Lipids of soil humic acids. I. The hymatomelanic acid fraction

Abstract

Gas chromatography and gas chromatography-mass spectrometry have been used for the analysis of the hymatomelanic acids of four soil samples (a Typic Xerorthent, a Typic Rendoll and two Typic Xerochrepts, on shale and on granite) encompassing a wide diversity of properties in terms of pH, organic carbon, nitrogen content and associated vegetation. These humic fractions are largely composed of distributions of C12-C34 fatty acids where microbial and higher plant contributions may be observed. Mixtures of C27-C29 stera-3,5-dien-7-ones are also present, representing microbial oxidation products of Δ2-sterols. Despite the wide diversity of soils considered no major qualitative differences have been observed. In all cases the corresponding hymatomelanic acids are composed of a rather uniform pattern of aerobic microbial components together with higher plant lipids.