The Effect of Rhizosphere Soil and Root Tissues Amendment on Microbial Mineralisation of Target 14 C-Hydrocarbons in Contaminated Soil

Abstract

The effect of rhizosphere soil or root tissues amendments on the microbial mineralisation of hydrocarbons in soil slurry by the indigenous microbial communities has been investigated. In this study, rhizosphere soil and root tissues of reed canary grass (Phalaris arundinacea), channel grass (Vallisneria spiralis), blackberry (Rubus fructicosus) and goat willow (Salix caprea) were collected from the former Shell and Imperial Industries (ICI) Refinery site in Lancaster, UK. The rates and extents of 14C–hydrocarbons (naphthalene, phenanthrene, hexadecane or octacosane) mineralisation in artificially spiked soils were monitored in the absence and presence of 5% (wet weight) of rhizosphere soil or root tissues. Respirometric and microbial assays were monitored in fresh (0 d) and pre–incubated (28 d) artificially spiked soils following amendment with rhizosphere soil or root tissues. There were significant increases (P < 0.001) in the extents of 14C–naphthalene and 14C–phenanthrene mineralisation in fresh artificially spiked soils amended with rhizosphere soil and root tissues compared to those measured in unamended soils. However, amendment of fresh artificially spiked soils with rhizosphere soil and root tissues did not enhance the microbial mineralisation of 14C–hexadecane or 14C–octacosane by indigenous microbial communities. Apart from artificially spiked soil systems containing naphthalene (amended with reed canary grass and channel grass rhizosphere) and hexadecane amended with goat willow rhizosphere, microbial mineralisation of hydrocarbons was further enhanced following 28 d soil–organic contaminants pre–exposure and subsequent amendment with rhizosphere soil or root tissues. This study suggests that organic chemicals in roots and/or rhizosphere can enhance the microbial degradation of petroleum hydrocarbons in freshly contaminated soil by supporting higher numbers of hydrocarbon–degrading populations, promoting microbial activity and/or enhancing bioavailability of organic contaminants.