From single fractions to undisturbed soil: Role of soil organic matter in denitrification

有机质（OM）是一种重要的反硝化燃料，因为有机化合物向氧化氮提供电子，从而控制土壤中的N2O和N2排放。目前，关于功能性OM组分（溶解OM、颗粒OM和矿物相关OM）对反硝化作用的数量、质量和时空有效性的影响信息很少。第一阶段的结果表明，所有OM馏分，甚至相对稳定的矿物相关OM，在定量上都有助于反硝化。一旦水溶性物质被浸出，颗粒植物物质就失去了促进反硝化的能力。因此，溶解的OM似乎是至关重要的，考虑到这部分可能来自几个来源（例如，凋落物分解过程中的释放，矿物表面的解吸）。在第二阶段，我们的目标是提高对这些过程的机制理解，提供描述OM在反硝化模型中的贡献的质量指标。我们正在计划一个凋落物分解实验，结合标准化的培养，以便根据植物残留物和溶解OM的质量的时间变化来检查气体产量（CO2, N2O, N2）。培养实验还将了解与矿物相关的OM对反硝化的贡献，特别是解决由于活性矿物表面的存在而导致的c限制问题。最后，我们将用未受干扰的土壤样品进行渗滤试验，检验OM质量指标是否可以预测土壤尺度上的反硝化作用。

Organic matter (OM) is an important fuel for denitrification since organic compounds donate electrons to oxidized nitrogen and thus control N2O und N2 emissions from soils. Currently only little information is available about the effects of functional OM fractions (dissolved, particulate, and mineral-associated OM) on denitrification regarding to their quantity, quality, and spatiotemporal availability. Results of Phase I reveal that all OM fractions, even the relatively stable mineral-associated OM, quantitatively contribute to denitrification. Particulate plant material loses its ability to promote denitrification once water-soluble substances are removed by leaching. Dissolved OM thus seems to be of central importance, considering that this fraction may originate from several sources (e.g., release during litter decomposition, desorption from mineral surfaces). During Phase II we aim at an improved mechanistic understanding of these processes, delivering quality indicators describing the contribution of OM in denitrification models. We are planning a litter decomposition experiment in combination with standardized incubations in order to examine the gas production (CO2, N2O, N2) based on the temporal changing quality of plant residues and dissolved OM. Incubation experiments will also access the contribution of mineral-associated OM on denitrification, specifically addressing the question of C-limitation due to the presence of reactive mineral surfaces. Finally, we will test by lysimeter experiments with undisturbed soil samples if the indicators of OM quality allow to predict denitrification on the pedon scale.