Phytoremediation of petroleum-polluted soils: application of Polygonum aviculare and its root-associated (penetrated) fungal strains for bioremediation of petroleum-polluted soils.

Petroleum-polluted soils are a common disaster in many countries. Bioremediation of oil contamination in soils is based on the stimulation of petroleum-hydrocarbon-degrading fungal and microbial communities. A field study was conducted in a petroleum-contaminated site to find petroleum-resistant plants and their root-associated fungal strains for use in bioremediation of petroleum-polluted soils. Results and observations showed that the amounts of petroleum pollution in nonvegetated soils were several times higher than in vegetated soils. Plants collected from petroleum-polluted areas were identified using morphological characters. Results indicated that seven plant species were growing on the contaminated sites: Alhaji cameleron L. (Fabaceae), Amaranthus retroflexus L. var. retroflexus (Amaranthaceae), Convolvulus arvensis L. (Convolvulaceae), Chrozophora hierosolymitana Spreg. (Euphorbiaceae), Noea mucronata L. (Boraginaceae), Poa sp. (Poaceae), and Polygonum aviculare L. (Polygonaceae). The root-associated fungi of each plant were determined and results showed the presence of 11 species that associated with and also penetrated the roots of plants growing in the polluted areas. Altenaria sp. was common to all of the plants and the others had species-specific distribution within the plants. The largest numbers of fungal species (six) were determined for P. aviculare and Poa sp. in polluted areas. However, the variation of fungal strains in the plants collected from petroleum-polluted areas was greater than for nonpolluted ones. Culture of fungi in oil-contaminated media showed that all the studied fungi were resistant to low petroleum pollution (1% v/v) and a few species, especially Fusarium species, showed resistance to higher petroleum pollution (10% v/v) and may be suitable for bioremediation in highly polluted areas. Bioremediation tests with P. aviculare, with and without fungal strains, showed that application of both the plant and its root-associated fungal strains was more effective than of the plant and fungi separately, and Fusarium species were the most effective. Results indicated that fungal strains had the main role in bioremediation of petroleum-polluted soils, but plant roots enhanced the process.