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铅(Pb)是所有元素中仅次于砷的第二大有害重金属[1],土壤和水体中铅污染主要为人类活动所致,铅的主要来源有含铅油漆的使用、铅弹、含砷酸铅农药的应用、烧煤、汽油、炸药等[2],铅污染被认为是最严重的金属污染,是造成环境污染的主要原因[3]。铅可通过食物链进入人体,从而对人体健康造成潜在的危害[4]。因此,对铅污染土壤进行修复是一项十分迫切的环境治理课题。
植物修复(Phytoremediation)是一种绿色、低成本的土壤污染修复技术[5],选择合适的植物是植物修复技术能否成功的一个关键因素[6]。木本植物具有生物量大、根系发达的特点[7],并且木本植物在一定程度上有能力积累重金属并将其转运到地上部分[8-11],速生木本植物地上部积累的重金属含量可能比草本超富集植物地上部多[12-13]。因此,了解具有修复潜力的速生木本植物在重金属胁迫下生长响应和重金属积累模式,将有助于评估其在田间修复中的应用前景。
枫香(Liquidambar formosana Hance)为金缕梅科(Hamamelidaceae)枫香树亚科(Subfam. Liquidambaroideae Harms)枫香属(Liquidambar Linn)高大落叶乔木,是第三纪孑遗植物[14],在我国分布广泛,是重要的乡土树种。枫香适应性很强,属典型的“荒山先锋”树种[15],在改善生态环境等方面具有重要作用。近年来,南京林业大学相关研究组在枫香植物修复等方面开展了较多研究,主要集中在不同年龄段的枫香对重金属的吸收积累能力[16]以及不同表面活性剂与镉复合污染对枫香生长的影响等[14, 17]。本项目组在前期的矿区造林试验以及室内盆栽试验也表明,枫香在矿区有较好的耐性,并且其对重金属有一定的吸收转运能力。通常铅胁迫下,植物的代谢和生理过程会受到影响[4],同时植物也进化形成一些铅的耐性机制,如铅在植物体内的化学形态和亚细胞分布与植物的铅耐受性有关[10, 18]。但目前有关枫香对重金属的耐性机制方面缺乏深入研究。因此,本文以1年生枫香幼苗为试验材料,采用水培法,研究不同浓度铅胁迫下叶和根中铅化学提取态的变化情况,并通过同步辐射X射线荧光(Synchrotron radiation X-ray fluorescence,SRXRF)技术,研究铅以及其它元素在枫香根系的微区分布,初步探讨枫香铅耐受机制,为铅污染土壤植物修复提供参考。
枫香幼苗对铅胁迫的生理生化响应与元素分布
Tolerance of Liquidambar formosana Seedlings to Pb: Physiological and Biochemical Response and Elements Distribution
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摘要:
目的 研究木本植物枫香幼苗在不同浓度铅胁迫下的生长及元素微区分布和化学形态特征,探讨枫香铅耐受机制。 方法 利用水培法,研究枫香幼苗在不同浓度铅(0、50、100、200和400 mg·L-1)胁迫下其生物量、叶绿素含量的变化及对铅的吸收与积累。采用化学试剂提取法分析铅在枫香植株体内存在的化学形态,并进一步采用同步辐射X射线荧光(SRXRF)技术研究铅以及其它元素在枫香根系的微区分布。 结果 枫香幼苗在不同浓度铅胁迫下叶片表现一定程度的毒害效应。根系生物量在铅低浓度处理(50 mg·L-1)时较对照组有一定程度增加,并且各处理组生物量耐性指数均大于0.90。铅胁迫下枫香幼苗叶片光合色素较对照组显著下降。短期试验表明,枫香幼苗对铅的吸收量大,且主要积累在植株根系,其转移系数均小于0.10。枫香幼苗叶片和根系中以盐酸提取态和醋酸提取态铅为主,其次为氯化钠提取态铅。SRXRF分析表明,枫香根组织中的表皮层区域铅浓度较高。 结论 短期水培试验表明,铅主要赋存在枫香幼苗根系表皮层区域,同时铅主要与磷酸盐配体和草酸盐配体相结合,这可能是枫香幼苗在不同铅浓度胁迫下具有较高耐性的原因。 Abstract:Objective A greenhouse pot experiment was conducted to determine the characteristics of Pb micro-distribution and chemical forms in Liquidambar formosana seedlings and evaluate the implication on Pb toxicity and the plant tolerance. Method The response of seedlings to Pb concentrations (0, 50, 100, 200 and 400 mg·L-1) in the solution was studied. the seedling growth, chlorophyll, carotenoid, Pb accumulation and translocation were assessed. Different chemical reagent extraction techniques were carried out to analyze the chemical forms of Pb. The characteristics of Pb distribution in root of L. formosana were investigated by synchrotron radiation X-ray fluorescence analysis. Result The results showed that Pb concentration treatments induced toxicity symptoms in seedlings' leaves. Compared to the control, the biomass increased slightly at low concentration (50 mg·L-1), and the tolerance index values of all Pb treatments were great than 0.9. Under Pb stress conditions, the photosynthetic pigments significantly declined. During the experiment, a greater quantity of Pb was uptake and mostly retained in L. formosana roots, and the translocation factor values of all Pb treatments were lower than 0.1. Most of Pb in L. formosana tissues was stored in the cell wall with HAc-, HCl-, and NaCl-extractable form. The synchrotron radiation X-ray fluorescence analysis indicated that most of Pb was detected in the epidermal cells of roots. Conclusion Our results suggested that Pb deposited in the epidermal cells of roots and integration with phosphate or oxalate might be responsible for the tolerance of L. formosana under Pb stress in short period. -
Key words:
- lead
- / Liquidambar formosana
- / tolerance and accumulation
- / chemical forms
- / micro-distribution
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