几种高富集禾本科植物在矿区Cd污染农田的提取修复及农艺强化研究

Phytoextraction has gained world-wide attention as an environmentally friendly and potentially cost-effective technique to remove metals from soil.To maximize phytoextraction efficiency, it is important to select a phytoextractor species that is compatible with mechanized cultivation techniques and local climatic conditions. Comparating to screening hyper-accumulator, the use of species adapted to these growing conditions may therefore be a better alternative. In this study, a pot experiment would be conducted in a greenhouse to evaluate the phytoextraction abilities of some high-Cd-accumulating graminaceous plants (Indica-type rice cultivars, Pennisetum purpureum and Pennisetum sp.) with respect to soil Cd pollution and distribution of Cd inside the plants. It is necessary to assess the effects of the phytoextractors on mobilizing and depleting several Cd fractions in soil. To identify the critical factor in determining root-to-shoot Cd translocation of graminaceous plants, the study assesses the dynamic relationship between root rhizosphere soil (changes of low-molecular-weight organic acids, Eh, pH and root oxidation ability) and Cd accumulation in gramineae at different growth stages. A simulation experiment on the mechanism of adsorption and desorption of LMWOA on Cd-contaminated soil would be also carryed out. The stress and subcellular distribution of cadmium in plants was analyzed by scanning electron microscopy ∕ energy dispersive spectrometer (SEM ∕ EDS) analyses and differential centrifugation techniques. Finally, we investigated the enhancement effects of agronomic practices (water management, ammonium nutrition, and biodegradable chelating ligand) on soil cadmium bioavailability to gramineae. Our results is expected to support a viable strategy to improve soil cadmium phytoextraction in southeast of China.

植物提取技术二次污染小、成本低、易操作，是污染土壤原位治理技术的前沿。相对筛选超积累植物，选择与区域气候和栽培技术协调的高富集植物，更易达到实际修复效果。以高富集禾本科植物（籼稻、象草和巨菌草）为对象，通过盆栽实验，比较土壤Cd 在禾本科植物体内的分布及对Cd 的植物提取效果，明确对土壤Cd 库固定和耗竭的影响；揭示典型生育阶段，根际环境（LMWOA、Eh、pH、根系泌氧能力和胶膜）与Cd 在禾本科植物体内分配的动态关系，结合根际LMWOA 主成分对土壤Cd 的解吸模拟实验，阐明控制Cd 由根际向地上部迁移的主控因素；运用SEM／EDS 和差速离心技术，探明禾本科植物胁迫生理及Cd 在微组织结构的分布与解毒机制；探明农艺措施（氮源、生物可降解螯合剂和土壤水分）在强化高富集禾本科植物提取修复Cd 污染土壤的效果及机制；研究结果可为南方Cd 污染土壤的提取修复提供材料和强化措施选择。

以高富集禾本科植物（籼稻、象草和巨菌草）为对象，通过盆栽实验，研究了Cd 在禾本科植物体内的分布及对Cd 的植物提取效果。结果表明，常规籼型水稻地上部生物量均显著高于旱稻；Cd在籼稻不同部位含量分布依次为：根系>茎秆>叶>谷壳>糙米。旱稻转移系数TF比常规水稻强，顺序依次为：赣农旱稻1号＞中旱209＞中旱211≈旱优3号＞沪旱15号＞常规中稻Ⅱ优明86≈常规中籼稻扬Ⅱ优6号。随着土壤Cd浓度（全量和DTPA浸提量）增加，巨菌草地上部（茎、叶）和总生物量均呈极显著递减趋势。巨菌草根、茎和叶组织中的Cd浓度均与土壤Cd浓度呈显著正相关关系。同种植物镉胁迫下，根系分泌有机酸种类的影响不太大,而对各有机酸分泌量的变化幅度影响较大。解吸试验表明，高浓度柠檬酸或草酸可显著提高土壤Cd2+的解吸。Cd主要分布在旱稻根系和地上部中的细胞壁，其次是可溶组分。巨菌草根部Cd主要分布在细胞壁，施用(NH4)2SO4 、NH4Cl、EDTA和NTA提高了Cd在可溶组分和细胞壁的比例，降低了Cd在细胞质的比例。狼尾草属巨菌草、象草对Cd污染土壤表现出较强的耐性，能够在供试污染土壤中正常生长，未出现毒害现象。巨菌草、象草的茎部、叶部生物量均显著增加，其中施用NH4Cl+NTA，巨菌草地上部生物量达到最高，施用(NH4)2SO4+NTA，象草地上部生物量达到最高，且表现出巨菌草叶部生物量>茎部生物量；象草茎部生物量>叶部生物量。施用NH4Cl+EDTA处理后，狼尾草属巨菌草、象草地上部累积的Cd含量达到最高。施用NH4Cl+NTA耦合处理，巨菌草地上部Cd累积量达到最高，施用NH4Cl + EDTA耦合处理，象草地上部Cd累积量达到最高值，且满足植物根系对重金属的低累积量且地上部高累积量。以巨菌草为例，施用NH4Cl +NTA耦合处理后，若收割次数为3茬∕年，估算其有效量Cd理论修复时间为11.6年，而施用NH4Cl + EDTA耦合处理，象草仅需要9.5年。