氮、水交互对长白山原始阔叶红松林土壤N2O排放影响的机制研究

Continuous increase of global nitrogen deposition and the changing distribution of precipitation significantly affect the nitrogen cycle of terrestrial ecosystems, and thus make an important impact on soil N2O emissions. There are a lot of weak areas related to N2O research in forest soil. Previous studies mainly focus on flux observation and mechanisms of environmental control factors, while the research on the internal mechanisms of N2O production is not perfect, which greatly limits the relevant mode development and large-scale emission assessment. Moreover, the effect of nitrogen and water is not isolated. However, there are few field control experiments considering multi-factor interaction influence on nitrogen deposition and precipitation change. Therefore, 15N isotope labeling, acetylene inhibition, whole process nitrogen transformation model and biological inhibitors were applied in this study, relying on the experimental platform of artificial nitrogen control and precipitation control in broadleaved Korean pine forest ecosystem in Changbai Mountains. From three aspects, including nitrogen sources, production pathways, and biotic and abiotic processes, we systematically studied the internal mechanism of the difference between nitrogen and water interaction on forest soil N2O emissions. The results are of great scientific significance for accurate prediction of forest N2O emission under the changing background of nitrogen and water input, effective reduction in uncertainty of estimation on the sources and sinks of greenhouse gas in forest ecosystem of China, improving response ability to global change of China.

全球氮沉降持续增加和降水格局变化显著影响陆地生态系统氮循环，进而对土壤N2O排放造成重要影响。关于森林土壤N2O相关研究存在很多薄弱区域，已有研究主要集中于通量观测和环境控制机制方面，而对N2O产生的内在机制研究尚不完善，这大大限制了相关模式发展和大尺度排放的评估。并且氮、水的作用不是孤立的，而目前考虑氮沉降增加和降水变化的多因素交互作用对森林影响的野外控制实验较少。为此，本研究依托长白山原始阔叶红松林人工施氮和控制降水实验平台，采用15N同位素标记、乙炔抑制、全过程氮转化模型和生物抑制剂等技术手段，从氮来源、产生途径，以及生物和非生物过程三个方面系统研究氮、水交互对森林土壤N2O排放影响的内在机制。研究结果对于准确预测未来氮、水输入变化背景下我国森林N2O排放，有效降低我国森林生态系统温室气体源汇估算的不确定性，提高我国全球变化应对能力具有重要的科学意义。

以我国温带典型植被类型阔叶红松林为研究对象，依托长期人工增氮和控制降水实验平台，通过15N同位素标记、氮转化模型、生物抑制剂等技术手段，研究了阔叶红松林土壤氮初级转化速率及其对土壤N2O排放的影响，重点分析了土壤有机氮异养硝化途径的N2O排放；并区分了细菌，真菌和非生物过程对土壤产生N2O的贡献。研究工作按照计划完成，并获得主要研究结果：（1）阔叶红松林长期施氮处理促进了土壤N2O排放，可能原因是施氮促进了土壤氮初级矿化速率、硝化速率和反硝化速率，而抑制了硝态氮的异化还原速率，从而增加土壤N2O排放潜力；（2）建立了土壤有机碳（SOC）、pH、异养硝化（Rnt）和土壤温度对有机氮异养硝化生成N2O的响应函数，并估算了全球森林土壤有机氮异养硝化过程N2O的排放量约为1.1099 ± 0.3486 Tg N yr-1， 约贡献天然土壤N2O排放量的19.82%，占全球N2O的排放量的6.53%；（3）自然林地土壤细菌、真菌和非生物过程N2O排放速率分别为0.11±0.02、0.04±0.01和0.01±0.00 ug N kg-1 h-1，对土壤N2O排放贡献分别为56%、22%和5%，长期施氮显著促进全土及真菌N2O排放速率（P < 0.05），减少穿透雨对全土、细菌、真菌和非生物过程N2O排放影响不显著（P > 0.05）；氮、水交互作用显著促进了非生物过程N2O排放（P < 0.05）。