Detection of heavy metals in oak mycorrhizae of northeastern Pennsylvania forests, using x-ray microanalysis

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Abstract
A survey of red and white oak mycorrhizae, using semi-quantitative x-ray microanalysis, has shown a significant difference in heavy-metal deposition between the forest-grown oaks on acidic (mor) and neutral (mull) soils. There are significantly higher levels of nickel, iron, aluminum, and copper within oak roots of Pocono (mor) forests than of Lehigh Valley (mull) forests. The Pocono oak roots were taken from acidic soils derived from sandstone, shales, and conglomerate parent rock materials, while Lehigh Valley oak roots were removed from neutral soils derived from carbonate-rich limestone and dolomite. Chemical analysis of these soils demonstrated higher plant-available heavy-metal content in the acidic soils. Digital line profiles indicated that heavy metals, especially nickel and iron, were concentrated in the peripheral mycorrhizal mantle region of cross-sectioned roots. Since nickel and other heavy metals are known to be toxic to fungi and plant tissues, the high concentrations of metals may be responsible for the decreased frequencies of advantageous ectomycorrhizal associations in oaks growing under certain acid-stressed conditions.