Arbuscular mycorrhizal fungal communities across a heavy metal contamination gradient and their relationships with indigenous Deschampsia flexuosa

Background/Question/Methods

In Palmerton, PA, the New Jersey Zinc Company smelted zinc from 1898-1980, polluting the surrounding soil and streams with high levels of zinc, cadmium, and lead and defoliating over 2000 acres. Current day contamination exists as a gradient with the highest levels close to the smelters. This contamination has been shown to reduce both the diversity and abundance of a wide variety of organisms, including vertebrates, arthropods, trees, and microbes. A survey of the arbuscular mycorrhizal (AM) fungi had never been conducted. Arbuscular mycorrhizal fungi can help plants tolerate heavy metal-contaminated soils and have been used in restoration efforts in other systems. We first characterized the AM fungal community in soil collected under Deschampsia flexuosa, a dominant grass found throughout the contamination gradient, at three points along the gradient. We relied on the morphology of field-collected spores and spores extracted from greenhouse trap cultures. We also quantified percentage colonization by AM fungi in roots of D. flexuosa extracted from the same field-soil collections. We also performed a greenhouse experiment to determine if the AM fungal community from the area of lower contamination or from a naturally metalliferous serpentine site would increase the growth of D. flexuosa in highly contaminated soil and help with revegetation efforts.

Results/Conclusions

In field soils, the AM fungal community at the low end of the metal gradient is twice as diverse as the fungal community at the high end of the gradient, although two morphotypes were present regardless of contamination level: Acaulospora mellea and an unidentified brown Glomus. A second unidentified Acaulospora species was found in soils with either medium or low levels of contamination while Glomus rubiforme and an unidentified white morphotype were found exclusively in soils with low levels of contamination. Acaulospora mellea was by far the most common morphotype. Plants in soils with the lowest contamination had a higher percentage root colonization (54% ± 3.9%) than roots from the middle of the gradient (15% ± 3.8%) and the highly contaminated soil (1% ± 0.75%). The growth of D. flexuosa in highly contaminated soil was not improved by the addition of fungal inoculum in the form of infected roots from either the low contamination or serpentines communities. It appears that this plant species relies very little on arbuscular mycorrhizal fungi in soils that are heavily contaminated with metals.