Preprints
https://doi.org/10.5194/egusphere-2024-186
https://doi.org/10.5194/egusphere-2024-186
29 Jan 2024
 | 29 Jan 2024

Drought counteracts soil warming more strongly in the subsoil than in the topsoil according to a vertical microbial SOC model

Marleen Pallandt, Marion Schrumpf, Holger Lange, Markus Reichstein, Lin Yu, and Bernhard Ahrens

Abstract. Soil organic carbon (SOC) is the largest terrestrial carbon pool, but it is still uncertain how it will respond to climate change. Especially the fate of SOC due to concurrent changes in soil temperature and moisture is uncertain. It is generally accepted that microbially driven SOC decomposition will increase with warming, provided that sufficient soil moisture, and hence enough C substrate, is available for microbial decomposition. We use a mechanistic, microbially explicit SOC decomposition model, the Jena Soil Model (JSM), and focus on the depolymerisation of litter and microbial residues by microbes at different soil depths, and its sensitivities to soil warming and different drought intensities. In a series of model experiments we test the effects of soil warming and droughts on SOC stocks, in combination with different temperature sensitivities (Q10 values) for the half-saturation constant Km (Q10,Km) associated with the breakdown of litter or microbial residues. Microbial depolymerisation rates of litter and residues are proportional to microbial biomass (reverse kinetics), so that at low microbial biomass, the temperature sensitivity of Km plays a more prominent role. We find that soil warming leads to long-term SOC losses, but depending on SOC composition and its associated Q10,Km values, these losses can be either reduced or further accelerated, especially in the subsoil where microbial biomass is low. Droughts can alleviate the effects of soil warming and reduce SOC losses, and even lead to SOC gains, provided unchanged litter inputs. Furthermore, a combination of drought and different Q10,Km values associated with the breakdown of litter or microbial residues can have counteracting effects on the overall decomposition rates. In this study, we show that while absolute SOC changes driven by soil warming and drought are highest in the topsoil, SOC in the subsoil is more sensitive to the (sometimes counteracting) interplay between Km, temperature and soil moisture changes, and mineral-associated SOC.

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Marleen Pallandt, Marion Schrumpf, Holger Lange, Markus Reichstein, Lin Yu, and Bernhard Ahrens

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-186', Anonymous Referee #1, 25 Feb 2024
    • AC1: 'Reply on RC1', Marleen Pallandt, 10 May 2024
  • RC2: 'Comment on egusphere-2024-186', Anonymous Referee #2, 27 Feb 2024
    • AC2: 'Reply on RC2', Marleen Pallandt, 10 May 2024
Marleen Pallandt, Marion Schrumpf, Holger Lange, Markus Reichstein, Lin Yu, and Bernhard Ahrens
Marleen Pallandt, Marion Schrumpf, Holger Lange, Markus Reichstein, Lin Yu, and Bernhard Ahrens

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Short summary
As soils get warmer due to climate change, SOC decomposes faster because of higher microbial activity, but only with sufficient soil moisture. We modelled how microbes decompose plant litter and microbial residues at different soil depths. We found that deep soil layers are more sensitive than topsoils. SOC is lost from the soil with warming, but this can be mitigated or worsened depending on the type of litter and its sensitivity to temperature. Droughts can reduce warming-induced SOC losses.