Chemical characterization and function of soil organic nitrogen in prairie agroecosystems

我的项目主要研究土壤氮和氮循环。特别感兴趣的是土壤有机氮（SON）分数的检查，目的是从农业可持续性的角度（即土壤质量和土壤肥力）和环境的角度（即环境损失）了解各种有机氮库如何贡献生物可利用氮。在现有的工作中，我们使用基于同步加速器的N和C k边缘x射线吸收近边缘结构（N-和C- xanes）来检测大块土壤中的SON，以及土壤化学和物理组分。长期目标是表征关键化学和物理SON库的分子组成，目标是确定可测量的生物可利用SON库，并研究其对农业生态系统内生态功能的影响。本研究的短期目标是：1)研究和描述受农业管理措施影响的独特氮素化合物的发生和性质，并确定这些化合物的结构与氮素生物利用度之间的关系；2)研究稳定土壤微观和宏观团聚体中SON的形态，目的是阐明N（和C）在这些物理组分中稳定和保护的潜在机制。虽然其他人已经使用同步辐射来检查土壤和环境样本，但对SON的关注有限，主要是因为土壤中通常存在低水平的N，以及相对较低的检测限。探测极限的不断改进为探索SON开辟了新的途径。我们的工作代表了N-XANES在土壤和环境样品中的一些最早应用，我们有能力进一步推进这种高度新颖的分析技术，作为在分子水平上检查SON的一种可辩护的方法，解决文献中关于SON性质的一些争议，并确定SON在土壤化学和物理（即土壤团聚体）组分中稳定的机制。

My program focuses on soil N and N-cycling. Of particular interest has been the examination of soil organic N (SON) fractions with the goal of understanding how various organic N pools contribute to bioavailable N, both from an agricultural sustainability perspective (i.e., soil quality and soil fertility) and from an environmental perspective (i.e., environmental losses). The proposed research builds on existing work in which we use synchrotron-based N and C K-edge X-ray absorption near-edge structure (N- and C-XANES) to examine SON in bulk soil, and soil chemical and physical fractions. The long-term objective is to characterize the molecular composition of key chemical and physical SON pools, with the goal of identifying measureable bioavailable SON pools and examining their implications for ecological functions within agricultural ecosystems. The short-term objectives of the proposed research are: 1) to examine and characterize the occurrence and nature of unique SON compounds as affected by agricultural management practices and define relationships between the structure of these compounds and N bioavailability; and 2) to examine the speciation of SON in stable soil micro- and macro-aggregates, with the goal of elucidating potential mechanisms by which N (and C) is stabilized and protected in these physical fractions. Although others have used synchrotron radiation to examine soil and environmental samples, limited attention has been paid to SON largely due to the low levels of N typically present in soils, together with relatively low detection limits. Ongoing improvements to detections limits have opened new avenues for exploration of SON. Our work represents some of the earliest applications of N-XANES to soil and environmental samples, and we are well positioned to further advance this highly novel analytical technique as a defendable approach to examining SON at the molecular level, to resolve some of the controversy existing in the literature regarding the nature of SON, and to ascertain mechanisms by which SON is stabilized in soil chemical and physical (i.e., soil aggregates) fractions.