Origin and fate of dissolved organic matter in the subsoil driven by dynamic exchange and remobilization processes

到目前为止，从地下观测站和连续柱实验中获得的结果表明，溶解有机质（DOM）在土壤矿物质上的吸附-解吸过程是级联的。此外，研究结果表明，底土的吸附能力有限，可能是由于沙质土壤中活性矿物的高碳负荷所致。我们认为微生物活性可能取决于控制再活化过程的矿物的碳负荷，以及矿物表面有机质的组成。因此，在第二阶段，我们将根据OM的来源和组成以及矿物相的表面特征，解决与微生物过程相结合的连续吸附过程和随后的再活化的复杂相互作用。我们假设：(1)随着土壤深度的增加，进入矿质土壤的DOM的组成对土壤上部的交换/再活化过程的影响比对深层土壤的影响更大，这是由于微生物作用随着土壤深度的增加而增加；(2)随着矿物质碳负荷的增加，吸附的OM的交换/再活化也增加；(3)在较大的土壤深度中，矿物相关OM的微生物转化是DOM的重要来源。我们将通过从复杂的现场条件到受控的实验室方法的一系列实验来接近这些假设。实地方法包括在格林德瓦尔德天文台进行DO13C关闭脉冲，在格林德瓦尔德和两个区域站点进行DO13C注射实验，以根据矿物学性质和微生物活动研究不同来源和组成的DOM在地下土壤中的命运。相比之下，DOM在矿物表面的吸附能力、C载荷、空间C分布、C交换、OM组成和可分解性（后者由P6决定）将与DOM的来源、组成、C交换和微生物稳定性有关。类似的分析方法将在流动池实验中进行，在定义的边界条件下，将评估所应用的DO13C的运输，吸附和矿化。最后，在13c标记DOM的实验室柱实验中，研究了不同培养温度下微生物活性对DOM吸附和交换/再活化过程的影响，这取决于矿物表面性质。P5专注于框架提案的中心假设3，但也涉及假设2。P5将为地下土壤中有机碳的综合建模提供关键数据，如DOC和DO13C浓度和通量、DOM对微生物衰变的稳定性、土壤的吸收能力和碳负荷，从而验证中心假设5。

Results obtained so far from the subsoil observatories and sequential column experiments indicate a cascade of sorption-desorption processes of dissolved organic matter (DOM) on soil minerals while travelling to the subsoil. Further, results suggest that the sorption capacity of the subsoil is limited, possibly due to high C loading of the reactive minerals in the sandy soil. We assume that the microbial activity might depend on the C loading of the minerals controlling remobilization processes, in addition to the composition of organic matter (OM) on mineral surfaces. Consequently, in the second phase we will address the complex interplay of continuous sorption processes combined with microbial processes and subsequent remobilization depending on source and composition of OM and surface characteristics of the mineral phase. We hypothesize that (i) the composition of DOM entering the mineral soil affects exchange/remobilization processes stronger in the upper part of the soil than deeper subsoil due to an increased microbial processing with increasing soil depth, (ii) the exchange/remobilization of sorbed OM increases with increasing C loading of the minerals, and (iii) microbial transformation of mineral-associated OM is an important source of DOM in larger soil depths. We will approach these hypotheses by a set of experiments starting from complex field conditions to controlled laboratory approaches. The field approaches include a DO13C switch-off pulse in the Grinderwald observatories and a DO13C injection experiment at Grinderwald and two regional sites to study the fate of DOM of different source and composition in the subsoil depending on mineralogical properties and microbial activity. In a comparative way, sorption capacity, C loading, spatial C distribution, C exchange, and OM composition and decomposability (the latter determined by P6) on mineral surfaces will be related to source, composition, C exchange, and microbial stability of DOM. A similar analytical approach will be performed in flow cell experiments, where under defined boundary conditions transport, sorption, and mineralization of the applied DO13C will be assessed. Finally, in a laboratory column experiment with 13C-labeled DOM the effects of microbial activity, manipulated by different incubation temperatures, on the translocation of DOM by sorption and exchange/remobilization processes depending on the mineral surface properties will be studied. With that P5 focuses on the central hypothesis 3 of the frame proposal but also addresses hypotheses 2. P5 will deliver crucial data for the integrative modeling of OC in subsoils such as DOC and DO13C concentration and fluxes, DOM stability against microbial decay, sorption capacity and C loading of the soils and, therefore, for testing the central hypothesis 5.