Measuring N2 and N2O fluxes and related processes at high sensitivity and resolution in the field using advanced stable isotopic tools as a basis for model evaluation

由于以往方法的局限性和反硝化作用的极端时空异质性，目前尚缺乏适用于验证反硝化模型中氮气通量的现场尺度反硝化数据。因此，到目前为止，还不可能评估在田间尺度上预测反硝化作用的模型的准确性。因此，有必要获得这一规模的活动数据，以更好地了解反硝化控制，并作为支持评估和扩大我们研究单位第一阶段提出的模拟概念的基础。我们将使用新的和改进的稳定同位素方法来提供包含尽可能详细的活动和调节的反硝化数据集，作为评估DASIM子项目(P7、P8、PC)应用和/或开发的现有和新的反硝化模型的基础。在第一阶段，我们目前的工作重点是建立实验室和现场方法，并包括受控的实验室孵化。对于第二阶段的当前应用，我们将重点放在田间范围内，并建议开展以下工作：任务1和任务2将完成前面在阶段1中看到的工作，并包括(任务1)耕地土壤中氮气和N2O通量的最小平均土壤体积，以及(任务2)DASIM土壤的厌氧土壤体积分数。任务3至5将涵盖后续实地通量研究的筹备工作，包括进一步开发和实地测试15N气体通量方法(任务3)，建立实地测量系统(任务4)，以及校准同位素映射方法，以根据N2O的自然丰度同位素特征识别真菌的反硝化作用(任务5)。任务6将包括田间试验，以量化种植土壤中的氮气和N2O通量、贡献过程和控制因素，以阐明田间尺度的反硝化动力学，并作为校准和验证DASIM合作伙伴开发的现有和新模型的基础。最后，预计任务7将使用从任务6获得的数据来评估选定的现有生物地球化学模型。该工作计划将与五个合作伙伴合作实现，这些合作伙伴提供现场基础设施和实验、扩散气体通量建模、土壤硝酸盐连续原位测量、稳定同位素分析和生物地球化学模型评估方面的支持。

Field scale denitrification data suitable to validate N2 fluxes in denitrification models are cur-rently missing due to previous methodical limitations and the extreme spatio-temporal hetero-geneity of denitrification. Until now, it was thus not possible to evaluate accuracy of models to predict denitrification at the field scale. Therefore, it is necessary to obtain activity data at this scale to better understand denitrification control and as a basis to support the evaluation and upscaling of modelling concepts developed in phase I of our research unit. We will use new and improved stable isotope approaches to provide denitrification data sets comprising as much detail on activity and regulation as possible as a basis to evaluate existing and new de-nitrification models that are applied and/or developed by DASIM subprojects (P7, P8, PC). During phase I our current work focussed on establishing lab and field methods and included controlled lab incubations. For the current application of phase II we will focus at the field scale and propose to work on the following tasks: Tasks 1 and 2 will complete work that was fore-seen for phase I and include determination of (Task 1) the minimum averaging soil volume for N2 and N2O fluxes from arable soils, and (Task 2) the anaerobic soil volume fraction of DASIM soils. Tasks 3 to 5 will cover preparatory work for subsequent field flux studies, including fur-ther development and field-scale testing of the 15N gas flux method (Task 3), establishing a field measurement system (Task 4), and calibrating the isotopocule mapping approach to iden-tify fungal denitrification based on natural abundance isotopic signatures of N2O (Task 5). Task 6 will include field experiments to quantify N2 and N2O fluxes, contributing processes and control factors in cropped soils to elucidate field-scale denitrification dynamics and as a basis for calibration and validation of existing as well as new models developed by DASIM partners. Finally, Task 7 is foreseen to use the data obtained from Task 6 to evaluate selected existing biogeochemical models. The work program will be realised in collaboration with five partners supplying support in field infrastructure and experimentation, modelling of diffusive gas fluxes, continuous in situ measurement of soil nitrate, stable isotope analysis and evaluation of bio-geochemical models.