Axonopus compressus (Beauv.) used a mechanism of soil pH modification to sustain growth in heavily oil polluted soil

Abstract

The objective of this study is to assess the survival of three grass species, Cynodon dactylon (L.) Pers, Eleusine indica (L.) Gaertn and Axonopus compressus (Beauv.)  in contaminated crude oil polluted soil as potential phytoremediant as well as propose a mechanistic explanation for their responses. Top soil (0-15 cm depth) was air-dried, sieved (˂2mm) and the composite sample was treated with crude oil in the following concentration, 0%, 10%, 20% (w/w) in three replicate arranged in a Complete Randomized Design. The vegetative parameters assessed were plant height, number of leaves, stem circumference, leaf length, root length and biomass. Soil pH was measured every two weeks. Total petroleum hydrocarbon (TPH) content of soil samples before and after plant growth was also analysed. Bacterial species associated with the soil samples after plant harvest were determined. Result obtained showed that growth parameters of the test species were suppressed by the contaminant when compared to plants grown in unpolluted soil. These differences were significant (p<0.05). One significant finding was the ability of Axonopus compressus to thrive and sustain growth in all concentration of polluted soils with survival rate of 100% in comparison to others. The study suggests that A. compressus is able to sustain growth in 20% crude oil polluted soil by employing a mechanism of soil chemistry that modifies pH of the soil from acidic to neutral conditions.