Nitrogen cycling" hotspots": An approach for watershed scale assessments

摘要: The high level of spatial and temporal heterogeneity in nitrogen cycling processes hinders our ability to develop an ecosystem-wide understanding of this cycle. Determining nitrogen cycling “hotspots” has proved to be very complicated. In the southern Appalachians nitrogen cycling varies along elevation gradients. This study examines how the incorporation of spatial “hotspots” of soil moisture, carbon, nutrients, and soil texture can better explain ecosystem nitrogen cycling? Sites (80 mx 80 m) distributed over an elevation gradient (788 m-1389 m), and vegetation (mixed oak hardwood, northern hardwood, cove hardwood, mixed oak-pine) gradient were sampled monthly for estimates of soil moisture using a non-destructive technique based on electromagnetic induction (EMI). The sites were sampled quarterly for assessments of soil nutrient and carbon content (extractable NH 4+, acid extractable PO 4 3+, total C, and total N) using near infrared reflectance spectroscopy (NIRS). Clay content was determined on georeferenced soil cores (0-20 cm) and collected in June of 2011. As indicators of potential nitrogen cycling rates, we conducted laboratory estimates of denitrification (0-5, 5-10, and 10-20 cm) and nitrification (0-5 and 5-20 cm) in November 2010 and March 2011. Stepwise multivariate regression analysis with minimum corrected Akaike Information Criterion (AICc) was used to determine the most appropriate model of predictors for nitrogen cycling processes.