Abstract: The decomposition and nutrition release of the dead canopy leaves and branches are critical for the nutrient cycling in Chinese fir (Cunninghamia lanceolata) because they can cling to stems for several years and are of large biomass. In this paper, we estimated the decomposition degree of these dead leaves in the canopy of different heights in a 17yearold C. lanceolata plantation by determining the leaf mass per area. We also measured carbon (C)/nitrogen (N) ratio, C and N isotope compositions and chemical compositions of the dead leaves. The results showed that the leaf mass per area of the dead leaves at the lower canopy was lower. The leaf mass per area of the dead leaves in 8-10 m (26.02 mg·cm^-2) was much higher than the leaves that just died (23.12 mg·cm^-2) and the leaves in 6-8 m (15.39 mg·cm^-2). However, there was no significant difference in the leaf mass per area of dead leaves at 0-2, 2-4, or 4-6 m. C and N concentrations in the recently dead leaves were significantly lower than in the dead leaves clinging to branches of different heights. No significant differences in C and N concentrations and in C/N ratio were found between the dead leaves clinging at different heights of canopy. The C/N ratio (67.58) in the recently dead leaves was significantly higher than that in the dead leaves clinging to the branches of different heights. When the C/N ratio in the dead leaves clinging to the branches reached 45.91±0.45, the nitrogen started to release. The values of δ¹⁵N of the recently dead leaves and the dead leaves clinging at canopy of 8-10 m height were greater than in that of the dead leaves clinging at canopy of other heights. However, no difference was found for the dead leaves clinging at the canopy of 0-2, 2-4, 4-6, and 6-8 m. The values of δ¹³C in dead leaves clinging at the canopy of different heights were not significantly different. Moreover, we demonstrated that polysaccharide C and aldehyde acetal C in the dead leaves clinging at the canopy decomposed firstly and then followed by alkyl C, aromatic C, phenol and carboxyl C.

Key words: photosynthesis, physiological integration, Zoysia japonica, nutrient heterogeneity