Probing microbial carbon use efficiency in soil as a function of substrate chemistry, redox heterogeneity and soil aggregate structure

• Applicant: Professor Dr. Tillmann Lüders, since 10/2021
• Subject Area: Soil Sciences ; Microbial Ecology and Applied Microbiology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465123239

The current understanding of how organic carbon pools are formed, turned over, stabilized or mineralized in soil is more than partial. At the same time, a solid understanding of the controls of these biogeochemical processes is key to any reliable predictions for long-term trends in soil carbon storage, one of the most important sinks for globally increasing atmospheric CO2. Most centrally, such predictions are currently limited by the lack of a quantitative thermodynamic understanding of how soil microbiomes consume and utilize available organic substrates, how substrate composition and energy content translate to microbial growth, and how physicochemical boundary conditions modulate carbon turnover. Amongst the many different aspects of soil functioning to be addressed in the SoilSystems Priority Programme (SPP 2322), this proposal aims to focus on two central hypothesis of soil carbon cycling: we propose that (I) microbial carbon use efficiency in soil can only be predicted when the chemical characteristics of the utilized substrates (oxidation state of C, No. of C atoms, functionalization) are considered; and that (II) the structural and physicochemical heterogeneities of the soil habitat can decrease substrate-dependent carbon use efficiency and thermodynamics. We aim to test these hypotheses by a combination of quantitative stable isotope probing (qSIP) experiments using both 13C-labelled substrates and general growth-targeted 18O-labeling, microcosms with modulated aggregate structure to increase physicochemical heterogeneity of the soil, as well as fundamental bioenergetic modeling for microbial growth prediction. We also address whether active microbial cell extracts can alleviate methodological uncertainties in quantifying microbial growth and CUE in a habitat as complex as soil. Our planned work contributes to the central hypotheses B (substrates) and C (boundary conditions) of the SoilSystems call. Embedded in vital collaborations with several partners of the SPP, this project will thus make central and innovative contribution towards an improved quantitative understanding of carbon and energy fluxes in soil.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2322: Systems ecology of soils – Energy Discharge Modulated by Microbiome and Boundary Conditions (SoilSystems)
• Ehemaliger Antragsteller: Dr. Felix Beulig, until 10/2021