Abstract
The litter decomposition process is generally studied through the measurement of lignin and cellulose, both strongly involved in the process. The determination of these two components, and in particular of lignin, presents some limits because, of the several methods available, not one would be considered a standard unambiguous method. Thermal analysis has been successfully applied to organic materials from different origin since this technique simultaneously gives qualitative and quantitative information of the main classes of organic compounds in the sample. In the present study thermal analysis (TG-DTA) was used to follow a short-term litter decomposition study of two broadleaf forests of different ages, together with NMR spectroscopy that helped to highlight the main changes in chemical composition of the degrading litters. The results of thermal analysis were also compared to those obtained with a wet chemical method (Klason method) normally used in the determination of cellulose and lignin. TG-DTA was applied: (i) to the cell walls (CW) extracted from the litter on which the determination of cellulose and lignin using the Klason method was carried out; and (ii) to the untreated litter. A good correlation between cellulose and lignin determined with thermal analysis and wet chemical method, was found, however, TG-DTA highlighted evident changes of CW structure compared to that of the untreated litters due to the extraction procedure, that removed the most thermally resistant C compounds such as waxes and cuticles as supported by NMR data. Since these compounds increased in the litters during the decomposition, they could influence the process in later stages. Moreover, a recently proposed concept of quality of decomposing litter, based on the balance between the energy stored in the organic substrate and the energy needed to release it, obtained by DTA data, was applied. The energetic balance calculated for the CW showed, at the end of the decomposing period, a decrease in quality for both forests while the same parameter calculated for the whole litters, whose complex structure is made by intimate connections and linkages among several components, highlighted that in the studied period the quality does not change.