BOOK OF ABSTRACTS 9 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Using examples from recent experimental work, I will show how heat production rates, respiratory fluxes, isotope-labelled substrates, and energycontent measurements can be combined to quantify microbial turnover processes in soil systems. Particular emphasis will be placed on the methodological challenges of applying calorimetric and thermal analytical techniques to heterogeneous, low-carbon soil samples and on the opportunities arising from linking energetics with stoichiometric and thermodynamic modelling. Overall, the presentation proposes that energy should be treated as an explicit state and balance variable in soil biogeochemistry. Such a thermodynamic perspective does not replace carbon-based approaches, but can reveal constraints, efficiencies, and transformation pathways that remain hidden when soil organic matter turnover is considered only as a redistribution of carbon. References 1. M. Kästner, T. Maskow, A. Miltner, M. Lorenz, S. Thiele-Bruhn, Soil Biology and Biochemistry (2024) 109403. Acknowledgement We acknowledge financial support from the Helmholtz Centre for Environmental Research – UFZ and from the German Research Foundation (DFG) through projects TH 678/25-1, MA 3746/8-1, MA 3746/8-2, MA 3746/9-1, and MA 3746/9-2.
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