中文摘要：

采集某污染区千金子（Euphorbia lathyris L.）和酢浆草（Oxalis corniculata L.）的离根表0~3、3~6、6~9 mm的根际土壤,分析了多环芳烃（PAHs）结合态残留中母体化合物（Parent compound of bound residue,PCBR）在根际土壤中的含量及梯度分布规律。供试土壤类型为黄棕壤。结果表明,在非根际和根际土壤中均可检出10种PAHs的PCBR,非根际土壤中PCBR总含量为3.31 mg kg-1,高于根际土壤（1.07~1.82mg kg-1）。根际土壤中PAHs的PCBR含量随离根表距离（0~9 mm）的增加而增大。可用根际效应（R）来衡量根际土壤中PAHs的PCBR含量与非根际土壤相比减少的比例;R值随离根表距离（0~9 mm）的增加而变小。3个连续根际区中,PAHs总PCBR的R值为45.15%~67.66%,其中2环PAH的R值最大（61.18%~93.50%）,4环和5环PAHs的R值最小（2.39%~6.31%）,低环PAHs的PCBR在根际土壤中更易转化。PAHs的PCBR在千金子根际土壤中R值大于酢浆草,表明前者有更利于PAHs结合态残留转化的根际环境。PAHs结合态残留的根际梯度分布与根系分泌物的梯度分布关系密切,而PAHs种类、植物根际环境对PAHs结合态残留的分布影响显著。

英文摘要：

Polycyclic aromatic hydrocarbons （PAHs） with highly mutagenic and carcinogenic properties are com- monly found in the soil environment. Soil contamination by PAHs has become a major health risk issue. PAHs are wide- spread and occur at high concentrations （hundreds of mg kg-1 ） in soils of many countries. Since natural and xenobiotic PAHs present in soil may be absorbed by plants, PAHs can enter human and animal bodies through the food chain/web. Because of the health hazards of PAHs, understanding the distribution of PAH residues in rhizospheric soils is of crucial importance for risk assessment of PAH-contaminated areas. The distribution of PAHs in the rhizosphere affects their fate in the soil-plant system. After diffusion into rhizosphere soil, root exudates gradually disappear as a result of radial dilution and microbial consumption. Because these root exu- dates are ready carbon and energy sources to bacteria, a bacterial gradient is observed with a greater number of hetero- trophs and PAH-degrading bacteria closest to the roots, which may generate a gradient of PAH degradation between the rhizosphere and bulk soil. Recently, it was reported that the residual concentrations of PAHs showed a rising gradient from the rhizoplane to the loosely adhering soil after 40 and 50 d, and were significantly and negatively correlated with the amount of root exudates in the rhizosphere. This was further supported by an in situ observation that concentrations of 11 EPA-priority PAHs in rhizosphere soils increased with the distance （0 -9 ram） from the root surface. However, the docu- mented gradient distributions in rhizosphere soils are overwhelmingly about the total concentrations of PAHs as well as oth- er organic compounds. The International Union of Pure and Applied Chemistry （IUPAC） definition reserves the term of bound residues for the parent compound and its metabolites that cannot be extracted from soil using organic solvents. Bound residues have a direct effect on long-term partitioning behavior