毛竹笋用林土壤重金属形态转化特征及其影响机制

In view of the long term application of organic fertilizer in moso shoot productive forest, the production increases significantly, while the risk of heavy metal pollution also increased. In the previous studies, the research on the soil quality of bamboo shoots usually concentrated on the total amount of heavy metals in soil, and the systematic research on the characteristics of the transformation of the speciation and influential mechanism were ignored. Based on the early study of the activation mechanism of heavy metal in the rhizosphere soil grown with moso bamboo, start with the soil heavy metal availability present project establish moso bamboo forest soil heavy metal pollution environmental risk model using geo-statistics method and Moran's I analysis techniques. By using chemical extraction method and synchrotron radiation µ XRF and XAS technology, the chemical speciation and ultra distributions were studied. Through the leaching simulation experiment, migration pattern and morphology characteristics of soil heavy metal based on colloidal particles were clarified by using ultra-structural analysis technology of SEM, TEM-EDX and SRXAS. Through root box experiment, the mechanism of the effect of rhizosphere soil physical and chemical properties, root exudates and microorganisms on the speciation of heavy metals was revealed. The characteristics and mechanism of heavy metal speciation in the soil of Mao bamboo shoot were systematically expounded, which could provide theoretical basis and scientific basis for the quality regulation and control in heavy metal contaminated bamboo soil.

有机肥调控措施在毛竹林中的长期施用显著提升了竹笋产量，但同时也增加了竹林土壤重金属污染风险。前期诸多有关毛竹笋用林土壤重金属污染的研究，多集中在总量范畴，而对其形态转化特征及其影响机制缺乏系统研究。本项目基于前期青年基金对毛竹林根际土壤重金属活化机制的研究，从土壤重金属有效性入手，运用地质统计学方法和Moran's I分析技术，建立毛竹林地土壤重金属污染环境风险模型；通过化学提取法、同步辐射µ-SXRF和XAS技术，研究毛竹林土壤重金属的化学形态和微区分布；通过淋洗模拟实验，并运用SEM、TEM-EDX、SRXAS等技术，阐明基于胶体颗粒的土壤重金属迁移规律和形貌特征；通过根箱实验，揭示根际土壤理化性质、根系分泌物、土壤微生物对重金属形态转化的影响；从而较系统地阐明毛竹笋用林土壤重金属形态转化特征及其影响机制；为竹林重金属污染土壤质量调控提供理论基础与科学依据。

本项目以毛竹笋林地为研究对象，通过野外采样与室内淋洗柱、根箱相结合的试验方法，系统地阐明毛竹林土壤重金属形态转化特征及其影响机制。研究成果主要包括：.（1）土壤有效态Pb、Zn的提取量因提取剂的不同存在显著性差异，其中，EDTA、HNO3和HCl对重金属Pb和Zn的提取量最大，而NH4OAc和NaNO3对重金属Pb的提取量最小，NH4OAc和H2O对重金属Zn的提取量最小；对于有效态Pb，各提取剂除NaNO3、CaNO3和H2O外与全量和毛竹笋重金属含量具有良好的相关性，而在有效态Zn中，各提取剂与全量和毛竹笋重金属含量都有良好的相关性，酸性提取剂和有机螯合剂提取态Pb和Zn可有效表征该污染土壤的生物有效性。.（2）土壤重金属Pb的化学形态主要以铁锰氧化物结合态和残渣态为主，随离矿区距离增加，交换态含量上升，而Zn主要以交换态和残渣态存在；矿区土壤可移动颗粒表面Pb分布相对比较集中，Zn的分布相对比较分散。.（3）土壤中颗粒粒径主要集中在大于50μm范围，其中小于50μm颗粒的重金属含量相对较高。在pH为3、4和5.6的模拟酸雨淋洗下，土壤中重金属Pb、Zn主要吸附在胶体颗粒上迁移，在三种不同pH模拟酸雨淋洗下，滤液中胶体颗粒重金属迁移量占总迁移量的80%以上，其中Zn的迁移效率最明显；pH为3的模拟酸雨淋溶出来的土壤颗粒粒径大小约为10μm，显现絮状，且颗粒物中存在更小的微粒；pH为5.6的模拟雨水淋溶出来有较大的土壤颗粒，且表面覆盖较多粒径约1μm的胶体态颗粒。.（4）毛竹的根际效应导致了根际与非根际土壤不同重金属的形态存在差异；在重金属Pb、Zn的化学形态研究中，易还原态、晶体铁结合态和残渣态含量相对较高，根际土壤富啡酸结合态Pb、Zn，有机结合态Pb和晶体铁结合态Zn显著高于非根际土壤；土壤重金属形态的转化与土壤有机碳，土壤微生物量碳及土壤酶活性密切相关，这取决于根系分泌物与根际微生物的作用。