Preprints
https://doi.org/10.5194/soil-2021-14
https://doi.org/10.5194/soil-2021-14

  16 Feb 2021

16 Feb 2021

Review status: this preprint is currently under review for the journal SOIL.

Whole soil warming decreases abundance and modifies community structure of microorganisms in subsoil but not in surface soil

Cyrill U. Zosso1, Nicholas O. E. Ofiti1, Jennifer L. Soong2, Emily F. Solly3, Margaret S. Torn2, Arnaud Huguet4, Guido L. B. Wiesenberg1, and Michael W. I. Schmidt1 Cyrill U. Zosso et al.
  • 1Department of Geography, University of Zurich, Zurich, Switzerland
  • 2Climate and Ecosystem Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
  • 3Group for Sustainable Agroecosystems, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland
  • 4Sorbonne Université, CNRS, EPHE, PSL, UMR METIS, Paris, France

Abstract. The microbial community composition in subsoils remains understudied and it is largely unknown whether subsoil microorganisms show a similar response to global warming as do microorganisms at the soil surface. Since microorganisms are key drivers of soil organic carbon decomposition, this knowledge gap causes uncertainty in predictions of future carbon cycling in the subsoil carbon pool (>50 % of the soil organic carbon stocks are below 30 cm soil depth).

In the Blodgett forest field warming experiment (California, USA) we investigated how +4 °C warming the whole soil profile to 100 cm soil depth for 4.5 years has affected the abundance and community structure of microorganisms. We used proxies for bulk microbial biomass carbon (MBC) and functional microbial groups based on lipid biomarkers, such as phospholipid fatty acids (PLFAs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). Microbial biomass decreased and community composition changed with depth. Our results show that the concentration of PLFAs decreased with warming in the subsoil (below 30 cm) by 28 % but was not affected in the topsoil. Phospholipid fatty acid concentrations changed in concert with soil organic carbon. The microbial community response to warming was depth dependent. The relative abundance of actinobacteria increased in subsoil, and gram+ bacteria in subsoils adapted their cell-membrane structure to warming induced stress as indicated by the ratio of anteiso to iso PLFAs. Our results show for the first time that subsoil microorganisms can be more affected by warming as compared to topsoil microorganisms. These microbial responses could be explained by the observed decrease in subsoil organic carbon concentration in the warmed plots. A decrease in microbial abundance in warmed subsoils might reduce the magnitude of the respiration response over time. The shift in the subsoil microbial community towards more actinobacteria might disproportionately enhance degradation of previously stable subsoil carbon, as this group is able to metabolize complex carbon sources.

Cyrill U. Zosso et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on soil-2021-14', Grace Pold, 25 Feb 2021
    • AC1: 'Reply on RC1', Cyrill Zosso, 27 Apr 2021
  • RC2: 'Comment on soil-2021-14', Anonymous Referee #2, 05 Mar 2021
    • AC2: 'Reply on RC2', Cyrill Zosso, 27 Apr 2021
  • EC1: 'Comment on soil-2021-14', Ashish Malik, 08 Mar 2021
    • AC3: 'Reply on EC1', Cyrill Zosso, 27 Apr 2021

Cyrill U. Zosso et al.

Cyrill U. Zosso et al.

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Short summary
How subsoil microorganisms respond to warming is largely unknown, despite their crucial role in the soil organic carbon cycle. We observed that the subsoil microbial community composition was more responsive to warming compared to the topsoil community composition. Decreased microbial abundance in subsoils as observed in this study might reduce the magnitude of the respiration response over time and a shift in the microbial community will likely affect the cycling of soil organic carbon.