长三角典型城郊农田土壤-浙贝母重金属迁移特征研究

城郊生态系统中土壤重金属分布及其在土壤—植物系统的迁移和富集特征是城乡共生体土壤安全研究的热点问题。以典型经济作物浙贝母(Fritillaria thunbergii)为例,基于野外采样和实验分析,对长三角代表性城郊农田中土壤—植物系统重金属的分布、富集和迁移特征开展研究。结果表明:受人类活动的影响,城郊农田土壤中重金属除Cr外,Cu、Zn、As、Cd和Pb的平均含量超过土壤背景值,并且不同重金属在空间分布上表现较高的空间异质性。除Cd和Cr外,浙贝母植株不同部位重金属含量表现为叶、茎显著高于鳞茎,叶中重金属含量可达到鳞茎的5～10倍,表明叶比鳞茎更易富集重金属。重金属迁移系数分析表明,Cr、Cu、Zn、As、Cd和Pb主要富集在浙贝母植株的地上部分,且不同重金属在植株中的迁移和富集能力具有较大的差异。浙贝母地上部分对Cr、As和Pb的富集能力较低,对Cu、Zn和Cd的富集能力相对较强。相比而言,鳞茎对不同重金属的富集能力均较弱,综合污染评价也表明,浙贝母鳞茎中重金属含量并未超过污染标准。

Identifying the Characteristics of Heavy Metal Migration in the Soil: Fritillaria thunbergii System of Peri-urban Ecosystem

The concentration and distribution of soil heavy metals in the peri-urban ecosystem and their transfer and enrichment features in the soil-plant systems are key issues in soil security. In this study, Fritillariae Thunbergii Bulbus was selected to study the heavy metal migrations in soil-plant system. The concentrations of heavy metals including Cr, Cu, Zn, As, Cd and Pb in soil and plant samples were analyzed in Zhangxi watershed of Yangtze River Delta in eastern China. Results of this study showed that average concentrations of Cu, Zn, As, Cd and Pb in cropland soil were higher than the background values of soil in Ningbo. The spatial distribution of heavy metals had high spatial variability and varied with different heavy metal types. Comparison of heavy metal concentrations in different tissues of Fritillariae thunbergii showed that concentrations of heavy metal in leaves and stem were significantly higher than those in bulb. The concentrations of heavy metal in leaves were 5~10 times than those in bulb. This suggested that leaves of Fritillariae thunbergii was more likely to absorb heavy metals than bulb. Analysis of transfer factor in Fritillariae thunbergii plant indicated that Cr, Cu, Zn, As, Cd and Pb were mainly enriched in aboveground tissues. The migration and enrichment abilities of heavy metals in soil-plant system were varied with metal types. Results also showed the aboveground tissues had low enrichment ability for Cr, As and Pb, but had strong enrichment ability for Cu, Zn and Cd. Both the low migration and enrichment abilities of heavy metals in bulb and the integrated pollution evaluation showed the bulb was not contaminated by soil heavy metals.