Thermodynamic quantification of microbial energy turnover in soils using calorespirometry

Microbial processes play a key role in soil organic matter turnover and stabilisation, by controlling both matter and energy fluxes. While carbon cycling has been intensively studied, microbial energy fluxes - and their conservation during soil biogeochemical processes - remain insufficiently explored. Existing thermodynamic concepts and calorimetric approaches provide important insights, but they often rely on oversimplified representations of microbial metabolism and do not sufficiently account for soil heterogeneity, redox dynamics, and the simultaneous occurrence of multiple turnover processes

This study aims to develop a solid thermodynamic framework for assessing microbial energy turnover in soils by linking calorimetric heat flux measurements with carbon-fluxes (CO₂ evolution, substrate consumption, biomass formation, etc.) within an enthalpy-based balance approach, using cellobiose turnover as an example.

The framework will be explored in controlled soil experiments covering a range of redox conditions, availability of biomass building blocks, and the abundance of the microbial catalysts. A key focus will be the quantitative reliability of thermodynamic balances derived from current experimental methods. To address this, we are initiating a calorimetric interlaboratory comparison. Furthermore, we will outline first concepts for extending the framework toward Gibbs energy changes, entropy production, and energy conservation in complex soil systems.

The poster presents the conceptional framework and experimental approaches, together with initial results demonstrating how calorespirometric and C-flux data can be integrated to quantify microbial energy turnover in soils.

 

[1] M. Kästner et al., Assessing energy fluxes and carbon use in soil as controlled by microbial activity – a thermodynamic perspective, Soil Biology & Biochemistry, 193, 109403 (2024).