Antioxidant Defense Response and Growth Reaction of Amorpha fruticosa Seedlings in Petroleum-Contaminated Soil

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.