HR: 1340h
AN: B13C-0243    [Abstracts]
TI: Soil Organic Matter Stores and Dynamics in a Chaparral Ecosystem After Eight Years of Exposure to a Gradient of Atmospheric CO$_{2}$ Concentrations, From pre-Industrial Level to 750 ppm
AU: * Del Galdo, I
EM: ilaria.delgaldo@unina2.it
AF: Department of Environmental Sciences, Second University of Naples, Via Vivaldi, 43, Caserta, CE 81100 Italy
AU: Oechel, W C
AF: Global Change Research Group Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182 United States
AU: Cotrufo, F
EM: mfrancesca.cotrufo@unina2.it
AF: Department of Environmental Sciences, Second University of Naples, Via Vivaldi, 43, Caserta, CE 81100 Italy
AB: Due to the continuously increasing concentration of atmospheric CO$_{2}$, it has become a priority to understand if soil organic matter (SOM) will act as a sink or a source of CO$_{2}$, under future environmental change. Although many studies have addressed the question, a clear answer, in particular on the long term response, is still missing. Here we report the results of an experiment where we quantified the soil C stores and investigated the dynamics of SOM, its aggregation and pool composition, in a Californian chaparral ecosystem, exposed to a gradient of atmospheric CO$_{2}$ concentrations. In the study site of Sky Oaks (Warner Springs, CA, USA), twelve closed chambers were installed in 1992, and for 8 years they were fumigated with different concentration of CO$_{2}$, ranging from pre-industrial levels (250 ppm) to 750 ppm CO$_{2}$, with step increments of 100 ppm. Fossil fuel-derived CO$_{2}$, depleted in $^{13}$C, was used to fumigate the chambers, thus allowed to trace the C input from the vegetation to the soil at all levels of CO$_{2}$ exposure. In January 2003, soil were sampled from each chamber and shipped to the SUN (Italy). Here, soil samples were separated by wet sieving into different classes of aggregates, namely, macroaggregates ($>$250$\mu$m), microaggregates (53-250 $\mu$m) and silt&clay ($<$53 $\mu$m). Within macroaggregates, we isolated three different structural and functional pools: the coarse particulate organic matter (POM), the microaggregates and the occluded silt&clay. Lastly, a density floatation with Sodium Polytungstate allowed the separation of light fraction contained in the microaggregates from the intra and inter-POM. The isotope mixing-model approach was used to quantify the net C input from the vegetation to the soil along the entire gradient of atmospheric CO$_{2}$ concentrations.
DE: 4805 Biogeochemical cycles (1615)
DE: 1694 Instruments and techniques
DE: 1040 Isotopic composition/chemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting