Organic matter of subsoil horizons under broadleaved forest: Highly processed or labile and plant-derived?

► We evaluate NaOH-extractable subsoil-C in broadleaved forests by pyrolysis-GC/MS. ► All sites show a significant shift in composition from topsoil-C to subsoil-C. ► Subsoil-C shows high relative amounts of aliphatics or polysaccharides. ► Lignins or aromatics are not major contributors to NaOH-extractable subsoil-C. ► Plant-derived labile long-chain aliphatics and anhydrosugars are present in subsoil-C.