Decomposition of sun and shade leaves from three deciduous tree species, as affected by their chemical composition

Abstract

Freshly fallen leaf litter from sweet chestnut (Castanea sativa Mill), oak (Quercus robur L.) and beech (Fagus sylvatica L.) trees were classified into sun, intermediate and shade leaf types and analysed for N, acid detergent fibre, holocellulose, and lignin. In addition, the sugar constituents of structural polysaccharides (mainly from hemicelluloses) were determined after trifluoracetic acid (TFA) hydrolysis, and the phenylpropanoid (PPD) derivatives of lignin after alkaline CuO oxidation. The litters were decomposed in laboratory microcosms for 2 years. Decomposition rates were initially rapid and then plateaued, but differences in mass losses for the leaf litter categories, and between the three species, were significant at 6, 12, 18 and 24 months. Mean mass losses after 24 months were 49.6% for chestnut, 40.4% for oak and 26.3% for beech. Mean losses for chestnut, oak and beech litter categories were 48.6%, 38.2% and 24.6%, respectively, for sun leaves, and 51.0%, 44.5% and 28.5%, respectively, for shade leaves. Initial lignin concentrations showed a negative correlation with mass losses over the first 6 months but initial acid detergent fibre was a better predictor of decomposition rates after 24 months. Within species, however, total extractable sugars and PPD concentrations reflected differences in decomposition rates between the different categories of leaf types. The analysis for specific carbohydrates and lignin derivatives improved the resolution of litter quality characterisation but did not explain the observed patterns of decomposition in long-term laboratory incubations. It is suggested that these may be affected by influence of the culture conditions on the composition of fungal communities.