Nitrogen dynamics in a small arctic watershed: retention and downhill movement of 15 N

• Main Authors: Yano, Yuriko, Gaius R. Shaver, Giblin, Anne E., Rastetter, Edward B., Knute J. Nadelhoffer
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Figshare 2016
• Subjects: Environmental Science; Ecology; FOS Biological sciences; Arctic; Tundra; Alaska
• Online Access: https://dx.doi.org/10.6084/m9.figshare.c.3309546.v1; https://figshare.com/collections/Nitrogen_dynamics_in_a_small_arctic_watershed_retention_and_downhill_movement_of_sup_15_sup_N/3309546/1

We examined short- and long-term nitrogen (N) dynamics and availability along an arctic hillslope in Alaska, USA, using a stable isotope of nitrogen ( 15 N), as a tracer. Tracer levels of 15 NH 4 + were sprayed once onto the tundra at six sites in four tundra types: heath (crest), tussock with high and low water flux (mid- and footslope), and wet sedge (riparian). 15 N in vegetation and soil was monitored to estimate retention and loss over a 3-year period. Nearly all 15 NH 4 + was immediately retained in the surface moss–detritus–plant layer, and >57% of the 15 N added remained in this layer at the end of the second year. Organic soil was the second largest 15 N sink. By the end of the third growing season, the moss–detritus–plant layer and organic soil combined retained ≥87% of the 15 N added except at the Midslope site with high water flux, where recovery declined to 68%. At all sites, non-extractable and non-labile-N pools were the principal sinks for added 15 N in the organic soil. Hydrology played an important role in downslope movement of dissolved 15 N. Crest and Midslope with high-water-flux sites were most susceptible to 15 N losses via leaching, perhaps because of deep permeable mineral soil (crest) and high water flow (Midslope with high water flux). Late spring melt season also resulted in downslope dissolved- 15 N losses, perhaps because of an asynchrony between N release into melt water and soil immobilization capacity. We conclude that separation of the rooting zone from the strong sink for incoming N in the moss–detritus–plant layer, rapid incorporation of new N into relatively recalcitrant-soil-N pools within the rooting zone, and leaching loss from the upper hillslope would all contribute to the strong N-limitation of this ecosystem. An extended snow-free season and deeper depth of thaw under warmer climate may significantly alter current N dynamics in this arctic ecosystem.