Crude oil induces plant growth and antioxidant production in Leersia hexandra Sw

The potential of Leersia hexandra grass in phytoremediation and natural attenuation of three groups of bacteria in soil contaminated with crude oil was evaluated for 180 days. The quantities of new shoots, root and aerial biomass were evaluated; changes in antioxidant concentrations in leaf and root caused by abiotic stress; population densities of Azotobacter, Azospirillum and Pseudomonas; and microbial respiration. The experimental data showed oil-induced increases of 315% and 196% in new shoots and root phytomass, respectively, and a 44% decrease in leaf + stem phytomass. The enzymatic defence in the grass leaf was manifested by higher concentrations of hydrogen peroxide, phenylalanine ammonium lyase and total flavonoids; the increases fluctuated from 35% to 52%. The response in the root was positive in catalase (16%), and in ammonium phenylalanine lyase, it increased 275% due to the effect of crude oil. The group of indigenous Azotobacter bacteria were tolerant to crude oil exposure, both in the phytoremediation process and in natural attenuation; the population densities varied from 212 to 438 × 103 colony-forming units (CFUs); they are greater than 49% to 106% compared to densities in control soil. Azospirillum spp. and Pseudomonas spp. recorded population abiotic stress. The grass activates enzymatic and plant defence, complementing microbial respiration in response to adaptation to crude oil.