摘要:全球氮沉降对生态系统造成了深远的影响，研究长时间氮沉降对草地生态系统土壤理化特征的影响有助于加强生态系统对氮沉降响应的长效机制的理解。通过连续14年长期施加N0（0 g N m^-2 a^-1）、N2（2 g N m^-2 a^-1）、N4（4 g N m^-2 a^-1）、N8（8 g N m^-2 a^-1）、N16（16 g N m^-2 a^-1）、N32（32 g N m^-2 a^-1）六种浓度尿素模拟氮沉降，并将土壤分成0-10、10-20和20-40 cm三个深度土层，研究温带草原生态系统土壤碳氮组分及物理结构对氮添加的响应及其相互关系，结果表明：（1）氮添加显著降低0-10 cm土壤酸碱度及土壤微生物量碳含量，N32相比N0分别下降了27.63%和58.40%（P<0.05）；各土层总有机碳和全氮含量对氮添加处理无显著响应，0-10 cm土层显著高于20-40 cm土层。（2）同一土层深度不同梯度氮添加处理显著增加土壤无机氮离子含量（P<0.05），0-10 cm土层铵态氮含量N32相比N0增加了88.72%，20-40 cm土层硝态氮含量N32相比N0增加了19.55倍，土壤深度与氮添加对无机氮离子含量影响具有显著的交互效应。（3）同一土壤深度不同梯度氮添加处理土壤粒度分形维数及土壤团聚体差异不显著，相关分析表明土壤碳氮元素含量与土壤结构显著相关。土壤碳氮组分在适宜浓度氮添加的增加趋势说明氮添加在一定程度上可能促进土壤理化性质的改良，氮添加对土壤物理结构的影响还需要进一步的深入研究。



Abstract:Global nitrogen deposition has a profound impact on terrestrial ecosystems. Studying the effects of long-term nitrogen (N) deposition on the soil physical and chemical characteristics of the grassland ecosystem help to understand the permanent mechanism of ecosystem response to nitrogen deposition. In this study, six gradients of urea application (0, 2, 4, 8, 16 and 32 g N m^-2 a^-1, treatments demonstrated as N0-N32) were applied to simulate N deposition for 14 consecutive years, and the soil samples were collected with three soil depths (0-10, 10-20, 20-40 cm from soil surface), to study the response of soil carbon (C) and nitrogen (N) components and physical structure to N addition and their correlations in temperate grassland ecosystem. The results showed that: (1) N addition significantly reduced soil pH and microbial biomass carbon (MBC) in the 0-10 cm soil layer, and N32 decreased by 27.63% and 58.40% (P<0.05), respectively, compared with N0. The content of total organic carbon and total nitrogen in all soil layers showed no significant response to N addition treatment, but the content in 0-10 cm soil layer was significantly higher than that in 20-40 cm soil layer. (2) N addition at each soil depth significantly increased inorganic nitrogen (ION) content (P<0.05); The ammonium nitrogen content in the 0-10 cm soil layer increased by 88.72% compared to N0, and the nitrate nitrogen content in the 20-40 cm soil layer increased by 19.55 times compared to N0; Soil depth and N addition had significant interaction effect on ION. (3) There was no significant difference in the fractal dimension of soil particle sizes or soil aggregates at each soil depth, and correlation analysis demonstrated that soil carbon and nitrogen nutrient contents were significantly associated with the soil structure. In conclusion, the increasing trend of C and N components in soil with optimal N addition concentration indicates that N addition may favor soil physical and chemical properties to some extent, thus the effect of N addition on soil physical structure needs further in-depth study.





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