M. v. Lützow a, I. Kögel-Knabner a, K. Ekschmitt b, E. Matzner c, G. Guggenberger d, B. Marschner e & H. Flessa f a TUM, Lehrstuhl für Bodenkunde, WZW, Department für Ökologie, TU München b IFZ – Tierökologie, Justus Liebig Universität, Gießen c Lehrstuhl für Bodenökologie, Universität Bayreuth d Institut für Bodenkunde und Pflanzenernährung, Universität Halle e Geographisches Institut, Ruhr-Universität, Bochum f Institut für Bodenkunde und Waldernährung, Universität Göttingen Mechanisms for organic matter stabilization in soils Schwerpunktprogramm der Deutschen Forschungsgemeinschaft SPP 1090 Böden als Quelle und Senke für CO 2 – Mechanismen und Regulation der Stabilisierung organischer Substanz in Böden Relevance of mechanisms relevant?, B-horizon podzol soils under vegetation fires, soils with deposition of combusted particles and coal dust loamy and clay rich surface soils acid soils, little evidence more likely in top-soils more likely in sub-soils loamy and clay rich surface soils biologically active soils Differentiation & fractionation of the passive SOM pool. Characterization of soil OM fractions by their pool size and turnover times. Differentiation between simultaneously acting mechanisms requires special methodologies. Examination of key stabilization mechanisms in different horizons along whole soil profiles. Use of biomarkers and compound- specific stable isotope analyses to show soil internal turnover processes Figure: Conceptual model of organic matter (OM) stabilization. Italic: Mechanisms; 3 process groups of mechanisms according to Sollins et al. (1996) a : primary and secondary recalcitrance, spatial inaccessibility, organo-mineral interactions. Pools within broken lines indicate postulated pools but their existence is not verified by direct measurements. DOM = dissolved organic matter. forest floor, A-horizons, biologically active soils * v. Lützow, M., I. Kögel-Knabner, K. Ekschmitt, E. Matzner, G. Guggenberger, B. Marschner, and H. Flessa The relevance of different mechanisms for organic matter stabilization in temperate soils. Eur. J. Soil Sci. submitted. ** v. Lützow, M., I. Kögel-Knabner, K. Ekschmitt, E. Matzner, G. Guggenberger, B. Marschner, and H. Flessa Relation of soil organic matter fractions to functional pools of different turnover and to stabilization mechanisms. To be submitted Soil Biol. Biochem. Selective preservation of recalcitrant organic matter & biogenic aggregation are only important during early decomposition and in active surface soils. Recalcitrance can not explain long-term SOM stabilization. Spatial inaccessibility & organo-mineral interactions operate at long-term scales and dominate in sub-soils Some postulated stabilization mechanisms that characterize the formation of the passive pool are not or only weakly supported by data (intercalation, polymerization, encapsulation). Several mechanisms may act simultaneously e.g:aggregation: recalcitrance + spatial inaccessibility hydrophobicity: recalcitrance + spatial inaccessibility charcoal: recalcitrance + organo-mineral interactions + hydrophobicity plant residues & exudates A C T I V E P O O L yr faunal & microbial residues protected microbial biomass decomposed residues I N T E R M E D I A T E P O O L yr Transport of DOM & colloids OM in clay microstructures charcoal P A S S I V E P O O L > 100 yr microbial / faunal biomass & residues G O A L S Estimation of time scales of stabilization mechanisms in relation to conceptional pools Identification of key stabilization mechanisms in different soil types and soil horizons R E S U L T S *** Interactions with mineral surfaces Production of charcoal by fire intercalated OM humic polymers pseudo-macromolecules organo-mineral associations Selective preservation and resynthesis Biogenic aggregation organo-mineral associations acid and calcareous soils heavy metal contaminated soils Complexation with Fe 3+, Al 3+, Ca 2+ occluded particulate OM acid soils, top-soils, forest floor Formation of hydrophobic surfaces Polymerisation Intercalation Abiotic microaggregation Encapsulation P E R S P E C T I V E a Sollins, P., Homann, P. & Caldwell, B.A Stabilisation and destabilisation of soil organic matter: mechanisms and controls. Geoderma: