毛竹林根际土壤重金属活化机制研究

Phyllostachys pubescens (moso bamboo) had fast growth speed, and which is endurable to the heavy metals in soil, and so it could be used as a good phytoremediation species. However, the activation mechanism of heavy metal in the rhizosphere soil grown with Phyllostachys pubescens was still unknown. Based on the investigation of the soil and plant in Phyllostachys pubescens forestry, the following points were studied in present project: first of all, the dynamic changes of the activation of heavy metals through field experiment were explored; secondly, by using the technique of HPLC-ICP-MS the composition and distribution of the organic acids in root exudation via the multi layer root box. At the same time, the effects on the activation during the period of the explosive growth of Phyllostachys pubescens were studied by making the model compound according with the composition of organic acids in root exudation; finally, the characteristics of chemical form of heavy metal in the rhizosphere soil were studied by the technique of EXAFS, and the influences of bioavailability on the heavy metals by the organic acids in root exudation were studied through the method of DGT in the soil column leaching experiment. Through the studies above all, the activation mechanism of heavy metal in the rhizosphere soil grown with Phyllostachys pubescens maybe could be disclosed, and it was expected that the results would be beneficial to the development of the theory and technique of phytoremediation.

毛竹生长迅速并具备良好的重金属耐性，因此其在重金属污染土壤修复上具有独特的优势。然而，毛竹林根际土壤重金属的活化机制尚不明确。本项目基于前期对矿山毛竹林森林土壤及植被的现状调查，首先采用长期野外定位实验方法，探明矿山毛竹林土壤重金属活化动态变化规律；其次，利用多隔层透明根箱土培方法，应用高效液相色谱-电感耦合等离子体质谱联用技术，深入研究根系分泌有机酸的组成特点及其分布特征，并根据根系分泌有机酸组成特征配制系列模型化合物样品，研究其对野外毛竹"爆发式生长"阶段重金属活化的影响；最后，利用同步辐射技术深入探究根际重金属的化学形态特征，并通过土柱淋洗试验，应用DGT技术研究毛竹根际分泌物对土壤重金属生物有效性的影响。从而全面揭示毛竹根际土壤重金属活化机制，以期为重金属污染土壤的修复技术提供新的理论探索与技术支撑。

本项目主要开展了矿区多维度土壤重金属污染分布研究及其风险评价，同时考察了重金属胁迫下毛竹根系分泌物有机酸的组成特点，揭示了毛竹根系对重金属的活化效应，主要研究结果如下所示：.（1）以上方镇矿区为例多维度研究矿山修复场地研究发现，测定了九种微量元素铜、镉、铬、锰、铅、锌、钙、镁和铝。结果表明，大部分元素的浓度在林地和农田超过浙江省标准值，相关性、聚类和多重主成分分析揭示了铅、镉、锌、铜的富集可能是由于农药混合输入、尾矿堆和采矿运输造成的。通过风险评估发现在农田土壤中有四个区域重金属可能严重污染，此外，75%的林地样点可能被严重污染。.（2）毛竹根系分泌物能显著的影响土壤中重金属的赋存形态。重金属胁迫下毛竹根系分泌物的有机酸主要由草酸、苹果酸和乳酸组成，并且草酸含量占据了总有机酸组成的50%以上。通过砂培实验可以证明毛竹根系可以活化难溶态重金属，并富集转运至体内；混合有机酸对土壤吸附重金属有显著影响，添加有机酸后可有效促进土壤对铅和镉的吸附，抑制土壤对锌和铜的吸附，土壤对重金属的最大吸附量表现为铅>镉>铜>锌。 .（3）螯合剂对毛竹吸收重金属具有一定促进作用。乙二胺二乙酸（EDTA）处理后土壤pH变化不显著，有机酸处理导致土壤pH显著上升；EDTA和有机酸均能抑制毛竹叶片的光合作用，抑制程度为30 mmol•kg-1有机酸>3 mmol•kg-1EDTA> 1.5 mmol•kg-1EDTA>15 mmol•kg-1有机酸；EDTA施加能够促进毛竹对铜、锌、镉的吸收，而有机酸则无促进作用；EDTA对土壤中难溶态重金属有明显的活化作用，有机酸对土壤难溶态重金属的活化作用则不显著。