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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。
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