Energy Structures - Energy sustains dissipative structures in soil systems

• Applicants: Professor Dr. Thomas Maskow; Professorin Dr. Gabriele Schaumann; Professor Dr. Sören Thiele-Bruhn
• Subject Area: Soil Sciences
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465122757

Soil organic matter (SOM) is not locked away in soil but a constant flow of matter (or carbon – C) and energy (E). This flow is driven by gradients generated by soil (micro)biota making them an integral part of it. It enables the microbiota to self-organise and approach steady states, so that temporally and spatially ordered, dissipative processes and/or structures emerge. Characteristic flows and maximum transfer rates are assumed to approach towards a thermodynamic optimum, as e.g. formulated by the maximum power principle (MPP). Through these processes, E is distributed into qualitatively (entropy vs. enthalpy) different pools: a) heat, b) sequestered SOM, c) bioavailable SOM, d) biomass. However, the organisms use only a proportion of the E provided by the substrate. This bioavailable E depends on the energetic properties of the substrate, its status in the soil (e.g. sorption), and the co-utilization of SOM components (priming). Our aim is to understand how E input controls the occurrence of and/or the change between dissipative structures (process states) in soil. We aim to investigate this based on the following knowledge and assumptions. Dissipative structures can be recognized in experiments with different substrate additions, i.e. 1) a single pulse, 2) repeated additions and 3) a quasi-steady state. While 1) shows the transformation between dissipative structures, 2) leads to oscillations showing the resilience of the dissipative structure and 3) allows to identify properties of the dissipative structure in its near steady state. Steady states facilitate the testing of thermodynamic optimization principles (e.g. MPP) and are more readily described by irreversible thermodynamics models. The combination of matter balances and E measurements (calo(respiro)metry) is the appropriate tool, since dissipative structures are to be understood as dynamic flows of matter and E. The bioavailable E is decisive for the maintenance of existing or the establishment of new (possibly temporary) dissipative structures. It depends on thermodynamic molecular substrate properties and the soil reserves (priming), being modified by soil-substrate interaction. This will be investigated using the aforementioned approaches 1-3 in microcosm, calorespirometer and continuous tubular reactor experiments. In part, 13C labelled selected chemicals will be used as substrates to obtain full balances. Experimental results will be used to derive QSAR models (additional parameters determined by quantum chemical modelling) to estimate the bioavailable E. Thermokinetic modeling will be applied to all experimental results to calculate Gibbs E and entropy changes of SOM reactions. It is expected to reach a model based estimation of C and E retention by the soil biota, to determine utilization efficiencies of C and E, and to estimate the stabilization/storage of OM in soil. Overall, this contributes to a better understanding, estimation and management of the C budget of soils.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2322: Systems ecology of soils – Energy Discharge Modulated by Microbiome and Boundary Conditions (SoilSystems)
• International Connection: Austria
• Cooperation Partner: Privatdozent Dr. Daniel Tunega