时植物对它们的吸收,这一结果说明复合污染条件下镉、锌之间存在着加和协同作用,即重金属元素的复合污染大于单元素污染对玉米产生的毒害效应;（4）外源性磷浓度达到一定水平后,土壤中镉、锌的有效态减少,从而使植物根系对重金属的吸收和积累得到调控。 应用电镜分析技术,研究了镉、锌复合污染条件下外源性磷对植物细胞超显微结构的影响。首先用透射电镜（Transmission electron microscope,TEM）对受重金属复合污染的植株的叶绿体、细胞核和植物根的细胞壁进行观察,发现外源性磷能在一定程度上缓解镉、锌对植物细胞器所造成的损害,并在叶绿体、细胞壁上有沉积物的存在;用扫描电镜（Scanning electron microscope,SEM）对植物的根尖进行观察,在根尖表面发现了磷酸盐的沉积物,即磷与重金属离子形成的磷酸盐在根系的沉积,降低了重金属离子通过木质部向地上部运输,减少了地上部对有毒元素的吸收和积累。 以盆栽模拟试验研究重金属镉、锌与不同浓度磷交互作用的环境化学及生理机制,实验结果表明,外源性磷浓度为2500mg/kg时,植株的干重高于对照及其它浓度磷处理,土壤中有效态的镉、锌的含量以及植株所吸收的镉、锌的量最少,表明高浓度磷可以将大量的重金属离子固持在土壤中,减少了植物对重金属离子的吸收和积累。但在镉浓度为5mg/kg时,土壤pH呈现降低趋势,叶绿素和土壤磷酸酶含量减少;外源性磷浓度为500mg/kg时,对土壤中重金属离子的固定及减少植物对重金属的吸收效果明显,使土壤的pH和土壤磷酸酶含量均显著升高（p<0.05）;外源性磷浓度为50mg/kg时,土壤中有效态的镉在低磷浓度范围内含量增加,促进了植株对镉的吸收,但对锌有一定的抑制作用;高浓度的磷可以降低镉和锌之间产生的协同作用,并且磷与锌之间的拮抗作用强于磷与镉之间的拮抗作用;通过扫描电镜观察,在土壤表层及根尖的表面有晶体颗粒沉淀物,推测为磷与镉和锌所形成的磷酸盐沉淀。 综合以上研究可知:针对不同浓度镉、锌复合污染的农田土壤,外源性磷能够改变土壤中镉和锌的吸附-解吸、转化和固持,并且能与活性镉和锌形成磷酸盐类化合物,降低土壤中镉和锌的迁移特性及生物有效性,从而实现在施用磷肥过程中对重金属污染土壤的有效修复。更多还原

【Abstract】 Content: Soil contaminated with heavy metals is one of the environmental problems that should be resolved urgently, because it is accumulative, lagging, dormant, and irreversible. Aiming at the actuality that the soils contaminated with the complex pollution of Cd and Zn in most cultivated land in China, this paper based on the previous researches and combined with the actual conditions in China, the mechanism of remediation was conducted using the agricultural measure of external P.First of all, we made use of the isotopes tracer techniques of ¹⁰⁹Cd, ⁶⁵Zn together to study the absorption kinetics of complex pollution of Cd and Zn to maize under different concentration of external P, exploring the interaction among P, Cd and Zn.The results showed as follows: （1） Along with the time went on, there two process of absorption in the soil to root system existed, one was the process of fast accumulation, the other was of low accumulation, up to a balance state relatively at last;（2） Whatever contaminated by Cd and Zn in a complex pollution or as a single element of Cd or Zn individual, as the increasing concentration of external P, it occurred in a trend that the specific activity of cadmium and zinc of roots and shoots in maize were increased while external P used as 0.25 to 0.6 mmol/L. When P at 3.0 mmol/L, the specific activity of cadmium and zinc of roots and shoots in maize were decreased. Comparing the quantity of Cd and Zn in roots and shoots respectively, the most of Cd and Zn were accumulated in roots and few of those were conveyed to shoots （p< 0.05）;（3） When the concentration of external P keeping under invariability, comparing the quantity of Cd and Zn in roots and shoots by single and combination of Cd and Zn, it was discovered that the quantity of Cd and Zn in roots and shoots with the complex pollution accumulated more than those with a single element pollution. The result showed that there was synergism between Cd and Zn, so it could be more harmful to the plant;（4） when the external P reached the definite concentration, it could decrease the valid quantity of Cd and Zn, thereby the absorption, accumulation and translocation of Cd and Zn in the roots were regulated commendably and reduced the absorption of toxic elements by the shoots.The techniques of scanning electron microscope （SEM） and transmission electron microscope （TEM） were applied in the trial to study the effects of external P on the cell ultrastructure of maize under Cd and Zn stress. Firstly, the chloroplasts of leaf cells and nuclei and cell wall in adventitious roots were observed by TEM analysis. The results indicated that external P could reduce the damage of the cytoarchitecture obviously, at the same time some deposits were found within the chloroplasts and cell walls. Second, the surface of roots were observed through SEM technique, which showed that the deposits of phosphate with Cd and those with Zn could exist on the surface of the root, consequently, which prevented the translocation of Cd and Zn from the roots to the shoots. The external P performed an important role to prevent the translocation of Cd and Zn from the roots to the shoots.The pot experiment was employed to study the interactions of external P with Zn and Cd, as well as the chemical and physiological mechanisms under various levels of P simulating the circumstance of the field. The results indicated that the biomass of the maize was higher than that of the others treated with P at 2500 mg/kg. Exchangeable Cd and Zn in soil and the concentration of Cd and Zn of maize tissue were least, it showed that high concentration of P could make plenty of Cd and Zn be fixed in the soils and the uptake of Cd and Zn reduced in plant. But while the concentration of Cd was 5mg/kg, it occurred in a trend that the pH was decreased in soil, soils phosphatase and the content of chlorophyll of the leaves were reduced. When P at 500mg/kg, the phosphate amendments could decreased the biologic effect of Cd and Zn and reduced Cd and Zn uptake by plant significantly （p<0.05）. When P at 50mg/kg, the low concentration of P increased the available form （exchangeable） of Cd in soils and enhance Cduptake by plant, whereas restricted Zn uptake by the plant. In addition, from the results we could find that P could decrease the synergism between Cd and Zn and that the antagonism between P and Zn was more stronger than antagonism between P and Cd: Scanning the surface of soil and the roots of the maize> the deposits which we speculated the phosphate with Cd and those with Zn may exist.Above all the results showed that aiming at the complex pollution with different levels of Cd and Zn concentrations, external P could change the sorption-desorption in contaminated soils and came into being the deposits with P, Cd, Zn to decrease the bioavailability and translocation, accordingly achieved the intention to remediate the contaminated soils in the course of the application of phosphate fertilizer.更多还原