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

有机质是土壤反硝化的重要燃料，它能为土壤中的氮氧化物提供电子，从而控制土壤中N2O和N2的排放。目前，只有很少的信息是关于功能OM组分（溶解，颗粒和矿物相关的OM）对反硝化作用的影响，其数量，质量和时空可用性。第一阶段的结果表明，所有的OM馏分，即使是相对稳定的矿物相关的OM，定量有助于反硝化。一旦水溶性物质被沥滤去除，颗粒状植物材料就失去了促进反硝化作用的能力。因此，溶解的OM似乎是至关重要的，考虑到这一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，我们的目标是提高这些过程的机械理解，提供质量指标描述反硝化模型中的OM的贡献。我们正在计划一个凋落物分解实验结合标准化的孵化，以检查气体的生产（CO2，N2O，N2）的时间变化的基础上的植物残留物和溶解OM的质量。培养实验还将访问矿物相关的OM对反硝化作用的贡献，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，我们将测试蒸渗仪实验与原状土样，如果有机质质量指标允许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.