水溶性羧乙基壳聚糖强化八宝景天吸收转运Cd的机理

Recently, contamination of cadmium (Cd) in farmland soils is a growing concern in China. Cd accumulator Sedum spectabile Boreau adopted north and south of China can play an important role in remediating contaminated soil. The effect of water-soluble carboxyethyl chitosan on Cd phytoextraction by S. spectabile might have a synergistic effect for improving efficiency of remediation. However, mechanism of carboxyethyl chitosan on Cd translocation in soil- S.spectabile system is still unclear. The investigation will be carried out to study the rhizosphere effect of water-soluble carboxyethyl chitosan coupling with on Cd phytoextraction by S. spectabile and whether they could have a synergistic effect. To investigate the mechanism, S. spectabile genotypes with different Cd enrichment ability were grown in mildly and moderate Cd-contaminated soils added by water-soluble chitosan in pot and field experiments. Using X-ray Diffraction (XRD), infrared spectroscopy, scanning electron microscope and rhizobag to identify the interact mechanisms of Cd in farmland soils added by water-soluble chitosan, specific plant physiology-soil development system is constructed. Cadmium occurrence form in soil- S. spectabile system and rhizosphere micro-morphology, physiological and biochemical response characteristic and change of Cd activation process and mechanism in the soil- S. spectabile are explored. The research will provide the scientific basis for phytoremediation in mild and moderate Cd-contaminated soils in China.

目前我国农田中、低程度镉（Cd）污染严重，适应于南北方的Cd富集植物八宝景天在修复污染土壤方面具有广泛的应用前景。以八宝景天为主，辅以水溶性羧乙基壳聚糖强化的手段，有望进一步提高对中、低度Cd污染农田的修复效率。鉴于水溶性羧乙基壳聚糖-八宝景天根际效应-Cd活性之间的机理目前尚不明晰，本研究以不同八宝景天生态型为试验材料，结合盆栽和田间试验，筛选Cd富集生态型八宝景天，并在此基础上开展水溶性羧乙基壳聚糖强化Cd富集生态型八宝景天Cd吸收转运作用机制研究，并结合X-射线衍射、红外光谱等现代分析技术和根际袋等手段，构建特定的植物生理-土壤发育体系，微观比对土壤-八宝景天系统中Cd的赋存形态、根际微结构和生化响应特征及变化，探讨Cd在土壤-八宝景天系统中的转运过程。本研究能够为我国典型中低、度Cd污染农田土壤的植物修复技术提供一定的科学支撑和依据。

本研究以不同八宝景天生态型为试验材料，结合室内和田间试验，筛选Cd富集生态型八宝景天，并在此基础上开展水溶性羧乙基壳聚糖强化Cd富集生态型八宝景天Cd吸收转运作用机制研究。结论如下：（1）盆栽条件下，选取八种不同生态型八宝景天，研究其在河南济源、河北栾城、湖南石门和四川绵竹四个典型Cd污染农田土壤条件下的Cd富集特征，结果表明不同生态型Cd富集能力有显著差异，以济源Cd污染土壤为例，八宝景天生态型间地上部Cd平均浓度在17.06-35.72 mg/kg之间，差异最大可达2.6倍；聚类分析结果表明，LN为Cd高富集生态型。（2）水培条件下选取四种Cd富集能力不同的八宝景天生态型研究其Cd耐性及解毒机理的差异。结果表明，各生态型八宝景天叶中Cd在MRG组分的分布达41.2%-58.7%，将Cd区隔在金属富集颗粒组分（MRG）是八宝景天在亚细胞水平上重要解毒机理；不同生态型八宝景天体内过氧化物酶（POD）活性的差异是导致其Cd富集能力差异的重要因素。（3）通过田间小区试验研究了水溶性壳聚糖对八宝景天Cd修复效率及其对土壤Cd形态及官能团含量的影响。结果表明，壳聚糖处理使土壤水溶态和弱酸提取态Cd含量显著提高了20.3%～143.5%和2.4～39.5%。红外光谱分析结果也表明壳聚糖显著提高了土壤胶体表面的氨基（-NH2）和羟基（-OH）等官能团含量，官能团与土壤中Cd形成络合物是壳聚糖提高土壤Cd有效性的重要机制。壳聚糖使四种八宝景天生态型地上部Cd提取量显著提高56.1%～115.7%且均没有表现出明显的生长抑制。（4）以济源Cd污染土壤修复基地连续两年种植八宝景天的实际数据为基准，结合试验得出的富集型八宝景天联合水溶性壳聚糖模式，其两年修复效率可达近5%。通过修复成本分析，发现配施水溶性壳聚糖每亩每年修复成本增加35%（667元），但大田研究结果表明水溶性壳聚糖投入后八宝景天Cd修复效率可提高1倍左右，同时施加壳聚糖可提供土壤所需的氮素养分和有机质。.综上，富集型八宝景天联合水溶性壳聚糖模式在修复中低度Cd污染土壤具有较好的应用前景。