Soil properties associated with net nitrification following watershed conversion from Appalachian hardwoods to Norway spruce

Abstract

Nitrate (NO3-N) in soil solution and streamwater can be an important vector of nitrogen (N) loss from forested watersheds, and nitrification is associated with negative consequences of soil acidi- fication and eutrophication of aquatic ecosystems. The purpose of this study was to identify vegetation- mediated soil properties that may control potential net nitrification dynamics and to determine if net nitrifi- cation is a function of abiotic retention or biotic inhibition. We performed a soil inoculation and incubation study and analyzed a suite of soil chemical and biological properties in soils from a 40-year-old Appalachian hardwood forest and an adjacent 37-year-old Norway spruce forest converted from Appalachian hardwoods. Our results indicate that net NO3-N production was nine times higher in hardwood soil (mean = 183.51 mg N/kg/28 days) than in the spruce soil (mean = 18.97 mg N/kg/28 days) and differences in net NO3-N production were attributed to differences in soil substrate quality. Soil properties that were most strongly correlated with NO3-N production across vegetation types included total soil N, soil C:N ratio, oxalate concentration, and sulfate concentration.Establishmentofasprucemonoculturein the central Appalachian hardwood ecoregion signifi- cantly altered N cycling, likely depleted soil N stores, increased soil acidity, and altered soil organic matter dynamics, thus leading to low net nitrification rates.