Project coordination: Field site management, data synthesis and modeling of subsoil C-turnover

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The high 14C age of subsoil organic matter suggests very slow turnover rates. However, analyses of archived soil samples and 14CO2 and DO14C flux measurements indicate that a sub-stantial part of the subsoil C-pool has annual to decadal turnover times and thus contributes to the global Ccycle. Distinct differences in 14C content and microbial activity between preferential flow paths and bulk soil indicate that the long-term stability of soil organic matter (SOM) may also result from its spatial segregation from hot spots of microbial activity. Other subsoil specific factors such as low O2 partial pressure, low temperatures and low moisture dynamics may additionally control SOM turnover. In order to model C-dynamics in subsoils, the influence of these factors with the underlying mechanisms on turnover needs to be understood and quantified wherever possible. In addition, C-fluxes have to be quantified and their sources have to be identified. The central objective of this coordination subproject is to ensure the close collaboration between the subprojects in order to compile and synthesize all relevant results for model development. To this end, the set-up and installation of the subsoil observatories and all field activities like sampling campaigns, flux measurements and additional field experiments will be planned in detail and coordinated by this project. This will be supported by the creation of a web-based common database and communication platform together with a regularly updated table of all activities accessible to all participants. The subsoil observatory will be managed by a technician. The coordinating scientist will regularly call in meetings with the other groups or with subgroups for discussion of results and coordination of experiments. Furthermore he/she will organize a summer school for the participating PhD students and workshops for the communication of results to an international audience. The compiled data on C-fluxes and 14C analyses will be synthesized to gain an improved understanding of C dynamics in subsoils with a conceptual model and it will be used as input parameters for the improvement and adaptation of a numerical model of C-turnover in soils. The development and validation of the numerical model is the task of a PhD-student.