Influence of natural rhizosediments characteristics on hydrocarbons degradation potential of microorganisms associated to Juncus maritimus roots

The influence of natural sediments colonized by Juncus maritimus (rhizosediments) on the microbial rhizosphere communities and their potential for hydrocarbons degradation was investigated. Rhizosediments from four salt-marsh sites of a temperate estuary (Lima River, NW Portugal) were sampled throughout the plant phenological cycle, for sediment characterization, total petroleum hydrocarbons, abundance and structure of microbial community, and hydrocarbon degrading microorganisms. Additionally, evaluation of hydrocarbon degradation potential was assessed from fortnight laboratory experiments, with and without crude oil amendment. Silt+Clay and organic matter (OM) content influenced the retention of hydrocarbons around plant roots by increasing their levels. Those parameters tended to correlate positively with total microbial abundance but negatively with hydrocarbon degrading microorganisms, a fact that could be related to lower hydrocarbon bioavailability. Rhizosediment laboratory experiments without crude oil amendment showed a significant (p<0.05) negative correlation between hydrocarbon degradation rates and OM and Silt+Clay content, confirming the strong influence of rhizosediment characteristics on hydrocarbons bioavailability. This is the first insight into the influence of natural sediment characteristic on the hydrocarbon degradation potential of salt marsh microorganisms, a feature that should be considered when designing rhizoremediation strategies in estuaries.