INSOLUBLE ORGANIC MATTER FRACTIONS IN INCIPIENT PODZOL B HORIZONS: PRESERVATION OF ALIPHATIC BIOPOLYMERS FROM ROOTS

Organic matter in podzol B horizons is generally considered as the result of illuviation from upper ho­ rizons. This illuviatcd organic matter is thought to be largely, if not completely, extractable by sodium pyrophosphate. In incipient podzols Crom the Lcuvcnum Forest, 17-37% of the B organic matter re­ mained insoluble after extraction with NaOH. Extraction of these insoluble fractions by sodium pyro­ phosphate hardly enlarged the amounts of soluble organic matter. Combining pyrolysis, thcrmochemolysis and SEM revealed that the insoluble organic matter consisted almost completely of root rem­ nants. It appeared to be highly aliphatic, being composed of subcrin and a 'subcran-like' polymer, whereas lignin and polysaccharides were virtually absent. This suggested that the aliphatic biopolymers were (highly) selectively preserved, not transported by illuviation and that root organic matter is an important constituent in B horizons.