| 甘蓝(Brassica oleracea L. var. capitata L.)富集铊的环境地球化学研究 |
| 其他题名 | Environmental Geochemistry Study on High Uptake of Thallium by Green Cabbage (Brassica oleracea L. var. capitata L.)
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| 何立斌
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| 2008-04-28
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| 学位授予单位 | 中国科学院地球化学研究所
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| 学位授予地点 | 地球化学研究所
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| 学位名称 | 博士
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| 关键词 | 铊
甘蓝
亚细胞
营养元素
根际分泌物
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| 摘要 | 通过对甘蓝进行品种差异、亚细胞分析、根际分泌物提取污染土壤中的铊、营养元素添加以及野外甘蓝样品采集分析，结合地球化学理论。分析了甘蓝对铊吸收富集的机理，并得出以下几点结论：
(1) 甘蓝叶、根及茎对铊的吸收存在着明显差异，表明在面临土壤铊胁迫时，叶是铊的主要储存部位，而根和茎主要起到了转运作用。甘蓝中铊含量的升高导致了对钙和镁吸收能力的提高。不同品种甘蓝之间的吸收能力差别不大，通过选择种植对铊吸收能力小的甘蓝来控制铊的食物链危害是不可行的。此外，还应该避免在高铊土壤地区种植甘蓝。
(2) 高达92%的铊存在于甘蓝叶细胞液组分中，表明细胞液组分是铊在甘蓝叶细胞中的一个重要储存部位。但是在不同品种甘蓝叶中，铊的亚细胞分布形态没有显著差异，在甘蓝面对铊胁迫时，其叶细胞器组分中铊含量始终维持很低的含量。甘蓝对铊的解毒机制很可能就是通过在细胞内的区隔化作用(compartmentalization)，把进入体内的铊结合到细胞液组分以及细胞壁上，从而减少了铊对重要细胞器官的损伤。铊在甘蓝叶各亚细胞组分中的分配与常量元素存在一定的关系。在甘蓝叶细胞内，Tl+往细胞液组分中的传输很有可能是通过Na+/K+/2Cl–联合传输机制、Ca2+活化的钾离子通道以及一些需Mg2+或Mn2+的K+活化酶完成的。需要Mn2+参与的K+活化酶可能对于铊往细胞器中的转移起到了主导作用。在细胞壁中，很可能Ca2+活化的K+通道或者是某些特定的需要Mn2+的K+活化酶对铊的迁移或固定起了影响作用。
(3) 随着氮、磷、钾营养元素的加入，甘蓝地上部的生物量有一定程度的上升。影响主次因素依次均为氮>磷>钾。随着氮、磷、钾营养元素的加入，甘蓝地上部和地下部的铊含量并没有上升，而是有一定程度的下降。甘蓝地上部中铊含量的影响主次因素依次为磷>氮>钾，甘蓝地下部中铊含量的影响主次因素依次为氮>磷>钾。氮、磷、钾营养元素的加入都提高了甘蓝对铊的吸收量。甘蓝对铊吸收量的影响主次因素依次均为氮>磷>钾。因此我们认为，氮，磷，钾的加入显著提高了甘蓝生物量和铊的吸收量，但是随之而来的生物稀释效应，导致了甘蓝地上部和地下部含量的降低。运用铊累积量来判断营养元素对甘蓝吸收铊的影响更为客观和可靠。
(4) 通过对比蒸馏水和根际分泌物提取液对污染土壤中铊的提取能力，发现甘蓝根际分泌物提取液(root exudates)对污染土壤中的铊具有明显的活化作用。提取液的pH和土壤铊的提取率存在一定的正相关(R2=0.1659)，也就是说提取液的pH与其对污染土壤中铊的提取能力成正比。但是甘蓝体内各部分铊含量与其根际分泌物提取液对土壤铊的提取率没有任何关系，表明大量的植物非必需元素铊进入甘蓝后，并没有对其根际分泌物的产生任何影响。土壤pH越高，生长的甘蓝的根际分泌物提取液对土壤提取率就越高，甘蓝分泌物提取液对铊的提取率升高可以补偿由于土壤pH升高而造成的水溶态存在的铊减少。
(5) 铊在甘蓝叶片和叶柄中的分布状况为老叶叶片>新叶叶片>老叶叶柄>新叶叶柄，表明叶柄也是运输铊的一个重要器官。但是叶柄对铊的转运能力并没有茎那么强烈，而叶片才是甘蓝中最主要的铊储存部位。铊在根、茎、老叶和新叶中亚细胞的分布均为细胞液>>细胞壁>细胞器，这和前期室内温室培养甘蓝叶片中的分布结果是一致的。根据植物采矿经济理论的计算结果，很显然甘蓝可以成为土壤铊污染的植物修复和采矿的备选对象。 |
| 其他摘要 | Thallium (Tl), one of the highly toxic metals, has been receiving more environmental concerns worldwide. It tends to enrich in crops, and particularly presents high accumulation in green cabbage. This thesis aims to study the accumulation mechanism of thallium in green cabbage, by means of pot experiments and field investigation. The scope of the present study includes five parts, i.e. the selection of cultivars, the investigation of subcellular distribution of thallium, the mobilization of thallium by root exudates, and the effect of N, P and K on uptake of thallium, and the following findings are obtained.
(1) Significant differences are observed in uptake of thallium among leaf, stem and root of green cabbage. It is clearly that leaf is a major storage site for thallium in green cabbage under excess thallium threat. Stem and root play important role in uptaking and transferring thallium from soil to leaf. The increase of thallium content in green cabbage results in elevated uptake rate of Ca and Mg; No significant differences are found among six selected cultivars of green cabbage. Hence, it is impossible to reduce the health risk by selecting and growing cultivars of green cabbage with relatively low ability to uptake Tl. Green cabbage is highly recommended not to grow in soils contaminated by thallium.
(2) The majority of Tl (up to 92%) in leaf of green cabbage is found in cytoplasmic supernatant. Cytoplasmic supernatant is apparently a major storage site for thallium in leaf. No significant differences in subcellular distribution of thallium are found among cultivars. The proportion of Tl bound to cytoplasmic organelles is maintained no more than 2% at different Tl levels. The possible detoxification of Tl by green cabbage is vacuole compartmentalization, which pertains to transport of Tl to cell wall and cytoplasmic supernatant to avoid the toxicity of Tl to vital organelles. It is possible that the transport of Tl+ to cytoplasmic supernatant, which constitutes cytosol and vacuole, follows the pathways of Na+/K+/2Cl– cotransport, Ca2+-activated K+ channel and some certain K+-activated enzymes that required Mg2+ or Mn2+. These multiple mechanisms might play important roles in uptake of Tl by green cabbage because almost 90% of Tl was bound to cytoplasmic supernatant. Only K+-activated enzymes associated with Mn2+ might be responsible for transport of Tl+ to cytoplasmic organelles. In the cell wall, it seems that Ca2+-activated K+ channel and some certain K+-activated enzymes required Mn2+ are responsible for Tl+ transport or stabilization.
(3) The applications of different doses of N, P and K have resulted in elevated biomass production of green cabbage. In contrast, a decreased thallium content in both above-ground and below-ground parts of green cabbage are found as a result of fertilization. The effect of nutrient supply on thallium uptake is P>N>K for the above-ground parts, but is N>P>K for the below-ground parts. The amounts of thallium uptake by green cabbage are considerably increased as a result of fertilization. The effect of nutrient supply on the amount of thallium uptake is N>P>K. It is clearly that biomass and amount of thallium simultaneously increased due to fertilization. This increase in biomass results in lowered Tl concentration due to an effect of biological effect. It is more reliable to study effect of nutrient on thallium uptake by plant based on uptake amounts other than concentrations.
(4) Study on extraction of thallium by root exudates of green cabbage and deionized water shows that the mobilization of thallium is strongly enhanced by root exudates. A positive correlation is found between pH of root exudates and extraction rate of thallium in contaminated soil (R2=0.1659). No correlations are observed between thallium contents in green cabbage and extraction rates of root exudates. As a none-essential element for plants, thallium does not interference with the production process of root exudates. The pH of the rhizosphere soil is positively correlated to the extraction rate of exudates.
(5) The distribution pattern of thallium in leaf of green cabbage follows the order of old blade>new blade>old petiole>new petiole, in respect to decrease of thallium concentration. This result shows that petiole is also a key part that responsible for transferring thallium from stem to blade. Blade is apparently the major storage site in green cabbage for thallium. The subcellular distribution pattern for thallium in root, stem, old leaf and new leaf presents the order of cytoplasmic supernatant>cell wall>cytoplasmic organelles. It is economically available to apply with green cabbage for both phytoremediation and phytomining in Tl-contaminated soils. |
| 页数 | 125
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| 语种 | 中文
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| 文献类型 | 学位论文
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| 条目标识符 | http://ir.gyig.ac.cn/handle/352002/3370
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| 专题 | 研究生_研究生_学位论文
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推荐引用方式
GB/T 7714 |
何立斌. 甘蓝(Brassica oleracea L. var. capitata L.)富集铊的环境地球化学研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2008.
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