Improved Understanding of Nitrous Oxide Emissions from Seasonally Frozen Cropland for Mitigation of Agricultural Greenhouse Gas Emissions

农业土壤是温室气体一氧化二氮（N2O）和二氧化碳（CO2）的重要排放源，这些排放与种植系统的氮和碳输入有关。我的项目的长期目标是验证和修改预测农业生态系统温室气体净通量的模型，并确定可持续农业生态系统的土壤和作物管理做法。在寒冷地区，由于土壤冻融（FT）事件，超过一半的农业土壤年N2O排放可能发生在生长季节之外。季节性冻结的土地与大面积的集约化种植相吻合，但对ft引起的一氧化二氮排放的研究有限。这是因为N2O排放在时间和空间上变化很大，对典型的测量方法提出了挑战，特别是在寒冷地区。我的研究小组是世界上少数几个使用微气象技术解决这一挑战的小组之一。在我们的长期研究现场，我们观察到管理差异通常在非生长季节最为普遍，但我们还没有确定在一系列条件下导致大量FT N2O排放的根本原因。如果了解了这些差异，就可以设计出减少解冻时氧化亚氮排放的做法。本提案的目标是：1)量化土壤和作物管理下农业生态系统CO2和N2O通量的大小和时间动态，从而导致不同的FT条件；2)评价冬季增暖对两种土壤类型非生长期N2O通量的影响；3)探讨多年生作物与一年生作物在ft诱导下N2O含量的差异；4)比较不同土壤类型中FT和干湿循环中N2O排放增加的潜在因子；5)改进基于过程模型和经验模型对ft诱导N2O通量的预测。我提出了一种方法组合：1)在加拿大重要的农业区进行微气象实验，在此之前没有使用全年微气象方法进行研究；2)新型高精度称重式冬暖土壤溶渗仪；3)利用土壤柱进行FT和干湿循环来控制影响排放的驱动因素的实验室实验。可调谐二极管激光痕量气体和傅里叶变换红外分析将与微腔或自动腔相结合，以高时间分辨率测量气体通量。由FT事件和增强的微生物过程释放的碳和氮底物将通过复杂的技术（例如核磁共振，分子微生物分析）进行表征。将与政府科学家合作改进基于过程的模型。6名研究生和10名本科生将在这种刺激的环境中接受培训。研究结果将对加拿大预测农业温室气体排放的能力产生重大影响。

Agricultural soils are significant emitters of the greenhouse gases nitrous oxide (N2O) and carbon dioxide (CO2) and these emissions are related to nitrogen and carbon inputs of cropping systems. The long-term objectives of my program are to validate and modify models predicting net GHG fluxes from agro-ecosystems and to identify soil and crop management practices for sustainable agro-ecosystems. In cold regions more than half of annual N2O emissions for agricultural soils can occur outside the growing season due to soil freeze-thaw (FT) events. Seasonally frozen land coincides with large areas of intensive cropping, but research into FT-induced N2O emissions has been limited. This is because N2O emissions are highly variable in time and space and present a challenge for typical measurement methods, particularly in cold regions. My research group is one of few in the world using micrometeorological techniques addressing this challenge. At our long-term study site, we have observed that differences in management are often most prevalent during the non-growing season, but we have not identified the underlying causes leading to large FT N2O emissions in a range of conditions. If these differences are understood, then practices for reduced N2O emissions at thaw could be designed.The objectives of this proposal are: 1) to quantify the magnitude and temporal dynamics of CO2 and N2O fluxes from agro-ecosystems under soil and crop management that result in contrasting FT conditions; 2) to evaluate the effect of winter warming on non-growing season N2O fluxes on two soil types; 3) to investigate the differences in FT-induced N2O between perennial and annual crops; 4) to compare the underlying factors for enhanced N2O emissions in FT and dry-wet cycles in a range of soil types; and 5) to improve the prediction of FT-induced N2O fluxes in process-based and empirical models. I propose a combination of approaches: 1) micrometeorological experiments in an agricultural area of importance for Canada, that has not been studied before using year-round micromet methods; 2) new high-precision weighing soil lysimeters with winter warming; 3) laboratory experiments using soil columns subjected to FT and dry-wet cycles to control drivers affecting emissions. Tunable diode laser trace gas and Fourier Transform Infra-red analyses will be coupled with micromet or automatic chambers to measure gas fluxes at high temporal resolution. Carbon and nitrogen substrates released by FT events and enhanced microbial processes will be characterized through sophisticated techniques (e.g. NMR, molecular microbial analysis). Process-based models will be improved in collaboration with government scientists. Six graduate and 10 undergraduate students will be trained in this stimulating environment. Findings will have a significant impact on Canada's ability to predict agricultural GHG emissions.