NATIVE MICHIGAN PLANTS STIMULATE SOIL MICROBIAL SPECIES CHANGES AND PAH REMEDIATION AT A LEGACY STEEL MILL

Abstract

A 1.3-acre phytoremediation site was constructed to mitigate polyaromatic hydrocarbon (PAH) contamination from a former steel mill in Michigan. Soil was amended with 10% (v/v) compost and 5% (v/v) poultry litter. The site was divided into twelve 11.89 m X 27.13 m plots, planted with approximately 35,000 native Michigan perennials, and soils sampled for three seasons. Soil microbial density generally increased in subplots of Eupatorium perfoliatum (boneset), Aster novae-angliae (New England aster), Andropogon gerardii (big bluestem), and Scirpus atrovirens (green bulrush) versus unplanted subplots. Using enumeration assays with root exudates, PAH degrading bacteria were greatest in soils beneath plants. Initially predominant, Arthrobacter were found capable of degrading a PAH cocktail in vitro, especially upon the addition of root exudate. Growth of some Arthrobacter isolates was stimulated by root exudate. The frequency of Arthrobacter declined in planted subplots with a concurrent increase in other species, including secondary PAH degraders Bacillus and Nocardioides. In subplots supporting only weeds, an increase in Pseudomonas density and little PAH removal were observed. This study supports the notion that a dynamic interplay between the soil, bacteria, and native plant root secretions likely contributes to in situ PAH phytoremediation.

KEY WORDS::

• PAH phytoremediation
• root exudate
• alleopathy

ACKNOWLEDGMENTS

We thank Teresa Wood, Susan Redwine, Rachada Settavongsin, Edang Susilawati, and Sarah Kinder for their help in establishing and sampling in the Rouge phytoremediation site. This work was supported from grants from Consortium for Plant Biotechnology, EPA, EPA R-82947901, CPBR EPA82947901, and Ford Motor Company. NSF is acknowledged for supporting two CCLI grants allowing the acquisition of the HPLC and the ICP/MS and the support and encouragement from the University of Michigan-Dearborn Office of Sponsored Research (Dr. Drew Buchanan).