Alkyl C and hydrophobicity in B and C horizons of an acid forest soil

Aliphatic C most probably derived from ester‐bound moieties was found to be present in sandy subsoil horizons. The hydrophobic nature of such compounds may increase their stabilization potential. Therefore, the aim of this study was to investigate the potential of aliphatic compounds in mineral soil horizons along a Dystric Cambisol profile under beech forest to increase hydrophobicity. The conceptual approach included the analyses of soil samples before and after solvent extraction and base hydrolysis for elemental and isotopic composition. Additionally, the advancing contact angle was measured to quantify hydrophobicity. Curie‐point pyrolysis GC/MS was carried out to characterize the nature of alkyl C present in subsoil samples. A close correlation between the 14C activity and the stable‐C‐isotope ratio (δ13C) indicates isotopic fractionation upon C stabilization in subsoils. Free lipids contributed less than 10% to the organic C found in subsoil horizons. Base hydrolysis revealed very high amounts of hydroxyalkanoic acids in the B horizons of the acid forest soil. Hydrophobicity of SOM was not found to be correlated to esterified‐ or free‐lipid content. The contact angle was in a similar range for all bulk soil horizons, suggesting greater hydrophobicity of organic matter in subsoil horizons considering their very low concentrations of organic C compared to the A horizon. The quantity and nature of pyrolysis products change with increasing depth in the soil profile. Aliphatic products cannot be detected in B and C horizons by Curie‐point pyrolysis GC/MS. Alkyl‐C und Hydrophobizität in B‐ und C‐Horizonten eines sauren Waldbodens In den Horizonten sandiger Unterböden kommt es zur Anreicherung aliphatischer Substanzen, die vermutlich estergebunden sind. Die hydrophobe Natur dieser Verbindungen könnte ihre Stabilisierung gegenüber mikrobiellem Abbau begünstigen. Das Ziel unserer Arbeiten war es, zu untersuchen, ob aliphatische Verbindungen die Hydrophobizität organischer Substanzen im Bodenprofil einer sauren Braunerde unter Buche erhöhen können. Hierzu wurde die Element‐ und Isotopenzusammensetzung von Bodenproben vor und nach Lipidextraktion sowie basischer Hydrolyse untersucht. Zusätzlich wurden Kontaktwinkelmessungen zur Quantifizierung der Hydrophobizität durchgeführt. Curie‐Punkt‐Pyrolyse‐GC/MS wurde angewandt, um die Zusammensetzung des Alkyl‐C zu charakterisieren. Eine Korrelation zwischen der 14C‐Aktivität und dem Verhältnis der stabilen C‐Isotope