Physiological and microbiological hormesis in sedge Eleocharis palustris induced by crude oil in phytoremediation of flooded clay soil

Abstract

Soil contamination with petroleum hydrocarbons affects plants and rhizospheric microorganisms. A nine-month experiment was set up to study the effect over time of oil on plant height, new plant production, plant matter production, and the population of rhizospheric microorganisms in the sedge Eleocharis palustris. The removal of total petroleum hydrocarbons from the soil was also evaluated. The results showed that plants responded differently depending on age and petroleum concentration. Concentration of 60 g of petroleum per kg of soil induced a significant increase in height (weeks 28 to 38) and new plant production (weeks 13 to 38). At the end of the evaluation period, a high petroleum concentration induced a significant increase in the number of primary roots, root and aerial dry matter, population of microalgae, total fungi, actinomycetes, Pseudomonas spp and hydrocarbonoclastic bacteria. Physiological and microbiological hormetic index values ≥1 showed a linear response to petroleum concentration in plant height and new plant production from weeks 3 and 2 to 38, respectively. A similar response curve was found for the number of primary roots, root and aerial dry matter, microalgae, total fungi, actinomycetes, Pseudomonas, and hydrocarbonoclastic bacteria (week 38). After 38 weeks of exposure to petroleum-contaminated soil, the rhizosphere of E. palustris showed petroleum removal percentages of 71, 72, 56, 42, 33 and 23% in soil that initially contained 3, 15, 30, 45, 60 and 75 g oil, respectively. The increase in petroleum removal was significantly and negatively correlated with the populations of microalgae, actinomycetes, Pseudomonas bacteria and hydrocarbonoclast bacteria.