Characterization and decomposition of Nothofagus pumilio fine woody material

Wood is one of the main reservoirs of carbon (C) and nutrients in Nothofagus pumilio (Poepp. & Endl.) Krasser forests; hence, its decomposition is essential for C and nutrient cycling. Chemical traits are one of the factors affecting wood decomposition, but there is little information describing these chemical characteristics. Our objective was to analyze the chemical traits of N. pumilio fine woody material (FWM) and their relationships with decomposition. We determined the contents of nitrogen (N), phosphorus (P), C, hemicellulose, cellulose, lignin, and extractives in two diameter categories (branches and twigs) and in two decay classes (DC1, sound wood; DC2, intermediate stage of decomposition). We also determined the decomposition rate constant (k) of each type of material. Contents of P, extractives, C, and hemicellulose in DC1 and C, cellulose, and lignin in DC2 showed differences between diameters. In twigs, all chemical traits showed differences between DCs, but in branches, only N and C showed differences. Mean k was similar between diameters and was greater in DC2 than in DC1. Hemicellulose and P showed positive relations with increasing decomposition, whereas cellulose showed a negative one. Our results support the use of classical DCs. We hypothesize that the presence (or absence) and proportional amount of bark partially explain the differences found between DCs and between diameters.