HR: 1340h
AN: B23D-1598    [Abstracts]
TI: Spatial Variability of the Stocks of Different Organic Carbon Fractions in a Leptic Cambisol under Norway Spruce
AU: * Spielvogel, S
EM: spielvogel@wzw.tum.de
AF: Lehrstuhl fuer Bodenkunde TUM, Am Hochanger 2, Freising, 85354, Germany
AU: Prietzel, J
EM: prietzel@wzw.tum.de
AU: Koegel-Knabner, I
EM: koegel@wzw.tum.de
AB: Soil organic carbon (OC) stocks of forest soils are known to be characterized by large small scale variability. The variability of different OC fractions (HF-soluble OC fraction, representing mineral associated OC; HF-resistant OC fraction, representing the non-mineral associated OC) is largely unknown. The same is true for their relation to site specific factors (e.g. bulk density, pH, content of oxalate extractable iron and aluminum oxides). We studied a dystric, laxic Leptic Cambisol site (0.09 ha) stocked with Norway spruce in the Nationalpark Bayerischer Wald, Germany. Soil samples from the Ah and the Bw1 horizon were taken at the knots of a rectangular grid with distances of 5 m. Small scale variability was determined using a nested sampling scheme with a minimum horizontal sampling distance of 0.2 m. Mineral associated and non-mineral associated OC stocks in the soil were characterized by ordinary statistics and geostatistics. In order to examine spatial relations between OC stocks and site specific factors, experimental crossvariograms were calculated. Additionally, we compared the spatial variability of different OC species of the HF-soluble and non-soluble fraction as determined by 13C CPMAS NMR spectroscopy with and without prior HF-treatment. Comparison of the HF-soluble and the non-soluble OC stocks showed that only the HF-soluble OC stock exhibited a spatial pattern. In contrast, the non-soluble OC stocks were characterized by a pure nugget effect. HF- soluble OC stocks were significantly negatively spatially correlated with the pH, but positively correlated with the amount of oxalate extractable iron and aluminum oxides in both horizons. In contrast, bulk density showed a significant spatial correlation with the HF-soluble OC stock only in the subsoil. Comparison of the spatial variability of different HF-soluble OC species showed an increasing spatial variability in the order aryl C < carboxyl C < alkyl C < O/N-alkyl C. Our results indicate that the spatial variability of OC stocks is mainly due to the spatial variability of the HF-soluble, i.e. mineral-associated OC. HF-soluble OC stocks consequently increase with increasing amounts of oxalate extractable iron and aluminum oxides and with decreasing pH. This is due to an increasing sorption capacity of these oxides at lower pH. Different spatial distribution patterns of different OC species indicate specific stabilization mechanisms for the respective species.
DE: 0428 Carbon cycling (4806)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting