Experimental exploration of denitrification in multiscale porous media and soil

本项目的目的是提高我们对原状结构性土壤中反硝化作用机理的理解。在第一个项目期间，我们基于人工多孔介质和重新填充的土壤研究了结构异质性对反硝化作用的发生和动力学的重要性，现在，我们在原状土芯中实验探索反硝化过程，同时通过X射线显微断层扫描测量相同土样的孔隙结构。这使得结构特征和反硝化作用之间存在直接联系。这种复杂的结构是由从充满空气的孔隙空间到水饱和土壤基质的距离分布描述的，该距离分布是宏观含水量的函数。我们假设这是一个有意义的有效属性，可以用于放大模型，以反映重要的结构材料属性。我们的实验将证明这在多大程度上是可能的。此外，我们测试两个关键的假设所需的模拟反硝化作用在较大的规模。首先，碳源的空间分布，这是可视化的3D原状土壤使用锇染色和第二，相对于多孔结构的微生物的空间分布。这将提供必要的证据，证明可能简化的建模假设是合理的。所有这些都将在与项目伙伴的密切合作下完成。 最终的目标是预测N排放响应大气强迫土壤结构属性，可以观察到的基础上。

The aim of this project is to improve our mechanistic understanding of denitrification in undisturbed structured soil. The importance of structural heterogeneity for the onset and dynamics of denitrification was investigated based on artificial porous media and repacked soil during the first project period.Now we experimentally explore denitrification processes in undisturbed soil cores while measuring the porous structure via X-ray microtomography for the identical soil samples. This allows for a direct link between structural features and denitrification. The complex structure is described by a distance distribution from air filled pore space into the water saturated soil matrix which is a function of the macroscopic water content. We hypothesise that this is a meaningful effective property that can be used in an upscaled model to reflect the important structural material properties. Our experiments will demonstrate in how far this is possible. Moreover, we test two critical assumptions required for modelling denitrification at the larger scales. First, the spatial distribution of carbon sources which is visualised in 3D for undisturbed soil using osmium staining and second, the spatial distribution of microorganisms relative to the porous structure. This will provide the required evidence to justify possible simplifying assumptions for modelling. All this will be accomplished in close cooperation with the project partners. The ultimate goal is to predict N emissions in response to atmospheric forcing based on soil structural attributes which can be observed.