Diesel Impacts on Functional Bacterial Groups and Collembolans During Phytoremediation in a Mesocosm System

Phytoremediation of contaminated soils relies on the ability of plants to stimulate microbial rhizosphere diversity, by releasing root exudates. This work assessed the impact of diesel contamination on soil populations of culturable bacterial groups (fast growing, N2-fixing, phosphate (P) solubilizing, and lipolytic bacteria), and collembolans under mesocosm conditions with and without the influence Medicago sativa. We set up six treatments sampled initially within 24 h and examined at 4, 8, and 12 months. Bacterial groups were isolated and identified with 16S rRNA sequencing, while collembolans were classified using taxonomic keys. The populations of P-solubilizing and fast-growing bacteria were stimulated after 4 months in the polluted treatments in absence of M. sativa. On the M. sativa treatments, P-solubilizing and lipolytic bacteria increased after 8 months. Stenotrophomonas and Achromobacter were the most predominant bacterial genera. Collembolans mainly belonging to Poduromorpha and Entomobryomorpha orders, were observed in contaminated treatments on the 12th month, while in the uncontaminated control were found at the 4th month. Hydrocarbon degradation was higher than 80% in all treatments after 12 months. Diesel contamination and soil management reduced significantly the collembolan abundance; these organisms may be considered as biological indicators of soil quality and recovery after an event of diesel contamination.