Decomposition of mediterranean leaf litters: A microcosm experiment investigating relationships between decomposition rates and litter quality

The decomposition of four mediterranean species leaf litter (Sessile oak, Quercus petraea L.; Helm oak, Quercus ilex L.; Sweet chestnut, Castanea sativa Mill and beech, Fagus sylvatica L.) was studied for 90 days under controlled conditions. Respiration and litter mass loss were measured in three types of microcosms: (1) Soil only; (2) Soil + 1-y old litter and (3) Soil + 1-y old litter + newly senescent litter (freshly fallen). Variations in chemical composition of the litters were determined before and after incubation by the pyroanalysis method. For newly senescent litters decomposition rates per day K-co2 (calculated from CO2 release) and K-w (calculated from mass losses) fitted to the first order exponential decay decreased as follows: sessile oak (K-co2 = 0.0043; K-w = 0.0049) > holm oak (K-co2 = 0.0031; K-w = 0.0040) = beech (K-co2 = 0.0030; K-w = 0.0030) > sweet chestnut (K-co2 = 0.0001; K-w = non-significant regression); For 1-y old litters sweet chestnut (K-co2 = 0.0040; K-w = 0.0065) > sessile oak (K-co2 = 0.0035; K-w = 0.0039) > beech (K-co2 = 0.0030; K-w = non-significant regression). All litters showed a reduction of lipid (mean loss 90.5%), hydrosoluble (mean loss, 54.2%), hemicellulose plus cellulose (mean loss, 40.6%) content and a relative increase of lignin content (mean gain, 34.4%). Among indicators of litter quality (C-to-N ratio, %N, %lignin, lignin-to-N ratio, HLQ), only some of them were correlated with litter decay. The best relationships were established between the decomposition rates (K-w) and parameters integrating lignin contents (r = 0.997; n = 3; P < 0.01). The decomposition of 1-y old litters fitted well with most of these parameters (0.999 < r < 0.997; n = 3; P < 0.01) in contrast to newly senescent litters. Copyright (C) 1996 Elsevier Science Ltd