Nitrogen deposition and cycling across an elevation and vegetation gradient in southern Appalachian forests

We studied nitrogen (N) cycling pools and processes across vegetation and elevation gradients in the southern Appalachian Mountains in SE USA. Measurements included bulk deposition input, watershed export, throughfall fluxes, litterfall, soil N pools and processes, and soil solution N. N deposition increased with elevation and ranged from 9.5 to 12.4 kg ha⁻¹ yr⁻¹. In all sites canopies retained inorganic N and lost organic N; net canopy retention varied among vegetation types. The high elevation site had the greatest litterfall N, soil N transformations, soil solution N, and greater stream N exports (0.60 kg ha⁻¹ yr⁻¹). Low elevation sites had lower litterfall N, soil N transformations, and soil solution N. Low stream N exports (0.14 kg ha⁻¹ yr⁻¹) suggested N limitation. Multivariate analyses showed that abiotic variables account for up to 63% of the variation in biotic site characteristics.

Keywords

• Elevation gradient,
• N cycling,
• N deposition,
• Coweeta Hydrologic Laboratory,
• Soil nitrogen,
• Litterfall