The effects of petroleum contaminated soils on the growth, gas exchange and antioxidative level of sea-buckthorn

Background and aims Sea-buckthorn ( Hippophae rhamnoides ) is widely domesticated and cultivated in orchards worldwide. With the advantages of a large root system and the symbiosis of fibrous roots with Frankia, a group of N 2 fixing bacteria which form nodules with the roots, sea-buckthorn can grow in harsh environment under extreme weather conditions. However, its tolerance to petroleum contamination in the soil has so far not been studied. To elucidate whether sea-buckthorn can be employed for phytoremediation of petroleum contamination, its remediation efficiency as well as its growth and metabolic traits in petroleum contaminated soil were examined in an experiment with potted plants. Methods Sea-buckthorn seedlings were planted in soils with four different petroleum concentrations from April to September in a pot experiment. The responses of growth, gas exchange and the antioxidative system were examined on three sampling dates. After 5.5-month of exposure, soil petroleum remediation was evaluated in planted and unplanted soils. Results The petroleum decontamination rate was significantly enhanced by H. rhamnoides in soils with petroleum contamination up to 15 g kg −1 after one growing season. The root to shoot ratio increased continuously with the increase of the petroleum concentration as a consequence of reduced biomass allocated to the shoots, probably as a mechanism to counteract stress by the petroleum contamination of the soil. Photosynthesis was enhanced by lower petroleum concentrations in the soil (≦15 g kg −1 ) in September. Short-term exposure (in July) to high petroleum concentrations (20 g kg −1 ) in the soil enhanced ascorbate peroxidase (APX), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT) activity and increased ascorbic acid (AsA) and glutathione (GSH) contents, indicating elevated activity of the Foyer-Haliwell-Asada-Cycle. However, similar effects were not observed at long-term exposure. Conclusions Our results prove that sea-buckthorn is a promising tool for phytoremediation of petroleum contaminated soils up to 15 g kg −1 in loess plateau soil in China.