Decomposition of Different Litter Fractions in a Subtropical Bamboo Ecosystem as Affected by Experimental Nitrogen Deposition

As an important component of the global carbon (C) budget, litter decomposition in terrestrial ecosystems is greatly affected by the increasing nitrogen (N) deposition observed globally. We hypothesized that different, litter fractions derived from a single tree species may respond to N deposition differently depending on the quality of the litter substrate. To test the hypothesis, a two-year field experiment was conducted using the litterbag method in a Pleioblastus amarus plantation in the rainy region of Southwest China. Four N treatment levels were applied: control (no N added), low-N (50 kg N ha(-1) year(-1)), medium-N (150 kg N ha(-1) year(-1)), and high-N (300 kg N ha(-1) year(-1)). We observed different patterns of mass loss for the three P. arnarus litter fractions (leaves, sheaths, and twigs) of varying substrate quality in the control plots. There were two decomposition stages with different decay rates (fast rate in early stages and slow rate in the later stages) for leaves and sheaths, while we did not observe a slower phase for the decay of twigs during the 2-year study period. The annual decompoition rate (k) of twigs was significantly lower than that of leaves or sheaths. Addition of N slowed the decomposition of leaves and twigs in the later stages of decomposition by inhibiting the decay of lignin and cellulose, while addition of N did not affect the mass loss of sheaths during the study period. In the decomposition of all three litter fractions, experimental N deposition reduced the net N accumulation in the early stages and also decreased the net N release in the later stages. The results of this study suggest that litter substrate quality may be an important factor affecting litter decomposition in a bamboo ecosystem affected by N deposition.