Characterization of a Mediterranean litter by 13C CPMAS NMR:: relationships between litter depth, enzyme activities and temperature

Organic matter mineralization of forest litter is catalysed by the action of different extracellular enzymes produced by microorganisms. Coupling enzyme activities with data on the general macromolecular structure of organic matter, provided by cross-polarization magic angle spinning C-13 nuclear magnetic resonance (C-13 CPMAS NMR), allows researchers new insights into organic matter degradation processes. In this paper, the effect of the temperature of incubation on the degradation processes was evaluated in three distinct layers (OhLn, OhLv and OhLf) of an evergreen oak litter (Quercus ilex L.), located in the Mediterranean area of south-eastern France. We studied degradation phenomena by a combination of C-13 CPMAS NMR and microbiological analysis. In order to determine the microbial activity of litter layers, three enzyme activities (laccase, cellulase and butyrate esterase) were measured in a 6-month mesocosm study. Results showed an increase in the alkyl C to O-alkyl-C ratio and an increase of the phenolic C and carboxyl C regions, indicating a preferential degradation of polysaccharides. The aromaticity also increased with litter depth and degradation, and humification processes were more elevated at 30 degrees C. ANOVA showed significant effects (P < 0.001) of increased temperature, depth and time of degradation on microbiological variables. Further information is needed about the variations in temperature and temperature-litter response and soil functions to link fundamental understanding of carbon stabilization, climate change and global C cycling.