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来源，也是无机氮的汇，因此对全球氮循环具有重要意义。土壤有机氮（SON）被微生物分解，释放出农业生产所必需的无机氮（铵态氮和硝态氮），但也会造成严重的环境污染（如地下水硝酸盐污染和重要温室气体一氧化二氮的排放）。尽管SON很重要，但人们对它的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”，主要是因为缺乏明确的分析方法阻碍了研究。现代分析技术的应用取得了一些进展，如热解质谱和15N核磁共振（15N NMR）光谱，但这两种技术都因分析缺陷而受到批评。最近，加拿大首个同步加速器设施，即加拿大光源（CLS）在萨斯喀彻温大学的安装，有望为加拿大研究人员提供独特的机会，使用基于同步加速器的技术来检查土壤有机质，并明确记录以前未识别的SON的性质。拟议研究的长期目标是使用基于同步加速器的技术表征SON化合物，最终目标是利用这些知识预测土壤N的生物有效性（即对植物生产力和环境损失的潜在贡献），并确定和/或开发更方便用户的化学土壤测试，以准确估计生物可利用N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。这一信息对加拿大农民和其他努力模拟环境氮损失（包括温室气体排放）的科学家都很重要，因为加拿大农民需要在农学和环境可持续农业中有效利用氮肥方面做出明智的决定。

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.