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，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，从而释放出对农业生产至关重要的无机N(铵和硝酸盐)，但也会造成严重的环境污染(如地下水的硝酸盐污染和重要的温室气体一氧化二氮的排放)。尽管SON很重要，但它的化学结构仍然知之甚少。事实上，三分之一到一半的儿子通常被归类为“未知N”，这主要是因为缺乏明确的分析方法阻碍了研究。裂解-质谱仪和15N核磁共振波谱等现代分析技术的应用取得了一些进展，但这两种技术都因分析上的缺陷而受到批评。最近，加拿大第一个同步加速器设施的安装，即萨斯喀彻温大学的加拿大光源(CLS)，有望为加拿大研究人员提供一个独特的机会，使用基于同步加速器的技术来检查土壤有机质，并明确记录以前未确认的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来表征SON化合物，最终目的是利用这一知识来预测土壤N的生物有效性(即对植物生产力和环境损失的潜在贡献)，并识别和/或开发更用户友好的化学土壤测试以准确地估计生物有效N库。通过在分子水平上记录SON结构，我们预测N向生物和环境敏感的无机N池中释放的能力将大大提高。这一信息对加拿大农民来说很重要，他们需要就有效使用氮肥进行农业和环境可持续农业的明智决策，也对其他致力于建立包括温室气体排放在内的环境氮素损失模型的科学家来说很重要。

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.