Polyaromatic Hydrocarbon Phytoremediation Stimulated By Root Exudates

To encourage polyaromatic hydrocarbon (PAH) degradation in a historic steel production facility, contaminated soil was amended with 10% (v/v) compost and 5% (v/v) poultry litter. Within twelve 11.89 m X 27.13 m plots, 35,000 native Michigan perennials were planted. Soil and heterotrophic bacteria were sampled over several years beneath unplanted (control), Eupatorium perfoliatum (Boneset), Aster novae-angliae (New England Aster), Andropogon gerardii (Big Bluestem), and Scirpus atrovirens (Green Bulrush). All soils were found to degrade many PAHs, in one case up to 37% of the total. Cultivable microbes from the beneath plants were recovered, and 16S rDNA sequencing was used to identify microbial species. Implicated in phytoremediation, root exudates were prepared from select plants. Exudate amino acid composition changed with increasing plant age. A shift from Met and Lys to Glu and Asn was observed in exudates obtained from Swamp Goldenrod (Solidago patula). In Boneset, and New England Aster, Gly and Ala comprised at least 10% the total amino acids. Besides remediating a large fraction of the soil PAHs, the majority of planted plants survived the 3-year experiment. Root secretions and indigenous microbial communities may establish beneficial relationships that promote in situ PAH phytoremediation.