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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/bg-2019-232
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-232
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Jun 2019

Submitted as: research article | 28 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Using Respiration Quotients to Track Changing Sources of Soil Respiration Seasonally and with Experimental Warming

Caitlin Hicks Pries1,2, Alon Angert3, Cristina Castanha2, Boaz Hilman3,a, and Margaret S. Torn2 Caitlin Hicks Pries et al.
  • 1Department of Biological Sciences, Dartmouth College, Hanover, NH,03784, USA
  • 2Climate and Ecosystem Science Division, Earth and Environmental Science Area, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
  • 3The Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat-Ram, Jerusalem 91904, Israel
  • acurrently at: Department of Biogeochemical Processes, Max-Planck Institute for Biogeochemistry, Jena, 07745, 8Germany

Abstract. Developing a more mechanistic understanding of soil respiration is hampered by the difficulty in determining the contribution of different organic substrates to respiration and in disentangling autotrophic versus heterotrophic and aerobic versus anaerobic processes. Here, we present a relatively novel tool for better understanding soil respiration: the apparent respiration quotient (ARQ). ARQ is the amount of CO2 produced in the soil divided by the amount of O2 consumed and it changes according to which organic substrates are being consumed and whether oxygen is being used as an electron acceptor. We investigated how the ARQ of soil gas varied seasonally, by soil depth, and by experimental warming in situ in a coniferous forest whole-soil-profile warming experiment over two years. We then compared the patterns in ARQ to those of soil δ13CO2. Our measurements showed strong seasonal variations in ARQ from ≈ 0.9 during the late spring and summer to ≈ 0.7 during the winter. This pattern likely reflected a shift from respiration being fueled by oxidized substrates like sugars and organic acids derived from root and root respiration during the growing season to more reduced substrates such as lipids and proteins derived from microbial necromass during the winter. This interpretation was supported by δ13CO2 values, which were relatively depleted, like lipids, in the winter and more enriched, like sugars, in the summer. Furthermore, wintertime ARQ was higher in warmed (+4 °C) than in control plots, probably due to an increase in the use of more oxidized carbon substrates with warming. Our results demonstrate that soil ARQ shows strong seasonal patterns in line the phenology of carbon inputs and patterns in soil δ13CO2, verifying ARQ as a tool for disentangling the biological sources contributing to soil respiration.

Caitlin Hicks Pries et al.
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Caitlin Hicks Pries et al.
Caitlin Hicks Pries et al.
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Short summary
The apparent respiration quotient (ARQ) is the amount of CO2 produced divided by the amount of O2 consumed. ARQ changes according to which organic substrates are being consumed by microbes, allowing scientists to trace sources of soil respiration. ARQ had a strong seasonal pattern in a forest soil that reflected a shift from respiration being fueled by sugars and organic acids derived from roots during the growing season to respiration being fueled by dead microbes during the winter.
The apparent respiration quotient (ARQ) is the amount of CO2 produced divided by the amount of...
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