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Effects of NH₄ ⁺ and NO₃ ⁻ on litter and soil organic carbon decomposition in a Chinese fir plantation forest in South China

Zhang, Weidong, Wang, Silong
Soil biology & biochemistry 2012 v.47 pp. 116-122
Alnus, Cunninghamia lanceolata, adverse effects, carbon dioxide, carbon nitrogen ratio, forest plantations, forest soils, nutrient availability, plant litter, soil fertility, soil organic carbon, soil treatment, China
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 100mg NH₄ ⁺ 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 ¹³C–CO₂, 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 (235d). The PE dynamics showed that positive PE can last for at least 87d. However, the possible occurrence of a significant negative PE with a sufficient incubation period is difficult to confirm. The application of both NH₄ ⁺ and NO₃ ⁻ was found to have a stimulating effect on the decomposition of Chinese fir and alder leaf litter in the early stage (0–15d) of incubation, but an adverse effect in the late stage. Compared with NO₃ ⁻, NH₄ ⁺ caused a greater decrease in the PE induced by both Chinese fir and alder leaf litter. The effects of NH₄ ⁺ 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.