佛山城市典型森林群落土壤重金属分布、流通及枯落物富集特征

富集重金属的枯落物分解可能提高重金属暴露率，增加人体接触健康风险。为了解南方城市土壤重金属在森林生态系统中的分布及流转情况，通过调查研究了佛山市8个典型森林群落土壤及枯落物重金属含量，分析了各森林群落枯落物对不同重金属的富集效应及重金属随枯落物回归土壤流通量。结果表明：1）城市森林各土壤重金属含量在不同典型群落间差异显著（P<0.05），差异最大为Pb、Cr、Zn，As、Cu、Ni次之，Hg、Cd最小；土层深度（0-20，20-40，40-60 cm）对重金属含量影响显著（P<0.05），差异最大为Cd、Hg，其次为As、Cu，最小为Zn、Ni、Pb、Cr。整体上，Cd、Hg、As、Pb、Zn在0-20 cm最高，表层富集特征明显，Cr和Ni在40-60 cm最高。2）8个森林群落中阴香-白楸-醉香含笑群落（CMMC）枯落物对8种重金属的综合富集系数（TBCF，66.76）最高，其中以Cd的富集效果最突出，富集系数为44.45，且对Pb、Cu、Zn也相对富集；最低的为黧蒴锥-香椿-樟树群落（CTCC），综合富集系数（TBCF）为8.09，仅对Cd、Cr、Cu相对富集，对其余重金属富集效应不明显。3）相关分析显示，群落重金属枯落物流通量与0-60 cm土壤重金属平均含量（Cr和Ni除外）无显著相关性。本研究对城市森林建设管理及筛选重金属富集植物及群落具有较强理论及实践意义。

Heavy metals distribution and circulation in soils and their enrichment characteristics by litter in urban typical forest communities in Foshan, China

Decomposition of heavy metal-enriched litter may increase the exposure risk levels of toxic metals in some urban forest communities, resulting in the human health risk of exposure to these elements. In the present study, the concentrations of 8 heavy metals (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in soil and litter samples from 8 urban typical forest communities in Foshan, an industrial developed city of Guangdong Province, China was investigated, in order to understand the distribution and circulation of soil heavy metals in urban forest ecosystems in Southern China. Meanwhile, the enrichment effects of different heavy metals by litter and the return fluxes of these heavy metals from litter to the soils were analyzed. Results showed as follows: 1) The urban typical forest communities varied significantly with the different heavy metals in soils (P<0.05), showing the largest concentration differences for Pb, Cr, and Zn, followed by As, Cu, and Ni, while Hg and Cd being the smallest. In addition, the soil depth (0-20 cm, 20-40 cm, and 40-60 cm) had a significant effect on the concentrations of 8 heavy metals in soils (P<0.05), with the largest differences seen in the concentrations of Cd and Hg, followed by As and Cu, and the smallest differences observed in the concentrations of Zn, Ni, Pb and Cr. In most cases, Cd, Hg, As, Pb, Cu, and Zn had the highest concentrations in soils at a 0-20 cm depth, showing the obvious characteristics of surface enrichment, while Cr and Ni showed the highest values in soils at a 40-60 cm depth. 2) Among 8 kinds of plant communities, the highest comprehensive enrichment coefficient, also referred to as total bioconcentration factor (TBCF; 66.76) for different heavy metals by litter, was achieved in Cinnamomum burmannii (C. G. et Th. Nees) Bl.-Mallotus paniculatus (Lam.) Muell. Arg.-Michelia macclurei Dandy (CMMC) community. With the enrichment coefficient of 44.45 for Cd, its enrichment effect was most evident in the CMMC community, while those for Pb, Cu and Zn were relatively enriched. On the contrary, the lowest TBCF (8.09) for different heavy metals by litter was found in Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils.-Toona sinensis (A. Juss.) Roem.-Cinnamomum camphora (L.) Presl (CTCC) community. The enrichment effects, only for Cd, Cr, and Cu, were still evident in the CTCC community, but for other heavy metals, were not at all obvious. 3) The results from the bivariate correlation analysis revealed that no significant correlation was found between the return flux of heavy metals from litter to soil and the concentration of heavy metals in soil (except for Cr and Ni). This study has strong thoretical and practical significance for the construction and management of urban forest parks, and also for the screening and selection of heavy metal-enriched plants.