HR: 0830h
AN: B31D-0334    [PDF]
TI: Large Scale Structural Sequestration of Subsurface Soil Organic Carbon
AU: * Sanderman, J
EM: jsandman@nature.berkeley.edu
AF: Ecosystem Sciences Division - Department of ESPM University of California, Berkeley, 151 Hilgard Hall - MC3110, Berkeley, CA 94720 United States
AU: Ewing, S A
EM: saewing@nature.berkeley.edu
AF: Ecosystem Sciences Division - Department of ESPM University of California, Berkeley, 151 Hilgard Hall - MC3110, Berkeley, CA 94720 United States
AU: Amundson, R G
EM: earthy@nature.berkeley.edu
AF: Ecosystem Sciences Division - Department of ESPM University of California, Berkeley, 151 Hilgard Hall - MC3110, Berkeley, CA 94720 United States
AU: Baisden, W T
EM: BaisdenT@landcare.cri.nz
AF: Ecosystem Sciences Division - Department of ESPM University of California, Berkeley, 151 Hilgard Hall - MC3110, Berkeley, CA 94720 United States
AB: Aggregation of soil particles can have a profound influence on the retention and turnover of soil organic carbon. Most research on this topic has been focused on aggregates $<$ 2 mm in diameter, thus neglecting the mega-scale structure (often 20-50 mm or greater in size) observable in situ in the field. These large soil units have the potential to create distinct spatial distributions of soil C pools that vary in both age and recalcitrance. In a 60-day controlled laboratory incubation of sieved and homogenized soil, we observed a large initial pulse of old (14C depleted) CO$_{2}$ followed by decreasing effluxes of progressively younger CO$_{2}$ in both surface and subsurface samples of an undisturbed grassland in central California. $\Delta^{14}$C values of -147 and -596 per mil for these initial pulses from the surface and subsurface incubations, respectively, indicate a pool of potentially labile but physically protected organic matter. In subsoil ped samples (65-85 cm depth) from a similar soil, we found that the ped surfaces had significantly higher C and N percentages, C/N ratios and $\Delta^{14}$C values than the material in the ped interiors. In fact, a $\Delta^{14}$C value of -550 per mil for the subsurface interior C closely matched the $\Delta^{14}$C value of the initial CO$_{2}$ pulse from the subsurface incubation experiment, lending additional support to the hypothesis that these large soil aggregates are effective in protecting otherwise easily degraded organic matter for long periods of time. The lack of clear spatial trends (for both total C and 14C) in the surface horizon samples is likely a result of frequent disruptions to soil structure due to enhanced biological mixing activity, and low residence times of entrapped organic matter. These two complementary studies demonstrate that aggregate stabilization of organic C likely occurs at all levels of a cascading scale of soil aggregates, and that large-scale subsurface physical structure is likely a far more important control on C cycling rates than previously assumed.
DE: 0315 Biosphere/atmosphere interactions
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting