小麦/玉米两熟农田土壤包气带CO2来源及更新机制研究

Soil profile CO2 directly drives soil respiration at soil/atmosphere interface. However, most studies implicitly consider soil CO2 efflux as the instantaneous soil respiration and thereby neglect possible changes in the amount of CO2 stored in the soil pore-space, especially in agricultural ecosystems. The North China plain has become an important source of carbon emissions in China because of the managements of high water and chemical fertilizer inputs and straw returning during the past 30 years. The project is carried out in a wheat/maize rotation system on the North China Plain. The CO2 source partitioning and its renewal mechanisms in the zone of aeration (0-300 cm) were studied in situ based on the carbon isotope techniques and the law of conservation of mass in the field. Soil air samples (10, 30, 60, 90, 150, 210 and 300 cm) were collected in situ by using soil-air equilibration tubes which are installed in soil profile. And the CO2 flux and transport rate are estimated based on Fick's law after the concentrations are analyzed by a gas chromatograph. The δ13C values of soil CO2 ,root and soil organic matter in the zone of aeration (0-300 cm) are determined by a mass spectrometer, then the CO2 source partitioning is evaluated based on a two-terminal component model. The CO2 renewal mechanisms in the zone of aeration are evaluated based on the Carbon-14 dating technique. Meanwhile, the responding mechanisms of the CO2 source partitioning and its renewal mechanisms to environment factors are evaluated based on the measurements of soil temperature, water content and soil organic matter content in the zone of aeration. The research possesses important values in defining the distribution, transformation and biogeochemical processes of soil carbon gas pool. Moreover, the research has important academic values for fairly understanding the processes of reducing soil respiration carbon loss and increasing ecosystem carbon sequestration and storage.

土壤包气带CO2产生和传输过程直接驱动土壤-大气界面CO2通量变化，但目前对包气带CO2通量动力学过程鲜有研究。近30年来由于高水肥和秸秆还田等措施华北集约化农田已成为我国重要的碳排放源之一。本项目以华北平原小麦/玉米轮作农田为研究对象，利用碳同位素技术结合田间原位观测揭示0-300cm土壤包气带CO2的来源构成、更新特征及其与环境因素的响应机制。利用剖面气体采集器原位采集10,30,60,90,150,210和300cm土壤空气，在测定浓度后用Fick定律估算CO2通量和传输速率；通过质谱仪测定剖面CO2、根系及有机质的δ13C值并基于二端元混合模型估算其来源，利用14C年代测定揭示剖面CO2更新速率；并进一步探索CO2来源及更新与环境因素的响应机制。本研究对揭示农田地下气体碳库在土壤中的分配、转化及其生物地球化学过程具有重要价值；同时对探索降低土壤呼吸碳损耗并提高碳储存具有重要意义。

土壤包气带CO2产生和传输过程直接驱动土壤-大气界面CO2通量变化，但目前对包气带CO2通量动力学过程鲜有研究。近30年来由于高水肥和秸秆还田等措施华北集约化农田已成为我国重要的碳排放源之一。本项目以华北平原小麦/玉米轮作农田为研究对象，利用碳同位素技术结合田间原位观测揭示0-300cm土壤包气带CO2的来源构成、更新特征及其与环境因素的响应机制。研究结果表明华北平原小麦/玉米两熟农田0-300 cm土壤剖面土壤CO2浓度随着层深度增加呈上升趋势且具有明显的季节变化趋势，即夏玉米季显著高于冬小麦季（p＜0.01）。0-300 cm土壤剖面CO2通量随着土壤深度的增加呈下降趋势，其中冬小麦季10-60 cm土层显著高于150-300 cm；夏玉米季10-30 cm土层显著高于其他土层（p<0.05）。0-300 cm土壤剖面δ13C-CO2数值随着土层深度的增加呈现显著贫化趋势，其中冬小麦季0-10 cm土层δ13C-CO2显著富集于30-300cm，夏玉米季0-90 cm土层δ13C-CO2显著富集于150-300 cm（p<0.05）；δ13C-CO2数值呈现显著的季节趋势即夏玉米季显著富集于冬小麦季（p＜0.01）。0-300 cm土壤剖面冬小麦季和夏玉米季的δ13C-CO2同位素特征数值变化范围分别为-19.4~-14.1‰和-18.0~-9.7‰。虽然本研究中冬小麦（C3，26‰）和夏玉米(C4，12‰)轮作且实施上季作物秸秆全部粉碎还田管理，但是土壤剖面冬小麦季δ13C-CO2同位素特征较夏玉米仍然呈现显著贫化趋势（p<0.05）。土壤剖面CO2的14C年龄和13C同位素特征与SOC的14C年龄和13C同位素特征一致，说明深层土壤释放的CO2主要来源于古有机碳分解。0-300 cm土壤剖面δ13C-CO2同位素特征主要受温度，水分含量和DOC三个因子共同控制（P<0.001）。本研究对揭示农田地下气体碳库在土壤中的分配、转化及其生物地球化学过程具有重要价值；同时对探索降低土壤呼吸碳损耗并提高碳储存具有重要意义。