Molecular structure and bioavailability of soil organic N in prairie agricultural and wetland soils

土壤中的有机氮化合物既是无机氮的源又是无机氮的汇，因此对全球氮循环至关重要。土壤有机氮（SON）被微生物分解，从而释放出农业生产所必需的无机氮（铵和硝酸盐），但也会造成严重的环境污染（例如，硝酸盐污染地下水和排放一氧化二氮（一种重要的温室气体）。尽管SON的重要性，其化学结构仍然知之甚少。事实上，三分之一到二分之一的SON通常被归类为“未知N”，这主要是因为缺乏明确的分析方法阻碍了研究。通过应用现代分析技术，如热解质谱和15 N核磁共振（15 N NMR）光谱，取得了一些进展，但由于分析时间短，这两种技术都受到了批评。最近，加拿大的第一个同步加速器设施，即加拿大光源（CLS）在萨斯喀彻温大学的安装，承诺提供加拿大研究人员的独特机会，使用同步加速器为基础的技术，以检查土壤有机质和明确的文件的性质，以前身份不明的SON。拟议研究的长期目标是使用基于同步加速器的技术来表征SON化合物，最终目标是使用这些知识来预测土壤氮的生物利用度（即，潜在的贡献，植物生产力和环境损失），并确定和/或开发更方便用户的化学土壤测试，以准确地估计生物有效氮库。通过在分子水平上记录SON结构，我们预测N释放到生物和环境敏感的无机N库的能力将大大提高。这些信息对于加拿大农民来说非常重要，他们需要就有效使用氮肥进行农艺和环境可持续农业做出明智的决定，以及其他科学家努力模拟环境氮损失，包括温室气体排放。

Organic nitrogen (N) compounds in the soil serve as both a source and sink for inorganic N and thus are important to the global N cycle. Soil organic N (SON) is decomposed by microorganisms, thereby releasing inorganic N (ammonium and nitrate) which is essential for agricultural production, but also can cause serious environmental pollution (e.g., nitrate contamination of groundwater and emissions of nitrous oxide, an important greenhouse gas). Despite the importance of SON, its chemical structure remains poorly understood. Indeed, one-third to one-half of SON typically is classified as 'unknown N' largely because research has been hampered by the absence of definitive analytical methods. Some advances were achieved by the application of modern analytical techniques such as pyrolysis-mass spectrometry and 15N nuclear magnetic resonance (15N NMR) spectroscopy but both techniques have been criticized due to analytical short-comings. Recently, the installation of Canada's first synchrotron facility, namely the Canadian Light Source (CLS) at the University of Saskatchewan, promises to provide Canadian researchers with the unique opportunity to use synchrotron-based techniques to examine soil organic matter and unambiguously document the nature of previously unidentified SON. The long-term objective of the proposed research is to characterize SON compounds using synchrotron-based techniques, with the ultimate goal of using this knowledge to predict soil N bioavailability (i.e., potential contribution to plant productivity and environmental losses), and identify and/or develop more user-friendly chemical soil tests to accurately estimate bioavailable N pools. By documenting SON structures at the molecular level, our ability to predict release of N into biologically and environmentally sensitive inorganic N pools will be greatly improved. This information is important to Canadian farmers who need to make informed decisions regarding efficient use of N fertilizers for agronomically and environmentally sustainable agriculture, and to other scientists who strive to model environmental N losses, including greenhouse gas emissions.