HR: 14:25h
AN: B53D-03    [Abstracts]
TI: Land use Effects on Storage, Stability and Structure of Organic Carbon in Soil Density Fractions Revealed by 13C Natural Abundance and CPMAS 13C NMR
AU: * Flessa, H
EM: hflessa@gwdg.de
AF: Institute of Soil Science and Forest Nutrition, University of Goettingen, Buesgenweg 2, Goettingen, 37077 Germany
AU: Helfrich, M
EM: mhelfri@gwdg.de
AF: Institute of Soil Science and Forest Nutrition, University of Goettingen, Buesgenweg 2, Goettingen, 37077 Germany
AU: John, B
EM: bjohn@gwdg.de
AF: Institute of Soil Science and Forest Nutrition, University of Goettingen, Buesgenweg 2, Goettingen, 37077 Germany
AU: Yamashita, T
EM: tamonyam@life.shimane-u.ac.jp
AF: Education and Research Centre for Biological Resources, Shimane University, Matsue, 690-8504 Japan
AU: Ludwig, B
EM: bludwig@uni-kassel.de
AF: Department of Environmental Chemistry, University of Kassel, Nordbahnhofstr. 1a, Witzenhausen, 37213 Germany
AB: The type of land use and soil cultivation are important factors controlling organic carbon storage (SOC) in soils and they can also influence the relative importance, the structure, and the stability of different SOC pools. The objectives of our study were: i) to quantify the SOC stocks in different density fractions (mineral-associated soil organic matter $>$ 2 g cm-3 (Mineral-SOM), free particulate organic matter $<$ 1.6 g cm-3 (free POM), light occluded particulate organic matter $<$ 1.6 g cm-3 (occluded POM$<$1.6) and dense occluded particulate organic matter 1.6 to 2.0 g cm-3 (occluded POM1.6-2.0)) of silty soils under different land use (spruce forest, grassland, maize, wheat), ii) to determine the structure of these SOC fractions by CPMAS 13C NMR spectroscopy, and iii) to analyse the stability of these SOC fractions in the maize soil on the basis of the stable isotope composition of SOC. The SOC concentration in the A horizon increased in the order wheat (12.7 g kg-1) $<$ maize (13.0 g kg-1) $<$ grassland (24.5 g kg-1) $<$ spruce (40.5 g kg-1). The major part (86-91%) of the SOC was associated with the heavy mineral fraction at the grassland, maize and wheat site. In the A horizon of the spruce soil, the particulate organic matter accounted for 52% of the total SOC content. The chemical structure of the soil organic matter (SOM) was influenced by litter quality, the intensity of litter decomposition and the related production and storage of microbially-derived substances. SOM of the acid forest soil was characterized by large amounts of POM with a high content of spruce litter-derived alkyl C. In the biologically more active grassland and maize soil, litter-derived POM was decomposed more rapidly and SOC stocks were dominated by mineral-associated SOM which contained greater proportions of aryl and carbonyl C. The cultivation of the grassland soil induced enhanced mineralization of POM and in particular of mineral-associated SOM. The faster SOC turnover was associated with a relative accumulation of aromatic and carbonyl C structures in the mineral-bound SOM. In all soils, the free particulate organic matter had a smaller proportion of alkyl C and a larger proportion of O-alkyl C than the particulate organic matter occluded in aggregates. The mean age of the SOM in the density fractions of the maize soil increased with increasing aromaticity in the order free POM (22 yr) $<$ occluded POM1.6-2.0 (49 yr) $<$ mineral-associated SOM (63 yr). The results showed that the type of land use influenced the distribution pattern of litter carbon to functionally different SOM pools which represented different stages of SOM decomposition and humification. Additionally, the type of land use influenced the chemical structure of SOM in soil density fractions. Thus, the effect of land use on SOM storage should not only be assessed in terms of total C stocks but also with respect to changes of SOC structure, stability and function.
DE: 1040 Isotopic composition/chemistry
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting