HR: 11:20h
AN: C41D-05    [PDF]
TI: The Effect of Trees on Nitrogen Cycling in the Forest-Alpine Tundra Ecotone, Niwot Ridge, Colorado
AU: * Liptzin, D
EM: liptzin@colorado.eu
AF: University of Colorado, INSTAAR and Department of EEB CB450 University of Colorado, Boulder, CO 80303 United States
AU: Seastedt, T R
EM: timothy.seastedt@colorado.edu
AF: University of Colorado, INSTAAR and Department of EEB CB450 University of Colorado, Boulder, CO 80303 United States
AB: A unique unidirectional flux of materials characterizes the forest-alpine tundra ecotone (FATE) on Niwot Ridge, Colorado. In the alpine it is known that topography affects the redistribution of resources. Trees at treeline are hypothesized to accumulate water nutrients, and organic matter by functioning as snow fences, trapping materials blown from the adjacent tundra. In addition, the heterogeneity of snow redistribution dramatically changes the moisture content of soils and the growing season length. This redistributed material likely includes nitrogen of anthropogenic origin. These subsidies were hypothesized to be greatest nearest the alpine tundra, the source of the material, and downwind of trees, because of the tree-wind interaction. The goal of this research was to look for indirect evidence for this redistribution by measuring the total pools of carbon and nitrogen, nitrogen cycling rates and resin bag available nitrogen. Total soil carbon and nitrogen, in situ N mineralization, and resin bag available N were measured upwind and downwind of individual trees at three sites within the FATE. Total carbon and nitrogen generally increased with altitude across the ecotone and were higher downwind than upwind of trees. Resin bag available nitrogen was greater downwind of trees than upwind of trees and decreased with elevation. The predominant form of nitrogen was nitrate. Nitrogen mineralization was also lower upwind of trees than downwind of trees, significantly so at the tree island site, and increased with elevation. At the closed forest site, ammonium was the dominant form of nitrogen produced, but nitrate was more abundant at the higher elevation sites. These results indicate the spatial heterogeneity in soil pools and fluxes of nutrients. Future work aims to link these processes directly to the eolian inputs, quantify the inputs and losses of nitrogen to these soils and determine if this ecotone, or select locations within it, is approaching nitrogen saturation.
DE: 1615 Biogeochemical processes (4805)
SC: Cryosphere [C]
MN: 2003 Fall Meeting