HR: 0830h
AN: B31D-0335    [PDF]
TI: N isotope fractionation and measures of organic matter alteration during decomposition
AU: * Kramer, M G
EM: mkramer@mail.arc.nasa.gov
AF: NASA Ames Research Center, Ecosystem Science and Technology Branch, Moffett Field, CA 94035 United States
AU: Sollins, P
EM: phil.sollins@orst.edu
AF: Oregon State University, Department of Forest Science, Corvallis, OR 97331 United States
AU: Sletten, R S
EM: sletten@u.washington.edu
AF: University of Washington, Earth and Space Science Departmnet of Geological Sciences, Seattle, WA 98195-1300 United States
AU: Swart, P K
EM: pswart@rsmas.miami.edu
AF: University of Miami, Rosentiel School of Marine Science 4600 Rickenbacker Causeway, Maimi,, FLA 33149 United States
AB: Most soil organic matter (SOM) derives from plant material but there are substantial gaps in our understanding of its transformation mechanisms. Alterations that occur as SOM decays and is stabilized have proven difficult to study owing largely to its diverse initial chemical composition and stable isotope values. We examined SOM stable isotope ratios in relation to composition using solid-state $^{13}$C CPMAS nuclear magnetic resonance (NMR) in sequentially deeper organic and mineral horizon soil samples collected from an unpolluted ecosystem in southeast Alaska dominated by C$_{3}$ vegetation. We found that as humified carbon (C)--C not respired as CO$_{2}$ during decomposition--increased in aliphaticity (ratio of unsubstituted aliphatics to carbohydrates), it also increased in $^{15}$N (P<0.0001) but showed no clear trend in $^{13}$C or C:N ratio. These results imply that humification (and the concomitant stabilization of soil C) at our site resulted from microbial alteration of organics rather than from accumulation of recalcitrant compounds. The strong, and previously unreported, relation between $^{15}$N and SOM composition found at our study site suggests that degree of SOM humification may be correlated with an increase in $\delta^{15}$N SOM values relative to $\delta^{15}$N for fresh litter and other source material.
DE: 0315 Biosphere/atmosphere interactions
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting