2026/01/01 by Ekaterina Anatolievna Filimonenko, Yakov Kuzyakov · 1 voice
Agricultural and Biological Sciences · Chemistry · Engineering · #Anaerobic Digestion and Biogas Production #Soil Carbon and Nitrogen Dynamics #thermodynamics and calorimetric analyses
paper · pdf · doi:10.1111/gcb.70714
openalex publication_date 2026/01/01 · openalex created_date 2026/01/22 · openalex updated_date 2026/07/02
We thank Alster et al. (2026) for raising the importance of activation energy (Ea) for soil organic matter (SOM) decomposition. We agree that describing organic matter decomposition only with Ea is a simplification of simultaneously ongoing parallel and sequential processes. To understand their combined effects on element fluxes and cycling, the cumulative result is crucial. Here, we respond to the three points raised by Alster et al. (2026) and show that the Arrhenius Ea is a useful proxy for experimental and theoretical applications. We showed that Ea is independent of temperature, but the energy barrier to reach the Ea level decreases with increasing temperature (figure 1 in Filimonenko and Kuzyakov 2025). The enzymatic reactions have temperature optima, above which the reaction rate decreases due to changes in enzyme heat capacity and denaturation (Schipper et al. 2014). In contrast, the abiotic SOM oxidation continuously increases with temperature. The divergence between the temperature effect on reaction rate based on a simplified approach (figure 2 in Filimonenko and Kuzyakov 2025) and estimates from figure 1c in Alster et al. (2026) is significant solely with glucose addition because: (i) the calculated k reflects not only SOM decomposition, but is the weighted average between k of glucose decomposition and k of SOM decomposition; and (ii) the induced positive priming intensifies decomposition of other SOM pools compared to that without glucose. This supports our data by nearly identical Ea values without glucose addition and under temperatures below 25°C (figure 1b in Alster et al. 2026). We discussed the Ea for four processes of organic matter transformation (Filimonenko and Kuzyakov 2025), but did not review their temperature sensitivity. The reactions with high Ea are especially sensitive to warming (Davidson and Janssens 2006). Applying precise methods to assess temperature sensitivity (Hobbs et al. 2013; Alster et al. 2016, 2020) is limited by complex calculations and analytical overload. Our simplification helps to generalize temperature sensitivity of SOM decomposition. Assuming that Ea is not a good SOM stability metric (Alster et al. 2026), we expect an absence of or a negative correlation between Ea of SOM obtained by TGA-DSC and Ea of CO2 released by microbial mineralization of organic matter. To our knowledge, no such negative correlation has ever been obtained. The reverse is instead true: the Ea of the thermally labile SOM pools is well correlated with CO2 respired by microorganisms (Figure S1). At issue is the general organic matter stability in soil. The three mechanisms of this stabilization are (Figure 1): (1) selective preservation (intrinsic stability), (2) spatial inaccessibility, and (3) organo-mineral interactions. Even though these mechanisms were suggested three decades ago (Sollins et al. 1996), they are always described by indirect approaches (Figure 1). Using Ea based on the widely accepted Arrhenius equation, our approach directly quantifies organic matter stability in soils. Yakov Kuzyakov: conceptualization, investigation, funding acquisition, writing – original draft, visualization, writing – review and editing, supervision. Ekaterina Filimonenko: investigation, funding acquisition, writing – original draft and editing. This study was supported by the state program of the Sirius Federal Territory ‘Scientific and technological development of the Sirius Federal Territory’ (Agreement No. 18-03 date 10.09.2024), Shandong Provincial “811” Project of First-class Discipline Construction, and the National Key Research and Development Program of China (2023YFD200140403), and the RUDN University Strategic Academic Leadership Program. This work was supported by Scientific and technological development of the Sirius Federal Territory (18-03). Shandong Provincial “811” Project of First-class Discipline Construction. National Key Research and Development Program of China (2023YFD200140403). RUDN University Strategic Academic Leadership Program. The authors declare no conflicts of interest. This article is a Response to a Letter to the Editor by Alster et al., https://doi.org/10.1111/gcb.70713 regarding Filimonenko and Kuzyakov, https://doi.org/10.1111/gcb.70472. The data that support the findings of this study are openly available in Figshare at https://doi.org/10.6084/m9.figshare.29949164.v1, reference number 29949164. Figure S1: Comparison of activation energies (Ea) of microbial mineralization (analyzed by CO2 efflux from soil, X axis) with Ea for chemical mineralization of the thermally labile pool (200°C–400°C) of SOM (by thermal analysis, Y axis). Own unpublished data from thermal analysis and incubation (blue circles, and mean ± SE as red triangle) of forest-tundra soils from Western Siberia. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.