砂姜黑土农田土壤N2O排放特征及产生机制

Lime Concretion Black soil is an important medium and low yield field soil type. High content of clay and sand ginger layer in the profile easily causes the mineral nitrogen(NH4 + NO3) accumulation in the surface of Lime Concretion Black soil. This kind of soil has high coefficients of linear extensibility and easily forms extensive cracks.. Not only does this provide a substrate for nitrification and denitrification, it also provides suitable environmental conditions for N2O gas emissions from the deep soil of Lime Concretion Black soil. This type of soil may have significant emission of N2O gas. Based on this hypothesis, this project will examine the dynamics of N2O emissions and seasonal variation of conventional tillage in the Lime Concretion Black soil for maize and wheat rotations using the Static Chamber meteorological chromatography method, soil profile meteorological chromatography method, and 15N isotope tracer method. Specifically we will (1)explore the characteristics of N2O emission and its key influencing factors during the early stages of multiple fractures (water and nitrogen deposition), multiple fractures and post-multiple fractures; (2) explore the emission characteristics and mechanism of nitrous oxide in sand ginger layer (formation and destruction of the Sand Ginger Layer), (3) build the relationship between the dynamic process of water and nitrogen transport and N2O emission, (4) reveal the key driving mechanism that led to the difference of N2O emission from other soils in the Lime Concretion Black soil, and (5) provide theoretical support for the reasonable application of nitrogen and greenhouse gas reduction in farmland of Lime Concretion Black soil.

砂姜黑土是一种重要的中低产田土壤，其土壤粘重，剖面聚集砂姜层，导致水氮多聚集于地表。同时，该土壤线性延展系数高，易产生多发性裂隙。这些特点既有助于硝化与反硝化反应的发生，也为深层土壤N2O气体溢出提供条件，所以砂姜黑土有可能是一种高N2O排放土壤。基于此，本项目以豫南典型砂姜黑土小麦玉米轮作农田为研究对象，通过静态箱/气相色谱法、土壤轮廓/气相色谱法、15N示踪法以及分子生态学方法，探究砂姜黑土常规耕作方式下N2O排放通量及季节性变化；区分多发性裂隙前期（水氮淤积期）、裂隙产生期和多发性裂隙后期三个阶段N2O的排放特征及关键影响因素；探明砂姜层存在与否（维持砂姜层和破坏砂姜层）N2O的排放特征及产生机制，建立水氮运移与N2O气体排放的耦合关系，从而揭示导致砂姜黑土农田N2O排放不同于其他土壤的关键驱动机制，为此类土壤农田温室气体合理评估及减排提供理论依据。

砂姜黑土是黄淮海地区典型的地域性土壤，质地黏重，富含蒙脱石，使得灌溉后水肥不易下移，干湿及冻融交替后易产生裂隙；同时，犁底层深处易形成以铁锰氧化物和碳酸钙为主的砂姜层，导致砂姜黑土水肥运移存在一定的独特性，进而可能导致砂姜黑土的N2O排放不同于其他土壤。基于此，开展了砂姜黑土典型施肥方式下小麦玉米轮作体系N2O原位监测研究，探明了不同施氮量条件下砂姜黑土农田土壤N2O累积排放量，确定了导致砂姜黑土N2O异于其他土壤的关键环境因素，发现了砂姜黑土不属于高N2O排放土壤，裂隙期N2O排放量并不显著高于裂隙前后期，小麦季是砂姜黑土N2O的高排时期；2)在对砂姜黑土剖面不同深度N2O浓度监测研究发现，砂姜黑土玉米季N2O浓度峰值主要集中在60cm土层，小麦季主要集中在30cm土层，砂姜黑土剖面N2O排放峰值的体积含水量主要集中在0.23-0.30m3∙m−3，土壤温度主要集中在25-30℃之间；（3）15N标记尿素示踪试验结果显示，砂姜黑土三季施肥后氮素仍然主要集中在0-100cm土层，甚至河南7.20暴雨事件下15N仍主要集中在0-100cm土层，后一季的15N有进一步下移的趋势。15N的土壤残留量及其他损失量较高，作物氮素回收率相对较低；（4）不同氮肥种类和硝化抑制剂添加条件下室内培养实验结果显示，铵态氮肥产生的N2O排放量显著高于硝态氮肥，但硝态氮氮的N2O排放量仍不可忽视，由此说明砂姜黑土存在较强的硝化作用，同时不可忽视反硝化作用；（5）在对砂姜黑土和潮土室内培养对比实验中发现，培养条件下砂姜黑土的N2O排放量高于潮土，尤其来自于反硝化过程中产生的N2O排放量显著高于潮土，然而这个结论与田间试验结果出现了矛盾的一面，可能与培养条件下氮素在土壤迁移分布以及环境条件与田间试验差异较大有关。同时，由于砂姜黑土还存在较高丰度的nosZ基因，因此推断砂姜黑土可能存在着一定程度的N2损失。