Spatial patterns of organic matter formation in subsoil: Hierarchical preferential flow pathways

研究单位以前的研究结果表明，有机物（OM），微生物和胞外酶活性的空间分离的生物和物理过程的脱钩显然是最重要的机制之一，导致保护和稳定的凋落物和表土衍生的溶解有机碳（DOC）在更深的底土层。优先流（PF）路径的发生应该是一个主要的驱动力，形成的热点微生物活性和有机质转化和稳定在底土。因此，采用全球独特的地下观测站在Grinderwald，我们的新的研究计划的目的是调查OM形成在底土的空间格局。补充研究活动将涵盖以下方面：-分层优先流动途径-微生物碳保留和周转-微生物热点形成和动态的营养控制-矿物相关有机物的形成我们的项目是尝试多尺度方法来捕获土壤中活跃和不活跃的运输区。多年来，实验证据已经证实了cm至dm尺度上的PF途径的稳定网络。我们假设，这种中尺度的流动异质性可以捕获荧光染料灌溉实验在现场。随后的染料引导采样将确定具有关于活跃或不太活跃的流域的系统差异的位置。新开发的技术，以提取未受干扰的流动细胞（FC）允许通过高分辨率的测量和成像的重要的物理化学和微生物的表面特性（如润湿性，官能团，exoenzyme活性的毫米到厘米尺度）的原位状态的全面分析。相应的采样策略将允许量化嵌套PF结构。为了评估DOC的运输和转化，我们将使用13 C标记的DOC模拟流动过程。渗滤实验将进行两个未受干扰的系列FC在现实的原位水分，DOC浓度，流速和温度条件下，模拟平均通量率在采样点在冬季排水季节。将比较从活跃和不太活跃的运输领域取样的土壤的微生物状况，以调查微生物群落模式的差异（与Kandeler等人合作）。在这里，我们的目标是实现一个完整的13 C质量平衡恢复量化13 C（i）吸附到固相，（ii）纳入微生物生物质，（iii）释放的CO2，和（iv）运输DOC。这种方法（与所有项目合作）将最终允许评估微PF模式与现场规模PF途径的重要性，以阐明触发微生物热点空间模式的机制。

Previous results of the Research Unit suggest that decoupling of biological and physical processes by spatial separation of organic matter (OM), microorganisms and extracellular enzyme activity is apparently one of the most important mechanisms leading to the protection and stabilization of litter- and topsoil-derived dissolved organic carbon (DOC) in deeper subsoil layers. The occurrence of preferential flow (PF) paths is supposed to be a major driver for the formation of hot spots of microbial activity and OM transformation and stabilization in subsoil. Consequently, employing the globally unique subsoil observatories at Grinderwald, our new research initiative aims at investigating the spatial patterns of OM formation in subsoil. The following aspects will be covered in the complementary research activity:- Hierarchical preferential flow pathways - Microbial carbon retention and turnover - Nutritional control of microbial hot spot formation and dynamics - Formation of mineral-associated organic matter Our project is the attempt of a multi-scale approach to capture active and less active transport zones in soil. Experimental evidence already confirmed a stable network of PF pathways on the cm to dm scale over years. We assume that this meso-scaled flow heterogeneity can be captured with fluorescent dye irrigation experiments in the field. Subsequent dye-guided sampling will identify locations with systematic differences regarding active or less active flow domains. The newly developed technique to extract undisturbed flow cells (FC) allows a comprehensive analysis of the in situ state by highly resolved measurements and imaging of important physicochemical and microbiological surface properties (e.g. wettability, functional groups, exoenzyme activity on the mm- to cm-scale). Corresponding sampling strategy will allow to quantify nested PF structures. To assess DOC transport and transformation we will simulate flow processes using 13C-labeled DOC. The percolation experiments will be conducted with two undisturbed serial FC under realistic in situ moisture, DOC concentration, flow rate and temperature conditions, simulating the average flux rate at the sampling site during the winter drainage season. The microbial status of soils sampled from active vs. less active transport domains will be compared to investigate differences in microbial community patterns (in cooperation with Kandeler et al.). Here, we aim to achieve a complete 13C mass balance recovery by quantifying 13C (i) adsorbed to the solid phase, (ii) incorporated into microbial biomass, (iii) released as CO2, and (iv) transported as DOC. This approach (in cooperation with all projects) will finally allow to evaluate the importance of micro-PF patterns versus field scale PF pathways to elucidate the mechanisms triggering the spatial pattern of microbial hot spots.