Chemical composition and carbon mineralisation potential of Scots pine needles at different stages of decomposition

Chemical changes in decomposing Scots pine needles exposed for 22 months in litter bags in central France forest were determined using near infrared reflectance spectroscopy (NIRS). Concentrations of N, P, cellulose, lignin, lignin-C and lignin-N content were related to accumulated mass loss. Litters from the litter bags exposed for 2, 4, 8, 12 and 16 months in situ were incubated for 1 additional year in the laboratory under controlled conditions, and CO2 release was measured (carbon mineralisation potential). Asymptotic and exponential functions were fitted to these data and defined respirometric fractions with low, intermediate and high decomposition rates. In addition, litter (L), fermentation (F) and humus (H) layers from the site were incubated in the laboratory under the same conditions. The correspondence analysis, using the parameters of the asymptotic functions as variables, showed that the carbon mineralisation potential of the naturally-decomposing litter collected at the site was similar to the mineralisation potential of the material in the litter exposed in bags for about 1 yr in the field. Nevertheless the decomposition rates observed under laboratory conditions should be interpreted with caution since they were considerably lower than the decomposition rates of the same litter exposed in situ.