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Abstract
Rhizoremediation involves the breakdown of contaminants in soil resulting from microbial
activity that is enhanced in the plant root zone. The objective of this study was
to assess Australian native grasses for their ability to stimulate removal of aliphatic
hydrocarbons from a mine site soil. Time-course pot experiments were conducted in
a greenhouse with three grass species (Cymbopogon ambiguus, Brachiaria decumbens,
and Microlaena stipoides) in a mine site soil experimentally contaminated with a 60:40
diesel:oil mixture at 1% (w/w) concentration. Plants were cultivated for 100days with
periodic evaluation of changes in soil total petroleum hydrocarbon (TPH) concentration,
soil lipase activity, and abundance of hydrocarbon-degrading microorganisms. Results
were compared to unplanted control treatments. Significantly lower endpoint TPH concentrations
were recorded in planted soil compared to unplanted soil (p=0.01). Final TPH concentrations
and rates of TPH removal varied between grass species, with total TPH removal of between
50% and 88% achieved in planted treatments. The presence of grasses significantly
increased the abundance of hydrocarbon-degrading microorganisms and soil lipase activity
relative to unplanted soil (p<0.05). Residual TPH concentration was found to be closely
(negatively) correlated with abundance of hydrocarbon-degrading microorganisms and
to a lesser extent with soil lipase activity. Australian native grass species were
identified that effectively enhance the remediation of diesel/oil contaminated soil,
without any requirement for nutrient supplementation. Results may have extensive application
to the nationwide problems associated with hydrocarbon contaminated sites.