Mechanisms for organic matter stabilization in soils

1. 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 Schwerpunktprogramm der Deutschen Forschungsgemeinschaft SPP 1090Böden als Quelle und Senke für CO2 – Mechanismen und Regulation der Stabilisierung organischer Substanz in Böden Mechanisms for organic matter stabilization in soils M. v. Lützowa, I. Kögel-Knabnera, K. Ekschmittb, E. Matznerc, G. Guggenbergerd, B. Marschnere & H. Flessaf a TUM, Lehrstuhl für Bodenkunde, WZW, Department für Ökologie, TU München bIFZ – Tierökologie, Justus Liebig Universität, Gießen c Lehrstuhl für Bodenökologie, Universität Bayreuth dInstitut für Bodenkunde und Pflanzenernährung, Universität Halle e Geographisches Institut, Ruhr-Universität, Bochum fInstitut für Bodenkunde und Waldernährung, Universität Göttingen Relevance of mechanisms A C T I V E P O O L 1 - 10 yr forest floor, A-horizons,biologically active soils plant residues &exudates Selective preservation and resynthesis microbial / faunal biomass & residues I N T E R M E D I A T E P O O L 10 - 100 yr loamy and clay rich surface soils biologically active soils decomposed residues Biogenic aggregation protected microbial biomass occluded particulate OM acid and calcareous soils heavy metal contaminated soils Complexation with Fe3+, Al3+, Ca2+ faunal & microbial residues organo-mineral associations P A S S I V E P O O L > 100 yr soils under vegetation fires, soils with deposition of combusted particles and coal dust Production of charcoal by fire charcoal relevant?, B-horizon podzol Polymerisation humic polymers acid soils, top-soils, forest floor Formation of hydrophobic surfaces more likely in top-soils pseudo-macromolecules Encapsulation Transport of DOM & colloids acid soils, little evidence intercalated OM Intercalation loamy and clay rich surface soils OM in clay microstructures Abiotic microaggregation Interactions with mineral surfaces more likely in sub-soils organo-mineral associations 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. * ** R E S U L T S P E R S P E C T I V E • 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 simultaneouslye.g: aggregation: recalcitrance + spatial inaccessibility hydrophobicity: recalcitrance + spatial inaccessibility charcoal: recalcitrance + organo-mineral interactions + hydrophobicity • 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 * v. Lützow, M., I. Kögel-Knabner, K. Ekschmitt, E. Matzner, G. Guggenberger, B. Marschner, and H. Flessa. 2006. 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. 2006. Relation of soil organic matter fractions to functional pools of different turnover and to stabilization mechanisms. To be submitted Soil Biol. Biochem. a Sollins, P., Homann, P. & Caldwell, B.A. 1996. Stabilisation and destabilisation of soil organic matter: mechanisms and controls. Geoderma:65-105.