土壤N2O负排放途径

Nitrous oxide (N2O) is one of most important greenhouse gases with a high global warming potential. Soil is not only a source, but also a sink of N2O. The process of soil N2O uptake (consumption) is important for both the net emission of N2O to, and the N2O concentration in, the atmosphere. However, N2O uptake is easily overlooked due to its high net emission rates from the soil, thus leading to a poor understanding of the mechanisms through which soil can uptake N2O. To better understand the potential pathways and magnitude of N2O uptake in soil, the isotope dilution methods (15NH4NO3 - NH415NO3 and 15N2O), combined with the use of specific pathway inhibitors C2H2 and CH3F, will be used to test the hypothesis that is it coupled with the nitrogen fixation processes (N2O→NH4+) and determine the main way of soil N2O uptake under different soil environmental conditions. Thus, the mechanisms of soil N2O uptake will be explained through all potential pathways. Additionally, Real-time PCR will be used to detect the abundance of the functional genes (nifH, nosZ) of the nitrogenase enzyme and nitrous oxide reductase. The results of this study will help us to deepen understanding of the mechanisms of soil N2O sources and sinks, and provide basic theory for the control measures of N2O emissions.

氧化亚氮(N2O)是一种重要的温室气体，具有很高的增温潜势。土壤既是N2O最主要排放源，也是主要汇。N2O负排放（吸收与消耗）过程对其净排放量及其在大气中的浓度具有至关重要的调控作用；但是N2O负排放过程容易被其较高的产生量所掩盖而被忽略，导致土壤N2O负排放机制仍不够明确。本项目拟采用15NH4NO3和NH415NO3成对示踪及15N2O标记技术，结合CH3F与C2H2抑制法，研究不同土壤环境条件下N2O负排放过程主导途径，分析其主要影响因素，探讨N2O负排放是否关联土壤固氮（N2O→NH4+）过程，从负排放途径的角度阐释N2O负排放机制；同时利用Real-time PCR等生物学手段测定反硝化菌和固氮酶功能基因（nosZ和nifH）丰度，验证相关研究结果。该项目研究有助于揭示土壤N2O负排放机制，为N2O净排放量的估算和减排措施的制订提供理论参考，具有较高的学术价值和实践意义。

氧化亚氮(N2O)是一种重要的温室气体，具有很高的增温潜势。土壤既是N2O最主要排放源，也是主要汇。N2O负排放（吸收与消耗）过程对其净排放量及其在大气中的浓度具有至关重要的调控作用；但是N2O负排放过程容易被其较高的产生量所掩盖而被忽略，导致土壤N2O负排放机制仍不够明确。本项目采用15N2O标记技术，结合C2H2抑制法，研究不同土壤环境条件下N2O负排放潜势与主导途径，分析了土地利用方式、土壤水分含量、pH值、温度等因素对土壤N2O负排通量的影响。研究结果表明，土壤N2O负排放速率与产生速率呈正相关关系，对N2O净排放过程具有重要的决定意义；特别是水分含量较低条件下，土壤N2O负排放速率和净排放速率基本处于同一数量级。当水分含量接近淹水状态时，土壤N2O负排放速率和总产生速率均显著升高，但总排放速率对水分的响应大于负排放速率，导致净排放速率显著增加。林地土壤N2O负排放通量高于草地、果园和旱地土壤，这与林地土壤具有较高的有机碳含量有关。土壤pH值与温度也是土壤N2O负排放过程最主要的影响因素，酸性土壤pH值升高(3.8-7.32)同时提高了土壤N2O负排放速率、总产生速率和净排放速率；随着温度的增加(5-45℃)，土壤N2O负排放速率、总产生速率和净排放速率呈增加趋势。反硝化过程是土壤N2O负排放过程最主要途径；本研究中，应用15N示踪方法没有得到土壤微生物固定N2O为NH4+的直接证据，但从酶促动力学的角度来分析，固氮酶同化N2O→NH4+比N2→NH4+更具有生态学上的优势。本研究发现，在反硝化受抑制条件下土壤N2O负排放过程仍可发生，说明土壤中可能存在除反硝化过程外的负排放途径。项目研究有助于揭示土壤N2O负排放机制，为N2O净排放量的估算和减排措施的制订提供理论参考，具有较高的学术价值和实践意义。