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https://doi.org/10.5194/egusphere-2025-481
https://doi.org/10.5194/egusphere-2025-481
21 Feb 2025
 | 21 Feb 2025

Aeration and mineral composition of soil determine microbial CUE

Jolanta Niedźwiecka, Roey Angel, Petr Čapek, Ana Catalina Lara, Stanislav Jabinski, Travis B. Meador, and Hana Šantrůčková

Abstract. Microbial carbon use efficiency (CUE) in soils is used to estimate the balance of CO2 respired by heterotrophs versus the accumulation of organic carbon (C). While most CUE studies assume that aerobic respiration is the predominant degradation process of organic C, anoxic microniches are common inside soil aggregates. Microorganisms in these microniches carry out fermentation and anaerobic respiration using alternative electron acceptors, e.g. NO3-, Fe, SO42-. Extracellular metabolites are also not traditionally accounted for but may represent a significant C flux. Moreover, climate change may modulate soil microbial activity by altering soil aeration status on a local level due to warming and elevated frequency of extreme precipitation events. Therefore, CUE should be measured under more realistic assumptions regarding soil aeration. This study focused on the effect of oxygen and Fe on C mineralisation in forest soils and quantified C distribution between biomass and different extracellular metabolites. Forest soils were collected from two Bohemian Forest (Czechia) sites with low and high Fe content and incubated under oxic and anoxic conditions. A solution of 13C-labelled glucose was used to track stable isotope incorporation into the biomass, respired CO2, and extracellular metabolites. We estimated CUE based on microbial respiration, glucose consumption, biomass growth, and extracellular metabolites. RNA-SIP was used to identify the active bacteria under each treatment. As expected, the oxic incubation showed a rapid utilisation and immediate production of biomass and CO2. Under anoxic conditions, 90 % of the added glucose was still present after 72 h, and anoxic soils showed significantly lower microbial activity. The low-Fe soil samples were more active under oxic conditions, while the high-Fe samples were more active under anoxia.

Our findings confirm that anoxia in soils enhances short-term C preservation. Accordingly, excluding exudates in mass flux calculations would underestimate apparent CUE values.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Jolanta Niedźwiecka, Roey Angel, Petr Čapek, Ana Catalina Lara, Stanislav Jabinski, Travis B. Meador, and Hana Šantrůčková

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-481', Wolfgang Wanek, 02 Apr 2025
    • AC1: 'Reply on RC1', Roey Angel, 16 May 2025
  • RC2: 'Comment on egusphere-2025-481', Anonymous Referee #2, 08 Apr 2025
    • AC2: 'Reply on RC2', Roey Angel, 16 May 2025
  • RC3: 'Comment on egusphere-2025-481', Anonymous Referee #3, 06 May 2025
    • AC3: 'Reply on RC3', Roey Angel, 16 May 2025

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-481', Wolfgang Wanek, 02 Apr 2025
    • AC1: 'Reply on RC1', Roey Angel, 16 May 2025
  • RC2: 'Comment on egusphere-2025-481', Anonymous Referee #2, 08 Apr 2025
    • AC2: 'Reply on RC2', Roey Angel, 16 May 2025
  • RC3: 'Comment on egusphere-2025-481', Anonymous Referee #3, 06 May 2025
    • AC3: 'Reply on RC3', Roey Angel, 16 May 2025
Jolanta Niedźwiecka, Roey Angel, Petr Čapek, Ana Catalina Lara, Stanislav Jabinski, Travis B. Meador, and Hana Šantrůčková
Jolanta Niedźwiecka, Roey Angel, Petr Čapek, Ana Catalina Lara, Stanislav Jabinski, Travis B. Meador, and Hana Šantrůčková

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Short summary
Studies on how microbes use C in soils typically assume oxic conditions, but often overlook anaerobic processes and extracellular metabolite release. We examined how O2 and Fe content affect C mineralisation in forest soils by tracking 13C flow into biomass, CO2, metabolites and the active microbes under oxic and anoxic conditions. Results showed that anoxic conditions preserved C longer, especially in the high-Fe soils. We conclude that microbial exudates play a role in anoxic C stabilisation.
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