Chemical change in organic matter decomposing in and on a forest Rendzina under beech (Fagus sylvatica L.)



The chemical characteristics of the organic matter of five horizons from a Terra fusca Rendzina under beech were compared by fractionation. Two litter layers, sampled in autumn, were compared: fresh leaf litter and the remains of the previous years’ litter. Three mineral horizons, A, B and C were also sampled.

While decomposition in the litter layer led only to slight redistribution of the fractions, much greater changes occurred when the organic matter became incorporated into the mineral soil. The proportion of C and N in amino sugars rose markedly down the profile. The percentage of more readily soluble substances, such as the hot water-soluble fraction or the unidentified, hydrolysable component, in the mineral soil was twice the amount found in the leaf litter. The percentage of non-hydrolysable compounds in the mineral horizons was nearly half that found in the leaf litter. The C/N ratio fell from 44 in fresh leaf litter to 10 in the C horizon. The amino acid C/amino sugar C ratio fell from 45 in fresh leaf litter to 3.0 in the B horizon. The glucosamine/galactosamine ratio fell from infinite in galactosamine-free fresh leaf litter to 1.2 in residual litter and increased again to 2.5 in the C horizon. The hexose/pentose ratios were virtually the same in all horizons. The glucose/ mannose ratio showed a steady fall down the profile, from 7.7 to 1.6. The glucuronic/ galacturonic acid ratio increased from 0.1 and 0.2 in the two litter layers to 4.7 in the C horizon.