Organic geochemical studies of soils from the Rothamsted classical experiments — VI. The occurrence and source of organic acids in an experimental grassland soil

Total lipid extracts (TLEs) of grass (aerial and sub-aerial, Holcus lanatus) from a plot on a long-term grassland experiment, and associated soil, along with the organic fraction of the TLE hydrolysates and the hydrolysates of the solvent extracted vegetation have been separated into fractions containing specific compound classes and analysed using gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The distributions of n-alkylcarboxylic acids, ω-hydroxycarboxylic acids and dicarboxylic acids in the grass and the underlying soil have been determined. Short-chain (<C20) n-alkylcarboxylic acids were designated as having derived from both aerial and sub-aerial vegetation. However, longer-chain n-alkylcarboxylic acids were ascribed to suberin as a predominant source. Moreover, ω-hydroxycarboxylic acids and dicarboxylic acids observed in the soil were designated as having predominantly derived from inputs of free, extractable polyesters and suberin intimately associated with plant roots. This study indicates the importance of root material as a predominant source of aliphatic, organic acids in the soil of temperate grassland biomes.