6种交通重金属污染物在悬铃木叶、枝条组织中的分布研究

以南京市常见行道树二球悬铃木为试材，通过对交通繁忙区和相对清洁区道路两边悬铃木叶和一年生枝条中6种重金属元素在组织水平分布的研究，揭示其在悬铃木各组织中可能的分布机理，以及对重金属可能的抵御机制。结果表明，置于空气污染下悬铃木叶片与一年生枝条各组织具有累积重金属元素的能力，且污染区相对含量高于清洁区（除Ni外）；叶片各组织累积能力大小为下表皮＞上表皮、海绵组织＞栅栏组织。悬铃木一年生枝条表皮因具有皮孔、表皮毛和蜡质，故也有一定的重金属累积能力；悬铃木表皮系统是重要的重金属吸滞组织，且累积于表皮的重金属元素可通过表皮进入皮层和髓，这与一年生枝条内重金属元素的运输途径有关，具体运输机理有待于进一步探讨。根据悬铃木各组织重金属的分布，认为叶片和茎的表皮系统更能反映空气污染的真实情况，且这两种材料采集容易、破坏性小，建议在空气污染监测中大力采用。

Tissue Distribution of 6 Kinds of Transport Heavy Metal Pollutants in Platanus hispanica Leaves and Annual Branches

Common street trees Platanus hispanica in Nanjing were used to study the distribution of six heavy metal elements (Pb, Cd, Cr, Cu, Ni and Zn) in their leaves and annual branches tissue on both sides of the road in the heavy traffic areas and the relatively clean areas, in order to determine the distribution mechanism of heavy metal elements in tissues and their possible mechanisms to resist heavy metals. The results showed that leaves and annual branches of P.hispanica could absorb heavy metal pollutants to different extent depending on the kinds of heavy metals and tree tissues. Heavy metal contents in tissues of two kinds of organs in pollution regions were obviously higher than control sites (except Ni). Accumulation ability of leaf tissues to heavy metals is lower epidermis>upper epidermis, and sponge tissue>palisade tissue. Annual branches of P.hispanica have picon, wax and trichomes, therefore it can absorb heavy metal elements. The surface systems of branches that contacts directly with air pollutants are the main tissues to monitor and instruct, and heavy metals accumulated in the epidermis entered into the cortex and marrow by picon. It is related with the transport pathway of heavy metal elements, and the specific transport mechanism is to be further investigated. Finally, based on the experimental results, this study suggested that leaves and epidermis of stems were suitable for heavy metal pollution monitoring in the atmosphere, and both materials were easily collected with small damage. Therefore, it is strongly suggested to use leaves and barks of P.hispanica in air pollution monitoring.