Chemical composition of decomposing stumps in successive rotation of Chinese fir (Cunninghamia lance

Decomposition of stumps in successive rotation of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations was studied using a chronosequence approach. The results showed that decomposition rate constant of Chinese fir stump was 0.02695 as calculated from Olson's model. The N content of stump increased during the first two-year decomposition. When the dead stump C/N ratio was 463.2 ± 27.3, the stumps started to release N. The pattern of P release was similar to that for N. However, K content of stumps showed a consistent declining trend over time during the whole decomposition. 13C nuclear magnetic resonance spectroscopy with cross polarization and magic-angle spinning (13C CPMAS-NMR) was used to analyse organic carbon (C) components in decomposing stumps. The 13C CPMAS-NMR spectra of stumps displayed that stump was dominated by cellulose and hemicellulose. The spectra also showed the accumulation of intensity in alkyl C, aromatic C, and carboxyl C spectral regions, which was expected as the labile cellulose and hemicellulose components in O-alkyl C spectral region were selectively decomposed first.