HR: 09:00h
AN: B51E-05    [Abstracts]
TI: Stabilization of C and N from Decomposing Fine Roots and Needles in Soil Organic Matter Fractions
AU: * Bird, J A
EM: jabird@nature.berkeley.edu
AF: Ecosystem Sciences Division Dept. of Environmental Science, Policy and Management, 137 Mulford Hall University of California, Berkeley, CA 94720-3114 United States
AU: Kleber, M
EM: MKleber@lbl.gov
AF: Earth Sciences Division Lawrence Berkeley National Lab, One Cyclotron Road MS 90R1116, Berkeley, CA 94720-8126 United States
AU: Torn, M
EM: mstorn@lbl.gov
AF: Earth Sciences Division Lawrence Berkeley National Lab, One Cyclotron Road MS 90R1116, Berkeley, CA 94720-8126 United States
AB: We investigated the contributions of Pinus ponderosa needles and fine roots to forest soil organic matter C and N storage. The fates of dual-labeled (¹³C/¹⁵N) ponderosa pine fine roots (< 2 mm) and needles were followed in situ during 2 years in an Ultic Haploxeralf located in a Mediterranean climate. We determined the net fluxes of litter ¹³C and ¹⁵N in four operationally-defined soil organic matter (SOM) fractions (light, fulvic, humic, and humin). The C turnover times (defined by natural abundance ¹⁴C) of these SOM fractions were distinct and ranged from 5 years (light fraction) to 260 years (insoluble humin). Overall, input of C as roots resulted in much more C retained in soil (70.5 ± 2.2 % of applied was retained) compared with needle C (42.9 ± 1.3 % of applied was retained) after 1.5 years. Greater complex C compounds in fine roots likely contributed to the longer initial C residence time and lower degree of transformation in the soil. In contrast, litter N recovery in soil was similar between above- and belowground substrates. During the first 1.5 years in situ, more of the needle ¹³C retained in soil was in humic and humin fractions and less as light fraction than for ¹³C from fine roots. The ¹³C:¹⁵N ratios of the SOM fractions suggest that the types of organic molecules stabilized differed fundamentally between needle and fine root sources. Predominately nitrogen-rich biomolecules from fine roots were stabilized in humic, fulvic and humin fractions. In contrast, carbon-rich biomolecules from needles were preferentially stabilized, especially initially, in the humin fraction.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0496 Water quality
SC: Biogeosciences [B]
MN: Fall Meeting 2005