Intractable methodological problems in estimations of the potential energy return on investment obtained from soil organic matter decomposition
Abstract
Recent interest in microbial energy use during soil carbon dynamics has resulted in several approaches for estimating the potential energy return on investment (ROI) that microbes can obtain from soil organic matter (SOM) decomposition. They assume that microorganisms need to make an initial energy investment, such as the production of extracellular enzymes or transport channels, in order to satisfy their energy requirements via the decomposition of SOM. The ROI is the ratio of the energy acquisition potential (i.e., the return) over the initial energy investment. Two approaches for approximating the potential ROI have been taken in the past: an Arrhenius-based approach and one based on the nominal oxidation state of carbon (NOSC). Both approaches estimate the energy acquisition potential as the enthalpy of combustion of SOM (ΔCH°). The required energy investments are quantified as either the activation energy (Ea) of the SOM combustion reaction, derived from Arrhenius plots, or as the Gibbs free energy for oxidation half reactions of organic carbon (ΔG°Cox), derived from the NOSC. All three variables—ΔCH°, Ea, and ΔG°Cox—are expressed in different units, necessitating unit conversion before ROI values can be calculated. Here, we show that it is not possible to convert units in the Arrhenius-based ROI approach, because it is still not possible to quantify the average molar mass of SOM. The previously applied unit conversion procedures or the lack of unit conversion lead to inaccurate ROI values, which can be an order of magnitude smaller than actual ROI values and do not rank potential ROIs values correctly. The Arrhenius-based ROI approach should therefore not be used and conclusions from previously published studies that have used this approach should be carefully reconsidered. The NOSC-based ROI approach is unaffected, but contains uncertainties due to the error margins in the NOSC– ΔG°Cox relationship. Therefore, conclusions drawn from the NOSC-based ROI need also critical reconsideration.
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BibTeX
@article{bolscher2026intractable,
title = {{Intractable methodological problems in estimations of the potential energy return on investment obtained from soil organic matter decomposition}},
author = {Tobias Bölscher and Jonathan Rodenfels and Claire Chenu and Naoise Nunan},
journal = {Soil Biology and Biochemistry},
year = {2026},
month = sep,
doi = {10.1016/j.soilbio.2026.110312},
url = {https://hal.science/hal-05758066v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Intractable methodological problems in estimations of the potential energy return on investment obtained from soil organic matter decomposition
AU - Tobias Bölscher
AU - Jonathan Rodenfels
AU - Claire Chenu
AU - Naoise Nunan
PY - 2026
DA - 2026/09/18
JO - Soil Biology and Biochemistry
DO - 10.1016/j.soilbio.2026.110312
UR - https://hal.science/hal-05758066v1
AB - Recent interest in microbial energy use during soil carbon dynamics has resulted in several approaches for estimating the potential energy return on investment (ROI) that microbes can obtain from soil organic matter (SOM) decomposition. They assume that microorganisms need to make an initial energy investment, such as the production of extracellular enzymes or transport channels, in order to satisfy their energy requirements via the decomposition of SOM. The ROI is the ratio of the energy acquisition potential (i.e., the return) over the initial energy investment. Two approaches for approximating the potential ROI have been taken in the past: an Arrhenius-based approach and one based on the nominal oxidation state of carbon (NOSC). Both approaches estimate the energy acquisition potential as the enthalpy of combustion of SOM (ΔCH°). The required energy investments are quantified as either the activation energy (Ea) of the SOM combustion reaction, derived from Arrhenius plots, or as the Gibbs free energy for oxidation half reactions of organic carbon (ΔG°Cox), derived from the NOSC. All three variables—ΔCH°, Ea, and ΔG°Cox—are expressed in different units, necessitating unit conversion before ROI values can be calculated. Here, we show that it is not possible to convert units in the Arrhenius-based ROI approach, because it is still not possible to quantify the average molar mass of SOM. The previously applied unit conversion procedures or the lack of unit conversion lead to inaccurate ROI values, which can be an order of magnitude smaller than actual ROI values and do not rank potential ROIs values correctly. The Arrhenius-based ROI approach should therefore not be used and conclusions from previously published studies that have used this approach should be carefully reconsidered. The NOSC-based ROI approach is unaffected, but contains uncertainties due to the error margins in the NOSC– ΔG°Cox relationship. Therefore, conclusions drawn from the NOSC-based ROI need also critical reconsideration.
SN - 0038-0717
ER -