Spatial patterns of organic matter formation in subsoil: Formation of mineral-associated organic matter

在研究单元内，我们从底土观察站和田间操纵实验中提供了强有力的证据，证明溶解有机质(DOM)通过多次吸附-解吸事件在土壤中迁移。我们发现，高有机质(OM)含量的矿物是微生物研究的热点，微生物活动强烈地参与了OM在矿物表面的交换过程。分段吸板的结果表明，水和溶解有机碳(DOC)通量以及DOM组分具有很大且稳定的空间非均质性。优先流动路径和基质土壤之间的差异表明有机质滞留是水平控制的。基于这些发现，我们旨在研究DOM动力学的小尺度水平非均质性如何转化为矿物伴生有机质(MAOM)的形成和性质的小尺度水平非均质性。我们推测，在优先流动路径中，大量输入的易得有机质为矿物表面的微生物热点提供燃料，从而为微生物在体内的周转途径创造了条件。相反，在基质流动条件下，较少的OM输入和低C负载的矿物，包括更多的植物衍生化合物的直接吸附占优势。拟议的项目是基于在文中确定的底土观测站的分段吸盘中DOC通量的小规模模式。位于每一段正上方的土壤将被取样，并与优先流或基质流域相关。将分析这些不同领域的物理和矿物学特征，这些特征是OM移动性和保留性的重要驱动因素。将吸盘各部分上方土壤中的13C与这些区域中累积的13C通量/保留量进行比较，将提供关于凋落物来源的DOM在空间上的截然不同的保留量的信息。营养物质和生物标志物(木质素、氨基糖、胞外聚合物)的分析以及基于X射线光电子能谱的光谱数据将有助于了解不同流动区域中OM的微生物转化来源和程度。这些关于MAOM形成途径的数据将与MAOM的生物利用度以及伙伴项目提供的关于不同微生物参数的信息相联系。该项目直接解决了一揽子提案中的主要假设，即基质和优先流道区域是底土有机质形成的主要决定因素，因为它们控制着水和物质通量的时空模式，并为微生物有机质周转提供了不同于基质土壤的栖息地。

Within the research unit, we provided strong evidence from subsoil observatories and field manipulation experiments that dissolved organic matter (DOM) is translocated through soils by multiple sorption-desorption events. We showed that highly organic matter (OM)-loaded minerals are microbial hotspots, and microbial activity is strongly involved in the exchange processes of OM on mineral surfaces. Results obtained from segmented suction plates revealed a large and stable spatial heterogeneity of water and dissolved organic carbon (DOC) fluxes as well as of DOM com-position. The differentiation between preferential flow paths and matric soil suggests a horizontal control of OM retention. Based on these findings, we here aim at investigating how the small-scale horizontal heterogeneity of the DOM dynamics translates into a small-scale horizontal heterogeneity in the formation and properties of mineral-associated organic matter (MAOM). We hypothesize that in preferential flow paths, the large input of easily available OM fuels microbial hot spots on mineral surfaces, thus creating conditions for a dominating in vivo microbial turnover pathway in the for-mation of MAOM. In contrast, under matric flow conditions with less OM input and minerals of low C loading, direct sorption including more plant-derived compounds prevails. The proposed project bases on the small-scale pattern of DOC fluxes in the segmented suction plates of the subsoil ob-servatories identified within. Soil located directly above each segment will be sampled and related to domains of preferential or matric flow. These different domains will be analyzed for physical and mineralogical characteristics that are important drivers for OM mobility and retention. A comparison of 13C in the soil above the individual segments of suction plates with the cumulative 13C flux/retention in these domains will provide information on the spatially distinct retention of the litter-derived DOM. The analysis of nutrients and biomarkers (lignin, amino sugars, extracellular polymeric substances) as well as spectroscopic data based on X-ray photoelectron spectroscopy will inform on the source and degree of microbial transformation of the OM in the different flow domains. These data on the pathways of MAOM formation will be linked to the bioavailability of MAOM and to information on different microbial parameters, provided by partner projects. The proposed project directly addresses the overarching hypothesis of the proposal package that matric and preferential flow path domains are major determinants in the formation of subsoil OM as they control the spatiotemporal patterns of water and matter fluxes and provide habitats for microbial OM turnover that differ from matric soil.