INITIAL LITTER PROPERTIES AND DECAY-RATE - A MICROCOSM EXPERIMENT ON MEDITERRANEAN SPECIES

Twelve leaf litters belonging to 10 Mediterranean species of coniferou s and broad-leaved trees and shrubs and grass species were incubated i n microcosms in the laboratory at 22 degrees C and constant humidity f or 14 months. Samples were collected at 0.5, 1, 2, 4, 6, 10, and 14 mo nths, the remaining dry weight being measured at each sampling time. A t the end of 14 months, the litters had lost between 52 and 74% of the ir original mass. The comparison of regressions fitted to the various functions showed that for the species studied, the litter mass loss in relation to incubation time best fitted a double-exponential decay fu nction. The mass loss therefore resulted from the simultaneous decompo sition of two main compartments, a labile compartment that decreased r apidly (half-life of 20-60 days under the experimental conditions) and a resistant compartment that depending on the species, either did not decrease significantly or decreased 10 to 20 times slower than the la bile compartment (half-life of 320-630 days). The litters studied coul d be categorized according to the relative importance of these two com partments. This was related to the initial content of water-soluble su bstances and of carbon in the litters. It was also strongly correlated with the spectral information of the initial litters obtained by near -infrared reflectance spectroscopy. In contrast, the rate at which the labile and resistant compartments decreased was related to the permea bility of the leaves for the former and to their thickness and mass pe r surface area for the latter. Near-infrared reflectance spectroscopy provides new perspectives for characterizing the capacity of litters t o decompose.