The petroleum production has been raised sharply over the past decades, whereas the petroleum exploitation has also caused serious environmental contamination. A pot experiment has been conducted to monitor the dynamic response of antioxidant defense system and the growth reaction of Amorpha fruticosa seedlings to soil petroleum contamination. The results show that (1) in 5 g kg⁻¹ contaminated soil, A. fruticosa removes reactive oxygen species (ROS) by increasing the activities of antioxidant enzymes (glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT)), while in 10–15 g kg⁻¹ long-term contaminated soil, A. fruticosa removes ROS by the cooperation of antioxidant enzymes and antioxidants (SOD, CAT, ascorbate peroxidase (APX), GR, ascorbic acid (AsA), glutathione (GSH), and proline (Pro)). In long-term 20 g kg⁻¹ contaminated soil, the defense ability of APX and AsA decreases sharply, and A. fruticosa removes the ROS by the synergistic effect of antioxidant enzymes (SOD and CAT) and antioxidants (GSH and Pro). Only in 20 g kg⁻¹ long-term petroleum contamination caused significant (P < 0.05) increase in H₂O₂ content in seedlings. (2) SOD, CAT, GR, GSH, and Pro exhibit increases in long-term severely contaminated soil, and these enzymes and antioxidants are the most important defender of A. fruticosa to ROS accumulation caused by petroleum contamination. (3) The growth of A. fruticosa seedlings is less affected in 5 g kg⁻¹ petroleum-contaminated soil, while it significantly decreases in 10, 15, and 20 g kg⁻¹ petroleum-contaminated soils (P < 0.05). (4) Considering comprehensively the response of antioxidant defense system and the growth reaction of seedlings to petroleum contamination, A. fruticosa could be utilized for phytoremediation in ≤15 g kg⁻¹ contaminated soil.

Litter from Amorpha fruticosa, a potential phytoremediating plant, was collected and used in a decomposition experiment that involved the litterbag in soil polluted by crude oil. The dynamics of the biological properties of soil and the nutrient release of the litter were detected. The results indicated that (1) in lightly polluted soil (LP, petroleum concentration was 15 g kg⁻¹), the bacteria (including actinomycetes), and fungi populations were significant higher than those in unpolluted soil (CK) at the 1st month after pollution, and the bacteria (including actinomycetes) populations were higher than those in the CK at the 6th and 12th months. In moderately polluted soil (MP, 30 g kg⁻¹), the bacteria (including actinomycetes) populations were higher than those in the CK at the 1st and 6th months, whereas only the actinomycetes population was greater than that in the CK at the 12th month. In seriously polluted soil (SP, 45 g kg⁻¹), only the fungi population was higher than that in the CK at the 6th month. (2) The activities of soil protease, carboxymethyl cellulase, and sucrase were generally inhibited in polluted soil. Peroxidase activity was generally inhibited in the LP and MP soil, and polyphenol oxidase activity was inhibited in the SP soil at 6–12 months. (3) At the end of litter decomposition, the LP soil significantly increased the release rate of all nutrients, except for K. The MP soil reduced the release rate of Fe and Mn, whereas it increased that of C and Cu. The SP soil decreased the release rate of all nutrients except for Cu and Zn. In conclusion, SP by crude oil would lead to limitations in the release of nutrients from the litter and to decreases in the community stability of a phytoremediating plant. A. fruticosa could only be used in phytoremediation of polluted soil at concentrations below 45 g kg⁻¹ (crude).

Fast-growing metal-accumulating woody plants are considered potential candidates for phytoextraction of metals. Shuikoushan mining, one of the biggest Pb and Zn production bases in China, presents an important source of the pollution of environment during the last 100 years. Over 150 km²of fertile soil have been contaminated by the dust, slag, and tailings from this mining. The goal of the present work has been to determine the content of Pb, Zn, Cd, and Cu in wild woody plants (18 species) naturally growing in this area. Two hundred five plant and soil samples from 11 contaminated sites were collected and analyzed. In addition, to assess the ability of multi-metal accumulation of these trees, we proposed a predictive comprehensive bio-concentration index (CBCI) based on fuzzy synthetic assessment. Our data suggest some adult trees could also accumulate a large amount of metals. Pb concentrations in leaves of Paulownia fortunei (Seem.) Hemsl. (1,179 mg/kg) exceeded the hyperaccumulation threshold (1,000 mg/kg). Elevated Pb concentrations (973.38 mg/kg) were also found in the leaves of Broussonetia papyrifera (L.) Vent., with a Pb bio-concentration factor of up to 0.701. Endemic species, Zenia insignis Chun exhibited huge potential for Zn and Cd phytoextraction, with the highest concentrations of Zn (1,968 mg/kg) and Cd (44.40 mg/kg), characteristic root nodules, and fast growth rates in poor soils. As for multi-metal accumulation ability, native species B. papyrifera was calculated to have the most exceptional ability to accumulate various metals simultaneously (CBCI 2.93), followed by Amorpha fruticosa L. (CBCI 2.72) and Lagerstroemia indica L. (CBCI 2.53). A trend of increasing metal from trunks to leaves (trunks < branches < leaves) and towards fine roots has been shown by metal partitioning between tissues. The proposed CBCI would allow for the selection of suitable trees for phytoremediation in the future.