Experimental exploration of denitrification in multiscale porous media and soil

该项目的目的是提高我们对原状结构性土壤中反硝化作用的机械理解。在第一个项目期间，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开始和动力学的重要性。现在，我们在相同土样的X射线显微层析成像测量孔隙结构的同时，对原状土芯的反硝化过程进行了实验研究。这允许结构特征和反硝化之间的直接联系。这种复杂的结构可以用从充满空气的孔隙空间到饱和土壤基质的距离分布来描述，该分布是宏观含水率的函数。我们假设这是一个有意义的有效属性，可以在放大的模型中使用，以反映重要的结构材料属性。我们的实验将证明这一点的可能性有多大。此外，我们测试了在更大范围内模拟反硝化所需的两个关键假设。首先，利用Os染色在3D中显示原状土壤的碳源的空间分布；其次，微生物相对于孔隙结构的空间分布。这将提供必要的证据来证明可能简化建模假设的合理性。所有这些都将在与项目伙伴的密切合作下完成。最终目标是根据可以观测到的土壤结构属性来预测N排放对大气强迫的响应。

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.