HR: 16:15h
AN: B32D-02    [PDF]
TI: Decomposition and Stabilization Dynamics of C and N from Fine Roots Versus Needles
AU: * Bird, J A
EM: jabird@socrates.berkeley.edu
AF: University of California, Berkeley, Dept. of Integrative Biology, 3060 Valley Life Sciences Building, University of California, Berkeley, CA 94720-3140 United States
AU: Torn, M S
EM: mstorn@lbl.gov
AF: Lawrence Berkeley National Laboratory, One Cyclotron Road Bldg. 90R-1116, Berkeley, CA 94720 United States
AB: Do fine roots or needles ultimately produce the most C sequestered as stable soil organic matter (SOM)? How does the soil microclimate/soil horizon influence the efficiency of decomposition and C and N humification dynamics? We present the first 1.5 yr results of a study using $^{13}$C- and $^{15}$N-labeled {\it Pinus ponderosa} litter to track the short- and long-term fate of fine root vs. needle C and N inputs to soil. Labeled substrates were placed into either the O or A horizons of an Ultic Haploxeralf in the Sierra Nevada, CA. We determined the amount of label respired as CO$_{2}$ and the amount remaining in the soil. The movement of the $^{13}$C and $^{15}$N into and through the microbial community (PLFA/CFE) and SOM fractions was determined to compare the humification rates and pathways of the added $^{13}$C and $^{15}$N. Total soil recovery of fine root C far exceeded that of needles after 1 yr (76.9 vs. 52.4%). Twice as much of the needle C was reduced to a smaller size class (less than 2 mm) than for fine roots. Soil $^{15}$N retention was high and unaffected by soil depth or substrate type (88%) after 1 yr. The proportion of $^{15}$N recovered in microbial biomass was twice as great from needles as from fine roots (10.2 vs. 5.1%). Leaching losses of $^{13}$C and $^{15}$N were apparently very low with only 1-2% of $^{13}$C or $^{15}$N transported from the O to the A horizon after 1 yr. Due to moisture limitation in the surface soil during the summer, $^{13}$CO$_{2}$ respiration was faster for both substrates in the A horizon, while during the winter and spring, substrates in the O horizon had faster rates of $^{13}$CO$_{2}$ respiration than those in the A horizon. Although soil depth and microclimate influenced seasonal C loss by respiration, it did not affect total soil C recovery after 1 yr. The C quality of the substrates appeared to be more important than soil placement depth in affecting C residence time after the first year.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4815 Ecosystems, structure and dynamics
DE: 4840 Microbiology
DE: 4870 Stable isotopes
SC: Biogeosciences [B]
MN: 2003 Fall Meeting