Plant-Derived Phenolic Antioxidants Inhibit Degradation of Petroleum Hydrocarbons via Denitrification in Coastal Wetlands Soils.

Plant-derived phenolic compounds could regulate redox reactions due to their antioxidative properties. In this study, soils from coastal wetlands including bare flat (BF), cyperus(Cyperus malaccensis) (CY), reed (Phragmites australis) (RE), and mangrove(Kandelia obovata) (MA) in Minjiang estuary region were selected. Anaerobic microcosm incubation experiments were conducted to investigate the petroleum hydrocarbon (PH) degradation process through denitrification. In addition, effect of plant-derived antioxidants (carotenoids, anthocyanins, flavones, and phenolic acids) on the activity of denitrifying bacteria, enzymes, and genes were studied. The results showed that addition of NO significantly (p<0.05) promoted PH degradation in BF, RE, and CY by 14.1% - 31.7% while not influenced on PH degradation in MA. Bacteria that could degrade petroleum through denitrification (e.g., Burkholderia and Rhodococcus) showed much higher abundances in CY and RE than in MA. Antioxidants of cover plants showed large varieties with RE containing highest contents of carotenoids while MA containing highest contents of phenolic compounds (anthocyanins, flavones, and phenolic acids). These phenolic antioxidants significantly reduced the activity of NO and NO reductase and abundances of denitrification genes (nirK) and the inhibition effect was positively correlated to Trolox Equivalent Antioxidant Capacity (TEAC). Overall, our results demonstrate the key regulation role of plant-derived antioxidants in OC degradation in eutrophic wetlands.