Total lipid extracts from characteristic soil horizons in a podzol profile

Abstract

The podzolization process is studied through lipids in nine characteristic podzol horizons. Organic matter accumulates particularly with aluminium in the Bh horizon, while the hard, cemented Bs horizon below this is formedma inly by iron oxides. The low soil pH seems to have no great influence on the preservation of lipids as reflected by the absolute amounts present and the presence of bacterial lipid markers throughout the profile. Independent of soil pH, lipids accumulate in organically enriched horizons. Albeit, high molecular weight organic compounds accumulate to a relatively greater extent than lipids in these horizons. A lipidsi gnal relatedto the aerial parts, i.e. leaves andfl owers, of Calluna is observedo nly in the O horizon. This ‘n-alkane, steroida nd triterpenoids’ signal is quickly lost in the underlying Ah horizon due to (bacterial) oxidation. The other total lipid extracts obtaineda re dominated by root-derivedco mpounds. In subsoil horizons rich in organic matter, i.e. the Ahb andB h horizons, root-derived friedooleanan and steroidc ompounds dominate the total lipid signal. Degradedho rizons, poor in organic matter, i.e. the E2, Bhs, Bs andB/ C horizons, are dominated by C22 andC 24 o-hydroxy acids, long-chain (>C20) n-alkanoic acids with a strong even-over-oddp redominance andC 22 andC 24 n-alkanols. Steroida ndro ot-derived triterpenoids with a friedooleanan structure have been removed from these horizons through degradation. Basedo n total organic carbon content and lipidc omposition, the formation of an E1 horizon has started, but is not yet complete. In the Ahb horizon, a contribution from buriedve getation to the total lipidsi gnal is still present, although degradation and an input from roots have significantly altered the original signal. Overall, lipid data indicate that degradation (microbial oxidation) is an important process that should be taken into account, in addition to leaching, when describing podzolization processes in soils.