QUANTIFYING NITROGEN CYCLING ON SURFACE MINED LANDS USING NATURAL D15N ABUNDANCES AND FUNGAL RELATIONSHIPS: AN EXPLORATORY STUDY

The use of isotopes to measure the role of mycorrhizal fungi in cycling nitrogen between soil and plants is applied to a reclaimed surface mine to illustrate the impact of surface mining on soil nutrient cycling in a terrestrial ecosystem. Isotopic relationships between soil, plants, and fungi were examined for a ~10 year old pitch pine reclaimed valley fill in Breathitt County, KY and for an undisturbed mixed mesophytic forest in Letcher County, KY. A quantitative inventory of sporocarps present, their size and substrate was performed at each site. Isotopic signatures of fungal and presumed substrate samples, dominant foliage samples (beech, Fagus grandifolia, in the undisturbed forest; and pitch pine, Pinus rigida, on the reclaimed site), and bulk soil samples were analyzed to quantify the nitrogen flux occurring between soil, mycorrhizal fungi, and trees at each site. It was found that ~20% of mycorrhizal fungal N is transferred to host trees in the old growth forest and ~74% of host plant N comes from mycorrhizal fungi, while in the reclaimed forest ~38% of mycorrhizal fungal N is transferred and ~43% of plant N is fungi-derived. While on a reclaimed site trees obtain less of their total N from fungi than in an undisturbed forest, the mycorrhizal fungi that is present in a reclaimed area give more of their N to plants, indicating a shortage of mycorrhizal fungi relative to the undisturbed forest, an interpretation consistent with the quantity of sporocarps observed at each site. These results suggest the lack of mycorrhizal fungi as a limiting factor in N supply and cycling on reclaimed surface mine lands, and emphasize the need for reclamation practices that promote the growth of mycorrhizal fungi.