HR: 0830h
AN: B31D-0337    [PDF]
TI: Nitrogen Addition Reduces Decomposition of Native Recalcitrant Soil Carbon Under Plants With High Root Lignin and Low Cell Soluble Content
AU: * Dijkstra, F A
EM: dijks002@umn.edu
AF: Department of Ecology, Evolution, and Behavior University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108
AU: Hobbie, S E
EM: shobbie@umn.edu
AF: Department of Ecology, Evolution, and Behavior University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108
AU: Knops, J M
EM: jknops@unlnotes.unl.edu
AF: School of Biological Sciences, University of Nebraska, 348 Manter Hall, Lincoln, NE 68588
AU: Reich, P B
EM: preich@umn.edu
AF: Department of Forest Resources, University of Minnesota, 1530 Cleveland Ave. N., St. Paul, MN 55108
AB: The effect of increased atmospheric nitrogen (N) deposition on long-term soil carbon (C) storage remains unclear. Both enhanced and retarded decomposition of lignin and other recalcitrant C substrates in the soil have been reported with N addition. We examined the effect of N addition on soil C pools under 12 different grassland species planted as monoculture plots treated with 560 ppm atmospheric CO$_{2}$ concentrations, and 0 and 4 g N fertilizer m$^{-2}$ yr$^{-1}$ in Minnesota, USA. After 5 years of treatment we separated soil C into light and heavy fractions and used the distinct $^{13}$C isotopic signature of C3 plants in elevated CO$_{2}$ plots to separate the more recalcitrant native or pre-treatment C from newly formed C. As fertilizer N was labeled with $^{15}$N, we also calculated the amount of N fertilizer retained in the soil. Nitrogen addition significantly increased the pre-treatment C pool of the light soil fraction by 18% compared to plots receiving no N addition, suggesting reduced decomposition of C with added N. Added N did not affect the more stable heavy soil C fraction. In plots with added N, the pre-treatment C pool of the light fraction was especially high for plants that produced roots high in lignin and low in cell soluble content. These results suggest that high lignin content interacted with high levels of N to stimulate chemical stabilization of native soil C. The amount of fertilizer N retained in the light fraction was significantly positively related to pre-treatment soil C content, further evidence that N fertilization promoted stabilization of pre-treatment C. We conclude that plant species composition (via its effects on root lignin concentrations) determines the influence of atmospheric N deposition on the decomposition of soil organic matter under elevated CO$_{2}$.
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting