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Soil organic carbon (SOC) dynamics and nutrient availability determine the soil quality and fertility in a Chinese fir plantation forest in subtropical China. Uniformly 13C-labeled Chinese fir (Cunninghamia lanceolata) and alder (Alnus cremastogyne) leaf litter with or without 100 mg NH4þ or NO3 were added to the soil. The purpose was to investigate the influence of N availability on the decomposition of the litter and native SOC. The production of CO2, the natural abundance of 13CeCO2, and the inorganic N dynamics were monitored. The results showed that Chinese fir (with a high C:N ratio) and alder (with a low C:N ratio) leaf litter caused significant positive priming effects (PEs) of 24% and 42%, respectively, at the end of the experiment (235 d). The PE dynamics showed that positive PE can last for at least 87 d. However, the possible occurrence of a significant negative PE with a sufficient incubation period is difficult to confirm. The application of both NH4þ and NO3 was found to have a stimulating effect on the decomposition of Chinese fir and alder leaf litter in the early stage (0e15 d) of incubation, but an adverse effect in the late stage. Compared with NO3, NH4þ caused a greater decrease in the PE induced by both Chinese fir and alder leaf litter. The effects of NH4þ and NO3 on the PE dynamics had different patterns for different incubation stages. This result may indicate that the stability or recalcitrance of SOC, especially in such plantation forest soils, strongly depends on available leaf litter and application of N to the soil.

Key words: Inorganic N;13C-labeled litter;Priming effect;Chinese fir;Soil organic carbon