近日，国际土壤学刊物Soil Biology and Biochemistry在线刊登了中科院沈阳应用生态研究所研究人员的最新研究成果“Effects of NH4+ and NO3− on litter and soil organic carbon decomposition in a Chinese fir plantation forest in South China”，文章中，研究人员揭示了在氮素对凋落物和土壤有机碳的影响研究中取得的最新进展。
凋落物和土壤有机碳是人工林土壤养分的主要来源，其分解过程对维持杉木人工林土壤质量及肥力具有重要意义。氮素是影响凋落物及土壤有机碳分解速率的重要控制因素，以往研究多将凋落物和土壤分开考虑，而凋落物和土壤是一个不可分割的完整系统，这个系统如何对氮素改变做出响应仍知之甚少。
中国科学院沈阳应用生态研究所张伟东博士采用13C稳定同位素技术，对杉木凋落物-土壤系统分解开展了相关研究。结果发现，杉木凋落物诱导的激发效应至少可以维持87天，且激发效应随着培养时间的延长而呈下降趋势。无机氮在培养前期促进凋落物分解并诱导更强的正激发效应，在培养后期则对凋落物分解具有抑制作用，并诱导出显著的负激发效应。
研究还发现，铵态氮和硝态氮对杉木凋落物和土壤有机碳分解影响的程度不同。虽然凋落物在一定时期促进了土壤有机碳分解，但在培养结束时，土壤仍呈现正的碳平衡，这主要是因为被激发的碳仍然小于凋落物在土壤中的存留量；此外，无机氮添加进一步增加了土壤碳平衡。
该研究表明施加氮肥不仅可以提高杉木人工林养分，而且对维持土壤有机碳稳定性具有重要意义。该项目得到了国家自然科学基金的支持。（生物谷Bioon.com）
doi:10.1016/j.soilbio.2011.12.004
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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
Weidong Zhanga, b, Silong Wanga, b
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 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 (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 NH4+ and NO3− was found to have a stimulating effect on the decomposition of Chinese fir and alder leaf litter in the early stage (0–15 d) 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.
