Wednesday, November 15, 2006 - 8:45 AM

Dynamics of Lipids in Soils.

Guido L.B. Wiesenberg1, Michael Schmidt2, Jan Schwarzbauer3, and Lorenz Schwark1. (1) Univ. of Cologne, Dept. for Geology and Mineralogy, Zuelpicher Str. 49a, Koeln, 50674, Germany, (2) SWITZERLAND,Zurich Univ., Univ. Zurich Dept. of Geography, Winterthurerstr. 190, Zurich, 8057, SWITZERLAND, (3) RWTH Aachen Univ., Institute of Geology and Geochemistry of Petroleum and Coal, Lochnerstr. 4-20, Aachen, 52056, Germany

It is well established that lipids constitute a major part of the organic components of fresh plant materials and soils (Gregorich et al., 1996). They play an important role in the incorporation of plant material into soil organic matter (SOM) (Koegel-Knabner, 2002) and contain several diagnostic markers for source apportionment and turnover rate determinations. In contrast to macromolecular SOM-fractions, lipids are suitable for detailed structural and compound-specific δ13C-isotope characterization. In addition to the standard approach for assessment of SOM turnover rates using natural isotopic labelling after monoculture crop switching (e.g. from a C3- to a C4-crop), carbon enrichment experiments (FACE) facilitate turnover estimations of bulk SOC and organic substances as a result of labelling with 13C-depleted CO2. Source apportionment of soil lipids is a prerequisite for interpreting those dynamics, because soil lipids can be derived from numerous sources like bacteria, fungi, algae, plants and others (Dinel et al., 1990). Traditionally, lipids were regarded as a stable SOM-fraction with a high residence time (Bol et al., 1996), although this was only shown for peaty soils. Contrastingly, recent studies on lipids in arable soils demonstrate a faster turnover in the range of decades (Wiesenberg et al., 2004). Plant derived lipids including long-chain alkanes and long-chain carboxylic acids comprise a major part of soil lipids and are thus suitable for detailed lipid dynamic studies. For long-chain carboxylic acids, we introduced the carboxylic acid ratio (CAR), which allows for a differentiation between C3- and C4-crop lipids in plant biomass and to estimate the proportions of C3- and C4-plant derived carbon in soils on a molecular level. New molecular biogeochemical results on arable soils and FACE experiments support the hypothesis of rapid lipid turnover within several decades. However, turnover of lipids is a highly heterogeneous process, controlled by accessibility and degradability.