Thermally assisted hydrolysis and methylation of organic matter in two allophanic volcanic ash soils from the Azores Islands

Thermally assisted Hydrolysis and Methylation was used to analyse in more detail the aromatic and aliphatic building blocks of the organic matter of two soil profiles from the Azores. Both Ah horizons showed significant contributions of lignin, tannins, cutin and suberin, which were virtually absent from the underlying horizons. Alkanoic acids were present throughout both soil profiles, with long-chain acids (>C₂₀) decreasing with depth in comparison with short-chain acids in EUR05, whereas having a relative minimum in AB2 and 2Bw1 horizons in EUR06. Despite the huge potential of Andosols to store carbon, the studied soils did not exhibit a great preservation potential of plant-derived molecules (lignin, cutin/suberin-derived lipids, C₂₆ alkanol) in comparison with other soils as studied by THM. By contrast, bacterial-derived branched alkanoic acids are better preserved than the plant-derived alkanoic acids, which confirms the high degree of microbial and insect-derived OM in the Andosols studied.