Chemical characterization and function of soil organic nitrogen in prairie agroecosystems

我的项目重点是土壤氮素和氮素循环。特别令人感兴趣的是对土壤有机氮(SON)组分的研究，目的是从农业可持续发展的角度(即土壤质量和土壤肥力)和从环境角度(即环境损失)了解各种有机N库如何对生物有效氮做出贡献。建议的研究建立在现有工作的基础上，我们使用基于同步加速器的N和C K边X射线吸收近边结构(N-和C-XANES)来检测散装土壤中的SON以及土壤化学和物理组分。长期目标是确定关键的化学和物理SON池的分子组成，目的是确定可测量的生物可用SON池，并研究它们对农业生态系统生态功能的影响。这项研究的短期目标是：1)检查和表征受农业管理措施影响的独特SON化合物的存在和性质，并确定这些化合物的结构与N的生物有效性之间的关系；2)研究稳定的土壤微团聚体和大团聚体中SON的形态，目的是阐明N(和C)在这些物理部分中稳定和保护的潜在机制。虽然其他人使用同步辐射来检查土壤和环境样品，但对SON的关注有限，这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下限。对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的应用，我们处于有利地位，进一步推进这一高度新颖的分析技术，作为在分子水平上检测SON的一种可防御的方法，解决文献中存在的关于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.