Phytoremediation of crude oil-contaminated soils using a wild ornamental plant Gerbera jamesonii in eastern Gansu Province of the Loess Plateau

In order to verify whether Gerbera jamesonii can biodegrade the crude oil-contaminated pollutants in the east part of the Loess Plateau, we studied the response of plant growth index and rhizosphere soil environmental index under different soil total petroleum hydrocarbons (TPH) concentrations stress. The plant growth index, rhizosphere soil environmental index, as well as removal and degradation rates of soil TPH, alkane and aromatic hydrocarbon under different soil TPH concentrations (1%, 3%, 5%, and 7%) were investigated by conventional methods. We found that removal rate of soil TPH, alkane, and aromatic hydrocarbon were decreased with the increase in soil TPH concentration and achieved its highest degradation rate in the soil TPH up to 5% (P < 0.05). Besides, plant height, root length, and germination rate of the G. jamesonii were similarly decreased with the increase in soil TPH concentration (P < 0.05). Moreover, the soil TPH at 7% could significantly inhibit its biomass above the ground, but both biomasses above and under the ground were significantly promoted when the soil TPH was up to 5% (P < 0.05). Next, at the soil TPH less than 5%, its removal rate was improved by the increase in soil dehydrogenase activity, biomasses above and under the ground as well as soil microbial diversity. Non-metric multidimensional scaling (NMDS) analysis showed that combined action of plant biomass, soil enzyme activity, and soil microbial community could be the main factors that determine the soil TPH removal rate. Meanwhile, when the soil TPH was up to 7%, severe inhibition of the plant biomass of G. jamesonii was the key factor leading to the significant reduction of soil TPH removal rate. All the results indicated that soil TPH concentration at 5% should be determined as the threshold tolerance concentration of Gerbera jamesonii, when it is applied to the ecological restoration of crude oil-contaminated soil. In conclusion, we propose that the adaptable plant of eastern Gansu Province of the Loess Plateau, G. jamesonii, is a superior plant variety with the ability for crude oil-contaminated soil restoration when soil TPH concentration is less than 5%.