Lipid Components of Soils: A Review

Lipid components are a large heterogeneous group of hydrophobic organic compounds extracted from soils by low-polarity organic solvents. The composition of lipid fraction varies from complex esterified structures, such as phospholipids, glycolipids, and sphingolipids, to simpler molecules, such as aliphatic carboxylic acids, alcohols, aldehydes, and ketones. The inherent chemical stability of most lipid components limits the rate of decomposition of soil organic matter, ensuring its stability primarily through the incorporation of lipids into the mineral matrix of soils. The specific features in biosynthesis and structure of lipids provide information about the origin and evolution of soil organic matter and allow us to evaluate agricultural management practices and the degree of anthropogenic impact on ecosystems. Fatty acids, which are part of phospholipid components, are widely used to characterize various soil microbial communities. This review briefs the characteristics of the main lipid components of soil and analyzes the use of these compounds as biomarkers of soil microbiota; various calculated indices are applied to diagnose the origin and transformation of lipid components. The review also focuses on the state-of-the-art methodological approaches for quantification of lipid components in soil, including a series of sequential steps—extraction, fractionation, chemical modification, and chromatographic analysis.